Adding new panels to existing inverter

jimjames

I had a quick look but the info here seemed to relate more to completely new installations alongside existing ones and the new ones having their own inverters.

I'm looking at having an extension to the house and if we go ahead then the roof would be able to take more panels. The existing roof has as many as we could fit on at the time.

Our inverter is rated 3kW and our panels come in around the same so there is some potential headroom there based on the panels generally generating less than their maximum.

Has anyone added panels to an existing inverter and if so how is the FIT tariff calculated? We'd be able to increase up to the full 4kWp so adding another 1kWp to our existing but retaining the current inverter.

theboylard

I believe, but happy to be corrected, that if you add new panels to an existing installation then the whole FiT is recalculated from the new commision date - with the current FiT applying - so if you were on a higher rate and for longer, then you would lose that.

A new install is just that, hence why some of the guys/gals here have 2/3 inverters.

Martyn1981

jimjames wrote: »

I had a quick look but the info here seemed to relate more to completely new installations alongside existing ones and the new ones having their own inverters.

I'm looking at having an extension to the house and if we go ahead then the roof would be able to take more panels. The existing roof has as many as we could fit on at the time.

Our inverter is rated 3kW and our panels come in around the same so there is some potential headroom there based on the panels generally generating less than their maximum.

Has anyone added panels to an existing inverter and if so how is the FIT tariff calculated? We'd be able to increase up to the full 4kWp so adding another 1kWp to our existing but retaining the current inverter.

See FAQ section 10.

Your old FiT won't be affected, so long as you don't change/upgrade any of the original panels. You could even change the inverter if you wanted to, but as you say, it may be fine (subject to a little capping) but check it's tech specs for voltage limits.

Your FiT provider will class the new extension FiT rate depending on total system size, so if you add 1kWp (to 3kWp) the new system will get the current upto 4kW rate, but if you added 1.1kWp, then the new system would get the 4-10kWp FiT rate.

Your FiT provider will assume generation split entirely on kWp rating, so therefore if you add 1kWp, they'll split the TGM figures 3:1.

Speak to your FiT provider (make sure the person understands all the rules) and double check all of this. Would be helpful if you could feedback afterwards.

Mart.

tunnel

Exactly what mart says.
I increased my capacity from 2kWp to 4kWp after I rebuilt my garage, I was told it would be apportioned according to panel capacity(split). I decided on a separate inverter and TGM purely because the garage faces a completely different direction and does suffer shading


Can you not go bigger? Why stop at 4kWp? For the difference in the FiT these days you could look at the next FiT band, it wasn't any real hassle for me getting the DNO approval when I extended again...all done via email by my installer

jimjames

tunnel wrote: »

Exactly what mart says.
I increased my capacity from 2kWp to 4kWp after I rebuilt my garage, I was told it would be apportioned according to panel capacity(split). I decided on a separate inverter and TGM purely because the garage faces a completely different direction and does suffer shading


Can you not go bigger? Why stop at 4kWp? For the difference in the FiT these days you could look at the next FiT band, it wasn't any real hassle for me getting the DNO approval when I extended again...all done via email by my installer

Based on the info from Mart I think that may be worth looking at adding more as a separate system. The problem I can see adding an extra 1 kWp panels to our existing is that on very good days the new 1kWp will be the bit being capped by the inverter limit but the overall amount generated will be split 3:1 for FIT payments.

So on a day where I currently get 20kWh from 3kWp, I may get 24kWh from 4kWp due to inverter limit so rather than being paid my current FIT rate on 20kWh as now, I'd get 18 (3/4 x 24) paid at current and 6kWh (1/4 x 24) at the lower new rate.

Multiply that up across the year(s) and it could make a substantial difference.

tunnel

Think you may have answered your own question JJ, it's either a new inverter or an extension. How much more can you get up there when the house extension is done, would it be possible to go bigger?

Martyn1981

jimjames wrote: »

So on a day where I currently get 20kWh from 3kWp, I may get 24kWh from 4kWp due to inverter limit so rather than being paid my current FIT rate on 20kWh as now, I'd get 18 (3/4 x 24) paid at current and 6kWh (1/4 x 24) at the lower new rate.

Multiply that up across the year(s) and it could make a substantial difference.

That's a really good point! I'm annoyed I didn't think of it.

Given how well (extremely well) your system is operating, then shifting top FiT units onto bottom FiT via capping would change the economics, especially given that the extension will be proportionately expensive already due to size.

I had the same issue with my WNW system, so didn't want it to share the TGM with the older ESE system.

Obviously your system is performing well, so I'm sticking my neck out a bit here, but if you 'only' added 1(ish)kWp then I'd have thought a 3.68kW capped inverter wouldn't cap too much.

If you do decide to go bigger, and need DNO approval for the sum of the systems (actually the sum of your inverter outputs) then as another option you could still share a single inverter, but obviously it would need to be a bigger one, 4kW+. Just worth considering for the future, less inverters to fail, and you could flog the old one on FleaBay.

Lots of options, lots to think about. How much more kWp do you think you could add?

Mart.

theboylard

So I was talking Shiite then?!

Top tip, don't listen to me when bars may be open!

tunnel

theboylard wrote: »

Top tip, don't listen to me when bars may be open!

That's put a smile on me face says me who posts more when I've been drinking..oops

jimjames

Martyn1981 wrote: »

Lots of options, lots to think about. How much more kWp do you think you could add?

Mart.

It really depends which part of the roof we put panels on.



The extension would go to the left on this picture so it would probably only get 2kWp there. We've not got panels on the lower roof as it was getting shaded earlier (as in the photo) but it might be worth getting some there as well as extension with new inverter as we are doing so well with the existing ones.

As you say, lots to think about!

Martyn1981

jimjames wrote: »

It really depends which part of the roof we put panels on.

The extension would go to the left on this picture so it would probably only get 2kWp there. We've not got panels on the lower roof as it was getting shaded earlier (as in the photo) but it might be worth getting some there as well as extension with new inverter as we are doing so well with the existing ones.

As you say, lots to think about!

Quick fire suggestions (even though you didn't ask for any!)

1. If only side extension and 1 to 1.5kWp then upgrade inverter to 3.68kW capped. Double check with installers that 'increasing' to 3.68kW is treated the same as jumping straight in at 3.68kW by the DNO.

2. If only side extension and 1 to 2kWp (yes I know 1. and 2. overlap, can't make up my mind) then ask DNO for permission and if they say 'yeah' replace inverter with 4.5 to 5kW model.

3. If side and lower roof, then ask DNO but go for separate system as lower shading may compromise FiT ratios. Make sure it's a dual MPPT inverter as the pitches are different (upper looks like 30 to 35d and lower 20 to 22d?) and also so that lower shading doesn't affect upper.

4. If lower is shaded all of a sudden/at the same time then as 3., but if shading affects lower bit by bit, then SolarEdge system for the new system (side and lower) perhaps 3kW model.

5. ...... must stop, cement going off and block wall that ain't gonna build itself, no matter how much I wish it would!

This is fun.

Mart.