Buzz
The location plays a vital role in determining the number of solar cells needed to power a home.
Digital Vision/Getty ImagesIf you’ve read the HSW article titled How Solar Yard Lights Work, you’ll have an idea of the power output of a solar cell. The solar panel shown in that article includes 4 cells, each capable of producing 0.45 volts and 100 milliamps, or 45 milliwatts. Each cell is 2 inches by 0.5 inches. Essentially, these solar cells can generate 45 milliwatts per square inch (6.45 square cm). For the purpose of this discussion, let’s assume a panel can produce 70 milliwatts per square inch.
To determine the number of square inches of solar panel required for a house, you must know the following:
- The average power consumption of the house.
- The location of the house (to calculate factors like mean solar days, average rainfall, etc.). This question cannot be answered without a specific location. For this example, let’s assume that the solar panels operate at maximum power for 5 hours on an average day.
The first question is genuinely intriguing, so let's tackle it.
A typical household in America relies on either electricity or gas for heating — including heat for the home, hot water, the clothes dryer, and the stove/oven. If you decide to power your house with solar electricity, you would almost certainly still use gas-powered appliances because solar electricity is relatively expensive. This means that solar electricity would be used for devices like the refrigerator, lights, computer, TV, stereo system, motors in appliances like furnace fans and washing machines, and more. Let’s assume these devices use an average of 600 watts. Over a full 24-hour period, you’d need 600 watts * 24 hours = 14,400 watt-hours per day.
Based on our previous calculations, we know that a solar panel can produce 70 milliwatts per square inch * 5 hours = 350 milliwatt-hours each day. Therefore, you would need about 41,000 square inches of solar panels to meet the house's energy needs. This equals roughly 285 square feet (or about 26 square meters), which would cost approximately $16,000. Since the sun isn’t always shining, you’d also need to buy a battery bank, an inverter, and other components, which typically doubles the cost of installation.
If you want to install a small air conditioner in your bedroom, simply double everything.
Because solar electricity is so costly, you'd likely take various steps to minimize your energy consumption. Instead of using a desktop computer and a monitor, you would switch to a laptop. You’d replace incandescent bulbs with fluorescent lighting. You might opt for a small black-and-white TV instead of a large color set. You could also choose a compact, highly efficient refrigerator. By making these changes, you could lower your average power consumption to 100 watts. This would reduce the size and cost of your solar panel by a factor of six, making it more affordable and feasible.
It's important to keep in mind that purchasing 100 watts per hour from the power grid currently costs around 24 cents per day, or $91 per year. This is why solar-powered homes are uncommon unless they’re in remote areas. With the cost of grid electricity being only about $100 annually, it’s difficult to justify spending thousands on a solar system.
