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UK Home Charging - Best Tariff's

PITA

Model 3 Performance
Sep 2, 2021
924
862
West Midlands, UK
My nerding numbers are weird...

Last year in April 2021 we used 359 kWh of Home Electric Consumption. But since then we installed our 7.2kWp Solar Array, 2 x Powerwalls, Heat Pump, 2 x Ev Chargers, Induction Hob, Ev Car...

So this year in April 2022 we used 1239 kWh which is a 3.5 fold increase.

39 kWh of that car charging I know came from the Grid. As it's registered on the 3 Phase Charger.

672 kWh of that came from Solar Array, and we consumed 98% of it. Only 12 kWh escaped over the fence.

540 kWh of that was imported at Cheap Rate from the Grid into the Powerwalls for Home / Car use. (5p / 7.5p crossover on Go Tariff)

But I have absolutely no idea how much Car Charging I did on the 7kW Ev Charger, as it's connected to the Powerwalls. So I've no way of telling how much of it is from Solar, and how much of it was low-tariff Grid Import Storage.

On the Tesla App, it just tells me I've been charging the car at Peak Rate during the day, and the App add's the Peak Rate Cost to this charging... but I know that's not true, as I regularly set the car to charge when Powerwalls are getting full during the day with Solar Energy, and the Ev Charger takes the power from the Powerwalls and puts it into the car (as like an overflow), not from the Grid at Peak Rate. So really it should be costed at £0 most of the time, with a bit of 7.5p mixed in, but there's no way of updating the Tesla App to show this.

We also had two Power Cuts during April. One for 5 Minutes at 04:20am, and One for a few seconds around 10:30pm... I only know because the Gateway says so in the Tesla App :D

So far our average Solar Consumption is 98% ... which I'm keen to maintain. Not much is going back to the Grid.
 
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WannabeOwner

Well-Known Member
Nov 2, 2015
6,920
3,665
Suffolk, UK
I have absolutely no idea how much Car Charging I did on the 7kW Ev Charger, as it's connected to the Powerwalls. So I've no way of telling how much of it is from Solar, and how much of it was low-tariff Grid Import Storage.

I am taking the view that charging during daylight hours is PV (might be PowerWall, but most likely that is just balancing during charging so either came from PV or will be replenished from PV that day). But I'd like better quality data in that regard ...
 
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I am taking the view that charging during daylight hours is PV (might be PowerWall, but most likely that is just balancing during charging so either came from PV or will be replenished from PV that day). But I'd like better quality data in that regard ...
That's also my assumption. I have a home-made power monitor measuring current/voltage to both my Tesla Wall Connectors. That feeds data back to an MQTT broker, to be distributed to various other processes. I also feed the MQTT broker with realtime data from the Powerwall's local API. Another process subscribes to MQTT to generate a .CSV file per day, plus daily/monthly summaries (for my wife's benefit - she's a bit of a spreadsheet wiz).

There's a home-made In-Home-Display in the pipeline too. It's become quite a retirement project!
 

WannabeOwner

Well-Known Member
Nov 2, 2015
6,920
3,665
Suffolk, UK
My days of deadlines, sprints, stand-ups, reviews, etc, are over!

Damn! I was hoping for a desire for nostalgia :)

I have a home-made power monitor measuring current/voltage to both my Tesla Wall Connectors

Presumably can have any number of clamps on a cable? so can double-up with those for Gateway and Zapping et al.

I want some alerts. Dunno why that is not more common - if a circuit in the house tripped (like the one that controls the sewage treatment) I'd like it to send me an email!

My PV trips once in a while. I wouldn't know until I got my next quarterly bill ... except that I (manually) read-and-record the meters (all of them, including Water and Solar Thermal) and thus discover if any of them are below-expectation. Solar Thermal gets air in it once every half dozen years ... nothing in all its clever electronics alerts to obvious faults. Thermostat? "Temperature has fallen below set-point, turn on request-for-heat" ... OK ... then what about "Temperature continues to fall" because boiler is faulty? Nix. Until I come home to a cold house ...
 
I'm investigating moving to an EV tariff but by logic I think I'd be worse off than just sticking to my British Gas tariff? Here is a rough example:

Screenshot 2022-05-03 at 08.54.54.png


Obviously the night rate is much better so charging my car would be cheaper on the EV tariff but the day rate and daily standard charge are so much higher I think I'd be worse off in terms of my total electricity bill. Am I wrong?

Oh and for clarity I think our average mileage each day would be something like 20-30 miles max (apart from the odd road trip every now and then when we'd probably be using a SuC anyway) so we'd be topping up about 20-30 miles range most days at home.
 

WannabeOwner

Well-Known Member
Nov 2, 2015
6,920
3,665
Suffolk, UK
we'd be topping up about 20-30 miles range most days at home

30 miles of short journeys probably not going to do better than 3 miles / kWh. So charging would only be 10 "units" per day.

Maybe you can move some "other stuff" to Off Peak - dish washer / washing machine using its inbuilt delay timer. But I doubt that amounts to a bag-of-beans. Although doing that "during the night" anyway would help with utilisation of North Sea Wind, so the planet may be better off ...

What's your day time usage? Do you know your "baseline" usage? - no cooking / lighting etc. You could use those as "day time" (daily usage minus overnight background usage) and "both daytime and off peak" (background) rates.

If your daytime is 1.5 kW and night time 0.5kw (plus 10kWh for car charging) that would be:

1.5 * 20 hours and ( 0.5 x 4 hours plus 10kWh)

30 kWh peak and 12 kWh off-peak

30 * 0.21347 + 12 * 0.21347 + 0.28217 = £9.25

30 * 0.3986 + 12 * 0.045 + 0.4823 =£12.98

Needs a lot more off peak proportion ... e.g. a much lower background load (electric immersion water heating (overnight) would help) - or a lot more miles on the car!
 

Adopado

Well-Known Member
Aug 19, 2019
5,979
4,534
Scotland
I'm investigating moving to an EV tariff but by logic I think I'd be worse off than just sticking to my British Gas tariff? Here is a rough example:

View attachment 800000

Obviously the night rate is much better so charging my car would be cheaper on the EV tariff but the day rate and daily standard charge are so much higher I think I'd be worse off in terms of my total electricity bill. Am I wrong?

Oh and for clarity I think our average mileage each day would be something like 20-30 miles max (apart from the odd road trip every now and then when we'd probably be using a SuC anyway) so we'd be topping up about 20-30 miles range most days at home.
It depends on how much day rate consumption your household (without car) uses. For the car consumption, with some leeway and losses added in, say 3000kWh annually which you can stick in your calculation entirely (hopefully) at the night rate. (You may be able to reduce your household day rate consumption by running some high consumption items during the night rate period too.) For equal ratio of daytime/night rate consumption you will be slightly worse off on the GoElectric (and even worse still if your day consumption is higher than 3000kWh annually, which it likely is) ... you would have to be using more on the night rate than the day rate to make it work in your favour. (But also bear in mind this may depend on you keeping your BG tariff longterm.)
 
There are more than a few pocket protectors in this group... saying that, it is great to see different numbers being shared.

I am a little disappointed to hear about the lack of monitoring - this is mainly on individual component consumptions right? We have nice app for monitoring the PV but I thought the Gateway was the answer?

We won't really know how ours all goes together till the Powerwall is installed in May (we will believe it when we actually see it, delivery was promised early this year).

Second question was - those of you with two Powerwalls, are you in the north? Or was the thinking that extra storage capacity was really necessary based on consumption?
 

PITA

Model 3 Performance
Sep 2, 2021
924
862
West Midlands, UK
There are more than a few pocket protectors in this group... saying that, it is great to see different numbers being shared.

I am a little disappointed to hear about the lack of monitoring - this is mainly on individual component consumptions right? We have nice app for monitoring the PV but I thought the Gateway was the answer?

We won't really know how ours all goes together till the Powerwall is installed in May (we will believe it when we actually see it, delivery was promised early this year).

Second question was - those of you with two Powerwalls, are you in the north? Or was the thinking that extra storage capacity was really necessary based on consumption?

My 'lack of monitoring' is only because I can draw power directly from the Powerwalls.. So if the Powerwalls are full, with a mix of Solar & low cost Grid... I can't easily see which is being used to fill the car. Except as a calculated percentage.

The Tesla App will only show me that I'm charging the car during Peak Rate time (so assumes I'm paying peak rate)... which isn't true, because I'm charging from the Powerwalls, not the Grid at peak rate.

The Zappi App will just tell me what my charge quantity was, not where it came from... as it isn't directly Grid Power, and it isn't directly Solar Power. It's coming mixed from the Powerwalls.

My 3 Phase Ev Charger is easier, as that's always directly from the Grid... but then my Tesla App can't see this Power flow, as it's not going through the Gateway. Only my Zappi App can see this Grid only data

I live in the West Midlands and chose two Powerwalls because of their ability to discharge at 10kW... this keeps me from drawing Grid Power at peak daytime rate... and the ability to run my house fully off-grid in the event of Blackouts.
 
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Dilly

Active Member
Feb 24, 2020
2,919
2,369
Norfolk
There are more than a few pocket protectors in this group... saying that, it is great to see different numbers being shared.

I am a little disappointed to hear about the lack of monitoring - this is mainly on individual component consumptions right? We have nice app for monitoring the PV but I thought the Gateway was the answer?

We won't really know how ours all goes together till the Powerwall is installed in May (we will believe it when we actually see it, delivery was promised early this year).

Second question was - those of you with two Powerwalls, are you in the north? Or was the thinking that extra storage capacity was really necessary based on consumption?
I’m in North Norfolk. My issue is shading from surrounding trees during the winter months, knocking generation down quite considerably.
Two gives ample power to get through 24 hours and of course the 10kWh discharge rate.
 
Crazy that its cheaper to public charge at a 50kWh charger than use home electricity during the day. I am not even on an EV tarriff and it is still cheaper to use a pod point charger with full fat VAT than the home electric that I also still need to pay a standing charge for the right to use.
even cheaper to use the Tesco 7kw charger while shopping - it's free :)
 
I’m in North Norfolk. My issue is shading from surrounding trees during the winter months, knocking generation down quite considerably.
Two gives ample power to get through 24 hours and of course the 10kWh discharge rate.
I've got the same problem. Winter shading - drops my generation down to 1-2kWh over a entire day (300w peak). While in summer I can do 30-40kWh on a good day, peaking at 6kW.
I've got the Alpha ESS 3kW system with 11.5kWh storage now - that's enough to get me through most winter days before the next 00:30-04:30 charge time.
Oh - and you mean 10kW peak discharge rate, not 10kWh. Although I think it's more like 7kW for minutes? 10kW for a few seconds.
As long as we're not running too many appliances at once 3kW is actually good enough for 99% of the day. ie. don't run the dishwasher, washing machine and oven at once. In fact all 3 of those don't use 3kW in our house. The first 2 are 13amp plugs that peak at 2.2kW.
 
I've got the same problem. Winter shading - drops my generation down to 1-2kWh over a entire day (300w peak). While in summer I can do 30-40kWh on a good day, peaking at 6kW.
I've got the Alpha ESS 3kW system with 11.5kWh storage now - that's enough to get me through most winter days before the next 00:30-04:30 charge time.
Oh - and you mean 10kW peak discharge rate, not 10kWh. Although I think it's more like 7kW for minutes? 10kW for a few seconds.
As long as we're not running too many appliances at once 3kW is actually good enough for 99% of the day. ie. don't run the dishwasher, washing machine and oven at once. In fact all 3 of those don't use 3kW in our house. The first 2 are 13amp plugs that peak at 2.2kW.
so in this case you charge your alpha at the same time as your car..? your draw during off peak rate would be at least 10 kwh if I assume correctly?
 
so in this case you charge your alpha at the same time as your car..? your draw during off peak rate would be at least 10 kwh if I assume correctly?
I charge the car:
1. in winter, only between 00:30 and 04:30 at 5p at the same time I'm charging the Alpha. Then the car does not pull from the Alpha. The Alpha is pulling 3kW to charge itself, the car is pulling up to 6kW charging itself. I've only got a SR+ so just manually set the car to charge. 11% is about 1hour at 6kW. So if I plug in at say 10% I set the car to start at 00:30/1 (as the Alpha wont allow me to set minutes) and set the limit to say 55% (roughly 4x11 + 10% startpoint). It'll then stop around 04:30.
2.In spring-Autumn. When I know the SOLIC 200 is heating my hot water (it's set to pull about 1100w as long as it's sunny) + the house battery is going to hit 100% and I want some car charging I'll plug in the car and set the Tesla's screen (or app) to charge at between 7 and 15 amps (depending on how sunny) so I'm only pulling off solar. If it's 3pm and the sun's going to be dropping low at 6pm then I set the charge limit % so it stops in 3 hours :)
It's annoying the Model 3 does not have a "only charge between xx:xx and xx;xx". It only has a "start time start charging" or a "depart by".
2b. If I am doing a long drive and need the 85-95% charge setting then sometimes I'll add that last 10% before leaving - it's best to keep the car in the 0-20 and 80-100% for the least amount of time... so I've read.
Gives me an idea for another youtube video...
 
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