So what is kWc? Never heard of that unit.
this post was submitted on 25 Dec 2024
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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?
Itβs 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.
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 48Β° 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?
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.
You can't convert the kWh to W, that's not how it works. The amount of sunlight is highly variable during the day and the way the sunslight gets converted into usable energy differs a lot depending on the installation.
Normally those calculators assume you can connect the solar installation to the grid and use the grid as a buffer. So when there is sun and you're not using it, you deliver the power back to the grid. And when there is no sun, you get your power from the grid. When there is a little sun, or you're using a lot, you use some energy from the solar panels and some from the grid.
It starts getting complicated depending on how your local grid works. Often supplying back energy to the grid means the power provider credits you a certain amount. Depending on your contract, this might be a day price or even hourly. Or it may be a fixed price. This often means you pay a lot more using power from the grid then you get back pushing power back into the grid. So you need to think more in terms of money and using the energy in a way that's cheapest.
If you are thinking about an off grid installation, the amount of power is almost always dependent on your equipment and not so much the solar panels. For example you can charge up a large bank of batteries from the sun during say a week. Then when fully charged, you can draw huge amounts of power from them till the bank is empty. But depending on the batteries used and the inverter used to convert DC into AC, the amount of amps it can push can be limited.
When thinking of something simple like a use case where you directly use the DC from the solar panel, the panel specs always include the Wp value. You can use that to calculate the exact amount depending on your location, time of day and angle of the panel. Weather services these days also include a watt per square meter of solar energy for different locations, which is useful. And keep in mind it only works when it's sunny, with clouds the output drops a lot.
I've seen huge swings in my pv installation year on year. So it isn't a sure thing how much energy you get from the sun.
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.
I did a calculation for a 20kWh battery for my installation, which would cost me about 18k to purchase and setup. I can do a lot of the work myself, so the equipment costs are the bulk of the price. Figuring a prediction in the price of energy, my usage pattern and a lifetime of 15 years for the batteries, it figured out to be not worth it.
In winter where I live I'm totally fucked, there is basically no sun at all and it's cold AF so energy usage is highest. Any battery would be empty within days and not really able to charge it because the little bit of solar that might be available is used right away in heating. So it would be down to spring and fall where there is still some sun and also some request for energy.
For a house of 6 people we installed 5kWh which is basically perfect for them, but they are also very resourceful with their electricity usage, running washing, cleaning and cooking during the day as to not drain the battery at night.
But yeah if you dont get enough sun in your area its just a waste of money. My parents system will be payed off after 11 years if the sun stays at the level it has been at for the past 2 years.
Predicting how import vs export costs might develop is also a big factor
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.
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.
Wow that's kind of technical :-) but monthly irradiation is accessible!
Edit: according to those figures a 1mΒ²@20% panel would yield 55w averaged out on 24h, in the summer, and 14w/mΒ² 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.
Check out this: https://globalsolaratlas.info/map
Be sure to check out the details, it has the exact specs for your location.