Does Your Rooftop Solar System Reduce Your Carbon Footprint? It Depends…

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At first glance this is a pretty straight forward issue. If you put solar modules on your home or business, you are generating clean, emissions-free electricity. Right? Well, it depends…in part on how you paid for your system. If you bought it either with cash or with your own source of financing, you can claim that your electricity is clean. If you worked with a third party to install solar as part of a power purchase agreement (PPA) or leasing arrangement, it is likely that you don’t have a claim to the “cleanness” and “greenness” associated with your electricity.

This not only has implications for greenhouse gas (GHG) accounting for individual residents or businesses but also California counties and cities that are trying to estimate how a large uptick in distributed solar projects in the last couple years affects their climate action plan. For that matter, it also could affect how California estimates the effects of distributed solar on statewide GHG emissions.

Renewable Energy Credits

My EPIC colleague Nilmini Silva-Send has posted recently on this blog about renewable energy credits (see here, here, and here). Her posts do a good job of explaining what renewable energy credits (RECs) are and how they work. To summarize here, RECs are the clean energy attributes of renewable electricity. By way of analogy think about milk. When you milk a cow you have both milk and cream, which can be sold separately. Renewable electricity similarly can be seen as two products – electrons and renewable attributes (or “greenness”). The upshot here is that when you split electricity into two products and sell off the renewable attributes or RECs, you are left with “null” power, which has the same environmental impacts or attributes as the average electricity from the grid.

As Severin Borenstein explained in a post earlier this year for UC Berkeley’s Energy Institute at Haas blog, solar companies that own the system and sell you electricity or lease the system to you typically own the renewable energy credits and are basically selling the customer the remaining “null” power. In such cases, as Borenstein explains, you can’t have your cake (claim that your electricity is renewable) and eat it too (allow your solar provider to sell your RECs, presumably in exchange for a slightly reduced energy rate).

Trends in Third Party Ownership

The third party ownership model for solar emerged in the mid-2000s but really took off around 2010, when it accounted for about 20% of all new installation in California. It has helped to expand the solar market and has made it easy to get customers to “yes.” The figure below shows this trend.


Source: U.S. Solar Market Insight Report, Q3 2012 via US DOE

In 2014, according to GTM, 72% of all new installations nationwide were third-party-owned. A quick look at publicly available data on solar in California (see CA Solar Statistics) to determine the capacity of systems owned by third parties was inconclusive since the data set appears to be incomplete, at least as far as indicating whether systems are owned by third parties. Nonetheless, given the trends in the figure below including the projected decline in market share, it is likely that about half of all systems would fall under third party ownership model.


Source: GTM

Implications for GHG Accounting

The prospect of having null power on rooftops throughout the community raises a couple issues related to GHG accounting. First, it will increase the total level of emissions in a GHG inventory. When determining the level of emissions in a particular geographic area (e.g., city or county) for a GHG inventory, we start with the total electric supply – often called gross generation. We are not concerned only with the electricity supplied by the grid but also the electricity self-generated by customers, after all some of that generation has emissions too (think cogeneration). If only a portion of the self-generated PV is emission free, the total emissions will be higher than if all of it is.

Second, if only half of the electricity generated by distributed PV is emissions free, then the GHG reductions into the future from that PV will be smaller. This effect may be minor today but as the amount of PV increases and supplies a higher percentage of gross generation, it could be more significant. As noted above, some have projected that the market share of third-party owned systems will decline. Nonetheless, they will represent a large proportion of currently installed systems and likely will continue to be a sizeable chunk of the market.

To illustrate the potential effects of third-party ownership on GHG accounting, we developed a simple example (figure below). We took the CEC electric forecast for SDG&E to see what would happen if we assumed that half of the distributed PV was null power. We also assumed that all RECs were owned by the third-party company, which may not be true in all cases, including some large commercial or institutional systems. Nonetheless, here is what we found. (For basics on climate projections see this post) While the emissions for the baseline year (2014) and business-as-usual projection would increase slightly (an average of about 1.5% or 100,000 metric tons CO2e), the level of emissions after we took into account the effects of increased PV and the Renewable Portfolio Standard (RPS) through 2030 increased by almost 5% (or 275,000 metric tons CO2e) by 2020 and about 14% (or 600,000 metric tons) in 2030. In other words, if we don’t take into account the REC ownership issue for third-party owned systems, we could be underestimating the overall level of projected emissions and overestimating the potential reductions resulting from distributed PV.

Effects of Third Party OWnership

The range of error in GHG accounting is relatively high. It is necessary to make assumptions and rely on forecasts and model results, which contain their own range of error. And the third-party ownership of PV systems is no different. While we suspect that a large chunk of distributed PV installed in CA could be considered null power, we have little evidence to back up this suspicion. As mentioned above, the publicly available data on this is spotty at best. Further, even if we did come up with a good estimate of how many PV systems were owned by third parties, we would then need to know how many (if any) customers own the RECs. More assumptions! On the other hand, not attempting to quantify an effect that we think is probably not zero could compound the errors in the process. And as the amount of installed PV grows, so to0 will the overall error in our GHG estimates.

I want to be clear that third-party-owned systems represent additional PV and reduce overall emissions. It is just a matter of who gets to claim those reductions. It is really a GHG accounting issue, which seems to be playing an increasingly important role as we attempt to demonstrate that the reductions we think we are getting are real, additional, and verifiable. As I have written about before, it is important that we identify these sorts of issues and develop commonly accepted methods to address them.


About Scott Anders

Mr. Anders is the Director of the Energy Policy Initiatives Center (EPIC), an academic and research center of the University of San Diego School of Law. He joined EPIC in October 2005 as its inaugural director and developed both its academic and research programs. Mr. Anders has 15 years of experience working on energy issues in California. His current work focuses on regulatory and policy issues relating to the electricity and natural gas industries and greenhouse gases. He has authored or co-authored numerous reports and papers on topics including energy efficiency, distributed generation, mitigating greenhouse gases, and smart grid strategies.
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6 Responses to Does Your Rooftop Solar System Reduce Your Carbon Footprint? It Depends…

  1. James Fish says:

    And then there’s still that pesky problem of the amount of energy (largely carbon-based) that it took to manufacture the cells and peripherals in the first place. Emissions-wise solar comes out about on par with natural gas according to recent IEEE publications.

  2. Greg San Martin says:

    To be a legitimate credit under the clean air act, a credit must be enforeable. Almost every owner of rooftop solar brags. The carbon credit system that has grown up around solar seems flawed.

    California is most definitely a ringleader in building a patchwork and that will not make Congress’s job easier. A patchwork of state level carbon accounting systems, regulations and property rights, will make it harder for Congress to act. The principle of uniformity needs to be elevated in the design of cap and trade programs.

    As for life cycle emissions, I would have to review the reference by IEEE (I have not seen much lifecycle emission work by IEEE in the past).

    Increased use of batteries may force agencies and marketers to stop claiming that solar is exclusively displacing inefficient gas on the margin. As the average emissions rate of a KWh from PG&E continues to significantly decline over the life of all rooftop solar systems in its territory, so will the net emissions savings from those systems. At some point, upstream emissions due to manufacturing may become relevant, but I kind of doubt it.

  3. Don Wood says:

    Given the complexity of this enterprise, I expect that private consultants will get richer selling IOUs and other stakeholders whatever conclusions they want. That factor has seriously handicapped the state’s energy efficiency efforts over the past three decades.

  4. Bruce Karney says:

    It’s true that the leasing company or PPA provider owns the non-energy attributes of a leased residential solar PV system, but they don’t own any RECs because (as I understand it) the inverter’s measurement of the rooftop generation is not a “revenue-grade” device. Although there has been discussion of companies like SolarCity aggregating RECs from the tens of thousands of PV systems that they own and selling them, as far as I know none of the certification entities would be willing to certify those RECs because the measurement devices don’t meet the revenue grade standard. If I’m wrong about this, I would appreciate being enlightened about what part of the puzzle I’m missing.

  5. Nancy Rader says:

    I believe that the rooftop solar companies own the RECs in many cases. (When I was approached by SolarCity a few years ago, their unmodifiable contract required customers to waive rights to the RECs. BTW, it also barred them from joining class-action lawsuits.) However, without production meters, these RECs cannot be certified by the Western regional clearinghouse, WREGIS. But there was an effort last year by the Energy Trust of Oregon to enable estimates of production from rooftop systems to qualify for WREGIS certification. This proposal was controversial and was tabled. Still, it might be possible to use non-WREGIS-certified RECs to support voluntary marketing claims (though they would not earn the endorsement of credible labels like Green-e). If the solar companies have made known what they do with these RECs, I have not heard it.
    For more information on the Oregon Trust Proposal, see:—%20FINAL%20%203-31-15.pdf

  6. Nancy Rader says:

    I am glad to see attention being paid to this long-overlooked issue in this blog. Just a note, though, that the statement in the last paragraph that, “I want to be clear that third-party-owned systems represent additional PV and reduce overall emissions. It is just a matter of who gets to claim those reductions” is at odds with the thrust of the article. If the RECs from a rooftop system are being claimed by the owner of the rooftop system (the solar company) — or whoever buys those RECs from the solar company — and by the homeowner (who reasonably believes, despite the fine print in her solar contract, that they are consuming solar, not null, power), then potentially those RECs, and any associated emissions reductions are being counted twice. In that case, one of them would not be “additional.” Therefore, indeed, it is important that we develop commonly accepted methods to address this issue. In my view, RECs should be inextricably linked with the rooftop-solar customer to avoid any confusion (and potential fraud).

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