Quick answer
Kilowatt-Hour A kilowatt-hour (kWh) is a unit of energy equal to one kilowatt of power used or produced for one hour, or 1,000 watt-hours.
It is the unit on your electric bill, on a solar production estimate and on a battery's capacity, which makes it the one number that connects all three. The average US home bought about 899 kWh a month in 2022, according to EIA.
Quick facts
The key facts about kilowatt-hour, with sources:
Key takeaways
- A kWh is an amount of energy: 1,000 watts used for one hour.
- Your bill, your solar estimate and your battery size all use kWh.
- kWh = watts × hours ÷ 1,000. A 1,500 W heater for two hours uses 3 kWh.
- A kWh you use from your own panels saves the full rate. An exported kWh may earn much less.
- Size solar from your last 12 months of kWh, not from one bill.
From watt-hours to kilowatt-hours
The base unit is the watt-hour (Wh): one watt for one hour. EIA's example is a 40-watt bulb left on for five hours, which uses 200 Wh. Watt-hours are handy for phones and small batteries. For a whole house they get clumsy, so utilities bill in thousands of them.
Formula: kWh = watts × hours ÷ 1,000. A 1,500 W space heater running two hours uses 3 kWh. Scale up again and 1,000 kWh is one megawatt-hour (MWh), the unit utilities and solar farms report in. A typical US home uses about 10.8 MWh a year.
Sources: [1]
How your meter counts kWh
Your electric meter adds up energy as it flows, the way a car’s odometer adds up miles. The utility reads it each month. Your bill shows the kWh used, often as the gap between two readings and a 12-month chart.
With solar, the meter usually counts both ways. It tracks kWh you buy from the grid and kWh your panels send back.
How those two counts are netted depends on your utility’s rules. The DOE describes net metering as paying system owners for solar power sent to the grid, with rules set by each state and utility.
Panels count kWh too. The inverter or monitoring app logs how many kWh the system made each day. That is how you check a system against its estimate.
The kinds of kWh you will see
| Label | What it counts | Where |
|---|---|---|
| kWh delivered / used | Energy bought from the grid | Utility bill |
| kWh received / exported | Solar energy sent to the grid | Bill on a solar rate |
| kWh produced | Energy the panels made | Monitoring app, estimate |
| kWh by time period | Energy split into on-peak, off-peak and other hours | Time-of-use bill 4 |
| kWh capacity | Energy a battery can store, e.g. 13.5 kWh | Battery data sheet 9 |
Worked example: an average bill on Duke Energy Carolinas (SC)
Take EIA's national average of 899 kWh a month 2 and price it on Duke Energy Carolinas' South Carolina residential Schedule RS 4. Taxes and riders are left out.
| Line | Math | Amount |
|---|---|---|
| Basic facilities charge | Fixed monthly charge | $11.96 |
| Energy charge | 899 kWh × $0.138125 (first 1,000 kWh) | $124.17 |
| Subtotal | $136.13 | |
| Same usage at the July 2026 US average price | 899 kWh × $0.1831 3 | $164.61 |
Only the energy line moves with kWh. That is the part solar can cut; the fixed charge stays whatever you produce. Your own bill lists the kWh used each month, usually as a meter reading difference and a 12-month history chart.
Where one kWh shows up
- Panels make kWh (production estimate) → your home uses kWh (bill) → a battery stores kWh (capacity) → exports earn a credit per kWh (net metering or net billing)
Matching solar kWh to the kWh you buy
| Number | Value | Source |
|---|---|---|
| Average home use | 10,791 kWh/yr | EIA, 2022 2 |
| 6 kW array near Columbia, SC (25° tilt, south) | 8,765 kWh/yr modelled | PVWatts v8 8 |
| Share of average use covered | ≈ 81% | Our division |
| Array needed for 100% | ≈ 7.4 kW | 10,791 ÷ 1,461 kWh per kW |
kWh compared with related units
| Unit | Measures | Example |
|---|---|---|
| Watt-hour (Wh) | Small amounts of energy | A 40 W bulb for 5 hours = 200 Wh 1 |
| Kilowatt-hour (kWh) | Household energy | 899 kWh a month, average home 2 |
| Megawatt-hour (MWh) | Large energy amounts | 1,000 kWh |
| Kilowatt (kW) | Power, the rate | A 6 kW system |
| kWh/m²/day | Sunlight on a surface | Same number as peak sun hours |
Why kWh is the number to track, and its limits
What kWh is good for
- It is how you are billed, so it ties straight to money.
- It lets you size a system from real use.
- It shows whether a system makes what was promised.
- It tells you how long a battery can run a load.
What kWh misses
- It hides when you used the energy, which matters on time-of-use rates.
- It misses fixed and demand charges, which do not change with kWh.
- A kWh you export may be worth less than one you buy.
Things the kWh does not tell you
- Myth "Every kWh I make is worth my retail rate."
- Reality Only kWh you use at home avoid the full rate. Exported kWh earn whatever your utility's export credit is, which can be much lower.
- Myth "Lower kWh always means a lower bill."
- Reality Fixed and demand charges do not shrink with kWh, and time-of-use rates price the same kWh differently by hour.
What decides the value of a solar kWh
A kWh you make and use at once saves you the rate you would have paid.
On Duke Energy Carolinas’ SC Schedule RS, that is 13.8125¢ for each of the first 1,000 kWh and 14.4661¢ above that. A kWh you export earns the utility’s export credit instead. Duke’s Rider RSC pays $0.0419 for net excess kWh.
So the same panel can be worth more or less depending on when you use power. Running the dishwasher or charging an EV at midday turns exports into self-use. A battery can do the same at night.
The cost of a solar kWh over a system’s life is called the levelized cost of energy. It depends on system price, financing, sunlight and how long the parts last. We do not list prices here; see solar cost.
How kWh are used to plan a system
- Gather 12 months of bills and add up the kWh. One month is not enough, since use swings with the seasons.
- Note any big changes coming, like an EV or a heat pump.
- An installer models your roof in a tool such as PVWatts to get kWh per kW 12.
- They divide your kWh by that figure to get a size, then fit it to the roof and utility rules.
- The quote should list yearly kWh produced. Keep it to check the system later.
Keeping solar kWh on track
Compare each month’s produced kWh with the same month last year and with the installer’s estimate. Weather changes from year to year, so a few percent either way is normal.
Panels lose a little output with age. Qcells warrants at least 98.5% of rated power in year one and no more than 0.33% loss a year after that. A bigger, sudden drop points to shade, dirt or failed equipment. See solar underproduction.
Sources: [10]
Warning signs in your kWh numbers
- Produced kWh drop by much more than weather explains.
- Your bill’s kWh bought jumps after solar starts. See your first bill after solar.
- The monitoring app shows zero kWh for a sunny day.
- Exported kWh never appear on the bill after the system is approved.
- Call your installer or utility. Never open equipment yourself.
Who sets the rules on kWh
The unit. NIST SP 330 defines the watt and the hour; the kWh is the product of the two. The SI unit of energy is the joule. One kWh equals 3.6 million joules.
Prices per kWh. State regulators approve investor-owned utility rates. Duke’s SC Schedule RS sits under Docket No. 2025-172-E. Cooperatives and city utilities set their own rates.
Export credits per kWh. In SC, Act 62 of 2019 moved new customers to Solar Choice tariffs. Duke’s Rider RSC took effect 1 January 2026. Virginia sets net metering in Code §56-594.
Common mix-ups
- Myth "kWh and kW are the same thing."
- Reality kW is the rate; kWh is the total. See the kilowatt page for the comparison.
- Myth "kWh per hour" is a unit.
- Reality It reduces to kW. Energy per hour is power.
- Myth "One summer bill tells me my size."
- Reality Summer and winter use can differ a lot. Use 12 months.
kWh prices and credits in SC, GA and VA
EIA put the July 2026 South Carolina residential average at 15.47¢/kWh, below the US average of 18.31¢ 3.
Each SC utility credits exported kWh its own way: Duke Energy Carolinas pays $0.0419 for net excess kWh 5, Santee Cooper’s DG-25 rider $0.0415 6, and Berkeley Electric’s Renewable Surplus Rider $0.0603 7.
Georgia and Virginia rules differ by utility; Virginia sets net metering in law 13.
When the kWh matters to you
- Before a quote: total your 12-month kWh.
- Reading a quote: find the yearly kWh it promises.
- Choosing a battery: compare its kWh with what you use overnight.
- After install: track monthly kWh made and bought.
Next steps
- System size calculatorFrom your annual kWh to a kW size
- Solar savings calculatorWhat your kWh are worth over 25 years
- Time-of-use rates and solarWhen a kWh costs more
- Electricity consumption by stateHow your use compares
Questions about kilowatt-hour
How many kWh does a house use per month?
EIA reports an average of 10,791 kWh a year for US residential customers in 2022, about 899 kWh a month. Louisiana homes averaged the most (14,774 kWh a year) and Hawaii the least (6,178). Your own bill shows your monthly kWh.
How much is 1 kWh of electricity?
The US residential average was 18.31¢ per kWh in July 2026 and 15.47¢ in South Carolina, per EIA. Your rate is on your bill and varies by utility, season and time of use. Fixed monthly charges come on top.
How do I calculate kWh from watts?
Multiply the watts by hours of use, then divide by 1,000. A 100 W device for 10 hours uses 1 kWh. A 1,500 W heater for two hours uses 3 kWh. Check the nameplate on the device for its watts.
How many kWh does a solar panel produce per day?
Roughly panel kW × peak sun hours × about 0.75 for real-world losses. A 425 W panel in a location with 5.35 peak sun hours makes around 1.7 kWh on an average day. Winter days make less and summer days more.
What is a watt-hour?
One watt used for one hour. A kilowatt-hour is 1,000 of them, the unit utilities bill in. Phone and laptop batteries are often rated in watt-hours because their energy is small.
How many kWh does a solar system make in a year?
About 1,461 kWh per kW of panels near Columbia, SC, in NREL’s PVWatts model for a south-facing roof at 25°. A 6 kW system comes to about 8,765 kWh. Atlanta and Richmond come out a little lower.
How many kWh is a home battery?
It varies by model. Tesla lists Powerwall 3 at 13.5 kWh of energy. That could run a steady 1 kW load for about 13.5 hours before losses and reserve settings. Check each battery’s data sheet.
Why did my kWh use go up after solar?
Often it did not. Your bill may now show only the kWh you bought from the grid, not what your panels supplied directly. Some homes also add loads like an EV. Compare your monitoring app with your bill to see the full picture.
Sources
- US EIA, Electricity explained: Measuring electricity, retrieved .
- US EIA, FAQ: How much electricity does an American home use? (2022 data), retrieved .
- US EIA, Electric Power Monthly Table 5.6.A, average price to residential customers, July 2026, retrieved .
- Duke Energy Carolinas (SC), Schedule RS (Docket No. 2025-172-E), retrieved .
- Duke Energy Carolinas (SC), Rider RSC Residential Solar Choice (effective 1 January 2026), retrieved .
- Santee Cooper, Distributed Generation Rider DG-25, retrieved .
- Berkeley Electric Cooperative, renewable energy (Renewable Surplus Rider), retrieved .
- NREL (National Laboratory of the Rockies), PVWatts v8 API, NSRDB PSM V3 TMY; 6 kW, 25° tilt, south, 14.08% losses, Columbia SC (34.0, −81.03), retrieved .
- Tesla, Powerwall 3 Datasheet (2024), retrieved .
- Qcells, Q.TRON BLK M-G2+ series data sheet (420–440 W, 2026-02 Rev01 NA), retrieved .
- NIST, SP 330 (The International System of Units), Section 2, retrieved .
- US DOE Solar Energy Technologies Office, Homeowner’s Guide to Going Solar, retrieved .
- Code of Virginia §56-594 (net energy metering), retrieved .
Expert review
Written by the HyreSolar Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Consumption from the EIA FAQ (2022 data) and prices from EIA Electric Power Monthly Table 5.6.A (July 2026). Duke, Santee Cooper and Berkeley tariff figures from sc-local/facts.js (retrieved 5 Oct 2026). Production from a PVWatts v8 run on 7 Oct 2026. The bill example multiplies those figures only.
Suggest a correction. We fix errors and say what changed.