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[Waynemarlow]

A quick catchup for anyone not wanting to watch the mixed tennis/squash game above.

On Rob's Tarif. Daytime electric is 42 Pence per KWH. Cheap rate is 10 Pence Per KWH (1000w for one hour). He'll also pay a standing charge of about 45p a day just to be connected to the electricity supply.

Rather than paying 42p for his daytime rate, he'd like to capture and store 20kwh's (for example) in batteries on the cheap rate and use that during the day.

To do that he needs to invest in a large pile of (relatively) expensive batteries and some equipment to control the charge/discharge/change the voltages/stop the batteries getting damaged.

That then leads to the economy question.

How long does it take to pay off that investment on the 32p (42p-10p) saving he makes per KWH, also keeping in mind that the batteries and possibly other parts of his system, will need replacing over time.

If his land allows he could also build two ponds and use the cheap electric to pump water to the upper pond and then run that water through a mini hydroelectric generator during the day to create his electricity. Or just use a motor to lift an obscenely heavy weight up a ramp/pole on cheap rate and lower it to create power during the day. Gravity examples. Alternatively, he could put a load of sand in a large well insulated container, heat that to about 700c with his cheap electric and then use that heat to create electricity during the day.

The other issue being discussed is Supply.

He has a 100 amp supply (limited by the thickness of the cable to the house). Therefore 230v * 100 = 23000w he can use at once (peak)

The electric cars can charge on 32amp (7360w) or 16amp (3680w).

He also needs to pull about 3500w per hour to charge his 20000wh batteries (ignoring efficiency losses for simplicity)

Ummm some of that is some what incorrect and that is the nub of the dilemma.

Rob has the choice of paying on several tariffs for his electricity. He has chosen a variable tariff of 42P for 20hours and only 10P for the other 4 hours. He could also only pay 28.2P across the entire 24 hours.

Although he has a 100A surge fuse in his incoming electric cable he cannot pull constantly that current, to prevent overheating and excessive power load on the likes of local inter connectors in the street supply, it would be normal not to exceed a constant max of 63A on a local 16mm2 cable or 80A if the street supply to his house is 25mm2 ( only relatively new supplies will have this ).

Just to confuse the issue for the non electrical versed amongst you, no Rob will not be charging at 32A’s, the 32A’s he is talking about is the inline 32A fuse to prevent the charger overloading his house supply board. Now that lower figure of the actual charge rate ( possibly as low as 3.6KW or 7KWs if he has the car and EV charger to match ) will dictate just how much he can download in the 4 hours he has the cheap tariff ( 7KW x 4 = 28KWh, most EV‘s these days are 60KWh or more ).

As with all these tariffs it’s a bit of a maths game to actually see who wins, Rob or his suppliers in the monetary stakes.

 

[Zimmerframe]

he can download in the 4 hours he has the cheap tariff

Intelligent Octopus KWh is 10p for 6 hours

Just so were clear here as a large part of the discussion is "is it worth it" ... 10p kwh not 12p kwh and 6 hours of cheap rate , not 4 hours of cheap.

On the supply side, if his charger is limited to 32a - then that's the maximum it can draw and you're discussing maximums.

So 32a for one car 16a for another car and 16a for charging his battery's gets you to/or around the 63a your worried about (which is also hypothetical as we don't know any of the other details, cable lengths/quality/age)

Ummm some of that is some what incorrect and that is the nub of the dilemma.

What is incorrect ? We are discussing his situation based on the tarif he's selected. If he was on 28p constantly, we wouldn't be having the discussion and he'd just pay 28p.

As with all these tariffs it’s a bit of a maths game to actually see who wins, Rob or his suppliers in the monetary stakes.

I think this is effectively what we're talking about ? Yes, there's a degree of man maths as arguably you could say i'ts not a 32p saving per KWH as it's only an 18p saving over the 28p fixed rate. But as he has electric cars its logical to have the 10p/42p rate as most of his usage is charging the cars. It would cost him more on the fixed rate therefore the 10/42 rate applies to the argument. If you discount having the cars, then yes, the 28p argument applies.

In it's most simplistic form : at 10p kwh can he cover the cost of his new infrastructure before he has to invest more ? For example .. if it pays for itself in 3 years and we assume his system lasts 6 years (just examples). Then for the first three years it's cost him the same as it would now and for the second three years he's saving money.

 

[Rob Rides EMTB]

Exactly Zim

10p for 6 hours is totally worth it to charge the EV's

And the entire point of the discussion is CAN money be saved by purchasing house batteries to harness that cheap 10p rate and use it to power the house when the rate increases to the peak cost of 42p!

 

[Waynemarlow]

Guys I’m going to withdraw gracefully here and let you work out what’s best for you as it would seem the electrical parameter that of charging the EV’s and battery bank is your only focus and somewhat distracting you from the full set of electrical parameters.

Do let us know though Rob how you get on as it’s something we all will have to consider in the not too distant future. I see a future Vid of the installation and maths on a blackboard being on the Rob agenda.

 

[downunderdallas]

Exactly Zim

10p for 6 hours is totally worth it to charge the EV's

And the entire point of the discussion is CAN money be saved by purchasing house batteries to harness that cheap 10p rate and use it to power the house when the rate increases to the peak cost of 42p!

The situation is similar here is Western Australia albeit our power is significantly cheaper. We can source power at 8c (4.5p/kWh) during peak solar hours 9am-3pm and then 50 cents (28p) peak 3-9 pm and another should rate 28c 9pm -9am. One factor to consider is whether the Ukraine war has temporarily bumped up prices in the UK and will that eat into your "payback" should power prices decrease in coming years. If you have a meter that accurately tracks usage over time you should be able to do the maths. Here payback is still marginal at circa 7-10 years Tesla being just about the most expensive if the most sophisticated option.

We also have solar and 2 EV's and I keep an eye on batteries, haven't pulled the trigger yet... You probably have more e-bikes than my one Rob!

 

[billwarwick]

Interesting thread though. Someone mentioned disposing [legally] of the battery banks at the end of life. how do you do that, and what would the approx cost be?

 

[dobbyhasfriends]

Interesting thread though. Someone mentioned disposing [legally] of the battery banks at the end of life. how do you do that, and what would the approx cost be?

from my badly dredged memory, its part of the original manufacturing / purchase price etc? details are hazy because its years since i had to know them but they are here: Regulations: Waste Electrical and Electronic Equipment (WEEE)

 

[fenwick458]

And the entire point of the discussion is CAN money be saved by purchasing house batteries to harness that cheap 10p rate and use it to power the house when the rate increases to the peak cost of 42p!

the only way to confirm this is to get quotes from some installers, and the do some costings. It's difficult to figure out with current energy prices being so volatile.

I am not personally sold on the idea of the current battery systems they are expensive for what they are i.e £10k for 10kwh and it'll maybe last 5-8 years.
If you have 2 EV's already chances are you'll be one of them to another EV in 3 years, by that time there's a good chance that Bi-directional charging (V2G) will be standard and you will be able to use the EV's battery to power the house as long as it's plugged in

 

[Rob Rides EMTB]

I am not personally sold on the idea of the current battery systems they are expensive for what they are i.e £10k for 10kwh and it'll maybe last 5-8 years.

Not that expensive at the moment. As an example, I have found these all in one systems below that include battery and inverter. Its 20.48 KWH and priced at £8.5K

With current pricing I have worked out that on my Intelligent Octopus tarrif (essential for running EV's, makes it cost around £7 to fully charge).

The battery listed here is rated for 6000 full charge cycles (16 years by my calcs if cycled every day) and 10 year warranty.

Eco 7 tariffs have been around since i was a kid and maybe longer, so i think that there will always be cheaper rate off peak vs peak rates.

Hmm, more research to do still though!

 

[Mikerb]

just a few other considerations..........fire hazard, insurance, effect of temperature on batteries ( high and low)......possible H and S testing and authorisation.
Personally, I think efficient insulation is the answer to energy cost management, plus maximum use of LED lighting and observance of the golden rule.........if you are not using it, switch it off!!
Fortunately I live in a modern very well insulated house which despite being a fairly large 4 bedroom property is fairly cheap to run so have no incentive to spend significant sums on battery banks etc. My only concern would be power cuts and I already have a Jackory which is used for lighting our stables ( no mains there) and would be prepared to buy another bigger capacity model for home standby use. It would only really need to power a freezer, fridge, a few lights and the broadband hub for however long a power cut lasted and all of that can be done with extension cables.

ps I really do not think increased use of batteries when there are existing alternative sources of energy, is green!!

 

[steve_sordy]

Irrespective of whether you'd get your money back in a reasonable time, an important factor must be the software to make all the hardware actually work for you!

Unless you set yourself up as a day trader, trading in energy, then you will not have the time to sit on it the whole time, switching stuff on/off/over. I would want the system of batteries, power sources and sinks, energy in (from where), energy out (to where); all to be as automatic as possible. I want the system to decide when to charge the battery, from what source, and when to discharge and to where; or even both at the same time! All set up within user-defined parameters of course! And, of course, to keep track of the energy balance and the cost balance and to present it to me in a nice summary chart.
Then I can ride my bike!

I assume something like this Is this available with the systems being advertised, but how good are they?

Five mins with Mr Google and I got this, offered by Sunsynk, but I have no idea how good it is compared to the competition. This is not a recommendation as I have no user experience.

‎Sunsynk Connect

‎Sunsynk Logger App has been developed to help you get the most out of your Sunsynk inverter. It has been specially tailored for the customers and installers. Using the Sunsynk Logger app with your Sunsynk inverter gives you complete remote control of your system from anywhere in the world...

apps.apple.com

 

[fenwick458]

Not that expensive at the moment. As an example, I have found these all in one systems below that include battery and inverter. Its 20.48 KWH and priced at £8.5K

With current pricing I have worked out that on my Intelligent Octopus tarrif (essential for running EV's, makes it cost around £7 to fully charge).

The battery listed here is rated for 6000 full charge cycles (16 years by my calcs if cycled every day) and 10 year warranty.

cost to charge your 20kW battery at night 20 x 0.1 =£2, that would cost you (20x0.42)=£8.40 using daytime rates, so assuming you use all that 20kw every day you'd save (£6.40 x 365)=£2336 per year (in an ideal world with no losses)
but if the daytime rates drop to 20p/kwh next year then you'd only be saving £4.40/year, also the EV charging rate could go up
the 10 year warranty sounds good, but I bet it doesn't account for degradation. in general they are not lasting well, see here

Personally, I think efficient insulation is the answer to energy cost management

I agree. I've looked at a few energy saving ideas recently and it all seems to be a gamble. doing an accurate payback calculation just isn't possible we don't have crystal balls. Insulation on the other hand is a sure bet, you can bet it is going to reduce your bills for ever

ps I really do not think increased use of batteries when there are existing alternative sources of energy, is green!!

It's anything but green. an energy storage solution I like the sound of is heating your hot water cylinder using electric, If I had solar panels to capture the excess generation I'd just get a solar diverter (myenergi Eddi) and heat the water, instead of installing batteries. a water cylinder can store way more energy than any home battery, and much cheaper with much less maintenance.

 

[dobbyhasfriends]

a water cylinder can store way more energy than any home battery

there are also thermal batteries available, quite often used in conjunction with other renewables installs to make use of another PV diverter relay in addition to the one you already mentioned.
I was supposed to install 2 of them recently but like a lot of other work lately, got cancelled because of spiralling costs of materials.

 

[Zimmerframe]

Just curious if any conclusions were made on this one ???

 

[billwarwick]

Just curious if any conclusions were made on this one ???

Yes.. I have concluded that my brain still hurts .

 

[Zimmerframe]

Yes.. I have concluded that my brain still hurts .

This can only be good news ?

If it hurts, you can feel it - so it's still there. That fact that you can feel pain, which is processed by the brain proves it's working to some degree.

Moving onto advanced computation and decision making, you've made a conclusion. Concluding it hurts now in the same way that it did hurt. Proving that it's not only working, but working in spectacular fashion like a finely oiled machine.

Based on that, the better news is that you can rely on what it's concluding. It's obviously working 100% rationally. Therefore, if it thinks you want a beer or a wine later - it's right .. If it thinks you might want a new bike - it's right !

Happy shopping.

 

[billwarwick]

Thanks for clearing that up……and you need to get out more!

 

[Waynemarlow]

Not that expensive at the moment. As an example, I have found these all in one systems below that include battery and inverter. Its 20.48 KWH and priced at £8.5K

With current pricing I have worked out that on my Intelligent Octopus tarrif (essential for running EV's, makes it cost around £7 to fully charge).

The battery listed here is rated for 6000 full charge cycles (16 years by my calcs if cycled every day) and 10 year warranty.

Eco 7 tariffs have been around since i was a kid and maybe longer, so i think that there will always be cheaper rate off peak vs peak rates.

Hmm, more research to do still though!

View attachment 104357

Rob, did you go for a battery bank in the end and any updates of actual running costs / benefits ?