Some Skepticism on Solar Thermal Power’s Storage Potential

January 24th, 2012 by John Farrell

This post originally appeared on Energy Self-Reliant States, a resource of the Institute for Local Self-Reliance’s New Rules Project.

Earlier this month, New York Times reporter Matt Wald had a piece on the role of energy storage in supporting the expansion of renewable energy. However, his specific focus on solar thermal power generation overlooks the potentially high costs of relying on solar thermal power and also overlooks the potential for distributed “storehousing” of renewable energy.

Solar thermal power is generally understood as centralized electricity generation created by concentrating solar energy to heat water, make stream, and power a turbine. Solar thermal supports heat storage (for an additional cost) that allows the power plant to shift electricity production to other times of day. It’s a technology at the early stages of commercialization, and is generally pursued because the cost of solar thermal storage is low compared to the total capital cost (although the cost of solar electricity is much higher than for other solar technology).

For example, the article highlights the SolarReserve solar thermal project, a 110-megawatt power plant that received a federal loan guarantee worth $737 million. If the SolarReserve project is built at the same cost as its loan guarantee (unlikely, as it seems the guarantees are usually for about 80% of the project cost), then its cost is around $6.70 per peak Watt. In contrast, the Solar Energy Industries Association reported that utility-scale solar PV in the second quarter of 2011 was installing at an average cost of $3.75 per Watt.

The comparison isn’t precisely apples-to-apples, of course. The SolarReserve project will operate at a higher capacity factor than a PV project of comparable size. The bigger question is whether the $3 per Watt difference justifies the amount of storage provided. Battery storage for PV costs about $0.50 per Watt for each hour. So a PV project at the average 2011 price could add 6 hours of battery storage and be built for the same cost as the SolarReserve. It may explain why a fair number of solar developers have switched from concentrating solar thermal power technology to PV in the past year.

The other consideration is how much storage makes economic sense. In general, battery storage doesn’t have to last all night, but merely fill the gaps between production and consumption of electricity. Storage for solar thermal is relatively cheap, so the SolarReserve project has 10 hours or more of energy storage and only adds about 5% to the cost of the project. But does solar PV need 10 hours of storage to compete? Unlikely.

With solar, the goal is to generate power during the time of peak demand for electricity (hot, sunny afternoons). The NREL researcher quoted in Wald’s article suggests that widespread adoption of PV (a phrase not explained, unfortunately) would quell demand for electricity during the afternoon and make the early evening – when PV no longer produces – the key timeframe for electricity generation, implying a big advantage for solar thermal. But solar PV projects don’t need to match solar thermal’s storage capacity to win the economic argument. If a PV project has just 2-3 hours of storage, enough to shift its output into the evening peak hours, it will largely fulfill peak demand and still cost less than solar thermal.

The NREL researcher suggested that energy storage could be worth as much as 4 cents per kWh (largely from the avoided cost of building new natural gas plants). But if solar PV can meet the peak electricity demand with shorter storage and at lower cost, it’s unlikely that the solar thermal power plants will be able to compete. Shifting production into early evening to serve peak electricity demand can be very profitable, but trying to sell noontime sunshine at 10 PM when wind power is increasing is something else entirely.

Storage doesn’t have to be a power plant add-on, either. Other sources of storage, like electric vehicles, may be able to have an increasing impact. Researchers at the University of California, Berkeley, project that the U.S. will have 10 million electric vehicles on the road by 2020, offering a combined storage capacity – if they are similar to the Nissan Leaf – of 240 million kWh (enough to power over 7 million homes for an hour). PNNL did a study late last year and found that 2.1 million EVs in the Pacific Northwest could support enough storage to add an additional 10 GW of wind power in the region.

I’m also skeptical of the ability of solar thermal to have anything more than a marginal impact, simply because of the development timeframe. According to Greentech Media, the total concentrating solar thermal power capacity under construction or with a permit and PPA in hand is just over 1.1 GW. That probably won’t be fully deployed until 2017. In the meantime, there was over 1 GW of solar PV deployed in the U.S. in 2011 alone. With no growth at all, solar PV would install 5 times the capacity of solar thermal power by 2017. And, by 2017, the cost of solar PV (if continuing to fall at current rates of ~7% per year) would be $2.45 per Watt. Solar thermal electricity generation doesn’t seem to be benefiting from the same learning curve nor installing at a pace that will allow it to catch up. And the ongoing cost differential allows for many other options for storing solar power other than combining storage and solar power generation in costly, centralized solar thermal power plants.

I don’t have the answer to the storage question, but I’m skeptical that costly, centralized solar thermal power plants are the best answer to matching renewable energy supply with electricity demand.

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Tags: Concentrating solar thermal power, Electricity, Energy, renewable energy storage, solar thermal power, storage, US

About the Author

John Farrell directs the Democratic Energy program at ILSR and he focuses on energy policy developments that best expand the benefits of local ownership and dispersed generation of renewable energy. His seminal paper, Democratizing the Electricity System, describes how to blast the roadblocks to distributed renewable energy generation, and how such small-scale renewable energy projects are the key to the biggest strides in renewable energy development. Farrell also authored the landmark report Energy Self-Reliant States, which serves as the definitive energy atlas for the United States, detailing the state-by-state renewable electricity generation potential. Farrell regularly provides discussion and analysis of distributed renewable energy policy on his blog, Energy Self-Reliant States (energyselfreliantstates.org), and articles are regularly syndicated on Grist and Renewable Energy World. John Farrell can also be found on Twitter @johnffarrell, or at jfarrell@ilsr.org.

Will Stewart

Comparing emerging solar thermal storage generation against commercially established PV is comparing apples to crescent wrenches, especially given the huge difference in NRE costs, labor pool skill acquisition, OEM efficiencies, etc. I’m puzzled why such a comparison is being made at all.
- Breath on the Wind
  
  There are several common denominators. Both solar thermal and PV are used to generate electricity. Both use solar radiation as a source of power. Beyond this people are intrigued with a seeming paradox that solar thermal can be twice as efficient as PV but PV is cheaper. This might be credited to the economies of scale from mass production for PV compared to the custom installation for PV plants.
  
  Your wording also suggests some confusion. There is “solar thermal electricity generation.” Concurrently there can be “solar thermal storage” which can make power plants more efficient with a higher ROI and with a substantially higher capacity factor but storage is not generation.
  - Bob_Wallace
    
    People sometimes get hung up on efficiency, capacity or energy density. All those things are important, but only to the extent that they help drive cost. Cost, in particular cost to deliver at the time desired, is the important metric.
  - Bob_Wallace
    
    Will thermal solar be competitive? It’s kind of hard to see it directly competing with PV solar when the Sun is shining.
    
    Thermal solar with storage could find a role if it can produce cheaper power in between the time the Sun goes down and the wind comes up in places like SoCal. But PV and cheap storage could beat it out.
    
    A more likely competitor will be wind imported from Wyoming. IIRC the evening wind starts picking up about the same time Pacific Coast sunshine starts to fade. We’ve got most of the transmission line in place, actually two of them. There’s the “coal line”, the Intermountain Intertie that comes down from Utah and the “hydro line”, the Pacific Intertie that carriers PNW power to SoCal. Plans are underway to connect the upper end of the two, creating a loop and then running a spur up to Wyoming’s excellent wind.
    
    Then there’s offshore wind. Floaters off the Pacific coast could disrupt bunches of plans.
    
    Thermal solar might have a more important role in parts of the world that doesn’t have the evening/nighttime wind resource, making thermal storage more valuable.
CB

I’m not sure price per watt is a sensible way to compare different technologies. From my understanding, you can install PV for cheap and then it goes bad in a few years and you have to replace it, whereas with solar thermal, it keeps working and working with minimal repairs.

A better way to compare would be price per watt-hour (or kilowatt-hour) over the lifetime of the plant.
- Bob_Wallace
  
  What’s your timeline for “goes bad in a few years”?
  
  The oldest solar arrays are now over 30 years old and have lost little of their output. A few individual panels have failed, largely due to terminal corrosion or panel delamination, but that’s been a very minor problem.
  
  I do agree that price per kWh over lifetime makes a lot of sense.
  
  We generally compare generation technologies over 20 years, paying off the capital expense over that time period. But that ignores the following years. While, for example, a fossil fuel plant and a wind farm might generate power at roughly the same cost over 20 years, at the end of that 20 years the wind farm both will continue to produce power but the wind farm will not have a fuel cost, meaning significantly cheaper power.
  
  Same for solar. It’s now cheaper than new nuclear and new coal. After the 20 year payoff period the price of power falls to almost zero per kWh. And that goes on for …, well, we just don’t know how many decades. There is no indication that at some point solar panels quit working. They could be producing 90% of their starting power when they are a century old.
  - CB
    
    I don’t think that’s quite true. It looks like PV suffers about 1% degradation per year, so the panels are basically worthless after 100 years… which is a pretty long time, but during the same period, things like wind and solar thermal are still running 100%.
    
    I wouldn’t ordinarily even consider the cost of coal, given the catastrophic economic damage it does to the environment, but I’m seeing a levelised cost of 10-20 cents for coal vs. 20-30 cents for PV… and with wind costs between 10-25 cents, it suggests to me wind is still the way to go for generation, but you still have that pesky storage problem. :S
    - Bob_Wallace
      
      Please show us some documentation of 1% degradation per year.
      - CB
        
        There are tons of papers about PV degradation on the internet. This one looks like it’s found a 0.7% average:
        
        http://www.nrel.gov/docs/fy11osti/47704.pdf
        
        I’m surprised it’s not worse, PV is basically like putting a computer into a wet microwave. You can only do so much to weatherproof it. Mirrors tend to be a little tougher, but I’m suspicious what really makes solar thermal expensive is moving parts like heliostats.
        
        In an article like this, I’d love to know which part of solar thermal costs the most. I’m still betting you could pair something cheap like wind with thermal storage and get yourself renewable baseload power for less.
      - Bob_Wallace
        
        That average is not the best estimate. It is pulled higher by old-tech panels which degraded faster than what is now being manufactured.
        
        Panels manufactured post 2000 show lower loss over time.
        
        —
        
        Thermal storage would have to get far more than 40% efficient to be a player when it comes to storing electricity. It has to compete with 85% efficient storage systems.
        
        Being so inefficient means that more than 2x the amount of power has to be generated in order to produce the same output.
        
        That means that you’ve got twelve cent wind going in rather than six cent wind. Capital/operating expenses would have to be vastly cheaper in order to offset that daily higher supply price.
        
        —
        
        Solar panels are nothing like computers. Bad analogy.
      - Breath on the Wind
        
        Inefficiency is found in converting energy from one form to another. Solar thermal energy is responsible for the wind is already one conversion. Converting wind energy to mechanical rotation then to electricity and then to heat storage will always be less efficient than storing the sun’s radiant heat to thermal storage. This is why converting wind energy to mechanical rotation energy and then to compressed air seems more practical.
      - Heartboxer
        
        The site wont let me comment on your next comment so I have to do it here. But please clarify by what you mean by “more than 2x the amount of power has to be generated to create the same amount of power.” The way I read it I would assume you mean once the energy is generated then only 40% goes into usable energy this is not the case the 40% is the percent of energy that hits the earth in the form of light. Compared to pv which is around 15% its much better. I will agree though that the analogy that a solar panel is like putting a computer in a wet microwave might makes less sense than an ex president Bush speech.
      - Bob_Wallace
        
        CB is suggesting that generating electricity and using thermal storage to time-shift it makes sense.
        
        I’m pointing out that if thermal storage is only 40% efficient (his estimate) then you have to generate/store 2.5kWh in order to get 1kWh out.
        
        With pump-up hydro and battery storage efficiency is a bit over 80%. That means that you have to generate/store only 1.25kWh in order to end up with 1kWh of usable electricity.
        
        That puts a huge burden on the cost of building thermal storage. It would have to be so incredibly cheap to build and operate that it could offset a 2x input cost on a daily basis.
      - Bob_Wallace
        
        CB is suggesting that generating electricity and using thermal storage to time-shift it makes sense.
        
        I’m pointing out that if thermal storage is only 40% efficient (his estimate) then you have to generate/store 2.5kWh in order to get 1kWh out.
        
        With pump-up hydro and battery storage efficiency is a bit over 80%. That means that you have to generate/store only 1.25kWh in order to end up with 1kWh of usable electricity.
        
        That puts a huge burden on the cost of building thermal storage. It would have to be so incredibly cheap to build and operate that it could offset a 2x input cost on a daily basis.
      - CB
        
        Bob is absolutely correct. If you can only retrieve half of the electricity that goes into a thermal storage system, you need to build out twice as much primary electrical generation, so your generation cost is effectively doubled.
        
        My point is that you could use some of that lost heat energy to sequester carbon and manufacture things, which we’ll need to do anyway. Why not get the most bang for your buck?
        
        PV is totally the same as a computer chip. It’s all just silicon, and it’s fairly delicate. I think they protect it the best they can, but there’s no reason to expect it to last forever with the wind, rain and sun eating away at it. Windmills are tough and last much longer.
    - Bob_Wallace
      
      “Two aspects of major importance for any solar module are energy conversion efficiency and product life. As a pioneer in multicrystalline silicon solar cell manufacturing technology with one of the highest conversion efficiency rates in the industry, and with a longer track record than the vast majority of market players, Kyocera points to a number of case studies from around the world which demonstrate its modules’ long product life and quality.
      
      In 1984, Sweden’s first grid-connected photovoltaic system was built in Stockholm. Since its installation, the façade-mounted 2.1kW system has been continuously and reliably providing the residents of an apartment building with environmentally-friendly electricity. The modules’ average annual power generation performance is still reliable — with no significant change since the system was installed 27 years ago.
      
      Also in 1984, Kyocera established its Sakura Solar Energy Center just outside of Tokyo. At the time, the Center was equipped with a 43kW solar power generating system which to this day continues to generate a stable amount of power for the facility.
      
      In 1985, Kyocera made a donation of a 10kW solar power generation system to a small farming village with no electrical infrastructure located at an elevation of 2,600m (8,500ft) in Gansu Province, China. In 1993, the area received electrical infrastructure, and the solar modules were moved to a regional research facility for clean energy, where after more than 25 years, they are still producing consistent levels of electricity.”
      
      http://kyocerasolarnews.wordpress.com/2011/12/20/kyocera-solar-modules-deliver-reliable-performance-after-more-than-25-years-in-the-field/
      - CB
        
        There’s something else you need to consider when comparing relative levelised generation costs: carbon output per kilowatt.
        
        http://www.parliament.uk/documents/post/postpn268.pdf
        
        PV produces up to 5 to 10 times more carbon per kilowatt-hour than wind. If you consider the cost of continuing to produce atmospheric carbon goes to infinity (which it does), wind comes out on top, even if it costs at minimum 5 times more than PV (and it looks like offshore wind is getting more expensive, given the latest EIA report):
        
        http://www.eia.gov/forecasts/aeo/pdf/electricity_generation.pdf
        
        Thermal storage has to compete with systems that are twice as efficient and at bare minimum 7 times as expensive… plus they wear out more quickly… plus they are distributed over a wide area… plus they don’t have waste heat you can use to sequester carbon in our waste stream, make cement sustainably or even process the silicon needed to make PV panels or the parts required for windmills!
        
        I’m not sure why you wouldn’t be suspicious of a company’s claims about their own product… not saying Kyocera is wrong, but it’s not an impartial source…
        
        I’m also not sure where you’re confused about solar panels being similar to computer chips. Both computer chips and PV panels are electronic components precision-crafted from silicon in clean rooms. They are both extraordinarily delicate, but one is housed in plastic boxes indoors and one is thrown out into the elements. It looks to me like the EIA report has taken the delicacy of PV into account, and without carbon accounting, it looks like PV would still be more cost-competitive than offshore wind, but not onshore wind.
      - Bob_Wallace
        
        Divide the amount of CO2 produced during the manufacturing of PV by 50 to 100 years.
        
        Wind may or may not cause more CO2 to be produced. We don’t have evidence of wind turbines lasting more than 30 years to date.
        
        With either the CO2 footprint is low enough to be totally acceptable.
        
        What are the costs of thermal storage? And what are you using for the price of pump-up and battery storage? Where does your “7x” come from?
        
        Your comparison of PV panels to computers is bull. I suspect you’ve never seen a solar panel. Silicon solar panels are basically thin sheets of rock placed behind glass covers. To say that PV panels are “extraordinarily delicate” is a crock.
        
        Will PV become less expensive than onshore wind? It doesn’t matter. It’s likely to become cheap enough to be the ‘daylight’ producer while wind will be the major ‘nighttime’ producer.
      - CB
        
        Why would you need to divide the amount of CO2 produced during the manufacturing of PV by 50 or 100 years? What does this have to do with the relative cost of sustainable energy production? I’m not comparing it to coal, I’m comparing it to wind. Do you disbelieve the UK study that shows PV produces 5 – 10 times more carbon per kWh than wind? If so, why?
        
        I’ll give you a very good reason why we should expect this to be so: In terms of sheer energy density, wind is many times higher than solar. This means the amount of machinery required to capture it is many times less. Given fossil fuels are currently being used to create this machinery, it is no surprise that the carbon footprint of wind is smaller than the carbon footprint of PV.
        
        I’m going to have to take issue with the concept that any carbon footprint is acceptable. For the earth to remain habitable, we need to be taking carbon out of the atmosphere, not simply reducing the amount we put in.
        
        Photovoltaics are thin sheets of rock. Correct. What do you think silicon chips are? o_O
        
        Reducing buffering requirements by balancing nighttime production with daytime production is a good idea, but does not eliminate the need for energy buffering.
        
        I just gave you a real world comparison of storage space required in a sodium-sulphur storage system set up by Xcel Energy vs. the storage space required in the Andasol salt storage tanks which showed the former would need 7 times the physical space to achieve the same energy storage. If you are suggesting a cubic foot of salt costs same as a battery of the same size, that’s a 7-fold cost advantage for molten salt storage straight out the gate, not to mention the other benefits of sequestered atmospheric carbon, free usable biogas and biofuels, carbon-free manufacturing of cement, steel and other industrial processes, leveraging of existing centralised infrastructure and technical expertise, and the fact that batteries are going to continue be far more expensive and far less durable than salt!
        
        I’m not comparing the costs of pump-up storage. At 6 gW maximum capacity, it’s not going to be able to provide the amount of peak power the country is capable of demanding.
      - Bob_Wallace
        
        CO2 footprint over lifetime is the most important measurement.
        
        Cost is a separate issue from CO2 footprint.
        
        Time of production is important. Solar produces during peak demand hours.
        
        You seem to be unable to understand the role of efficiency in storage. It doesn’t matter if one system is somewhat cheaper if it costs multiple times more to operate over its lifetime.
        
        You don’t comprehend how much pump-up we could build if that was the smartest way to store power.
        
        We already have somewhere around 22GWs. We could build hundreds of GWs more if desired.
      - CB
        
        The CO2 footprint over the lifetime of what is important? The unit? Is the goal to emit the least carbon per unit or per kilowatt-hour?
        
        Please tell the people of New Orleans there is no cost associated with a carbon footprint.
        
        Maybe there is more available power we could extract from pump-up systems. The paper you gave me cited 6GW of additional power capacity possible to build out. That is not enough to supply the nation with the 800GW of power it’s capable of demanding… so unless you’ve got another source that contradicts your first one, let’s table discussion of pump-up systems for now. I know you love them and I do too, but I don’t think they’ll be able to solve this dilemma.
        
        Let’s do a thought experiment: What if we built out enough PV and enough batteries to supply the entire nation with baseload power. You’re still left with a system that’s producing carbon and continuing to make our planet uninhabitable. If you wanted to make such a system sustainable, you’d have to take a portion of that energy you produced and create heat with it to create the solar panels and batteries needed to run your system plus pyrolise your waste stream in order to remove carbon from the atmosphere.
        
        If you used windmills and buffered your energy with heat, on the other hand, you’d start off with a fifth to a tenth of the carbon debt and you’d already have a readily available source of heat for carbon sequestration and industrial processes that make our way of life possible.
        
        The 60% “waste” heat isn’t actually waste at all, it’s replacing the heat from fossil fuel now used for cement, steel and silicon production AND once you ran out of demand for that, you can use it to pyrolise your waste stream, create fossil-free fertiliser, fossil-free chemical energy for mobile applications and actually reduce atmospheric carbon concentrations.
        
        Now do you understand why this is the least expensive option? You have to think of the long term…
      - Bob_Wallace
        
        CB, I’m getting tired of trying to discuss stuff with you. You make up numbers and treat them like facts. You can’t seem to wrap your brain around concepts.
        
        Lifetime CO2 footprint is what is most important when comparing generation methods. Think about it.
        
        The paper I linked found that there were approximately 6GW of additional generation available from existing federal lands. Consider the fact that only a small percentage of our 80,000 existing dams are on federal land.
        
        Additionally, and you failed to do this, dive deeper into the data and you’ll see that there are many additional existing dams which are not usable for generation – they don’t have adequate inflow. But they are find for pump-up.
        
        Thermal – it’s too damned inefficient. You cannot double your supply cost and compete unless your technology is incredibly cheap, and turbines don’t get given away.
        
        As for your heat issues, you’ve moved off into the land of bullshit.
        
        Now, you make the final post to this conversation. I’ve got more important ways to spend my time.
      - CB
        
        Lol! Which numbers have I made up? Please be specific.
        
        Lifetime CO2 footprint per WHAT is most important? Pound? Are we trying to produce pounds here or kilowatt-hours? This paper:
        
        http://www.parliament.uk/documents/post/postpn268.pdf
        
        says PV produces from 5 to 10 times more carbon per kilowatt-hour than wind over the lifetime of each system. If you disagree with the analysis, please let me know why. Saying the numbers are made up does not necessarily make it so.
        
        I like pump-up storage. It’s efficient and has a low carbon footprint, but it also doesn’t solve the problem of industrial production of carbon, whereas thermal storage does.
        
        Your cost valuation is based on a short-term analysis. The system you would have us build is more sustainable than that which we currently have, but still unsustainable in the long run.
        
        In order to make it sustainable, you’d have to create additional infrastructure. You’d have to create every bit of the heat in a thermal-buffered system for industrial production, plus 5 to 10 times the heat for carbon sequestration, but instead of capturing 40% of it for electricity generation, you’d just be flushing the rest down the toilet… so you’d have 60% greater costs for generation (9 cents per kWh wind vs. 15 cents per kWh PV), more than 7 times the cost for storage (7.6 x 10^9 cubic feet of battery storage vs 1.0 x 10^9 cubic feet of molten salt in a 240 gWh system), the cost of an entirely separate infrastructure for the production of steel, cement, silicon and other industrial products, and the cost of an entirely separate infrastructure for carbon sequestration which will be at minimum 5 times more expensive than colocated carbon sequestration thermal storage facilities…
        
        How in the world is all of that supposed to be less than twice as expensive as a wind-thermal system?
        
        If you disagree with any of my numbers, please let me know. I’ll be happy to admit if any of them are off-base.
        
        What don’t you understand about the use of heat in the production of steel, concrete and silicon and its use in the sequestration of carbon in garbage, sewage and agricultural waste through anaerobic thermal processing? I know this stuff is difficult to understand, but I don’t mind explaining it if you need me to.
    - http://crissa.twu.net/ Crissa
      
      I find the UK parliament paper you state of dubious value when comparing power generation to their carbon footprint. While solar has a big investment in glass and silicon, and this footprint doesn’t change per installed size, the footprint for wind generation takes an investment in steel and oil that’s not calculated in, and has a different footprint based upon its size.
      
      And the preamble of the document basically states that their numbers are comparing apples and oranges, as well as different suppliers will sit outside the range.
      
      Lastly, like in this comment, you don’t seem to care about any externalized costs – such as the huge health impact of coal mining, distribution, burning, and dealing with its waste. And you’re constantly on about storage – storage is also a problem for any system that creates power intermittently, such as wind.
      
      Solar’s big advantage is that its peak production is similar to peak demand when other types of production are more expensive – even coal is more expensive to run during the summer than the winter. (Turbines require a differential between internal and environmental temperature, the greater the differential the greater the theoretical power output, and hence, can produce less power during warmer times than cooler ones).
      - CB
        
        Well, that’s absolutely true, there is a good deal of CO2 created in the production of the steel, concrete and other components in windmills. The UK paper takes this into account, and the reason why wind still comes out on top is because of the energy density of the relative sources. If you consider PV produces around 10 watts per square foot, you’d need 600,000 square feet of paneling to match a 6MW windmill! … so even though a 6MW windmill is gigantic, the size of an equivalent amount of PV is even greater, plus it’s distributed over a wider area, and it goes bad and needs maintenance quicker. All of this adds up to a greater CO2 footprint per kWh.
        
        I realise in an age when denialists seem to have a science-free stranglehold on the public discourse, one might want to do something personally, and I see PV as a much better course of action than doing nothing (The new water-cooled PV looks especially promising), but if we as a nation really wanted to maximise our sustainability efforts, wind is the way to go. I don’t like arbitrary credits being given out for different technologies. There should be a simple, gradually-increasing carbon tax, not micro-managing different industries.
        
        Storage is absolutely key to shutting down coal plants. I didn’t quite understand how power generation works when I first started researching it, but you can’t just shut down coal plants when you don’t need them and fire them up again when you do. They provide baseload power, which means they just run and everything else is auxiliary to them. If you set up thermal storage tanks in these plants, however, you could concentrate energy from windmills (or solar panels, or any other type of intermittent generation source), and provide a constant renewable supply of electrical generation… but what’s really nice about thermal storage is you can also use heat to do things like cast steel and melt silicon as well as stripping energetic hydrogen off sewage, garbage and ag waste, capturing that chemical energy for later use and producing carbon in a much more stable state that won’t be turned into methane by bugs and fungi… so you can actually go carbon-negative with it.
        
        I would never suggest there is anything reasonable, moral or acceptable about the mining, transportation or burning of coal. It’s a horrendous toxic nightmare from start to finish.
      - http://crissa.twu.net/ Crissa
        
        A better way to go is to go with what makes energy when we need it the most and choose many sources of energy.
        
        Which means solar should be a large part of our energy solution. Another thing I think should be big that isn’t yet: Natural gas generation in landfills. We have alot of landfill and garbage that could be consumed for energy production, but is not.
      - CB
        
        … but this is what I’m talking about. Most of the stuff in landfills can be treated to separate the high-energy hydrogen from the low-energy carbon. Instead of letting bugs chew on it and turning it all back into greenhouse gas, you can throw it into pyrolising chambers and produce pure hydrogen instead of methane. All you have to do is add heat in an oxygen-free environment. The carbon deposition is nice and sterile for crops too.
        
        There is a lot of talk about matching generation to demand, most of which is overly-optimistic and missing the point. I’m all for load-matching when it will result in lower carbon emissions, but it will not be possible to get to negative carbon with load-matching alone. Right now we are at around 14% renewable electric production and we’re already having trouble with brownouts and stability. We need buffering capacity and we need it now! To my mind, thermal storage is one of the least expensive ways to provide it with the fewest drawbacks and the most additional advantages.
        
        … but there are so many moving parts to all this, it’s hard to tell the optimum way to plan it. How large should you size your facilities, for example? Moving electricity around is extraordinarily efficient; moving waste and raw materials around far less so, which suggests facilities should be more distributed. If we make storage too small, on the other hand, at what point is the heat loss so great that you have to build more specialised containers which increases your carbon footprint?… or what if some superior permanent carbon sequestration technology comes along which is so simple, it’s more worthwhile to build out PV and batteries, or even simply to burn coal!? (if you could scrub it enough to get the toxic waste out, of course).
        
        To answer these questions it would be far better to levy a global, slowly increasing carbon tax (and rebate for sequestration) which will allow people to put their money where their mouths are and bet on different technologies until the system is optimally efficient.
Breath on the Wind

The article could perhaps be more clear to say it is discussing only electrical power. When heat energy is needed as Solar Thermal has been used for thousands of years and stored in thermal mass of our homes. Solar thermal is far more efficient than PV for heating.

Even within the scope of commericial energy the given numbers only discuss the initial cost and not the long term or replacement costs of batteries. The cheapest storage batteries will last only about 3 years. The major unsolved problem with V2G technology is that increase use of the vehicle battery will shorten the useful life of the battery.

Solar thermal Electrical production remains about 2X as efficient as PV electric, but power plants must be large and will not produce power until the entire project is completed. Projects may be mechanically complex but not electrically sensitive or chemically toxic.

Today PV is cheaper. The trend is likely to continue. But Solar Thermal has a place, particularly in association with longer term storage, use as peaking plants. There should be little argument to Solar PV or Solar Thermal power stations when both are an alternative to fossil fuels.

Solar thermal is a bridge to older thermal power plant technology, and if Mit’s chemical heat storage batteries ever become commercially available the technology they will be a bridge to the future.
greg

The idea that most people will buy electric vehicles then plug them into the grid at night and this will balance the load clearly has not truly been thought out. Let me lay down an example. I would go home from work and lets say type into my computer that I want to have my car fully charged by morning so i can actually make it to work the next day. Then my car would make the decision to buy and sell electricity throughout the night to make a profit for me. It would also need to take into account the fact that it has around a 10% loss from charging and discharging not to mention the fact that the electric company looses 7% through transmission. Then taking all that into account you would need the price swing throughout the night to be so large it would make the economics work out. That idea is somewhat nuts because the prices should be highest during the day when people are driving. The idea is good in theory but it simply hasn’t been fully thought out. And if you think people will be motivated by the money you really think Americans especially will say hey I can go through all this hassle to save a couple pennies you have to be out of your mind.
I think we need to think long term here you build these concentrated solar farms in conjunction with the PV this way when the sun doesn’t shine you aren’t out of luck. I understand right now you can install solar for cheaper then CSP but when the sun isn’t shinning you simply charge more for the power. Its the same thing for diesel engines or gas powered turbines they don’t run continuously but when the demand is highest they charge more then coal or nuclear per kWh because they can match the load.
- http://cleantechnica.com/ Zachary Shahan
  
  i really think you’re over-complicating it. it is quite well known when electricity is cheapest — in the middle of the night. schedule your car to charge up during that time period. you’re not scheduling it to go back and forth throughout the night.
  - Bob_Wallace
    
    Consider the computer.
    
    The average person will need to charge less than 3 hours per night using a 240vac outlet. Simply being able to spread charging over off-peak hours has value to the grid.
    
    Many people will not need to be 100% charged at the beginning of the day. If the average daily drive is around 35 miles that means that roughly half of all drivers could skip a day or two if supply was short and fully charge on a night when power was very available/cheap.
    
    Even short time wind peaks could be sold to waiting EVs that might not use that power for several days, offsetting their need to charge on nights with lower supply.
    
    If the grid is smart enough to send information to the car and the car smart enough to act on it we’ll likely see some very innovative ways to make efficient use of dispatchable loads like EV batteries. Aps to be written.
    
    Yes, there will be some (likely few) people who need to charge 100%/100 miles every night. They can do so with the Leaf built in charger in 8 hours. Say 11pm to 7am, a simple timer function.
    
    They won’t get as good a price as drivers with more forgiving needs, but their price per mile will still be sweet.
    
    If someone drives 100 miles almost every day they might find it advantageous to install a faster (higher amperage) 240vac charger and take advantage of time of use pricing.
    - greg
      
      I was more referring to the fact that people keep stating using ev to store energy to balance the load. If you simply use a smart grid to get the cheapest electricity then yea it makes sense. But I was referring to people who claim to offset intermitency of renewables by using EV to charge when there is energy and discharge when there is none seems like a crazy idea because of what I said in my last post. Im not saying its a bad idea but I feel the need for cheap energy storage is the real solution to a sustainable future.
      - Bob_Wallace
        
        Well, there are companies that are testing out programs that “rent” battery storage from EV owners as a way to provide less expensive power to utilities.
        
        Think about 2am wind getting shifted to 7am when demand rises.
        
        If the grid can rent storage for a decent price then they avoid the capex of purchasing storage.
      - http://cleantechnica.com/ Zachary Shahan
        
        i’m all for other types of energy storage, but i’ve actually seen utility CEOs talk about this EV storage potential as a big potential help — these guys aren’t naive about the subject.
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CP

Batteries are expensive storage technology. G2V makes sense – many electric vehicles allow for load shifting, not storage, but load shifting would help support large shares of variable renewables in avoiding curtailment of energy. Pumped hydro is the reference storage solution, but it still comes at a significantly higher price than thermal storage in CSP plants. Plus, CSP plants are very flexible. A recent NREL report showed how they would help integrate more PV.
CleanEnergyInvestor

Maybe the energy could come from other EVs!
CleanEnergyInvestor

Using EVs for grid storage is a very bad idea. I don’t understand why it is still mentioned so frequently.

Energy density is very important for EV batteries. Using them to support the grid doesn’t make sense economically – because they are very expensive and using them for grid storage will wear them down more quickly. Also, they have a very limited capacity for the purpose for which they are intended – so it just doesn’t make sense to try to use them to support the grid. The numbers used here do not make sense at all – because you could only count on a very small fraction of of the total ever being available at one time – even at night – so all these things together makes using EVs for grid storage a very bad and completely unrealistic idea for many many years.
- Anonymous
  
  The use of EVs for the grid is as a time-insensitive load. You don’t care whether your car is charging at 1 AM or 4 AM, so long as it’s done by morning. Neither solar thermal or PV is going to be supplying the power, of course. Wind is more relevant.
- dcmeserve
  
  When EVs have enough battery capacity to resolve the “range anxiety” issue — and therefore become the majority of vehicles — the batteries will be *very* oversized for the average commuter’s needs. Such commuters could then allocate 1/3 or 1/2 their capacity to “play the market”, and buy and sell electricity depending on price signals. If most of these EVs can be plugged in while at workplaces, they will collectively offer quite a lot of buffering capacity to the grid.
  
  Sure, current EV capacities don’t allow for this kind of flexibility. But they are currently a niche product for the very same reason. As battery tech advances, this will be resolved.
  
  However, you might have a point in that other, less energy-dense but cheaper battery technologies are also advancing. By the time there is enough spare EV capacity out there to really help the grid, other battery technology may completely out-compete it economically (and due to the fact that the power companies can own them outright, instead of having to play market games).