Sizing up 6k Solar PV, am I on the right track?

[magutosh]

Hi girls and guys,

 

I'm sizing and pricing up solar pv for our new build, came across an mcs installer that happy for us to source our own panels. 

 

We try to maximise half of our roof for a 6k system, since electricity will be our sole energy source in the future, which powers ashp, appliances, electric vehicle and possibly a storage battery.

 

Previously we've been quoted 4k system which I wasn't keen on based on our potential usage (4 bed house with electric car), then I found out the reason they all quote 4k system so they don't need to deal with DNO (lazy buggers!), I thought being certified they'd help you size up panel according to demand, clearly not!

 

If we can source panels without markup, it would make sense to increase the size at material cost, with hope it would generate enough for our own consumption, also a good amount to export back to the grid. 

 

What would be your approach given a similar circumstance? 

 

Regards

Dominic (Stockport, Northwest)

[A_L]

Assuming you are referring to a 6kWp system, occupying about 40m²  of roof, it will generate an average of about 4.5kWh/day in December with many zero days. Total over year will be around 5100kWh.

Why do you want a MCS installer? It is only useful for paying you for export which you may have very little of and will come at a significant premium.

 

Edit:- Production will be about 4.5kWh per kWp per month in December!

Edited December 4, 2020 by A_L
To correct big whoopsie!

[Nickfromwales]

16 minutes ago, magutosh said:

with hope it would generate enough for our own consumption, also a good amount to export back to the grid. 

You want to export little or nothing back to the grid  .

Consider not getting the battery system as you’ll own a very very big battery on wheels if you have or buy an EV. 6kWp array will deffo not be big enough to satisfy that lot, and you’d have to strategically utilise the PV to maximise the benefits. 
Has your MCS installer done a survey and generated numbers yet? If not, you need to do that eg before considering anything. 

[Nickfromwales]

Just now, A_L said:

Assuming you are referring to a 6kWp system, occupying about 40m²  of roof, it will generate an average of about 4.5kWh/day in December with many zero days. Total over year will be around 5100kWh.

Why do you want a MCS installer? It is only useful for paying you for export which you may have very little of and will come at a significant premium.

Prob a lot less than 4.5 in winter!!

[A_L]

@Nickfromwales Agreed!!!!!! - To early in the morning for me! I meant 4.5kWh/kWp  per  month (of December)

Edited December 4, 2020 by A_L

[SteamyTea]

29 minutes ago, magutosh said:

came across an mcs installer that happy for us to source our own panels. 

 

That is interesting as it used to be the case that customers could not supply own modules, inverters yes, but not the modules.

Worth checking on the MCS site about that.

[ProDave]

I don't want to sound like a part pooper, but there is no way a 6kWp solar PV system is going to provide all your energy needs.  It will make a dent in your bills but do not kid yourself you will be anywhere near self sufficient.

 

Absolutely no point in MCS.  Just you or your roofer fit the panels and get any competent electrician to connect them.

 

The DNO notification thing is not just a case of being "lazy"  Up to an output of 3.68kW you can fit the panels and notify the DNO and they have no choice but accept it.  Above that you have to get prior permission from the DNO and they might or might not make a charge for network upgrades.  I asked the question of SSE where we are and I never got as far as requesting a quote as they made it clear there would be a charge.  Solar PV without any FIT payments is marginally viable if you just have to buy the kit and connect it.  If there was an additional DNO upgrade charge, that would almost certainly imho make in not worthwhile, which is why I stuck at 3.68kW

[magutosh]

19 minutes ago, A_L said:

Assuming you are referring to a 6kWp system, occupying about 40m²  of roof, it will generate an average of about 4.5kWh/day in December with many zero days. Total over year will be around 5100kWh.

Why do you want a MCS installer? It is only useful for paying you for export which you may have very little of and will come at a significant premium.

 

Edit:- Production will be about 4.5kWh per kWp per month in December!

I've not yet found anyone installs solar pv who's not mcs certified, I was told without mcs certified, it would be a nightmare if I were to sell the house in the future?

Edited December 4, 2020 by magutosh

[SteamyTea]

2 minutes ago, magutosh said:

I was told without mcs certified, it would be a nightmare if I were to sell the house in the future

Was that buy a MCS installer, or a solicitor?

[magutosh]

5 minutes ago, ProDave said:

I don't want to sound like a part pooper, but there is no way a 6kWp solar PV system is going to provide all your energy needs.  It will make a dent in your bills but do not kid yourself you will be anywhere near self sufficient.

 

Absolutely no point in MCS.  Just you or your roofer fit the panels and get any competent electrician to connect them.

 

The DNO notification thing is not just a case of being "lazy"  Up to an output of 3.68kW you can fit the panels and notify the DNO and they have no choice but accept it.  Above that you have to get prior permission from the DNO and they might or might not make a charge for network upgrades.  I asked the question of SSE where we are and I never got as far as requesting a quote as they made it clear there would be a charge.  Solar PV without any FIT payments is marginally viable if you just have to buy the kit and connect it.  If there was an additional DNO upgrade charge, that would almost certainly imho make in not worthwhile, which is why I stuck at 3.68kW

 

Thank you for that.

 

I actively explored non MCS installer option with little success, along the line someone mentioned that I could not sell the house with solar panels if they weren't installed by MCS certified installers? Was that a bluff? 

[magutosh]

1 minute ago, SteamyTea said:

Was that buy a MCS installer, or a solicitor?

 

I think it was by a builder actually who's considering putting solar pv on his roof, but I haven't verified that yet.

 

Either way, by separating material and labour, it became instantly a cost saving approach comparing to other quotes. If the difference isn't substantial, I would probably go down the MCS route.

 

I'm hoping summer time would somehow compensate with dismal winter days.

[magutosh]

26 minutes ago, Nickfromwales said:

You want to export little or nothing back to the grid  .

Consider not getting the battery system as you’ll own a very very big battery on wheels if you have or buy an EV. 6kWp array will deffo not be big enough to satisfy that lot, and you’d have to strategically utilise the PV to maximise the benefits. 
Has your MCS installer done a survey and generated numbers yet? If not, you need to do that eg before considering anything. 

 

Not a survey, but he did send me case studies and some figures that I"m going through now. Other quotes have included a performance report, but they seem to support what they quoted for, rather than an impartial. 

[ProDave]

If it is an on, or in roof system then you might have issues from a grumpy buyers solicitor about roof loading etc.  But that is usually an issue with retro fit systems to old houses not designed for solar pv on their roofs.

 

Yours is a new house with the PV fitted at the time of build and the PV will be there when BC issue the completion certificate so I cannot see an issue at sale time, just refer them to the BC completion and state no alterations have been done since then.

 

Out of interest what is the MCS installer quoting to install panels that you supply?

 

Any competent electrician should be able to connect them. That is where you need to be looking for quotes. How about the electrician that will be wiring the house?

[magutosh]

7 minutes ago, ProDave said:

If it is an on, or in roof system then you might have issues from a grumpy buyers solicitor about roof loading etc.  But that is usually an issue with retro fit systems to old houses not designed for solar pv on their roofs.

 

Yours is a new house with the PV fitted at the time of build and the PV will be there when BC issue the completion certificate so I cannot see an issue at sale time, just refer them to the BC completion and state no alterations have been done since then.

 

Out of interest what is the MCS installer quoting to install panels that you supply?

 

Any competent electrician should be able to connect them. That is where you need to be looking for quotes. How about the electrician that will be wiring the house?

 

We got quoted £1800 to install solar pv and storage battery.

 

Out of all the electricians we asked, none of them would touch solar pv, but all of them say they use someone else just for that.

 

I did some reading just now, there doesn't seem to be a consensus on the MCS certificate, though every article mentioned it when it comes to lender concerns, seems to me the main focus is on if the panels are leased or owned outright.

[ProDave]

The only issues I have heard of with PV and house sales are "rent a roof" schemes, and concerns over the roof integrity.  You will have neither of these issues.

[Nickfromwales]

Big question is then over warranty issues with a Tom, Dick & Harry installation. 
Panels are usually warranties for 25 years but you have to get the agent up there eg provide scaffolding etc ( which needs to be put up by a certified scaffolder with all tickets in place ) and then if the installer is at fault then you have to pay that agents fees plus the required repairs

 

If you’re a self employed / qualified trade with building and electrical competency then crack on, if not think twice.  

[markharro]

We are hoping to put about  a 18kWp array on our PH+ ultimately. We are in Edinburgh. I am assuming that even with a battery and EV and working from home to soak up generation in summer that will still leave an excess at peak times which ideally we would want to export to grid. The consultant I have asked basically says that we either restrict output to the 3.68kW max without permission or pay £600-800 to the DNO for them to consider and they MIGHT allow more export either with or without cost to upgrade their equipment. Who in their right mind would gamble this amount of cash for a possibility when the whole enterprise is so marginal with the economics in the first place. Surely the DNO should be forced to assess for free so householders don't run the risk of throwing a significant amount of case down the drain. 

On a connected point I have never really understood the consequences of fitting such a large array and then throttling its export. Does this throttling just reduce the export or does it also reduce the total that you could otherwise self-consume?

 

thanks

[Pocster]

3 hours ago, Nickfromwales said:

If you’re a self employed / qualified trade with building and electrical competency then crack on, if not think twice.  

That's me!

[A_L]

1 hour ago, markharro said:

or pay £600-800 to the DNO for them to consider and they MIGHT allow more export either with or without cost to upgrade their equipment.

 

I would ask Scottish Power how much they would allow you to export without grid reinforcement and see how far you get without paying up. You can only  try.

 

Attached is pdf of how SP handle things, although it is fairly standard.

 

1 hour ago, markharro said:

Does this throttling just reduce the export or does it also reduce the total that you could otherwise self-consume?

 

All on site consumption is satisfied first, the inverter changes its electrical characteristics to reduce the output to just meet the onsite consumption + export limit if there is actually more potential available.

 

It might be an idea to see if you can get a three phase supply, then you can get three times the export.

 

Finally I think you should contact Home Energy Scotland, (actually the Energy Saving Trust) on 0808 808 2282 an see if they have a Renewables Officer with experience of this situation

ESDD-01-008.pdf

[markharro]

Thanks AL I think I understand this but for the avoidance of doubt lets say its a blue sky June morning and I hook up an EV with a drained battery and we have the useual household load as well.  Assuming say a a spare capacity of 70 kWh in the car's battery to charge will we get the full benefit from a 18kWp array in charging without any throttling with the standard export limit. My understanding from what you write is that we will and that its only after the car and house batteries are full and generation starts to exceed our background house demand that we will have the inverter restriction kick in.  So in essence the only financial loss to us is in a lower potential export income? The greater loss to the planet of course being that available energy for export is lost? 

[ProDave]

How about splitting the system.

 

3.68kW grid tied just plain and simple.

 

The rest completely off grid charging a battery system.  Obviously the loads that drives are all on a separate off grid electrical system but could feed your EV chargers and other high loads.

 

You would need a changeover switch to power up the off grid circuits from the grid in the event of prolonged poor sunlight and running out of power.

 

If you are talking of a 14kWp off grid system it might be worthwhile, but you would have to cost it properly to make sure your "free" electricity is not costing you more than what you can import.

[markharro]

Thanks Dave but this is just adding to my confusion at the moment. Can you comment on the basic points I have enquired about so I can understand if I am on the right track with those? Thanks

[Nickfromwales]

27 minutes ago, markharro said:

Thanks Dave but this is just adding to my confusion at the moment. Can you comment on the basic points I have enquired about so I can understand if I am on the right track with those? Thanks

What is the size of the inverter and what is its maximum throughput? Without that info there can be no answer yet  

[markharro]

We don't even have planning yet so don't have that level of detail. What I do know is that our shading is likely to be 25% so we are thinking to use a Solar edge inverter along with their optimisers. Don't we just need an inverter rated to deal with the maximum the panels will produce at full capacity but that is also capable of the grid throttling?

[Nickfromwales]

It’s hard to find a reliable / robust inverter over 10kW as you’re then up at around 50a. For 18kW you’ll need to go 3-phase with a 3-phase inverter. 
18kW is academic until you’re told you can fit an array that size......so cart is waaaaay in front of the horse atm. 
 

1 hour ago, markharro said:

Can you comment on the basic points I have enquired about so I can understand if I am on the right track with those? Thanks

You can self consume everything that the inverter throws out. 
“Export limitation” is exactly what it says it is ?. 

Get 3-phase connection is the bottom line. AFTER you get permission to install / fully utilise it that is  

Edited December 6, 2020 by Nickfromwales