Thinking about solar power for your home? Here are 5 things that you should consider.
Powering your home using solar energy does require more maintenance than using the regular old grid power. But not much, solar panels have no moving parts. They are part of a completely stationary system. So once they're installed, there's not a whole lot that can go wrong. Pretty much the only thing a homeowner needs to do is keep the panels clean. It's an important task, though -- too much dust and bird droppings on the panels can reduce the amount of sunlight striking them. Dust buildup can reduce the amount of electricity produced by the system by as much as 7 percent. Aside from that, you're just looking at occasional check-ups to make sure all parts are in working order. You may eventually have to have the inverter replaced (and the batteries if you have a battery-storage system), but that's a once-a-decade type of maintenance event.
Where your home is situated has a big effect on your solar-power efficiency. It's an obvious concern: If your electrical-power generation depends on sunlight, things like towering shade trees and tall, shadow-casting buildings are going to be a problem.
So to build a solar-powered home, it's necessary to make sure there are no shadows on the roof's panel area during the sunniest hours of the day (typically from 10 a.m. to 2 p.m.), and preferably during all sunny hours. The more hours the panels spend exposed to full sun, the more efficient the power generation will be.
Sunlight is obviously key when it comes to solar power and not all regions are created equal in this regard. It's important to know how much sunlight reaches ground level in the area where your potential solar house is located. What we're talking about here is insolation -- a measure of how much solar radiation hits the ground in any given area in a specified time period. It's typically measured in kWh/m2/day, and it tells you how much sunlight will be available for your solar panels to turn into electricity (see chart on last page). If you live in a place like Burley, Idaho, you have an average insolation rating of 5.38. This means in Burley the annual average sunlight that falls on each square meter of ground in the course of one day is equivalent to 5.38 kWh.
The higher the insolation value of your location, the more electricity each of your panels will be able to generate. A high insolation value means you can get more power out of fewer panels. A low insolation value means you could end up spending more to achieve the same power output.
How many panels do you need? Contrary to what most people think, the size of a solar-power installation has nothing to do with the size of the house it's powering. Instead, it's all about two things: insolation, which we just discussed, and how much power you need. To get a very rough estimate of how big a system you need, look at your electric bill and figure out how many kWh you use per day. The average home in United Electric’s service territory uses about 1,800 kWh every month or about 60 kWh per day. Multiply that by 0.25, which is 15, so you need a 15 kW system.
A typical solar panel produces a maximum of 120 watts, or 0.12 kW, in a day. For a 15 kW setup you would need about 125 panels. A single panel might measure about 56 by 25 inches, so a 125-panel solar setup would measure roughly 1,150 square feet.
There's more that goes into this calculation, though. You have to figure in insolation and how many hours of peak sunlight you get per day, and you'd also make adjustments if you're using a battery-storage system with the panels. So it's best to consult a pro.
In 1956, solar panels ran about $300 per watt. A 15 kW system would have been out of the question for all but the shockingly rich. Today, prices are down considerably. In most areas, solar arrays run about $5 to $8 per watt. You'll be paying closer to $5 if you install it yourself and closer to $8 if you have a professional do it. For a 15 kW array, or 15,000 watts, you could pay anywhere from $75,000 to $120,000. There are tax credit dollars available for home installations. Still, tens of thousands of dollars for a solar array is pretty cost-prohibitive -- especially since it can take decades to make that money back in energy savings.
The following solar data chart represents the amount of solar radiation can be expected each day for Burley, Idaho. For instance, in May the average amount of solar radiation that strikes Burley is 6.47. This means the sunlight that falls on each square meter of ground in the course of one day is equivalent to 6.47 kWh. With a 15 kW system and perfect conditions you would receive about 2,153 kWh of energy at a value of $127 for the month of May. The cost to generate electricity with solar system is about 0.21 cents per kWh; the cost to buy electricity from United Electric is about 0.06 cents per kWh.
( kWh / m2 / day )
( kWh )