Hello everyone and happy holidays!
I’m interested in photovoltaic panels, it’s the future and all!
But with the subsidiaries and the general enshittification of search engines, all search results about photovoltaics leads to sites with wildly misleading information, IMO.
I don’t care about a 3kWc system with installation. What even is a kWc (I know what it is) and why is nobody explaining how much power the panels would typically yield instead? Per month? During the day?
I guess it is less selling if your installation is generating near nothing in December when you need it the most?
Okay sorry, rant off. My question is, where can I find reliable information about how much panels generate every month, during the day?
I know places have more or less sun, but that’s quite easy to figure out if you have the numbers for any place.
🌞
Edit: I don’t need a web calculator for how many panels I need. I’d like to know roughly how many watt a typical panel produces a specific day (or better hour) in the year.
Edit2: I am not looking for how to install or calculate a typical solar panel setup. I’m looking for the typical real world output of solar panels around the day and year.
Edit3: got my information, thanks oo1@lemmings.world ! You all can now continue explaining how many panels a home needs or what a kwh is, Merry Christmas to you all!
There are web calculators where you put in your latitude, angle of the panels and total kWp of your installation. It then spits out a kWh prediction for the year. Might still be shitty to find a good one tho. I can tell you that the system i installed at my parents house with 10 kWp has produced 8.4MWh of AC output this year. I live in southern Germany which is around 48° latitude and it was pretty gray and rainy this summer so could be much better.
This is daily total generation in kWh split up by how much went into the battery vs directly into live usage in the house vs exported to the grid.
This shows the sources of all the electricity that the house used over the year on any given day. Red being imported electricity.
This. There is too much local variation in sunlight angle and weather to give a straight answer. An easy method is to take the rated output and multiply by 0.2, but even that is merely a rough average over a year.
But there should be data on weather and climate variations. So theoretically you could include that data into the calculation. Theoretically. Who’s gonna do it?
There is. I do it, it’s my job as a solar engineer.
Basically, there are several leading softwares that solar engineers use to account for just about anything that happens in the real world.
I mainly use PVsol premium where I 3d model each site and the panel placements and electrical components and so on, then run a minute scale simulation based on the exact location weather data (using Metronorm 8.3)…
Almost no one outside my field understands what goes into my job. It doesn’t help that there’s a lot of untrained people pretending to do what I do…
I was having a smoke break with some colleagues once and was talking about how it should be possible to simulate solar panels in 3D, to account for occlusions by roofs, other buildings, trees etc. Didn’t know there was a dedicated software and job for that, that’s so cool!
That’s what the calculators are for. This has been done.
Yeah, solar panels put out power in proportion to the light that hits it and its efficiency. The latter is in the specs but the former requires knowing how it will be installed before you can determine expected output.
Some calculators can also consider weather predictions (cloudy days, etc)
Some calculator sites;
Thanks but link 2 and 3 doesnt work for non US/UK? Adress needed
Link 1 seems completely useless, like no I don’t want to know how many “panels” I need for an installation.
“Panel” in most cases means “400W nominal panel,” which may include higher-efficiency, same-size panels with 420W nominal, so you can just math whatever panel numbers they give you by 400 to get the answers you want. Like, if they tell you a “10 panel” system will generate 3240 W, you can figure that means 75-85% of nominal peak power. A lot of the calculators are meant to help sell installations, based on people’s current electric usage and constrained by their roof area. That makes ‘number of panels’ a very handy measure.
Yes but that is not the information I am looking for, I have edited the question forore clarity.
For every month? That would be helpful, just then need to convert the energy (kWh) to power (W) which is easy.
I edited my comment and added a screenshot from my grafana dashboard to show the trend over the year and some other numbers. Batteries are expensive but they are worth imo. ~75% of the electricity usage of this house with 6 people comes from its own solar production. There is however a cut off for how much battery capacity makes sense. To get the last 20% of self sufficiency you would need a disproportionally larger battery to make up for long periods of low sun. so 80% is as good as its gonna get while staying cost effective.
It’s very circumstantial, slope and orientation make a big difference. so it has to be a calculator where you put in specific information.
I think this does it: https://pvgis.com/
There’d nbe loads of others. I’d expect most reputable solar installers aimed at residential to have calculators, or recommend one as part of the planning process. Maybe with localised assumptions. There’s one from a govt funded body in my country that makes cost and price assumptions too tand gives a ‘return on investment’ guess.
Wow that’s kind of technical :-) but monthly irradiation is accessible!
Edit: according to those figures a 1m²@20% panel would yield 55w averaged out on 24h, in the summer, and 14w/m² in December.
That’s numbers I can work with, thanks!
The solar atlas is another good starting point for making these calculations. Just by looking at the map, you can easily see how location makes a big difference. Solar power in Spain will be pretty good, while in Germany it’s a bit meh. If you’re in Scotland or Norway, solar power will be even worse. Well, you can always compensate by buying more panels, but that’s not great either.
The actual output is also greatly influenced by quite a few variables, like angle, and efficiency of the panel. As the panel ages, the efficiency goes down. Also, higher temperatures decrease the efficiency of the panel, so the burning hot panels in Libya might not produce as much as you thought based on the solar irradiance map. In other words, it’s complicated.
That’s a neat tool. But it’s giving me a slightly confusing result. I have a solar installation and I’ve plugged in the details so far as I know them, just to see if I’m producing about what I “should” be. The peak production month is about right, but the minimal production month is only estimated to be like 25% less than that. My system has more like 50-60% drop, and some quick googling suggests that’s about normal.
Any thoughts on why this tool suggests a much smaller drop?
No idea. The ‘typical meterological year’ is likely smooth some extremes - that will likely have less variance than any actual year. Maybe the geographical resolution is poor leading to more averaging. But that sounds a bit large of a difference to be just that. Was the total annual production way out?
Check some other tools , maybe a local one - another one might have better data on some things. Some consensus of several estimates might be better than relying on one calculator only.
So what is kWc? Never heard of that unit.
Max theoretical output under ideal conditions, so only useful comparing different panels.
Do you mean kWp? So (kilo) Watt peak? Which directly tells you how much power (or energy over some time) you can expect?
It’s not hard.
Take the rated wattage. Adjust for system wiring loss, shading, age, soiling, etc. most importantly adjust for location. Your angle of sun makes a difference.
Pvwatts is a good tool for this.
