My wife and I decided that it would be a good idea to add a solar electric system to our home in light of the imminent electric price deregulation in our state. We had already greatly reduced our electric usage by installing compact fluorescent bulbs in our home, and already have plans to switch our electric water heater to a gas fired tankless unit.
Normally, the cost of a solar electric system is such that it is not a good investment. However, the recent economic stimulus packages have made it marginally affordable. The federal government rebates 30% of the cost of the system via the federal income tax and my state, PA, rebates $2.25 per watt of power capacity. These two incentives pay for more than half the cost of the system.
Several months ago, when I started looking for systems, I quickly discovered that there were very few companies which had turnkey solar solutions. The few companies I did call didn’t even bother to return my phone calls. Eventually though I did find a contractor who had a system similar to what I was looking for.
There are two basic kinds of solar electric installations. The first is called a ‘grid-tied’ system where the home is still powered mainly from the electric utility, but the solar system generates power and feeds it back (essentially sells it) to the power company. As the solar panels produce power, the generated electricity first feeds the home, and if any is left over, it feeds the power lines, and turns the electric meter backwards. This reduces a homes electric bill.
The second kind of solar electric system is called an ‘off grid’ system where the home is not connected to any electric utility company. The solar system itself produces all of the electric power used by the home. Usually, the solar panels are used to charge a bank of lead-acid batteries during daylight hours, and the batteries run the home when the panels are not producing power.
Either system requires a device called an ‘inverter’ which takes the direct current (DC) produced by the solar panels and converts it into 220volt alternating current (AC) which is the same as supplied by the utility company.
I had hoped to find a system which combined both systems, because the power fails frequently at our location. However, it seems that it is not possible to have a grid tied system with battery backup because of the possibility of feeding back power into dead lines while workmen try to repair the power grid. That would make a really bad day for some unsuspecting lineman.
So, we opted for the grid-tie system which needs no batteries, but doesn’t work at all if the power grid is out. In that case, we are back to using a generator until the utility company fixes the problem.
The system we installed is a 4 kilowatt Brilliance system made by General Electric. It was very easy to install, taking only one day to get up and running. The hardest part was mounting the panels on the roof. Our system has 20 panels, each producing 200 watts in bright sun. The panels are wired in series as two banks of 10 panels each. Each bank of panels produces about 250 volts in bright sunlight. The inverter converts this 250 volt DC power into 220 volt AC power. This AC power is simply fed into our breaker box through an ordinary two pole circuit breaker.
Of course, nothing is ever simple, and there is usually some unexpected problem. In this case, it was with the system specifications. We bought a 4kw system, fully expecting that it would be capable of producing 4000 watts of power in full sun. However, after it was installed, I found out that the inverter supplied with the system had a maximum capacity of 3,500 watts of output power. It seems GE rates the input power to the inverter instead of the output power, and never did the contractor’s salesman disclose that important point. To rectify that, we upgraded the inverter to 4800 watts, and now have the option of adding more panels in the future.
For the first two months of operation (September and October), the system produced about 22 Kilowatt Hours of electric energy per day. This exceeded our expectations, but I expect the output to drop off substantially during the winter months.
I will provide an update on the system when I have more data to report.