Solar Savings

How Many Solar Panels Do You Need for Your Home?

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One of the most common questions we get from prospective clients is: How many solar panels will I need for my house? It’s a good question, because the number of solar panels you need will of course affect the price of your solar panel installation.

The number of solar panels you need for your home will depend on how much energy you typically use, where you live, and the efficiency of your solar panels. According to the U.S. Energy Information Administration, in 2016 the average U.S. family used roughly 10,000 kWh (kilowatt hours) of electricity, which would require about 16-20 solar panels.

That’s the average, but you’re not average, right? In this article, we’ll help you figure out how many solar panels you need to power your life here in sunshine-rich Southern California.

Your Energy Usage

Woman lounging in heated swimming pool

The first step in determining the size of your solar installation is to figure out how much energy you use. The last thing you want is to invest in a solar power system that doesn’t produce enough energy or produces more than you need.

This average household data we mentioned above provides a baseline, but it might not be relevant to you. A family of six in a 5,000-square-foot home in San Marcos with a heated pool and two electric vehicles is going to use a lot more energy than a couple living in a 2,000-square-foot home in Carlsbad who don’t drive electric cars or have a swimming pool.

You can find your typical energy usage by looking up your energy bills for the past year. These should be available by logging into your electric company’s customer portal. Each bill should include your total energy usage in kilowatt hours for that month. Add up the amount for the past twelve months and then divide by 12.

Viola! You’ll have your average monthly energy usage (typically between 850 and 1,000 kWh). Assuming you want your solar panel system to cover all of your electricity needs, you’ll need to install a system that can produce this amount each month.

Where You Live

Woman standing under an umbrella on a rainy day

Where you live also plays a role in how many solar panels you need for your home. Americans who live in states like Washington and Maine have to endure long winter nights and many overcast days of the year. Their solar panels get less sunlight, which means they have to put more panels on their roof to produce the same amount of electricity as someone living in a sun-rich state like California.

Of course, just because the sun is in the sky doesn’t mean your solar panels are producing at max capacity. For example, sunrise and sunset won’t help your panels generate much solar energy, because when the sun sits at such a low angle, the atmosphere filters a lot of the light. Also, rates of sun can even vary from house to house depending on external features (like tall trees or a big hill behind your home) that affect how much sun you get.

When calculating how much electricity your solar panels can produce, it’s more important to figure out how many peak sun hours your location receives on an average day rather than just the amount of time the sun is in the sky. Without getting too technical, you can think of a peak sun hour as an hour when your panels are receiving strong, direct sunlight. (If you do want to get technical, a peak sun hour is when the intensity of sun is 1,000 watts per square meter.) In the U.S., most areas receive an average of three to five peak sun hours per day.

When you schedule your energy analysis with a solar installation company, an energy expert will help you determine the average daily usable hours of sunlight your home receives.

Solar Panel Efficiency

Not every solar panel is alike. Different brands offer different levels of efficiency. When we talk about efficiency, we mean how much electricity each panel can generate in an hour. Depending on which brand of solar panel you choose, you can expect an efficiency anywhere from 250 to 350 watts per hour. (Note – these numbers always refer to the amount of energy produced during peak sun hours.)

That difference adds up. Let’s assume your home receives four hours of peak sun hours a day. A 250-watt panel will produce 1kWh per day (250 watts x 4 hours). That’s around 30 kWh per month in a 30-day month. A solar panel that produces 350 watts will give you 42 kWh in that same month.

While higher efficiency solar panels tend to be a little more expensive than their less efficient counterparts, they can end up saving you money if you need to purchase fewer solar panels. They’ll also take up less room on your roof!

At Semper Solaris, we are proud to use SunPower solar panels, one of the highest quality and most efficient solar panels on the market.

Calculating How Many Solar Panels You Need for Your Home

As mentioned above, our energy experts will help you determine how many solar panels you’ll need. If you’d like to estimate this beforehand to start your planning, here’s a quick example of how you can crunch the numbers:

Say that you own an electric car and aren’t about to scrimp on using your air conditioning in the summer. Your average monthly electricity usage rate is a little higher than average at 1,000 kWh per month. During your energy audit, the solar representative mentions that your area receives a daily average of 4.5 peak sun hours. After discussing your options, you consider high-efficiency solar panels that can produce 300 watts per peak sun hour. Let’s do the math.

300 watts x 4.5 peak sun-hours = 1,350 watts

One solar panel on your roof will produce an average of 1,350 watts or 1.35 kWh per day.

1.35 X 30 = 40.5 kWh per month (assuming a 30-day month).

You need a solar panel system that produces 1,000 kWh per month.

1000 kWh / 40.5 kWh = 24.69 solar panels.

Whew! That was a lot of math, but we got our answer. Your home would need roughly 25 solar panels in order to meet your existing energy needs. You’ll notice that this number is actually lower than the average mentioned at the beginning of this article. That’s because we get higher-than-average amount of peak sun hours here in San Diego, and because this scenario incorporates high-efficiency solar panels. No wonder Californians love solar panels!

This article should help you get a general idea of the number of solar panels you need, but to get an accurate estimate, request a consultation with a knowledgeable and reliable solar panel installer in your area. If you live in California, take a look at our serviced locations and schedule a free energy audit with Semper Solaris.

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