Solar panels are pretty easy to count once they’re on a roof. Figuring out how many should go up there in the first place takes a little more work.
You might hear that the average home in the U.S. needs 16 to 23 panels, but those numbers don’t tell you much about your own house. A family charging two EVs every night is going to use electricity very differently than a small home with no EVs.
Your roof gets a say, too. Its size, direction, shade, and usable space change what makes sense.
How Many Solar Panels Does the Average California Home Need?
Most California homes need between 15 and 30 solar panels. The average residential solar system in California is about 8.95 kilowatts. Using 400-watt solar panels, a system that size would need roughly 23 panels. With lower-wattage panels, that number would be a little higher.
That’s a good ballpark for the typical California home, but your own electricity use will give you a much more accurate number.
Example Solar Panel Counts by System Size
Solar systems come in a range of sizes, and even a few extra kilowatts can mean several more panels on your roof. Here’s what common residential system sizes look like using 400-watt panels:
| Solar System Size | Approximate Number of 400-Watt Panels |
| 4 kW | 10 |
| 5 kW | 13 |
| 6 kW | 15 |
| 7 kW | 18 |
| 8 kW | 20 |
| 9 kW | 23 |
| 10 kW | 25 |
How to Calculate How Many Solar Panels Your Home Needs
You don’t need to climb onto the roof with a tape measure to figure out how many solar panels you’ll need. In fact, your electric bill is a much better place to start.
Start With Your Electricity Usage
Start by adding up the kilowatt-hours (kWh) you used during the past 12 months. This tells you how much electricity your solar system would need to generate annually if your goal were to produce roughly as much electricity as your household consumes.
Say your bills show that you used 9,000 kWh over the past year. That works out to an average of about 750 kWh per month, but the annual total is more useful for solar planning. It accounts for seasonal swings, such as heavier air conditioner use during the hot California summer.
Estimate How Much Solar Energy Your Property Can Produce
Next, you need an idea of how much sunlight your solar panels can actually turn into electricity. California gets plenty of sunshine, but solar production still varies by location, roof direction, pitch, shade, and time of year.
Solar pros use property-specific data to estimate this production. For a rough DIY calculation, tools like NREL’s PVWatts Calculator can estimate how much electricity a solar system could produce at your address based on local solar resource and weather data.
For this example, we’ll say the estimate shows that 1 kW of solar capacity could produce about 1,500 kWh per year at your property.
Calculate the System Size You Need
Now, we can compare your annual electricity use with the amount of electricity a solar system is expected to produce.
Using our example:
9,000 kWh annual electricity use / 1,500 kWh produced per kW = 6 kW solar system
So, this example household would be looking at roughly a 6-kilowatt system based on its current electricity consumption.
Convert System Size Into a Number of Panels
The last step is where panel wattage comes into play. Divide the wattage of the entire system by the wattage of the panels you plan to use.
A 6-kW system is 6,000 watts. If you’re using 400-watt panels:
6,000 watts / 400 watts = 15 solar panels
This household would need roughly 15 400-watt solar panels. Of course, that could vary a bit once we factor in roof space, shade, panel placement, and so on, but it’s a good example.
What Affects How Many Solar Panels You Need?
The math is a great jump-off point, but your house gets the final say. Factors that affect how many solar panels you need include:
- Electricity Use: A home that uses a lot of electricity will need more panels to keep up. Your last year of electric bills is the best place to see what your household actually uses.
- Panel Wattage: More powerful panels can do the same job with fewer of them. An 8-kW system would take 20 400-watt panels, compared to about 15 550-watt panels.
- Usable Roof Space: A roof may not actually offer a ton of space once you factor in skylights, chimneys, vents, and required clearance. The shape of the roof can affect how many panels fit comfortably, too.
- Roof Direction, Pitch, and Shade: A sunny, well-positioned section of roof can produce more electricity than one shaded by trees or nearby buildings for part of the day. That difference can affect how the system is laid out and how many panels you need.
- Future Electricity Use: Thinking about an EV, heat pump, pool, or ADU? Factor that in now so your system can be sized with that extra electricity use in mind.
How Much Do Solar Panels Cost in California?
More panels mean a bigger system, and a bigger system usually means a bigger bill upfront. On average, homeowners in California pay $2.46 per watt, including installation.
Here’s how that price looks for different system sizes:
| System Size | Estimated Cost |
| 4 kW | $9,800 |
| 5 kW | $12,300 |
| 6 kW | $14,800 |
| 7 kW | $17,200 |
| 8 kW | $19,700 |
| 9 kW | $22,100 |
| 10 kW | $24,600 |
Frequently Asked Questions
Solar math can point you in the right direction, but there are always a few questions that don’t fit neatly into the calculation. Here are a few that tend to come up when Californians start planning their systems.
How many solar panels do I need for a 2,000-square-foot house?
Square footage alone can’t tell you how many solar panels you need. Two 2,000-square-foot homes can have very different electric bills depending on the number of people living there, the appliances they use, EV charging, air conditioning, and other electrical loads.
Your annual electricity use is a much better starting point.
Can 20 solar panels power a house?
Yep, they can, though how much of the house they can power depends on how much electricity it uses.
Twenty 400-watt panels make an 8-kW solar system, which may be enough for a home with moderate electricity needs and good solar exposure. It does vary based on the specifics of your home and setup, though.
Do I need more solar panels if I have an electric vehicle?
Probably. Charging an EV at home adds to your electricity consumption, so that extra usage should be considered when sizing your solar system. If you plan to buy an EV soon, mention that before designing your system around last year’s electricity bills.
Can you install too many solar panels?
You sure can. Installing more solar capacity than your household can reasonably use may add unnecessary upfront cost.
You could store some of that excess in a solar battery, but anything you don’t use would go back to the grid, and California’s current net billing compensation for exported electricity is usually lower than the retail electricity rate.
So, it’s better to size the system properly based on what you actually need.
Do I need a solar battery in California?
A battery isn’t a must-have for every solar installation in California, but it can store excess electricity your panels produce during the day for later use. It can be especially useful if you want to use more of your own solar power after sunset or have backup power during an outage.
Are solar panels required on new homes in California?
California’s building energy standards generally require solar photovoltaic systems on newly constructed single-family homes, with some exceptions.
However, these requirements apply to new construction rather than existing California homes, so installing solar on an older house is a separate decision.
Can solar panels power my home during an outage?
A standard grid-tied solar system typically shuts down when the grid goes down to protect utility workers. If you want electricity available during an outage, you’ll generally need a properly designed battery backup system that can safely disconnect your home from the grid.
Find Out How Many Solar Panels Your Home Needs
You can get pretty close with a calculator and a year’s worth of electric bills. Getting the number right for your actual roof takes a closer look.
Fisher Electric can evaluate your electricity use, roof, sun exposure, and plans for future energy use to design a solar system that fits your home. If you’re considering solar for your California home, contact us to schedule a consultation and find out what your system could look like.
Sources & References
- California Public Utilities Commission – “Net Energy Metering and Net Billing”
Explains California’s current Net Billing Tariff for solar customers, including how electricity exported to the grid is valued and compensated.
https://www.cpuc.ca.gov/industries-and-topics/electrical-energy/demand-side-management/customer-generation/net-energy-metering-and-net-billing - California Energy Commission – “Solar”
Outlines California Energy Code requirements for solar photovoltaic systems on newly constructed homes, including applicable exceptions and requirements for residential buildings.
https://www.energy.ca.gov/programs-and-topics/programs/building-energy-efficiency-standards/energy-code-support-center/solar - EnergySage – “How Much Do Solar Panels Cost in California?”
Provides current California solar pricing data, including average cost per watt, typical system size, and estimated installation costs before available incentives.
https://www.energysage.com/local-data/solar-panel-cost/ca - EnergySage – “How Many Solar Panels Do I Need?”
Explains how electricity consumption, system size, panel wattage, and other factors affect the number of solar panels a home may need.
https://www.energysage.com/solar/how-many-solar-panels-do-i-need
