Octopus Tesla and Powerwall

[PITA]

On my Tesla plan, once my Powerwall is full, I can charge off of solar, otherwise it just gets exported!

I have a 7kw solar array, 2 x electric cars, 12kw heatpump, solar thermal hot water, and 1x power wall.

On average across the whole year, we are using 28Kwh per day. Low day is 8.2Kwh and a high day is 77.9kwh. Looking at the Winter months, the average is 56.2Kwh per day, with a high day of 115.2kwh. The summer is naturally much less, during which we are pretty much exporting 40% to the grid everyday, as it doesn't all get used. In the winter, solar generates approx 7-8kwh per day. Powerwall is say 13kwh usable with losses, so we have a short fall, which gets very expensive outside of the 4 hour Go window.

Lets say, during winter, I could charge my car at 7kwh and Powerwall at 5kwh during the 4 hours window, Im only going to get 42kw of benefit. I can ignore export benefit as I dont export anything in the winter due to lack of solar.

Average Day:
42kw x 0.05 = £2.10
14kw x 0.16 = £2.24
+0.25p SC = £4.59
vs
56kw x 0.083+0.22p = £4.87

Heavy use day:
42kw x 0.05 = £2.10
73kw x 0.16 = £11.68
+0.25p SC = £14.03
vs
115kw x 0.083 + 0.22p = £9.77


Then, for me during the summer, I export around 40% of solar, so get huge cost recoup via that, along with the fact I import around 40% less as well,

Go Tariff would work out much more expensive for me personally, plus I am free to use energy when I would like too, rather than during defined periods.

Very similar to our setup, very nice...

7.2 kWp Solar Array
27 kWh Two Tesla Batteries (plus Gateway 2)
3.5 kW Emersion Heater controlled by Solar Eddie
7 kW Induction Hob
8 kW Electric Showers (x2)
8 kW Toshiba Haori Heat Pump (x4 indoor 2.5 kW units) Air to Air Reversible
7 kW Zappi EV Charger
82 kWh Tesla M3P EV

Just finished our house with an EPC Rating of A+ (105 Score) so we feel reasonably well set up now for a while.

 

[Dilly]

Very similar to our setup, very nice...

7.2 kWp Solar Array
27 kWh Two Tesla Batteries (plus Gateway 2)
3.5 kW Emersion Heater controlled by Solar Eddie
7 kW Induction Hob
8 kW Electric Showers (x2)
8 kW Toshiba Haori Heat Pump (x4 indoor 2.5 kW units) Air to Air Reversible
7 kW Zappi EV Charger
82 kWh Tesla M3P EV

Just finished our house with an EPC Rating of A+ (105 Score) so we feel reasonably well set up now for a while.

…and mine, though I still have an oil boiler. ASHP would probably struggle in our bungalow. Ground source is more feasible for us and we have the space for it. The price just has to drop!

 

[PITA]

…and mine, though I still have an oil boiler. ASHP would probably struggle in our bungalow. Ground source is more feasible for us and we have the space for it. The price just has to drop!

That's exactly why we installed an Air to Air Heat Pump, thats reversible.

We get Air Conditioning in all the living spaces, plus warm air in Winter when needed.

It's efficiency is A++ so about 1 unit in power equals about 4 units of heat.

This meant we didn't have to remove the Gas Boiler water central heating system. So we run the two in parallel on very cold Winters days... but only the Heat Pump on cold mornings in Spring... and then full air conditioning in Summer heat.

Perfect for us, as we get the best of all worlds...

 

[Dilly]

That's exactly why we installed an Air to Air Heat Pump, thats reversible.

We get Air Conditioning in all the living spaces, plus warm air in Winter when needed.

It's efficiency is A++ so about 1 unit in power equals about 4 units of heat.

This meant we didn't have to remove the Gas Boiler water central heating system. So we run the two in parallel on very cold Winters days... but only the Heat Pump on cold mornings in Spring... and then full air conditioning in Summer heat.

Perfect for us, as we get the best of all worlds...

Interesting. I hadn’t considered air to air. I can see the sense in that. do you duct it through ceilings or walls?
when gas finally pops it’s clogs, any thought what you’ll replace it with?

 

[PITA]

Interesting. I hadn’t considered air to air. I can see the sense in that. do you duct it through ceilings or walls?
when gas finally pops it’s clogs, any thought what you’ll replace it with?

Yes, for some reason nobody does !!

Everything is Air to water or Ground to water...

But rarely can these then offer air conditioning as well...

Our setup needs Wall Units in each room, which are plumbed in through the loft space with peristalitic pumps (completely silent).

It's lovely. Wall units are Wifi enabled for remote connectivity and fully integrated into our Smarthome with voice activation or app control.

Take a look at Toshiba Haori Air Conditioning.

Our Gas Boiler is being used less and less, but is there as a failover secondary backup.

Eventually might upgrade it to Hydrogen? ... or just keep my powder dry until something suitable comes along.

In the meantime, it's now off the radar as our house has an EPC Rating of A+ (Scored 105)

 

[PITA]

Just to add...

Our Solar Array produces power in Summer which feeds the house, this excess power is used to power the Air conditioning system. Further excess then goes to two Powerwall 2 batteries, then goes to the Tesla M3P EV for charging... So we waste nothing.

In Winter we download cheap tariff electric overnight into the car & home batteries, which lasts us the day.

 

[ACarneiro]

I find that my ASHP drops efficiency pretty dramatically in the really cold winter days, so I do use it for heating during autumn and spring but resort back to gas in winter.

 

[Dilly]

Just to add...

Our Solar Array produces power in Summer which feeds the house, this excess power is used to power the Air conditioning system. Further excess then goes to two Powerwall 2 batteries, then goes to the Tesla M3P EV for charging... So we waste nothing.

In Winter we download cheap tariff electric overnight into the car & home batteries, which lasts us the day.

We’re much the same. the last two years imported 2000kWh and exported 1000. Generated 8500 from solar. When both cars and Powerwalls are full and the water’s hot, can’t help but export. Winter is my problem, my panels get shaded by tall trees & low sun. Conversely in summer, my secondary panels shut down if their power isn’t used because they can’t export. I must do some sums…

 

[PITA]

We’re much the same. the last two years imported 2000kWh and exported 1000. Generated 8500 from solar. When both cars and Powerwalls are full and the water’s hot, can’t help but export. Winter is my problem, my panels get shaded by tall trees & low sun. Conversely in summer, my secondary panels shut down if their power isn’t used because they can’t export. I must do some sums…

Do you have one Powerwall 2 ... or more?

 

[PITA]

I find that my ASHP drops efficiency pretty dramatically in the really cold winter days, so I do use it for heating during autumn and spring but resort back to gas in winter.

Exactly our strategy. Works a treat.

Having Air Conditioning at home during Summer was the big motivator. Especially being so energy efficient and effective.

Total game changer being reversible, as it can now be used all year round.

 

[Dilly]

Do you have one Powerwall 2 ... or more?

We’ve got two.

 

[PITA]

We’ve got two.

Yes, perfect !!

Having the power delivery of at least 10kW constant deals with most daily demands without going to Solar or Grid. Perfect in Winter to keep everything running on cheap rate.

Nice setup.

 

[johnmwingnut]

Very similar to our setup, very nice...

7.2 kWp Solar Array
27 kWh Two Tesla Batteries (plus Gateway 2)
3.5 kW Emersion Heater controlled by Solar Eddie
7 kW Induction Hob
8 kW Electric Showers (x2)
8 kW Toshiba Haori Heat Pump (x4 indoor 2.5 kW units) Air to Air Reversible
7 kW Zappi EV Charger
82 kWh Tesla M3P EV

Just finished our house with an EPC Rating of A+ (105 Score) so we feel reasonably well set up now for a while.

Interesting to see you got A+. We only got given a B.

 

[johnmwingnut]

…and mine, though I still have an oil boiler. ASHP would probably struggle in our bungalow. Ground source is more feasible for us and we have the space for it. The price just has to drop!

We had the same choice to make. Ground source was way too much money for us and we have a huge field that it could have been run in. You say ASHP would struggle in your Bungalow - how so? We have around 186sqm of floor space and our ASHP has no issue heating it at all.

 

[johnmwingnut]

Yes, for some reason nobody does !!

Everything is Air to water or Ground to water...

But rarely can these then offer air conditioning as well...

Our setup needs Wall Units in each room, which are plumbed in through the loft space with peristalitic pumps (completely silent).

It's lovely. Wall units are Wifi enabled for remote connectivity and fully integrated into our Smarthome with voice activation or app control.

Take a look at Toshiba Haori Air Conditioning.

Our Gas Boiler is being used less and less, but is there as a failover secondary backup.

Eventually might upgrade it to Hydrogen? ... or just keep my powder dry until something suitable comes along.

In the meantime, it's now off the radar as our house has an EPC Rating of A+ (Scored 105)

I’m going to look this up, very intrigued. I’m planning an upstairs extension to our Bungalow and plan on putting in MVHR, as it would then only require us to put towel rads in the en-suites upstairs to fully heat the place, given the ground floor slab is already heated. No match for aircon in the summer, but can bypass the heat exchanger to dump heat out of the house.

 

[johnmwingnut]

I find that my ASHP drops efficiency pretty dramatically in the really cold winter days, so I do use it for heating during autumn and spring but resort back to gas in winter.

How do you have it setup to function? I’ve found that ours is much more efficient when only asked for lower flow line temps at around 25-30degrees max.

 

[johnmwingnut]

Yes, perfect !!

Having the power delivery of at least 10kW constant deals with most daily demands without going to Solar or Grid. Perfect in Winter to keep everything running on cheap rate.

Nice setup.

Maybe only having 1 PW is where I have gone wrong then. Your setup is very similar to mine, and maybe 4 hours of off peak electricity would work if I changed charging behaviours / had a second power wall.

How do you get your Solar Eddie to work with the ASHP / Solar thermal? as we were told we could not have that along with our ASHP, as it’s control unit governs the use of the immersion heaters.

I assume you also have the Zappi charger which then gets to work either when export is detected or in off peak 4hr window?

John

 

[PITA]

Interesting to see you got A+. We only got given a B.

Yep, it was the very first EPC A Rating he'd ever given... and apparently he's some Supervisor/trainer/commitee member as well.

So he was as excited as we were.

 

[PITA]

I’m going to look this up, very intrigued. I’m planning an upstairs extension to our Bungalow and plan on putting in MVHR, as it would then only require us to put towel rads in the en-suites upstairs to fully heat the place, given the ground floor slab is already heated. No match for aircon in the summer, but can bypass the heat exchanger to dump heat out of the house.

Yes... that's my plan for next year. I want a MVHR system for filtered air circulation... as we've also had full 6mm laminate glass double glazing & doors fitted for thermal efficiency & sealing.

I plan to balance the MVHR Pumps myself...

 

[PITA]

Maybe only having 1 PW is where I have gone wrong then. Your setup is very similar to mine, and maybe 4 hours of off peak electricity would work if I changed charging behaviours / had a second power wall.

How do you get your Solar Eddie to work with the ASHP / Solar thermal? as we were told we could not have that along with our ASHP, as it’s control unit governs the use of the immersion heaters.

I assume you also have the Zappi charger which then gets to work either when export is detected or in off peak 4hr window?

John

Yes... I specifically chose two Powerwall 2 units because of the power draw demand in our house is around 8kW maximum. So this'll keep us within the 10kW power draw limits for continuous use.

It's due to timing, but we have one Powerwall 2 & one Powerwall 2 Plus which can handle more load.

Anyways... it's having two Powerwalls that keeps our daily loading within scope for 'off-grid' blackouts and Winter cheap rate use.

No point going for a 3rd Powerwall as I don't have a cheap rate tariff window big enough to fill 40kWh of battery. So 27kWh is enough.

Our ASHP is an Air to Air system, completely independant to the Water Central Heating System.

So Eddie operates from Solar Excess and heats the water tank via emersion heater. Even if Solar isn't much... the Gas boiler then tops up the water tank heat. Both work alongside each other 100% happy.

Yep, Zappy charger again works via Solar Excess... and I had it wired directly into the Tesla Gateway 2 unit... this means it can be used to charge the car during Grid blackouts from Solar or Battery... or isolated completely.