Calculate How Much Solar Do I Need? (2024)

First, you will need to know the annual electricity consumption for the property. You can find this information on the utility power bills for 12 months. Add the monthly kilo-watt hours (kWh) for an annual total. If you don't have power bills, there are other ways to create an estimate. Order the solar design service and we can help.

Once you know the kWh desired, use the calculator here to determine the kilo-watts (kW) of solar power you will need to generate the kWh for your location.

Solar Power Calculator

The NEXT STEP, now that you have an estimate for the desired kW, VIEW SOLAR KIT SIZES to compare prices, brands and, options.

Remember, you decide how much solar to get based on the need, available space, and budget. There is no rule that you have to offset 100% of current energy use. Utilities will generally allow grid-connected systems up to 120% of the previous 12 months consumption. They will also allow for consumption increases from an electric vehicle, home expansion or other needs.

How to Calculate Your Solar Video Tutorial

Watch this video to learn how much solar power in kilo-watts or kW is needed to generate the kilo-watt hours or kWh of energy used at your property.

SOLAR HOURS PER DAY

The following table provides a lookup for the solar hours per day in the biggest cities in each state of the USA. Use the solar hours per day in the calculator above. If you know the annual kWh consumed at the property, then divide it by the kWh per 1kW to determine the solar array size needed for the project.

The solar hours per day table uses PV Watts calculations for each location using these input standards:

• Module Type - Premium 19% or greater efficiency
• Array Type - Fixed (roof mount)
• System Losses - 12% standard or 15% snow county
• Tilt - 20 degrees
• Azimuth - 180 degrees
• Inverter Efficiency - 98

Actual results will vary for each project.

Solar Power Map of the United States

Find your Solar Hours per Day using the color-coding on this map. Enter the value for your location into the solar calculator.

The solar map uses insolation, a measure of solar radiation energy received on a given surface area in a given time. This is typically measured in kilo-watt hours per square meter per day (kWh/m2/day). The map shows the average daily total solar radiation throughout the United States. The U.S. Department of Energy, National Renewable Energy Laboratory (NREL) developed it.

Steps to calculate how much solar you need

At SunWatts, we make solar simple, and calculating how much solar you need has never been easier. On our Calculate How Much Solar page, you will learn how much solar power in kilo-watts or kW is needed to generate the kilo-watt hours or kWh of energy used at your property.

To estimate your solar system size, you will need three pieces of information to calculate the solar kilowatts.

1. Your utility power bill for the last 12 months
2. The solar hours per day for your location
3. The percentage amount of the power bill you want to be covered

Now, let's look at each item in more detail.

YOUR POWER BILL
It would be best if you had a year's worth of monthly power bills. On each power bill, locate the kilo-watt hours or kWh for each month. That is how much energy you consumed. Some power bills have a summary chart. You might find your kWh there. The summary chart may show the average daily kWh used for the past 12 months. If so, you can enter the total kWh for the year.

If no total is provided, then add the kilo-watt hours for each month and enter the total into #1 on our Solar Power Calculator. Do NOT include comma or decimal point. As an example, the average home in the USA uses 30 kWh per Day. Multiply that by 365 days, and the average home in the USA uses 11,000 kWh of electricity per year. So let's enter 11000 into field #1.

SOLAR HOURS PER DAY
The next piece of information to look at are the solar hours per day for your location. In the USA, the average solar hours per day is between 4-6 hours. The AVERAGE solar hours per day. It's longer in the summer, shorter in winter. Now, scroll down the page to find your state and nearest city for the solar hours. For our example, let's use the first location on the list. Birmingham Alabama has 5.26 solar hours per day. Enter this number into #2, Solar Hours per Day.

POWER BILL OFFSET
The final piece of information is the amount of your electricity bill you want to cover. 50%, 80%, 100%, 150%; It’s up to you. But let's start with 100. Enter the whole number into #3, Do NOT include the % symbol. For our example, you should enter #1 11000, #2 5.26 and #3 100 You're ready to click calculate!

The example answer should be 7.64. This means that 7.64 kW or 7,640 watts of solar should generate 11,000 kilo-watt hours per year in Birmingham Alabama. You now know how to calculate the kW size you will need for a solar kit that will generate the kWh you consume. To find the price and more details for a solar kit, click the red link to VIEW SOLAR KIT SIZES, or use the menu by choosing Solar Kit, then Solar Kit Sizes.

You will see that we have many different size solar kits, from 1,000 to 1 million watts. SunWatts. Solar Made Simple.