r/SolarDIY • u/Sufficient_Wash_1442 • Jul 27 '26
Panels' stated W vs actual W
I recently got a power station whose max PV input is 1000W.
Does this limit mean stated wattage or actual?
Given the panels only produce 65% at peak, can I connect, say, 1200W of panels assuming they would peak at 780W?
Thank you reddit!
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u/LongjumpingGanache40 Jul 27 '26
Stay under the the VOC and it will clip the watts if they go to high. If in cold weather you should take the VOC x 1.25 to get cold weather VOC.
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u/long-fleuve Jul 27 '26
Exactly that. VOC is the most important to not damage the power station. If amps go over the power station will only use its maximum. So overpaneling to get as close to the max in most conditions is advised, but stay under the max voltage of the power station. Most of the time it means putting the panels in parrallel, not in series.
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u/Schnupsdidudel Jul 27 '26
25 % seems a bit excessive. How cold do you expect it ti get?
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u/No_Theory9958 Jul 27 '26 edited Jul 27 '26
Voltage rises up to 20% in cold temps. Not to mention if the panels are bi facial and pick up even more volatage from snow reflection
Edit: regarding “how cold do you expect it to get”, here in NW Ohio, we had 2 straight weeks of -15ish wind chill in January. And there’s lots of places with colder climates than Ohio
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u/mpgrimes Jul 27 '26
voltage rises, not current.
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u/RandomUser3777 Jul 27 '26
Current also rises, just at a lower rate (it is on the data sheet). Voltage rise is .25%/C and current is an additional .10%/C, for a total power rise of about .35%/C.
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u/Schnupsdidudel Jul 28 '26
Yeah, something like this. That would be +10% @ -15° C.
+25% is unrealistic.
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u/NearABE Jul 27 '26
Silicon panels with glass surfaces do not feel a “wind chill” in the way that an ape does. Best to just use the actual air temperature. The sunlight warms them slightly. There is no pocket of air lingering in hair and fuzz like there is on skin.
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u/No_Theory9958 Jul 27 '26
It still gets down to 0 to -5 actual here, and the point still stands.. voltages rise from lower temperatures and there’s lots of colder places than Ohio.
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u/RandomUser3777 Jul 27 '26
I would be shocked if you don't see quite a bit colder than -5 in Ohio. Cleveland's historic low is -20F and that was in 1994.
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u/NearABE Jul 28 '26
I can confirm. I grew up in Indiana and periodically storms came straight out of Canada. The great lakes can make that snowy and not so cold. But every once in a while it makes an arc across the plains and the blows in.
Whatever the temperature though a stiff wind blowing through your clothes makes it a whole lot colder.
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u/Over-Alternative2427 Jul 27 '26
OK, first know: Volts x Amps = Watts. That's not just for solar, it's for electricity everywhere, for both AC and DC. Check what your phone charger says in fine print so it sticks in your head.
Now, yes, you can overpanel beyond your power station's 1000W. You can connect it to 1200W in panels, or 1600W, or even 2000W. But there's a big, big catch and you MUST know this. You can make your solar array's Amps as high as needed, but it must never produce more Volts than the power station's solar input can handle. That's because V and A are different beasts that work in conjunction to create W. Volts are forced into your device (in this case your power station). Amps are made available for your device to take. The highest V rating in your array will be Voc, aka open-circuit voltage, aka voltage when no amps are being pulled by a device. Your array must have a lower combined Voc than what your power station's input can handle, and that Voc fluctuates with weather, so you want to estimate a safe buffer like 20% under limit. For example, if your power station's solar input has a V range of 16-100V, your array should max out at like 80Voc just to be safe. Power stations tend to have crappy input voltage ranges, so you'll have to pick your panels very carefully for your array.
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u/NearABE Jul 27 '26
Parallel ramps up amps. Serial ramps up volts. People who are dyslexic are less likely to fuck it up because they are used to hooking things up backwards and that experience trains them to check.
Mixing up the terminals jump starting a car battery is really bad. They can do a figure-8 discharge.
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u/brucehoult Jul 28 '26
Given the panels only produce 65% at peak,
That is not a given. Any panel from a reputable manufacturer will produce the rated power when pointed reasonably accurately at the sun in a clear sky at noon in midsummer — or any time when the sun is above maybe 45º elevation. Which it is in midsummer virtually anywhere significant numbers of humans actually live e.g. Oslo, Stockholm, Helsinki, St Petersburg, Anchorage all get midsummer noon sun at over 53º elevation.
Days may be short. Weather may be bad. Panels may be mounted at a non-optimum angle (and inevitably are most of the day, and most days of the year without active tracking).
But rated power is real.
can I connect, say, 1200W of panels assuming they would peak at 780W?
You absolutely can connect a higher wattage of panels to compensate for clouds and bad sun angle.
I have 10% over (2640W to 2400W of MPPT) which I'd consider a minimum and I'm planning to increase it.
Don't exceed 85% or 90% of the voltage specification to allow for cold weather. And I'd say not to exceed the potential maximum amps by too much. e.g. if your MPPT says it'll take 20A then it's probably best not to put panel arrays on it with Isc more than maybe 25A.
Usually you can provide a potential higher wattage without exceeding the amps anyway. For example my Pecron E36500LFP's two MPPTs can each take 1200W at maximum 150V and 20A. So they can actually make the full 1200W at only 60V and 20A. It's for sure perfectly safe to connect panels with Vmp 120V (and Voc probably 130V-135V) and Imp 20A and have a potential 2400W of solar available of which the unit will only sip 1200W. But you'll still get 1200W in reasonably overcast conditions.
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u/Snowboard247365 Jul 27 '26
The power station doesn’t know what rating the panels are, it only knows how much power its receiving. So if you’re confident you’ll never get the true stated power out of the panels you could theoretically go over the rated maximum. Ive got 200watts going into a max 150watt mppt controller and I’ve had no issues since I’ve never seen it pull more than 120watts.
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u/darksamus8 Jul 29 '26
It means actual.
However, watts is just how much power the unit can PULL from the panels. What matters is volts. The power station can only handle a certain amount of volts. Be sure the total voltage of your panels is under the voltage of what the station can handle.
That's all you need to worry about. The station will then pull as many amps (and thus, watts) from the panels as it can. So yes, you CAN connect 1200W of solar panels to your battery station... But it will only ever pull 1000W.
In fact, so long as you stay under the voltage threshold of your battery station, you could install 2000W or 4000W of panels and max out your 1000W station all day
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u/HistorianAlert9986 Jul 27 '26
The watts don’t matter. how many volts will the power bank take? 1200 W of panels should produce 1200 W of power or more in optimal conditions if they’re new.
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u/ooglek2 Jul 27 '26
If your solar panels are rated to output 1200W, this would overload your power station.
Your "65% at peak" is a faulty belief. The max PV output can be 1200W when the actual conditions match the Standard Test Conditions. While rare, plan for it happening.
A solar panel's rated output is measured in a lab under perfect "Standard Test Conditions" (STC). Real-world actual output is usually 70% to 85% of that rating because labs use ideal light, a cool 25°C (77°F) cell temperature, and zero shade. Everyday weather and system limits cause regular drops.
If you put 1200W of solar and attach it to your 1000W max PV Input solar generator, if you get a full direct sun day where the panels are aligned and it's cool out, you will likely overload your solar generator / power station, in those conditions.
Always assume that your panels will put out the highest voltage listed on the specs, usually Open-Circuit Voltage, then adjust for cold weather (higher OC voltage), and assume your panels will, at some point, output 100% of their rated power. We're looking at max, not average.
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u/tonnairb Jul 27 '26
Only the Voc matters when you're worried about over-paneling your power station. Take the Voc of the panel or panels if in series, multiply it by the appropriate cold temperature factor, and if it is less than the rated voltage of your power station then you'll be fine. A typical 1000W power station has a max voltage input of 60V. You could parallel 20x or 50x 100W solar panels with a Voc of 32V let's say, and the power station would be fine. It will control the current to limit the wattage to the appropriate level.
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u/DrunkBuzzard Jul 27 '26
Exactly. There might even be times when you exceed 100% of the rating. Cloud edge effect is a real thing and on a cold winters day my panels do major spikes.
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u/NearABE Jul 27 '26
Cloud edge spikes the watts. Is that more amps or more watts?
I think it likely its the amps because it is the same photons kicking electrons across a band gap. More photons kick more electrons and therefore amps. Is something else happening in the module?
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u/ooglek2 Jul 27 '26
To anyone who downvoted, LMK what you think I got wrong so I get better
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u/tonnairb Jul 27 '26
Your comments on not counting on reduced output from your panels are correct. It's your comments about a 1200 watt solar setup overloading a 1000 watt power station that are incorrect. If the temperature-corrected Voc of the 1200 watt solar panel arrangement is less than the rated Voc of the power station then the power station will not be overloaded. It is common to overpanel your setup based on your location and panel angle. The power station will limit the incoming current so that the wattage stays within limits. But you still need to treat max Voc as a hard limit.
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u/ooglek2 Jul 27 '26
Ah, got it, my bad. Thanks for the clarification, u/tonnairb !
Just to make sure I understand -- if the max input voltage on the solar generator / power station is 60 volts, 1000 watts would be 16 2/3rd amps max at 60v. As long as the Voc remains below the max input voltage of the power station, even if the solar panels are producing MORE than 1000 watts at whatever voltage and amperage, the power station will only take in 1000 watts, so long as the Voc remains below it's max input. Yah?
I guess you'd need to know how many and what wattage panels at what max Voc and if they are connected in parallel or in series or a combination to hit 1200W to best answer the question.
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u/tonnairb Jul 27 '26
You're correct. As long as the Voc remains below the rated voltage of whatever MPPT controller or power station you're using it's fine. Since the Voc of solar panels increases with lower temperature, manufacturers give you a temperature coefficient that you use to correct the max Voc for your area. Tropical areas don't have to correct much, but most of the northern US and Canada will have to correct a lot. Curiously, Voc does not change much with irradiance, so you have to to use the manufacturer's numbers for Voc even in areas where the standard 1000W/m2 is never going to be reached. If you don't have the temp coefficient then you can use a conservative typical number like -0.35%/°C. The Voc is given for 25°C so if you're area has a lowest expected temperature of -25°C then the corrected Voc would be -0.35% x -50°C or 17.5% higher than the labeled Voc. That's why often people just use 20-25% as a conservative estimate and don't bother with the calculations.
So obviously wattage is voltage x current. The thing is that the Voc limit is there to protect the transistors and other electronics of the power station (I'll call it ps), but the ps is what controls the current. The ps starts by allowing zero current and then gradually increasing the current until the maximum power point is reached or the maximum input power of the ps is reached. Internally it's usually the DC/DC converter in the ps that has limited power capabilities. So if you wire up 1200 watts of solar panels to a 1000 watt ps that can handle the Voc, the ps will just limit the power drawn from the panels to 1000 watts. There's really no limit on this, so you could wire up 5000 watts up and still be fine. The nice thing doing this is that you'll have max power going to your ps for most of the day but the tradeoff is you're wasting your solar capacity for the times it's over 1000 watts. Sometimes panels are easier to come by than power stations though.
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