We don’t want you to get tangled up in technical details you’re not comfortable with, so if you want to call us at any time, please do. Or just go ahead and have fun using the information on this page.
Deciding the size of a solar electric system for your house depends on:
- the amount of electricity you use per year
- how much of that amount you want to generate
- how much unobstructed space you have (on a roof or the ground)
- your budget
Net Metering: Why you don't want to generate too much electricity
In some states, residents can install as big a system as they can afford and make money selling excess electricity to their power companies. However, DC, MD, and VA residents are limited by “net metering.” Net metering means:
- In months when you produce more electricity than you use, you are credited for the excess against the next month’s bill
- In months when you produce less electricity than you use, you pay for the difference
On an annual basis, net metering also means the utility will not pay you “extra” if you generate more electricity than you use. This is why we ask if you are planning any significant energy improvements (such as installing a high-efficiency air conditioner or heat pump) before we size your system.
Can You Cover All Your Electrical Needs?
You can, but it will take a lot of space and a large budget. Here’s why:
The average DC-area house uses 850 kWhs (kilowatt-hours) a month, or 9700 kWhs a year. A system with a capacity of 1kW will produce 1kWh of electricity per hour under ideal conditions – enough electricity to power ten 100-watt light bulbs. Because conditions are seldom ideal, a system’s capacity and the actual energy it produces are seldom the same. In the DC area, an optimally positioned 1 kW system will generate an average of 1292 kWh of electricity in a year.
So it would take a 7.5 kW system to completely “cover” an average house’s electrical use. Because a 1 kW system takes up about 90 square feet, most homes don’t have space for a system that will fully cover their needs. For perspective, the average system in California – the most “solarized” state in the country – is 4 to 5 kW.
In the DC area, solar system costs range from $6,000 to $10,000 per kW, installed. Smaller systems on flat roofs are at the high end of that scale, while larger systems on sloped roofs are at the low end of that scale. So that 7.5 kW system would cost at least $45,000 before incentives.
So What is Realistic?
Take your annual electrical consumption in kW-hours.
Divide by 1292 to see what capacity system will cover your needs.
This is the required system capacity in kW.
Multiply the system capacity by 90 square feet.
This is how much open, relatively unshaded space you need on your roof or in your yard.
Multiply the system capacity by $6,000 and by $10,000.
These are the approximate minimum and maximum costs of the system.
Multiply the minimum and maximum costs by 65% (DC), 70% (MD), and 75% (VA).
When local incentives are available, this will be your approximate out-of-pocket cost until you collect the federal tax credit. (Switch offers no interest, no payment financing for 6 months to cover this “gap.”)
If you can manage that out-of-pocket cost, you're on your way.