What to do with Excess/Cheap Power?

[Nick Thomas]

14 hours ago, puntloos said:

As in, is any cooling I put into that room (at 300% efficiency) more value for my kwh than seling it to octopus?

 

I woke up this morning thinking that the 300% efficiency thing is a bit of a red herring here ^^.

 

If you export at 25p (peak) in summer, then buy at regular prices in winter (again ~25p) to put into your heat pump, it still gets the CoP boost - it ends up being the same number of kWh of heating or cooling, the only difference is that you actually need the heating in winter, whereas the cooling in summer is marginal at best.

 

If your export is at the regular 15p in summer, then importing at 25 or even 35p (peak) in winter, then you take a loss - but it's 50%ish, rather than 300%.

 

 

 

[Marvin]

On 01/06/2024 at 18:17, MikeSharp01 said:

Can we know more about what this comprises - bikes, scooters, rodeo simulators......

Err... mobility scooters

[puntloos]

On 02/06/2024 at 10:46, Nick Thomas said:

 

I woke up this morning thinking that the 300% efficiency thing is a bit of a red herring here ^^.

 

If you export at 25p (peak) in summer, then buy at regular prices in winter (again ~25p) to put into your heat pump, it still gets the CoP boost - it ends up being the same number of kWh of heating or cooling, the only difference is that you actually need the heating in winter, whereas the cooling in summer is marginal at best.

 

If your export is at the regular 15p in summer, then importing at 25 or even 35p (peak) in winter, then you take a loss - but it's 50%ish, rather than 300%.

 

 

Certainly a fair point - of course I don't know what losses are involved when importing/exporting. Is a kwh exported truly a kwh? Assuming 25p important and export, is the grid a 'temporal' battery?

 

I suppose in the end it is all about losses. If you keep your house "closed" and any losses are at least as good as they get through your amazing airtightness and U-values then it doesn't matter too much when you put it into the house. My problem is that if anything my house is overheating somewhat so cooling in summer doesn't seem like a terrible idea. 

[gc100]

How do you all control the flow of electricity from inverter to HW, ASHP, etc when you are generating excess power? What control unit do use ?

[Andehh]

I just manually turn on the ASHP when the sun is really out, especially if it coincides with our cheap afternoon Octopus Cosy tariff.

[Nick Thomas]

On 08/06/2024 at 23:13, puntloos said:

I don't know what losses are involved when importing/exporting. Is a kwh exported truly a kwh? Assuming 25p important and export, is the grid a 'temporal' battery?

 

I'm not up on the logistics of it all, but export is measured at the meter in your house, not out in the grid somewhere, so I'd imagine the scope for losses is pretty minimal. Going through the inverter has an efficiency cost, but that's small - and paid whether you're using it locally or exporting it. Battery storage does imply some loss - I think the peak export rate is slightly more than the regular import rate to compensate, on flux? These kinds of adjustments to the overall picture are small, though, whereas the CoP idea was giving an impression of a very large adjustment. 

 

I do treat the grid as interseasonal storage, but it doesn't really have any of it, so doing this doesn't contribute to, say, burning less gas in winter in the same way real interseasonal storage would.

 

If you need cooling, absolutely use it for cooling, though ^^.

[puntloos]

On 09/06/2024 at 09:38, gc100 said:

How do you all control the flow of electricity from inverter to HW, ASHP, etc when you are generating excess power? What control unit do use ?

Sorry for the long delay, but to answer your question, my home is pretty smart with Loxone as the central brain. It's interfaced with my (solax) inverter so I know when I have excess power. Secondly it allows me to directly control heating (A2A, A2W ASHPs, including which FCUs should aim for which temperature, which UFH zones should heat or cool). My car charger is also loxone, so if I have excess power I have the option of cooling/heating my underfloor (and I have concrete floors so good thermal mass), export to grid, or put power into my car battery.

 

I am still somewhat struggling to wrap my head around what's the best to do with excess power. I find myself mulling over @Nick Thomas point:

On 02/06/2024 at 10:46, Nick Thomas said:

I woke up this morning thinking that the 300% efficiency thing is a bit of a red herring here ^^.

If you export at 25p (peak) in summer, then buy at regular prices in winter (again ~25p) to put into your heat pump, it still gets the CoP boost

 

This seems to certainly be true. So to make that a bit more explicit:

 

Peak: 16:00-19:00

- Avoid importing - Easy, normally, even on gloomy days. 

- Export everything I can - 23.63p gained.

    -> Arguably, fully emptying my battery into export might make sense because importing it during day rate is cheaper (23.08). I don't have that level of control on my inverter I think. 

    -> Similarly, not charging my battery during peak might make sense. (noting the above to not have to import during peak)

 

Flux: 02:00-05:00

- Do everything that can be done. 

    -> Wash laundry, wash dishes, heat hot water, heat/cool slab, charge car.

  

All other times:

- Charge battery if possible

- Do normal things

 

I guess I'll have to take a look at my inverter to see if I can tell it to do the above. 

[Nick Thomas]

2 hours ago, puntloos said:

    -> Arguably, fully emptying my battery into export might make sense because importing it during day rate is cheaper (23.08). I don't have that level of control on my inverter I think. 

 

I wouldn't worry too much about doing this. I've read that the difference between peak export and normal rate import is there to compensate for the inefficiencies in battery storage, although I forget where.

[Bramco]

22 hours ago, Nick Thomas said:

I've read that the difference between peak export and normal rate import is there to compensate for the inefficiencies in battery storage, although I forget where.

 

On Octopus Go Intelligent, cheap rate import is 7p and export is 15p - so that's a lot more than compensating for the inefficiencies of battery storage. So dumping what's the left in the battery before reloading it at the end of the cheap rate makes sense.  But disable any diverter during the dump.

Edited July 8 by Bramco