A kilowatt-hour (kWh) measures how much electricity you use. One kilowatt-hour is the energy it takes to run something that draws 1,000 watts for one hour. It's the unit on your electricity bill, the unit your solar panels use to report how much they made, and the unit a battery uses to describe how much it can store. Once it clicks, all three become much easier to read.
Watts, kilowatts, and kilowatt-hours
- A watt measures power: how much electricity something draws at a given moment. A kilowatt (kW) is simply 1,000 watts.
- A kilowatt-hour adds time. It measures energy, power used over time. If a device draws 1 kilowatt and runs for one hour, it uses 1 kilowatt-hour.
The math works the same at any size. A 100-watt light left on for 10 hours uses 1 kWh, because 100 watts times 10 hours is 1,000 watt-hours. A 2,000-watt space heater running for 30 minutes also uses 1 kWh. Big or small, fast or slow, it all comes back to power multiplied by time.
kW vs kWh: the difference that matters
These two get mixed up all the time, so think of them like a car. Kilowatts are your speed: how fast electricity is flowing right now. Kilowatt-hours are your distance: how much you've used in total over a trip.
You'll see both when you look at solar and batteries, and they answer different questions. Kilowatts tell you how much power something can deliver at once. Kilowatt-hours tell you how much energy it uses, makes, or stores over time.
What a kilowatt-hour looks like at home
A few rough examples make the unit feel real. These vary by model, age, and how you use them, so treat them as ballpark figures:
- A modern refrigerator running all day uses somewhere around 1 to 2 kWh.
- A load in an electric clothes dryer often uses a few kWh.
- An electric car typically travels a few miles on each kWh, so a longer daily commute can add several kWh of charging.
- An LED bulb uses so little that it would take days of constant use to reach 1 kWh.
Big draws like heating, cooling, the dryer, and EV charging tend to account for most of a home's kilowatt-hours, which we break down in what uses the most electricity in your home.
Kilowatt-hours on your electricity bill
Your utility measures your use in kilowatt-hours and charges you a rate for each one. Your bill shows how many kWh you used during the billing period, and with a time-of-use plan, it also shows when you used them, because a kWh costs more during evening peak hours than at other times of day.
That's why two homes using the same number of kilowatt-hours can see different bills. When you use the power matters as much as how much you use. Our posts on how to read your PG&E bill and PG&E peak hours walk through both.
Kilowatt-hours and your solar system
Solar panels are rated in kilowatts, and they produce kilowatt-hours.
A system's size, like "6 kW," describes how much power the panels can produce at their peak, under strong, direct sun. That's the speed. What the system produces over a day, a month, or a year is measured in kilowatt-hours. That's the distance. A system's production depends on its size, how much sun your roof gets, which direction the panels face, and the season, so two 6 kW systems in different spots can produce different totals.
Your monitoring app reports production in kilowatt-hours, which makes it easy to compare with the kWh on your electricity bill. With those two numbers side by side, you can see how much of your home's use your solar covers.
Kilowatt-hours and your battery
Batteries use both units, and knowing the difference pays off.
A battery's capacity, in kilowatt-hours, is how much energy it can store. Its power rating, in kilowatts, is how much it can deliver at one moment. For example, a Tesla Powerwall 3 stores 13.5 kWh and can deliver 11.5 kW continuously. An Enphase IQ Battery 5P stores 5 kWh and delivers 3.84 kW per unit, and you can combine several units.
Both numbers shape what a battery can do for you. Capacity affects how long it can run your home. Power affects how many things you can run at once and whether it can handle bigger loads, like a well pump or an air conditioner starting up. The right combination depends on your goals. A Savings Battery stores solar during the day and discharges it during expensive evening hours to help lower your electricity bill. A Backup Battery does the same and also keeps your chosen circuits running in an outage. We go deeper on matching capacity to your home and how many solar batteries you need.
How we use your kilowatt-hours to design your system
Your past kilowatt-hour use is the starting point for every system we design. Before we suggest anything, we look at how many kWh your home uses each month over a full year, and when you use them during the day. That history shows how much solar makes sense for your roof and how much battery storage will carry your evenings.
It also helps to think ahead. If you're planning to buy an electric car, add an electric appliance, or build an ADU, your kilowatt-hour use will grow, and we can plan for that in the design so your system keeps up. Our guide to gathering your PG&E usage data shows you how to download your history, and it's helpful to have on hand before a consultation.
Putting it together
Once you know what a kilowatt-hour is, the numbers around your home start to connect. Your bill tells you how many kWh you buy and when. Your solar tells you how many kWh you make. Your battery tells you how many kWh you can save for later. Electricity rates in California have risen steadily over the past decade, so every kilowatt-hour your own system covers is one you don't have to buy.
We've been helping North Bay homeowners make sense of these numbers since 1984. We're 100% employee-owned, we've installed more than 9,000 systems across Marin, Sonoma, and Napa, and we're licensed as a General Contractor (B) and Electrical Contractor (C-10). We were also one of the first companies in California to earn the state's C-46 solar license.
Want help reading your usage and seeing what solar and a battery could cover? Contact SolarCraft or call Sonoma/Napa 707.778.0568 or Marin 415.382.7717.
