How Much Solar Power Can My Roof Generate?

Solar Power Variables

Many factors go into calculating the best solar system size. Some of these variables include your home’s energy usage, your roof's available square footage, the solar panel wattage, and amount of sun the solar panels will receive.

For example, in Maine where sunlight is often at a minimum, homeowners prefer higher-rated panels that generate more electricity in comparison to panels typically selected for homes in sunny California. For all residences, high efficiency panels generate more wattage which means fewer panels on your roof.

Design a Custom Solution

Each Sunrun solar system is custom designed and built for your energy needs using a proprietary solar design software platform. There’s definitely not a one-size-fits-all solution. It can be as small or large as you want or need. Sunrun doesn't install cookie-cutter systems. Our proprietary technology, called BrightPath enables us to design a system and solar plan specifically for your home.

Large photovoltaic systems produce the most electricity and reduce your carbon footprint more than a smaller system. Yet, even if you’re not limited by cost, the size of your south-facing roof may limit your system size. In that case, maximize your solar installation's yield by considering smaller, high efficiency panels to achieve your energy goals.

Solar Power Generation Choices - More Wattage or More Efficiency?

The broad selection of solar panel models available for household use are not created equal. And, they do not all generate the same amount of power.

Solar panels are rated based on the watts they generate. The higher the wattage rating, the greater amount of power your solar installation will produce. Most residential solar panels have power output ratings from 250 to 400 watts, depending on panel size and how well they convert sunlight into energy. While higher power ratings are considered preferable, power output is not the sole factor in judging a solar panel’s performance.

For instance, two solar panels may each have a 15% efficiency rating, yet the power output rating of one is 250 watts and the other is 300 watts.⁴ The higher output may simply be due to the 300 watt panel’s larger physical size--rather than having a high efficiency or more advanced technology. Therefore, panel efficiency is a better indicator of solar panel performance than just power output for meeting your energy needs.

Size vs. Quantity

In application, you could use either of these panels in a solar system to build a system with a total rated capacity of 5kW. The difference is it would have either 20 250-Watt panels or 16 300-Watt panels.⁴ With either panel’s wattage, the systems would generate an equal amount of power if installed in the same location.

How Much Energy Can a Solar Panel Generate?

A solar panel’s wattage represents its potential power production under ideal conditions. The table below shows the minimum, maximum, and average power outputs of the solar panels from a few leading manufacturers. Each company has a wide range because they produce multiple solar panel models. Panel wattage is important but just one factor that goes into your equation.

Maximize Power Production from the Sun

The electricity generated by a solar panel system is ruled by its rated power output. Yet, it’s dependent on other factors as well to best serve your energy usage. These include: panel efficiency, temperature sensitivity, shading, and the angle of your roof. A roof’s angle, though, has less impact on panel performance than the direction it faces. Top production occurs when solar panels face south a tilt angle of 30° to 45°.⁵

Additionally, available sunlight varies by location. This brief equation shows how sunlight and a solar panel’s specifications turn into the amount of power generated.

Let’s say on a good day, you average 5 hours of direct sunlight. Multiply 5 hours of sunlight x 290 watts from a solar panel = 1,450 watts or roughly 1.5 kilowatt hours per day. That’s about 500-550 kilowatt hours of energy per year from each panel on your roof.⁴ How does that compare to your annual energy usage?

Cost vs. Value

High efficiency solar panels tend to cost more than their less efficient counterparts. Yet, it's worth assessing whether the upfront cost difference is justified by the value of generating more electricity over the lifecycle of your solar system. Alternatively, you may wish to install a smaller system and still draw some electricity from the grid. This decision will in part be affected by whether you add solar battery storage.

Why Solar Panel Output Matters

The price of a home’s solar system is generally based on the total power output of the installation’s solar panels. Pricing in the solar market is typically measured in dollars per watt. Thus, your solar panels' total wattage plays a significant part in your system's overall cost.

Battery Storage Increases Energy Freedom

Harness and store the sun’s abundant energy. Across America, homeowners are installing battery storage systems with their solar panels.

A recent study predicts that by 2023, 90% of residential solar systems will include battery storage.⁶ Sunrun's Brightbox battery storage gives you the freedom to choose affordable, reliable power without inflated rates or usage restrictions.⁸

How a Solar Battery Adds Value

Add increased value to your solar panels by storing the energy they generate. Solar panels with battery storage maximizes the amount of electricity your installation retains for your use. By adding solar battery storage, you can take even greater control of powering your energy needs.

Surplus electricity created by your panels is stored in the battery until you need it. During an outage, when the sun sets, or if you're using extra power, electricity draws from the battery. It’s an easy, elegant solution with many benefits. 

Maximize Offset

With a home battery system, you can collect nearly every ray of sunshine on your rooftop. Sunrun’s Brightbox system intelligently and remotely optimizes your usage of electricity stored in the battery. If you have Time of Use Rates, when peak electricity rates are in effect, the battery storage system automatically releases stored energy to reduce your electricity costs.

Brightbox battery storage enables you to generate, store, and manage affordable solar energy on your terms. A battery also maximizes your electricity offset from the grid and ensures that you buy a minimum amount of energy from the electric company when prices are highest.

Preserve Peace of Mind

Rooftop solar panels with battery storage generate electricity and provide a backup power solution. During an outage, Brightbox keeps preferred circuits powered. Our energy storage system enables you to run four 15-20 Amp, 120V circuit breakers for approximately 8 to 12 hours—enough to keep essentials humming until the sun rises.

Solar can’t change the weather. But, having electricity during an outage gives you peace of mind and a value beyond money.

State Strategies Back Solar

Going solar is a wise decision. The Fourth National Climate Assessment warns that our antiquated electric grid was not built to withstand today’s extreme weather.⁷ Communities are bearing serious consequences.

You can assure a reliable energy future for your home with solar. Clean, sustainable solutions just make life better. Rooftop solar and home batteries build a safer, modern and resilient power grid.

Many states offer solar rebates and tax credits for home solar systems—in addition to the solar federal Investment Tax Credit.¹⁰ Check out why rooftop solar is part of California's wildfire mitigation plans and how the benefits of clean energy policies and strategies help build a sustainable planet.¹¹

Beyond tax credits, many states are passing solar initiatives. California has adopted forward-looking policies to create a more local, efficient electric grid not dependent on fossil fuel power plants. As a result, hundreds of thousands of residents have installed solar panels and added solar storage batteries.

Furthermore, Nevada is on track to rapidly expand solar installations, create thousands of new jobs, plus reduce pollution and lower electric bills across their state.

Brightbox Home Battery Storage Service

Let’s change the way we power our lives. Sunrun’s solar panels and a Brightbox battery can help lead America to a cleaner brighter future. We’ve been building toward this energy revolution for more than a decade. See if you qualify for solar panels and battery storage today. Take control of your energy costs and regain freedom from your electric bill.

The Time To Go Solar Is Now

Sunrun will ensure that you have the best number and style of solar panels to optimize your rooftop’s solar power production. You can rest easy with a customized solar solution from Sunrun. Our systems are designed for your house structure, lifestyle, energy and financial goals.

We have the resources and experience to maximize your solar systems’ performance. We’ll guide you every step of the way from contract through installation and maintenance. And, we’ll be there to support and guide you for many years to come.