Solar Electric System

What is the payback for a solar electric system? The question might as well be asked "What is the payback for kitchen cabinets made from cherry wood or granite counter tops?" But, you say, cherry and granite add value to my home ... the same can be said for a solar electric system, except that there is real income immediately and over time.

More and more states are implementing green energy programs. (If you live in CA, there are major incentives.) Here in Washington State, Puget Sound Energy has a solar rebate equal to $525 per installed kilowatt of peak capacity (ours is 4.5 kilowatts) from the system, we will get $2,000 from the recent national energy bill, and we'll get 15c for every kilowatt hour (kWh) generated for the next 10 years. Of course, I don't have to pay the power company for the electricity we generate and use ourselves. (Under a recent WA law, we could earn 25c if a solar panel company built collectors in Washington State.) Finally, solar electric panels do not carry a sales tax, which in Washington State is 8.4%.

By our calculations, the 1^st year return on this investment runs over 20.7% and the balance will earn us around 5.6% per year, comparable to a CD in the bank and close to our mortgage rate of interest Of course, the value of the house will go up because of the system. So what is the payback? In contrast, those cherry cabinets earn you nothing except a warm feeling.

Solar electric systems are expensive. You can expect to pay around $6.00-8.00 per watt of capacity, installed, collectors cost around $4 per watt capacity, and because of the demand, the price is going up. (25 years ago the cost was around $40 per watt, so prices are getting more competitive.) Our 4.5 kW system will generate an estimated 5,500 kWh per year, even in this cloudy climate. Western Washington State gets around 30% less sunlight per year than Las Vegas but only slightly less than Dallas Texas. Even here solar electric makes sense.

Our system is tied to the power grid. Thus, when it is sunny, my meter runs backwards, and when it is cloudy or at night, I pull from the power grid. Depending upon how we live, the 4.5 kW system will provide over 70% of our total designed power demand.

If you are close to the grid forget about batteries. They cost money, take up space, and require maintenance. The grid is our storage battery ... there to use during those long winter nights and cloudy winter days.

Before you consider solar, you need to spend the money on conservation. We have taken Herculean steps to reduce the demand, such the installation of a ground sourced heat pump for heating and hot water, use of only compact florescent bulbs, air to air heat exchanger, the purchase of the most energy efficient appliances on the market, etc.... (Chart of where home energy is used.) Why spend more for a solar system when there are cheaper ways to conserve?

To reach our goal of Zero Net Energy, we need to reduce our total energy use to around 15 kWh per day ... no small task. Our rental property used 835 kWh of electricity in December 2005 plus 99 thems of natural gas. In July 2005 the numbers were 418 kWh and 22 therms. One therm equals roughl;y 29.2 kWh. Thus. the energy use of our rental ranged from 124 to 35 kWh equivalent per day.

Solar electric panels generate direct current or DC electricity. You will need a inverter to transform this DC power to AC or alternative current electricity. In contrast to solar heating or hot water systems, solar electric systems have no moving parts, require minimal maintenance, and just keep cranking out power.

We have two inverters, one each for 12 panels. This will allow us to upgrade the system in the future with minimal rewiring.

Conventional wisdom says that the solar collectors should be oriented to true south. This is not quite accurate for our area. Mornings often have a marine level of fog which burns off by late morning. Thus, the maximum power is generated with an orientation of SSW to SW. The calculations are that you will get around 5% more sun after noon than before noon. The electric company also prefers this orientation because the greatest peak demand for electricity is on the sunniest, hottest summer days and in the afternoon. With our curved roof, we start at true south and bend around to just over SSW. (In Washington State true south is around 21o off magnetic south.)

There has been a great deal of discussion on time of day electric rates with higher rates during the day and lower rates at night. If this ever happens we will be well suited to optimize the benefit from out power plant.

Our system was installed by Jereemy Smithson owner of Puget Sound Solar. The picture above has Jeremy placing a panel on our roof.

We welcome your comments on this site.
You can email Christine Garst at cbgarst@aol.com
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Sunday December 17, 2006 05:34 PM -0800