Solar panels - which electricity am I using?

[bitstreams]

Thanks to everyone who replied. I have just had the statement of terms through from EDF and it shows that my Generation Tariff is 72.95 p/kWh and my export is 5.07 p/kWh (and I know this export rate is low by today's standards).

This suggests that I'll be getting 72.95 p/kWh regardless of whether I use the energy I export and a paltry sum if I don't use it. So it seems sensible to make best use of the electricity when I can (though that's probably always so).

 

[ericmark]

I have been looking at a report where someone went OTT with solar panel install, and I looked as one does at my own system, so yesterday

you can see I charge batteries for around 1 hour 20 minutes, and stop getting off-peak at 5 am, the battery state (purple) starts to droop, but rarely drops below 50% the inverter is only 5 kW so shower uses over that so uses peak electric, but if I could recharge battery at just 1.5 kW and only charge with off-peak to 70% it would be far better for both me and the grid.

But if the weather forecast could also adjust how much stored, it could be even better. However, the time taken to decide if to wash overnight or during day, one has to question, is it worth it?

 

[Lower]

Thanks to everyone who replied. I have just had the statement of terms through from EDF and it shows that my Generation Tariff is 72.95 p/kWh and my export is 5.07 p/kWh (and I know this export rate is low by today's standards).

This suggests that I'll be getting 72.95 p/kWh regardless of whether I use the energy I export and a paltry sum if I don't use it. So it seems sensible to make best use of the electricity when I can (though that's probably always so).

It’s actually better than that. If you generate and use the electricity, you get paid 73p per kWh and you save the 20p per kWh you would be pay to buy that electricity if you didn’t have solar panels.

 

[StephenStephen]

Wow - that's an impressive generation tariff!
You get paid that for the generation regardless of whether you use it or export it.
Your export tariff is very low - unless you have battery, or solar diverter, you're likely better off to get a smart meter, moving from deemed export (ie; they guess you export 50% of generation) to metered export and decent export tariff - have a look at the Octopus tariffs, eg flux, and if you do decide to move to Octopus, get a referral code from someone to save £50 off your bill.

 

[ericmark]

Not sure if it would help, for me rates are so the off-peak shorter (that's not a problem) but more expensive, 15.45p v 8.95p per kWh. The rest is split into two, 25.76p which is less than the 31.31p I pay now, and 36.06p which is more than I pay now, but that peak-rate is 4 pm to 7 pm and normally my battery will last to after 7 pm.

Where I will gain is 13.9p per kWh for export, OK 4 pm to 7 pm that jumps to 27.73p but most of the year, by then solar production has stopped, so does not really help. Tuesday as last day BG app shows,

7.31 kWh off-peak total 8.55 kWh cost £1.04 with £0.65 being off-peak, with standing charge £1.64. Hard to work out the flux cost, as not sure what used 4 pm to 7 pm. But midnight, 25% of battery left, so likely only the shower used peak power. As Excel is our friend

so because flex will pay for export, total for day 69p but if I had not exported it would have cost 47p more.

My tumble drier runs for around 3.5 hours, so in winter it will not complete within the 3 hours. So really not as good as it first seems, if I could get the export paid for with BG they would be better.

 

[bitstreams]

It looks like I would be better getting a battery or something to see that I'm exporting (solar diverter?) and heat up the hot water tank perhaps.
I was wondering if I could get a 2nd hand battery - presumably people upgrade - and store the excess. Not sure what I'd use it for - heating the greenhouse ?

It seems that excess solar is only really useful for tumble dryer, electric cars and hot tubs/pools.

 

[ericmark]

All down to tariffs, if the tariff for import and export was the same, then no point in a battery. The larger the gap, the more a battery helps.

I found a 3.2 kWh battery smoothed out the peaks and troughs nicely, so I could run equipment without worrying about the sun going in. But not enough to bridge the gap between dusk and off-peak starting. With Flex and off-peak not starting until 2 am, need even a bigger battery, with BG and EV tariff, off-peak started at midnight.

Every supplier asks for post code before they give rates, I don't know how rates vary through the UK.

But my inverter will work with up to 4 batteries, so moving from 3.2 kWh to 6.4 kWh was simply adding a battery, so no second hand battery as a result. But main thing is what the inverter can do. If the inverter is not designed to work with a battery, then cost to replace inverter likely not worth it.

 

[StephenStephen]

It looks like I would be better getting a battery or something to see that I'm exporting (solar diverter?) and heat up the hot water tank perhaps.
I was wondering if I could get a 2nd hand battery - presumably people upgrade - and store the excess. Not sure what I'd use it for - heating the greenhouse ?

It seems that excess solar is only really useful for tumble dryer, electric cars and hot tubs/pools.

Well it's also useful to sell to the grid, and to store in a battery to cover peak or no-solar times.
We have a solar diverter to the immersion heater - we rarely use it. It's bonkers that I can heat water from gas at about 5p/kWh (admittedly it's much less efficient than electricity), whereas if I use solar electricity to heat water I lose the (approx) 20 -25p/kWh I otherwise get paid to export that electricity. It makes no sense from a carbon reduction perspective.

 

[ericmark]

It's bonkers that I can heat water from gas at about 5p/kWh

Can you? What is the cost to heat up the boiler? OK, I am using oil not gas, I have no thermostat on the hot water cylinder so to heat it only control is time, so experiments showed if I switch on boiler (non modulating 20 kW) 4 times a week, for ½ hour at a time, in fact it only runs for 20 minutes on average, I have reasonably hot/warm water to wash with. So using around 25 kWh per week.

When solar fitted, got an iboost+ which actually tells me how much it has saved me, read that as how much solar used, as @StephenStephen says, need to work out how much one would be paid if not used to heat water, but the display said I had used less than 2.5 kWh for the week, 1/10th of energy used when using oil.

I have a run of pipe and a boiler to heat up every time it turns on, before it heats any domestic hot water. So, although loosing 13.9p per kWh by using solar to heat water, that is still likely lower cost to using gas or oil, unless in winter when boiler already hot.

However, once a battery is installed, really no point using an iboost+ may as well use a simple timer.

 

[Why Not Indeed]

It's bonkers that I can heat water from gas at about 5p/kWh (admittedly it's much less efficient than electricity)

Yeah, seems like it. Where are you getting gas at somewhat less than 5p/kWh?

 

[StephenStephen]

Yeah, seems like it. Where are you getting gas at somewhat less than 5p/kWh?

It's been a little higher than that in recent months I notice in fact - 6.01p/kWh today - it was below 4p for much of last year. It's an Octopus gas tracker tariff, which varies on a daily basis.