The effect of distributed solar power used in a zero energy home (ZEH) subdivision on peak demand is disccused in the paper Impact of Distributed Solar on SMUD’S Peak Load. The study was conducted on the Pemier Gardens Zero Energy Homes subdivision in the Sacramento Municipal Utility District (SMUD).
This paper, presented at POWER-GEN Renewable Energy & Fuels in Las Vegas in April, presents data from an opportunity to study two new adjacent housing developments, one designed with highly-efficient amenities and PV panels on the roofs and the other built in a traditional style with lessor efficiency improvements.
ConSol estimated that the energy efficiency measures would reduce the models’ total heating, cooling and water heating use by between 39% and 41% (of a normally constructed house of the same size). They also estimated that, in addition to the heating, cooling and water heating improvements, substituting fluorescent for incandescent lighting, and energy star for standard appliances could reduce total electrical and natural gas usage 44% to 59% and 22%-23%, respectively. Based on these analysis of the Premier model homes, it was estimated that adding a 2 kW of PV solar could reduce the home’s net annual electrical use to zero. Is this an error? I think they meant 40% of the energy consumed in a normally constructed home of the same size.
One of the advertised benefits of distributed solar energy is its ability to produce power during summertime peak periods. This is particularly true in Southwestern states, where summer peaks can be over twice the capacity of winter peaks. To date, however, a limited base of empirical data has been developed to quantify the peak shaving benefit.
The first step in designing a ZEH is to significantly reduce the home’s overall energy use, which enables the homebuilder to install a smaller photovoltaic system to meet the home’s electrical needs and, more importantly, helps to reduce the ZEH’s overall costs. Working with Premier, ConSol assembled an efficiency package that was agreeable to all members of the team and that was the same across all five models featured in Premier Gardens; this efficiency package included:1
- Low air infiltration;
- Vinyl, low-e, spectrally selective windows;
- 92 percent efficient furnace (AFUE .92); • SEER 14 with TXV air conditioner; • Engineered heating and cooling duct runs ;
- Tankless water heater with a .82 Energy Factor;
- Insulated hot water pipes;
- Fluorescent lighting for all permanent light fixtures; and
- Third-Party inspection and testing of the home’s energy efficiency features, such as the quality of the insulation installation, (qualifying the home as an Energy Star Home).
After the first year of use the PV systems in the Premier Garden ZEHs are supplying approximately 47% of the electricity used in the home, average 3,329 kWh of the total average 7,066 kWh consumed.
There is much data in graphical form contained in the paper which details the electrical use and compares the electrical use to that in the control subdivision. The following
One of the purported benefits of distributed solar energy is its ability to produce power during summertime peak periods. This is particularly true for a utility like SMUD where summer peaks can be over twice the demand of winter peaks. SMUD’s electric demand growth is largely driven by new homes. SMUD’s system load profile nearly matches the average new home’s load profile on the system’s peak day (July 15, 2005), confirming the contribution of new homes’ load to setting coincident peak electrical demand. Figure 11 shows how the ZEH homes shift the peak load to a later hour and reduce the peak demand on the system as a whole and have an even greater effect when compared to the peak of non ZEH homes.
Initial monitoring data indicates that Premier Garden residents are using about 10 percent less electricity than their neighbors with the homes’ PV system providing approximately 50 percent of the homes’ electricity needs.
Limited data provided by PG&E indicates that the Premier ZEH residents’ use 39% less gas compared to the Control group, 23.1 vs. 37.8 therms per month, and 49% less than less gas compared to an average PG&E customer at 45 therms per month.
The entire paper is quite lengthy, but worth the read if you are interested in this sort of thing.
Zero energy homes have been of particular interest to me in the past couple of months because they are the epitome of distributed energy and true 100% ZEHs can be very environmentally friendly and would eliminate a great deal of expansion of the grid. It would be interesting to see the effect of using geothermal heat pumps, adding solar hot water heating, adding some passive heat storage, doubling the size of the solar panels and adding 3 or 4 hours of active energy storage to augment the passive storage, if that wasn't sufficient. It would be fairly expensive, but I have read that adding the cost of these additional features to your mortgage would be more than offset the savings in electricity, especially with energy prices increasing.