Question
How did the Energy Commission calculate the emissions reduction benefits of the 2019 Standards and the PV requirements? Did Energy Commission consider the impact of midday “renewable curtailment” on CO2 emissions? California’s long-term policies require the energy grid to use more renewable resources, essentially making the grid greener. Do the new onsite PV requirements reduce CO2 emissions despite these policies?
Answer
Yes. The Energy Commission uses a detailed hourly simulation model, known as CBECC-Res, to determine energy savings and emission impacts of the 2019 Standards. For every hour of the year, the software tracks all house loads (HVAC, water heating, plug loads, appliances, lighting, and so forth) and PV generation. Based on these hourly calculations, the software calculates PV-generated kWh that serve the house loads (which reduces the kWh that is purchased from the grid), and the hourly exports back to the grid. Next, the software applies California hourly long-term marginal emission rates to the hourly kWh balances to calculate the CO2 generation impact for each hour of the year. Finally, the software adds all the hourly results to yield the annual CO2 reduction benefits.
Overabundance of PV resources can occasionally cause the grid operators to “curtail renewables” midday on some mild and sunny days; the California long-term marginal emission rates consider the impacts of “renewable curtailment” on the grid.
The 2019 Standards PV requirements will reduce building-based CO2 emissions significantly, even considering the Renewables Portfolio Standard (RPS) goal of 50 percent by 2020 for California grid, as indicated in the table below. Over the longer term, the PV requirement will help California reach the newly-established 100 percent clean energy goal.
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Prototype home: 2,700 sf, Climate Zone 12 – Sacramento, CA |
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CO2 Impact of Housing Choices |
Metric Tons of CO2 Generated/Year |
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Mixed-fuel |
1997 Standards, no PV |
6.5 |
|
Mixed-fuel |
2019 Standards, no PV |
3.1 |
|
Mixed-fuel |
2019 Standards, with 3.1 kW PV |
2.3 |
|
Mixed-fuel |
2019 Standards, 3.1 kW PV, no battery |
1.1 |
|
All-electric |
2019 Standards, 6 kW PV, with battery |
0.2 |
During the three-year cycle of the 2019 Residential Standards, CO2 emissions will be reduced by 700,000 metric tons, equivalent to taking 115,000 18-miles-per-gallon gas cars off the roads.
Further, the 2019 Standards compliance incentives for demand response and grid harmonization measures, such as precooling, thermal storage, and battery storage systems, can make the house invisible to the grid during most hours of the day, resulting in little or no CO2 emissions.