All electric house - back up power supply from BEV

[scotview]

dspp posted on the "gas matters" thread:

"Ban new gas boilers in UK from 2025 or risk missing net zero target, says CBI
Industry group says Britain’s climate goals may be doomed without heating overhaul"

This potential legislation kind of supersedes the strategy on my other thread re backup supply for a gas fired central heating system. So, as a thought experiment, could you consider the following future scenario.

A detached house with 3 bedrooms, all power is via electricity from the grid, nominal insulation. It's January in North Scotland, it's snowing, minimal daylight, there is a 4 day power cut.

Now assuming the occupiers have two BEV's and one is kept fully charged in the winter months and vehicle to consumer unit feed in is functional by then. How long could a typical BEV battery run the electrics for the above home and what would the maximum continuous safe power flow from the battery to the consumer unit ? (an alternative to the BEV might be,say, three Tesla powerwall batteries)

Hope I have made this scenario understandable, all feedback on this future scenario is welcome. Please keep this separate from my other thread re gas boiler backup power please.

Thanks in advance.

[Urbandreamer]

Now assuming the occupiers have two BEV's and one is kept fully charged in the winter months and vehicle to consumer unit feed in is functional by then. How long could a typical BEV battery run the electrics for the above home and what would the maximum continuous safe power flow from the battery to the consumer unit ?

How long is a ball of string?

I did a quick check and BEV's tend to have a 30-100 KWh battery. So which car?
https://greentransportation.info/energy ... izmos.html
I'll leave it to you to guess how much energy is used by the house in winter. I can only find TDCV's for the year.
https://www.ofgem.gov.uk/gas/retail-mar ... ion-values

Of course we could pluck figures out of the air, and get meaningless answers.

The concept of "safe" power is moot. Obviously the consumer unit should be designed to cope with the current requirments if there was no power cut. You are not talking about drawing more through it just because you get the power from a battery. You CERTAINLY won't be drawing more current than a car does in use. The Nissan Leaf has a 80KW motor. That's 26 electric fires runing all three bars (if anyone remembers them). Of course the car doesn't use power at that rate very often. Most EV fast charging is normally at 32A, so you can get flexible cables and plugs to cope with that current. At domestic voltages that would be 7.5 Kw, 2 1/2 fires. However BEV's are not currently designed to work that way.
A Tesla home charger can suppy up to 16Kw, but most homes don't have the supply cable to cope.
I beleave that the normal domestic feed is designed for 60-100A, that would be a 14-24Kw or 8 fires tops.

Personally I would suspect an occupent in such circumstances would reduce consumption radically and that the house would get pritty cold after a day, unless house design was significantly changed.

[JohnB]

Sorry about the 4 day power cut, presumably storm damage, as the wind turbines are still spinning, and the inter-connectors are bringing hydro-power from Norway and solar power from North Africa. Your heat pump is still working, though at reduced efficiency, but since you complied with new insulation requirements, its coping at 1kW, but are cautious about draining you BEVs flat as you are not sure when the powerline guys will be finished.

[dspp]

dspp posted on the "gas matters" thread:

"Ban new gas boilers in UK from 2025 or risk missing net zero target, says CBI
Industry group says Britain’s climate goals may be doomed without heating overhaul"

This potential legislation kind of supersedes the strategy on my other thread re backup supply for a gas fired central heating system. So, as a thought experiment, could you consider the following future scenario.

A detached house with 3 bedrooms, all power is via electricity from the grid, nominal insulation. It's January in North Scotland, it's snowing, minimal daylight, there is a 4 day power cut.

Now assuming the occupiers have two BEV's and one is kept fully charged in the winter months and vehicle to consumer unit feed in is functional by then. How long could a typical BEV battery run the electrics for the above home and what would the maximum continuous safe power flow from the battery to the consumer unit ? (an alternative to the BEV might be,say, three Tesla powerwall batteries)

Hope I have made this scenario understandable, all feedback on this future scenario is welcome. Please keep this separate from my other thread re gas boiler backup power please.

Thanks in advance.

If I recall you have a dream newbuild in your future.

A fairly standard Tesla is 80kWh.

My 4-bed terrace uses 1,000 kWh/yr of elec and 11,000 kWh/yr of gas, so 12,000 kWh/yr in total. If that was all-electric it would be lower as my gas boiler chucks a load of its heat out the exhaust, but for now let's use that 12,000 kWh/yr number.

So on an average day (I'll come to midwinter later) the house uses 33kWh at an average rate of 1.3kW. So you would get 2.4 days per car.

In peak winter months I use 2000kWh gas and 200kWh elec, so 2200 kWh divided by 30-days = 73kWh/day at an average rate of 3.0 kW. So you would get 1.1 days per car.

The peak rates are unlikely to be a problem. To get the bi-directional connectivity the technology will include a typical 4kW inverter as standard (and prob about 10kWh of storage), and these tend to surge to about 6kW, so really I don't think you would have a problem there.

I've ignored any input from the solar. Snowing in winter Scotland there is some, but not much.

However it is snowing, so it is warm. Conversely if it was a clear day/night then you'd get some solar but it might be a lot colder.

The things I have ignored are:
1) ASHP. Such a house ought to be run off an ASHP, and that will give you a real-world COP of (from memory) 3.2, so the actual elec consumption would be much lower. I'll let you do the maths, but this is very significant indeed.
2) Heat storage. Assuming you have been sensible and run wetloop underfloor heating in the well insulated concrete slab then you will get considerable heat storage. So you can probably live off that for at least a day.
3) User response. In such a circumstance I would expect you to turn the heating down a few degrees, and put on a sweater.
4) Log fire. If I was in sufficiently remote Scotland that a 4-day powercut was a realistic prospect (and I do know remote Scotland) then I'd include a logburning stove in the design. In a well insulated passivhaus that will run the whole place off one log per hour or two.

Take all those things into account and you ought to be able to deliver your stated 4-day target without too much concern.

This, by the way, is where we are going. The batteries may or may not be in the cars, or in the box in the house, or at some other level in the grid, but overall they will be sized for about a 4-5 day outage by about 2040.

regards, dspp

[bungeejumper]

Sounds like a case for keeping a smallish generator in the shed. Greta Thunberg won't like you, but surely an all-electric house with no electricity is one vulnerability too many?

BJ

(Don't forget, by the way, that even GT's solar superyacht was equipped with two diesel engines. Zero carbon my @rse.)

[PrincessB]

Sounds like a case for keeping a smallish generator in the shed.

Not a silly as it sounds.

Rather than consider the car, think of the old battery units which might only hold 60% of their original charge, but they are smaller than a car and a decent sized shed could hold the packs from a number of cars - I would assume they cells would be repackaged into a safe container with the associated electrics.

Add a small generator into the mix and the problem changes from how long you could run for to how complex do you want the system to be and how big is my fuel tank.

For example, a smallish water cooled engine would quite happily run a generator and the waste heat from the exhaust and to a degree hot water from the cooling system should be more than sufficient to heat a well insulated house.

Someone on here with a well built house that was all electric once said something along the lines of: Running about 1kW of heating to keep a big detached house warm, BTW it's -4ºC outside.

In the UK, going off grid with a generator and a fuel tank is possible and you can maintain a comfortable lifestyle.

Funny really, you can with sufficient effort live without gas or electric, depending on where you live fresh water may not be an issue and with sufficient space sewage might not be. Might be a bit of wrench to give up broadband though!

B.

[Urbandreamer]

It might be worth registering with this site and reading their old mag's
https://www.homepower.com/

I recall that they were a great resource.

[scotview]

Thanks for the comprehensive reply dspp.

If natural gas boilers are to be banned, I am surprised that you think that wood burners will still be allowed.

The premise of my scenario was that if natural gas is banned ALL fossil fuel burning would be banned.

If wood burning (not coal) was at be allowed, then that would be the better back up heating solution rather than BEV batteries.

I would seriously consider a wood burning system with gravity circulating back boiler (or BEV powered pumped circulation) but surely that will be banned too.

[scrumpyjack]

The new gas boiler ban, as I understand it, is only in newly built homes, not in existing homes.

I have an oil boiler, a very efficient woodburning stove, a lifetimes supply of firewood from trees blown over in the last couple of big storms (can't remember how many years ago that was but the wood will be really dry by now!) Also not on mains sewage etc, have 4kw solar panels

Suppose I could put in a Powerwall and a wind generator? What was that self sufficient series decades ago, The Good Life?

[dspp]

Thanks for the comprehensive reply dspp.

If natural gas boilers are to be banned, I am surprised that you think that wood burners will still be allowed.

The premise of my scenario was that if natural gas is banned ALL fossil fuel burning would be banned.

If wood burning (not coal) was at be allowed, then that would be the better back up heating solution rather than BEV batteries.

I would seriously consider a wood burning system with gravity circulating back boiler (or BEV powered pumped circulation) but surely that will be banned too.

1. Thanks for the thanks.

2. For the benefit of others, scotview is contemplating the situation where either he/she is doing a newbuild that is caught by the no-gas legislation; or the site is off-gas; or the proposed legislation is widened to include old-build; or just for the heck of it.

3. I don't think all fossil fuel use will be banned per se, at least not yet. I think that the gas grid access will be severely throttled (if ploticians take this seriously, which they don't) as I think in practice it will be unrealistic to do as deep a H2 penetration for most of the gas grid as the hydrogen-lobby are seeking (aka, please let me ignore all this for another couple of decades until I have made my £££ and departed the scene). In the global petrochem centres, yes / but not in the majority of the gas grid. I think coal will be pretty much banned. I think wood will be banned in urban settings (smog etc reasons). But occasional back-up / secondary wood use in country settings I think not in my lifetime. After all one would be primarily banning wood use in that scenario in order to ease enforcement (NO-burning!) rather than for CO2 purposes (a lot of country-wood for occasional use is stuff that would otherwise rot pretty quickly).

4. I was not proposing wood with a back boiler. I was proposing wood as a direct space heater for 'emergency / occasional ' usage only. If you were to do a passivhaus build then that would be perfectly adequate for the 4d scenario you envisage.

5. For those who are worrying about the COP of ASHP in deep cold periods I would say that it is always possible to construct a multiple-jeapordy scenario where everything fails. However the scenario is the somewhat more realistic one of:
- midwinter; AND
- deep snow, causing line failures; AND
- only one car charged (or the other kept in reserve (?? for getaway through such deep snow that the lines are down for 4-days ??!!)

That is already a double (or triple jeapordy) scenario. To get to very low temperatures you would have to add in;
- followed by immediate change in weather from near-freezing massive snow dump to clear skies and deep cold, but only after the high winds and deep snow have downed all the lines, switching almost immediately to a stable clear-skies no-wind cold. Hmmmm...... if you want you could add in an asteroid strike as well, it probably wouldn't make that much difference to the probability calcs.

6. It is always interesting to see others hobbying at postulating the sort of systems I have actually designed (and designed the design tools for) in the past. What do you think the run time between service intervals is on a small back-up generator, and what do you think the chances are that the OP will be able to (in practice) keep it running for 4d after unearthing it from the back of a shed in a blizzard. How many of the people in the UK population genuinely have those skills and can deploy them adequately in those conditions.

7. Yes, Homepower is good (does it still exist ?). I used to know the folks behind it quite well, but we all (mostly) lost contact with each other several years ago. But see 6 above for the reality of keeping the lash-ups going.

regards, dspp

[JohnB]

Wood is not a fossil fuel, obviously. It should be encouraged in areas with land suitable for forests and low population density where the particulates are not an issue. Northern Scotland would be an ideal place for that.

[scotview]

Evening all,

Many thanks for your very constructive comments.

Since EXISTING gas boilers will probably be allowed post 2025, I've posted a couple of my preferred scenarios on my other thread re PHEV battery backup.

The other thread covers dedicated battery backup and PHEV backup. These are technologies that I am familiar with so far. I am sure that BEV battery backup will also be a strong contender but haven't really studied this yet.

Anyway, many, many thanks for your input and please considered this thread closed.