Heating oil, Immersion and Export with Octopus Flux

I don't really know where to ask this so thought I'd try here as you're a friendly bunch. Trying to understand if my calculations are right.

I have an oil boiler for hot water (into a tank) and wet central heating. Recently had solar installed, GE battery as well as Solar iBoost+.

Looking online, I've seen kerosene will give out roughly 10.35 kWh of energy for every litre. The cost of oil around here is about £0.60 per litre incl VAT. By my calculations that's about £0.06p per kWh of energy in every litre.

When you look at how cheap that is, and the rates of export on Flux (23p-36p during day), it seems pointless to me to heat my tank with the iBoost using solar excess, and instead just export and use the oil instead?

Am I missing something or thinking about this wrong? Totally appreciate the additional environmental aspect to consider, that is also a big factor for me. Though also want to pay off my investment as fast as possible. Even at its worst, oil was £1.80 a litre when Russia invaded Ukraine, which is still less than what I'd make through Flux export.

pacemaker I'm in a very similar situation. Turned my iBoost off once my flux export started working last week because using it would 'cost' money.
I wouldn't have bothered buying an iBoost if the export tariffs had not been so bad last year when we were looking into installing the system and I thought it would be more cost effective than using oil in the summer. Even then it probably would never have paid for itself.

Of course our single immersion heater installed at the top of the tank has proven insufficient for heating the whole tank (switches off quite quickly only ever used about 3kWh) so it wasn't really going to work without adding a second immersion heater or replacing the tank with a heat battery. If we'd ever used the immersion heater in the last 30 years I'd have known that!

How many litres of oil a day do you use in summer months? I reckon we used to use 2.5 litres @ 65p/ litre. Say £2.50 a day. So I’ve switched to a 10kw Sunamp heat battery ( 210 litre equiv). I estimate that we will recharge this with 4 kWh of solar ( 2 folk in the house) each early afternoon( my 9.5kwh GE battery is usually fully recharged by solar by noon, given reasonable sunshine. The Sunamp has a 2.8 kw immersion heater. So will need about 100 mins per day. In winter this will be offpeak at 15p per kWh = 60p . So far not tried to look at exporting from my 10 x 390 w panels. Bought the Sunamp 2nd hand for 20% of the price of a new one! Regards Bill G

I’ll have a look at Flux tariffs as some days I’ve sent 12kwh to the grid for free!!!

If economy is the reason for anything then anyone that can get on flux would almost certainly be better off exporting than trying to use excess generation for heat water as both gas and oil are cheaper per kwh. An iboost or eddi are great options (we have 2 Eddis) if you a) can't get paid to export or b) are on the FIT and get deemed export. Even the latter is questionable, but signing away the deemed export leaves you with no guarantee of that income however little it might be.

It gets a bit more complicated if you have EVs or heat pumps and the different tariffs make the sums a bit more work to sus out.

We're on oil and I'm glad to hear prices have come down some. It was 90p per when we filled up last so we only did 1500l rather than the usual 2000.

billG How many litres of oil a day do you use in summer months?

unfortunately I have no idea... I have a oil tank sensor but the gauge just shows "bars" on the display, in 1/8ths to full, pretty useless to measure specific litre usage.

pacemaker @billG we are on oil and I dip the tank every week or so to compare actual to the contents reported by our atom tank level indicator. In summer we average about 1l/day for hot water but I would divert PV to heat water if we had a hot water tank or a Sunamp. For me it’s not about optimising income, it’s about minimising our fossil fuel consumption.