UKC

Regarding the flexi electric tariffs (usually for EV users), is there a consensus that they will be around for a while?

I don't have an EV or Solar (house waaaay too shady), however, with tariffs instead of 28p/kwh all day, you can get ones that offer 7.5p/kwh for circa 6 hours at night and 32p/kwh during the day (numbers from memory).

I've been seriously thinking about installing an inverter and battery to charge at night and run all the base loads off the inverter with main backup for peak loads. 

The savings are quite considerable and fairly quick pay back, even after accounting for efficiency losses.

But with more and more EV users around, I'd expect night demand to slowly creep up, and may shortly get to a point where energy companies can't offer the cheap rates at night anymore.

Anybody got what resembles a crystal ball that knows of any predictions on this?

Some insight is critical to know whether such an investment is viable or not.

Ta

UK (and the world) is moving more towards more flexible and intermittent generation. The classic Economy 7 tariffs that you mention will go away with the final shutdown of coal in 2030, if not sooner. They exist as it is cheaper for coal plants to be left ticking over all night generating a bit of power than shutting them down, however this is less relevant for gas.

On the flipside, with more intermittent generation and smarter grid management, all of which is actively being developed/trialled/used at the moment, you're more likely to have tariffs that benefit someone with battery storage who can capitalise on excess renewables generation during the day, and offset your higher usage at night when prices will be higher, or arbitrage and sell back to the grid at better rates (not sure where the future of feed-in tariffs are going however, they're pretty rubbish at the moment). This site has some pretty good examples of tariffs Octopus are playing with https://energy-stats.uk/octopus-tracker-tariff/ particularly the All the Smart Tariffs comparison graph to get an idea how pricing may work in the future. 

Over time electricity should also decouple from gas pricing and get cheaper overall, however its hard to say how the relative increase of complexity and significant grid upgrades required to achieve electrification of heat and transport will offset the lower cost of generation through renewables and where it'll land. 

You know how when you go to fill up the ICE car with fuel, the price at the pump varies almost on a daily basis... well that's how electricity is gonna be. Every morning, before you put the kettle on, it will make sense to compare-the-market-dot-com and choose your provider and tariff for the hours ahead.

Will smart kettles exist that you can set to not switch on if the electric price is above a certain set point? With an override button for emergencies.

I think I need that battery and inverter.

I will be quite surprised if time-of-use tariffs aren't here to stay.  I'll also be surprised if overnight doesn't remain the cheapest period (possibly excepting long bright summer days when PV will dominate).  There are plenty of them and they're not all EV specific; Octopus have one with two cheap periods specifically for heat pump users, for example, and anyone can use Agile (which is a truly variable time-of-use price system).

Having said that, I would not buy just a battery and AC inverter.  Quite regardless of CO2 considerations, I think you will find it incredibly hard to make it pay.  I had a 3kW AC inverter and 9.5kWh battery installed about a year ago for about £7000.  If you manage to cycle that fully every single day, and the saving per kWh is in the order of 20p, it saves slightly less than £2 per day, and break-even is just over ten years.  It'll be losing capacity and out of warranty before you actually save any money.

A battery only really makes any sense with PV, not least because our batsh1t government charges VAT on batteries unless installed alongside a zero-rated pV system.

My current plan is a bit more of a DIY approach. When on offer you can get the Victron 5Kva inverters for about £1100. £1500 more typical.

For the battery I was planning on putting a second hand EV battery and reconfigure it to 48V with an off the shelf BMS. Plenty of options these days and can achieve 10KWh and 20Kwh depending on which battery I can get my hands on and what cell voltage I go with (I'll want to stay on the safe side).  Should be able to pull this together for £1500. Maybe £2000 for the larger unit.

Call it £4000 all in with a few miscellaneous bit and teething problems.

If I end up with 20Kwh I could realistically save £1000 per year. Payback in 4 years. Assuming I don't burn my shed down.

I could theoretically get a larger unit than 20kwh for not much more, but with a 4kw charger it would probably be a waste.

Although I am impressed with your set up for £7000. I would have guessed it would be more than that all in.

OK, that does shift the economics if you're brave enough to DIY it.  Do you actually use 20kWh a day?  Not much point in a greater capacity than your typical daily usage.

My system (GivEnergy AC3kW and 9.5kWh) can be bought for £4500; the rest was installer fees plus sundries.

Edit to note: there are also substantial amounts to be made from taking part in grid balancing exercises over the winter months; these can be in the order of pounds per kWh export.  But you need an MCS certificate for that... 

My system is a 3.4 KWpeak solar array that generates FA in winter coupled with a Renault Zoe battery. Even in winter - considering its ability to store 50kWh of off peak electricity for use in porting me and my luggage around for about £3.50 I think its a lot more useful that a 9.5 kW battery attached to my house. 

Have you got V2H on your Zoe?  

I think this has got to be the future but there are precious few cars which can do it...

no I don't think so - haven't investigated that thoroughly but I don't think the car does support that.

I put a 3kW Victron inverter in my campervan and have a 7kWh self built battery. That cost about £2,250. The van charges at night on Octopus Go and feeds back into the house in the day. Pretty much paid for itself in 2 years.

It's definitely doable with just an inverter/battery if you can DIY.

With Lithium Iron Phosphate, the cycle life it so good, they will die of old age before the cycle life is reached. Especially since the load from the house is so small, they don't experience the extreme charge/discharge requirements you get in an EV. Mine charges at 70A which is only 0.25C. It'll likely do 6000 cycles.

Octopus are allowing non-MCS installs for export tariffs now but you need to pay £250 for the privilege.

Time-based tariffs will definitely still exist.  We have virtually no power-hungry industry here in Guernsey and the daytime demand is still double nighttime demand (or was the last time I had a power station tour about 8 years ago).  Not only do you have generation companies wanting steady load, you also have the grid operators wanting to reduce peak load in order to stop the grid breaking - we already have people being refused electric boilers or meaty EV chargers because the cable feeding their road is at maximum load.  In the UK you also have / will have the 'problem' of large amount of wind generation available at night - it makes a huge amount of sense to move discretionary load from the daytime to take advantage of that.  What I think will happen is a granularising of off-peak tariffs - instead of 'cheap 7pm-6am' it will be 'cheap 7-10 or 10-3 or 3-6' in order to smooth the offpeak demand - loads of people will charge their EVs as soon as they can in the evening, so alleviating some of the demand at that time will be key.  Our tariffs here already do that to an extent - the time at which our off-peak period starts/finishes varies by an hour and a half on a customer by customer basis.

There's an offer on to get the Cerbo free until the end of 2023: https://www.bimblesolar.com/offgrid/inverter-charger/inverter-charger-48V/C...

The MultiPlus-II 48/5000/70-50 230V GX (GX is Cerbo built-in to the inverter) was £700 for Black Friday!

What EV battery were you looking at? The old Leaf ones are cheapish but the voltages are a little weird and they're Li-NMC chemistry. I'd prefer the, a lot less combustible, LiFePO4 in my house.

You can get 15.5kWh of brand new LiFePO4 cells for £2,500 with the case and BMS. They sell out fast on Fogstar though:
https://www.fogstar.co.uk/collections/lifepo4/products/seplos-mason-280-and...

Grief, that is cheap.  I almost wish I'd looked more seriously at DIYing it myself now.  Although god knows I'm so busy that I'd never actually get it done.

Oh, that's news to me.  Sensible, though.

Either leaf, outlander hybrid, or if needs must then maybe the BMW hybrid battery (or two).

I really like the outlander battery as it can be split into individual cells allowing for a 13S 48V nominal voltage setup. The leaf batteries come in pairs so I'd probably use 14S and the BMW I think is 6 x 16S packs (so 60V packs). So would either have to pull them apart, or use the flexibility of the Victron to compensate.

As I understand all of the above have 3.7 nominal voltage cells. What do you mean by the leaf having weird voltage?

If I do this, it will all go in a detached shed.

It does make the above work and risk far less appealing. 

I've actually got an Outlander pack in my shed in 7S. It was the first battery I bought. It's supposed to be 40Ah but prob only get about 20Ah these days. It hasn't aged very well but it's hard to tell what kinda life it's had. It's just used as a buffer between the solar panels on my shed roof (MPPT) and a 24V/600W grid-tie inverter.

As you mentioned, the Leaf cells are in pairs so you have to have an even S configuration. I guess 14S would be fine so long as the inverter supports it. It would be fine with Victron. It's not as easy to make a 12 or 24V pack with them.

Yeah, I haven't got time for that these days, plus the risk you're getting hammered second-hand cells. That Fogstar battery will prob last you 20 years!

Pretty much sums up my current thinking.

I really just hadn't realised how affordable LFP batteries had become. Their energy density has also crept up to the point where we should see them in EVs more also. Reminder to stay up to date.

You get to build the Fogstar too, so it doesn't remove all the fun

This guy's a legend if you haven't come a across him:
youtube.com/watch?v=igO3Q8lK7H0&