Help with solar pv

[Mike_scotland]

5 minutes ago, SteamyTea said:

Yes.

 

The thing to remember is that you need to stop cold, outside air, blowing across/through the insulation.

If air flows across/through insulation, it is the same as having a greater wall area to loose energy through.

 

im not sure what it is, i thought plywood was not waterproof but OSB was hmmm ill need check with my builder this evening for clarity.

[BMcN]

5 minutes ago, Mike_scotland said:

 

im not sure what it is, i thought plywood was not waterproof but OSB was hmmm ill need check with my builder this evening for clarity.

 

 

I would expect your kit will be sheeted in 9mm OSB to provide racking strength and then covered in a breather membrane.

 

Also I would let your installer/manufacturer spec the size of the ASHP.  Mine is a similar spec and size to what you have suggested and I have a 10kw ASHP with 300L tank.

 

[SteamyTea]

5 minutes ago, BMcN said:

Also I would let your installer/manufacturer spec the size of the ASHP. 

Trouble with that is that there is not a huge knowledge base in the plumbing trade.

Many installers are the same people that jumped on the PV installation a decade ago.

 

The big difference between a thermal boiler and a HP is that efficiency is best when the HP is running below its maximum performance. This us why they are oversized. This us not the same as fitting a more powerful combi boiler. They are sized for DHW needs.

[jack]

4 hours ago, ProDave said:

In the present climate I doubt that will be available much longer. I just paused from switching to it as I suspect it won't be around much longer.

 

Probably true, although electricity is undoubtedly cheaper during off peak hours, so it may just be that the rate increases a bit. E7 and E10 tariffs are still going despite rises in the cost of electricity over the years.

[Mike_scotland]

26 minutes ago, BMcN said:

 

 

I would expect your kit will be sheeted in 9mm OSB to provide racking strength and then covered in a breather membrane.

 

Also I would let your installer/manufacturer spec the size of the ASHP.  Mine is a similar spec and size to what you have suggested and I have a 10kw ASHP with 300L tank.

 

i will try get some pictures this evening, but im pretty sure now i think about it its not OSB so likely plywood or similar

 

is this ok, in the groups opinion ?

[Mike_scotland]

20 minutes ago, SteamyTea said:

Trouble with that is that there is not a huge knowledge base in the plumbing trade.

Many installers are the same people that jumped on the PV installation a decade ago.

 

The big difference between a thermal boiler and a HP is that efficiency is best when the HP is running below its maximum performance. This us why they are oversized. This us not the same as fitting a more powerful combi boiler. They are sized for DHW needs.

the company owner i think is a plumber to trade and there also MCS registered (Probably does not mean f all lol ) but he has sized it at i think 12 or 14kw ashp and 300l tank.  i do remember him saying to me he over specs so its not running close to its limits. (something along the lines of that)

[SteamyTea]

1 minute ago, Mike_scotland said:

is this ok, in the groups opinion

If it is the correct grade, then yes.

[Mike_scotland]

2 minutes ago, SteamyTea said:

If it is the correct grade, then yes.

 

ok thanks SteamyTea, i imagine it would be as the builder is good and came highly recommended.

[BMcN]

27 minutes ago, SteamyTea said:

Trouble with that is that there is not a huge knowledge base in the plumbing trade.

Many installers are the same people that jumped on the PV installation a decade ago.

 

The big difference between a thermal boiler and a HP is that efficiency is best when the HP is running below its maximum performance. This us why they are oversized. This us not the same as fitting a more powerful combi boiler. They are sized for DHW needs.

 

 

In my case it was the heat pump manufacturer came out and measured every room.  Took into account the radiators, UFH spacing, flow temps, glass sizes etc and did a full heat loss calc and produced a report.  

 

While you may be correct that some MSC installers are not fully clued up, most will be far more experienced than a general builder taking a guess.  I would ask a few companies to quote and see what the consensus is - they won't under spec it as its less money for them.

 

Saying that you should oversize is fine - but if you find that a 10kw is more than enough, then jump up to 14kw the pump may not be able to run low enough and will end up cycling.  I dont know for sure but I'd guess an inverter driver pump will go down to 25-35%, so by speccing a 14kw it will start short cycling at around 4.2kw heat demand.

[SteamyTea]

1 minute ago, BMcN said:

dont know for sure but I'd guess an inverter driver pump will go down to 25-35%, so by speccing a 14kw it will start short cycling at around 4.2kw heat demand.

That is why buffer tanks must always be fitted.

[BMcN]

4 minutes ago, SteamyTea said:

That is why buffer tanks must always be fitted.

 

Just read my report and it came out at  7.13kw heat demand, so the 10kw pump is 40% oversized already.  

 

Anyway, if you want to go with builders best guess feel free.  Personally I would ask a few to quote for it and get a feel for what is recommended.

[SteamyTea]

3 minutes ago, BMcN said:

Personally I would ask a few to quote for it and get a feel for what is recommended.

Not my installation.

I would just dust off my old RE Science books, the laws of thermodynamics have not changed.

[Mike_scotland]

15 minutes ago, BMcN said:

 

 

In my case it was the heat pump manufacturer came out and measured every room.  Took into account the radiators, UFH spacing, flow temps, glass sizes etc and did a full heat loss calc and produced a report.  

 

While you may be correct that some MSC installers are not fully clued up, most will be far more experienced than a general builder taking a guess.  I would ask a few companies to quote and see what the consensus is - they won't under spec it as its less money for them.

 

Saying that you should oversize is fine - but if you find that a 10kw is more than enough, then jump up to 14kw the pump may not be able to run low enough and will end up cycling.  I dont know for sure but I'd guess an inverter driver pump will go down to 25-35%, so by speccing a 14kw it will start short cycling at around 4.2kw heat demand.

i agree,

i was in a fortunate position i suppose that i had a main builder who subbied the job out a mcs accredited heating engineering firm, they came back as 12kw but i fell out with that builder and we now have a new builder who is in fact a heating engineer to trade and i think he said 12kw or 14kw i cant remember exactly. so what im saying is having 2 comparable quotes makes me feel at ease, if one guy tol me a 6kw and the other said 12kw i would be a bit worried.

Edited September 27, 2021 by Mike_scotland

[Mike_scotland]

im assuming this is not OSB? looks like ply now i see it

[BMcN]

Just now, Mike_scotland said:

im assuming this is not OSB? looks like ply now i see it

19 minutes ago, SteamyTea said:

Not my installation.

I would just dust off my old RE Science books, the laws of thermodynamics have not changed.

Not mine either, however you did suggest that the installers and plumbing trade might have little knowledge on the subject.  I am suggesting to try a few and get a feel for it before pointlessly spending more on an oversized pump.  Laws of thermodynamics have not changed, times have though so I'd rather let the software do it.

 

If the builder has a heating company and you are happy with that then its fine, my point was to not simply just 'pick a big one'.

 

Yes that is plywood.  What thickness is it?  Was it specified by the structural engineer?

[Mike_scotland]

1 minute ago, BMcN said:

Not mine either, however you did suggest that the installers and plumbing trade might have little knowledge on the subject.  I am suggesting to try a few and get a feel for it before pointlessly spending more on an oversized pump.  Laws of thermodynamics have not changed, times have though so I'd rather let the software do it.

 

If the builder has a heating company and you are happy with that then its fine, my point was to not simply just 'pick a big one'.

 

Yes that is plywood.  What thickness is it?  Was it specified by the structural engineer?

unsure thickness. were would i find out if it was authorised from the engineer? would that be on building warrant?

[SteamyTea]

7 minutes ago, Mike_scotland said:

im assuming this is not OSB? looks like ply now i see it

Looks like shuttering ply.

 

[BMcN]

Normally the structural engineer will have a report stating everything like stud sizes & numbers, lintel sizes, loadings, racking strength etc.  On it it should state the sheathing material and nailing centres.

 

[Mike_scotland]

6 minutes ago, SteamyTea said:

Looks like shuttering ply.

 

good bad? normal, not normal?

[Mike_scotland]

i found a snippet from the building warrant looks legit enough

 

50 x 38 treated limber horizontal framing at not more than 600 mm centers on 50 x 50 treated limber vertical framing at centers to suit kit framing fixed through dpc over Protect TF200 Thermo breathable membrane on 10 mm thick sheathing ply on 140 x 45 timber framing

[SteamyTea]

18 minutes ago, Mike_scotland said:

good bad? normal, not normal?

Really don't know.

There is nothing inherently wrong with using ply, as long as it is the correct sort.

Sheets are usually marked up somewhere, so you should be able to find out what it is.

 

https://www.trada.co.uk/publications/info-from-other-organisations/the-builders-guide-to-plywood/

Edited September 27, 2021 by SteamyTea

[Mike_scotland]

Thanks for all your help guys and gals in this group, i have one final question, its more of a yes that sounds feasible or no your way off....

 

 

i have worked out that 8kw solar system would be around £8k I have also put this into the JRC Photovoltaic geographical spreadsheet i was offered at the start of the thread now - 

 

assuming £8k for the 8kw system and the 8kw system produces 7200kwh of energy a year.... (According to the spreadsheet)

assuming i used 50% on home energy and 50% went to the grid that would be

50% at home energy saving me £0.20p per kw (3600 x 0.20p = £720)
50% sell to grid for a measly but still something 0.05p per kw (3600 x 0.05p = £120) 

total saving hopefully of around £900 per year, now on a outlay of £8k it would take roughly 9 years to make that money back.... bearing in mind the 0.05p doesn't go down and the cost of Electricity stays the same.

What do you all think? does this seem ok or have i messed up some calculation ( Be kind) haha

[AliG]

The problem with such a big system is that when it is producing a lot of electricity in the summer it will be producing a lot more than you are using, so you are likely to use less than half the output. Thus the returns might well be less than on a smaller system.

 

Speaking of the returns, the good thing is that they are inflation proof. The returns should rise over time with the cost of electricity.

[BMcN]

5 minutes ago, Mike_scotland said:

Thanks for all your help guys and gals in this group, i have one final question, its more of a yes that sounds feasible or no your way off....

 

 

i have worked out that 8kw solar system would be around £8k I have also put this into the JRC Photovoltaic geographical spreadsheet i was offered at the start of the thread now - 

 

assuming £8k for the 8kw system and the 8kw system produces 7200kwh of energy a year.... (According to the spreadsheet)

assuming i used 50% on home energy and 50% went to the grid that would be

50% at home energy saving me £0.20p per kw (3600 x 0.20p = £720)
50% sell to grid for a measly but still something 0.05p per kw (3600 x 0.05p = £120) 

total saving hopefully of around £900 per year, now on a outlay of £8k it would take roughly 9 years to make that money back.... bearing in mind the 0.05p doesn't go down and the cost of Electricity stays the same.

What do you all think? does this seem ok or have i messed up some calculation ( Be kind) haha

 

 

When I did it you pay a huge premium for the MSC sign off.  Far better to do it yourself.  

 

I put in 3.6kw integrated.  The whole kit cost approx £2000 ex VAT including the GSE in roof mounts.  Using the same sort of figures as you have it will pay itself off in half the time as the MSC one.  Also you can factor in the square meterage of slate saved (I would guess around £700 worth of slate saved).

 

 

 

 

[Mike_scotland]

2 minutes ago, AliG said:

The problem with such a big system is that when it is producing a lot of electricity in the summer it will be producing a lot more than you are using, so you are likely to use less than half the output. Thus the returns might well be less than on a smaller system.

 

Speaking of the returns, the good thing is that they are inflation proof. The returns should rise over time with the cost of electricity.

hence why i was looking at batterys and i could put into the calculation im saving the 20p i would be using from the grid to the battery but like previously said in the winter months the battery would almost be obsolete. i will need to do a calculation and see if its worth it, sounds great doesnt it in the summer banking 10kwh or energy during the day for nighttime cooking etc is all free, the house im building is going to be all electric anyway due to location.