Which insulation do you use with your solar home?

[sunnyfield]

We are building a home and plan to have solar in the future. We’re going with geothermal for heating and cooling so we can really take advantage of the solar, and hopefully fully power it from the sun.

Of course, one of the most important factors with that is insulation. One of the geothermal reps I spoke to mentioned dense cellulose with a thin layer of spray foam, which would come in around R-40. She advised against purely doing spray foam because it prevents proper ventilation.

I looked up dense cellulose but it looks like many builders don’t know how to install it (could be wrong). Just wondering what everyone here opted for if they had the choice. Thanks!

 

[SSedan]

Geothermal is expensive, at least look at air source heat pumps and maybe roll the savings into larger solar.

I live near Green Bay and Fujitsu minisplits are working surprisingly well in my 40yo leaky house. House was all baseboard electric and those are still active in bathrooms and laundry room and I occasionally supplement the mostly glass living room with resistance heat if solidly below zero and the sun is down, but that I think is largely about unit placement, with the amount of glass, the location is not perfect for distribution.

The minisplits were my solution to not having a good way to run duct work, that wont be a problem for you

 

[miimura]

We are building a home and plan to have solar in the future. We’re going with geothermal for heating and cooling so we can really take advantage of the solar, and hopefully fully power it from the sun.

Of course, one of the most important factors with that is insulation. One of the geothermal reps I spoke to mentioned dense cellulose with a thin layer of spray foam, which would come in around R-40. She advised against purely doing spray foam because it prevents proper ventilation.

I looked up dense cellulose but it looks like many builders don’t know how to install it (could be wrong). Just wondering what everyone here opted for if they had the choice. Thanks!

Building a very tight house is the most efficient way. Proper ventilation should be done with actual ventilation, not purposely making it leaky. ERV / HRV is the proper way to ensure ventilation and air quality without throwing away the energy of conditioning the interior.

Proper insulation and air leakage are the biggest regrets I have from building my house in 2012. However, I'm in temperate Northern California, so the consequences are not that great in my situation.

 

[365gtb4]

I used spray foam. It's air tight and the highest R value. It's also the most expensive by a wide margin. The cellulose with spray foam over it might be more cost effective. Fiberglass bats has the advantage of being vermin and fire proof. A lot depends on where you live. Maine is very cold in the winter with winter moisture condensation is a big concern. On the solar make sure you pre-wire for it. I like ground mounted arrays because you can clean and service them easily.

Mini splits are much more efficient than conventional AC ducted systems. Ducted systems use about 30% more energy than mini splits. I have both types and will not buy a ducted system again. Note split systems have all kinds of registers ceiling, wall, floor. They are also quieter and easier to control the temperature and air flow.

 

[sunnyfield]

Geothermal is expensive, at least look at air source heat pumps and maybe roll the savings into larger solar.

I live near Green Bay and Fujitsu minisplits are working surprisingly well in my 40yo leaky house. House was all baseboard electric and those are still active in bathrooms and laundry room and I occasionally supplement the mostly glass living room with resistance heat if solidly below zero and the sun is down, but that I think is largely about unit placement, with the amount of glass, the location is not perfect for distribution.

The minisplits were my solution to not having a good way to run duct work, that wont be a problem for you

Thanks for mentioning this! My wife and I have gone back and forth between air source and ground source quite a bit, especially because it seems hit or miss with finding a geothermal installer that won't make your life a living nightmare come wintertime. The cost is pretty startling as well. Our solar contractor is trying to convince us to go with mini splits (which I actually prefer to duct work), but like you ran into, it's hard to really cover a whole house that way.

Just wondering, what's your electricity usage like in the winter with the heat pumps?

Building a very tight house is the most efficient way. Proper ventilation should be done with actual ventilation, not purposely making it leaky. ERV / HRV is the proper way to ensure ventilation and air quality without throwing away the energy of conditioning the interior.

Proper insulation and air leakage are the biggest regrets I have from building my house in 2012. However, I'm in temperate Northern California, so the consequences are not that great in my situation.

It's funny because that does make perfect sense haha. Never really thought about it that way. I'm guessing if you're out in Northern California you went with an ERV?

I used spray foam. It's air tight and the highest R value. It's also the most expensive by a wide margin. The cellulose with spray foam over it might be more cost effective. Fiberglass bats has the advantage of being vermin and fire proof. A lot depends on where you live. Maine is very cold in the winter with winter moisture condensation is a big concern. On the solar make sure you pre-wire for it. I like ground mounted arrays because you can clean and service them easily.

Mini splits are much more efficient than conventional AC ducted systems. Ducted systems use about 30% more energy than mini splits. I have both types and will not buy a ducted system again. Note split systems have all kinds of registers ceiling, wall, floor. They are also quieter and easier to control the temperature and air flow.

I definitely like the efficiency and hygienic factor of the mini split units. Did you end up using any special registers (unlike the typical ones that go on the wall)? We're also a bit into tech and were hoping to use Nests to control our zones. Do you know if you can use external thermostats with mini splits instead of the remote controls?

 

[SSedan]

I got the Tesla less than a year after doing the minisplits so I don't have a good handle on what they really did. Bill was down but then the Tesla made it spike again in winter. I think part of the issue was I only fed it via a 30amp outlet and I think the slow heating was inefficient, wall connector shipped today so I will feed it more, hopefully faster heating and charging while heating rather than having morning warmup consume range helps.

Could do under floor heating in the small rooms that don't get a wall unit.

 

[shs1]

We have ground source geothermal heating and cooling and solar. Our heat sink loops are not in the ground, however, but are at the bottom of one of our ponds. A very efficient way to go if you happen to have a pond. The walls and roof of the house are Structural Insulated Panels or SIPs. SIPs are not only great insulation with no thermal bridging via the 2x4s or 2x6 in the wall, but are also 10 times more air tight than a stick built house. As a result of the minimal air exchange via air leaks in the walls and around windows, we have an ERV or Energy (or Entropy) Recovery Ventilation system that exchanges inside with outside air while recovering, via a heat exchanger, the energy used to heat or cool the inside air. Good news is the we rarely need the AC and when I do, the heat pump in the geo system dumps the heat from the inside air into the domestic hot water. So you could say AC is free. While most people in the area spend several hundred dollars a month on electricity for AC during the summer months, we reliably get $100+ in solar credits. Once my Powerwall is installed, any day now, I expect to do even better.

 

[WannabeOwner]

Which insulation do you use with your solar home?

Passive House. Not sure about temperature range where you are, but you are a long way South of us so will get much more Solar than we do in Winter. Our Winter Solar is 10% of our mid summer (because of our Latitude). For us winter nights are a few degrees minus-C, and daytime < 10C. Night temperatures of -10C or below, and days not rising above 0C, are a once-or-twice-a-decade thing, and only lasts maybe a week. Summer is rare for > 30C, but does happen, and even then nights are usually 16C, rarely >20C, and night-venting lowers the temperature.

Passive House is very high levels of insulation, very very good air tightness, and mechanical-ventilation with heat-recovery (exhause air heat incoming air).

In mid Winter with house unoccupied for the day it will lose 1C. In Summer it gains 1C during a hot sunny day, and we easily lose that overnight by opening the windows. We've been in a heatwave in the UK for some time, next week 30C - 35C forecast. We haven't had rain for months (so hotter / sunnier than "normal"). Max day temperature in the house has been 24C (no air con installed here)

In principle Passive House (here in UK at least) needs no winter heating system installed, so the cost saved on that, fuel, and no maintenance / replace goes towards the insulation. It is reckoned that Passive House costs 7% more than "normal", but then close to zero fuel bills and no maintenance / replace costs for boiler/furnace - for the lifetime of the building.

The mechanical ventilation is also far better for health. A combination of no corners-of-rooms with bad airflow that then cause moulds etc. and the even temperature. We've had passive House for 5 years and wife and I not had a winter cold / cough in hat time. I, in particularly, have spent a good month shaking off a winter cold previous to that, and I cannot remember a single winter when I didn't have one.

Ours is actually an extension (to original house) and we already had a boiler, so we did install underfloor heating downstairs. Since the build we have lowered the thermostat in the main part of the house, as we don't actually "live" in it during the winter, bar a few festive days entertaining, and our total fuel usage has dropped by 50% - even including heat for the new part, so basically Passive House part is using "not much more than nothing". Upstairs has no heating and minimum temperature over winter is maybe 17C, mostly 18C plus.

Windows are triple glazed. Important that inner surface is no more than 4C less than room temperature, so that adjacent air doesn't "fall" which creates convection draughts and the feeling of "cold" (and then you turn up the thermostat to compensate).

Given that we have underfloor downstairs, and if we had used a heat exchanger, then I would have been able to use "cold side" to feed cold water through the floor in Summer. I was more focused on "eco" than I was "comfort", so now I've got over that!!, and we are so much more Green than everyone we know, I might persuade myself to retro fit that

A bit like buying first EV it was a leap of faith, but absolutely hands-down the best decision we ever made

 

[sashton]

Slightly different here as we live in a 600 - 1000yr old stone building. The conservation guys will not allow us to insulate externally nor will they allow us to attach anything externally (PV or solar hot water). Luckily the place is large enough for us to "tank" inside each external wall. Usually I've used 2x75mm foil backed PIR taped and offset but when Celotex had a huge fire a few years ago I have mixed and matched various thicknesses to get at least 150mm. Given that the stone walls were already up to 80mm thick we do have some very deep windowsills. I then dug up most of the stone slab floors, tanked, insulated them again and installed a wet underfloor heating system before re-laying the stone slabs. This is run from a 4000L thermal store which in turn is heated remotely by 40sqM of insulated tubes; a woodburner and our failsafe oil boiler. It has been in for over ten years now and we have used less than 100l/year of heating oil - mind you we coppice 8 acres of hybrid poplar and willow to keep the woodburner going. The massive thermal mass of the internal walls and floors means that the main rooms remain pretty stable between 17 - 21C for most of the year.
The whole house heat recovery unit works suprisingly well. I had assumed it wasn't needed as it is neigh on impossible to get old houses airtight but it does reduce the internal humidity dramatically especially in the winter months.
Away from the house we have 11.5kWp PV and currently one PWII. Western Power will permit me to generate 11kW more if I pay for our 11kV PMT to be upgraded. I think I'm going to have to bite the bullet and go for it as we have more PWII due in September and I'm replacing the PHEVs (Chevy Volt and Golf GTE) with EVs in September (Hyundai Konas as MS are just too big for the roads here and I think hell will freeze over before my RHD M3 reservation comes to fruition) - so more PV is the only answer if we want to keep net positive.

 

[WannabeOwner]

"tank" inside each external wall[ ... I then dug up most of the stone slab floors, tanked, insulated them again and installed a wet underfloor heating system before re-laying the stone slabs

Hats off to you Faced with similar we built the Passive House extension instead of retro-fit. This is a 60's build, mostly concrete (floors / roof / etc.) so already good air-tightness and great thermal mass, but digging up all the concrete floors (quite possibly containing asbestos pipe insulation) and losing the thermal mass by tanking the rooms wasn't what I wanted to do and an additional external wall and appropriate insulation was expensive and tricky to join insulation through the existing [pitched] roof (mounted on top of the original flat concrete one).

But once we found how effective the MVHR was in the Passive extension we retro retro fitted that to the old house too and that made a HUGE difference including all the damp etc. has gone away there.

We have used Aerogel where thickness was critical (e.g. behind boards in window reveals); not very nice to work with and not kind to wallet either!

Western Power will permit me to generate 11kW more if I pay for our 11kV PMT to be upgraded. I think I'm going to have to bite the bullet and go for it as we have more PWII due in September

We too have max PV but I have been advised that I could add PV dedicated to PowerWall with no export in order not to have to upgrade incoming supply. If that is indeed a Real Thing would that work for you?

hell will freeze over before my RHD M3 reservation comes to fruition

Nah, 2019 for sure ... "3 months maybe, 6 months definitely"

 

[sashton]

We too have max PV but I have been advised that I could add PV dedicated to PowerWall with no export in order not to have to upgrade incoming supply. If that is indeed a Real Thing would that work for you?

It seems that different UK DNOs treat the Powerwalls in different ways. Western Power(who really don't want you to generate your own electricity and if you do they want to extract all the cash they can from you) say they treat each PW II as a uncontrolled 5kW generator wheras SSE apparently don't add the PW to the equation.
The Tesla PW UK salesman said that the UK regs applying to the PWII are due to change shortly - permitting you one PWII alongside your 3.6kW PV even if you are G83 restricted. I have yet to see any evidence of this.
Tesla do not permit permanently standalone PWII and even a temporary disconnection would require the Backup gateway which is, as yet, not UK compliant and so not available here. It may arrive this year - I have my fingers crossed as WPD have delivered more than ten powercuts this year.

 

[sashton]

Nah, 2019 for sure ... "3 months maybe, 6 months definitely"

*grin* I'm not an early reservation holder (April 2017). I don't qualify as an existing Tesla customer (roadster doesn't count neither does the PW II). They didn't even bother to notify me about the Goodwood event - I even called them and they said they would send me tickets as they had some late cancellations but nothing arrived in the post and not even a whisper of an apology.
So forgive me if I am sceptical of their "early 2019" note.