Solar Energy for Everyone

Many builders assume they need a hot, sunny state to even consider installing a photovoltaic (PV) system. While there is a benefit to being in these areas, homes in colder climates may be equally good — or even better — candidates.

First, you'll need to discard any misperceptions you have about location.

"Solar thermal and photovoltaic devices depend on light, not heat — and this light does not need to be direct.

"While the Southwest enjoys particularly good resources, the entire U.S. has good solar resources," says Noah Kaye, a spokesman for the Solar Energy Industries Association (SEIA).

The NAHB Research Center tested homes with PV systems in upstate New York and in Tucson, Ariz., and discovered financial benefits in both areas.

While a 2-kilowatt (kW) capacity PV system in Tucson would generate about 9.4 kilowatt hours (kWh) per day, a similar size unit in New York would produce 6.2 kWh.

And while a unit in a less sunny area may produce fewer kWh per day, it could be more cost effective if the local utility has high summer peak rates because the output of a PV system has a higher value in summer than in winter.

Whatever the location, orientation is part of determining the cost-effectiveness of PV. Although a roof facing south is ideal, a system can still work at 95-percent capacity facing southeast or southwest.

"If you are 20 degrees off due south you can still be successful," says Joe Wiehagen, a research engineer at the NAHB Research Center.

"In fact, sometimes there is a real cost benefit to orienting somewhat west because the PV output can match peak utility demand more closely."

The tilt of the PV unit can affect its efficiency as well. It is ideal to allow the maximum exposure to sunlight, but even on a flat roof, a PV system can perform near maximum capacity as long as it has a south-facing array at the optimal tilt, which is an angle equal to the home's latitude.

Additionally, there should be little or no shading over the PV system.

Determining the price of the system — and the payback—will require some research. For upfront costs, builders will need to account for the cost of the components, labor, federal tax rebates and local incentives. (Go to www.ProBuilder.com/innovations [1] to learn how to calculate the costs). For information about local incentives, consult the Database of State Incentives for Renewable Energy at www.dsireusa.org [2]. For utility rates and payback periods, contact the utility.

The size of the unit that's installed has the most impact on price.

Generally, a PV system connected to the grid costs about $7,000 to $10,000 per kW of capacity, before incentives. Thirty-nine states also permit customers to sell excess energy back to the utility. (Contact the local utility to learn more.)

To determine the project's payback period, find out the local peak electric rates and the number of sunlight hours per day. Divide the upfront cost of the product by the local price of electricity, the hours of sunshine per year, and the size of the PV system.

To make a generic estimate, builders can use this formula: (Installed Cost — Incentives)/(Electric Rate * Hours of Sunshine/Yr * Size of PV System in kW).

This does not take into account all of the variables, however. For further assistance, use the Performance Calculator for Grid-Connected PV Systems, provided by the National Renewable Energy Laboratory at http://rredc.nrel.gov/solar/calculators/PVWATTS/ [3].

Builders who have never installed a PV system before shouldn't let any a fear of new technology daunt them, says John Graziose, vice president and co-owner of Gerber Homes in Rochester, N.Y.

"The systems were very simple to install," Graziose says. "We built the houses, and [the subcontractor] came and plopped them on. We had to run some feeds up into the attic, and we ran some conduits for them to use, but it was very convenient and very simple. On top of that, we didn't have any problems finding a subcontractor to install it."

But before installing the system, put some effort into improving the efficiency of the home that the system will serve.

Insulation, Low-E windows, air sealing and a high-efficiency HVAC system all have shorter paybacks, so it makes sense to do them first.