Looking for advice in a grid tie inverter installation.

[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.

... "technicians" claiming "I have to use an inverter that's rated 2kW lower in max kW than what my panels can generate".

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?

should I try to match max power generated by solar with max rated power of the inverter?

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?

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.

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. 

[nctnico]

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.

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. 

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.

[Jeroen3]

The separator switch is indeed a recommendation, in the code. It also features as a nice termination point for new cabling when the inverter is changed after it's rated life. They are €15 and should not be a major upsell. If they try it as upsell, find someone else.

[sergio_eevblog]

So, I have been looking at more options and contacted other installers to compare prices, which all of them were absolutely horrible. One of them told me that it's not possible to mix different panels ...

My family decided not to install more panels since they don't want to pay 8k€ to 10k€ on another loan, or mortgage (sorry I lack a lot of vocabulary so I don't know the proper word).

So I have been looking at 1kW to 1.5kW grid tie inverters, and I haven't been able to find much:
- There's sunny boy 1.5 with 5 year warranty and mppt range of 150V minimun, my panels were rated 12V. There's also a min. input voltage and initial input voltage, no idea what those are for. 750€.
- Growatt that I've read is not good in reddit, 1000s-dc, 70V min ppt, 80V start voltage and it says 10 year warranty. 95.5% efficiency.
- Growatt min-1000tl-x and 1500tl-x with some similar specs, 80V min ppt and 97.1% efficiency. I've seen the 1500tl-x for 400€.
- Goodwe gw1000-xs with apparently 5 year warranty and min mppt 40V and 97.2% efficiency (I've seen it at 500€). The gw1500-xs is min mppt 50V and I've found it at 300€.
- One of the installers only installs huawei, its smallest is the 2ktl for 700€, min mppt 120V.
- Fronius galvo 1.5 min mppt 120V 900€.
- Solaredge I've read they have high failing rate, so I don't know of I should look at them. se1000m and 1500m are 1000€.
- I haven't been able to find emphase inverters.
- There's also a ton of rebranded chinese inverters with 6 months warranty that I feel I shouldn't consider.

What would you do in my situation?, I want a reliable inverter from a company that has customer support (not having to wait 6 months for a replacement in case the inverter breaks, or things like that).

The thing about securing the installation was mostly for lightning storms, I have no idea what is necessary to protect an installation like this from them. My current off grid inverter broke due to a near lightning years ago and I was wondering if it would be possible to put protections for that.

Also, is the output of the inverter connected directly to a wall plug without protections or is it connected to the grid right before the breaker box? That is one of the things I still don't quite understand, I'll look into it as well.

Edit: I'd like to add something else about my panels info:
I have these things that apparently are measuring the wattage and amperage the panels are generating (attached image).
Can I get the amperage of the panels (the lowest amperage of the panels or group of panels I guess) and the average voltage from that? I would like to not get on top of the roof since I'm scared of heights.
I've measured the "panels" with the multimeter and I get between 28V and 29V, I was expecting 24V since I assumed they were in pairs in series, and then 3 pairs in parallel, but I don't know how are they wired to get that result.
Quick edit II: Apparently 12V panels won't mean their max output will be 12V ... I hate that I take everything so literaly. Does that mean my panels were generating at the point of the measuring around 14.0V and 14.5V?

[nctnico]

What kind of batteries do you have?

What you likely need is a solar inverter with an integrated battery charger/discharger AND a current transformer that measures the current going into the mains connection of the home. With the current transformer, the inverter can measure the amount of current going out or into your home and based on that adjust home much power from the solar panels is fed into the batteries when the sun shines and how much power must be taken from the batteries when you consume more than the solar panels can deliver at that moment.

The big question is whether the existing batteries are suitable for connecting them to a modern inverter. If you can post more info about the existing system (schematic, brand & model number for all parts) then maybe somebody might be able to give a good suggestion. Otherwise you'll need to consult an installer that know how to upgrade your existing system. I think you'll need to replace most of the existing electronics to get to a new setup that works well.

[sergio_eevblog]

The idea is to get rid of the batteries and off grid inverter to cover part of the grid tie inverter installation.

The batteries are really old and won't hold enough capacity anymore. For example, a sunny day where we consume barely anything and the battery indicator shows it's full, at 18:00 we put the microwave for 3 coffees and the batteries start beeping with red led so we have to immediately switch to grid.

[Jeroen3]

The installer is correct that you cannot mix panels in the same string. The inverter uses maximum power point tracking and it works best with the same panels without shades.
Solaredge compensates for this by using mini-trackers under each panel, hence they are more expensive and have more failure points.

Don't value warranty that highly. As soon as a family of inverters start fails too soon, they all fail like this and the company will fold. Many inverter companies are bankrupt already.
Installers also close a lot in order to not have to perform the warranty replacements. From what I can tell from my circles, Solar Edge WILL fund bad inverter/optimizer replacement within warranty.
Enphase will as well, but their distribution network makes it tricky. They are reasonably reliable. You can buy them from a few stores here in the netherlands, they should work all over 50 Hz europe.
They will not work for 12 Voc panels.

Looking at your solar trackers and battery chargers, you probably are paralleled 12V panels, not series. Meaning the hole thing needs to come down, because you won't find grid-tie inverters for this.
Maybe victron has some, but that's highly DIY for campervans/ships and such. Taking it down is good, PV technology has improved a lot!
However, current energy crisis has created a enormous surge in solar power. Causing prices to be 2 or 3 times as high as two years ago.

Depending on your abilities, doing an Enphase system yourself is very much doable. Here there are even companies selling diy kits with them.
The risks are quite low, since you onyl have to work on AC side of the system.

You do however need to expand your AC distribution board a bit I suspect, you cannot wire solar power to "just a socket". They must have their own circuit breaker and earth leakage protection relay. How complicated your AC system will be depends on your regulations. For example you may need an additional meter, which you are not allowed to install.

8-10k for 12 panels today is not a weird price anymore, unfortunately.

[nctnico]

8-10k for 12 panels today is not a weird price anymore, unfortunately.

Actually it is the installers that do the price gauging. Prices for the hardware went down a lot over the past 5 years. 2 months ago I bought a complete DIY kit with 4,2kW inverter, mounting rails, cabling and 12 panels / 4500Wp for 3400 euro (*). A similar installation costs around 8k euro to have it installed. A couple of weeks ago I stumbled across a job advertisement. As a self employed solar panel installer you can appearantly earn 8k to 12k euro per month in the NL.

* As a comparison: several years ago I looked into buying used panels and a used inverter which would cost around 2k euro in total and have a Wp rating of around 2800.

[Jeroen3]

There also is a shortage on inverters and mounting hardware. Plus in the netherlands they screwed up the liquidity of the installers with the new 0% VAT rules.
(The installers need to pay VAT, but only get it back months later. This puts them in negative balance.)

[nctnico]

There also is a shortage on inverters and mounting hardware. Plus in the netherlands they screwed up the liquidity of the installers with the new 0% VAT rules.
(The installers need to pay VAT, but only get it back months later. This puts them in negative balance.)

No. The margin on hardware alone is way more than the 21% VAT so this should not be a problem for any installer (unless they really suck at running a business).

Either way, now is not a good time to have a solar system installed. At least in the NL.