Attempting a straw bale, off-grid passive house in Somerset

[Smallholder]

There are a few straw bale certified passive houses in the UK, and we're in touch with Wellspring Architecture Ltd who seem to be the leading UK authority on building with straw bales.

They have done PH builds before, and if we get pp, they'll be working with us to meet this spec during the build. 

 

I'm not going to be dogmatic about it though. If the cons start to outweigh the pros, then I'm willing to forfeit certification. 

 

I'm not sure how limiting the PH approved electrical device thing will be. But we're obviously planning on MVHR, and high efficiency appliances.

[Gordo]

14 hours ago, Gordo said:

Most farmers have moved towards those huge round bales of hay in our area. Only hobby farmers seem to use traditional rectangular bales 

Live and learn lol. Not being farming background I didn’t know there was a difference. That’s why I would shy away personally. So many unknowns and loose ends to research

[SteamyTea]

2 hours ago, PeterW said:

you will struggle with air tightness on straw with lime plasters

Mildew and rot as well.

 

Timber frame with mineral wool or cellulose insulation.  Sensible windows and a roof optimised for PV yield.

Life is hard enough without having to get a farmer to set his bailler tension up correctly while he is waiting for the right weather.

[Mr Punter]

Good luck with the planning application.  As others have commented, perhaps do not make PH certification a condition of your consent as it may not be possible or practical to achieve.  It can be very time consuming to attempt to alter a planning condition, especially if the PH has become on of the main considerations in the para (whatever number it is now) approval.

[Smallholder]

29 minutes ago, Mr Punter said:

Good luck with the planning application.  As others have commented, perhaps do not make PH certification a condition of your consent as it may not be possible or practical to achieve.  It can be very time consuming to attempt to alter a planning condition, especially if the PH has become on of the main considerations in the para (whatever number it is now) approval.

 

This sounds like a very wise move.

We'll be sure to phrase things carefully, comitting to build using passive house techniques rather than specifically to achieve certification. 

[Smallholder]

There are about a thousand straw bale buildings in the UK now, with the first having been completed just 27 years ago in 1994.

 

In France they are building a thousand new straw bale buildings a year.

There are 200 year old straw bale homes in the US, still inhabited today. So it's not really a new technique. 

 

Buildings in the UK vary from small structures, right up to the 17,000 sqft Sworders fine-art auctioneers building in Essex.

The largest pre-fab straw building in the UK is 30,000 sqft.

 

I'm not saying it won't be a challenge, or that we won't make mistakes. I'm certain both will be the case. 

[SteamyTea]

8 minutes ago, Smallholder said:

There are about a thousand straw bale buildings in the UK now, with the first having been completed just 27 years ago in 1994.

How many use the straw/lime render as the structural element.

There was someone that made one and used to post up about it, not sure if it was on here, the predecessor of here, or the other place.

[gc100]

Have you really done you calculations on the 20k PV array.? I can’t see it generating enough power In the winter even with batteries, you’ll have to be very careful with your consumption which will be a pain. Also what about charging an EV car which as some point in the coming years you’ll need to do? 

Edited October 31, 2021 by gc100

[billt]

2 hours ago, gc100 said:

Have you really done you calculations on the 20k PV array.? I can’t see it generating enough power In the winter even with batteries, you’ll have to be very careful with your consumption which will be a pain. Also what about charging an EV car which as some point in the coming years you’ll need to do? 

 

Not the OP, but I have a 15kWish array with batteries. the PVGIS projections for our location give these average daily values, adjusted to 20kW.

 

Jan 14kWh

Feb 23kWh

Mar 41kWh

Apr 60kWh

May 65kWh

June 69kWh

July 67kWh

Aug 56kWh

Sep 47kWh

Oct 29kWh

Nov 18kWh

Dec 13kWh

 

These are theoretical results for a grid tied system, so the actual output in the summer will be limited to the storage capacity of the batteries. There is also a daily loss of about 2kWh due to inefficiencies in charging and inverting.

 

Of course averages hide significant daily variations, so to be off grid you would want at least a weeks worth of storage, which is likely to be a lot of batteries. Even that might not be enough as you can get many overcast (very low energy) days in a row.

 

We only have just over a days storage. So far we've had to supplement the PV on 8 days. Over winter it's likely to be every other day.

 

We are further north than Somerset, so the OP should get slightly better results.

[gc100]

8 hours ago, billt said:

 

Not the OP, but I have a 15kWish array with batteries. the PVGIS projections for our location give these average daily values, adjusted to 20kW.

 

Jan 14kWh

Feb 23kWh

Mar 41kWh

Apr 60kWh

May 65kWh

June 69kWh

July 67kWh

Aug 56kWh

Sep 47kWh

Oct 29kWh

Nov 18kWh

Dec 13kWh

 

These are theoretical results for a grid tied system, so the actual output in the summer will be limited to the storage capacity of the batteries. There is also a daily loss of about 2kWh due to inefficiencies in charging and inverting.

 

Of course averages hide significant daily variations, so to be off grid you would want at least a weeks worth of storage, which is likely to be a lot of batteries. Even that might not be enough as you can get many overcast (very low energy) days in a row.

 

We only have just over a days storage. So far we've had to supplement the PV on 8 days. Over winter it's likely to be every other day.

 

We are further north than Somerset, so the OP should get slightly better results.

we use about 500-700kWH a month so defo couldn’t do that !!! 

[billt]

Those are daily averages, so multiply by days in month to get monthly averages. e.g. November is 540kWh in the month.

[gc100]

Don’t think we could do it still given the heat pump is needed to most in those dark months . Maybe.

 

Question is where to buy affordable batteries that can store that? The maths doesn’t seem to add up for me. 

[Marvin]

25 minutes ago, gc100 said:

Don’t think we could do it still given the heat pump is needed to most in those dark months . Maybe.

 

Question is where to buy affordable batteries that can store that? The maths doesn’t seem to add up for me. 

I think your right about the maths. Espically as I think you can only use about 35% of a batteries capacity. 

 

I use this one for PV calculations:

https://www.google.com/url?sa=t&source=web&rct=j&url=http://re.jrc.ec.europa.eu/pvg_tools/en/tools.html&ved=2ahUKEwjewPf1qfXzAhVSsKQKHXFiC_UQFnoECB8QAQ&usg=AOvVaw2-K48UEog42OCvQZSZqZxU

 

Tricky on mobile to use otherwise ok. 

 

M

 

[billt]

23 minutes ago, Marvin said:

I think your right about the maths. Espically as I think you can only use about 35% of a batteries capacity.

 

No the maths doesn't add up, but usable capacity depends on the type of battery. Deep cycle lead acid is recommended to use not more than 50% of their capacity, they are also pretty inefficient as they need to be (in effect) over charged to keep them healthy.

 

LiFePO4 batteries can be used over 80% of their capacity and they are a lot more efficient than lead acid. The combination of greater usable capacity and much greater lifespan makes LiFePO4 batteries the rational choice for this sort of application. The most cost effective cells that I've seen are about $280 for 3.2V 280Ah. So a 4 parallel 16 series bank which could store over 100kWh would cost about $18,000.

 

On the other hand a 16S bank of Winston 1000Ah cells (which have a better reputation) would cost about $20,000

[Marvin]

9 minutes ago, billt said:

 

No the maths doesn't add up, but usable capacity depends on the type of battery. Deep cycle lead acid is recommended to use not more than 50% of their capacity, they are also pretty inefficient as they need to be (in effect) over charged to keep them healthy.

 

LiFePO4 batteries can be used over 80% of their capacity and they are a lot more efficient than lead acid. The combination of greater usable capacity and much greater lifespan makes LiFePO4 batteries the rational choice for this sort of application. The most cost effective cells that I've seen are about $280 for 3.2V 280Ah. So a 4 parallel 16 series bank which could store over 100kWh would cost about $18,000.

 

On the other hand a 16S bank of Winston 1000Ah cells (which have a better reputation) would cost about $20,000

As my brother says it's not if it's how much!  We only use about 7000kW a year.

[Smallholder]

On 29/10/2021 at 07:06, SteamyTea said:

No.

Part of the Passivhaus standard, if you want to get a certificate, is that they specify all sorts of things, like washing machines, that meet their criteria. (Ecolabel)  This is why many people do not bother with certification.

There is also the airtightness, which may prove difficult to achieve with a structural straw bail build, it is hard enough to achieve with cast concrete.

Maybe you're right, I'm not aware how restrictive Passive House standards are in terms of which appliances we are allowed to install. But if it's as simple as buying stuff that's top end in terms of efficiency, then I'm happy with that.
Obviously doors, windows and the MVHR system will need to meet PH spec, but from what I've seen so far, that's a zero issue.

 

Worst case scenario, we could install the appliances we want, after certification?

As for air tightness, there are at least a few PH spec strawbale houses in the UK, so it's certainly possible.
We will likely partner with Wellspring Architecture (a strawbale building specialist) for the building stage, and they have been involved in building to PH standard in the past.

[Dan F]

17 minutes ago, Smallholder said:

Maybe you're right, I'm not aware how restrictive Passive House standards are in terms of which appliances we are allowed to install. But if it's as simple as buying stuff that's top end in terms of efficiency, then I'm happy with that.

It's not restrictive at all in terms of appliances.  The spreadsheet does include consumption values for household appliances which it takes into account in the PER calculation, but unless you are aiming for PH Plus or Premium this is complelty non-consequential.

 

Quote

Obviously doors, windows and the MVHR system will need to meet PH spec, but from what I've seen so far, that's a zero issue.

MVHR needs to be PH certified I believe, but no other items need to be PH-certified, just your total heating demand and airtighness need to be within certain limits.  That said, using certified components can make the paperwork a bit easier.

 

Quote

Worst case scenario, we could install the appliances we want, after certification?

I'm not sure what the concern with appliances is?

 

BTW, why is off-grid important?  Do you have a not have, or can't get, a grid connection?

 

If you think about it, if you don't have a grid connection then you'll want a large PV arrary to cover as much as possible of winter electicity demand.  Even if you have a large array it'll be very hard to cover all winter electricity demand and you'll probably need to need to generate electicity in some way in the winter (wind turbine or burning fuel or some sort etc.).  The other issue is that in the summer you'll have a huge amount of excess generation that you won't be able to use of export!!

 

In my view off-grid makes sense if a grid connection isn't possible or if you are building yourself an interseasonal store, but otherwise best to have the grid connection and think that in the summer you are exporting green energy to it, and in the winter you are importing a lot less (ideally green) electicity, than you exported in the summer making you a net exporter, helping greenify the gird and making a small amount of money too.

Edited November 3, 2021 by Dan F

[Smallholder]

On 31/10/2021 at 07:42, gc100 said:

Have you really done you calculations on the 20k PV array.? I can’t see it generating enough power In the winter even with batteries, you’ll have to be very careful with your consumption which will be a pain. Also what about charging an EV car which as some point in the coming years you’ll need to do? 

I've been working with a very knowledgeable chap locally, who has created modelling software to help with this.
Using downloaded solar intensity data, hour by hour over the course of a whole year, we are able to calculate how much the array should produce every hour. We then compared this back to a local solar array of 4kw, plugging in the specs of this array to make sure it is accurate, which it was.

Then we add battery storage (I'm thinking I'll start with 28kWh, it's modular so we can add more if needed. About £850 per 3.5kWh unit) information, and the software gives us an hour by hour battery capacity. When it reaches 100%, further solar generation is ignored, until the battery capacity dips below 100%.

This then shows the instances over the course of a year, when the batteries run down to zero. This modelling includes a small wind turbine, that helps as it runs at night and slightly more during the winter.
It sounds counter intuitive, but it may well be environmentally wise to run a small diesel generator for those few occasions each year, rather than investing in more and more PV and batteries. These, of course have a carbon footprint like everything else.

 

We already have an EV, which we charge at home, but also at the farm where I have already set up a small (2.25kW) solar array with small (7kWh) battery storage.

 

We've modelled home electrical consumption based on best guesses.

In winter, if possible I plan to use a biomass boiler for DHW and underfloor, which will take load off the electrical system

[Smallholder]

2 minutes ago, Dan F said:

It's not restrictive at all in terms of appliances.  The spreadsheet does include consumption values for household appliances which it takes into account in the PER calculation, but unless you are aiming for PH Plus or Premium this is complelty non-consequential.

 

MVHR needs to be PH certified beleive, but no other items need to be PH-certified, just your total heating demand and airtighness need to be within certain limits.  That said, using certified components can make the paperwork a bit easier.

 

I'm not sure what the concern with appliances is?

 

BTW, why is off-grid importment?  Do you have a not have a grid connection?

 

If you think about it, if you don't have a grid connection then you'll want a large PV arrary to cover as much as possible of winter electicity demand.  Even if you have a large array it'll be very hard to cover all winter electricity demand and you'll probably need to need to generate electicity in some way in the winter (wind turbine or burning diesel etc.).  The other issue is that in the summer you'll have a huge amount of excess generation that you won't be able to use of export!!

 

In my view off-grid makes sense if a grid connection isn't possible or if you are building yourself an interseasonal store, but otherwise best to have the grid connection and think that in the summer you are exporting green energy to it, and in the winter you are importing a lot less (ideally green) electicity, than you exported in the summer.

 

We don't have a grid connection, and I believe the cost of running all that copper to the site would be prohibitive.

I like the idea of being off-grid, and would rather spend money on off-grid generation and storage rather than to the power company to install a grid connection. 

 

It would be better to be on-grid, as you said. Exporting power, and making the national grid a bit greener. But at what financial cost?

I'm aware we'll be wasting a lot of energy in the summer, and that it's far from ideal.

[Smallholder]

On 31/10/2021 at 19:01, Marvin said:

I think your right about the maths. Espically as I think you can only use about 35% of a batteries capacity. 

 

I use this one for PV calculations:

https://www.google.com/url?sa=t&source=web&rct=j&url=http://re.jrc.ec.europa.eu/pvg_tools/en/tools.html&ved=2ahUKEwjewPf1qfXzAhVSsKQKHXFiC_UQFnoECB8QAQ&usg=AOvVaw2-K48UEog42OCvQZSZqZxU

 

Tricky on mobile to use otherwise ok. 

 

M

 

 

Modern lithium batteries are 90% to 100% DOD, depth of discharge
So you can certainly use a lot more than 35%

[Dan F]

4 minutes ago, Smallholder said:

 

We don't have a grid connection, and I believe the cost of running all that copper to the site would be prohibitive.

I like the idea of being off-grid, and would rather spend money on off-grid generation and storage rather than to the power company to install a grid connection. 

 

It would be better to be on-grid, as you said. Exporting power, and making the national grid a bit greener. But at what financial cost?

I'm aware we'll be wasting a lot of energy in the summer, and that it's far from ideal.

 

Compeltly understand if the connection cost if prohibitive, I'd get a quote to make sure though myself.   What doesn't make sense for me is going off-grid solely due to the idea of it..

 

What is the modelling software you are using by the way?  PV*SOL is fantastic and will be able to model this minute-by-minute, the only caveat is that for it to be accurate you'll need to set up your own load profiles manually as using a static x kW/day isn't realistic.   Creating a load profile before you live in the house is also a challenge.

 

Edited November 3, 2021 by Dan F

[Smallholder]

5 minutes ago, Dan F said:

 

Compeltly understand if the connection cost if prohibitive, I'd get a quote to make sure though myself.   What doesn't make sense for me is going off-grid solely due to the idea of it..

 

What is the modelling software you are using by the way?  PV*SOL is fantastic and will be able to model this minute-by-minute, the only caveat is that for it to be accurate you'll need to set up your own load profiles manually as using a static x kW/day isn't realistic.   Creating a load profile before you live in the house is also a challenge.

 

 

This chap actually wrote the software himself. I've said he ought to put it online for anyone to use, as I've not seen anything this comprehensive online before, or not for free anyway.
I did look at the PV*SOL, but it doesn't seem to allow for input of battery storage (assumes you are on-grid?)

[Smallholder]

15 minutes ago, Dan F said:

 

Compeltly understand if the connection cost if prohibitive, I'd get a quote to make sure though myself.   What doesn't make sense for me is going off-grid solely due to the idea of it..

 

What is the modelling software you are using by the way?  PV*SOL is fantastic and will be able to model this minute-by-minute, the only caveat is that for it to be accurate you'll need to set up your own load profiles manually as using a static x kW/day isn't realistic.   Creating a load profile before you live in the house is also a challenge.

 

 

The rough online quotation tool (Western Power website) gives me an estimate of £21,575.50

[Dan F]

12 minutes ago, Smallholder said:

 

This chap actually wrote the software himself. I've said he ought to put it online for anyone to use, as I've not seen anything this comprehensive online before, or not for free anyway.
I did look at the PV*SOL, but it doesn't seem to allow for input of battery storage (assumes you are on-grid?)

PV*SOL is very comprenshive and includes all specs for panels, batteries etc, it even takes into account historic temperature to adjust panel ouput using temperatuer coefficient as well as the difference that balanced/unbalanced strings have on inverter efficiency based on specific inverter spec.  I didn't use it for an off-grid set-up, but looking online it does support this as well as load-shedding and configuring of backup generators etc.  https://help.valentin-software.com/pvsol/en/calculation/offgrid-systems/

 

Your guys software may be fantastic, but I'd personally validate with PV*SOL too before you go out and build the system.

 

Quote

The rough online quotation tool (Western Power website) gives me an estimate of £21,575.50

Ouch!

[Marvin]

On 28/10/2021 at 21:37, SteamyTea said:

You are very brave.

Is that a quote from Yes Prime Minister?