Calculating Your Roof's Solar Needs

It can be tricky knowing how many solar panels you need for your rooftop. Obviously, the simplest way to answer this question is by getting in touch with one of our representatives to inspect your rooftop. Depending on each individual’s reasoning behind going solar, budget, and rooftop size or location - the answer is different for everyone. If you want to do the calculations yourself, the following questions need to be answered. Let’s get started. 

How Much Energy Does my Household or Commercial Building Use?

This can be answered by looking at previous utility bills. Determine how many solar panels your rooftop needs by multiplying your household’s hourly energy requirement by the peak sunlight hours for your area and dividing that by a panel’s wattage. Use a low-wattage (150W) and high-wattage (370W) example to get a range (ex: 17-42 panels to gain 11,000 kWh/year). Something to remember, the amount of sunlight your roof receives and other elements like roof size and battery storage will also be a determining factor. 


What is my Roof’s Available Surface Area?

Have a look at your electricity bill and look for average usage; “Kilowatt Hours”, or something along those same words, and jot down the time period represented (usually 30 days). If you don’t see this information on your bill, look for the beginning and end meter readings and subtract the prior reading from the most recent. What you’re really looking for is daily and hourly usage. If you can’t find these, simply divide the monthly or annual average by 30 or 365 days - then divide again by 24 to find out your hourly average electricity usage. The answer will be in kilowatt-hours.


What is the Climate and Peak Sunlight in my Location?

Climate and peak hours play a huge determining factor in how much energy your panels will produce. If you live somewhere very warm, you will expect to have more peak sunlight hours than somewhere cooler. This simply means you will need more panels if you live somewhere in cooler weather. You can find sunlight information for each state and their major cities on the Renewable Resource Data Center

Once you figure out what your hourly usage is, multiply that number by 1,000 to convert it to watts. Divide your hourly wattage requirement by the number of daily peak hours for your area. This will give you the amount of energy needed for panels to generate effectively on your roof every hour. 

What Affects a Solar Panel’s Output Productivity?

The most obvious answer to this question is the quality of the panels. Most photovoltaic solar panels range in wattage from 150-370 watts per panel, depending on the panel size, efficiency, and cell technology. Consider, for example, solar cells with no grid lines. These will take in more sunlight than conventional cells, and do not peel or break down over time. The construction of cells by SunPower by Solar Vast are more durable and resist cracking or corrosion more easily. A microinverter on each panel can optimize power conversion at the source, as opposed to a large inverter that would be mounted on the side of the building. The greatest takeaway to consider is that the more efficient the panels, the more wattage they produce - and the less panels you will need on your roof to generate the same amount of energy. 

We're Here to Help!

We hope this helped answer your questions regarding how to calculate your solar panel needs. While it’s great to do the math on your own, we want you to know that we’re here to do the work for you. Give us a call or shoot us a message anytime to get started on figuring out your rooftop’s needs today.