Insulation...do I need more?

[SuperJohnG]

2 minutes ago, Nickfromwales said:

Don't forget ducts for cables, if not already in  A more modest sized array could just feed into the shed CU. Size the SWA accordingly. 

I do have ducts back into the house plant room from outside, so can run a cable any size in at any point. By shed - I'm thinking agricultural easy, 10m x 6m so should manage a 4kW array up there no problem. 

 

I could run cables inside the main house in case I ever decide to add PV on that elevation and rip the slates up but maybe need to do some research before I close it up inside. 

[Nickfromwales]

Just now, SuperJohnG said:

I do have ducts back into the house plant room from outside, so can run a cable any size in at any point. By shed - I'm thinking agricultural easy, 10m x 6m so should manage a 4kW array up there no problem. 

 

I could run cables inside the main house in case I ever decide to add PV on that elevation and rip the slates up but maybe need to do some research before I close it up inside. 

Bite the bullet now. You will kick yourself afterwards, even more so if the outbuilding isn't an 'immaculate' elevation eg to max out the 4kWp. Scaffold costs alone will piss you off if you don't.

Just install the panels and the trays now, 2-3kWp on the house if it helps, and install the rest 1-2kWp on the outbuilding roof later, when you've completed and you know if you can stretch to it.

 

FYI, you CANOT temporarily connect the PV up to a CU which has not been signed off anyways, if you're going MCS installer ( highest cost route but export payments can be had that way ) so you'll not miss not having the inverter etc in right now as they'll not connect it up immediately anyways. We've done 2 installs recently which have panels on the outbuildings as well as the house and we've simply ducted the D/C cable(s) back to the single inverter in the house ( to reduce costs and complexity ). Working very well. 

[Nickfromwales]

At the least, put redundant D/C 4mm or 6mm singles in now and run them from the roof to the plant room in anticipation.

[SuperJohnG]

1 hour ago, Nickfromwales said:

Just install the panels and the trays now, 2-3kWp on the house if it helps, and install the rest 1-2kWp on the outbuilding roof later, when you've completed and you know if you can stretch to it.

 

Ah...shit I want to. But I'll need to rip all the slates off, then install trays, and my slates are on sarking, which is on counterbattens, nothing shy of a nightmare. 

 

1 hour ago, Nickfromwales said:

At the least, put redundant D/C 4mm or 6mm singles in now and run them from the roof to the plant room in anticipation.

 

This I can add, then just open it up when I required. Seems silly not to install the panels just now but at least I can leave a cable. Need to look at how the wiring works. 

 

 

[Nickfromwales]

55 minutes ago, SuperJohnG said:

 

Ah...shit I want to. But I'll need to rip all the slates off, then install trays, and my slates are on sarking, which is on counterbattens, nothing shy of a nightmare. 

 

 

This I can add, then just open it up when I required. Seems silly not to install the panels just now but at least I can leave a cable. Need to look at how the wiring works. 

 

 

I reckon 2 pints of medium strength ale on Friday and you’ll be on the roof yanking the slates off on the Saturday morning.
Mark my words, there’s a shit-storm-a-coming with electricity costs. Going to throw all this into a spin. PV price ( for supply ) will inevitably follow.

[MikeGrahamT21]

These do installation, though not advertised, it gets subcontracted, and will sort all of the paperwork out for you - https://www.solar-battery-energy-ev-store.co.uk/

 

Also, these offer to pay more than the standard 5p (20p), in return for grid balancing (I think), maybe worth considering? - https://social.energy/homeowners/

Edited February 2, 2022 by MikeGrahamT21

[SuperJohnG]

On 02/02/2022 at 10:14, Nickfromwales said:

Budget for midnight to midnight at 30p/kWh.

I redone these calcs (I'd actually made a mess of them before) for 17p/kWh and then redone for 30 and 35p too.. 

Results for over 20 years assuming a COP of 3 on the ASHP and usuing my 900m2 of wall and ceiling area. I've attached the excel for anyone who would like to figure this out in the future. 

 

 

On 01/02/2022 at 12:32, LA3222 said:

just to get the 0.11 figures quoted by Kingspan Tek for SIP.

 

On 01/02/2022 at 11:05, MikeGrahamT21 said:

Your u-values look good...if you've achieved them.

Both your comments I hadn't really thought about - sounds daft but why wouldn't; you achieve the stated U values? also just why would you need to add insulation to get stated values from Kingspan? I can't fathom it. 

 

I had some pricing back for 25mm and 50mm PIR, this was for 100 sheets of each just for comparison, which would be around the area of my internal roof (300 sqm), so vs the figures above it would be 3 times the costs (as above is based on ceilings and walls at 900m2) so for 50mm to do above it would be £6300. At 3% starting at 35p/kWh over 20 years, the cost won't theoretically have been recovered. That is just on the basis of pure heat loss, doesn't factor in thermal bridging or airtightness which are seperate issues.  

 

 

 

I still may do it but helps make an informed decision. 

 

Now reading seems insulation is law of diminishing returns which I haven't quite figured out yet where the optimal balance of my existing insulation and adding extra becomes not value for money. 

 

Airtightness - I have covered and will focus of doing a comprehensive job. 

 

Thermal bridging - isn't quite covered. The walls have SIPS splines, but are areas of studs that are solid wood. 

On the roof panels the splines are timber for the strength and hence this means lots of thermal bridges, which I would like to get rid of but is there a simpler more cost effective way to do this locally rather than blanket adding PIR throughout the roof? would it be reasonable to add 50mm of PIR at each timber spline over the top of the panel, say 100mm wider than the timber spline then it would do the same as doing the whole ceiling in terms of thermal bridging the only downside is I haven't added and extra 50mm PIR throughout all the panel, but it might not be adding value there as per above the law of diminishing returns? 

 

It seems silly but from a cost point of view makes sense, drawback being maybe a little harder than putting full sheets up but not that much more difficult.  

 

Compund heat costs.xlsx

Edited February 24, 2022 by SuperJohnG

[LA3222]

22 minutes ago, SuperJohnG said:

I redone these calcs (I'd actually made a mess of them before) for 17p/kWh and then redone for 30 and 35p too.. 

Results for over 20 years assuming a COP of 3 on the ASHP and usuing my 900m2 of wall and ceiling area. I've attached the excel for anyone who would like to figure this out in the future. 

 

 

 

Both your comments I hadn't really thought about - sounds daft but why wouldn't; you achieve the stated U values? also just why would you need to add insulation to get stated values from Kingspan? I can't fathom it. 

 

I had some pricing back for 25mm and 50mm PIR, this was for 100 sheets of each just for comparison, which would be around the area of my internal roof (300 sqm), so vs the figures above it would be 3 times the costs (as above is based on ceilings and walls at 900m2) so for 50mm to do above it would be £6300. At 3% starting at 35p/kWh over 20 years, the cost won't theoretically have been recovered. That is just on the basis of pure heat loss, doesn't factor in thermal bridging or airtightness which are seperate issues.  

 

 

 

I still may do it but helps make an informed decision. 

 

Now reading seems insulation is law of diminishing returns which I haven't quite figured out yet where the optimal balance of my existing insulation and adding extra becomes not value for money. 

 

Airtightness - I have covered and will focus of doing a comprehensive job. 

 

Thermal bridging - isn't quite covered. The walls have SIPS splines, but are areas of studs that are solid wood. 

On the roof panels the splines are timber for the strength and hence this means lots of thermal bridges, which I would like to get rid of but is there a simpler more cost effective way to do this locally rather than blanket adding PIR throughout the roof? would it be reasonable to add 50mm of PIR at each timber spline over the top of the panel, say 100mm wider than the timber spline then it would do the same as doing the whole ceiling in terms of thermal bridging the only downside is I haven't added and extra 50mm PIR throughout all the panel, but it might not be adding value there as per above the law of diminishing returns? 

 

It seems silly but from a cost point of view makes sense, drawback being maybe a little harder than putting full sheets up but not that much more difficult.  

 

Compund heat costs.xlsx 17.33 kB · 0 downloads

What I meant by the comment 'to achieve the 0.11 stated by kingspan tek' is that in order to achieve 0.11 u-vakue with kingspan tek, I would need to add an additional layer of 70mm insulation internally. 142mm tek is something like 0.18 on its own (off top of my head).

 

There is another piece to this puzzle you haven't considered bud. Cooling.

 

Adding that layer of insulation internally will also increase the decrement delay of your build - maybe not by much,  Ultimately it may be enough to help.

 

Summers are getting hotter, people tend to think of insulation only from the keeping heat out perspective, there will be times where keeping heat out is also of value.

 

One of my concerns at the minute is to see how living here in the summer months work out. I'm hoping that the decrement delay combined with ASHP providing cooling on both ground and first floor will be enough. Unfortunately, we have a sunroom which will gain heat via solar gain but we shall see!

 

Also, 35p/kwh may be low balling the cost after 20yrs?

Edited February 24, 2022 by LA3222

[SuperJohnG]

9 minutes ago, LA3222 said:

What I meant by the comment 'to achieve the 0.11 stated by kingspan tek' is that in order to achieve 0.11 u-vakue with kingspan tek, I would need to add an additional layer of 70mm insulation internally. 142mm tek is something like 0.18 on its own (off top of my head)

Ah I see. 

10 minutes ago, LA3222 said:

One of my concerns at the minute is to see how living here in the summer months work out. I'm hoping that the decrement delay combined with ASHP providing cooling on both ground and first floor will be enough. Unfortunately, we have a sunroom which will gain heat via solar gain but we shall see!

Wasn't something I had considered about decrement delay or cooling in my thoughts here.I'll bet it's toasty in there this summer!

 

11 minutes ago, LA3222 said:

Also, 35p/kwh may be low balling the cost after 20yrs?

The price is compounded per yer, so starts at 35p now, and ends up at 61p (jesus (expletive deleted) can you imagine!) in 20 years, even worse at 8% that will be £1.51 per kWh 

 

[Nickfromwales]

2 hours ago, SuperJohnG said:

The price is compounded per yer, so starts at 35p now, and ends up at 61p (jesus (expletive deleted) can you imagine!) in 20 years, even worse at 8% that will be £1.51 per kWh

Yup. And all the current nay-sayers moaning about the lack of returns on the PV installs will all be crawling over broken glass to fit some then. Prob is, then the PV will have gone up too.

We've just quoted 9kWp at £11.6k ( before VAT ) with a breakeven point in year 6.5!! 80% performance warranty ( guaranteed ) for 25 years. Irrefutable sense, and PV is your best defence against rising electricity prices. Hoping to get time to do mine this year.......fingers crossed. Sun will keep rising, so will fuel costs.

[SuperJohnG]

10 hours ago, Nickfromwales said:

Yup. And all the current nay-sayers moaning about the lack of returns on the PV installs will all be crawling over broken glass to fit some then. Prob is, then the PV will have gone up too.

We've just quoted 9kWp at £11.6k ( before VAT ) with a breakeven point in year 6.5!! 80% performance warranty ( guaranteed ) for 25 years. Irrefutable sense, and PV is your best defence against rising electricity prices. Hoping to get time to do mine this year.......fingers crossed. Sun will keep rising, so will fuel costs.

Absolutely makes sense to do. Interested in how you can get a realistic PV generation value- just use PVGIS? I'd like to do the sums on that just now. 

[SuperJohnG]

edit- just did it:

 

seems like 3143 kWH per year just need a realistic utilisation figure now, doing some sums on 50% utilisation and 3% interest  starting at 30p/kWh now payback is around 10 years (assumed total install costs £5k for a fully installed system with me managing subcontractors). 

 

[Nickfromwales]

2 hours ago, SuperJohnG said:

Absolutely makes sense to do. Interested in how you can get a realistic PV generation value- just use PVGIS? I'd like to do the sums on that just now. 

Yup. Plus a reasonable amount of diligence with a site survey before submitting figures.
Just about every single proposal we’ve ( collectively ) put forward for my projects have either met or exceeded expectations. It shows the software allows a bit of ‘real world’ accountancy.

[SuperJohnG]

36 minutes ago, Nickfromwales said:

Yup. Plus a reasonable amount of diligence with a site survey before submitting figures.
Just about every single proposal we’ve ( collectively ) put forward for my projects have either met or exceeded expectations. It shows the software allows a bit of ‘real world’ accountancy.

The PVGIS ones? Thats good, so reasonably I can assume that say 75% would be generated and then its just a utilisation question. 

[MikeGrahamT21]

The manufacturer quoted u values assume that the installation is perfect, a continuous layer with no imperfections, no gaps, and no air movement.

 

in reality you’ll knock it and damage bits when you put it in damaging the structure, you can of course make it airtight and gap free, which you need to do, and you’ll have have a psi value to consider, in that there will be thermal bridging in some areas, which can be mitigated by installing more insulation where this occurs. Also remember that any foil side must be followed by a 25mm airtight gap to make use of the foil for low emissivity, otherwise I’m pretty sure it just becomes a conductor being metal, read this a while ago somewhere, makes sense really 

[Nickfromwales]

23 hours ago, SuperJohnG said:

The PVGIS ones? Thats good, so reasonably I can assume that say 75% would be generated and then its just a utilisation question. 

Yes, that would be a healthy benchmark for sure. Also, the figures usually do not allow for maxed out self-consumption either, so the projected economics can be improved upon by something as simple as a PV diversion controller to DHW. Adding an EV charger of the same family / software base ( eg so they ‘talk’ to each other ) would allow pretty much 100% self-consumption, if the EV is routinely tethered during the hours of sunlight of course.

Cases change for retired / working full time / working from home etc so no 2 scenarios are really the same.

[SuperJohnG]

On 01/02/2022 at 19:25, A_L said:

 

This will reduce heatloss by about 2-2.5kWh/m²/yr, 

@A_L It's likely easy but can you walk through the calc to go from R value of a 50mm board to your figure here?

 

On 02/02/2022 at 11:31, Nickfromwales said:

At the least, put redundant D/C 4mm or 6mm singles in now and run them from the roof to the plant room in anticipation.

@Nickfromwales Is this just a single set of cables internally to where the inverter is, plus an earth? I'm at minimum going to add these right now. 

 

 

I have ran some final figures now. 

 

Going to likely add 50mm PIR to the ceilings internally which works out at 300m2. Cost of this is £2100 plus my labour time which is free. The simple economics of this don't really add up as even considering 33p/kWh, with a COP of 3 on the ASHP, the saving over 20 years is only £1700 and that's allowing for starting point of the 33p compounded out at 3% - however it will remove the thermal bridges in the ceiling which is my main focus there. 

 

In stark contrast - given the same 33p/kWh and allowing for the same 20 years and compounded interest with a 4kWp array and getting 50% utilisation from that I would recoup £8k, from generating £14k worth of kWh minus a £6k outlay right now. Which is quite significant. If I up that utilisation to 75%, which shoudl be easily achievable with a PV diverter that £8k increases to £15k which is unreal. 

 

I've absolutely no doubt the PV I need to do now, it's just the wrong time from a cash flow perspective in the build stage and definitely reeling from not doing it while slates were going on. but such is life. 

 

The plan now is to run in the cables so I can do at end of build if I have cash easily. Also add the 50mm PIR as that just cannot be done later and regardless of the economics it will no doubt have other benefits.  

[Nickfromwales]

9 hours ago, SuperJohnG said:

Is this just a single set of cables internally to where the inverter is, plus an earth? I'm at minimum going to add these right now. 

It depends on the size of the array and the placement of the panels. You really need to get some advice from whomever would be your preferred downstream installer. Remember you’ll need MCS for selling exported energy.

If its an array with all the panels together on a single elevation then you could be a single ‘string’ ( pair of cables ) but if east / west split then you’d be dual string and need 2 pairs. You’ll also need to allow enough coiled up cable to be able to reach the furthest panel from where you’ve left the cables. 
It would be a proper piss-you-off to find you’ve done the prep incorrectly   

Go ask some questions, and offer to pay that person for their professional time eg tell them you’re expecting a service from them vs a “can you take a quick look”.