Triassic

Can you have too much PV

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I’m limited in how much I can export to the grid ( 3.8Kw ) -  fine, this can be achieved using settings in the inverter. So the plan is to install 4Kw’s worth of solar panel in the roof. However, could I install 5 or even 6Kw worth of panels?

 

What happens if I’m exporting to the 3.8Kw limit and NOT using any of the extra power being generated in the house? Am I going to blow something, a fuse, the panels, an immersion element? 

 

I never did understand electrikery.

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4 hours ago, Triassic said:

I’m limited in how much I can export to the grid ( 3.8Kw ) -  fine, this can be achieved using settings in the inverter. So the plan is to install 4Kw’s worth of solar panel in the roof. However, could I install 5 or even 6Kw worth of panels?

 

What happens if I’m exporting to the 3.8Kw limit and NOT using any of the extra power being generated in the house? Am I going to blow something, a fuse, the panels, an immersion element? 

 

I can't remember where I read it, but I believe the limitation is on panels, not inverter. You can't install more and limit with the inverter.

 

Putting up a bit more than you're allowed isn't likely to cause any problems to you or the grid. On sunny days, your voltage may be slightly higher, but not enough to cause any issues for your stuff. 

 

I don't know how likely it is that the network provider would even find out. However, I'd be looking closely at the fines for getting it wrong before going any further. You'll also find that installers will be all over this and are unlikely to install something that isn't allowable.

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We've kept it simple.

 

No FIT.

Part P electrician installation (used to be a solar fitter but stopped when the market was kicked out from under his feet.)

Focus on self-consumption.

If others benefit because we aren't consuming, tough (on us).

Watch the battery storage system price like a hawk - aim to store our PV production as soon as we can afford it.

 

ian

 

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Doesn't the local DNO have to 'approve' export levels once you hit a certain amount. Isn't there also a drop off point where for the FIT, it's not worth going over 4Kw unless you go a lot higher? I'm assuming people don't do it for the tariff rates these days anyway.

 

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3 minutes ago, PeterW said:

I’m sure @Nickfromwales had a link to an inverter that could hard limit the output to the grid

This is what I’m going to install. So I’m within the DNOs rules and The 3.8kw  export limit. It’s the excess generation I’m questioning, when I’ve hit the limit and not using any power within the home, what  happens to all those unused electrons? 

 

 

Edited by Triassic

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Nothing. The inverter will limit the current taken from the panels.

 

The panels will only transfer power if they are connected to a load. If the panels aren't connected to anything they will produce a voltage at their terminals, but if there is no load to take current they will produce no power. That's what the inverter will do, it will not take all the current that the panels are capable of delivering.

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1 hour ago, jack said:

I can't remember where I read it, but I believe the limitation is on panels, not inverter. You can't install more and limit with the inverter.

You're thinking of the FiT limit which is on the panels. The DNO should be happy with the inverter limit.

 

Double check the 3.8 kW though; that's 16 amps at 240 V (3840 W) whereas I thought that if you were limiting on power (rather than on current) they'd want you to keep to 16 amps at 230 V (3680 W). Not sure, though, and might even be different per DNO.

 

There likely will be an upper limit on the amount of panels you can have with the inverter, related to the short-circuit current in fault conditions, but it'll be quite a bit more than the nominal output. Worth checking though.

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2 hours ago, Triassic said:

What happens if I’m exporting to the 3.8Kw limit and NOT using any of the extra power being generated in the house? Am I going to blow something, a fuse, the panels, an immersion element? 

 

No, the inverter will just take less current from the panels so their voltage will rise. The inverter will always be able to withstand the full open-circuit voltage of the panels in any half-competently designed system so no harm will be done. The extra power will just be dissipated as heat in the panels, something like the panels being 14% efficient rather than 18% efficient so instead of 82% of the sunlight turning into heat it'll be 86%. Considering that the panels are quite safe in sunshine with nothing connected to the output so 100% of the sunlight becoming heat this isn't a problem. Yeah, OK, some of the sunlight is reflected.

 

Depending on how the system is configured you might not have the option to use extra power between 3.8 kW and a peak of, say, 5 kW in the house anyway. Normally inverter limiting will be on the output of the inverter itself. I'm a bit behind the times on this sort of thing so maybe there are inverters which have a current clamp on the meter tails which limits the house export but you'd need to check with the DNO that they're OK with that. Direct limiting totally within the inverter is quite robust but having a bit of wire trailing down to the meter tails is a bit more fragile and they frowned a bit on that, or used to.

 

The point of having more panels than the inverter can deal with is that most of the time the panels are not producing nominal power anyway. Even with a 3.8 kW inverter and 5 kW of panels you'll only be losing power for a few hours around midday on a few dozen summer days. Days you'll be producing lots of energy anyway so the loss doesn't really matter.

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I think the idea of having more panels than would be allowed for a "no DNO consent" installation, using the 16 A per phase limit in G83/2 is a good one, but what might be more useful would be if you had an inverter rated to deliver a higher current per phase, which would normally be one set to operate under G59/3, but an export current limiting capability that complied with the G83/2 16 A limit.

 

The advantage would be that you could self-consume more power, so if you were generating, say, 6 kW, then you could use 6 kW if you wished, with the export limiting function only kicking in once the house load drops.  Might be useful if using AC coupled battery storage, as you could have a potentially higher output from the inverter that would allow for battery charging and house consumption, whilst remaining OK as far as the DNO are concerned.

 

The snag would be the added complexity of measuring export and using that to control the inverter limiting.  I'm not sure if there is anything around that will do that at the moment.

 

The alternative for battery storage would be to opt for a DC coupled system, where the panels charge the batteries.  Not as straightforward to set up, in that there aren't many off-the-shelf systems that allow this, but in theory it could be more efficient (although I think in practice the battery charge management stuff may well not be that much more efficient than a decent inverter).

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On 13/09/2018 at 08:50, PeterW said:

I’m sure @Nickfromwales had a link to an inverter that could hard limit the output to the grid

Solar Edge ;)  

Fill the roof up and export only 3.8kW 👍

Remember you should use this to mitigate against costly uplift caused by mandatory DNO infrastructure improvements. Fit a solar edge and tell them to FO. 

Aside from that the SE inverter is also attractive because it uses dry capacitors and comes with a 12 year warranty. Happy days. 

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On 13/09/2018 at 13:07, Nickfromwales said:

Solar Edge ;)  

Fill the roof up and export only 3.8kW 👍

Remember you should use this to mitigate against costly uplift caused by mandatory DNO infrastructure improvements. Fit a solar edge and tell them to FO. 

Aside from that the SE inverter is also attractive because it uses dry capacitors and comes with a 12 year warranty. Happy days. 

Was it a DIY installation, where did you get your kit from?

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We have 5kw cut back to 3.8 (Or 3.68?) with a SMA sunnyboy inverter.

 

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I use a strategic partner to undertake my PV referrals. They supply and fit direct to the client. 

I did look at undertaking the install on a non MCS basis, but it still has to be registered and notified to the DNO with the equipment listed so for larger or more bespoke installs I just found it wasn’t worth ‘getting in the middle’ tbh. 

PM if you want details of the installers, but for DIY you’ll get all the answers right here. ;)

Ill post a link to the SE inverter ASAP. 

 

3 minutes ago, Alexphd1 said:

We have 5kw cut back to 3.8 (Or 3.68?) with a SMA sunnyboy inverter.

 

What’s the warranty like with the SB inverter please? 

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Not sure on warranty, I bought it 4 years ago in solar thermal bulk buy.

Edited by Alexphd1

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Do PV panels run hotter if you don't draw all the power they can deliver?

 

The law of conservation of energy suggests there must be an energy balance.  eg If the panels operate at a constant temperature then the power going in must equal that coming out. If you don't draw energy from them in the form of electricity it must come out as heat (unless they somehow become more reflective).

 

 

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I've 8.8kW panels limited to 5kW export via solaredge inverters and power optimisers. The max generation I've seen is 7.7kW i.e. the house was consuming at least 2.7kW and the rest was being dumped/sold to the grid. More panels and different orientations helps extend the useful working time of the panels over the day and the year. If I could I would move a couple of my panels from SW to NW to grab more of the summer setting sunshine and reduce my import further. Though it seems moving panels is not allowed under the MCS scheme.

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2 minutes ago, readiescards said:

I've 8.8kW panels limited to 5kW export via solaredge inverters and power optimisers. The max generation I've seen is 7.7kW i.e. the house was consuming at least 2.7kW and the rest was being dumped/sold to the grid. More panels and different orientations helps extend the useful working time of the panels over the day and the year. If I could I would move a couple of my panels from SW to NW to grab more of the summer setting sunshine and reduce my import further. Though it seems moving panels is not allowed under the MCS scheme.

Its a strange scheme tbh. If export is to the DNO, and the FiT is deemed from installation, as is, then the only thing that should happen if you move things around or add a couple more NW panels is the FiT stays the same and you export a little more to the DNO......So bloody what ?!?

Would adding panels afterwards see you getting more out of the government or do they use your total deemed 'revenue' as the benchmark for your payments? Another ill-thought-through sack-o-crap afaic. With a recognised export limiting device there should be no repercussions if you decide to 'beef up' or optimise your system later down the line. 

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If you move panels so your total generation suddenly jumps up, they may start asking questions thinking you have added panels.  Your FIT payment would go up and they would want to know why.

 

I'll bet they would not question it if your total generation went down.

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8 minutes ago, ProDave said:

If you move panels so your total generation suddenly jumps up, they may start asking questions thinking you have added panels.  Your FIT payment would go up and they would want to know why.

 

I'll bet they would not question it if your total generation went down.

 

I doubt they would notice as it’s a fully automated system. There are loads of factors that affect generation, and adding something like an optimiser to an existing MCS install could do the same, as could just trimming trees. 

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6 minutes ago, ProDave said:

If you move panels so your total generation suddenly jumps up, they may start asking questions thinking you have added panels.  Your FIT payment would go up and they would want to know why.

 

 

^^ this! But may = will. They know exactly how much you should be generating! 

 

 

 

 

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2 minutes ago, PeterW said:

 

I doubt they would notice as it’s a fully automated system. There are loads of factors that affect generation, and adding something like an optimiser to an existing MCS install could do the same, as could just trimming trees. 

 

 

If they think you are generating too much you get a letter saying they want to visit ... 

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27 minutes ago, newhome said:

If you move panels so your total generation suddenly jumps up, they may start asking questions thinking you have added panels.  Your FIT payment would go up and they would want to know why.

 

Tell them it’s global warming 😎

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