PHEV, battery storage and back-up supply

[scotview]

There is a possibility our next car will be a PHEV, probably a Ford Kuga.

We don't have solar but I am also considering the feasibility of a battery system for the following purposes :
1 Capitalising on night time electricity tariff.
2 Utilising battery storage as a back-up power supply (in the colder months) to provide power for our gas fired central heating system in the event of a power cut, to keep the central heating going for say 5 days.

As a first step I have contacted our gas boiler installer (BG) and boiler manufacturer (Worcester) and both say that they cannot approve a battery back-up system due to earthing incompatibility issues and/or damage to boiler electronics.

Has anyone looked at this type of battery installation/application and come across similar technical issues/limitations as per the above.

Thanks in advance.

[Mike4]

I am not an electrician but I take a passing interest in renewables and your plan sounds a good one to me.

I think the product that does what you describe is the Tesla "Powerwall". Other brands may be available but Tesla have tied it all up in a neat box and with a pretty bow on top. It is basically a lithium iron battery bank with an inverter in the same box IIRC. Nosebleed money though which will make the savings from using off peak tariffs seem trivial.

For economy of purchase I'd suggest looking at designing your own system using second hand batteries from a written off EV but if you're not up for that, then Tesla with their the Powerwall has (I think) done all the development work for you.

I think the guff you have been given by BG is well, guff because they have no idea what you plan to install, so the legal team probably drafted their stock reply to limit the chances of you blaming them if you design it all wrong. This is all very 'off piste' however and with 240Vac there is plenty of scope to get it badly wrong - so do take care.

There is a really big discussion forum about this sort of stuff, been going for years, where all sorts of truly expert advice can be found. https://www.navitron.org.uk/forum/

[Mike4]

Capitalising on night time electricity tariff.

Can you get a cheap night time electricity tariff when you have gas central heating? Not sure that you can (although things will likely change in the future)

We have a cheap night time electricity tariff because we have storage heaters fitted but (as far as I know) the cheap rate only goes to the heaters and the water heater, not to things like the lights etc.

I dunno about foreign lands like yours but down here in civilisation, an off peak tariff simply charges different prices for leccy at different times of day. Or more specifically, at night. So if yours is the same (highly likely really), you will be changed the lower price for all leccy burned in the low cost period including lights, washing machine, dishwasher, charging the car, ANYTHING.

The off peak output from your meter is simply a time-switched output for your convenience. The main output costs the low rate too when the off peak is ON.

[JonE]

If you only want to keep a gas boiler and heating water circulating pump operating, I'd think it perfectly feasible to run them off a three pin plug, plugged into an uninterruptible power supply as sold for servers/PCs etc...?

Not for very long. Powering a pump over a 5 day period (as OP suggested) is asking too much from a domestic UPS but at least the UPS as you describe it acts as a 'one-way valve': its output can't get back onto the mains wiring.

OP made passing mention of solar power but mains-connected PV inverters shut down when there's a cut in the mains power and will only resume when there's a good 50Hz mains supply re-established to which it can sync. They won't help at all during a power cut.

Haven't followed the topic closely but believe I've seen mention of an EV's own battery being integrated into an overall scheme and used for domestic storage (if you're not planning on going anywhere) - but that may not have applied to UK.

Cheers!

[PrincessB]

Robert Llewellyn (Better known as Kryten from Red Dwaft or more recently from the Fully Charged Show) has done this with at least one Tesla Powerwall and retrofitted the associated breakers and trips to switch over during power cuts.

He also put videos on YouTube to explain the process which is relatively simple for the powerwall and relatively complex for the circuit breaker for the power cuts.

Some parts of it sound like a fun project, an expensive project as a Powerwall installed seems to cost about £7-8 thousand and that's before the extra gubbins for unlinking from the mains.

What worth exploring would be whether the car can be fitted with a standard mains power outlet, I know some of the big electric offroad vehicles have something like this and supply sufficent power to boil kettles. While the electrical work required would be far more involved that running a power cable from the car to the boiler cupboard, it sounds possible to have the option to isolate the boiler and the pump from the mains and if and when you need to, to run just the heating system from the car.

B.

[scotview]

Interesting comment PrincessB, re the standard mains power outlet.

I did notice that the Kuga has a 3 pin socket outlet in the boot but wasn't sure if it was an inverter supply. I'll follow that one up, many thanks.

[JonE]

the Kuga has a 3 pin socket outlet in the boot but wasn't sure if it was an inverter supply.

'Live' only when 'ignition' turned on, extension lead strongly discouraged (risk of excessive loading and overcoming safety features apparently), max 150W, and, significantly, not suitable for loads such as motors (especially, I imagine, if any cycling on/off involved).

Cheers!
Edit: now found source in a manual:
http://www.fokuman.com/auxiliary_power_points-101.html

[richlist]

Ideal for plugging in a small fridge or coolbox.

[Mike4]

I know some of the big electric offroad vehicles have something like this and supply sufficent power to boil kettles.

For LiFePO4 batteries as found in EVs, even the tiniest ones, boiling kettles is a trivially light load for them. They are capable of delivering truly spectacularly high currents compared to LA batteries making them far more dangerous in the event of accidental short circuits. Equally when charging they can soak up every amp you can throw at them with a charge efficiency approaching 100%, unlike LA.

LiFePO4 batteries are truly wonderful things which behave differently from LA in every respect. For example they will be destroyed by both overcharging and over-discharging while LA batteries hardly care. Charge control of LiFePO4 is critical - the foundation when designing a high tech battery storage system. When utilising LiFePO4 batteries recovered from wrecked EVs, everything you thought you knew about batteries needs to be left at the door.

Here is some light bedtime reading about the characteristics of LiFePO4 cells, for those fascinated by this sort of thing.

http://nordkyndesign.com/practical-char ... ery-cells/

[JohnB]

Home batteries is still in enthusiast territory, and without government subsidy you will be paying a premium to do it now rather than wait. Most people do it to use their solar panels better, but you say you don't have any and if you are thinking of buying a hybrid with a small battery you'd not be diverting much power there. Its all sounds a rather expensive project if the main benefit is protecting your central heating.

I'd wait a few years until you can get full electric vehicles with reversible charging cables (only a very few can do so at moment), and use that as your backup supply.

the off/on peak rates for electricity will change over the next few years as BEVs race wind turbines and solar panels. I'd be wary about any major investment that relied on a particular on/off peak ratio

[richlist]

For the OP that may be good advice, maybe not. If you have a lot of spare money you can leave it in the bank earning say 1% or less. Alternatively you can spend £6K on solar panels or a storage battery and get an 8-10% return.

[88V8]

For the OP that may be good advice, maybe not. If you have a lot of spare money you can leave it in the bank earning say 1% or less. Alternatively you can spend £6K on solar panels or a storage battery and get an 8-10% return.

Or buy preference shares and get 5-6%. So, as has been said, it would currently be a hobby rather than a paying proposition, given that one has to amortise the battery and the inverter.

OP might also shop around for night rate. We are paying 10p to Ovo, which I gather is well ott. Will be investigating before we renew our contract come January.

V8

[richlist]

You don't have to amortise anything.......it's never compulsory is it. The expenditure is about return, an 8-10% return vs 1% means that the expenditure makes perfect sense.......provided you are not borrowing the money or using money earmarked for more important things.

[dspp]

There is a possibility our next car will be a PHEV, probably a Ford Kuga.

We don't have solar but I am also considering the feasibility of a battery system for the following purposes :
1 Capitalising on night time electricity tariff.
2 Utilising battery storage as a back-up power supply (in the colder months) to provide power for our gas fired central heating system in the event of a power cut, to keep the central heating going for say 5 days.

As a first step I have contacted our gas boiler installer (BG) and boiler manufacturer (Worcester) and both say that they cannot approve a battery back-up system due to earthing incompatibility issues and/or damage to boiler electronics.

Has anyone looked at this type of battery installation/application and come across similar technical issues/limitations as per the above.

Thanks in advance.

1. Tell BG & Worcester they are talking horlicks and damaging their already poor reputation even further by making such stupid uninformed and plain dumb remarks. They deserve to go bust. They will go bust.

2. The comments made by others about night time tariff likely becoming more rather than less expensive during the lifetime of a storage system are, to my mind, correct. So hesitate before making a decision based on that.

3. Early adopters are not doing this in the UK on economic grounds, so if you are economically-motivated then wait a bit.

4a. It is very much worth getting solar first, then storage later, especially if you are an EV owner.
4b. If you go for solar then I highly recommend the SolarEdge line of inverters and optimisers, and these are likely to be a good basis for battery storage integration either now or in the future.

5. Seriously consider going straight to BEV and not going for the con-trick that are most PHEV, which is relevant especially when you read 4 above.

6. AFAIK the only unit to have gone through the full certification process for automatic use as continuous uninterrupted whole-home power supply in a 'fit-and-forget' way for the UK market is the Tesla Powerwall. The others all have limitations in various ways. Most of them require additional system items to be fitted to be a zero-intervention grid-back-up; or you have to manually switch across to off-grid mode in even of grid/mains power cut (and manually switch back when grid/mains is restored); or they will only power some dedicated pre-selected home circuits; or multiples of these limitations. This is a real shame as I'd like to see the LG-Chem and Solar-Edge solutions introduced to the UK market in their fully-featured format, but at present these companies are not prepared to make the effort to certify the additional feature-sets that are available in other markets (making the UK market even smaller and more splintered off from the EU market by way of Brexit is not helping their decision making process either). That in turn means that Tesla, who are the ones who have made that investment, are able to charge a premium (yay, I'm a shareholder) and to restrict installers to those who are prepared to jump through some additional hoops (bad people Tesla, there are some excellent installers who you should be onboarding), and that in turn unnecessarily further drives up installed cost of a Tesla Powerwall system (bad, since I want one).

>>> --- (if anyone thinks I am missing a competitive product that is fully-featured for the UK market then please say so)

7. And the Tesla Powerwall can fully integrate into bi-directional Tesla vehicle charging and power management (now available to beta-testers), whereas nobody else is anywhere near mass-market for this.

(8. Personally if I had £3-5k spare and if LG-Chem or Solar-Edge had done the full-feature-certification thing, then I'd be fitting a 3kW x 9kWh system on my home as I have no driveway, so cannot bi-directional BEV integrate, except with an electric bike! So no point me paying a Tesla premium at present. But as yet the full-feature Solar-Edge is not available so this is a moot point. Note I already have 4kW of solar installed and am a big net exporter.)

(9. Personally, if I had a spare £10-£20k spare I would fit 2 x 6kWh Tesla Powerwalls at my GF's place, as she has off-street parking and we see BEVs in that mix. But first another 6kW of solar to add to the 4kW already installed to bring her towards being a net exporter rather than a net importer - it is a very large house with many residents).

(10. So in both cases, even for ardent adopters like us, we are waiting and doing other things first.)

... hope that helps.

regards, dspp

[dspp]

and for fun, here was my house with a 3.6kW solar PV system yesterday
- dspp

[dspp]

Very interesting. Makes sense to heat your hot water tank preferentially before exporting the surplus kw's?

RVF

I do, there is some of that immersion tank controller (using a Marlec iBoost) cycling going on in the self-consumption, although that is the secondary system due to time of use. At the moment I am only mopping up 40 kWh/month that way. So 1.3kWh of that 2.01 kWh is actually self-consumption into the immersion tank.

If I had a battery system I would probably switch from a gas cooker to a electric cooker and that would mop up a further 250-350 kWh/month, or 10 kWh/d eyeballing my Summer gas use (I would also reduce the timed hours on the gas >> hot water controller, to make that the secondary system as opposed to the primary system). That would balance me nicely for most of the year. But I want to wait until there is a fully-integrated battery solution at about the £3k price point before I do that. The LG-Chem one is at that price point but is not fully integrated in the version available & certified for UK use. So I will wait.

Then the decision making would be whether to squeeze a further 2-3 kW of PV onto the shed and go to a ASHP for heating, but that is a decision I expect to take in maybe 10-15 ?? years time when the (Weissman) boiler is at end of life.

regards, dspp

[PrincessB]

Always really interesting to read your posts dspp.

If I had a battery system I would probably switch from a gas cooker to a electric cooker and that would mop up a further 250-350 kWh/month, or 10 kWh/d eyeballing my Summer gas use

I'm assuming you're using the gas for the cooker and hot water? That then matches my Summer gas consumption of around 10 kWh per day. If you're using that amount of gas for just the cooker, I'm impressed.

Gas cookers are are not very efficient, the rings often seem to be designed to get as much heat up the side of the pan as possible while the oven needs a constant supply of gas, air and a vent to remain lit.

Electric ovens use a fair amount of power to reach cooking temperature, once they are hot, they only require enough electricity to remain hot. Similar situation with hotplates, especially induction ones - a 2kW induction hob will boil a pan of water far faster than a really big gas ring.

Essentially, you're likely to use fewer kWh of electric than gas should you make the switch.

Personally, when I get round to buying a plot and sticking a house on it, I'm going to take the advice offered by the housebuilders who say that if you've got access to mains gas then get a boiler in before they ban them.

B.

[richlist]

It's great to talk about summer months and virtually endless days of sunshine but this is not California. The winter months, approx late October - late February can produce very little solar energy in my part of England. Sometimes as little as 3 or 4kwh a day sometimes even less. After you've run your house, heated your water, tried to charge your car up, there isn't anything left to boost your battery storage. So, don't get to excited.

[dspp]

It's great to talk about summer months and virtually endless days of sunshine but this is not California. The winter months, approx late October - late February can produce very little solar energy in my part of England. Sometimes as little as 3 or 4kwh a day sometimes even less. After you've run your house, heated your water, tried to charge your car up, there isn't anything left to boost your battery storage. So, don't get to excited.

Every little helps. This is an elephant I am eating one limb at a time.

For the house with 4kW PV and 6kWh battery my calcs suggest I can go off-gas (or zero mains-elec-to-heat) for all except 12-weeks of the year in a typical year. But that is before I finish insulating my house and before I make the switch to elec cooking, which as PB below suggests may be more efficient. As my screenshot of yesterday shows most of my PV is spilling to grid at present, much more than the 50% assumed in the deeming calculation for FIT payments.

(I've yet to finish looking at this to understand i) how an extra 2kW of solar would affect things, and ii) how many months of the year I could run a BEV myself for)

Always really interesting to read your posts dspp.

If I had a battery system I would probably switch from a gas cooker to a electric cooker and that would mop up a further 250-350 kWh/month, or 10 kWh/d eyeballing my Summer gas use

I'm assuming you're using the gas for the cooker and hot water? That then matches my Summer gas consumption of around 10 kWh per day. If you're using that amount of gas for just the cooker, I'm impressed.

Gas cookers are are not very efficient, the rings often seem to be designed to get as much heat up the side of the pan as possible while the oven needs a constant supply of gas, air and a vent to remain lit.

Electric ovens use a fair amount of power to reach cooking temperature, once they are hot, they only require enough electricity to remain hot. Similar situation with hotplates, especially induction ones - a 2kW induction hob will boil a pan of water far faster than a really big gas ring.

Essentially, you're likely to use fewer kWh of electric than gas should you make the switch.

Personally, when I get round to buying a plot and sticking a house on it, I'm going to take the advice offered by the housebuilders who say that if you've got access to mains gas then get a boiler in before they ban them.

B.

Yes, that gas is hot water + cooking. At the moment the HW timer comes on about 6am which means the gas is the lead device in making hot water for the shift workers. If I had a battery I would make the immersion the lead fuel, but ideally there would be better integration at the HW controller as well. However I am also reluctant to adopt controller brands/products/kludges that I do not think will be supported by industry for 20-30 years so that also affects my decisions.

I understand your thoughts re a gas connection. However as I work my way down this pathway I am observing that the costs of the standing charge become more material. I guess it all depends on when and where you buy that plot.

Anyway I have just done another room with 100mm celotex or equivalent, finished on Fri, and that was the coldest & leakiest room in the house heat-wise. Just need some plaster for a skim coat, but plaster is as rare as rocking-horse-poop right now. It will be interesting to see how this winter works out for the heat load. Though that is driven by many other factors as well, mostly human ones. For me what is happening is that in practice I am using the same amount of gas but with more people and a higher temperature during winter (which both I and my lodgers appreciate).



regards, dspp

[richlist]

All of us with solar pv are exporting large amounts of energy to the grid at the moment.....because it's wall to wall sunshine.

Add electric cooking, heating, bev, battery storage & winter months and see how much you won't be exporting. I think your 12 weeks is to optimistic..... 16 weeks would be nearer the mark.

One thing is absolutely for sure.....with a 4kw solar array you cannot......run a house, heat water, charge a bev and top up a storage battery.....there just ain't enough bright days in the year.I

Perhaps a move to the West coast of the USA or Australia might help !