Advice on solar pv micro inverter

ernie-money

We have an existing system, run on a sunnyboy inverter, and in addition we also have two new panels that we need to install an inverter for. We had assumed that the cheapest option would be to get a micro inverter for the two new panels, but the electrician we spoke to suggested that it would be a better long term solution, to replace our existing inverter with a larger one, that can run the whole system, including the two new panels.
His reason was that a micro inverter is working at full capasity the whole time, and is therefore not likely to last as long, so it would be false economy to go for that option.
I was hoping that someone would know if this is right, or if he is just trying to get more money out of us...
I can provide details of the exact inverter and panels we have if its needed, but perhaps not necessary for just general advice on micro inverters?
Would be grateful for the opinion of someone knowledgeable in this field!

Martyn1981

Hiya, I think you'll need to give a few more details.

What inverter do you have, what make and model of panels, and how many?

Are the new panels exactly the same make and model as the other panels?

Will the new panels be installed on the same roof, or to be more specific, will the new panels share exactly the same orientation, and roof pitch (and shading (or lack of)) as the old panels?

Will you be applying for FITs for the extra panels?

Edit: When you say micro inverter, do you mean a small inverter like a Steca 500, or Soladin 600 etc?

Mart.

Fruit_and_Nut_Case

Excellent questions Martyn1981. The OP's question sounds quite straightforward but there are pitfalls aplenty for the unwary.

Dave_Fowler

ernie-money wrote: »

We have an existing system, run on a sunnyboy inverter, and in addition we also have two new panels that we need to install an inverter for. We had assumed that the cheapest option would be to get a micro inverter for the two new panels, but the electrician we spoke to suggested that it would be a better long term solution, to replace our existing inverter with a larger one, that can run the whole system, including the two new panels.
His reason was that a micro inverter is working at full capasity the whole time, and is therefore not likely to last as long, so it would be false economy to go for that option.
I was hoping that someone would know if this is right, or if he is just trying to get more money out of us...
I can provide details of the exact inverter and panels we have if its needed, but perhaps not necessary for just general advice on micro inverters?
Would be grateful for the opinion of someone knowledgeable in this field!

You will have to look at your specific system specifications before adding to it. There are various implications to the FITs rates. Adding to an existing system (by adding extra panels) is treated differently from adding panels as a separate new system. Also you would need to consider the total new capacity of the systems. There are many pit-falls which you need to fully understand before making any changes.

A definitive answer would depend on the answers to:

What is the current capacity (kWp) of the system? - the panels and the inverter. Will the new panels be identical to the existing ones? What would the total capacity be when you add the extra panels? When was the existing system installed?

I don't think that micro-inverters running at full capacity would be any more unreliable than a large inverter running at full capacity.

Dave F

Martyn1981

Dave_Fowler wrote: »

You will have to look at your specific system specifications before adding to it. There are various implications to the FITs rates. Adding to an existing system (by adding extra panels) is treated differently from adding panels as a separate new system. Also you would need to consider the total new capacity of the systems. There are many pit-falls which you need to fully understand before making any changes.

I don't think that micro-inverters running at full capacity would be any more unreliable than a large inverter running at full capacity.

Dave F

Hiya Dave, I'm glad you mentioned that, as my brain was already pondering whether an extension with it's own inverter, was treated the same as an extension that shared the 'old' inverter.

If you've got any info, I'd be grateful to update the FAQ extension section, as I hadn't thought of this before. TBH, my first thought was that they'd be treated the same, then I remembered that OFGEM is involved!

Regarding efficiencies, this is a bit of a stretch, but will be interesting to see what the current inverter is, as there is the chance that a couple of panels may allow the use of a more modern, more efficient model, boosting the performance of the 'old' system. As I say, bit of a stretch, but nice coincidence if that happens and is possible. (When my SB1200 dies, in will go a SB1300TL lifting efficiency from 91% to 94%.)

Mart.

ernie-money

Martyn1981 wrote: »

Hiya, I think you'll need to give a few more details.

What inverter do you have, what make and model of panels, and how many?

Are the new panels exactly the same make and model as the other panels?

Will the new panels be installed on the same roof, or to be more specific, will the new panels share exactly the same orientation, and roof pitch (and shading (or lack of)) as the old panels?

Will you be applying for FITs for the extra panels?

Edit: When you say micro inverter, do you mean a small inverter like a Steca 500, or Soladin 600 etc?

Mart.

Thanks for replying!
I haven't got the details to hand at this second, but I know that the two new panels are different to the existing ones (different make and output). They are also in a slightly shadier location (on the same roof) which I thought would lower the output of the others? I thought that all of this meant that a separate inverter would be the only solution, but the electrician seemed to think that he would be able to install one new inverter to run the whole lot.
Not looking for FIT for add on, just querying the inverter situation...

Martyn1981

ernie-money wrote: »

Thanks for replying!
I haven't got the details to hand at this second, but I know that the two new panels are different to the existing ones (different make and output). They are also in a slightly shadier location (on the same roof) which I thought would lower the output of the others? I thought that all of this meant that a separate inverter would be the only solution, but the electrician seemed to think that he would be able to install one new inverter to run the whole lot.
Not looking for FIT for add on, just querying the inverter situation...

No probs, happy to chat.

Obviously your installer is going to understand all this better than I, however, lots of issues (or at least thoughts) are jumping out at me.

Adding different panels to the same inverter is probably going to be very tricky, unless their voltage is a match to the old ones. Different output must surely complicate this further. Then you add on the shade factor you've spotted and this is really getting 'unusual'.

The only solution I can think of, sharing an inverter would be something similar to SolarEdge, which can operate different panel types, outputs, orientations, shading etc, all on the same system. Also very efficient inverters. My 2kWp system is a SE system. But, this involves adding power optimisers to all panels (including the existing ones), and a change of inverter, so extra expense, and more kit on the roof where access may be tricky.

Can't see how you could install on the same inverter, and not go via FITs extension, since the TGM is going to rack up extra units.

Your solution is much simpler, but even if you don't go for FITs, you'll still need to register the system with the DNO, even if it's only 500W.

Mart.

ernie-money

Thanks again!
What I meant to say is that I don't need FIT advice - it's a very long and complicated story of an installer who quoted & invoiced me for a larger system, but didn't actually install it on my roof. I realised this after paying him & after a lengthy complaint through Napit, he was supposed to add the additional panels, which he started, but never completed & hence I am left with the new panels to be wired in. I've already had the larger system approved & got microgen certificate or whatever it's called, so that bit is all sorted, just to complicated to go into detail...
Anyway, regarding the inverter, I was under the impression that if you wired panels of different capacity into the same inverter, then you reduce the output of the highest one, down to the output of the lowest one, if you understand what I mean? The electrician is saying that that is only true for the older inverters, and that now you can get new ones that can cope with panels of different capacity, and this is what I'm querying.
I would get a second opinion from another electrician, but its been neigh on impossible to find someone who knows anything about solar pv, who is prepared to get involved with just wiring in the panels, on an installation that was started, but not completed by another installer.
I can understand the reluctance, but I just want the panels sorted and finally start earning some money from them, now nearly two years after they should have been up and running...

rogerblack

ernie-money wrote: »

T now you can get new ones that can cope with panels of different capacity,

This is correct.
There exist several sorts, with multiple inputs.
The best optimise the use of all the panels all the time.
If the seprate strings of panels are connected to each input, and the voltages are in range - it all 'just works'.
The strings are entirely independant.

Martyn1981

ernie-money wrote: »

I would get a second opinion from another electrician, but its been neigh on impossible to find someone who knows anything about solar pv, who is prepared to get involved with just wiring in the panels, on an installation that was started, but not completed by another installer.
I can understand the reluctance, but I just want the panels sorted and finally start earning some money from them, now nearly two years after they should have been up and running...

Hiya Ernie-M, I can see why you're frustrated.

I'm only guessing here, as I don't know the full details of your system, or how many other panels those 2 extra will match, if at all. But if the FITs side is all sorted, and you're registered for all the panels, with all the people (boy, life gets complicated sometimes), then your solution sounds simplest. It might not be the best in the long run, alternatively, it might be the best, but if I'm understanding this correctly then:-

you have 2 additional panels in place,
they don't match the other panels,
their shading is also a little different,
they're included in your FITs, OFGEM and DNO registration,
their output should be showing up on your TGM.

Easiest solution, small inverter like the Steca500 feeding into the TGM. You may already have a small consumer unit between the existing inverter and TGM, if not, then adding one to create a Y junction to join the two inverter outputs should work (Dave/Roger, does that sound right? I have this set up on my ESE system joining the 1.2kWp and 2.4kWp systems).

But please don't discount what the installer is saying, he (or she) obviously has tons more experience and local knowledge than me. And as Roger says, if an inverter can cope with the differences through the use of multiple strings, then an upgrade might be worth thinking about.

Here's a link to some info on the Steca's, you can also find info on the Soladin 600, under Mastervolt:

http://www.swithenbanks.co.uk/shop.php?c1=Solar%20Photovoltaic%20Equipment&c2=Grid%20Tie%20Inverters&c3=Steca

Mart.

Edit: Sudden thought, if the small inverter solves the problem for now, then you could wait till the larger inverter fails, say in 10 years time, and revisit your options then, when there may be more choice. M.

ernie-money

Martyn1981 wrote: »

Edit: Sudden thought, if the small inverter solves the problem for now, then you could wait till the larger inverter fails, say in 10 years time, and revisit your options then, when there may be more choice. M.

Thanks again!
This was my thinking - doesn't seem worth paying the extra 500 quid or thereabouts to replace the existing inverter that works perfectly fine...
Obviously when it gives up the ghost, we could then look at a bigger one to do the whole lot, and see what's around then. Even if there is an inverter that might be more efficient, that could accommodate all the panels, I couldn't see that it would be that much better, that we'd get £500 more return before it'd be time to replace the inverter again...