One of the most common questions in solar is:
How much energy (megawatt hours / MWh) comes from 1 megawatt (MW) of solar power?
The answer varies tremendously based on the geographic location and the amount of sunshine but a US national average can be calculated by using capacity factor data from the US Energy Information Administration (EIA).
On average, across the US, the capacity factor of solar is 24.5%. This means that solar panels will generate 24.5% of their potential output, assuming the sun shone perfectly brightly 24 hours a day.
1 megawatt (MW) of solar panels will generate 2,146 megawatt hours (MWh) of solar energy per year.
Download the full spreadsheet via the button at the bottom of the embedded Excel document.
Code: m147 GWhSolPerMW math xbMath
This is interesting and useful – thanks.
I am looking at opportunities in the UK. I see that the Capacity Factor you’ve used as an average in the USA is 24.5%. Do you have a feel for the average Capacity Factor I should use for the southern half of the UK (say south of a line drawn through Birmingham ?
David, data on capacity factors as well as local irradiance and historical weather are available across the US from groups like the National Renewable Energy Laboratory (NREL). I assume similar data is available within the UK although it is often in a form that takes a lot of expertise to apply to the question you’re asking.
Using an eye estimate and extrapolating data from California, I would expect an average 10-11% capacity factor for a solar panel in London. This range can be higher (or lower) depending on the solar panel technology used and the type of axis tracking technology (or lack of) it has.
You’re not 24 hours a day
the sun light Is between 8h and 12h a day
The capacity factor takes the limited hours of sunlight each day into account. A 24% capacity factor implies that sunlight is only availble 24% of the day or year.
Your calculations should also take into account the decline in output power that solar panels experience over their projected 25 year lifetime. I know it’s not much (I believe a panel still produces 90% of its rated power after 25 years) but the anti solar crowd will inevitably point it out.
That is a very good point. Let me see if I can find some solid real-world data on older large scale projects to improve the averaging in this model.
You can use real world data to calculate annual energy harvest, but you can also just default to the manufacturers warrantied power output.
The warrantied power output from the front side is now 30 years for most PV module manufacturers.
Front side warranties typically start at 98% and decline 0.45% over 30 years (ends at 85%).
Bifacial modules produce power on the backside, too. It’s generally 5-7% additional energy harvest annually.
Also, some manufacturers offer a backside power warranty for bifacial modules.
Probably foolish question: Line 55
why would you divide, rather than multiply, the annual MW 0.466 by 25 to see the lifetime MW of panels?
How many watts of solar energy supply system that can allow us to supply 2 MWH on a little city?
If i can provide a sample financial model, would someone please assist in determining the ROI and Payback period?
It would really help us narrow down our decision of opening a solar farm.
We are also open to a new financial model analysis of a solar farm that provides maximum ROI and Payback.
I have issue with the 24.5 factor. I have a 7.28kw system installed for 4 years. I have produced about 9.5-10.1 mwh each year. Using the 24.5 factor it should produce ~15.5 mwh. So I calculate my system factor as ~13.73 which gives just under 10mwh.
I am suspicious of these industry claims about how many homes are powered by X gw of installed solar, mostly because they never use GWh they always use GW. This seems dishonest to me especially when my utility shows 2-3% solar in the annual report but the industry claims 4%.
Bob, the source data for the 24.5 is laid out in the spreadsheet. The implication is that this number applies to utility-scale solar projects. I completely agree that rooftop solar will be lower, and as you’ve found, maybe much lower. Rooftop solar brings in a range of new variables like shading, angle (roof angles vary) and alignment (few roofs are perfectly south facing).
I forgot to add panels are located on an 8 pitch roof ~34 degrees and I live in south Jersey at 40 degrees latitude. The roof is about 5 degrees from due south and morning shading is done by 9 am in winter, 8 am summer, the rest of the day is open field, so unlike most residential solar my panels are very well oriented. I am a pro solar and for the last 4 years my annual electric bill is about $100-120 /yr with pool and AC
I have a question regarding solar power. Which is “At 6 AM today, you purchased 1 MW of electricity contract for 12 PM at a price of 100 pounds/MWh. Two hours later, the forecast for solar generation for 12 PM has changed from 4 GW to 4.5 GW. The market is currently bid at 95 pounds/MWh and offered at 105 pounds/MWh. What would you do, and why?”
Can anyone please reply to this?
Ive looked extensively for the capacity factors that homeowners are actually experiencing from their real-world roof-top PV systems. The information provided above by Bob Faulke is the ONLY such data I’ve been able to find. Thanks Bob! But its only a sample of one. I would be grateful if anyone else would provide the data to calculate the capacity factor for their system. I would need to know the nameplate capacity of their system in either KWdc or KWac, plus the total KWh/year (in AC power) their system actually produced. (Inverters collect this data and make it available to homeowner via an app.) Would also be helpful to have a description of how the panels are oriented, how much shade they get, and of course the general location of where they live. I suspect that the sub-optimum orientation, shading and other real-world factors are important but again I can’t find any real-world data. Would need it for at least a dozen systems to get some rough average. (NREL and EIA do not have capacity factor data for these real-world installations.)
Bob ,we have a totally new type of mounting system for PV on farm land. Let me kn9w if you want to know more.Thanks Bob