Published on December 16th, 2015 | by Christopher Arcus


How The Grid Works, & Why Renewables Can Dominate

December 16th, 2015 by  

Can we really generate most of our power from renewables in a few decades? In a word, yes.

But to understand further, we must understand how we produce and distribute power today. Part of the difficulty lies in the concepts we use to understand the electrical power system. A simple model might show just one power plant and one load, like a light bulb. Stepping up some, we might view a model showing several loads and distribution equipment, like transformers. These step up the generator voltage to the high-voltage transmission lines, and lower the voltage down to the 120V AC we generally use. The electric power is distributed to the commercial, industrial, and residential loads.


Adding to the complexity, many generators contribute to generation, from many types of sources — gas, oil, nuclear, coal, wind, solar, and hydro, among others.

On the other side of things, demand varies daily, seasonally, monthly, and due to weather and other events. The demand curve has a daily peak in the middle of the day. The annual peak is in the summer due to air conditioning loads in most places. This is true in all US regions, even the Northeast. Here are some pictures that show how demand varies with season.


This first one is for New England.


Here is a summer day in California.


And here is a California winter day demand.

Here is a video showing how demand varies over a year on the East Coast on NYISO:

To meet the peak annual demand, extra generators must be available. These are not used year round. In fact, the generators are used as a pool to meet demand all the time. On any given day, some units are idle and not needed, and some are out for repairs or refueling. Others are in reserve, waiting and expected to be used that day. Others are generating electricity to meet demand.

The generators and power lines are operated by utilities. The power system is run by independent system operators (ISOs), and operators in control centers dispatch the power on a daily basis, requesting power from the various generators. Some can vary their output quickly. Others can take days to be available. This requires planning. Because the power system is generally a monopoly, public utilities commissions (PUC) are tasked with regulating the utilities to provide the lowest cost power to users. The system is operated by utilities bidding to provide power from their generators on a day-ahead basis. So the operator sees which generators are available and looks at the predicted demand and plans and dispatches to meet the load at lowest cost accordingly.

A look at one system, CAISO, the California Independent System Operator, shows how this works. The graph below shows the difference between the predicted day-ahead demand and the actual demand.


The bottom three curves show the predicted and actual demand. The upper yellow curve shows the reserves.

Lets look at how different sources provide energy to meet electricity demand. This is an approximate picture of how it was done in the past in California:


The amount of inflexible coal and nuclear is less than the lowest demand during the day so that it doesn’t have to change power output. Natural gas is used for most of the daily variation.

Now lets see what happens when we add renewables today:

California solar electricity curve

Here is the report, commissioned by then-Governor Arnold Schwarzenegger, that sources the graph (Fig. 15 page 35).

You can see that wind and solar displace the natural gas peak generation. And that, most of the year, reserves are available much greater than demand because they need to be there in case generation fails unexpectedly and because the power peak only happens during a short time of the year. The rest of the time, there is much excess generation available. That’s why up to 40% wind and solar can be integrated without much fuss. The grid is already set up to vary with load. Solar in particular works very well, because it happens when the daily demand is higher. And with so much flexible power available most of the year, wind and solar can be integrated even more often.

In California, we can see that large amounts of renewables are already integrated by exploiting the flexibility of natural gas. In fact, not just flexible generation, but flexible demand may be exploited. Right now, flexible demand is not used that much. One way to make demand flexible, is to set time of use (TOU) metering and pricing. This is not used yet in many areas of the US.

But how can we go higher than that? Well, we can look at the following video by Amory Lovins for guidance. As Lovins shows, even without storage, a high percentage of renewables can power the grid with a few techniques.

We don’t need storage breakthroughs, but they are welcome and can help.

For starters, all we need is flexible sources to meet the daily demand variation. Quite clearly, we could power the whole grid with natural gas or hydro. We wouldn’t do that everywhere for practical reasons, but it’s possible. In fact, some countries are predominantly powered by hydro or geothermal. They don’t require natural gas to meet demand. And some demand is met by importing excess power from other areas, as the next graph (shared above as well) from California shows.

California solar electricity curve

Next is one example scenario for meeting demand that was developed by NREL. It envisions having some excess renewables and curtailment to meet demand.

renewable energy curtailment

Keep in mind that every day in each location a different set of sources is used to meet the demand.

You can see that there is not one way, but many ways, and different ways on each day. In fact, since power is imported, it depends on how well operators are able to mix and predict power from many areas. This will be more important in the future as system operators in the Midwest dispatch wind and solar from the Midwest and Southwest to demand centers throughout the country, particularly the coasts. That’s why the electric energy regulation authority FERC has developed “Energy Imbalance Markets” as a solution. They provide quicker, more-up-to-date estimates of available power and demand so ISOs and utilities can better exchange power through the grid.

And meeting demand is done differently in each location, on each day, in different ways. Every town, in every location, on every day does not need to meet 80% renewables to get 80% renewables across the US as a yearly average.

The difference in regional resources is shown in this graph.

US renewable energy potential

And the mix by region is shown in this graph:

US renewable energy 80 percent

The same renewables are not used everywhere, but renewable resources are widespread. In fact, utilizing the wide distribution of renewables like wind acts to smooth and steady their output. Many seminal articles have been written by NREL’s Michael Milligan for example.

The combination of different sources acts to increase the ability to meet demand. The case for wind, solar, and other renewables being more than the sum of the parts is ably made by Ramez Naam here.

You can see how renewables work together to meet demand here:


And you can see how renewables output is smoothed by integration over wider areas here:

global irradiance

There are many other methods of integrating renewables besides storage.

But storage has become cheaper much faster than anticipated. The current wave of storage, Tesla’s Powerwall, can provide storage at prices low enough to displace gas peakers. And traditional sources like coal and combined cycle gas plants can also operate as flexible sources not just gas peakers. These flexible sources already exist, but operate using fuel today. Their use will be reduced, at first, making room for variable renewables. As time goes on, a mix of variable renewables like wind and solar, and flexible renewables like hydro, biomass, geothermal, and concentrating solar with thermal storage, as well as grid storage from flow batteries, lithium batteries, compressed air storage, and pumped hydro can make up the rest.

The combination of grid practices, transmission, flexible sources like CSP with thermal storage, geothermal, hydro, and biomass, plus 10% storage is all that is required to meet 80% renewables by 2050 economically by 2050.

The costs of storage and renewables are dropping quickly as volume increases:



But wait, there’s more. As wind capacity factor rises with increases in tower height and other changes, capacity factor increases. NREL recently found that wind power capacity factor improvements would have far-reaching implications allowing wind to displace more fossil fuels.

This will increase the amount of time wind is available, open more areas for wind farms, and bring some wind farms closer to load centers. Meanwhile, solar costs continue to plummet, soon to rival the already low costs of wind, and storage costs fall. As storage costs fall, utility storage enables more renewable integration, and more electric vehicles. The combination works as a positive feedback to increase the rapid deployment of all these technologies.

Buy a cool T-shirt or mug in the CleanTechnica store!
Keep up to date with all the hottest cleantech news by subscribing to our (free) cleantech daily newsletter or weekly newsletter, or keep an eye on sector-specific news by getting our (also free) solar energy newsletter, electric vehicle newsletter, or wind energy newsletter.

Tags: , , , , , , , , , , , , , ,

About the Author

has studied wind, electric vehicles, and environmental issues. An electrical engineer familiar with power and electronics, he has participated in the Automotive X Prize contest. He is an avid writer, specializing in electric vehicles, batteries, and wind energy.

  • OneHundredbyFifty

    What is the source for figure 54? I can only find it on Ramez’s site and he did not provide a source.

  • ROBwithaB

    Great article. Simple explanations of potentially complex subject matter.
    A comprehensive “start at the beginning” approach.
    And the writer is a real-life electrical engineer, apparently. Someone whose opinion is actually informed by relevant education.
    Which is a welcome change….

    • I’m sorry ROB i can’t agree with you.
      Just close down all the inefficient uses of power in your neighborhood.
      Make your own beer, grow your own food. Try and use the services of citizens who make a maximum of $15 an hour and never ever pay anyone $50 an hour or over.
      All accomplished by opening the doors to 3rd world immigrants to the good old USA.
      It’s so easy when you use Less Toil.

      • ROBwithaB

        Wait… which comment were you responding to?
        I was saying that the article was well written…

        • “real life electrical engineer”?
          How cheap can solar power get? What does that linear question mean in a”simple’ world….analogy?

  • John Ihle

    Very good article. pretty succinct discussion, broken down well, of a super complicated system.. I wonder about stranded assets and how they figure into the economics over time and what that means for rates on the retail side.
    Renewables will dominate, energy efficiency will factor in and storage will play a major role. The article assumes sort of an electric utility business model as usual scenario in terms of generation and transmission ownership and/or control through ppa’s, etc. At some point legislators may realize that despite lower wholesale costs those costs don’t manifest themselves usually in cheaper rates. Also, increasing concern over extreme weather, terrorist/hostile actions present a growing concerns. Consequently, DG policy, including storage, more and more will be developed to mitigate several issues related to economics, risk, reliability and the environment.
    I’m not saying that electric utilities are or will go away, some entity needs to manage the grid, but things are changing and that transition is for the better. It’s happening and it’s interesting.

    • Bob_Wallace

      Most of out coal plants are old and have likely been paid off for years. Closing them won’t leave utilities paying “the mortgage”. Utilities would have started replacing them already with new coal plants at a much higher price than they can now enjoy with wind, solar and CCNG. Utilities don’t own coal mines or railroad cars that transport coal. I don’t see utilities suffering from any real stranded asset problems. They will probably lose a bit of book value from closing coal plants early but that will be only a paper loss.

      I don’t see any of this hitting the meter. What may well happen, should happen, is that renewables will lower the wholesale cost of electricity and that should start lowering the retail cost.

      The losses will be for coal mines, railroads (lost business) and merchant coal plants. Those are all shareholder losses.

      • Kevin

        But utilities can own the power station that burns the coal ?
        So if the coal supply stops,, the power station loses it source of fuel.
        Doesn’t this then become a stranded asset ?

        • Bob_Wallace

          Yes, but utilities will have their rates restructured so that they will be find. Coal companies have the real stranded asset problem. They have no other source of income.

          • John Ihle

            I mostly disagree w the statement “Coal companies have the real stranded asset problem.” PUC’s or PSC’s or whatever don’t regulate the coal industry like it does utilities. There is separation, from a business sense, between coal/mining companies and the actual utility owned generator and transmission lines. Utilities invest in generation and transmission w roi/irr goals. Often the investments are “approved” by the commissions.. and consequently they may become stranded if other sources of electricity or means, transmission vs distribution, RE, efficiency, , become more competitive and then strands the asset.

  • Marion Meads

    This is nothing but a simple statistical averaging over a wider region and emphasizes the big role of the grids and even supergrids for the entire USA. An attempt to make the grid and thus the utility companies more relevant.

    However, one must not discount the tremendous role of battery energy storage system at the point of generation and use. This is a big factor that will make small the relevance of the grid, especially for daily fluctuations.

    Why shouldn’t we factor in the role of residential, small commercial, or community battery energy storages first before tackling the need for reallocating the regional availability of power from a wider area? This way, you prevent overdesigning and stranded assets.

    • Bob_Wallace

      Long distance transmission might be a factor if a particular region has a several day period of low wind, for example.

      Right now we have three major grids in the continental US. I’m not sure we’d need to move power outside those grids in order to supply demand 24/365. I expect we’ll need some transmission strengthening within the grids.

      It’s going to be an economic decision. Which is the cheapest way to supply demand – transmission, long term storage, over-building, dispatchable (clean) generation.

      I can see ERCOT building more transmission into the SE. They will likely want some of the wind-electricity sales that Oklahoma is enjoying.

      Someone needs to build the model. Along the lines of the Budischak paper, they worked out the basics. We have years of demand and wind/solar data. We’ve got ample wind and solar farm output data. We need a computer model that builds around the data we have and adjust for the optimal mix as prices and technology changes.

      It would make for a hell of a good dissertation.

      • JamesWimberley

        Somebody needs to actually start building the Tres Amigas interconnect. The project was around in 2007.

        • Bob_Wallace

          Texas wants no part of it.

          I think Texas, by being a single state utility, is able to dodge some of the EPA requirements that would come into play were they engaged in interstate commerce of energy. Or some convoluted thing like that.

          But that might be breaking down. Texas now has a couple of small connection to other states. Perhaps the profits to be made in selling wind is going to be more important than keeping their coal plants dirty.

          • eveee

            Convoluted is the right word. Something is fishy. Texas power has succeeded in getting permission to sell to Mexico. Don’t know what they have against selling to New Mexico, Az, and Ca. Baffling.

          • Bob_Wallace

            Mexico isn’t a US state. No interstate commerce involved.

          • eveee

            They had to get agency approval nonetheless for export. It was a NG generation plant.


            Odd that export outside US would be easier than between states.

          • Remove the invisible Canadian and Mexican borders and look at it again. The republicans elect a Maverick long shot candidate by mistake.

        • OneHundredbyFifty

          If they connect the three grids then low intermittency renewables begin to take shape. Intermittent renewables create a market for nat gas. A connected grid begins to diminish the market for gas. Think about how nicely solar plays with wind in TX and yet they have very little solar . . . You build out solar and you have dramatically less need for gas, day peaking solar, night peaking wind.

          • But big solar farms are now beating our natural gas for PPAs. Cost is now lower, and stable/predictable. See solar ramping up pretty well in TX soon.

          • OneHundredbyFifty

            Yay, Has Cleantechnica done an article on that yet. Eager to see TX do this, they really have the potential to be the country’s and possibly the world’s model of how these technologies can play together. Load shift with EVs to a night peaking wind resource and PV and higher wind floor offering much higher effective baseload from renewables.

          • eveee

            Yes. Texas is wide open for solar.

        • Bob_Wallace

          Update: Progress happened and went unnoticed. I’ve got an Alert set for Tres Amigas and nothing appeared before today –

          “Last November, construction workers began building the first piece of the first phase of the project: a 56-kilometer transmission line to connect three new wind farms to the superstation site and then to the Blackwater substation, which connects to the Western grid. The 345-kilovolt line is scheduled to be electrified by the end of this year; Blackwater will also be upgraded to handle the added capacity of up to 500 megawatts of wind power.

          The ultimate plan, with an estimated price tag of US $1.6 billion, is to construct three more lines to substations in Texas, one of which connects to the Texas grid (usually referred to as ERCOT, the acronym for the entity that runs it, the Electric Reliability Council of Texas), and the other two connecting to the Eastern grid.”

          “Harris came up with the idea for Tres Amigas shortly after he retired as CEO of PJM, a regional grid and wholesale electricity market spanning the Middle Atlantic United States. In 2008, he says, “we drew up our plan, and within a few months we had several million dollars lined up.” Funding dried up with the global financial crisis. “The utilities told us they wanted Tres Amigas,” Harris says, but investors accustomed to funding electricity generation or transmission projects “had trouble trying to fit it in a ‘generation or transmission’ box.”

          So Harris and his partners did everything except build the superstation: They completed the system assessments, lined up suppliers, leased land for the superstation, secured the rights of way, won regulatory approvals. The original timeline called for completion by 2013 but has been revised repeatedly.”

      • Carl Raymond S

        Makes perfect sense to me to have one grid. It’s the coin toss experiment – the more tosses, the closer the average gets to 50% heads.
        Also, the west has sunshine while the east is on dusk and peak usage.
        “Because the world is round” – could be a catchy song in that.

        • Bob_Wallace


          Is it cheaper to built transmission from Florida to California or just install more capacity and storage in those two places? I’ve not seen an answer to that question.

          • globi

            If storage was cheaper than transmission lines, China wouldn’t have been building all these HVDC-lines:

            A single 10 GW transmission line has essentially a maximum (virtual) storage capacity of 43800 GWh. (The Tesla Gigafactory produces 50 GWh per year for several billion $?).

          • JamesWimberley

            Can you elaborate? The line by itself has no storage capacity. The reserve depends on the generating pool it is linked to, and the extent to which that pool is despatchable. Existing US interconnects to Canada are based on despatchable hydro, but that would not hold for links to Midwest or Texas wind.

          • eveee

            Yes. Variable renewables combined over wider areas cover load variation better. Anytime you can match generation to load better, you don’t need to store as much.

            Heres the thing. Variable renewables are dispatch able, just not as dispatch able as some other sources. But multiple sources combined appear as an equivalent source with higher dispatch ability and load matching.

            The subject is complicated because its all about mixing a bunch of different sources to match loads in real time.

            We hardly ever discuss how energy forecasts improves load matching, but it is at least as important.

            “it was determined that the uncertainty in the wind forecasts used for economic dispatch would impact the regulating reserve much more than what was shown for the variability. ”


            Those graphs showing the generation mix vs demand variation give some idea of the task.

            When NREL researcher, Milligan first studied wind integration, he found that utilities wrongly concluded that they needed much more reserves to integrate renewables.

          • ROBwithaB

            I’ve been wondering about how one could improve the accuracy of wind forecasts. And part of the solution seems obvious: use collated real-time data from the increasing number of large anemometers popping up all over the country.
            Clearly, local weather systems don’t operate in isolation. If we feed in ALL the data from ALL the turbines spread around an entire continent, ALL the time, I have no doubt that trends would quickly start to become apparent.
            Something like: “If we have a 12 knot wind blowing NNE in SE Texas on a late Summer afternoon, then we can expect 15 knots ESE in California 12 hours later.”
            You wouldn’t even need to know what the weather systems looked like. It would be a purely numerical analysis.

          • OneHundredbyFifty

            The missing piece is that loads are also dispatchable and the current system does little to monetize time of use. Many loads can be flexible at little or no cost or inconvenience to the load side. If we monetize TOU AND provide a supergrid to aggregate generation then we have a recipe for optimization. If, further we monetize carbon then we have a fully market based and highly efficient solution to the problem.

          • eveee

            Yes. Its almost as if all our priorities are backwards. Just like when early researchers found wind required very little reserves and would not destabilized the grid, there is still widespread ignorance.

            Better forecast and demand management are much cheaper and should be highest on our priority list. Instead, the focus is on storage which won’t be needed for years.


          • So much optimism taken for granted in these Obama years of administration.
            You’re going to miss him when he’s gone.
            The beat will go on with Trudeaumania 2.0 for years in Canada.

          • eveee

            Yet who would have predicted a 5 year ITC and PTC extension for wind and solar? Or a successful Paris climate agreement? Or successful India, China, US climate agreements?
            IMO, progress goes on even if its not visible. Abbotts, and Tory governments, and US Congress come and go, but climate change.. thats permanent and cannot be ignored.
            Much of the progress already achieved remains unknown to the larger public.
            Conflict gets more attention than progress.

          • globi

            Take Norway as an example.
            It has an average power demand of 16 GW (29 GW peak power) and almost 100% flexible hydro power.
            If Germany were to build a 10 GW power line to Norway, Norway would essentially appear as a gigantic battery. (Norway would simply reduce hydro power output whenever Germany exports 10 GW of surplus power – but for the power line it appears as if it was pumping power into a gigantic battery).

          • Bob_Wallace

            But look at Texas/ERCOT. There’s no large hydro source within reach. One size will not fit all.

          • globi

            Mexico, Arizona and Colorado do have hydro power.

            And if US were to build an HVDC line like Brazil did, it could interconnect ERCOT with BPA (which possibly runs the largest hydro power network in the US).

          • Bob_Wallace

            Excess hydro?

            California’s hydro is down and with a disappearing snowpack it’s likely to be lower in the future.

            Look, I agree with you that transmission is part of the solution. Well, I’m not sure you view transmission as – part – of the solution. You write as if you think it the entire solution.

            I’ll repeat. We have at least three solutions, transmission is one of the three. In the end we’ll likely build a mix of the three with the amounts determined by economics.

          • globi

            Excess wind and solar power can help save water.

            Hydroelectric generation has declined after a winter-long
            Wind power has done much to fill the gap recently and has
            set new generation records by providing as much as 24 percent of
            total demand in a given day.

            I agree that we have several solutions and all do play a role. Transmission can take the major burden.

          • eveee

            Yes. You can see how NREL envisioned it in Table 3-4. IMO, CSP with storage and CAES are where they will go a decade down the line. And PV solar added to wind will also help. Right now they have so much flexible NG generation, they can still keep pushing more wind. But I would be pleased to see Texas exceed 30% wind in a decade and need to implement more transmission and storage. They might just do it now that the PTC has a 5 year extension. They have been installing wind at wonderful rates.


            Texas is now gets about 10% of its electrical energy from wind, about 50% from natural gas, and 32% from coal.


            Its headed for 20,000MW by next year.


          • eveee

            There are many undersea links being built. UK, Netherlands, France, Germany, and Denmark are all connecting to Scandinavia.


            Hydro conversion to pumped hydro is being studied.


          • ROBwithaB

            That one to Iceland is interesting. Long distance, under some rough seas on a nasty seabed.
            To make it viable, you’d think they might have some decent renewable resources there….

          • eveee

            Indeed they do and bountifully so.

          • JonathanMaddox

            Iceland is also exporting renewable electrons chemically, as methanol.


          • ROBwithaB

            That’s quite interesting, actually.
            I’ve heard about this technology in theory, but didn’t know that it was already up and running on a (semi) industrial scale.

            Millions of litres a year is tiny tiny number though, compared to current oil production.
            Do we have any number on costs per litre?

          • ROBwithaB

            Might be cheaper and easier to export electrons rather than aluminium.

          • eveee

            Interesting thought. The reverse is usually done.

          • Bob_Wallace

            But will storage become cheaper than transmission?

            And did China have enough transmission from its windy part to its consuming parts to allow only storage to solve the problem? I doubt that had any transmission from the windy plains to their power hungry coastal cities.

            It’s far too early to settle the transmit/store issue. Give it five years to see how storage costs settle in. There’s still hope that Ambri’s liquid metal batteries will come through and that cheaper flow batteries will prove out.

          • eveee

            I don’t think its either/or. Its how much of each in each situation. Transmission is quite cheap compared to storage. A few pennies/khwr on the larger grid.
            I have seen discussions of storage added to lower grid congestion. Transmission lines are like base load. They want to run at as near full capacity as possible. To do that, you can flatten the demand curve by charging when demand is low and discharging when demand is high. So sometimes grid expansion and storage go hand in hand.

          • Bob_Wallace

            But the question really is whether it makes sense to build enough transmission to run the Pacific Coast off East Coast solar from 6AM until West Coast solar kicks in. Or whether it makes sense to move Saudi Arabia electricity to Chile.

            (I’m thinking not.)

          • cesium62

            Depends on how you move the electricity. Move all your manufacturing plants to North Africa and ship your finished goods over the transmission lines.

          • ROBwithaB

            We all tend to do a lot of speculation in the comments.
            But the writer of the article is a real-life electrical engineer, who should have most of the answers we seek. Or at least know where to find them.
            How much does one kilometre of HVDC cost? And how many yottawatt hours can it carry per year? (New word: yotta)
            How do we tap into this resource of knowledgeable people?

          • globi

            It costs about $0.0000013/kW/km (300 kV, 1.4 GW HVDC underground system at a length of about 600 km, which can carry over 12 TWh per year).

          • ROBwithaB

            Thanks for the link.
            So, about one tenth of a US cent to transfer 1kWh over a distance of 600km?
            Indeed HVDC transmission seems like a complete no-brainer.
            As the man in the bar said “In that case, I’ll have TWO.”

            Will go read the full 23 pages now…

          • globi

            Let’s say the 600 km long transmission line lasts 40 years. This means it can transmit about 500 TWh over its lifetime. If you assume a capacity factor of about 70% that’s about 0.2 cents/kWh.
            Just jump to the second last page.

          • Bob_Wallace

            You can answer your question yourself by searching.

          • globi

            It is sensible to have interconnections in-between.

            For example: Nowadays German power plants export power to Switzerland and Swiss power plants export power to Italy.

            On a larger scale this could mean: Québec exports power to the Midwest and the Midwest exports power to California.

          • cesium62

            A few pennies per kwh is freaking expensive.

          • Bob_Wallace

            Few is a pretty loose measurement. We’ll need some solution for filling in when there’s not enough generation to match demand. That’s going to have to come from storage, dispatchable generation or ‘importing’.

            Right now we use a lot of gas peakers which, according to Lazard, runs 17 to 26 cents per kW.

            Short term storage (less than two days) should be fairly affordable. Under 5 cents plus the cost of the stored electricity (probably 3 cents). Long term storage will cost more.

            The EIA tacks a 3 cent per kWh ‘transmission’ charge onto wind. It’s not too clear how they derive that number, but if it costs 3 to 5 cents to import a 3 cent kWh from another grid that could be competitive.

            Problem is, we’re playing “What if” with almost no data. All that we can do, IMO, is to discuss concepts. We can’t accurately even guesstimate the cost of the alternatives. But that doesn’t really matter, we’re years away from needing fill-in power. For the next several years, possibly for the next decade or more we can add wind and solar and just use available grid flexibility to fill-in.

          • Frank

            Right, at 5% wind and 1% solar, we are a long ways from a difficult problem. A little forecasting, and maybe a little tweak here and there, and we’re good. I’m not saying we shouldn’t watch places with higher penetrations, and pilot storage, but we sure shouldn’t slow down.

          • ROBwithaB

            “Problem is, we’re playing “What if” with almost no data. All that we can do, IMO, is to discuss concepts.”

            Or we can try to get someone to actually inform us.
            Anyone have an uncle who works for a utility?
            A brother who’s a high voltage elec eng?

            Unfortunately, the comments section here ends up being a bit of an echo chamber, sometimes.
            Discussion is all very well, as long as the overall knowledge base is increasing. I come here to learn.
            Facts are usually more valuable than opinions.

          • eveee

            The cost per kwhr for an HVDC project connecting Midwest to East Coast is estimated in the 2c range. The cost of Wind is under 5c. The East Coast rates are 20c. That pencils out for me. Plently of economic incentive. No matter how you nitpick the numbers. And the cost of storage is greater. That doesn’t mean you don’t have storage any more than it means you don’t use gas peakers in todays system. I don’t know how I can emphasize this enough. The grid requires multiple methods and sources. Always has, always will. The reason why is that a variable load has to be matched all the time.
            Dozens of ways to do that with a different mix of ways in different regions.

            Thats the reason that isolating out one source or method and comparing LCOEs doesn’t do justice to the situation. Its too oversimplified.


          • Otis11

            There are quite a few professional electrical engineers on this forum (myself included – and I’d care to bet eveee is as well… With notable experience/exposure to project management given our previous discussions).

            Though I’m not sure what you’re asking… Or it simply might have already been answered? (I realize I’m late to the party…)

          • ROBwithaB

            Thanks for the reply. And for sticking your head out above the trenches…
            My grandfather used to say that “a little education is a dangerous thing”.
            There is sometimes very lively argument on these threads, from people with strong opinions. And sometimes there is very strong concurrence of opinions, to the extent that conversation is drowned by the sound of mutual back-patting.
            Which is all well and good, because it shows that people are emotionally invested in the issue. Lovely.

            But any opinion is worth only as much as the knowledge or experience that’s backing it up.
            Bob expressed the problem as “we’re playing “What if” with almost no data. All that we can do, IMO, is to discuss concepts.”
            Indeed. After dozens of concepts have been discussed, we realise that we can easily resolve any arguments by simply resorting to the FACTS. Some actual data.
            Here’s an example: Various numbers were proffered for the cost of HVDC transmission, per kWh per 100km. Numbers that differed by at least an order of magnitude. Obviously, somebody had the wrong numbers. No point in discussing the viability of HVDC vs storage (or whatever else) unless we understand the real-world constraints.
            I come here to learn. Sometimes I learn a lot from a single comment. Sometimes I wade through dozens and remain ignorant. Frustrating.

            So, basically, thanks for raising your flag. Hope you don’t mind if we occasionally turn to you for hard data, or trustworthy links.

            And do you happen to have some verifiable numbers for those HVDC transmission costs?

          • Otis11

            Well, I don’t happen to have any HVDC line prices. (I don’t even remember the correct order of magnitude per kwh/100 km). But I wouldn’t be so sure that the profits numbers were incorrect – costs can vary by more than an order of magnitude as most of the cost is in the interconnects and obtaining right-of-way. If the distance is long, the interconnect costs matter less. If the max power is higher or the capacity factor is higher, those costs can be spread over a significantly larger number of kwhs… Honestly, I would not be surprised to find two orders of magnitude between the highest and lowest average costs, especially across countries…

          • OneHundredbyFifty

            ” That’s going to have to come from storage, dispatchable generation or ‘importing’.”

            It can also come from monetizing time of use which creates incentive for load side to seek opportunities to match generation. Currently the paradigm is one sided and people think the name of the game is to match generation to load. But there are lots of opportunities to match load to generation. The most obvious is EV charging. Another simple example is to put timers in dishwashers like the Europeans do. Set it to run at midnight and suddenly you get a double win, not running the dishwasher at peak and reducing AC load since it does not have to pump the heat generated by the DW out of the house. LEDs have similar Two-fer benefits.

            I don’t see need for storage being eliminated but it can be reduced considerably with various smart grid solutions.

          • eveee

            Not compared to storage. And its a fraction of the difference in cost between Midwest generation and East Coast rates.
            East Coast rates are 20c/kwhr and up. In the middle of the wind belt, 10c. But thats not the main consideration. The question is whether local generation sources like solar and now wind with taller towers, and offshore wind can do it not only cheaper, but use less capital and less time to do it.
            Its not just the long term cost, Its the speed of implementation, the necessary capital, finance, and other issues.
            Its lucrative to sell cheap Midwest Wind to the East Coast.
            High East Coast rates are even opening up offshore wind.
            I suggest some of each will happen.
            A typical grid will mix as many sources as possible and needs to for reliability, cost, and to follow load variation. Same here.

          • eveee

            Storage is more expensive. East Coast rates are 20c/kwhr. Midwest wind is under 5c/kwr. Wind can easily be shipped east economically.

          • neroden

            I strongly suspect battery storage will be primarily used to handle millisecond variations in demand, and one-second variations in demand, and maybe one-minute variations in demand, with hourly variation being handled by transmission.

            Buffering the very-short-term fluctuations makes it much easier to handle the giant switching involved in the transmission.

          • ROBwithaB

            See info kindly posted by globi below.
            It would appear to be fractions of a penny per kWh, over distances of a few hundred kilometres.
            Even at very low capacity factors, still perhaps only a penny.

            If this is typical, then suddenly a LOT of options open up.
            And one understands why the Norwegians are laying a lot of cable under the North Sea.

          • eveee

            Yes. You got it. That quote is for long distance HVDC at distances of about 1,000 km. A bit higher for longer distance.

          • ROBwithaB

            Am I right in saying that a significant portion of the cost of HVDC transmission infrastructure is all the fiddly bits (switchgear?) on either end of the cable? Rectifiers, transformers, etc.
            So that favours longer distances?
            But the diameter of the entire cable would need to increase as distance increases, so that favours shorter distances?
            Somewhere there must be a natural “sweet spot”?
            Sorry for asking you to answer my “Elec Eng 101 for Dummies” type question here. Feel free to refer me to an appropriate online resource.

          • Bob_Wallace

            Yes. Wire is wire. A HVDC line can carry a huge amount more on the same diameter wire.

            I wired by solar system at 24vdc because it saved a huge amount of wire cost compared to 12vdc. I getting ready to double my system size and by wiring the panels in series I’ll end up at ~124vdc and the wire cost will be insignificant.

            Proper sizing is everything.

          • eveee

            Yes. HVDC favors longer distances. Let me put it this way. High voltage DC, HVDC, has to convert to DC, then transmit, then convert back to AC. Transmission losses by HVDC are lower than conventional HVAC. It takes a good distance, hundreds of miles, before the higher efficiency tips the economic scales in its favor. The converters are sized for the power transmitted. So the converter cost is fixed. That means they must transmit long distances to make economic sense. Regular high voltage AC, HVAC has higher losses per distance, and requires more material in transmission. (Thicker or more cables)But since it doesn’t require the converters, it’s cheaper for short distances. Transmission generally lasts over 40 years, longer than generation, and naturally doesnt have generations fuel costs. That’s why transmission tends to be a small fraction of the rate compared to generation.
            The transmission economic distances are set by capital cost, lifetimes, efficiency, and operation and maintenance. Independent system operators and utilities must do economic studies and make proposals for rate increases for projects.
            The US transmission network has been neglected. I suspect a careful look will show part of the reason is that the PUC system allows better utility payback for more capital intensive generation. IMO, this is a flaw in the system that guarantees a rate of return on capital. It discourages and reduces the value of conservation and efficiencies, methods that require less capital. It was intended to promote a “common good” approach, but only approximates it.

          • Bob_Wallace

            IIRC, there’s about a 0.75% loss when converting up to HVDC and a similar loss converting back to local AC voltages. That loss also adds to the cost calculation when deciding whether to run AC or HVDC transmission. AC is going to win on shorter runs.

          • ROBwithaB

            The return-on-capital model doesn’t seem to work very well.
            From what I’ve read, that’s exactly how things went pear-shaped in Australia.

          • eveee

            Thats right. Its one of the flaws in the public utility regulated monopoly scheme. It doesn’t monetize things like conservation, demand management, and many other beneficial practices that reduce costs and save energy.
            It just guarantees a rate of return on capital investment. Once the PUC grants it, a rate increase happens. In the utility world, its called “rate basing”. Its just a word describing jacking up utility rates. The utilities are doing that to increase their profits, as they should. But thats harmful. We need to change the PUC system to meet our changing goals.

          • neroden

            There’s something headscratching about the general claim that HVDC has lower transmission losses than HVAC, given that exactly the reverse result was found 150 years ago by Westinghouse.

            I have been told that the transmission losses are very *very* different for underwater cables, underground cables, and overhead line, and that HVDC is massively superior for underwater cables.

          • eveee

            The move by HVAC is toward highest voltages to decrease copper and lower weight. HVAC reaches a limit due to “corona loss”. HVDC can go higher. So HVDC can be cheaper once the distance is high enough, because the cost for the transmission lines is lower. The reason AC is still cheaper for short lines is mainly because HVDC must have gear to convert to DC and back again to AC.

            Here is a nice link.


          • globi

            China already has storage: ‘coal’. When there’s plenty of wind, coal power production can be reduced and vice versa.
            I can see how storage may be useful at end-consumer level in order to reduce self consumption of roof power, but I don’t think battery storage will play a significant role at utility level, since interconnection with existing, flexible (hydro) power is relatively inexpensive.

          • Bob_Wallace

            Storage is an added cost. But so is transmission. As is overbuilding.
            I doubt it will be a case of using only one solution but a mix.

          • globi

            I think transmission will be used for large grids and seasonal storage (hydro power) and daily-storage (hot water and batteries) in microgrids and single family homes.

            The advantage of transmission is that a lot of surplus power capacity (for example gas-peaker and hydro including seasonal storage) is already built.

          • eveee

            Thats right. 90% of the year we have unused capacity just waiting for the annual summertime peak load in the late afternoon. All that excess capacity is there in case the load changes or a variable renewable changes. Plenty for now, and more than enough to integrate 30% variable renewables.
            Given that there has to always be at least 30% reserve at the highest annual peak demand for reliability and stability, it makes no sense to worry about a few hours or even days lacking variable renewables in one location. Ditto and then some for adding transmission, forecast accuracy, demand management, overcapacity…
            Hey, hows this. In the future, we will carry excess solar and wind as reserves, too. Sounds like what we have been calling overcapacity and curtailment. After all, isn’t that what we are doing with NG peaker plants?

          • globi

            This is already happening now.

            All small German PV-systems installed since 2012 are already curtailed at 70% of nameplate capacity. And all modern wind turbines with a large rotor diameter relative to their generator size are essentially curtailing wind energy.

            More importantly all wind farms and large PV power plants can be remotely controlled by the grid operators anyway.

          • eveee

            You have a good insight about the oversized rotor vs generator being an equivalent of curtailment. Another perspective is that load matching may have more meaning or value than raw output. It’s mainly energy that matches load that matters.
            With increasing wind tower heights and capacity factors, load matching is better. The situation is dynamic and fluid. NRELs future study 5 years ago is already outdated.
            IEEE Power and Energy most recent issue details how wind and solar are increasingly superior to conventional generators for grid stability.

          • Bob_Wallace

            I hate to see ‘curtailment’ used in that fashion. What’s really being talked about is a device that isn’t optimally designed for the energy available at the site.

            Curtailment implies a purposeful turning off/down of a generator.

          • eveee

            Yes. Curtailment is active over time. Changing the rotor vs generator size is a permanent change to improve demand matching.

          • Bob_Wallace

            I am so looking forward to see capacity factor and generated electricity costs for the turbines we’re now installing.

            Will the price of PPAs in 2015 reach $0.03/kWh (unsubsidized) or will it take a bit more time? How long will it be before we see CFs higher than 60% (except for that uniquely sited Hawaiian wind farm)?

          • eveee

            We need to see some tall towers in the Midwest. Texas? They like big. And they have transmission.

          • neroden

            It makes absolutely no sense, in the long run, to permanently waste energy in that fashion.

            If the regulator is forcing residences to only sell 70% of their solar panels’ capacity, this provides a *huge* incentive to buy batteries so as not to waste it.

            Rather than putting an a generator which is undersized relative to the rotor, it would seem to make perfect sense to put in a right-sized generator and a big battery pack.

          • ROBwithaB

            Are the turbines remotely controlled on an individual basis? As in, are the adjustments made to the turbines themselves, feathering the pitch etc, or does the grid operator curtail the production in some other way across a wider area?
            And how are PV power plants controlled? Is there some sort of massive switch that you can just flick to take that power off the grid?
            Sorry about all the questions. Feel free to refer me to a suitable textbook or website.

          • globi

            The turbines can be controlled individually (they control themselves mostly automatically during any wind speed and wind direction change). However, the grid operator usually controls entire wind farms.

            Inverters of small PV system automatically reduce power output as soon as a certain voltage or frequency has been exceeded.
            Large PV systems also provide reactive power and thus stabilize the grid even at night and can in addition can also be remotely controlled by the grid operator:

          • eveee

            Good post. IEEE Power and Energy Nov/Dec just covered this. If you are power savvy, you know about grid codes. In EU, they are advanced. Voltage ride through, VARS, stability, and more. Just as you say. Its a mix of individual and centralized control. Quite sophisticated. Same thing is starting to happen with solar inverters. Renewables can make the grid much more stable than conventional.

          • OneHundredbyFifty

            Thanks for the link. This post has a good bit of info on HVDC and UHVDC – It is a bit outdated as it would appear that the 1100kV is close enough that people can consider 10GW as the carrying capacity for a bipole line rather than the 6GW in the graphics at the link.

          • Carl Raymond S

            Does a safer car require softer tyres, wider tyres or better brakes? I think the answer is ‘all of the above’. The market will sort out the ultimate ratio of each measure.

          • Bob_Wallace

            That’s true, and the point I’ve been trying to make.

            We have people who show up from time to time and declare that the solution is to string cables around the globe and run ever thing on solar.

            What they aren’t understanding is that they have no cost estimates and it may be far cheaper to use smaller regional grids.

          • The safer car has an increased ‘envelope’ surrounding it. Better driving habits/safer roads.
            Know your safe driving limit, stay with in it.

    • eveee

      There will be more DG in the future than today.
      The ISOs (independent system operators) are constantly doing financial analysis of these factors to determine whether local generation or transmission lines are justified. Transmission is actually only a small percentage of the energy cost, thus many transmission expansion plans have been approved. NIMBY is what slows development, not financial benefit. Both DG plus storage and network expansion are tools to increase renewables integration. We should use both. The situation is different in different locations. Australia and Hawaii are very favorable for DG plus storage. I expect many remote or rural locations will be.
      Not so city and urban environments, but still local generation, like offshore wind on the East Coast, is starting to appear profitable and desirable, At the same time. new taller tower turbines are arriving there, and new transmission is being built. The power system is so large that there is definitely need and usefulness for all of these solutions in a variety of different situations.
      I am a bit concerned that DG may not be accurately accounted for in utility planning. Seems so since EIA does not accurately track installation. Some states do a better job of tracking information.

    • OneHundredbyFifty

      “An attempt to make the grid and thus the utility companies more relevant.”

      Currently the best wind resources are highly underutilized due to the lack of geographic proximity of the best wind resources to the most voracious loads. The link below offers some poor man’s GIS work that makes the point quite clearly. The 50 to 65% CF wind available in the best Great Plains sites coupled with East Coast off shore wind, combined with solar offers considerable stability. Batteries will play a growing role but an industrialized society without the grid is like PCs without the Internet. Without the grid, energy intensive industries such as computer server farms and aluminum will have to continue to use fossil fuels. Batteries just don’t solve the problem for energy dense applications.

      • Bob_Wallace

        “Batteries just don’t solve the problem for energy dense applications.”
        Did you think that through? Applications don’t care whether the electrons come directly from the generator or from storage.

        • OneHundredbyFifty

          Let me clarify. Early in the thread a poster alluded to the idea that batteries made the grid less relevant and I understood the posters proposition to be that the grid would become irrelevant. Renewables are not a dense energy source and so are not practical for on-site production in combination with batteries and off of the grid. So an elimination of the grid would require high density generation for these industries which would almost surely be fossil fuels. My point was not to suggest that batteries have no role. My point was that the grid is good and batteries do not eliminate the need for it any more than the PC eliminated the need for the Internet.

          • Bob_Wallace

            “Renewables are not a dense energy source and so are not practical for on-site production in combination with batteries and off of the grid.”
            That sentence does not make sense. One can argue that sunshine and wind are less energy dense than uranium but energy density is not an important metric.

            The important metric is the cost of creating usable electricity from a given source.

            The issue is hours of availability. A grid (large or small) that can only produce electricity from solar, and to a less extent wind, would need a very large amount of storage in order to operate 24/365.

          • OneHundredbyFifty

            I don’t think we are in disagreement. My point is that the grid is important and likely will continue to be for the foreseeable future. Batteries do not change that. Better, lower cost batteries help but utilizing the grid to smooth renewables will be continue to be very important for the foreseeable future if we want to see high penetrations of renewables.

    • eveee

      Marion. There is much more to this picture than transmission and averaging.
      Take a look at the text in the graphic. Its all about minimizing the extra reserves necessary.

  • JamesWimberley

    Straight question. In Europe, FITs and similar mechanisms like CfDs do not SFIK include incentives for widening and flattening the wind output curve; it’s a flat rate pe kwh. American wind power is sold privately through PPAs, the public incentives being tax credits and renewables obligations. Do these PPAs reward widening?

    As far as I can tell, the recent increases in wind capacity factors have not been driven by incentives at all, but by technological factors. For example, towers have been getting taller to catch steadier high-level winds – the average in Germany is over 100m. Tower costs go up. They go up in proportion to the weight of the rotor+nacelle assembly, which is dominated by the heavy generator and gearbox, not the light rotors. So to keep the tower cost down, it pays to increase the ratio of the rotor area to the generator rating (the Su factor – see Bernard Chabot’s posts at Renewables International). This process would be accelerated if financial incentives for the broader output were added, in he interests of grid management.

    The chart illustrating the headline is drawn from a post on social media trends, not grid load patterns.

    • Jouni Valkonen

      The capacity factor of Windmill is depended on turbine optimization. High capacity factor yields lower production, because high wind production is curtailed. But on the other hand, high capacity factor can provide steadier production, because it can utilize better more common low winds. Therefore high capacity factor optimization produces less electricity, but it may produce more value.

      Of course, also technology has advanced as rotor diameter has been increased and hub height is taller. Also machinery is getting more advanced and more robust.

    • Bob_Wallace

      GE’s new wind farm software has increased output at some wind farms by up to 5%.

    • eveee

      You are opening up an interesting discussion about capacity factors and financial payback. Chabot has done a great service. Not sure how the EU system works vs US. PPAs benefit from anything that can lower operating cost or increase output, since PPAs are guaranteed costs per kwhr. There is a fundamental difference between capacity factor increases due to increased rotor size vs generator and tower heights. The former increases payback because wind power operates more often, at the expense of some peak output. Thats why you are asking about whether there are market mechanisms to facilitate it. Tower height increases capacity factor even with no change in generator or rotor and by a larger amount.
      Not too many new tall towers in the US, but they have been in EU for a while. The Enercon increased rotor and tower size, and is truly an impressive device.
      In the US, typical 2 to 3MW turbines were placed on taller towers. There is pretty good boost in output and capacity factor either way. I suspect its easier to start with a taller tower and a medium sized rotor, but I really hope the larger rotor and tower are adopted soon.

      • Bob_Wallace

        Chabot needs a better English language outlet. (And a style advisor. ;o)
        I’d love to see someone work with him to spruce up his presentations and put them online in a more accessible form and on sites with more traffic.

        • eveee

          Yes. I don’t like the pdf format. Something more accessible.

      • OneHundredbyFifty

        Here is some relatively current info on tall towers –

        And in the Great Plains they take wind power to about 65% CF according to NREL.

        • eveee

          I see new tower transport ideas here. The Lagerway article shows the steel section towers broken down to semicircles and bolted back together as a tube. Nice way of getting them past overpass limits. I see a bright future for taller towers and segmented blades to boost the size and height of onshore wind. I can’t wait to see it implemented more. Which do you think, taller towers, 2-3MW rotors, or both taller towers and bigger rotors?

          • Bob_Wallace

            Concrete towers. Sections can be transported on regular 18-wheelers or formed on site.

            Higher and bigger.

          • ROBwithaB

            Why not just steel lattice structures?
            Like they already do for construction cranes, transmission pylons, communication masts, bridges, etc etc.

            Less material, less wind loading, less worries about vortex shedding, easier to fabricate and much easier to transport.
            Is it aesthetics?

          • Bob_Wallace

            Lattice structures provide birds places to roost and can lead to more bird deaths. I would guess that labor costs would be a lot higher

            Concrete towers seem very promising. The sections can be transported on normal trucks or formed on site or at a concrete plant close by. They should last for a few generations of turbines and require little maintenance.

          • eveee
          • OneHundredbyFifty

            If I had to pick one it would be the GE spaceframe. But I really don’t know. I am just happy that the discussion has shifted from “can we build them that tall” to “which one is best”. I think higher capacity is likely. If we start building serious capacity in the Great Plains then I think we will also start mfg out there. The roads have little traffic and probably can handle long blades on a truck. Not a lot of bridges.

          • eveee

            Yes. I would like to see the economic signals reflect the true advantages of taller towers and get the ball rolling. These things have major implications for the future.

          • Bob_Wallace

            There are already factories in the Midwest.

          • eveee

            I thought about that. The taller tower may require more material and extra cost. But the energy reaped will be greater and may repay it sooner. If it does not increase the rotor size, the side loads are mostly limited by the cutout wind speed and rotor size, so the side load has not changed. The torque on the tower is a bit higher because of the longer length. The vertical load is about the same, a bit more because of added tower height.
            The bigger rotor has to be strengthened in both vertical and horizontal dimensions considerably. Enercons giant is an example. The base is wider and the tower more hefty overall. Probably why they went with concrete. Time will tell.
            I love the big beast, but they are putting up smaller units at 140m on the East Coast.
            I just can’t figure out why they don’t build them in the Midwest. That would be the ideal location.

          • ROBwithaB

            I see a lot of straight roads too, in the Great Plains.
            Really, really straight. Mind-numbingly boringly straight. Which makes the long blade thing a lot easier. I’ve watched videos of turbine blades inching up mountain passes on the backs of lowbed trucks. Agonisingly slow. And really disruptive to other traffic as a result.
            If one is planning to do a massive roll-out of wind capacity, the simplified mass production approach needs to extend to the transport/logistics as well.

          • Bob_Wallace

            I continue to wonder why no one has tried transporting with a lighter than air ship. Straight line from the blade factory to the wind farm. Lower them right where the crane can pick them up.

          • ROBwithaB

            Maybe because wind turbines like windy places.
            And airships don”t.

            Just a guess. Because otherwise it’s a great idea.

          • ROBwithaB

            How about a “towed” airship? If there are no bridges or overhead powerlines between the manufacturing plant and the windfarm, one could tether the airship to the back of a light truck. That way you get the horribly oversized load off the road surface.
            Something like a 3 tonner with some ballast on board. It would need to go quite slowly to avoid huge drag losses, but it might be easier than those huge flatbeds that clog up the roads.
            (This is probably one of those silly ideas that indicate I should now go to sleep.)

          • eveee

            Its an area of study, particularly in EU, where IMO, it has found solutions. In particular, the Enercon E-126 giant 6MW turbine. It uses concrete towers, and segmented blades, to allow easier blade transport. The concrete tower is on site construction.



    • The best wind designs have the generator at the bottom, like the solar chimneys.

      • Bob_Wallace

        If you have nothing of value to add to the conversation, please abstain.

        • What? I’ve done lots of research on generators and wind. Lol

          • Bob_Wallace

            That was a hint, Wayne.

            Best take it.

Back to Top ↑