What Size Solar Array Do You Need?

When going solar one of your main questions might be how large your array should be. You’ve probably seen homes with just a few solar modules, and also some with many more covering multiple roofs. What size do you need?

Ideally, your solar array will produce enough solar power to meet your energy needs throughout the year.

Sizing a solar array takes many factors into account – your usage, the solar resource at your location, what can physically fit on your roof, and your budget. 

Analyzing Your Electricity Consumption

When you think about your electricity consumption, you may use more in some months than others.  For example, you might have more summer usage because you are using air conditioning in your home or running a swimming pool.  Or, you might be using electric heat in the winter. A typical usage graph looks something like this:

Solar panels also produce different amounts of energy depending on the time of year–more in the summer due to the longer days. The good news is that the monthly values do not have to match exactly because of Net Metering. Net Metering allows solar customers to use their utility company as an energy bank. In this way, customers receive credit when an array is producing more than a household is using, like on long, sunny days, and drawing on those credits when the solar array is not producing enough to cover energy needs, at night or when it is rainy or cloudy. Therefore, we only have to consider your annual usage.

How Much Power Will your Solar Array Generate?

Many factors contribute to how much energy a solar array will produce, such as, how much shade an array will receive, if there will ever be snow covering the panels, weather, geography, and which direction the panels face. We gather this information during solar site evaluations using a state-of-the-art device, the SunEye 210, made by Solmetrics. You can read more about our process during Solar Site Evaluations here.

After a solar site evaluation, we input the information from the SunEye report into the PVWattsTM calculator. This calculator was created by the National Renewable Energy Laboratory to help solar installers estimate the performance of a solar array at a potential solar site.

The PV Watts report displays estimates of how much power an array is expected to produce over the course of a year using the variables entered in along with historical, local weather information to predict how many sunny, rainy, snowy and cloudy days are expected throughout the year. Then, we can adjust the number of panels in the proposed array until the amount of power expected to be produced covers the amount of energy a household needs based on their energy bill.

Designing the Array

Once we know how big the array needs to be, we move on to the fun part – designing the array. Using a special software, we can show customers a digital rendition of what the solar panels will look like either on the ground or on their roof. We use the images to make sure that the array will fit on the roof and that it looks good to the customer.

Sometimes customers cannot build an array that covers their entire energy consumption. This could be because they do not have enough space on their roof or ground, they don’t have enough shade-free area, or the upfront cost of a large array is simply too expensive at the time. Even if a customer cannot build an array that will cover their whole energy bill, going solar with a smaller array is still a smart option because it will still save them money and reduce carbon pollution.

Should I go Bigger?

Some customers wonder if there is a benefit to building an array that would produce more energy than what their electric bill suggests they would need. The answer is that it is sometimes advisable to build a larger array. One common reason for installing a larger array is if customers anticipate their energy needs will increase. Once customers decide to go solar, they often want to benefit from this new power source as much as possible by switching to electric appliances, electric heat pumps and electric vehicles. It is important to let your solar installer know if you are considering making these changes after you install a solar array so they can adjust their proposals to accommodate for this.

Another reason you may consider a larger array is if you have a place you can divert excess energy. With group net metering you can give your excess solar credits to anyone using the same utility company. Common places that customers will send their extra energy credits are rental properties they own, vacation homes, family members or their favorite local nonprofit.

We hope this discussion has helped to answer some questions about how we size a solar array. Because our work is always customized for your needs, the size will depend on how all of these factors apply to you. Please Contact Us, if you want more information or what to start the solar process.