Answer
MW measures power, while MWh measures energy produced or used over time. A constant 1 MW output for one hour delivers 1 MWh. Solar output varies, so annual generation requires a production profile or capacity-factor assumption. For batteries, check both power capacity and usable energy before calculating runtime.
Last updated: November 2026
A solar quote can show a large capacity number and still leave the most useful question unanswered: how much electricity will the project deliver over the period you are paying for?
MW and MWh describe different quantities. Mixing them up can distort a revenue model or leave a battery too small for its intended backup load. This guide explains the units, the conversion formula, and the assumptions to check in a proposal.
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Key Takeaway: Power Needs a Time Basis
MW measures power; MWh measures energy. Multiplying constant power by hours gives energy. For variable solar output, use interval data or average power across the period, not the nameplate rating alone.
What Is a Megawatt (MW)?
A megawatt measures power , the rate at which electricity flows at any single moment.
Think of it as the flow rate through a pipe. A measured output of 1 MW is 1 million watts at that moment. A source rated at 1 MW may be delivering less than that, or nothing. Its rating alone says nothing about how long that output lasts.
Quick conversions:
- 1 MW = 1,000 kilowatts (kW)
- 1 MW = 1,000,000 watts (W)
In solar, MW often describes the nameplate capacity of equipment under stated rating conditions. Distinguish the direct-current array rating, MWdc, from the alternating-current inverter or plant rating, MWac. A 10 MWdc array does not promise 10 MWac at the grid connection.
Definition: Nameplate Capacity
Nameplate capacity is a rated value under specified conditions. Check the module datasheet, inverter rating and connection limit separately. Weather, temperature, shading and electrical losses affect operating output; a module rating is not a prediction of continuous generation.
EIA’s electricity-measurement guide explains the watt, kilowatt and megawatt conversions used here.
A measured MW value answers the question: How much power can this system deliver right now?
It does not answer: How much energy will it produce today? That is where MWh comes in.
What Is a Megawatt-Hour (MWh)?
A megawatt-hour measures energy , the total amount of electricity produced or consumed over a period of time.
If MW is the speed of a car, MWh is the distance it travels. A car going 60 mph for 2 hours covers 120 miles. A power source running at 1 MW for 2 hours produces 2 MWh.
Quick conversions:
- 1 MWh = 1,000 kilowatt-hours (kWh)
- 1 MWh = 1,000,000 watt-hours (Wh)
Utility bills commonly show kWh. EIA reports 2022 average residential electricity purchases of 10,791 kWh per US utility customer, or 10.791 MWh. That is historical purchased electricity, not a universal household consumption figure. Use the customer’s bills and on-site generation records for an actual design.
MWh answers the question: How much energy did this system actually produce?
It is the number that shows up on electricity bills, in power purchase agreements, and in carbon offset calculations.
MW vs MWh: Side-by-Side Comparison
| Feature | MW (Megawatt) | MWh (Megawatt-Hour) |
|---|---|---|
| Measures | Power (instant rate) | Energy (total over time) |
| Analogy | Speed of a car | Distance traveled |
| Solar use | System capacity / inverter size | Annual production / energy delivered |
| Battery use | Maximum discharge rate | Total storage capacity |
| Billing | Demand charges (peak usage) | Energy charges (total consumption) |
| Time element | None , a snapshot | Always includes hours |
| Unit conversion | 1 MW = 1,000 kW | 1 MWh = 1,000 kWh |
| Buyer check | Is the rating DC or AC? | What period and meter boundary apply? |
The distinction is not academic. It changes how you size systems, how you price energy, and how you evaluate battery storage.
How to Convert MW to MWh
For constant power, multiply MW by elapsed hours. If output varies, use the average power over that period or sum the energy in each measurement interval.
Energy (MWh) = Power (MW) × Time (hours)
Illustrative example 1: A source delivers a constant 5 MW for 4 hours.
5 MW × 4 hours = 20 MWh
Illustrative example 2: A battery has 100 MWh of usable energy available at the delivery boundary and discharges at a constant 25 MW.
100 MWh ÷ 25 MW = 4 hours of runtime
Illustrative example 3: Annual output of a 10 MW solar farm at an assumed 22% capacity factor in a 365-day year.
Solar output varies. EIA defines capacity factor as actual energy divided by the energy that continuous full-power operation would produce over the same period. It is not the percentage of hours spent at full output. Keep the capacity rating basis consistent with the energy estimate.
10 MW × 24 hours × 365 days × 0.22 = 19,272 MWh per year
Pro Tip
Ask for the weather dataset, shading assumptions, loss allowances and AC/DC rating basis behind a production estimate. Do not select a capacity factor from a generic regional range and treat the result as a bankable forecast.
The table below changes only the assumed capacity factor. These are arithmetic scenarios for a 1 MW reference rating over 8,760 hours, not observed regional yields or predictions for your site.
| Assumed capacity factor | Calculation | Illustrative annual energy |
|---|---|---|
| 20% | 1 × 8,760 × 0.20 | 1,752 MWh |
| 22% | 1 × 8,760 × 0.22 | 1,927.2 MWh |
| 25% | 1 × 8,760 × 0.25 | 2,190 MWh |
- 20% capacity factor1,752
- 22% capacity factor1,927.2
- 25% capacity factor2,190
Source: Illustrative example, not market data; EIA capacity-factor formula, 8,760-hour year, checked November 2026.
Review the assumptions behind the MWh
Explore how site layout, shading, and yield estimates inform a project’s financial model.
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Why the MW-to-MWh Ratio Matters for Battery Storage
Battery energy storage systems (BESS) should specify both power capacity and energy capacity. Ask whether the energy figure is nominal or usable and whether it is stated at the cells, DC terminals, or AC delivery point.
For an illustrative 50 MW / 200 MWh system, the simple energy-to-power calculation gives 4 hours. That assumes all 200 MWh are available at the same boundary as the 50 MW rating, with no reserve or derating.
Practical runtime depends on state of charge, usable energy, temperature, aging and losses. Duration helps screen a design, but it does not by itself determine the services a battery qualifies for or the revenue it can earn.
| Illustrative power / usable energy | Ideal duration | Question for the buyer |
|---|---|---|
| 1 MW / 1 MWh | 1 hour | Is that enough for the required event? |
| 1 MW / 2 MWh | 2 hours | Can the system recharge before the next event? |
| 1 MW / 4 MWh | 4 hours | Does the usable rating include operating reserves? |
| 1 MW / 6 MWh | 6 hours | How will aging affect the required duration? |
Pro Tip: Check Both Battery Limits
Ask the supplier to state continuous discharge power and usable energy at the same delivery boundary. Then compare the load profile, starting loads and required runtime. A duration ratio alone is not a backup-system design.
There is no universal best ratio for frequency response, peak shaving or energy shifting. Market rules, dispatch requirements, connection capacity and the load profile all matter. Check those requirements before selecting equipment, and keep a separate allowance for the energy needed to recharge.
Real-World Examples: Solar Projects in MW and MWh
The first three examples below are illustrative calculations, not documented installations. The final example uses published project figures from Gemini’s developer.
Residential Rooftop Solar
Suppose a homeowner’s proposed 8 kW array is modeled to generate 11,000 kWh over a year. The array rating is 0.008 MW and the modeled energy is 11 MWh. Those are different quantities; neither tells you whether the home can run during an outage.
The buyer should ask for monthly production estimates and compare them with household consumption. Annual totals alone cannot show when electricity is imported or exported. Backup also depends on the system’s storage, controls and approved operating configuration.
Commercial Rooftop Solar
Suppose a 500 kW system has a site-specific forecast of 700 MWh per year. That is a 0.5 MW rating with an illustrative annual energy estimate, not a general output benchmark for every factory roof.
You cannot infer a percentage bill reduction from those two numbers. Savings depend on how generation overlaps with load, the applicable tariff, export compensation and other charges. Keep the production estimate and the financial assumptions in separate, traceable parts of the proposal.
Utility-Scale Solar Farm
For an illustrative 100 MW rating at an assumed 23% capacity factor in a 365-day year:
100 MW × 24 × 365 × 0.23 = 201,480 MWh per year
At a hypothetical flat price of ₹3.50 per kWh, equivalent to ₹3,500 per MWh, the arithmetic gross energy revenue is:
201,480 MWh × ₹3,500 = ₹705,180,000, or ₹70.518 crore per year
This is not a verified Gujarat project or market tariff. The calculation excludes curtailment adjustments, contractual settlement rules, taxes, operating costs and financing. An actual power purchase agreement determines what energy is billable and how it is valued.
Solar-Plus-Storage Project
Primergy’s July 18, 2024 Gemini announcement reports 690 MW of solar generation capacity and 380 MW of battery power with 1,400 MWh of storage energy. These figures illustrate why the solar rating and the battery’s power and energy ratings must stay separate.
Dividing 1,400 by 380 gives about 3.68 hours, while the announcement describes the battery as four-hour storage. Preserve that distinction rather than silently replacing one published number. For procurement, request the governing performance specification and usable-energy conditions. One project’s configuration is not a universal storage standard.
Common MW vs MWh Mistakes Buyers Make
Mistake 1: Comparing Quotes Using Only MW
In an illustrative comparison, an 8 MW proposal predicts 9,500 MWh per year and a 10 MW proposal predicts 14,000 MWh. The larger system’s forecast is about 47% higher than the smaller one; choosing the smaller system means about 32% less forecast energy relative to the larger one.
Neither prediction is verified by the capacity label. Compare weather files, rating bases, losses, connection limits and usable site area before attributing the difference to better equipment or design.
Fix: Always compare expected MWh production, not just MW capacity. Use a solar design tool that models actual generation from local weather data.
Mistake 2: Sizing Batteries by MW Alone
A commercial buyer wants 4 hours of backup for a 1 MW critical load. They buy a 1 MW battery. But the battery is only 1 MWh. It runs out in 1 hour.
Fix: Size batteries in two steps. First, calculate the load in MW (power). Then multiply by the hours of backup you need. A constant 1 MW load for 4 hours needs 4 MWh delivered to the load. The installed battery’s nominal energy may need to be greater to account for usable capacity, reserve, losses and aging.
Mistake 3: Confusing Inverter MW with Battery MWh
A buyer sees a “10 MW inverter” and assumes it can store 10 MWh. It cannot. An inverter converts power. It does not store energy. Storage requires batteries, which are measured in MWh.
Fix: Treat the inverter’s power rating and the battery’s power and energy ratings as separate specifications. Verify their compatibility and delivery limits together.
Mistake 4: Ignoring Capacity Factor in Revenue Models
A developer models a 50 MW solar farm at 50 MW × 24 × 365 = 438,000 MWh per year. That assumes the sun shines at full intensity 24 hours a day. At an assumed 22% capacity factor, the illustrative estimate is 96,360 MWh, 78% below the continuous-full-output calculation.
Fix: Use a site-specific production model, then check its implied capacity factor. Record the rating basis and period so another reviewer can reproduce the calculation.
Pro Tip
Use a sensitivity calculation before signing an energy contract. In an illustrative 8,760-hour year, changing the assumed capacity factor from 20% to 25% for a 50 MW rating changes modeled energy by 21,900 MWh. At a hypothetical flat $40/MWh, that changes gross energy revenue by $876,000 before costs and contract adjustments.
How MW and MWh Appear in Solar Proposals
Professional solar proposals should show both numbers clearly. Here is what to look for:
System capacity section:
- DC array size in kW or MW
- Inverter capacity in kW or MW
- DC-to-AC ratio
Production estimate section:
- First-year production in kWh or MWh
- Annual degradation assumption, with its source and applicability
- 25-year total production
Storage section (if applicable):
- Battery power in kW or MW
- Battery energy in kWh or MWh
- Duration at rated power
- Round-trip efficiency
If a proposal only shows MW, ask for the energy estimate and its assumptions. A capacity-only quote is insufficient for comparing projected energy value, but the omission alone does not prove misconduct.
Use a proposal workflow with generation estimates to present the design and its assumptions together. Check each exported value against the underlying model before release. Reviewing site shading also helps explain why two arrays with the same nameplate rating can have different energy forecasts.
Conclusion
MW and MWh are not interchangeable. One measures power. The other measures energy. Getting them mixed up leads to wrong system sizes, broken budgets, and missed revenue.
A rated MW figure describes equipment capacity; measured MW describes output at a moment. MWh describes energy over a period. Keep those labels visible when comparing alternatives.
Your next steps:
- Check your last solar quote. Does it show both MW (capacity) and MWh (production)? If not, ask for the production estimate
- If you are adding battery storage, compare the power limit and usable energy with the required load profile and runtime
- See the SurgePV design workflow before deciding how to present capacity, generation and financial assumptions in your next proposal
Frequently Asked Questions
What is the difference between MW and MWh in simple terms?
MW measures power, while MWh measures energy over time. A source delivering a constant 1 MW for two hours supplies 2 MWh. A nameplate MW rating alone cannot tell you annual generation.
How do you convert MW to MWh?
Multiply constant power in MW by time in hours to obtain MWh. For variable output, use average power over the period or sum interval energy. Nameplate capacity needs a generation profile or capacity-factor assumption before it can support an annual estimate.
Why do batteries list two numbers like 100 MW / 400 MWh?
The numbers describe battery power and energy capacity separately. Dividing 400 MWh by 100 MW gives four hours in an ideal calculation. Check usable energy, reserves, losses and rating boundaries before treating that as guaranteed runtime.
How many MWh does a 1 MW solar farm produce per year?
Annual output depends on the site, rating basis and capacity factor. At an illustrative 20% capacity factor over 8,760 hours, a 1 MW reference rating corresponds to 1,752 MWh. This is arithmetic, not a forecast for every 1 MW project.
Is a higher MW or a higher MWh better for battery storage?
The better specification depends on the required load and duration. Power limits how much load can be served at once, while usable energy helps determine runtime. Compare both at the same delivery boundary.
How many homes can 1 MW of solar power?
There is no fixed homes-per-MW conversion for solar. Divide a site-specific annual energy forecast by a stated annual household-use figure for an energy-equivalent comparison. That calculation does not demonstrate continuous supply or outage backup.
Where this fits
This article is part of SurgePV's Solar Design hub, which works through the topic from first principles to the decisions a project team actually has to make.
