Can Solar Panels Really Power a Whole House?

With the advancements in solar and battery storage technology today, solar has emerged as not only one of the most efficient energy sources, but also one of the most cost-effective ways to power a home. (The latest breakthrough is transparent solar panels, which may one day douvle as power-producing windows in your home!)

If you have a suitable roof and can afford the upfront investment of both solar panels and a storage battery, solar can be an excellent way to reduce your carbon footprint and lock in long-term savings on your electricity costs.

The long answer to that question, though, is more complicated.

While it is possible to take your home completely “off the grid” with the right solar and storage set-up, it is more common to keep your home connected to the grid and source your electricity from a combination of your solar panels and the electric grid.

Without a storage system, your solar panels will only be able to generate energy to power your home during the daytime. At night, when your solar panels are not producing electricity, you’d receive power from the grid.

In this case, even though your home isn’t entirely powered by solar, you could still offset your electricity bill by selling excess energy generated during the day back to the grid via your local utility company or state-run program. So, while your home wouldn’t be powered by solar 24/7, you could still generate enough clean energy to offset some of your electricity costs and your carbon footprint.

How many solar panels do I need to power my home?

The average U.S. household uses 893 kilowatt-hours (kWh) of electricity every month. That’s just under 30 kWh per day.

The number of panels needed to meet this daily average will depend on factors like the amount of sunlight your house receives, the size of your solar array, and the power rating of your solar panels (how many watts of power they generate). This is where a little math comes in, but the equations aren’t overly complex.

High-level, there are three key steps:

1. Solar panel power rating: convert watts to kilowatts

A solar panel’s power rating is measured in watts (W). Panels today typically have a power output ranging between 250 and 400 W, depending on which system you buy. That means they’ll produce 250-400 W of electricity per hour during peak conditions. But we’ll want to turn that into kW, so that you can more easily match it against your own electricity usage.

1,000 W equals 1 kW, so the average residential panel has an output of between 0.25 and 0.40 kW.

2. Estimate hours of sunlight

The next step is to calculate the daily output of your solar panels. To do this, you need to estimate how many hours of sunlight your solar panels will receive per day (or energy-producing conditions, as panels can still be effective, albeit less efficient, on cloudy days).

Understandably, your home’s sunlight exposure can vary drastically by location, seasonality, landscaping, and more factors—but there are tools out there to get average estimates based on historical scientific data. Google’s Project Sunroof is one such tool that takes this even further by showcasing your estimated savings and environmental impact, too.

Also, as part of any good solar contracting and installation process, companies will do this sunlight analysis on your home before recommending what system you should go with and how many panels you need to invest in.

Calculate the number of panels you’ll need

To get a rough estimate of how many solar panels you’ll need to meet your energy needs, follow the equation below. (Grab your electricity bill so you have your home’s latest power consumption on-hand.)

The amount of power your home consumes on average per day in kwH / (Your solar panels’ power rating in kW) x (Average hours of sunlight exposure per day)

For example, if your home energy usage is 30 kwH per day, you are looking to buy 320 W solar panels (0.32 kW power rating), and your home receives 4 hours of direct sunlight per day on average—you will need 23 panels to power your home.

30 / (0.32 x 4) = 23.4

Of course, this is just an average. The number of panels needed to power your home will depend on your electricity needs and many other factors. If you have a smaller roof or your home receives fewer hours of sunlight per day, you can purchase panels with a higher power rating to generate more electricity per hour.

What happens to excess energy produced by home solar panels?

In many cases, your solar panels will generate more electricity than you consume during the day. When this happens, the excess energy will either be stored in a battery if you have a solar storage system, or it will be sent to the electricity grid.

Utilities use a system called net metering to measure the amount of energy your home produces. They’ll give you solar credits in exchange for the excess energy you send to the grid. Net metering allows homeowners to offset their electricity bill—so even though you’re still using power from the electrical grid at night, you may not need to pay for that energy at the end of the month. The solar credits could offset some if not all your bill. Talk to your local utility about net metering for more information.

Will solar panels still power my home when the sun isn’t out?

On cloudy days, solar panels still produce electricity, just at a slower rate. Usually, on a beautiful sunny day, you’ll be able to generate enough energy throughout the day to power your home. On some days though, you simply won’t receive enough sunlight (or even partial sunlight) to completely power your home. This is where either having a storage system or being connected to the grid will come in handy.

A battery storage system will allow you to use reserve energy to power your home when your solar panels aren’t producing energy. This is the same reserve supply that you’ll use to power your home at night if you have an “off-grid” home.

If you don’t have solar storage installed, then your home will source energy from the electric grid when your solar panels aren’t actively producing it (like at night).

Remarkably, in the future, solar panels may be able to produce energy at night thanks to an incredible breakthrough by Stanford scientists. But that innovation is still a ways away from having practical, real-world uses.

How much do solar panels cost?

Installing solar panels on your home requires a sizeable financial investment—especially if you’re going to install a storage system too. The cost of just the solar panels will vary depending on the state, with recent data suggesting anywhere between $13,000 to $19,000 for solar installation. But this price does not include any discounts from federal tax credits or local state exemptions for which you may be eligible.

Regional price averages calculated using state averages for 6 kW solar installation from Consumer Affairs. Visit the link for state-specific data.

While the upfront cost may seem like a lot, you can also calculate the long-term savings that you’ll receive once your solar panels are up and running. Over the 20–30-year lifespan of your solar panels, you’re likely to more than cover the cost of installing your panels through those government tax incentives and exemptions, plus the savings that you’ll receive on your electricity costs and excess energy that you may be able to sell back to your utility or state. Look into whether there is a buy-back program in your state.

Adding storage to your solar system will likely add another couple thousand dollars upfront depending on the system that you choose. There are benefits to this investment too, though. You may be able to completely take your home off the grid—so you can have a completely self-sustaining home, which will come in handy during power outages. Not to mention, your electricity bill will cost $0 every month since you’re sourcing all your electricity from your own supply.

What if I can’t install my own solar panels?

Most homeowners and renters are unable to install their own solar panels, whether due to financial constraints or roof ineligibility (not enough sunlight or the infrastructure won’t support solar panels). But just because you can’t install your own panels doesn’t mean you can’t take advantage of the financial and environmental benefits of choosing solar.

Community solar programs allow you to access the financial benefits of solar without installing any of your own panels. Instead, you can subscribe to a local solar array near you and support the operations of that solar farm in exchange for discounts on your electricity bill. While you won’t be receiving solar electricity directly to your home, you’ll be supporting the addition of more clean solar power to the overall energy mix on the grid. With a community solar subscription, you’ll be able to save money on your electricity costs (not directly on your bill, but via the credits you’ll receive back)—and help support our transition to a cleaner energy future.

Check to see if there are community solar programs in your area. To learn more, check out Perch Community Solar.