How Much Solar Power Does My Home Need (Part 1)?
One of the first questions that many homeowners have when they’re planning to get a renewable energy solar system on their roof is exactly how much solar power you need. That can impact the total cost of your system, so you want to make sure you get enough to meet the power needs that you have day to day without getting so much that you have excess or wasted energy. Here are some guidelines on how to calculate your needs.
Calculate Your Energy Usage
The first step in knowing what size solar system you need is to figure out exactly how much energy you need on an average day. There are some relatively complex ways to figure this out by adding up the wattage of all your appliances, lights, HVAC, etc. but you can also get a rough idea by looking at your power bills. That will include the total kilowatt hours (kWh) of usage. Some power bills will break it down to a daily average, while others will just include a number for the entire billing period.
- Daily average: divide it by 24 to get an hourly average
- Entire billing period: divide it by the number of days in the period (probably 30 or 31), then by 24 to get your hourly average
If you live in a hot climate where you run the air conditioner a lot in summer or use electricity for heat in a cold winter climate, make sure you look at power bills for the entire year, and not just one month when the weather is mild, so you get the right estimates.
Factor in Your Solar Goals
If you want solar to cover 100% of your needs, then you can take your daily average calculations, build in a small “cushion” and figure out how many solar panels will generate enough energy to meet your needs. On the other hand, if you want to minimize your up-front costs but still get some energy savings, you may opt for fewer solar panels that will meet most of your energy needs but not all (with a grid-tied system to get the rest of your power from the local power company).
This is also a good time to determine if you want to get a battery backup, which will allow you to use solar energy that your panels capture during the day after it gets dark. Alternately you can choose to install a grid-tied system where you send excess power to the local power company during the day where they will store it, and give you “credits” toward your energy usage at night.
In part two of this blog post we will cover two additional factors that you need to take into account when calculating solar energy system size, as well as sample calculations.