Forgive my ignorance.

[CotswoldDoItUpper]

Hello all, 

 

Please forgive my ignorance and mistakes herein, however I just can’t get my head around this PV stuff.

 

Were currently using about 220kwh (or kWh or whatever) of electricity per week (yes high) and will likely increase when we change our second car from ICE to an EV. 

 

We’re on a standard EDF tariff after our previous supplier went bust. No E7 or anything like that.

 

We have space for a ground mounted PV I think. What size should I be aiming for? I’m not fussed about FIT or anything like that, or storing excess in batteries/thermal store (unless anyone can show it’s a simple thing) but am Reasonably happy to install myself and get a sparky to connect/commission. 
 

The questions are ‘how big a rig’ would I need and roughly ballpark £ figures?

 

sorry if this has already been covered. I feel like I have scrambled egg between my ears!

[Temp]

I'd be looking at the biggest you can. Probably a 4kW array unless you already have a three phase supply to the house. That's about 16 x 250W panels taking 26sqm. 

 

I can't really comment on prices as I'm out of date but have seen DIY kits advertised for around £1500. More if you want installation. I think all the subsidised feed in tarrifs have ended replaced by some companies offering a feed in rate. I think it pays to use as much as you can yourself. Perhaps fit a kit that diverts excess generation to an immersion heater element if your DHW tank is below max temperature. Think some here have a battery.

[SteamyTea]

32 minutes ago, CotswoldDoItUpper said:

ground mounted PV

I seem to remember that anything over 9 m², which is under 2 kW_p, needs planning permission.  I may be wrong on that, rules change.

 

[tonyshouse]

I think roof mounted systems on houses can come under permitted development but anything else need planning permission 

[SteamyTea]

41 minutes ago, CotswoldDoItUpper said:

I feel like I have scrambled egg between my ears

Been like that all day.

 

Basically, 1 kW_p of installed capacity will generate 1000 kWh.year^-1.

A single module is about 1 m by 1.6 m, so an area of 1.6 m², and has a peak power of 330 W.

So 3 modules gets you close to 1 kW_p. 4.8 m².

These have to be set at at optimal angle, luckily PVGIS can sort this out for your location.

If you have ever driven past a large solar farm, you may have wondered why there are large gaps between the rows of modules.  This is to reduce shading when the sun is low in the sky.  Shading is a real killer for PV, you don't need much of a shadow on module to seriously reduce performance.  That is any shadow, it does not have to be contiguous.  So trees, shrub, hedges, houses garden furniture or flag poles can cause a problem.

This basically means that ground mounted takes up more surface area than roof mounted, so what may seem like a large area, may not allow that many modules on it.

Can you put some on your roof? 

[CotswoldDoItUpper]

@SteamyTea thanks for this breakdown. We live on the side of a south facing hill with a bit of a paddock to the rear (above) the house so hopefully they’ll be closer together because of this. 
 

my wife is adamant that we won’t have them on the house because of the aesthetic - it’s a Cotswold stone cottage built in 1801 so m almost inclined to agree with her.

 

so by my calculations I’ll need about 11kWp which will cover 48sqm and a DIY kit cost about £4500 (using @Temp’s guidance) + instalation. This would save me about £2000/year on electricity bills so be ‘making money’ in y3. 
 

is this right? We don’t have 3 phase electricity.

[ProDave]

The elephant in the room is for anything over 4kWp (actually 3.68kW limited by the inverter) you need prior permission from your DNO before you connect it, and there may be a fee to even apply, and there may be network upgrade costs to pay before you are allowed to connect that much.

 

This is why 4kWp is such a common size, it is the largest you can connect by right, without having to seek prior approval and you only notify the DNO after is has been connected.

 

If you have 3 phase, you can connect 4kWp per phase so up to 12kWp may be possible without prior approval.

 

Don't for one moment think PV will do all your needs.  It won't.  In the summer it will generate loads more than you can use very often, in the winter when you need most energy it will not produce enough.

 

We have a typical 4kWp system and manage to use almost all we generate and that is saving us about £300 per year, about 1/4 of our total electricity usage.  Even if we had 4 times as much PV it would not do all our needs as in summer it would generate way more thay we could ever use or store, and in winter it would still be only generatig a tiny fraction of our needs.

[Marvin]

4 minutes ago, ProDave said:

The elephant in the room is for anything over 4kWp (actually 3.68kW limited by the inverter) you need prior permission from your DNO before you connect it, and there may be a fee to even apply, and there may be network upgrade costs to pay before you are allowed to connect that much.

+1. It cost us £360.00 inc VAT for our distribution network operator (DNO) to confirm that the local electric system could handle the 6kW potential our system could produce.  Furthermore the DNO would not take into consideration a CT clamp limiting the system output. The maximum output was assumed to be the maximum of the Inverter. (These assumptions by our DNO may not be the same as your DNO). The response from the DNO took 2 months and they advised that they aimed to respond within 3 months.

 

 

 

[Marvin]

12 minutes ago, ProDave said:

Don't for one moment think PV will do all your needs.  It won't.  In the summer it will generate loads more than you can use very often, in the winter when you need most energy it will not produce enough.

+1. 

[CotswoldDoItUpper]

Thanks all, guess 4kW is what to aim for then and use it to mitigate costs rather then remove them.

 

The concept of this system seems very straightforward and guess would save about £800/year (21p/kWh)? Am I missing something? Is it too simple? Am I paying more for the privilege of simplicity?

 

https://www.roofgiant.com/flat-roofing-solar/plug-in-solar-4kw-4000w-diy-solar-power-kit-with-renusol-console-tubs-for-ground-or-flat-roof/

[ProDave]

38 minutes ago, CotswoldDoItUpper said:

Thanks all, guess 4kW is what to aim for then and use it to mitigate costs rather then remove them.

 

The concept of this system seems very straightforward and guess would save about £800/year (21p/kWh)? Am I missing something? Is it too simple? Am I paying more for the privilege of simplicity?

 

https://www.roofgiant.com/flat-roofing-solar/plug-in-solar-4kw-4000w-diy-solar-power-kit-with-renusol-console-tubs-for-ground-or-flat-roof/

You are paying for the privilege of someone sourcing all the bits and selling you a kit.  I put together s similar system by seeking out the very cheapest components individually for about £1500.  Not much over £2000 would be my target.

 

There are some astonishing claims of how much you might save on that website as well.  Even your estimate of £800 per year savings is optomistic.

 

My system is a little poorer due to a lot of shading and being a lot further north but I am self using in the region of £300 worth in a year.  I think you would be doing well if you saved £600 in a year.

 

As you have a paddock, could you not build a shelter for the horses with a nice south facing roof and mount the panels on there?  I believe the horse shelter would be permitted development.

[SteamyTea]

Why is your usage so high if you do not have an EV already?

[epsilonGreedy]

9 minutes ago, SteamyTea said:

Why is your usage so high if you do not have an EV already?

 

 

If the house and hotwater heating is electric then 220 kWh weekly is not so bad for this time of year.

[Marvin]

20 minutes ago, CotswoldDoItUpper said:

Thanks all, guess 4kW is what to aim for then and use it to mitigate costs rather then remove them.

 

The concept of this system seems very straightforward and guess would save about £800/year (21p/kWh)? Am I missing something? Is it too simple? Am I paying more for the privilege of simplicity?

 

https://www.roofgiant.com/flat-roofing-solar/plug-in-solar-4kw-4000w-diy-solar-power-kit-with-renusol-console-tubs-for-ground-or-flat-roof/

If you spend a little time using this tool it will help you to understand a lot more about what results you will achieve from your system:

 

https://re.jrc.ec.europa.eu/pvg_tools/en/tools.html

 

First thing to do is to scroll on the map all the way down to your property. The results will then be based on the solar gain at your position on the planet. Play around with the options and you see what happens. 

 

For a 4kW system in December, where I am, will produce about 3kWh a day on average.

[CotswoldDoItUpper]

@epsilonGreedy our heating is LPG, 

@SteamyTea we have 1 EV and 1 ICE, soon changing to 2 EV. 
@ProDave we don’t have horses…. Should we build a shelter ‘just in case’?

[ProDave]

Well I went for ground mount to at least get away from some of the shading by the trees.  It had to be raised off the ground so see over the bank behind us.  I chose an east / west split to try and get longer meaningful generation rather than peak generation (easier to self use).

 

Then when the mounting frame was up and the panels were on, it was a no brainer to enclose the sides and make the "Swiss chalet solar shed"

 

[Marvin]

 

https://www.planningportal.co.uk/info/200130/common_projects/51/solar_panels/3

amongst other rules for off building set-ups

 

• Only the first stand alone solar installation will be permitted development. Further installations will require planning permission.
• No part of the installation should be higher than four metres
• The installation should be at least 5m from the boundary of the property
• The size of the array should be no more that 9 square metres or 3m wide by 3m deep

Edited December 28, 2021 by Marvin

[epsilonGreedy]

1 hour ago, CotswoldDoItUpper said:

@epsilonGreedy our heating is LPG, 

 

 

Ok in that case @SteamyTearaises an interesting question. Where are these weekly 220 kWh going?

 

One kWh = 3 to 4 EV vehicle miles. So a typical monthly mileage would account for 30% of your mains electric consumption if most charging is at home. Above that how often is the tumble drier on or is it lots of long showers heated from an electric element?

 

How much PV do you need? I think that comes down to lifestyle, daily EV miles and can you charge up during peak day light PV hours. As others have said you will experience a deficit in winter and will struggle to consume PV in the summer from a large array. 

[SteamyTea]

2 hours ago, CotswoldDoItUpper said:

we don’t have horses…. Should we build a shelter ‘just in case

Yes, and design it to make full use of the PV modules on the roof.  Could make something really quite good and useful, and a place to put lots of batteries/heat store in to soak up some excess generation.  May even be able to 'split' a system so some is totally off grid, therefore keeping within the 16A per phase generation limit.

 

On my weekly trips up country, I stop for a coffee in the Cotswolds.

Edited December 28, 2021 by SteamyTea

[Adam2]

@CotswoldDoItUpper I'm also looking at PV, was putting it off as too long a RoI but with prices of energy going up seems to make more sense now. I was starting to look at sourcing parts etc like mentioned above but stumbled across this kit which looks good to me. It doesn't use micro-inverters so will not be great if you have shading but for me it looks alright as my roof is clear of shading so may go with this - well a variation on it to have an adjustable angle for the panels. In that kit the panels could include the Jinko 325W all black panels so 12 panels would get you a 3900kW setup. Looks OK to me as 2400 ex VAT I'm happy with an RoI - we also have an EV, both work at home, have an ASHP so will have plenty of ability to use day time generation.

 

[SteamyTea]

1 hour ago, Adam2 said:

we also have an EV, both work at home, have an ASHP so will have plenty of ability to use day time generation.

Plan it right and the BEV will easily suck all the juice out the modules.

All you have to do now is find a decent day rate, or accept that you may still need to charge the BEV at night (on E7) and just take the hit if the ASHP needs to heat DHW (lower CoP than space heating) during the day.

Edited January 3, 2022 by SteamyTea

[TonyT]

My EV charger has a selector switch on the side to limit current, it can be set to various lower current settings might be helpful in  situations like this

[CotswoldDoItUpper]

Silly question perhaps, but given that the cost of e7 is so much lower, would it be worth just buying some batteries, fully charging them on e7 and using that during the expensive times of the day? Wouldn’t that work out more effective then solar panels during the over production in the summer and under production in the winter?

[PeterW]

2 minutes ago, CotswoldDoItUpper said:

Silly question perhaps, but given that the cost of e7 is so much lower, would it be worth just buying some batteries, fully charging them on e7 and using that during the expensive times of the day? Wouldn’t that work out more effective then solar panels during the over production in the summer and under production in the winter?

Not really viable as the saving is about £1 /day and the payback is around 12-14 years 

[CotswoldDoItUpper]

Surely @Peter if I’m using 220kWh at 21p/kWh then my weekly cost is £46.20. If I used e7 at about 8p/kWh then my weekly cost would be £17.60 saving me £28.60/week. Nigh on £1500 a year. 
I’d need about a 35kWh battery I guess. Any idea how much they cost? Could prob get away with a 15-20kWh ish battery buy running appliances etc overnight.

Just thinking out loud! An option for people who don’t want/can’t have solar?