Electronics > Power/Renewable Energy/EV's

Looking for advice in a grid tie inverter installation.

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sergio_eevblog:
Hi everyone, new here and kind of ignorant in many subjects like this one, so sorry in advance if I say silly or non-sensical things.

Located in Spain, EU, my family has an off grid solar installation, a really old one with 12V or 24V, 130W rated panels. Some of the batteries have gone bad and now we normally run out of juice at 17:00 or so, though we have a switch to switch from off grid consumption to grid consumption.

Since it's really annoying to be switching twice a day and we forget sometimes to switch to solar consumption we thought installing a grid tie inverter would be helpful. We could sell the batteries and the off grid inverter to recover some money and never have to worry about switching again.

We called a company and gave us a budget for the installation of 3000€, I saw that really abusive and many of the things the technician told me were really weird, so I don't think I can trust any of what he said.

Our solar installation consists on 12 panels rated 130W, no idea if they are 12V or 24V, I would have to check with a multimeter because there are no informations of those panels. I would like to connect those (and maybe in a near future install and connect a couple pair of modern panels as well) to a grid tie inverter, with all its needed protections (thunders scare me, I don't know what do I need to protect the installation against that).

I have no idea about what inverter brands to go for or what brands to completely avoid, I've heard bad things about huawei and fronius, the 2 brands the technician said "are the best and the rest are trash". I don't know if I can go better with micro grid tie inverters or if it's better a big one, I don't know about what protections I would need, etc.

If you could help me solve my doubts and give me advice I would appreciate it a lot, if you need any other info I'll try to post it asap. All I'm looking for is to have a decently installed grid tie inverter without being robbed or scammed by "technicians" claiming "I have to use an inverter that's rated 2kW lower in max kW than what my panels can generate".

Jeroen3:
You will probably run into some compatibility issues with the specifications of the panels from back then and the inverters of today.
But if you have enough panels you can make it work.

If your current panels are 24V, you could get any small cheap single phase goodwe unit of 1 kW for grid-tie operation. They're around €300 (GW1000-XS).
Verify the voltage and current range of the panels first.
But, are you allowed to export to the grid? I guess not otherwise you would not have batteries today.

3k for only replacing the inverter on this string for a grid-tie one without batteries is too much.


--- Quote from: sergio_eevblog on March 11, 2023, 04:54:35 pm ---... "technicians" claiming "I have to use an inverter that's rated 2kW lower in max kW than what my panels can generate".

--- End quote ---
So a -500W inverter, okay! Typically you want a bit more panels than inverter. But that is for economical reasons mostly.

You can also upgrade the entire setup, todays panels are 400W, maybe a bit larger, and get a hybrid inverter. But then 3k is not enough.

sergio_eevblog:
I'm going to verify with the electric company what legalization would I need to do to be able to inject some electricity to the grid. As for now the solar installation is legalized and the counter (Is it called counter? The thing that makes the company know how much I consume) is already bidirectional.

We might install 4 500W panelsi n the near future, should I try to match max power generated by solar with max rated power of the inverter? I've also read they're more efficient when power generated is 60 to 70% of the max rated power of the inverter.

I'll check that inverter and that brand. Also, what would I need as protections? I think there was a 100A mono phase over voltage device, 180€. Though I don't know why 100A.

Jeroen3:
Yeah, ask the grid company. Red Eléctrica?


--- Quote from: sergio_eevblog on March 11, 2023, 06:26:27 pm ---should I try to match max power generated by solar with max rated power of the inverter?

--- End quote ---
You should match the amount of panels to the nominals of the inverter. eg; GW1000-XS is a 1000W ac inverter, you can attach up to 1300Wp solar.
I don't know what the values are for the latitude of spain, but here in the netherlands, we use 80%. So the inverter is 80% rated of the Wattpeak.
Because half the year the panels see mostly night time, the tilt-angle and azimuth are non-ideal, and panels age. They call it DC/AC ratio, maybe you can find something in your language?


--- Quote from: sergio_eevblog on March 11, 2023, 06:26:27 pm ---Also, what would I need as protections? I think there was a 100A mono phase over voltage device, 180€. Though I don't know why 100A.

--- End quote ---
It depends*. The inverters typically require standard MCB type B16/20, possibly RCD type A 30mA. Most of the time installers put in the cheapest RCBO they can find.
Also DC and AC isolators near the inverter, but your local code may be more strict or relaxed. As you've seen with Dave's PV videos, an isolator on the roof. Because that makes sense.  |O

nctnico:

--- Quote from: Jeroen3 on March 11, 2023, 09:38:32 pm ---
--- Quote from: sergio_eevblog on March 11, 2023, 06:26:27 pm ---Also, what would I need as protections? I think there was a 100A mono phase over voltage device, 180€. Though I don't know why 100A.

--- End quote ---
It depends*. The inverters typically require standard MCB type B16/20, possibly RCD type A 30mA. Most of the time installers put in the cheapest RCBO they can find.
Also DC and AC isolators near the inverter, but your local code may be more strict or relaxed. As you've seen with Dave's PV videos, an isolator on the roof. Because that makes sense.  |O

--- End quote ---
You have to be carefull who you ask. Despite lots of solar panel sellers wanting to sell you an AC switch for the inverter, this is actually not required by the electrical code in the NL. Just a means somewhere to turn it off; a dual pole circuit breaker in the breaker panel does just fine for that purpose. Doing some research certainly helps.

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