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Published on January 10th, 2010 | by Susan Kraemer

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Rooftop Solar Installations Growing Faster than Utility-Scale Solar



Private solar installations are really taking off nationwide. In just two years, (about the same length of time it takes to get a pair of 250 MW solar power plants approved in California, for example), homeowners and businesses have added that much power to the Californian grid, just from individual rooftops throughout the state.

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By July last year, 50,000 installations were supplying the California grid with 500 MW of solar power; the equivalent of two average sized solar power plants now under review in the state.

Nearly all solar installations are now grid -connected in California, by contrast with the first wave of solar power in the 70′s when a battery was needed to supply power at night, and early adopters had to be careful not to exceed their power, turning off dishwashers on cloudy days.

Now however, nearly all solar is grid-connected, meaning that the power generated is stored in a giant battery: the grid. Output is measured as it enters the grid, by the utility, which gives a credit for the electricity generated.

Solar installers are able to size each system so that it generates the same kwh a month as the homeowner or business uses in total (including both nights and days), with the result that the credits on the utility bill will zero out the debits from night time use. Because of the grid acting as a cheap or free battery, whereas in 1999 average installed systems were 2.5 KW and included an expensive battery, now the average system for homeowners is 4.8 KW and is grid-connected.

The growth in solar power has been fast among homeowners, and even faster among commercial building owners. The faster adoption of commercial solar is due to the lower prices for larger scale installs (over 500 KW cost 17% less per watt than the under 10 KW systems typically installed on homes) and the wider availability of Power Purchase agreements, which are usually only available to businesses. Commercial installations grew from 19% in 2005 to 46% of all installations in 2008.

As the percentage of non-utility solar being added to the grid increases, some states, like California, are looking at raising the state imposed limit. Californian non-utility solar is now close to the current 2.5% of the state’s electricity coming from rooftops.

The Solar Alliance has sponsored a bill to allow up to 10% of the state’s electricity  to be generated by private homeowners and businesses. Other states, like North Carolina, are proposing no cap at all.

Source: Interstate Renewable Energy Council

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About the Author

writes at CleanTechnica, CSP-Today, PV-Insider , SmartGridUpdate, and GreenProphet. She has also been published at Ecoseed, NRDC OnEarth, MatterNetwork, Celsius, EnergyNow, and Scientific American. As a former serial entrepreneur in product design, Susan brings an innovator's perspective on inventing a carbon-constrained civilization: If necessity is the mother of invention, solving climate change is the mother of all necessities! As a lover of history and sci-fi, she enjoys chronicling the strange future we are creating in these interesting times.    Follow Susan on Twitter @dotcommodity.



  • Henrymckay

    Is there an update to this article?

    • http://cleantechnica.com/ Zachary Shahan

      not a specific Part II

  • Rich Rebman

    Standalone Distributed Power Generation

    I am retired from management of the Materials Analysis Laboratories of the Gates Rubber Advanced Technology and Engineering Division and have been working on ways to reduce our dependence on foreign oil and our declining reserves. I have conceived of a process to convert wind and water to chemical energy in aqueous borohydride solution, which can then be stored for when the wind isn’t blowing, or water isn’t flowing, so no backup is needed. This solution can be pipelined or otherwise transported to homes, businesses and agriculture for many fuel cell applications, including domestic power, and as a transportation fuel for automobiles, trucks and mass transit.

    I visualize a turbine (single or farm), borohydride recycle and storage, and pumping station for local and network distribution with borate return, providing hydrogen fuel, electricity and RO-purified water as utilities. This new technology would allow the power plant to be located anywhere there is wind and a water source. There would be no need for exposed, increasingly unreliable and costly transmission lines to link with conventional power plants. Both hydrogen and electric vehicles would be recharged inexpensively and without the pollution caused by burning coal somewhere else as is done now.

    The current big picture of the Hydrogen Economy is concisely, completely and clearly spelled out at http://fuelcellstocks.com/hydrogeneconomy.htm. From paragraph six of the 2003-2005 assessment, I quote in part: “The Shell hydrogen station in Iceland offers the dream solution, using Norsk Hydro electrolysis technology to produce hydrogen from water. The whole operation is powered by electricity generated by renewable geothermal and hydro energy. This is the future. Keep your eye on tiny, little Iceland, a nation of just 285,000 people”.

    Other more widely available natural energies, winds and tides, can also be used to produce hydrogen from water in a process to recycle inactive borate to active borohydride by ultrasound-powered hydrogenation that drives this energy-absorbing reaction rapidly to completion, making recycle commercially viable. Borax is the raw material for the recycle module, safe, available in southern states and inexpensive. To prevent a buildup of possibly undesirable minerals in the recycle process, purified makeup water may be used. For details on Ultrasonic Sonochemistry, Google will lead you to http://www.elsevier.com/wps/product/cws_home/525451, “Sonochemistry“ in Chemistry, Summer 2000,pp3, 17-22, and http://www.scs.uiuc.edu/suslick/britannica.html. See the Wikipedia page on Sonication. See the next two attached pages from Kinetics and Mechanism, 2nd Ed., 1961, LOC Cat. Card # 61-6773, Frost and Pearson, for the energy transfer mechanism of Einstein‘s experiments, transforming ultrasound energy into kinetic energy of molecules, rapidly.

    Before undergoing bankruptcy, Millennium Cell concentrated on its borohydride fuel cartridges and its battery technology, far superior to the lithium batteries currently proposed for the Volt and others, but ignored. See “Road-Testing Cars of the Future“, US News, April 2009. A brief description of the company and its borohydride solution technology is quoted from their previous site.

    “Millennium Cell (NASDAQ:MCEL) is engaged in the development of next generation energy sources for use primarily in consumer electronic, portable power and standby power application. The Company’s innovative and proprietary Hydrogen on Demand systems safely generate high-quality hydrogen from a water-based solution of sodium borohydride. This fuel is non-combustible, high in energy density, easily distributed, and convenient for refueling. Millennium Cell is developing technology in partnership with corporate and government entities. Based in Eatontown, New Jersey, Millennium Cell was founded in 1998 and currently employs nearly 40 people, primarily in technology development.”

    MCEL stock was originally issued at $10.00 but is now worthless (except for it‘s patents and technology). This company lost out for two reasons: They didn’t develop an inexpensive, large-scale way to synthesize or recycle borohydride from borate for extensive continuous applications so their marketing was directed away from domestic and transportation technology and toward specialized batch applications.

  • Rich Rebman

    Standalone Distributed Power Generation

    I am retired from management of the Materials Analysis Laboratories of the Gates Rubber Advanced Technology and Engineering Division and have been working on ways to reduce our dependence on foreign oil and our declining reserves. I have conceived of a process to convert wind and water to chemical energy in aqueous borohydride solution, which can then be stored for when the wind isn’t blowing, or water isn’t flowing, so no backup is needed. This solution can be pipelined or otherwise transported to homes, businesses and agriculture for many fuel cell applications, including domestic power, and as a transportation fuel for automobiles, trucks and mass transit.

    I visualize a turbine (single or farm), borohydride recycle and storage, and pumping station for local and network distribution with borate return, providing hydrogen fuel, electricity and RO-purified water as utilities. This new technology would allow the power plant to be located anywhere there is wind and a water source. There would be no need for exposed, increasingly unreliable and costly transmission lines to link with conventional power plants. Both hydrogen and electric vehicles would be recharged inexpensively and without the pollution caused by burning coal somewhere else as is done now.

    The current big picture of the Hydrogen Economy is concisely, completely and clearly spelled out at http://fuelcellstocks.com/hydrogeneconomy.htm. From paragraph six of the 2003-2005 assessment, I quote in part: “The Shell hydrogen station in Iceland offers the dream solution, using Norsk Hydro electrolysis technology to produce hydrogen from water. The whole operation is powered by electricity generated by renewable geothermal and hydro energy. This is the future. Keep your eye on tiny, little Iceland, a nation of just 285,000 people”.

    Other more widely available natural energies, winds and tides, can also be used to produce hydrogen from water in a process to recycle inactive borate to active borohydride by ultrasound-powered hydrogenation that drives this energy-absorbing reaction rapidly to completion, making recycle commercially viable. Borax is the raw material for the recycle module, safe, available in southern states and inexpensive. To prevent a buildup of possibly undesirable minerals in the recycle process, purified makeup water may be used. For details on Ultrasonic Sonochemistry, Google will lead you to http://www.elsevier.com/wps/product/cws_home/525451, “Sonochemistry“ in Chemistry, Summer 2000,pp3, 17-22, and http://www.scs.uiuc.edu/suslick/britannica.html. See the Wikipedia page on Sonication. See the next two attached pages from Kinetics and Mechanism, 2nd Ed., 1961, LOC Cat. Card # 61-6773, Frost and Pearson, for the energy transfer mechanism of Einstein‘s experiments, transforming ultrasound energy into kinetic energy of molecules, rapidly.

    Before undergoing bankruptcy, Millennium Cell concentrated on its borohydride fuel cartridges and its battery technology, far superior to the lithium batteries currently proposed for the Volt and others, but ignored. See “Road-Testing Cars of the Future“, US News, April 2009. A brief description of the company and its borohydride solution technology is quoted from their previous site.

    “Millennium Cell (NASDAQ:MCEL) is engaged in the development of next generation energy sources for use primarily in consumer electronic, portable power and standby power application. The Company’s innovative and proprietary Hydrogen on Demand systems safely generate high-quality hydrogen from a water-based solution of sodium borohydride. This fuel is non-combustible, high in energy density, easily distributed, and convenient for refueling. Millennium Cell is developing technology in partnership with corporate and government entities. Based in Eatontown, New Jersey, Millennium Cell was founded in 1998 and currently employs nearly 40 people, primarily in technology development.”

    MCEL stock was originally issued at $10.00 but is now worthless (except for it‘s patents and technology). This company lost out for two reasons: They didn’t develop an inexpensive, large-scale way to synthesize or recycle borohydride from borate for extensive continuous applications so their marketing was directed away from domestic and transportation technology and toward specialized batch applications.

  • Russell Gagnon

    Perhaps someone could provide some additional info/insight on why California, with all of their progressive policies towards cleaner energy, would want to cap non-utility power at 10% of total usage? Doesn’t seem to make sense to me – I would think CA would be one of the first to pioneer what seems to be NC’s approach of no cap.

  • Russell Gagnon

    Perhaps someone could provide some additional info/insight on why California, with all of their progressive policies towards cleaner energy, would want to cap non-utility power at 10% of total usage? Doesn’t seem to make sense to me – I would think CA would be one of the first to pioneer what seems to be NC’s approach of no cap.

  • Christof

    Frankly, I’d like to see as many residential AND commercial rooftops with solar on them in the U.S. and around the world as possible. There’s so much rooftop space — and blacktop space, as in solar carports over America’s, and the world’s, vast parking lots — that can be utilized. Let’s make sure we take advantage of this space, which also happens to be close to where the power is needed, in contrast to the Mojave desert and other places, before we push huge concentrated solar projects there.

    I’m not against those projects, per se. But I much prefer local, distributive solar because: a) it’s more democratic; b) it (often — yes I know there are huge SPPAs on rooftops) puts power in the hands of local businesses and individuals; c) localized solar power allows me, and potentially millions, to step into complete and total auto-fueling independence with the solar + EV equation.

    I see it as good news — great news — that rooftop solar, however defined, is growing faster than the concentrated solar installations in fragile ecosystems located far away from where the power will be used. BTW, concentrated solar can be local — see http://chromasun.com/

    Susan, thanks for focusing on this.

    If anyone’s interested, I riff more on BIG vs. little solar at — http://tinyurl.com/yb7wwwn

  • Christof

    Frankly, I’d like to see as many residential AND commercial rooftops with solar on them in the U.S. and around the world as possible. There’s so much rooftop space — and blacktop space, as in solar carports over America’s, and the world’s, vast parking lots — that can be utilized. Let’s make sure we take advantage of this space, which also happens to be close to where the power is needed, in contrast to the Mojave desert and other places, before we push huge concentrated solar projects there.

    I’m not against those projects, per se. But I much prefer local, distributive solar because: a) it’s more democratic; b) it (often — yes I know there are huge SPPAs on rooftops) puts power in the hands of local businesses and individuals; c) localized solar power allows me, and potentially millions, to step into complete and total auto-fueling independence with the solar + EV equation.

    I see it as good news — great news — that rooftop solar, however defined, is growing faster than the concentrated solar installations in fragile ecosystems located far away from where the power will be used. BTW, concentrated solar can be local — see http://chromasun.com/

    Susan, thanks for focusing on this.

    If anyone’s interested, I riff more on BIG vs. little solar at — http://tinyurl.com/yb7wwwn

  • Susan Kraemer

    GM is not a utility. So that rooftop install is an example of “rooftop” not utility owned or utility-scale.

    Utilities don’t put utility-scale solar on roofs. The one outlier example you can offer is only 2 MW.

    Most applications for utility-scale solar, (just like for utility-scale gas plants or wind farms) are for about 250 MW.

  • Susan Kraemer

    GM is not a utility. So that rooftop install is an example of “rooftop” not utility owned or utility-scale.

    Utilities don’t put utility-scale solar on roofs. The one outlier example you can offer is only 2 MW.

    Most applications for utility-scale solar, (just like for utility-scale gas plants or wind farms) are for about 250 MW.

  • ECD Fan

    Dear Susan:

    How do you figure most people accept “Rooftop” solar as shorthand for privately owned? Any survey you can point to? Or maybe you have asked around? I thought so. Please do not invent facts!

    The title of your article is “Rooftop Solar Installations Growing Faster than Utility-Scale Solar.” You have no basis, given the sources you have used, to make any statement about rooftop vs utility-scale. Because rooftop can be utility-scale, and utility-owned installations can be rooftop. For example, General Motors/Opel’s unfortunate 12MW rooftop installation in Zaragoza, Spain (actually, several rooftops next to each other) is large enough and it is not owned or developed by a utility, but by a private investor (it is still underperforming by more than 25% vs expectations, of course, according to the remote-monitoring system). And, as already mentioned, the 2MW rooftop installation in Fontana, CA is owned by a utility, namely SCE (they actually intend to construct and own 250MW on commercial rooftops).

    A title that states “Business-owned and Homeowner-owned Solar Installations Growing Faster than Utility-Scale Solar” has at least has some support in facts (up until the end of year 2008, that is).

  • ECD Fan

    Dear Susan:

    How do you figure most people accept “Rooftop” solar as shorthand for privately owned? Any survey you can point to? Or maybe you have asked around? I thought so. Please do not invent facts!

    The title of your article is “Rooftop Solar Installations Growing Faster than Utility-Scale Solar.” You have no basis, given the sources you have used, to make any statement about rooftop vs utility-scale. Because rooftop can be utility-scale, and utility-owned installations can be rooftop. For example, General Motors/Opel’s unfortunate 12MW rooftop installation in Zaragoza, Spain (actually, several rooftops next to each other) is large enough and it is not owned or developed by a utility, but by a private investor (it is still underperforming by more than 25% vs expectations, of course, according to the remote-monitoring system). And, as already mentioned, the 2MW rooftop installation in Fontana, CA is owned by a utility, namely SCE (they actually intend to construct and own 250MW on commercial rooftops).

    A title that states “Business-owned and Homeowner-owned Solar Installations Growing Faster than Utility-Scale Solar” has at least has some support in facts (up until the end of year 2008, that is).

  • Susan Kraemer

    No, ECD: The report compares “utility-owned” to “business-owned and homeowner-owned” solar, and so did I.

    I think you are getting too hung up on whether this “business-owned and homeowner-owned” is literally “on a rooftop” or not.

    Homeowners might put their “rooftop” solar in the yard, on the gazebo, on the garage and on the house roof. Businesses put theirs out in the fields (vineyards, dairies, agricultural businesses etc) or on the factory roof.

    So you prefer the catchy headline “Business-owned and Homeowner-owned Solar Installations Growing Faster than Utility-Scale Solar.”

    But I think most people accept “Rooftop” solar as shorthand for privately owned.

  • Susan Kraemer

    No, ECD: The report compares “utility-owned” to “business-owned and homeowner-owned” solar, and so did I.

    I think you are getting too hung up on whether this “business-owned and homeowner-owned” is literally “on a rooftop” or not.

    Homeowners might put their “rooftop” solar in the yard, on the gazebo, on the garage and on the house roof. Businesses put theirs out in the fields (vineyards, dairies, agricultural businesses etc) or on the factory roof.

    So you prefer the catchy headline “Business-owned and Homeowner-owned Solar Installations Growing Faster than Utility-Scale Solar.”

    But I think most people accept “Rooftop” solar as shorthand for privately owned.

  • ECD Fan

    Dear Susan:

    You are misusing the IREC report. The report never breaks down rooftop vs ground-mounted systems. Using “utility” systems as a proxy for ground-mounted and “residential” as a proxy for rooftop is just wrong. For example, SCE (an utility) put a 2MW rooftop PV instalation in Fontana, CA in 2008. And here is one residential installation that will be ground-mounted:

    http://blog.gogreensolar.com/2009/12/battle-of-solar-panel-brands.html

    “Non-residential” installations, of course, are a mixed bag as well (there are large ground-mounted installations, for example, and large rooftop installations).

    So you have no basis, given the report you are using, to state that “Rooftop Solar Installations [are] Growing Faster than Utility-Scale Solar.”

  • ECD Fan

    Dear Susan:

    You are misusing the IREC report. The report never breaks down rooftop vs ground-mounted systems. Using “utility” systems as a proxy for ground-mounted and “residential” as a proxy for rooftop is just wrong. For example, SCE (an utility) put a 2MW rooftop PV instalation in Fontana, CA in 2008. And here is one residential installation that will be ground-mounted:

    http://blog.gogreensolar.com/2009/12/battle-of-solar-panel-brands.html

    “Non-residential” installations, of course, are a mixed bag as well (there are large ground-mounted installations, for example, and large rooftop installations).

    So you have no basis, given the report you are using, to state that “Rooftop Solar Installations [are] Growing Faster than Utility-Scale Solar.”

  • Susan Kraemer

    Neal, Yes – because PG&E is not allowed by the CPUC to ever raise the baseline (so someone at poverty level can at least turn on the lights), increasingly any extra costs will indeed get passed to all of the higher tier users as time goes on.

  • Susan Kraemer

    Neal, Yes – because PG&E is not allowed by the CPUC to ever raise the baseline (so someone at poverty level can at least turn on the lights), increasingly any extra costs will indeed get passed to all of the higher tier users as time goes on.

  • Susan Kraemer

    @Brian, are you sure your baseline is 5 cents? Most of PG&E (half of CA)is 11 cents for baseline. But yes, the steep tiered pricing for high electricity usage makes it more economical for people who use more than 600 kwh a month to switch to solar.

  • Neal Reardon

    Also, PG&E’s 2010 rate increase will be applied to tier 1 and tier 2 rates (past rate increases have pushed up the higher tiers). This means that in Brian’s example, PV will be a more competitive alternative to the first 2/3 of the PG&E bill.

  • Neal Reardon

    Also, PG&E’s 2010 rate increase will be applied to tier 1 and tier 2 rates (past rate increases have pushed up the higher tiers). This means that in Brian’s example, PV will be a more competitive alternative to the first 2/3 of the PG&E bill.

  • Ben

    Wow! amazing. Do you think the exponential trend on that graph will continue?

  • Susan Kraemer

    @Brian, are you sure your baseline is 5 cents? Most of PG&E (half of CA)is 11 cents for baseline. But yes, the steep tiered pricing for high electricity usage makes it more economical for people who use more than 600 kwh a month to switch to solar.

  • Ben

    Wow! amazing. Do you think the exponential trend on that graph will continue?

  • Brian Schumer

    All we need to solve the energy problem is to come up with a solution that grows faster than the problem, and do so in a profitable fashion.

    It’s obvious that this bar has now been met! In California, there’s teired pricing for electricity, something like income tax. The base rate is like $0.05 per KWH. But then, as you use more electricity, you pay more for electricity.

    I did a breakdown of a recent, unusually large bill, and found that about 1/3 of my power bill was billed at around 5 cents a KWH. Another third was about 11 cents/KWH, and the last was billed at 31 cents per KWH! That last third kicked my utility bill from $300 to over $1000!

    Against this backdrop is the sales pitch for PV solar panels – if you can offset 50% of your utility usage, you can cut your bill (in my case) from $1000 to less than $200!

    And that’s the pitch, when I called – don’t bother trying to go 100% solar – just find the amount that you’d have to shave off the bill that would easily offset the payments on a loan for Solar Panels – any amount of solar less than that is profitable, any amount more than that is money thrown down the toilet.

    If I weren’t a renter, I’d do this tomorrow!

  • Brian Schumer

    All we need to solve the energy problem is to come up with a solution that grows faster than the problem, and do so in a profitable fashion.

    It’s obvious that this bar has now been met! In California, there’s teired pricing for electricity, something like income tax. The base rate is like $0.05 per KWH. But then, as you use more electricity, you pay more for electricity.

    I did a breakdown of a recent, unusually large bill, and found that about 1/3 of my power bill was billed at around 5 cents a KWH. Another third was about 11 cents/KWH, and the last was billed at 31 cents per KWH! That last third kicked my utility bill from $300 to over $1000!

    Against this backdrop is the sales pitch for PV solar panels – if you can offset 50% of your utility usage, you can cut your bill (in my case) from $1000 to less than $200!

    And that’s the pitch, when I called – don’t bother trying to go 100% solar – just find the amount that you’d have to shave off the bill that would easily offset the payments on a loan for Solar Panels – any amount of solar less than that is profitable, any amount more than that is money thrown down the toilet.

    If I weren’t a renter, I’d do this tomorrow!

  • Paul

    Wow… thanks for putting that together. Having just had a debate with a utility employee who claims EV charging could cause rolling brown outs in California, here’s cause for optimism

  • Paul

    Wow… thanks for putting that together. Having just had a debate with a utility employee who claims EV charging could cause rolling brown outs in California, here’s cause for optimism

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