Published on January 22nd, 2016 | by Daryl Elliott


10 Reasons To Overbuild Your Rooftop Solar

January 22nd, 2016 by  

The Case for Overbuilding Your Rooftop Solar Array

When a solar company analyzes a residence for rooftop solar, they look at several items, including available unobstructed space (that is free from shade), electric bill usage, and size of budget. What is meant by overbuilding a rooftop solar array is to build out more panels than would be needed to address the home’s current electricity demand.

Full use of primary roof. Credit: No license with commercial use allowed per Google images.

First, there are a couple of points worth discussing before diving into the enumerated list. The first is an obvious potential limitation regarding this plan, and that is whether or not there is enough usable space on the rooftop for additional panels. If there isn’t un-shaded available rooftop real estate, then overbuilding rooftop solar becomes a moot point.

The second consideration is whether or not the homeowner(s) can afford to overbuild their solar project. It may not be that difficult to overbuild, though, since the added solar panels will have a reduced cost per panel relative to the panels in the primary solar array footprint, due to reduced relative soft costs (more on that later).

This leads us to consider the reasons to overbuild, and whether or not they are compelling enough for such an investment. Here are some points for consideration. Everyone is likely to rate the value of each point differently depending upon one’s point of view, and it’s possible that not all points will apply to everyone.

1. Increased demand for core home functions that require electricity.

Core home functioning is moving away from fossil fuels and toward electricity use. We are seeing more “smart home” connected controls for the thermostat, security, light control, keypad locks, refrigerators, and more.

Many of us believe that all of HVAC in homes is moving in the direction of electrical systems. For example, when solar air heaters are installed on the sun-facing side of the home, electricity-using fans are used to move air, and when solar hot water systems are installed, electricity is needed for water pumps. Overbuilding solar arrays leaves capacity available to accommodate these converted home services. Deploying expanded electricity capacity makes sense in this increasingly electrified world.

2. #Driving on Sunshine.

You may have need now or in the future to add one or more EV vehicle charging stations. Odds should be increasing in the coming years that any overnight house guest who drives to your home may be driving an EV that needs a charge. Overbuilding solar leaves room for EV expansion and accommodation.

Photo credit: Leilani Munter

3. Environmental benefits include overall reduced GHGs produced when rooftop solar increases output.

The theory here in this point is that a larger solar array will benefit the environment more than a smaller rooftop solar array. One expanded home solar array will obviously not change the world, but if more and more people do this, then in aggregate it will to some extent contribute in the right direction by displacing fossil fuels.

One clear benefit in the migration from burning fossil fuels to increasing renewables electricity production is the retardation of climate disruption due to fewer GHGs (greenhouse gases) being emitted. As more solar electricity is produced, gas and/or coal plants are used less and ultimately, in time, taken offline faster as we migrate to a clean energy world.

The environmental benefits of solar is a well-discussed topic on CleanTechnica. If you have interest in learning more, please visit “Going Solar Simplest & Biggest Action Anyone Can Make, Says SolarCity” by Joshua S. Hill.

4. More localized solar decentralizes the production of energy.

Many utility-grade energy plants require long-distance transmission to get to the final consumption point. The first and most obvious benefit of decentralized energy is that it doesn’t have to be transmitted if it’s used at the point of production; this increases efficiency. Decentralized energy production also makes any country safer from a malicious attack on the grid. As Amory Lovins’ Rocky Mountain Institute states it:

“Centralized electricity systems with giant power plants are becoming obsolete. In their place are emerging “distributed resources” — smaller, decentralized electricity supply sources (including efficiency) that are cheaper, cleaner, less risky, more flexible, and quicker to deploy.” (A brief summary of Distributed Energy can be found on Rocky Mountain Institute’s site here.)

For additional information about distributed energy, please consider reading these two CleanTechnica articles:

Moving Beyond Utility 2.0, To Energy Democracy,” by John Farrell

How Would A 100% Distributed Energy Grid Work?” by Zachary Shahan

5. Installing more solar panels helps the solar power industry.

Whenever energy-related purchases can be diverted from the fossil fuels industry and directed to the solar power (or any renewable energy) industry, this helps with new R&D funds, more clean jobs, and further reduced costs for renewables due to increased production volume.

6. Home resale value.

It’s a well-known fact that solar increases a home’s value when it comes time to sell the home.

According to the Lawrence Berkeley National Laboratory (Berkeley Lab), as reported in an article on (run by The Motley Fool guys), it is claimed that rooftop solar can increase a home’s resale value by about $15,000.

By comparing the sale prices of around 4,000 solar rooftop homes across 8 states and 12 years to nearly 19,000 comparable non-solar homes, researchers found that, for an average 3.6kW solar system house, buyers were generally willing to pay around $15,000 more than for a comparable non-solar home.

How much some added overbuilt solar would increase a home’s value has not been studied, but it has been estimated. In the same Berkeley Lab document, the researchers state that their models “… indicate decreasing marginal returns to increasing PV system size.”

This means that, to a large extent, overbuilding solar would have to be a labor of love and for motives that consider the big picture, and that aren’t strictly related to financial return.

7. If you have a storage system, it makes even more sense to overbuild.

Especially if you have a Powerwall or other storage system, overbuilding your rooftop solar could effectively make your electricity production and use self sufficient. The combination of overproduction and storage can provide you with flexibility to bring you effectively offgrid while still being connected to the grid. The combination of solar and storage would allow you to at least not lose energy that you produce that you may otherwise be providing back to the grid for no compensation (depending upon your utility’s net metering policy). Overbuilding prepares you for the possibility that your utility could have a favorable-to-consumer net metering policy in place at the time of solar installation that may be withdrawn later by the utility.

8. Overbuilding rooftop solar projects may reduce the likelihood of new dirty coal and/or nat gas plants being built.

Overbuilt rooftop solar, if done by enough people, would likely contribute by some modicum amount to reducing the need for new dirty coal or nat gas plants to be built as your utility’s electricity demand increases over time. This increase in demand could potentially be satisfied by this extra solar electricity production if enough people did it. All renewable energy production contributes favorably to the global ecosystem to some degree by reducing electricity production from dirty fossil fuel energy or nuclear energy.

9. The soft costs for a normal-sized project are fixed, so increasing the number of panels has only a very slight impact on the project’s soft costs.

If you are already going to install rooftop solar, the soft costs are already calculated into that project. To add some more panels is an efficient increase per solar panel. According to Barry Cinnamon of Spice Solar of Campbell, California, most of the soft costs are already covered if you were to increase the size of your system. Barry states: “Soft costs are generally fixed for a residential system. The fixed soft costs such as system design, permitting, interconnection, customer acquisition, labor and monitoring changes only slightly if the system size increases.”

10. Overbuilding rooftop solar anticipates more new electricity-sucking devices.

New, fun gadgets are being developed every year that either use electricity directly or that use batteries, which require electricity to recharge those batteries. For example, how can we live without Samsung’s smart refrigerator announced this year here in Las Vegas at CES that notifies the user that some food item’s expiration date is about to go bad in the refrigerator? (To be fair to other manufacturers, this idea isn’t brand new.) Indeed, we are seeing more and more devices with no end in sight.

Alternative idea.

A variant concept is to get more efficient panels (if the project isn’t already using the best panels) that would theoretically generate a relative increased gain; ideally, one would both get more efficient panels and more solar panels.


Overall, if your rooftop solar project size can be increased, there will be a number of sure benefits, and other possible benefits. The increased array size has long-term benefits, but of course must be affordable for the buyers. Go big.

If you work in solar sales and wish to reprint this article for customers, you have permission to do so.

If you increase your project size due to this article, or if you work in solar sales and use it, please feel free to write a comment below the article even if the comment comes long after this article is published. I’ll see your comment and reply.

Check out our new 93-page EV report, based on over 2,000 surveys collected from EV drivers in 49 of 50 US states, 26 European countries, and 9 Canadian provinces.

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About the Author

I have followed and supported solar, wind, geothermal since the 1970s. After discovering its strong environmental benefits, became vegan in the late 70s. Go green.

  • Nice updated reference to the CSN&Y song, Our House.

    • Bob_Wallace

      Written by Graham Nash when he and his then-girlfriend Joni Mitchell came home after buying a vase, I think, at a flea market.

      He just sat down at the piano and played it out.

      Man, that has a lot to do with clean energy,doesn’t it?

  • Ramon A. Cardona

    Can you cite any state where what you claim has happened? In solar power friendly states, producing more energy can generate cash flow.

  • campbell2

    if we were allowed to use the previous generation meters which run backwards if you are generating more power than you are using
    but no uk is such a mess that this is not possible roll on the next affordable storage devices and you cannot be ripped off. With the old meter in place consumption down by 95% UK

  • cutter1954

    I recently bought a 24 panel tracker as opposed to a 20,for 10% more total,despite suspecting that I may well have overshot my electrical consumption.I suppose that one day,if alive,I will replace the volt with just an ev since it’s annoying that it has to run the gasoline motor slightly when I drive the four miles to work now when it’s 10 degrees outside.But that may not increase my electrical demand much,since where would I drive anyway?(presque isle,me)

  • JBArriola

    After a solar flare like the Carrington event, all that distributed energy production and other electronics will be junk piles.

    • Ronald Brakels

      Distributed? Powerlines from houses to local substations are what’s known as short. It is long distance powerlines that risk having currents induced that can wreck transformers, particularly some lovely long transmission lines in the US and Australia. It is distributed generation that will be safe and those with islanding distributed generation will consider themselves lucky should long distance transmission be taken down by a geomagnetic storm. Fortunately we will have from one half to several days warning of such an event since space is still big, even for charged particles, and so we are unlikely to suffer any prolonged interruption grid function.

  • vensonata .

    I think you can put up all the panels you want off grid. I certainly never asked anyone. Your neighbors might have an opinion though. You are right, PV is the best investment for your ratio of cooling days to heating days. Only attic insulation can compete with PV these days. Nothing else can, including heat pumps, windows etc.

    • neroden

      Actually, if you have a poorly insulated house, Superinsulation / PassivHaus retrofits can easily compete with PV. Don’t just do attic insulation, do it properly. (Windows are the absolute last priority: ceilings, walls, doors, and floors in that order)

  • Hank1946

    Did I do something wrong? My post a little over 4 hours ago is missing.

    • Bob_Wallace

      Mod is on the other side of the world where it was sleepy time….

      • Hank1946

        Thank you it just showed up.

  • Hank1946

    Here’s a thought just have the mounting system pre installed and with conduit maybe wired but not connected then you can install as you want. Where I live from what I have found permitting is easy and not to expensive so have everything installed you can’t do and then add more as money and time permit. May cost more to start but less when the need arises?

  • Freddy D

    Great points in the article. I would also add a heat-pump conversion in the future. Most residences are heated with natural gas and this can convert to a heat-pump. This is one of the energy heavy-hitters in a house, along with the automobile and summer AC. All the TVs, computers, lighting, is small stuff and getting smaller as LEDs take over.

    Furthermore, EVs are pretty marginally useful right now (Tesla and Volt excepted). This will change big time by the end of the decade and you’ll see more 2-EV households or exclusively EV households, vs today where it’s a mix of gasoline and EV at best. The EV is a huge power draw.

    • GCO

      I’ve been commuting almost 4 years, and well over 50’000 miles, on sunshine alone, so for me at least, EVs can be much more than “marginally useful”.

      Agreed on the rest though.

    • neroden

      Still waiting for EcoCutes (as Japan calls them) or other air-to-water heat pumps to become widely available in the US. Right now it’s not very practical to convert to a heat pump if your house uses steam or hot water heating.

  • Tim Brown

    In 2014, I said to the solar company, “Fill er up”. Just like asking the old (yep I’m old) petrol service station attendant to fill up my car with petrol, I asked for the roof to be filled with solar panels. I ended up with 12 West facing panels and 18 East facing panels. I since moved, but my plan was to charge my electric car when I buy one.

  • Garrick Staples

    I wish I had overbuilt! Now that electric cars are in my driveway, my pv system is too small. I will be adding panels soon, but unfortunately I have to replace my expensive inverter for a larger model.

    Not overbuilding will cost me nearly $2000.

    • Matt

      Well the key is the inverter, does it leave room for growth. Or when you add the second system do you add a new inverter.

      • Garrick Staples

        That’s my point. My inverter is too small. I have to replace it.

        Anyone want a slightly used solaredge se3000?

        • Benjamin Nead

          How large a panel array (kW) were you running
          with your SE3000?

          • Garrick Staples

            I have 3.2kw of panels on a nice south facing roof. Now I’m going to add another 2.5kw.

      • Freddy D

        Also, depending on whether someone does a permit or not, the permitting process and paying a contractor to pull the permit, etc might be more than the inverter even.

        • Hank1946

          In any area I know of you can pull your own permits or send your wife if need be. Since he already has a system he could change the inverter himself with a little knowledge.

      • scd

        Hi Matt

        Thanks for your posts and also thanks Daryll for the interesting article.

        We have been calculation a bit lately in order to better be able to optimize installations for self consumption specifically.

        We do overbuild on the panel side just like you do (as much as the roof can take from edge to edge) but stay conservative on the AC (Inverters) part. We build the inverters just as big as the cumulated demand of the installations in the house will be (with a little factor of the probability with which they run parallel and future consumers like ev, heatpump etc.).

        The reason why we keep conservative on the inverters is the yearly runtime of them, the daily and yearly production curve of the installation as well as the tariffs in switzerland (no net metering, shitty feed in tariffs, future looks like power metering with critical peak tariffs).

        Solar panels produce 95% of the energy (kWh) below the 70% line of their maximum Power output (kWp). So, if I dimension dc-power to ac-power 1:1, then 30% of my inverter power only puts out 5% of the value of the installation. The top 30% of the power are being feed-in for crappy tariffs (getting worse year by year if you don’t have net metering) while the lower 70% allow for i.E 50% autonomy and save highly tariffed grid electricity and produce real value.

        The extra energy that the panels produce in the mornings and afternoons as well as from fall to spring are very welcome to cover my energy bills but do not exceed the 70% line of the power.

        With the power metering ahead and critical peak pricing I save from the smaller inverters and still cover maximum of my energy.

        The little graph below shows the relation between power (vertical) and energy (worktime horizontal).

        I never found sympathy in the thought of underdimensioning the inverters. I like the idea of overdimensioning the Panels a lot better.

    • eveee

      I think the difference between a 10kw and a 3kw inverter is about 800 dollars. A 3kw inverter might be 1200, but a 10k is only 2,000. Its worth it to put a bigger one in to start. They get cheaper per watt as they get larger. (the newer solar edge inverter compatible with PowerWall is 3k, but it has intelligence built that saves you money)

  • Dan B

    You gotta love the picture; “i drove 25,000 gasoline free!” Whoo hoo, she saved aprox $2,500 (25k/25mpergal x $2.50 gal) WOW at that rate she only has another 250,000 miles to drive to make back $25k she spent on the overpriced Tesla.
    Environmental my patooty. Tesla cars and solar panels are SO VERY TOXIC for our environment. But hey let’s not talk about that truth.

    • Benjamin Nead

      Not all electric cars cost as much as a Tesla. My used i-MiEV cost about $7K
      and – even with gasoline in my locale costing below $2 per gallon these days – costs about one fifth to drive per mile when compared to my wife’s similarly-sized Honda FIT.

      Also . . . the FUD you spread regarding the environmental dirtiness of solar PV and EVs is laughable at best. We’ll keep it simple for you. Try this video first and, if needed, I link you to multi-paged studies . . .

      • @Benjamin, great video! Thanks.

        • Benjamin Nead

          We can thanks the Union of Concerned Scientists for that one. More comprehensively, they authored the 2012 State of Charge study., which is breaks everything down in further detail (link to 48 page PDF) . . .

          I get people at live local events where we have EVs displayed who, without malice, raise legitimate concerns about the cradle-to-grave aspects and they want to hear

          the truth: that EVs – simply by the nature that they’re automobiles – DO have an impact on the environment.

          You sometimes surprise them by being so upfront in admitting that the initial manufacturing might be more carbon intensive when compared to an ICE. But you also point out that it’s far less over the lifetime of the car, that the paybacks typically comes within a year of rubber hitting the road and it is directly proportion to where electricity comes from locally and regionally. Get the grid cleaner and the EV automatically becomes cleaner. You start to turn the argument around and get them to think about where their local or regional electricity comes from and why the local utilities aren’t embracing renewables more than they already are.

    • vensonata

      Man, you are like a kamikaze pilot who misses the ship when you come onto a green site and mouth those kind of absurdities.

    • Martin

      So in your view crude is non toxic, guess all he animals who died in oil spills did not know that!

    • Freddy D

      Important concerns to look at the cradle to grave impact of gas cars vs. electric cars. and photovoltaic vs. natural gas power. It’s been very well studied and documented and is sometimes captured in an “Energy ROI” or “energy payback time” type of calculation, where one asks “how long does it take a PV system to pay back the energy made to manufacture it?” These times run about 1-2 years and keep getting shorter. For a system that will last 30+ years. Battery technology is improving incredibly quickly as well.

  • harisA

    Unless there is a good Feed in Tariff available, the economics of producing excess energy does not make sense. Most system can be designed to add more capacity later when needed and that goes for future EV needs.
    We are talking thousands of dollars here that can be spent in other ways to reduce ones carbon footprint (like buying offsets etc)

  • Steve Grinwis

    I generally agree. I will comment on something else that was mentioned in passing:

    Solar thermal.

    I honestly believe that solar thermal is dead. With a heat pump, I can produce 3 watts of heat for every watt of electricity I put it, and that ratio is only going to climb, as the units get more efficient.

    When solar is $2 / watt, and I can get 3 watts of heat for that price, you need a 1 sq meter collector to cost less than $600 installed, and be as reliable as a solar panel to be competitive.

    Solar thermal also massively overproduces in the summer, and you can’t do anything for that. With panels, you can sell that energy, and reduce other peoples carbon footprint.

    • vensonata

      Right you are. PV has long passed solar thermal in so many ways. However perhaps the reference was to thermal storage vs battery storage. In that case thermal storage of energy is far cheaper than battery storage.

      • eveee

        Right. Hot water heaters and air conditioning come to mind. There is a gigantic opportunity there.

    • Omega Centauri

      Agreed. If you can run the PV to heatpump as a dedicated microgrid you could avoid much of the soft costs as well. Depending on climate a few dedicated panels to run a heat pump in winter and AC in summer could be the way to go.

      You can do something about solar thermal in summer, proper use of overhangs. I build a seasonal shade for the deck, and take the shades down for the winter. I even add reflectors for the winter. So it is possible to make it work as a supplemental. You could also use an underpowered airsource heat pump as a supplemental.

    • Freddy D

      Great points – I’ve been through the calculations for my own situation. Solar thermal makes more sense in climates with no freezing weather, and then for water heating. For space heating, it gets very complicated and might work for special climates like very cold very sunny locations, such as high altitudes in NM, CO, WY. For me, I just can’t make the numbers work and the heat-pump with PV is a much better approach for the reasons you mentioned. Let alone the cost of repairs and maintenance. Most PV systems will run decade after decade with no cost, except perhaps changing out an inverter here and there. Plumbing with pumps, storage tanks, heat exchangers, etc always seem to get ugly after 1 decade, at least in my experience.

    • GCO

      I think that, among other things, you forget to include the heat pump itself, in particular its cost, capabilities, and durability.

      For hot water production, still the only type sold in the US are “hybrid” hot water heaters, the kind with the heat pump on top of the tank itself. Those effectively cool down the surrounding areas, often inside the house; while useful in hot climates, it’s counterproductive even where I live, Northern California, as I have no AC but need to heat up my home a third to half of the year.

      Solar thermal now. Climate is key here too.
      In mine without hard/daytime freezing, I was able to use a dead simple “batch heater” aka “integral collector-storage” or ICS, basically a black tank behind glass insulation. Zero moving part, just copper and glass, it should last decades.
      I set it up at 45° tilt, so the difference between June and January is only 30% (per PVwatts); some people go even steeper and set those up on a wall, leaving more roof space for PV.

      Not only solar hot water was a better value in my situation, more importantly, it effectively allowed me to install more solar than I could have with PV alone (because of city requirements and roof limitations).
      [It’s also blackout-proof, and will reduce my electricity storage needs should I lose net metering in a decade or two…]

      • Steve Grinwis

        Heat pumps are less expensive than an equivalent furnace + air conditioner from what I’ve seen.

        In terms of reliability, they have 12 year warranties on the good ones now, and can expect to have a reliable service life of 20+ years.

        I’ve not gotten a full quote for solar thermal installed, but even the panels rated for my climate by themselves are more expensive than the equivalent number of watts in solar panels, and the install seems like it would make it substantially more expensive.

        We don’t have heat pump hot water yet here, but they are for sale in New Zealand. There’s no reason why they wouldn’t work here.

      • neroden

        I don’t know why they don’t have split-system heat pumps for hot water in the US. They do in Japan. I’m waiting for them. (In addition to domestic hot water my house has hydronic heating.)

    • karrlsam

      PV as solar heating. You can buy PV for $.60 a watt. Install it yourself for $1 a watt. ( be handy )
      14 watts a sq. ft. times 3.5 a watt. =50 btus a sq. ft. This is half the production of a wet panel, but has no fluid, pipes, pumps, diff. controllers, etc.
      Just a resistance element to create heat. With wires this cost $15 a sq ft for 50 btus/hr output
      A wet system would have to be installed for less than $30 per sq. ft. to compete. Only if you build your own panels can you do this.
      And, you have electricity that can be used for other things. Backup power. Run an air conditioner with a simple inverter .

      • Steve Grinwis

        Right. And when you throw a heat pump on there so you can get 3 watts of heat per watt of electricity… Solar thermal just can’t compete at all.

  • newnodm

    The economics work usually better slightly under building a grid connected system. Shooting for 90% is usually doing it right. Considering how more panels might be added later for , say, an EV, is a good idea. Guessing on future need and overbuilding a technical product with a falling price curve is generally dumb.

    • TatuSaloranta

      Still, economy is not the only reason for adding solar panels, at least not for everybody. I am planning to build as much capacity as roof can take (within limits of shadows, orientation), and even if extra electricity was used by utility unpaid, I’d consider that an improvement: someone, somewhere, will use that electricity, and avoid some amount of generation by dirtier sources.

      Whether overbuilding makes sense depends on many factors from personal preferences to alternative ways to achieve similar goals (if your house is badly insulated, certainly take care of that first). I think it is good to highlight _possible_ reasons, even if not all apply to every case.

      • Omega Centauri

        If you were able to invest/spend the money for the overbuild on a larger scale ground mount, you’d get two or three times the juice for your money. Also in the future your utility may try to limit distributed generation as the penetration level grows. That will take longer if you don’t overbuild. Overbuilding may use up the available KWs of allowed DG sooner, cheating someone alse out of the chance.

        • TatuSaloranta

          Yes, ground-mounting would make sense if available. For us it is not (urban setting), but definitely for more rural areas. Good point. Also: if there were community solar projects available for lower-cost installations, I would be interested. They seem like viable alternative in many cases.

          Thing about utilities is tricky. I think in practice ratio of area for just covering annual usage, and maximization, is limited, so that it is rarely difference over 1:2. In our case it’s like that we can barely overbuild (like, at most by 30%), so it may not be a bit thing in practice.

    • GCO

      I initially thought the same, installing just enough for my current needs, and add more for an EV later. I got the EV sooner than anticipated so didn’t split the project in two, which was a very good idea, as I found out while wanting to add more PV years later.

      Here are some reasons why extending a system will likely turn out more expensive and troublesome than doing it all in one shot:
      – Having any construction work done involves quite a bit of time, hassle and even risk (e.g. roof leak); personally I’d rather not go through it multiple times.
      – Most fixed costs (engineering, permitting, electrical etc) end up multiplied.
      – Hardware is cheaper in larger quantities. Labor too, to some extent.
      – Previous PV modules, racking etc likely won’t be manufactured anymore, making it difficult or impossible to make the extension fit the base system, mechanically, electrically and/or aesthetically.

      I agree with the author here: install as much as you can, instead of regretting later and/or end up with some ugly-looking patchwork.

      • neroden

        My plan is a little different. Based on the declining costs for solar, I decided to do all the *other* conversions, converting *everything* to electrical, *first*. Then I’m going to try to do solar + storage in one big go, once I actually know my electrical usage.

  • Harold Thiers

    If you have solar through a PPA agreement, It is unbeneficial to overbuild and produce more than you consume because you pay $0.145 per kwh to the PPA and the utility refunds $0.06 / kwh “Stored” at the reconciliation point annually. So producing in excess is not worth it. You’re throwing away $0.085 cents out the window.
    If you put in a system that captures 80-90% of your usage, you avoid the risk, and if your consumption goes up, they will gladly add panels if the effeciency is there, given the space to do it.
    As far as supporting an industry, or hoping not to have a coal plant built next to you, i think those are wishfull thoughts and unrealistic. #1 and #10 are really the same thing. How many ipads will you run to see a change in consumption. Switch to LEDs and efficient appliances as they fail, will reduce your consumption. Adding an EV, I already have one, $600-$800 in electricity per year, the real savings are comparing it to ICE with maintenance and fuel bills. Powering it by solar PPA saves me $0.045 per KWH. Not a big number. My 20,000 mile service was $37.58. First and likely last visit to the dealer on this lease.
    The Electric bill is down 25% which is nice.
    Overbuilding for anticipation is in my opinion a bad idea as prices are still dropping. Panels are getting cheaper and better. Your cash could be used somewhere else to better effect.
    The only consideration I would give to overbuilding would be if buying outright, that you have an inverter that has some overhead in it for a few extra panels.
    We have 2 arrays totaling 18.5kW from SolarCity and space but not sunshine space to add more. Each inverter can take more panels without significant additional work. So if we lose a few beautiful trees, we could potentially get some more sun on the roof. I’d rather keep the trees.

    • newnodm

      Good advice until it came to solarcity. You gave solarcity the economic advantage of solar that you could have retained for yourself.

      • Harold Thiers

        Cashflow and length of life determined that decision. If you’re likely going to be dead in 15 years per actuarial tables, then waiting 10 years for your return on investment to make a difference means you save nothing today. Cashflow with $0 down dictates I can use that cash to live life and at the same time lower my living expense.

        • newnodm

          I approve of any plan that screws solarcity out of future earnings.

        • Otis11

          Hahaha… well, I hadn’t thought of that one!

          So what does solarcity’s contract say if the owner passes away? Do they remove the panels, give them up, or is the inheritor of the house responsible for the remainder of the contract?

          • ROBwithaB

            I’ve wondered the same thing myself.
            And what about insolvent estates? Presumably the panels are sold off at auction, along with the house, leaving SolarCity standing in the queue behind the bank/s and the IRS.

          • newnodm

            Solarcity will get the value (excess value undoubtedly) of the system out at closing on the house sale. You can be sure the contract favors them under all possibilities. They just throw some upfront financial benefit to the homeowners to make the sale.

            Even if Harold burned the house down solarcity would take their money out when the land was sold.

    • vensonata

      18.5 kw array! And you don’t think you overbuilt? More explanation would be welcome.

      • Harold Thiers

        we use about 20,000kw anually. Big house with home offices and heat pumps that run electricity. Initial pitches were 7-10kW systems and then the north facing roof al of a sudden came into the picture to offering 69 panels. Electric car, offices, etc…. Shockingly so and effeciency tested.

        • vensonata

          Nice. Be interesting to do an article on your experience.

        • Otis11

          Yeah, I’d be interested in seeing the breakdown of this. (and the slope of the north facing roof?)

          Parent’s house is in a similar situation… south facing roof is non-solar friendly. West and North look pretty good though.

    • TatuSaloranta

      I think you missed the important points — it’s not all about your own personal financial benefit. If you care about co2 emissions, then ANY contribution you make — paid or not — WILL help. This may not be good enough reason to volunteer for you, but it is for some. As long as electricity produced will be used by someone and offsets other modes of production, it is helpful and valuable. It may not help you financially, but it will help reduce emissions.

      Many of the points listed are indeed bit dubious, and I think that “support industry” is bit suspicious. But the remaining point of “every watt counts” is important: someone somewhere will use that, instead of coal-/gas-originated electricity.

      • Dan B

        C02 emmissions VS. Lithium and a slew of other toxic materials. Not to mention the energy burned to produce all that plastic crap etc.
        Yeah; but it makes everyone feel warm and fuzzy.

        • TatuSaloranta

          What I am saying is that there is no one-size-fits all solution: there are many cases where simply retaining to “what I consume and only that, ever” is not the best optimization. Sometimes under-sizing makes sense as well.

          I alslo find it patronizing to try to summarize this as just green-washing (“warm fuzzy feeling”); and fail to see how you could such a conclusion.

        • Steve Grinwis

          PV isn’t free. It’s true. It has an environmental impact.

          It just so happens that that environmental impact is between 2 to 3 orders of magnitude less than the impact of most other forms of power generation.

  • Andy

    I built an oversize system only to later find out my utility is exempt from net-metering laws. Now I’m stuck with the wholesale rate. Yay. 🙁

    • Epicurus


    • John

      I hope the utility isn’t getting the benefit of your RECs. I would add batteries and disconnect from the utility.

      • Andy

        It’s too early for me too tell, but I don’t believe they are. The SREC’s here are based on my system’s production. This is in MA, one of the best state’s for solar from a policy perspective. Except for one glaring loophole I learned about after the fact where 41 municipal power companies can do whatever they want. I was lucky to get wholesale. Most of the ones I looked at take your power and give you nothing.

        It’s a serious problem because everyone in MA is getting marketing in the mail and on the internet about how much solar can cut costs, but they all assume a real net metering policy since that’s the law for investor owned utilities here. Even after approaching a solar installer and getting an offical estimate and system sizing for my power usage, the payoff period assumed net metering. So, should I have done more research? Yes. However, I assumed what the installer was telling me was correct.

    • Freddy D

      Consider some storage at some point. Then you can use your own power at night and while the AC cycles on and off. And get an electric car and charge it during the day, if you can swing it in your schedule. Might take some gymnastics, but it’s like free gasoline for you.

      • Andy

        I drive a Leaf and get home from work at 6:30. Tough to charge during the day, at least for now. Summer will still have some sun and my panels face more west than south, so that helps. I’m trying to switch as much as my energy use as possible to early afternoon. I’d love to switch to a storage setup eventually – prices are still a bit too high to make it worthwhile in my case.

        • vensonata

          Keep an eye on the 30% tax rebate being applied to home storage, and look for state incentives. Prices could suddenly be half, without any improvements necessary in the battery tech.

    • eveee

      Does your utility offer an EV rate or TOU? That could save you money.

  • vensonata

    The case for over paneling is even greater for off grid. The ratio of cost between batteries, panels, inverters, racking, charge controllers and the back up generator, has been changing rapidly in the last 2 years. Sometimes its hard to keep up. Panels used to be expensive, now they are not. Batteries used to be lead acid with maintenance and venting and space issues, now they are lithium. Inverters were murderously expensive ten years ago, now they are merely charged with aggravated assault. Generators, are about the same price, however because of more PV and batteries, the generator is hardly used, therefore maintenance, fuel and lifespan all are much less expensive. And then of course, there is no concern about the utility suddenly cutting your feed in tariff, arbitrarily…(Nevada).

    • Mike Dill

      I live in Nevada and NV energy decided not to read my meter this month as they sort out the new tariff. I would really like to know what my bill was last month, and what they will be charging for this month, but it looks like that is back in the hands of the Nevada PUC, which has stated that they will be looking into the matter once more. I do not expect them to change their mind, but it will delay the lawsuits that are being readied.

      I had two options planned, one of which was taking everything except my HVAC off the grid, which was possible present solar PV system, and adding a small amount of storage. This would have given me the ‘non-solar’ rate, but i would have still been paying whatever NV Energy wanted.

      I have now looked at the numbers a bit more, and decided, even though it is NOT ECONOMICAL, that if the grandfathering in Nevada does go away, in two years or less I will add another 4KW to my roof along with a day of storage, and tell NV energy that they can stop charging me.

      • vensonata

        And run an extension cord over from you neighbors for the 3 days a year you need a little juice. Actually there may be no law against it, since it has never occurred to anyone to do it!

        • Otis11

          Heck, if I were your neighbor while this were going on (and didn’t have solar/couldn’t have solar) you wouldn’t even have to ask – I’d invite you to plug in a few times a year if that’s what it took.

          Buy them a decent Christmas present with the money you save and you’re both better off – and made a new friend!

        • Bent LEAF

          If you are short, you run your electric car over to a public charger, fill ‘er up, and then use the power to partially replenish the home battery system.

      • Freddy D

        Yep – storage is your first priority in NV, but wait as long as possible for prices to improve and for the FIT/net metering to expire. 1 day is a good amount so you can meet your evening needs and in the summer, if you run AC, it can cycle on and off as it normally does and the batteries level it all out. Good luck – looks like you’re a pioneer consumer for what could ultimately be a more common model.

    • Freddy D

      “Batteries used to be lead acid with maintenance and venting and space issues” – Li-ion still has maintenance/ longevity issues big time. Which reinforces your point that more kw of PV might be MUCH cheaper than more storage and just forfeit the excess power. The PV panels will last many decades and inverters are getting cheaper quickly so when they need replacement they’ll be pretty simple.

      Yes you need storage off-grid or in NV (even on-grid storage makes sense there). The question is how many kw of PV vs. kwh of storage is the optimum.

      • vensonata

        This is such a delicious topic, and it needs a lot of pondering. How much storage? (by the way, I am off grid for 15 years, running a community of 15 – 25 adults, with a 10,000sq ft residence and a dozen out buildings all with solar, battery and diesel generator). I have been forced to learn about all this, and it has become a way of life. At this point it is simply fun, not burdensome, thanks to ever improving technology and price decreases.
        There are two kinds of “off grid houses” on the horizon. The Tesla model S and the BMW i3 with range extender. Take your choice. I put it in this frame of reference since many are familiar with mobile rather than stationary energy systems. Let us anticipate two things: a drop in home storage costs very soon by at least 30% (See Tesla claims for Gigafactory price effect) and factoring in a 30% tax rebate plus state incentives up to 20%. Factor that into the price of a 100 kwh Tesla powerpack. Currently they are $25,000. Reduce price 30%… $17,500. Now reduce that by 50% from rebates and state incentives and you arrive at a possible $8750 for 100 kwh. A battery that size can really eliminate the need for a generator. Personally, I would zero my generator use even in a rather poor solar climate in winter with 100 full kwh of storage.
        How long do batteries last? Welcome to the funhouse. Three years I have been researching this question regarding various lithium and flow chemistries! I warn you all: rush to hasty conclusions at your peril! I would tentatively suggest that suitable lithium chemistries (not all) can last 25 years. I won’t go into details here, but my opinion is based on close study, not casual guessing. However I will be the first to admit that “no one, but no one, knows for sure”. So many of these studies are based on simulations that may not extrapolate, as my favorite professor of engineering battery specialist Jeff Dahn repeatedly cautions. (Jeff Dahn by the way, has now been hired by Tesla, to finish off his long career by finally answering these questions with elaborate testing machinery that is still being invented.)

        • Formerly_Nom_De_Plume

          If you wrote a blog about living off-grid, I would read it.

          • kerrywebster

            Maybe a guest post here. Would love to hear real world experience.

          • vensonata

            I’ll be making a new little energy and efficiency, off-grid movie soon and will post on youtube. I did one a few years back and things have changed so much it is outdated. But I will show the whole package including super insulation, etc.

          • Matthew Rose

            I enjoyed your video. Thanks

          • neroden

            Sounds like you know your stuff. Superinsulation is job one!

  • John Calhoun

    1 Reason To Not Overbuild Your Rooftop Solar: the PUC will cut net metering benefits without grandfathering you in

    • Alaa

      use a salvaged Nissan leaf battery and store the electricity and forget about PUC.

      • David Galvan

        Your idea intrigues me, and I’d like to subscribe to your newsletter.

        • Kyle Field


          • David Galvan

            (A standard joke from the Simpsons.)


          • David Galvan

            But seriously, I am hoping that someone (Nissan or third parties) will start a business allowing you to use a salvaged Nissan Leaf battery and produce a Powerwall competitor. This would be especially useful if Leaf owners could purchase a new (upgraded?) battery for their car once their current battery is degraded, and use the degraded battery for home energy storage, instead of turning it back in to Nissan.

          • Dragon

            I don’t think there are enough salvaged LEAF batteries floating around to make such a business viable.

          • David Galvan

            Perhaps not yet. But the car has only been around for 5 years. . .

    • Epicurus

      Most utilities have a limit on their net metering obligation, don’t they? Am I correct that they won’t pay for any electricity over the amount the customer uses during the month?

      • Omega Centauri

        Or in most cases they pay a much reduced rate for overproduction.

        With a couple of exceptions I think your home electricity demand could drop due to increased efficiency of appliances. Replace your AC condensor with a new one and your demand is likely to drop dramatically.
        Replace your old pre LED TV and likewise. Replace your aging refrigerator likewise.

        Now for the exceptions:
        (1) If you plan to convert from a gas dryer to electric expect a big hit.
        Likewise if you do the same for hot water.
        (2) Convert from gas heating to a heat pump (air or ground source).
        (3) Start charging cars.

        Think about whether you plan on any of these things in the near future. Otherwise I would underbuild by a bit.

        Its always possible to install an upgrade, although you will pay extra soft costs for doing so. But if you won’t need the extra juice for a couple of years waiting will deliver price reductions that can more than offset the additional transaction/papaerwork costs.

        A case in point, I had a small system installed in 2009.
        I just had an additional system added, with capacity about 10% more than the original system, at about 2/3rds the price. So the net cost for my now slightly more than twice as large a system is a lot lower than if I had bought a large system in 2009.

        • Otis11

          I agree for the most part. Two things you overlooked (or undervalued):

          1) Power consumption from TVs is actually increasing on average. While some are decreasing their TV power usage from switching from an old CRT/Plasma to an LCD or LED display, many more are changing from a 720p LCD/LED to a larger 1080p or even 4k LCD/LED/OLED display. While these new TVs are significantly more power efficient per pixel (and often even per inch), the significant improvements in resolution and the decreasing prices of large screens is negating (or even reversing) much of this trend.

          2) EVs. While you mention this, I think it’s undervalued. People who are interested in installing solar have a higher probability of either a) being environmental conscious, b) seeking economic returns, or c) being techies. All 3 of these categories show an above-average tendency to consider EVs or PHEVs as their next car (or often have friends and family that will due to associating with like-minded people).

          That said, each person needs to do their own analysis and consider the near term upgrades/changes they are planning. It’s probably not economically recommended to oversize an EV array without plans to change your electricity usage.

      • Mike Dill

        NV Energy did not let me build anything more than my previous bills, and does not pay for any over production. You did get the net metering for what you put in and then used, but noting more.

        • Epicurus

          “NV Energy . . . does not pay for any over production”

          In other words, they take your electricity overproduction for free and then sell it to someone else. Good business plan. Republican capitalism.

        • smslaw

          Central Maine Power does the same thing-any excess over twelve months goes to the power company for free. As a result, there is no incentive to overbuild, once you produce as much as you use over the year.

    • TatuSaloranta

      Most things listed above are based on the fact that regardless of whether you, as a homeowner, get compensated, it will help environment. So even if they will not compensate you does not mean that your work would be worthless.

      I actually do not see this as changing the equation a lot; PUC will not consider relative sizing of your panels in decisions, as far as I know — they have no time or resources to do actual analysis work.

      But I guess some PUCs do have cut-off point; if so, there is certain maximum above which I agree you may not want to go.

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