5kw panels, G83 Inveter, 3.68 TIC. Anyone actually done this?

[GreggElectrical]

I've always stayed away from any of this sort of stuff but I have a very insistent customer. He says he will disconnect the other 4 panels if his fit application is not accepted (yeah right!). He basically has room for 5kw but obviously wants the 16p rate (install in August). Argument is that the system should be limited to 3.68kw by use of a g83 inverter so TIC and DNC should be no more than 4kw. I really cant see this working but wanted to know if anyone has ever tried it and what happened.

 

[BruceB]

I have done it on some installations without problem because I believe it is within the legal definition of TIC/DNC. I have also made sure the customer is careful what they write on the FIT application so as not to raise a hare.

However, I have become aware within the last few months of at least a couple of installers who have customers being told by their FIT supplier that TIC = kWp of panels rather than inverter output, thereby placing them in the 4-10kW FIT band rather than the 4kW or less band. Much grumpiness all round!

So if you do it, you and your customer must do so with the prospect that it might be challenged at some stage. And that could result in having to resort to OFGEM complaints process and legal action.

 

[FB.]

Is it a good idea, in one word:

No.


But......

If the panels face North, East or West, or are on a very steep or very flat roof, or suffer severe shading at peak generation time it might be a reasonable combination.

But if the panels are SouthEast, South or SouthWest, in normal conditions of roof slope and minimal shading, the inverter will be seriously overloaded and will probably send the "excess" electricity back round to the panels, causing overheating of the inverter and the panels - and reduction in performance on sunny days (panels drop in performance when hot, and having the "overload" power sent back from the inverter will overheat the panels even more - probably not helping the panel lifespan).

On particularly good days, it's not unusual to see panels outputting 10% more Wattage than their nominal rating. My 250W panels have reached 270W output per panel in ideal conditions. So your client might think he's got peak panel output of 5kW, when it could well reach 5.5kW or more.

Some inverters have a maximum input allowance for the warranty. My Aurora PVI 3.6 has a maximum allowance of 2 strings of 2kWp each, or a single string of 3.75kW. More than that and the warranty is theoretically void.

 

[BruceB]

........ the inverter will be seriously overloaded and will probably send the "excess" electricity back round to the panels, causing overheating of the inverter and the panels - and reduction in performance on sunny days (panels drop in performance when hot, and having the "overload" power sent back from the inverter will overheat the panels even more - probably not helping the panel lifespan).........

is a generalisation and not very accurate way of describing what happens to the power flows.

Plug some numbers into Sunny Design and you might be surprised what can be put on the inputs of say a 4000TL.

 

[Earthstore]

Just to add, if you add more panels and try to keep things quiet, say over 4 KWP and the system performs very well, when the customer sends in his meter reading if it is above what the provider expects (some have already been challenged) then questions will be asked, if the provider/OFGEM, do deem the panels as TIC then should you install 5KW it could be deemed as fraud if they claim the 4KW tariff.

There are many different views on TIC/DNC for PV, and the problem is the forms used are generic for all types of generation, I have looked into this in detail, and had different answers, helpful I know....

My advice would be so stick to 4KWP of panels, but install quality not quantity, or explain the risks to the customer and put all the risk onto them.
But take care, it looks like Barking is doing all he can to destroy this industry..

 

[Gavin A]

from a technical point of view, yes it's no problem, the system will work really well.

from a FITs point of view... after a long running argument with Ofgem, we've ended up having to remove a panel from a customers system to comply with their current unlawful interpretation of the legislation, that runs contrary to their own published guidance, because we didn't feel in a position to stump up £10k to take it to judicial review.

so, if you've got 10-15k to spare to challenge ofgem, then by all means go ahead as the 5kWp array limited to 3.68kW AC output should lawfully be classed in the 0-4kW FIT band (and we've paid for 2 legal opinions on this), but Ofgem's position on this says otherwise, and this is the guidance they've now issued to all FIT suppliers (but refuse to actually issue to MCS installers), which is why most of the FIT forms now expressly ask for the kWp rating of the panels.

so we're now sticking to 4kWp of panels, with gritted teeth, and an intention to sue Ofgem if we ever get our finances in order enough to spare the money to do it.

 

[GreggElectrical]

I thought this would be a bit of a mine field so I have always said no before. Only reason this one was tempting is it would be a post July booking and only 1/2 mile from my door. That said, I wont be doing it for him.

I always have seen this as a bit of a cheat. Basically the fit provider is looking at paying for no more that 3500 units at the <4kw rate per year. If everyone could stick on what they like and cap generation at 4.0kw during sunny times we would all have systems producing up to 5000+ units per year. This really would not sit well with ofgem, the fit provider and our beloved Barker. I think in the long run there are not enough people willing to throw cash around in court to make it stick however right they technically are. Which means it could get tricky for those willing to push the envelope on this.

To borrow a phrase from Dragons Den......Sorry but for that reason I'm out!

 

[Gary K]

Suggest he puts the 4kw of panels in his garden on a decent tracker and he will produce more than the fixed 5kw of panels!!!

 

[dimmer668]

eduction in performance on sunny days (panels drop in performance when hot, and having the "overload" power sent back from the inverter will overheat the panels even more



​

 

[Worcester]

From our studies a single tracker will add about 25% ... Double tracker about 35%

Of course on a tracker he'll need planning permission.

However using good old unistrut a single tracker is very easy to build, a commercial tracker will cost about the same as the extra kWp

 

[Gary K]

I would ground mount on individual mounts and get the wife to run out every hour and turn all the panels about 15 degrees to earn her keep -only during sunny weather though!
That would be about 3 days in the last 2 months.LOL

 

[Worcester]

Keeps her trim :53:

 

[SolarCity]

(panels drop in performance when hot, and having the "overload" power sent back from the inverter will overheat the panels even more - probably not helping the panel lifespan).

Is this possible? Surely there is no excess energy - just potential energy that isn't realised? Nothing will get sent back through the panels, will it?

Are you sure that Power One Inverters only have a warranty for strings of 2kWp each?

 

[Gavin A]

nope, you're fine upto 20% over the nominal rated string capacity as per their design tool.

 

[BruceB]

And on the power one data sheet I have, you can go to 2kW on each mppt on the 3.0kW inverter and 3kW per mppt on the 3.6 and 4.2kW inverters

 

[Gary K]

Keeps her trim :53:

Bonus - 2 FITS for the price of one

 

[FB.]

And on the power one data sheet I have, you can go to 2kW on each mppt on the 3.0kW inverter and 3kW per mppt on the 3.6 and 4.2kW inverters

Maybe the outdoor version, but not the indoor version? At least not the version I have.

 

[FB.]

Is this possible? Surely there is no excess energy - just potential energy that isn't realised? Nothing will get sent back through the panels, will it?

Are you sure that Power One Inverters only have a warranty for strings of 2kWp each?

If the electricity hasn't got anywhere to go, it will generate heat (resistance) and the panels/cables will get hotter than they normally would.

The indoor PVI 3.6 is limited to 3.75kW for a single string, or 2kW for each MPPT - according to the manual which came with mine.

Unless mine's an early version with different spec to the current models?

 

[SolarCity]

If the electricity hasn't got anywhere to go, it will generate heat (resistance) and the panels/cables will get hotter than they normally would.

Surely if it has nowhere to go, it goes nowhere? I could be wrong, but I've not seen it the way that you do.

 

[moggy1968]

without a flow of current it just sits there, as potential energy. Otherwise the whole grid would get hot if not enough electricity was being used.

 

[SolarCity]

Regarding power limits on inverters, I would have thought that voltage is the issue rather than power. I seem to remember an SMA rep claiming that only over-voltage could damage their inverters.

 

[solarfred]

Customer has insisted on 4.5kw as there are 2 strings on pitched roof and 1 string on flat roof using SMA4000TL. He is surrounded by trees which will affect the output at certain times hence the increase in panel numbers. Inverter limited to 3.68kw and supplier is EDF which have a form asking for TIC and DNC (Others just have "Installed Capacity")
What should he enter as the two figures now? The system cannot operate at 100% .

 

[FB.]

Surely if it has nowhere to go, it goes nowhere? I could be wrong, but I've not seen it the way that you do.

Energy of photons in sunlight are absorbed by the electrons in the solar cell.
Once the energy is in the electrons, they will move around the circuit and generate a flow of electricity.
If the energy in the electrons can't be vented-off as movement of the electrons through the system, then the energy must be ofloaded in some other form - heat, light, radiation, movement etc.
So if the solar panel can't move all the "energised" electrons, then those electrons will give up their absorbed energy to the solar panel as heat. This might not be noticed on an oversize array since the panels will be over-producing anyway, so there will still be "full power" flowing - but the panels will be working at a higher temperature and probably have a shortened lifespan due to more temperature fluctuation.

 

[FB.]

without a flow of current it just sits there, as potential energy. Otherwise the whole grid would get hot if not enough electricity was being used.

That would imply a solar panel acts like a battery; able to "store" energy.
It can't be stored; the energy absorbed from the photons in sunlight must be released almost instantly - as a flow of electricity or as heat.

 

[Gavin A]

sorry FB, but you're wrong on this.

The potential is there, but the excess is never converted to electricity in the first place, because the inverter draws the power from the panels at a less efficient voltage for the conversion process.

What excess energy there is will presumably either remain as light, or be converted directly to heat on the surface of the panel, but it won't be converted from light to electricity to heat.

 

[SolarCity]

FB, what about a panel which isn't connected? The photons will still hit the panel but no power is generated - the potential is there, but the power isn't.

 

[FB.]

FB, what about a panel which isn't connected? The photons will still hit the panel but no power is generated - the potential is there, but the power isn't.

It'll simply get hotter.

 

[FB.]

What excess energy there is will presumably either remain as light, or be converted directly to heat on the surface of the panel, but it won't be converted from light to electricity to heat.

The highlighted bit implies the panel will get hotter.
Which is what I was trying to say; if the sun's energy gathered by the panel can't be converted to electricity, it will become heat and the panel will get hotter than if it could send a flow of electrons around a circuit.

 

[PvNewbie]

To help answer SolarFred's question (as best I can). If you look at previous threads, TIC = DNC (effectively for PV). However, I've just filled in a Southern Electric FIT form and notice that their definition of TIC is number of panels * panel power (which to me is a redefinition) and DNC is 'what was entered on the MCS notification for DNC'. Which to me, would be 3.68kW. Why Southern Electric can't just ask for 'kWp of panels' instead of re-defining of TIC I don't know. There's underhand changes going on to the legal definitions and we need to keep a beady eye on the rules!

MCS help doc defines DNC as 'The declared net capacity should be entered in kilowatts (kW) and is the capacity of the system onceinstalled, taking into account any losses. It should be entered up to two decimal places only, withoutthe units for example 1.95. '

Is there not a help document with the form? On mine I had to answer TIC as the help document described it (panel power x number of panels) but felt like putting 'THIS IS INCORRECT AS THE LEGAL DEFINITION OF TIC.'

If you phone up and ask for help I bet you'll get a 'panel power x panels' answer. If not, perhaps you should go to the customer explain it to him and ask what he would like to put??

 

[solarfred]

Everyone has wasted a lot of time arguing around this pathetic situation. I know what I am going to suggest to the customer and it will be totally within the "current" definitions. What happens after that is none of my business. A system that is compromised by physical restrictions on available sunlight should not be further penalised by definitions of TIC just to suit various suppliers who are keen to restrict agreed payments via the FIT scheme.

 

[methley]

Energy of photons in sunlight are absorbed by the electrons in the solar cell.
Once the energy is in the electrons, they will move around the circuit and generate a flow of electricity.
If the energy in the electrons can't be vented-off as movement of the electrons through the system, then the energy must be ofloaded in some other form - heat, light, radiation, movement etc.
So if the solar panel can't move all the "energised" electrons, then those electrons will give up their absorbed energy to the solar panel as heat. This might not be noticed on an oversize array since the panels will be over-producing anyway, so there will still be "full power" flowing - but the panels will be working at a higher temperature and probably have a shortened lifespan due to more temperature fluctuation.

Eh? I think you need to go back to your physics books and understand the difference between energy and power.

A solar panel is basically a junction of p-type and n-type silicon. When the sun shines a free electron is generated in the n-type silicon and a corresponding "hole" in the p-type silicon. This process continues and builds up a potential across the panel. This is potential energy and can be measured at the panel terminals as the Voc value. No current is flowing at this stage and hence no work is being done and no power generated.

Only when the panel is connected to a load will current begin the flow and power be generated. This is what the tracker in your inverter does - it varies the load to extract the maximum power from your panel at any one time.

So as we now have current flow, this means power, and hence, heat will be generated across any resistive load in the system. An open circuit generates no current flow and hence no power, or heat, can be generated. Power is only expended when the energy does "work".

 

[moggy1968]

That would imply a solar panel acts like a battery; able to "store" energy.
It can't be stored; the energy absorbed from the photons in sunlight must be released almost instantly - as a flow of electricity or as heat.

I didn't say it was being stored, I said it is potential energy which is something altogether different.