How best to expand an existing PV system?

[richard_scotland]

Context

We live in one of the sunnier parts of Scotland (east fife).

Our overall electric use is high:

We have ASHP (uses about 7000 kwh a year for heating and DHW - its an old cottage), 1 electric car (possible we may get another one within 2 years), family of 5 so relatively high overall other domestic usage (washing machine, cooking etc), totals around 14-15000 kwh a year? Zappi car charger.

3.6 kw Grid connected system (Solis 3.6 hybrid invertor), connected to 4 kw of Viridian in-roof solar panels, about 2.5 years old now. 

 

Invertor is located in the loft, with access through a standard loft hatch. No batteries.

 

System generates about 3800 kwh a year, we use about 2700 kwh of that generation. 

 

We have a smart meter but it does not get signal (located in middle of house), so presently cannot access TOU tariffs, so everything is on standard rates and as much as I’d love to change that, we might be stuck with a non-functioning smart meter. 

 

Roof is directly south facing about 45 deg slope, easy access as its single story, mostly unshaded apart from in the depths of winter when it gets a bit of shade from tree branches. 

 

Room for around 5 or maybe 6 kw more panels on the roof, all on the same orientation.

 

What’s the best strategy for expanding this system? My gut feeling is better to get more generation than batteries, as the most batteries could save is ~ 1000 kwh a year without TOU tariffs. Whereas we would surely be able to use more extra generation than that. 

 

Do we replace our relatively new invertor with a bigger one (e.g. 6 kw connected to 8kw of panels), or simply add another 3.6 kw invertor? Any ideas welcome.  

[SteamyTea]

You can get E7 without a working smart meter.

Then you can do the heavy work during the night, and rely on the PV generation, plus some high price import  during the day.

 

Does your ASHP heat a concrete slab (a storage heater), if not, then the savings may not be worth it.

[richard_scotland]

4 minutes ago, SteamyTea said:

You can get E7 without a working smart meter.

Then you can do the heavy work during the night, and rely on the PV generation, plus some high price import  during the day.

 

Does your ASHP heat a concrete slab (a storage heater), if not, then the savings may not be worth it.

ASHP runs with radiators. I thought E7 was being phased out? 

[SteamyTea]

15 minutes ago, richard_scotland said:

I thought E7 was being phased out? 

I think with 7 million houses using, it is going to be a tong time till it goes.

[Dillsue]

If you want to go above 3.68kw potential export to the grid, you need permission from your DNO so you probably want to speak to them to see what they'll allow. Without knowing what they'll allow you'll be guessing at how you should expand.

 

The other thing to consider is if you're going to have circa 9kw of panels all facing the same way you'll end up with a peak of generation over a relatively short period of time. It might take a bit of effort to use much of that without being able to pack that into batteries.

[richard_scotland]

1 hour ago, Dillsue said:

f you want to go above 3.68kw potential export to the grid, you need permission from your DNO so you probably want to speak to them to see what they'll allow. Without knowing what they'll allow you'll be guessing at how you should expand.

 

That sounds like a good idea - are they happy for you to chat to them to see whats possible?

 

1 hour ago, Dillsue said:

The other thing to consider is if you're going to have circa 9kw of panels all facing the same way you'll end up with a peak of generation over a relatively short period of time. It might take a bit of effort to use much of that without being able to pack that into batteries.

Yes thats true, but I guess it would only be for a few months of the year? I wouldn't be adverse to getting batteries, but I think the economics of them is poor when you can't charge them cheaply in winter. 

[Dillsue]

25 minutes ago, richard_scotland said:

That sounds like a good idea - are they happy for you to chat to them to see whats possible?

 

Yes thats true, but I guess it would only be for a few months of the year? I wouldn't be adverse to getting batteries, but I think the economics of them is poor when you can't charge them cheaply in winter. 

My DNO was fine discussing things and over a couple of days we verbally agreed the limit I then formally applied for.

 

PVGIS will give you hourly forecast generation so you can get a good idea how much you'll generate, for how long and at what time. I suspect you'll be generating a fair wack for quite a few months but only you can guess at how much you'd be able to use

[richard_scotland]

On 24/10/2024 at 20:15, Dillsue said:

PVGIS will give you hourly forecast generation so you can get a good idea how much you'll generate, for how long and at what time. I suspect you'll be generating a fair wack for quite a few months but only you can guess at how much you'd be able to use

i will have a look at this. We have an 11Kv line with a transformer on within 10 m of the house and that line only supplies 4 houses, I don't know if this is a sign there is likely to be extra capacity in the system?

 

I guess the other option is to just get a few more panels and run them on the existing inverter. 

[Dillsue]

We're at the end of a 1/2 mile long 11kv supply with a dozen or so properties including a couple of farms but I've no idea if that means we got export consent automatically. 

 

You can build as big a system as you want if you implement export limitation. That way you can use all the power your system generates but your inverter will throttle its output to limit export to whatever your DNO allows, if you're not using the power

[frankmcs65]

Hi Richard,haveing lived in Scotland,Peterhead for a short time myself,may I say hello to a lovely side of the country.....

Having to cope with a rather heavy need of energy is always a challenging thing...adding usage is even more,while the goal would be reducing energy needs.Imho you have got three options: You try to add panels and storage,where ever you can,maybe you could build a support construction around or on sime sides of the house to have some bifacial's near ground,for ex. east/south or east/west, to cover longer hours of harvest.The second option would be a hybrid system with any other energy producer like wind or water.....The third option and maybe the most interesting and economic way,would be to get together with some neigbours and have a storage system installed which serves all.In this case you could concentrate on producing....and harvesting🤑Best regards Frank

[richard_scotland]

thanks all for the responses and @frankmcs65 for the interesting ideas.

 

Wondering about an alternative approach. The electric pole which is 5 m away from the house has 3 phases to it and a transformer on it. Our single phase supply is limited to 60A (due to size of cable apparently) and the cable goes under the slab to the middle of the house (the house was renovated in the early 90s). The fact we have a 12 kW heat pump, a car charger, induction hob + oven and everything else all on this 60A supply already makes me a bit nervous. We will likely go from one to two EV cars within a year or so, so the charger will get used several nights per week. 

 

Is there any merit in seeing how much it might be to have 3 phase installed to a new external meter box? as the pole is so close you hope the cost might not be too terrible...

 

This might mean any new meter works as a smart meter, as its no longer surrounded by thick solid walls, allowing us to access TOU tariffs.  From there we could connect up to the existing consumer boards internally? It used to be two cottages, so there are already two consumer boards, they could have a phase each and then the EV charger could be on its own phase? And doing this I would automatically get all the the extra PV export capacity I could want or use. 

 

An additional factor is that its reasonably likely we would want to build an accommodation annex in our garden at some point in the next few years - one of our children is disabled and has complex needs so ideally we will like to have additional accommodation for carers or helpers on site. That would be an additional load on our electric supply (heating, hot water, some basic cooking facilities etc) - so this might be another aspect pushing me towards looking into 3PH

 

Obviously how sensible this is depends on how much the 3PH upgrade might be and if any of the above plan actually makes sense!

[Dillsue]

There's no harm in asking for costs to upgrade either to 3 phase or 100A single phase, if that would work.

 

Has your transformer got 3 phase coming to it? Ours only has 2 phases at 11kv so if we wanted 3 phase there'd be quite a bit of work adding the third phase

 

Maybe worth checking that all the wiring from each consumer unit is separate from the other if you're going to put them on separate phases......you don't want any connections with 400volt in the house!

Edited November 13 by Dillsue

[richard_scotland]

This is the pole nearest to the house - it serves 4 properties. 

 

 

[Dillsue]

That's a 3 phase HV supply so you've got a 3 phase transformer....you can see the 3 isolation switches on the pole below the transformer. Shouldn't be crazy expensive to give you a 3 phase supply if you wanted, but..

 

With the electrification of the country there's going to be lots of distribution upgrades required and if the transformers been there a while it may not be up to supplying 4 houses with EVs, HPs etc. . If that's the case your DNO may upgrade it for free and give you a 100A supply. When we asked to double our PV export our DNO found our transformer wasn't adequate for a modern supply and replaced it free of charge together with refurbishment of all the poles and cabling around us.

 

If you initiate an enquiry and request a supply upgrade/ PV export you may find the same principle applies, particularly if the transformer is old and rated for electric demand from decades ago. If any of your neighbours are planning increasing demand then share that with your DNO

[SteamyTea]

16 minutes ago, richard_scotland said:

This is the pole nearest to the house

Looks the the one outside my house.

 

As you have a disabled child, see if you are on a priority list, or if any grants are available.

[richard_scotland]

On 13/11/2024 at 07:19, Dillsue said:

There's no harm in asking for costs to upgrade either to 3 phase or 100A single phase, if that would work.

I will get in touch my DNO and see what they say.