gc100

4K, 6K or 8K ?

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So I'm getting towards the end of my build and I want to make a decision on how much solar/PV to install.

 

My quotes are:

4K   ~£1700

6K   ~£2500

8K   ~£3100

 

+ electricians time to install.

 

My main point for me is to consume 'green' energy vs saving money *I don't want to go in to the argument of either of those points!

 

Until I've lived there for 12 months I'm not going to know my consumption. However I want to buy now as part of the house build so I can get the VAT back. I have no idea really which on to go for. I don't want to go say for the 4 and then 12/24 months later add to this as I will need another inverter which is a significant part of the cost.

 

Anyone else had the same situation?

 

FYI it a 3 bed house, single story, 160m2 , vaulted ceilings throughout, reasonably airtight and insulated. 4 people, 2 working from home, ASHP,  MVHR - electric everything (not a car yet though!)

 

 

 

 

Edited by gc100

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Our Sap predicted 17 years to get the cost back

Although it was a planning condition We didn’t install on that basis 

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I am surprised it is so cheap.  Is that supply only?  Does it cover all materials?

 

As it is only single storey it may be fairly easy to add panels later, when they may become cheaper / more efficient, so could you go for the 4K and allow for later add-on?

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Do you consider a storage  battery? Our array is c.6K, and on a very good day we are up to 70% solar-powered-only, but on bad days (like this week) we are barely 4%. Normally any surplus in our circuit goes into our Tesla Powerwall, which then discharges into the house either during the night or at least half-day next day. Without storage we won't be that efficient.

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17 minutes ago, Mr Punter said:

I am surprised it is so cheap.  Is that supply only?  Does it cover all materials?

 

As it is only single storey it may be fairly easy to add panels later, when they may become cheaper / more efficient, so could you go for the 4K and allow for later add-on?

 

As per first post. Supply + electrician time to install (2 days max ~£400). Don't want to add later as you loose the price of the inverter.

 

15 minutes ago, Bored Shopper said:

Do you consider a storage  battery? Our array is c.6K, and on a very good day we are up to 70% solar-powered-only, but on bad days (like this week) we are barely 4%. Normally any surplus in our circuit goes into our Tesla Powerwall, which then discharges into the house either during the night or at least half-day next day. Without storage we won't be that efficient.

 

Yes but too expensive for me and I can't justify personally. I can 'loose' 3K in the cost of my build and have the good feeling of consuming some energy I generate. But an additional £10K is too much for me.

 

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If you are not interested in ROI and cannot put a value on your consuming home grown energy it is difficult to give an answer.  It probably depends how much money you have!

 

Can you not get a bigger inverter now and add panels later or is that not how it works?

 

If it were me I would buy the 8K as it is a small price to pay to feel smug and virtuous.

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Those are good prices, I struggled to beat those with a lot of hard searching.

 

First thing the decision may not be yours.  Anyone can install up to 3.68kW without prior apporval and then notify it to the DNO.  Above that you need their prior permission and that may come with a network upgrade cost.  So ask that question first, find out what you are allowed and what costs may be involved.

 

We have a typical 4kW array with the standard inverter limited to 3.68kW output.  I manage to self use about £250 worth of electricity each year with little going to waste export.  To ensure the self use we use all the big domestic appliances in the daytime and divert surplus to the immersion heater, which ends up with about 1/3 of what we generate.

 

If you go higher than 4kW it becomes much harder to self use it all, not least because you would need 2 immersion heaters and a big water tank to dump it all, so you would really want to be considering battery storage as well. 

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thanks ProDave. I have the official Ok from the DNO for up to 8K so thats all sorted.

 

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Is that for the panels inverter and all the mounting equipment ..?? What brand is the inverter ..?

 

8k is 28-30 panels depending on power output, there is no way one person can install that in 2 days with all the rails etc to install.  That’s the equivalent of 20 mins per panel to rig the roof, install and wire. 
 

Do you still have scaffold on the building ..? 
 

And have you got planning permission for panels ..? 

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What orientation is the elevation you intend on installing? And is there an option to split into two arrays?

 

I am DNO limited to 3.68kW and have an inverter to match but have 6.0kWp installed split 50/50 East West. This means, on a good day, I should max out the inverter for a much longer portion of the day and as @ProDave days 4kW is much easier to self consume than 8kW

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41 minutes ago, PeterW said:

Is that for the panels inverter and all the mounting equipment ..?? What brand is the inverter ..?

 

8k is 28-30 panels depending on power output, there is no way one person can install that in 2 days with all the rails etc to install.  That’s the equivalent of 20 mins per panel to rig the roof, install and wire. 
 

Do you still have scaffold on the building ..? 
 

And have you got planning permission for panels ..? 

 

Regarding install time. Yes I don't know exactly how long it would take, but I would probably put that panels up myself and just get the sparky to guide/do the electrics. I'll ask him how long but I'm sure he said a couple of days the first time we discussed (though that might of been a 4K in his head). I already have the cable and can get less expensive clams than on this quote.

The lower roof line is very low and easy to get (2.5m) to either by the hand yougman scaffold or just a simple ladder. Yes we have permission.

I feel no believes me so here's the 8K quote from the supplier.

 

Screen Shot 2020-11-03 at 20.32.31.png

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Let's ignore the logical approach and cost weighted arguments, sometimes I feel we can assess too much here rather than just following what feels good. 

 

If you have the cash...spunk on the 8k, if not get what you can. Save the planet a little,.it might not be economically viable but its an easy way to pay back the earth by doing your little bit.

 

By the way who is that quote from? 

Edited by SuperJohnG

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Can I ask where you got the quote from? I will eventually be in the market for maybe 54-60 panels of around the same wattage for our proposed passive house + build and its only going to happen if I can source the kit for really keen prices. I had previously been looking at panels by the pallet load from Bimble solar but those were quite a bit more I think than your quote of £74 per panel. Are these new standard size panels for that price? Thanks.

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13 hours ago, gc100 said:

Yes but too expensive for me and I can't justify personally. I can 'loose' 3K in the cost of my build and have the good feeling of consuming some energy I generate. But an additional £10K is too much for me.

 

Batteries should still reduce in price over coming years, and some systems allow you to buy small and incrementally increase capacity.

So for your goals, I'd do the 8K now and live with it a year or two and see how much juice you are exporting and make a call how much battery to get down the line (if any). Correction: this in not what I would do, it really is what I currently am doing.

 

Also: if the goal is planet saving it is immeterial if you're using the home grown PV electricity yourself or feeding it to the grid. Each additional kWh you generate is one less needing to come from gas. (Caveats abound)

Edited by joth
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Just curious but is there a typical  maximum you can install with just a single phase supply to the house? 

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2 hours ago, Temp said:

Just curious but is there a typical  maximum you can install with just a single phase supply to the house? 

 

I have 9.98 kWp on a single phase, which needed a different extra  procedure. Not sure whether it is a procedural or technical thing. IIRC the process is called G83. The installer did everything.

 

F

 

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4 hours ago, Temp said:

Just curious but is there a typical  maximum you can install with just a single phase supply to the house? 

That is up to what your DNO will allow, but lets suppose you are close to the substation, there is plenty of capacity in the local network and you have a normal supply with a 100A main fuse, then in theory you could install up to 23kVA.

 

They calculate on the basis that there will be times when you are using nothing in the house, so all that you generate gets exported and you cn't export more than your main fuse and cabling will support.

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I cannot really share the supplier due to discounts applied, but its a national trade electricial supplies company. There aren't that many! Just get your electrician to phone around.

 

I think I'll be going 8K as per Joth logic about getting a batteries down the road.

 

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