PV and Off Peak Usage

lucifer8554

Can't get my head around this.
I get some Off-Peak between 1300 and 1600 (Economy 10, so the storage rads in our electric-only house get an afternoon top-up).
Assuming the sun is out all day, do I get the most benefit from the panels if I use my power-hungry devices then ?
Or would I benefit more by using them outside the Off-Peak period ?
Thanks
Michael

Exiled_Tyke

You always want to use as much of your PV as possible. That said it will vary according to each appliance and the amount of PV you are generating.  e.g. if the system is generating 1kW but your appliance needs 3kW then it may or may not be cheaper to buy all the power at off-peak rather than when the PV is generating 1kW and buying 2/3rds of the power at peak.   

That said won't you be generating most around the middle of the day anyway - in which case put your appliances on at 1pm to ensure they get the best of both? 

lucifer8554

Thanks Tyke
Yes it's not clear is it.
Depending on the time of year, midday to 1300 is probably the peak generation period ?
(also EDF only installed a fixed clockwork Off Peak clock, so it's 1400 to 1700 in the summer)
Michael

Exiled_Tyke

Peak generation time will depend on the orientation of the panels. If they face East you'll get more morning generation and West evening. South facing panels should be at the best during the middle of the day

lucifer8554

I should have said, I'm lucky enough to have south-facing panels.
I'll try a calculation, if I can get my kW and kWh right..... :->

My Plug-In Hybrid charges at 3.4kW.

For 3 hours that's 10.2kWh ??

If my 3.4kW of panels are only outputting say 2.0kW, then there's a 4.2kWh shortfall.

So it's 4.2kWh at 10.54p/kWh Off Peak = 44p, or 21.62p Normal = 90p, plus 3 x 0.83p/h Standing Charge.

And if the panels were outputting 2.4kw or more, then it would be "free" charging, on either Tariff?

Exiled_Tyke

Your calculations look ok except ignore the standing charge - it's not a relevant cost as is has to be paid whether or not you are charging. (Although it makes little difference in reality).   I think you last line should read '..if the panels are outputting 3.4kW....' to get free charging.   However don't forget the 'baseload' of the house which will reduce the amount of electricity for charging the EV. .  Mine varies between 100w and 400w - the latter when the fridge and freezer both come on.   

The conclusion however seems straightforward. Best PV should usually be in the middle of the day and that's also when you get cheap electricity so always charge when your on the lower tariff to make sure you get the best deal. 

lucifer8554

Thanks Tyke
Thanks for spotting that the baseload needs to be taken into consideration.