Home Solar System Size: How Many kW and kWh?

How can you get the right home solar system size for your real life needs? Learn the basic facts and vocabulary before you talk to an installation pro. How can you make sure you fully cover your household energy needs but don’t overpay for an oversized system? This guide to kH and kWh helps you find your just-right home solar system size by going step by step.

You will see solar installers talking about prices for a 2 kW system, a 5 kW system, and so on… but how can you know which size is right for you? Start with this breakdown of vocabulary and terms. Check out the average kWh (kilowatt hours) per household and see where your home might fall. Then use our interactive calculator to estimate your home solar panel cost based on real numbers for different home solar system sizes.

Home Solar System Size kW and kWhkW Definition

A kW is a unit of power. Your home solar system size will be measured in kilowatts (kW). You’ve probably seen watts as a measurement on lightbulbs, like 60w or 30w. A watt is a relatively small amount of power. Each kilowatt is a thousand watts of power.

The kW size of a home solar system can seem confusing: when you see a 2 kW system or a 10 kW system, does that number tell you how much energy the system can generate overall? Not exactly. It describes how many kW of power your system can generate under perfect conditions during one hour of peak sunlight. A 3 kW system can generate a maximum of three kilowatts of power in one hour. A 5 kW system can generate up to five per hour.

However, most systems won’t generate their peak kW per hour for your home because of the reality of weather conditions, dust, and other factors. The kW rating isn’t a guarantee of outcome, just a description of the maximum power cap. Although the kW number is not an accurate figure of exactly how much power your system will produce, it is the best and most important benchmark for comparing systems. In almost any real-world situation a higher kW system will pull more power from sunlight than a lower kW system.

kWh Definition

Now, what about the term kWh and how kW and kWh are related? The kW number describes the amount of power something can generate but the kWh number is based on how that energy might actually be used. You have probably seen kWh listed on your monthly electricity bill, but might not know exactly what it means.

kWh means “kilowatt-hours.” Basically, it means something that uses enough energy to burn a full kW of power over the course of sixty minutes. A 1 kWh appliance would use up a kW of energy over the course of an hour. A 2 kWh appliance would use a kW of energy in half an hour.

Average kWh For Homeowners

Home Solar System SizeThe average home in the U.S.A. used 10,649 kWh of energy in 2019.[1]US Energy Information Administration, 2020 That works out to about 877 kWh each month, or 29 kWh daily, for an average US household.

By those numbers, most households burned a bit more than a kilowatt of power each hour of the day. So, would a 1 kW or a 2 kW home solar system be big enough to keep those homes humming? Unfortunately it is not quite that simple, because you need to look not just at your average usage but at your usage during peak hours and peak seasons.

Your current electricity bill should have the information about exactly how many kWh your home is using. If you have a SmartMeter, you may even be able to get detailed tracking information about your usage online through your power company. This will be very helpful because you are not just looking for how much power you use overall, you are looking for how much power you use during the most power-heavy hours of day in your home.

When figuring out your home solar system size, be sure to consider how your energy use changes month to month. Most homeowners see their bills rise and fall from one season to another based on temperature systems. You should shop for home solar that can handle your biggest months of heating or cooling. Take a look at the last year of energy statistics for your home to get your own real-world information. When you know your kWh needs, talk to a few solar installation professionals in your area to compare price quotes and to get their opinions on the kW to kWh ratios in your specific geographic area.

kW and kWh For Home Solar System Size

How many kWh exactly will a 3 kW system or a 5 kW system generate? The truth is that it varies dramatically depending on the location of your home. Geography can alter the output of home solar panel systems by more than 25%. If we take a look at the Pacific Northwest for a specific example, we will find that west of the Cascade mountains a 1 kW home solar system can generate about 1,000 kWh per year. However, the same system just east of the Cascades will generate 1,250 kWh per year instead.[2]Washington State University, 2009 Elevation, shade, and other factors mean you need a trained solar installation professional to evaluate your plot of land for its kWh potential.

Before any solar panel installer can give you an exact quote, they will need an accurate picture of how many kWh your home solar system needs to produce at peak time. However, that alone won’t get you a quote. They also need to know details of your home, where your house sits on its lot, your roof size, and other information. Instead of going back and forth on all that before you get any numbers on price at all, wouldn’t you like to know a general figure of what your home solar installation might cost? Everything you have just learned can help you do that right now.

Calculate Home Solar System Size and Cost

Even though there is variation in the efficiency of solar panels systems per kW, the vast majority of home solar systems land between 3 kW and 6 kW in size. If you have a smaller home in a brighter area, you are likely to fall on the smaller end of that scale. If your home is larger or in an area with shorter or shadier days, you will more likely fall near the 6 kW side. Based on your state and your newly educated guess about home solar system size, our interactive home solar panel cost calculator can give you an estimate instantly.

(Illustration: Home Electricity by ProSymbols from the Noun Project)