What if solar panels are to powerful for grid tied inverter? - Page 1
Forum section: electronics / general

author: Circlotron
author_rank: Super Contributor
timestamp: September 09, 2025, 01:02:19 pm
content: I've got a 3kW inverter and nominally 1.5kw of panels. Real world is maybe 1100w at midday summer. Had it since April 2012. I've been thinking about getting another row of panels. The inverter has a second set of DC input terminals. My question is - if the total DC input goes above what the inverter is rated for, will the inverter automatically back off the MPPT to keep things within safe bounds?Inverter is Aero-Sharp HR-INV-X01-030.https://gold-coast-solar-power-solutions.com.au/wp-content/gallery/solar-power-inverters/Aero-Sharp-Inverter-Manual.pdf

author: Ice-Tea
author_rank: Super Contributor
timestamp: September 09, 2025, 01:36:02 pm
content: Pretty much, yes. Back in the day when you would have to pay taxes for inverter power over here it was quitte common to have quite a bit more PV than inverter power.

author: nctnico
author_rank: Super Contributor
timestamp: September 09, 2025, 03:13:46 pm
content: Quote from: Circlotron on September 09, 2025, 01:02:19 pmYes. But check if the inverter actually has 2 MPPTs inside. The new panels will be completely different compared to the panels you already have so each string will need its own MPPT. Another thing to check is the inverters minimum and maximum voltage. When unloaded, the inverter should be able to handle the (worst case) maximum voltages from the panels connected in series. The minimum voltage should be high enough to get the maximum power from the panels at the voltage of the maximum power output. Modern inverters have quite wide ranges but older inverters may not. Then again, you can opt to replace the inverter as well. Growatt inverters cost next to nothing nowadays and most are ready to connect to a battery storage system.

author: Siwastaja
author_rank: Super Contributor
timestamp: September 09, 2025, 03:34:54 pm
content: No harm done with panel power exceeding inverter power, except cost of panels going partially to "waste". But note that energy tends to be most valuable when production conditions are not optimal, so this might not be a problem for you at all. Inverter would be maxed out and clipping the power, wasting some potential production when everyone else is producing a lot, too. But you would get comparably more in early spring / late autumn / early in mornings / late in evenings / in cloudy days, compared to using fewer panels.Just be careful with maximum voltage. Like you always need to be anyway. As a rough estimate, total max open-circuit voltage (not MPP voltage!) of the panels should be some 20-25% less than the inverter maximum voltage rating, to cater for voltage rise in cold conditions.

author: Siwastaja
author_rank: Super Contributor
timestamp: September 09, 2025, 03:37:58 pm
content: Quote from: nctnico on September 09, 2025, 03:13:46 pmGrowatts are indeed some of most affordable hybrid inverters, but AFAIK (and I could be wrong), they only support Growatt's own battery system, unlike others who support any popular battery brand. And just like cheap inkjet printers have expensive ink, Growatt's battery system is not among the cheapest, so if you are seriously going to get a battery, consider total cost.

author: Sideways
author_rank: Contributor
timestamp: September 09, 2025, 07:04:52 pm
content: Sizing panels upto even 50% above the inverter power rating isn't uncommon.I second the advice above to be careful of max string voltage. I have two different inverters, they have different maximum ratings and had to reconfigure my strings because one was a little sensitive and would trip out when pushed to 10V short of specified maximum.

author: brucehoult
author_rank: Super Contributor
timestamp: September 09, 2025, 08:54:49 pm
content: Quote from: Siwastaja on September 09, 2025, 03:34:54 pmPanels are sooo cheap now that it only seems sensible. I'm very slightly "over panelled" now with 3x 440W on a 1200W MPPT. I'm seeing regularly maybe 1185W indicated when it's sunny, have never seen an actual 1200. But right now it's raining and I'm getting 200W. When it's merely cloudy I get 400-600.The MPPT controller (2x 1200W), 3600W inverter, 1800W charger, and 3kWh battery (all in one) cost US$1600. The 6x 440W panels I got last week (2640W total) cost US$400. The 6 mm^2 cables for two arrays (which I'm putting in different places on the section) cost $240. A 2nd 3kWh battery cost $900. Parts for a ground mount to secure and angle the panels (they're just lying on the ground right now) will be another $600.So the panels are only 11% of the total system cost! 26% counting the mounting.Doubling up the panels (putting a string of three more in series, in parallel with the existing 3, in the same location, pointing the same direction) would increase the total cost by 26%, while coming quite close to doubling the electricity production in winter and spring -- and summer too, for that matter, as we don't get clear blue skies in summer (or not often). It starts clear, but by 10 or 11 AM the sky is fully of fluffy cumulous clouds, with some getting big enough to produce localised showers (that pass in 10 min).QuoteI see people saying that a lot, but no one ever seems to quantify what they mean by "cold".Can you define your terms?If it's daytime then it's basically never below 10C here. Maybe right at sunrise. Average winter maximum is 15. It gets to 3 or 4 at night, but I've measure my panels and they're making maybe 5V at night. At first light -- actually 10 or 15 min before the official "first light", when the sky starts to get light but it's pitch black on the ground -- they pop up to around 110V and the MPPT recognises that there are panels attached, but at 0W production until 30-60 min after sunrise.Normal working voltage is around 96-104, Voc is supposedly just under 120V but I haven't seen more than 110, and my MPPT is rated for 150V.Weirdly, yesterday I saw 100W produced in two very different ways: 1) it was actually raining, and it was 60V 1.7A, 2) near sunset, clouds blocking the sun on the horizon, but blue sky overhead 100V @1.0A. The latter one is common also in very thick overcast. I don't know what induced it to think 60V was the best solution when it was raining!SO .. when you say "cold conditions", does 5C count, or more like -20?

author: bsdphk
author_rank: Regular Contributor
timestamp: September 09, 2025, 09:50:06 pm
content: As long as your panels dont exceed the inverters maximal input voltage, nothing happens: Electrons are available but go nowhere.Many people overlook that solar panels nominal power is measured under conditions corresponding to Münich (Germany) and if you live on a different lattitude the do not perform at that number.Here in Denmark (56°N) I have 4.2kW panels for a 3kW inverter on a roof which is more flat than optimal.

author: brucehoult
author_rank: Super Contributor
timestamp: September 09, 2025, 10:32:32 pm
content: Quote from: bsdphk on September 09, 2025, 09:50:06 pmWith the sun only 11 or 12 degrees at noon in winter the optimal angle is pretty steep!On June 21 the sun gets to 31º high here, and 34º in May and July, which is a LOT better than 12º for atmosphere path length. Midsummer it gets to 78º high -- flat on the ground is close enough optimal.

author: Siwastaja
author_rank: Super Contributor
timestamp: September 10, 2025, 07:08:34 am
content: Quote from: brucehoult on September 09, 2025, 08:54:49 pmThen again inverters are so cheap too, marginal cost of getting a bigger inverter is similar to that of getting a few extra panels, so, you can get both: enough panels and big enough inverter.I think the biggest reason to get "undersized" inverter is not cost-optimization as such, but if you know in advance that you don't ever have use for that much peak power yourself, and you have very poor compensation, or outright limitations to exported power. Then a small inverter makes sense - and oversized panels (in comparison) help produce more in poor conditions.

author: Siwastaja
author_rank: Super Contributor
timestamp: September 10, 2025, 07:20:04 am
content: Quote from: brucehoult on September 09, 2025, 08:54:49 pmReally - you should be using professionals to do the dimensioning. They have software to calculate it, including climate and panel database. It's how it was done in good old days, nowadays sales companies just sell and installers just install - and diyers diy as always.This is for liability - exceeding maximum voltage has risk of serious equipment damage, even fire risk (although normally inverter just blows up, should not catch fire).The formula is simply:Inverter max voltage > n_panels * (Vopen_circuit * (T_record_low_for_climate - Topen_circuit_v_defined_at) * open_circuit_V_temp_coeff))where "inverter max voltage" is the survival voltage, not necessarily max mppt voltage (of course bonus points for using max mppt voltage, so that it's also operating optimally in that condition, but that's not necessary),and rest of the parameters from the solar panel datasheet.Usual mistakes made include forgetting to apply the open circuit temperature coefficient at all, or not understanding to use worst-case value for low temperature.Ask yourself, are you fine with your system self-destructing every 10 years on average? Every 100 years? Every 1000 years? You can't know in advance when you have exceptional record low temperature, so that panels are still cold and sun suddenly starts to shine on the panels.

author: Psi
author_rank: Super Contributor
timestamp: September 10, 2025, 07:26:12 am
content: Quote from: bsdphk on September 09, 2025, 09:50:06 pmIt does mean you are running your inverter with it limiting itself to its absolute max power rating for long periods of time.Should it be able to handle that, yes. Will it, I'm sure it will work fine until it's at least outside the warranty period. heheDefinitely something to keep an eye on thermal wise. They might be pushing things further than you would.

author: nctnico
author_rank: Super Contributor
timestamp: September 10, 2025, 07:56:49 am
content: Quote from: Siwastaja on September 10, 2025, 07:08:34 amAnother reason to stay at or below 3.3kW (-ish) is that you can use an existing, dedicated circuit (for example for a washing machine) to connect the solar panels to (with some extra breakers in between). It can be quite a bit of extra work to install an extra, higher amperage circuit which eats into the earnings.