Grid connection limit?

EricMears

I agree with most of Zarch's points except this one:-

Zarch wrote: »

So if you already put in place 5kWh on the original install, then add say another 2kWh.... are you really going to use that extra 2kWh? You'd need a lot of appliances running at once to make use of 7kWh for example.

The difference between a 5kWp & a 7 kWp system isn't just that under peak conditions the bigger system might generate an extra 2kW. Under less favourable conditions when the 5kWp system might only generate around 1kW, the 7kWp system would offer almost an extra half kW.

Zarch

EricMears wrote: »

I agree with most of Zarch's points except this one:-


The difference between a 5kWp & a 7 kWp system isn't just that under peak conditions the bigger system might generate an extra 2kW. Under less favourable conditions when the 5kWp system might only generate around 1kW, the 7kWp system would offer almost an extra half kW.

Yep, fair point.... I was thinking about sunny days. You're right, it might help you out on less than favourable days. But you still wouldn't be getting paid for it!

pile-o-stone

Zarch wrote: »

Yep, fair point.... I was thinking about sunny days. You're right, it might help you out on less than favourable days. But you still wouldn't be getting paid for it!

You also don't get paid for export, but with the FiT & Export payments being so low these days, I'm not sure it'd make a huge difference.

pensionpawn

Hi Iotum,
My 7.12kW system is over both pitches of my E-W facing house. I was sized a 6kW inverter which did require DNO approval which fortunately sailed through without a hitch, or additional cost. I concur with the 80% estimate having seen a highest (brief, minutes) peak of around 5.8kWs. Please bear in mind that two aspects need to be managed by a two string inverter or by employing micro-optimisers, otherwise the maximum generation of each panel will be limited to the output of the lowest performing panel (think shading from trees, chimney etc...) in the string. As you elude to, the silver lining an E-W two array installation is an earlier ramp up / later ramp down at the expense of a flatter middle of the day. It also gives you more surface area affording better generation on mediocre days. 27th June this year was my best ever daily generation of 47.36kWhrs with 1kW at around 5:40am and 7:55pm and over 4kWs from around 10:05am to around 3:10pm, over 4.5kWs between 11:15am - 1:15pm!

pensionpawn

Regarding adding more panels to your system surely there's no fiscal penalty unless you exceed the next FiT threshold? When I had my 7.12kWs installed I knew that I would be in the >4kW to 10kW FiT band and although I presently have no reason to add extra panels I had always assumed that I could throw additional panels on (and receive increased FiT) as long as I didn't exceed the 10kW limit? I have a neighbour who only has a ~3.2kW system because of legacy solar thermal water taking up roof space. He would much rather dispense with the solar thermal and install additional panels up to the 4kW limit however he is also unsure on how that could impact his existing FiT agreement, which he doesn't want to risk at ~ 55p / kWhr!

Martyn1981

pensionpawn wrote: »

Regarding adding more panels to your system surely there's no fiscal penalty unless you exceed the next FiT threshold? When I had my 7.12kWs installed I knew that I would be in the >4kW to 10kW FiT band and although I presently have no reason to add extra panels I had always assumed that I could throw additional panels on (and receive increased FiT) as long as I didn't exceed the 10kW limit? I have a neighbour who only has a ~3.2kW system because of legacy solar thermal water taking up roof space. He would much rather dispense with the solar thermal and install additional panels up to the 4kW limit however he is also unsure on how that could impact his existing FiT agreement, which he doesn't want to risk at ~ 55p / kWhr!

Hiya. the 2016 changes to the FiT scheme mean that extensions no longer qualify, so you get nowt for them, but they won't affect your existing contract.

pile-o-stone

Martyn1981 wrote: »

Hiya. the 2016 changes to the FiT scheme mean that extensions no longer qualify, so you get nowt for them, but they won't affect your existing contract.

To add.. You just have the new panels connected to their own inverter which must not be connected to your existing solar meter.

You don't need a meter on the new panels but you can fit one if you want to keep track of your generation. Just make sure you don't confuse which meter you're using to record your FiT generation.

Having to fit two inverters and not being able to claim for FiT and export for the extension is a big incentive to have everything fitted in one go. However, if like me you couldn't afford it, then doing it piecemeal is better than nothing.

reddragon66

I have a 6.75kW PV system linked to a 6kW inverter. I needed DNO permission which the installer said would be 6kW.

I have an EV charged via a Zappi charger so can use that energy. I also got a low wattage 1kW kettle to capture the free power when cloudy.

It is peaking at 6.3kw output.

Why stick to a 3.68kw limit?

jcontest

reddragon66 wrote: »

I have a 6.75kW PV system linked to a 6kW inverter. I needed DNO permission which the installer said would be 6kW.

I have an EV charged via a Zappi charger so can use that energy. I also got a low wattage 1kW kettle to capture the free power when cloudy.

It is peaking at 6.3kw output.

Why stick to a 3.68kw limit?

There has to be a line somewhere. Some older homes cant even cope with >16a input, so it may just be a way of forcing the proper checks to be done. The limit is also per phase, so really you could get more like 12kw worth of solar pv with the inverter rate limiter probably never going over the trigger.


The better solution today is probably to use a battery system and export nothing. Payback on a battery system will be about 7/8~ years for LiNiMnCo (NMC) Batteries (Tesla Powerwall), and for LiFePO4 (LFP) Batteries you should probably expect payback to take like 15/16 years. NMC will last probably half as long as LFP but one thing I am unsure of is how long the chargers and inverters will last in those systems, so there could be extra unexpected cost.


The FIT ends at the end of this month for all new installs, so I would think battery systems will be the way to go, there's a lot of numbers to churn to say if it's good or bad, and I doubt many people have the tools at hand to fully see if it's worth while.



Not feeding excess power back also allows you to keep your lights on when the national grid goes down. I have lived in the UK for ~20 years and have only seen my power go out once, but I know a lot of people who work in the power sector who are really worried that it's not a matter of if or when, just a matter of how many whens once it starts, and they rekon it could be soon.

zeupater

jcontest wrote: »

.... Payback on a battery system will be about 7/8~ years for LiNiMnCo (NMC) Batteries (Tesla Powerwall), and for LiFePO4 (LFP) Batteries you should probably expect payback to take like 15/16 years. NMC will last probably half as long as LFP but one thing I am unsure of is how long the chargers and inverters will last in those systems, so there could be extra unexpected cost ...

Hi

Whatever the payback period would be stated to be for any individual site would depend on the combination of site energy consumption -AND- the installed capacity & performance of the solar PV system -AND- the installed capacity, charge & discharge specification/capabilities as well as round-trip losses etc of a battery storage solution -AND- the energy management system employed to control the system. -AND- whether the battery also utilises cheap rate grid energy to supplement charging -AND- utilising the most appropriate energy tariffs at any applicable import requirement (As demand changes, the effect on average unit rates will also so this must be modelled & allowed for!)

For a typical UK household with statistically average energy requirements, it is unlikely that the 7/8 payback period for a Powerwall2 system could be supported as being correct unless the sizing model is totally flawed! ... 15/16 years may be possible with some lower priced systems (£/kWh storage) with reasonable charge & discharge capabilities when capacity is well matched to a requirement sweet-spot and site demand is atypically high.

The ultimate decision crunch is simple ... if consumers want to install a solar PV battery storage system on purely environmental grounds then that's really a decision based on personal morals, however, until prices (£/kWp) of suitably sized systems fall significantly below where they currently are, householders with anything like average electricity consumption should expect any domestic battery system to be unviable on financial return grounds.

Additionally, those looking towards 'grid-share' type schemes & supply packages to assist with battery storage financial justification should really attempt to understand how the scheme may adversely impact on the ability of a system (that they are financing) to meet their own demand as & when required .... the expression 'robbing Peter to pay Paul' may be something to consider when number crunching ...


HTH
Z