Maybe solar modules have been facing the wrong way. The California Energy Commission's (CEC) New Solar Homes Partnership (NSHP) thinks they might be and is encouraging builders of new homes to install rooftop solar panels that face west instead of south, the industry norm.
In September 2014, the CEC announced the new NSHP incentives for homeowners, builders and developers installing solar energy systems on new homes in the Pacific Gas & Electric Co., Southern California Edison and San Diego Gas & Electric Co. territories.
According to its updated guidelines, the NSHP offers incentives based on the expected performance of a solar energy system installed in a specific location. These expected-performance-based incentives are determined by a PV calculator, which takes into account parameters such as the specific module and inverter, the mounting type, the orientation and tilt of the modules, and the amount of shade on the system.
The calculation also includes the time"of"use value of the electric generation to the utility system, or the time-dependent valuation (TDV). The weighted TDV annual kilowatt-hour production of the applicant system is compared to the weighted TDV annual kilowatt-hour production of a reference system to determine the amount of incentive.
The new guidelines offer an additional incentive of 15% of the NSHP amount – up to $500 – for installing the panels facing west. The incentive is for the portion of a solar energy system installed with an azimuth between 259 degrees and 281 degrees. (North azimuth is zero degrees, east is 90 degrees, south is 180 degrees, and west is 270 degrees.) The azimuth can be determined by the home builder's site plans, or by using a compass with a sighting feature. The guidelines contain sketches of plot plan examples and photos of compasses.
Installing the modules facing west makes better use of late afternoon sun, says David Hochschild, lead commissioner for the NSHP.Â He explains that in California, a west-facing solar project will generate fewer kilowatt hours of electricity over the course of a year, but generate more kilowatt hours during 2 p.m. to 8 p.m. ‘The late afternoon peak is what we are trying to address,’ he says.
Recent research supports the west-facing modules concept. An analysis by University of Texas researchers examined optimal solar placement for modules on homes in Austin, Texas. The study authors wrote that the optimal azimuth to maximize energy production is about 187 degrees to 188 degrees – seven to eight degrees west of south – while the optimal azimuth to maximize economic output based on the value of the solar energy produced is about 200 degrees to 231 degrees – 20 degrees to 51 degrees west of south. In fact, the authors wrote, ‘The differences between due south (which is the conventional orientation) and the optimal placement were on the order of 1% – 7%.’
The authors also noted that based on the results, utilities should consider altering their rate structures to encourage solar generation that more closely matches peak demand, and use west-of-south solar placements as a hedge against future wholesale electricity price volatility.
Last year, Arizona Public Service proposed a rooftop solar program that would be available to 1,500 customers to generate a total of up to 10 MW of power. Customers would receive $30 per month in credits if they met certain requirements, and west-facing roofs would be allowed. At the end of 2014, the Arizona Corporation Commission had not yet announced a decision on the utility's proposal.
Other utilities are not exactly endorsing west-facing panels. In Nevada, NV Energy's SolarGenerations Electric program requires that solar panels not face more than 90 degrees from true south. According to the SolarGenerations 2014 Program Handbook, ‘For systems 25 kW and smaller that are oriented between 70 and 90 degrees from true south, the final incentive payment is reduced by 10 percent as a result of the expected reduction in system output.’
Still, Hochschild is optimistic the west-facing modules will take hold in California, and he says feedback from builders has been positive.
‘Most of the builders are generally familiar with the challenge,’ he says. ‘The peak has shifted over the last few years from the middle of the day to late afternoon, and most people know that is the shape of the load in California. They understood the rationale for it in California. We have no stated opposition.’