Any domestic solar PV experts here?

[Martinf]

I had a PV system installed in January this year so I am not particularly aware of the detail of FITs. However I would be concerned that if an existing system was altered to comprise a smaller number of newer panels then the new MCS certification would not match with that registered for the FIT. Could this then invalidate the FIT?

I suggest that a competent PV installer should be able to advise different courses of action that are available.

My own new 6.66kW PV system comprises 18 panels, dual input inverter and a 9.6kW battery. When I ordered it I didn’t think it would actually pay for itself, considering the life expectancy of inverter and battery. But for once I seem to be ahead of things and with the large increase in energy costs I now hope for a payback after about 8 years (calculated simplistically). The recipient of the power I export under the ‘Smart Export Guarantee’ needed careful consideration due to hugely varying payments. Export is capped at 6 kW.

 

[Ozi]

I completely missed this thread, otherwise i would have piped up sooner. i don't confess to being an expert, but i did work for an inverter manufacture for a number of years and did work with installers to commission the inverters for both PV and wind applications.

On the face of it t looks like your installer has wired your new 400W panel in series with the existing string of 250W panels. this is not a good idea, a string like this will be limited to the lowest wattage inverter(s) in the string (in effect your inverter is seeing 9 x 250W panels)

Regarding why your new panel wouldn't allow the inverter to power up, i think it may be to do with the minimum voltage required - I'm speculating at to the ratings of your old panels and your new one but I'm guessing your old panels on their own have a string voltage of about 250V. Your new single panel however has only a voltage of about 35V and your inverter has a min voltage of 175 and a max of 700. ideally when your using both strings, you want to balance them however the inverter does have a minimum 'start up voltage' (on yours 220V) before it will wake up.

Moving on to what you can do....

You could change your roof panels as you suggest however your inverter can only handle up to 2100W, regarding the concern over exporting me than you are allowed, you could fit an export limiter - it basically monitors power going out to the grid (at your meter) and if that is greater than your set amount it communicates with the inverter and dials it don so it outputs less. This is a great idea as you can run a bigger inverter, more panels etc and in effect generate far more tan your allowed to feed back - whilst you cant feed it back, you can use it in your home, so lets say your generating 4000w, and your house usage is 3kw (assume cookers on for example) it will export 1kw back to the grid. when you turn off your cooker, your usage house usage drops to 1000w, the export limiter will dial back your inverter to 3000w, 2000w will go back to the grid and the remaining 1000w will be powering your house.

Adding a battery storage system will again allow you to get more from your system, for example in that same example as above, inverter outputting 4000w, house using 1000w battery charging gets priority over export, so potentially 3000w going in to the battery's when can then get used overnight.

Hope this is of interest,

The only problem I can see with this is the solar generation meter. A. FIT payment has two rates, the higher one for electricity which is exported, and a lower rate for everything you’ve generated. The meter sees it all, and looking at mine, it’s wired directly to the inverter as the next link in the chain before power enters the house/grid.

So if you were running it all through the same inverter, but with an export limiter, yes you’d overcome the export issue, but you’d still have a problem with overall generation and it would be obvious you’d updated the system.

Only way round this would appear to be second array with its own inverter and generation meter.

 

[russ_e]

Payback is really only possible if you use 100% of the energy generated, for a domestic installation at least.

If you have a battery then you are really only 'saving' the cost of charging up your batteries. Which can be as low as 3p kWh overnight.

 

[Martinf]

Payback is really only possible if you use 100% of the energy generated, for a domestic installation at least.

If you have a battery then you are really only 'saving' the cost of charging up your batteries. Which can be as low as 3p kWh overnight.

From my experience to date I wouldn’t have said this was the case. I am now projecting a return on my domestic installation but have exported 66% of PV output. The PV has supplied 88% of my needs.
Currently my Supplier’s variable rate Is at or very near their 34.997p price cap through the 24 hours.

 

[Skyliner33]

From my experience to date I wouldn’t have said this was the case. I am now projecting a return on my domestic installation but have exported 66% of PV output. The PV has supplied 88% of my needs.
Currently my Supplier’s variable rate Is at or very near their 34.997p price cap through the 24 hours.

Do you have a meter that specifically measures the energy fed back into the grid?

 

[Martinf]

Do you have a meter that specifically measures the energy fed back into the grid?

Yes, incoming and outgoing is measured and recorded in I believe 30 minute time slices. I didn’t think my original Smart meter had this capability but was pleased to find that it did. The Supplier provides daily a record of the totals of power flow in direction.

The caveat is that as the system is relatively new I haven’t yet received any payment for outgoing. However I would say that I am very pleased to date.

 

[Skyliner33]

Ah i see. Older systems don’t have the abilty to feed back into the grid.

 

[Martinf]

Ah i see. Older systems don’t have the abilty to feed back into the grid.

I presume they could if a modern meter was installed.

There will also be a debate with the DNO on output current cap. The default output for us was something under 4kW but the DNO agreed to a revised limit of 6kW. This limit was organised by the installation company although I had to look round Suppliers to find the most appropriate SEG tariff for export.

Incoming and outgoing power do not have to be with the same Supplier but the best SEG will likely be obtained if the same company is used.

 

[Skyliner33]

I presume they could if a modern meter was installed.

There will also be a debate with the DNO on output current cap. The default output for us was something under 4kW but the DNO agreed to a revised limit of 6kW. This limit was organised by the installation company although I had to look round Suppliers to find the most appropriate SEG tariff for export.

Incoming and outgoing power do not have to be with the same Supplier but the best SEG will likely be obtained if the same company is used.

Possibly. But that may take me off the Tariff that i am on now. I get paid tir feeding in even though my system doesn’t.

 

[russ_e]

SEG is about 3p-5p kWh Exporting this back to the grid and then buying energy at 40p kWh you can soon see how this has a massive impact on getting back your original investment in the next two decades.

It's also worth pointing out you don't make any savings until you have made back your original expenditure.

I've yet to see any real world figures in which I would class solar as a good investment financially when installed within a residential setting. This excludes of course anyone on the original FIT scheme.

For tax payers you would be much better off investing in your pension than buying solar.

 

[Skyliner33]

SEG is about 3p-5p kWh Exporting this back to the grid and then buying energy at 40p kWh you can soon see how this has a massive impact on getting back your original investment in the next two decades.

It's also worth pointing out you don't make any savings until you have made back your original expenditure.

I've yet to see any real world figures in which I would class solar as a good investment financially when installed within a residential setting. This excludes of course anyone on the original FIT scheme.

For tax payers you would be much better off investing in your pension than buying solar.

I am on the original FiT scheme.

 

[russ_e]

I am on the original FiT scheme.

Happy days! Just make sure you never move house

 

[Skyliner33]

Happy days! Just make sure you never move house

I get the option yo sell the panels income to the new owner. Or keep the income, the bew owner just gets the electricity generated.

 

[Martinf]

SEG is about 3p-5p kWh Exporting this back to the grid and then buying energy at 40p kWh you can soon see how this has a massive impact on getting back your original investment
<snip>
For tax payers you would be much better off investing in your pension than buying solar.

I would certainly agree Pension should be a priority, I’ve been there and done that!

I estimate that overall my PV installation will cut my imported power by around 8.5kWh per day (although I’m paying less than 40p kWh) and a flexible export tariff should do much better than 3-5p kWh. For example at the moment of writing Octopus Agile is reportedly paying 33.78p kWh which is more than the import tariff. So there is value in the SEG export payments.

 

[EdH]

Had this response from EDF this morning regarding my panel replacement.

 

[Skyliner33]

View attachment 164657
Had this response from EDF this morning regarding my panel replacement.

Will the new panels be compatible with the old inverter?
Have you estimated how long it will take to recoup the investment?

 

[EdH]

Will the new panels be compatible with the old inverter?
Have you estimated how long it will take to recoup the investment?

Hopefully. This is spec sheet for my inverter. Proposal is to install 5 x Jinko Tiger Neo 415w panels. What do you think?

 

[Skyliner33]

Hopefully. This is spec sheet for my inverter. Proposal is to install 5 x Jinko Tiger Neo 415w panels. What do you think?View attachment 164719

View attachment 164718

Not sure to be honest.
It seems to me a big expense, how long do you think before you see a profit?

 

[EdH]

Not sure to be honest.
It seems to me a big expense, how long do you think before you see a profit?

Did some rough calculations about 8 years or so. We are also considering additional separate system as we will gain additional space on the roof by removing the old ones.

 

[Skyliner33]

Did some rough calculations about 8 years or so. We are also considering additional separate system as we will gain additional space on the roof by removing the old ones.

That takes into account only the money generated by the new system? But the cost of the bew system plus the cost of the panels replacing the old ones? Id be interested in seen the calculations. You can pm if you dont want to post on here.