It's all very complex comparing, every house needs are different.

I don't get paid for export, so try hard not to, drive an immersion if I need via diverter. On the GivEnergy App this sometimes appears as export and other times as usage and sometimes as both.

Have just over 6kW of PV, but lots of shading morning and evening due to trees, so generated 3100kWh.

Hopefully you can get paid in future? I think Octopus and some energy Co will pay for exports even if not signed off by MCS? 

https://octopus.energy/policies/export-tariffs-terms-conditions/

Condition 5.8

I guess you can use almost all pv solar roughly from end Sept to say end Apr? But peak solar prod is harder to use unless you can use it on EV, hot tub or other higher usage?

On sunny summer days I think my rough base usage (without ev, hot tub) is 10 - 12kwh/day.

Solar prod on sunny days is around 30 - 35kwh

But again highly variable.

@tim441 As you say, ‘highly variable’, daily solar production for me can be 35kWh or so but…. the last week or two has seen daily production as low as 5 kWh. 😒 My daily consumption during the summer months is approx. 13 - 14.5 kWh (we are all-electric and as the Sunamp Thermino uses approx. 3- 3.5 kWh per day for DHW our ‘normal’ house consumption is approx 11kWh.)

My Tesla Gateway and the app are set so that all solar production is exported @ 15pence per kWh and the Powerwall battery (27 kWh) charges on the cheapest Cosy rate (as does the Sunamp too). I suppose the difference between paying 11.2 pence import and the 15 pence for export is only marginal when allowing for the 10% charge/discharge losses - but it ensures I always have fresh electrons in the battery! 😉 Only kidding - I am still keeping my eye on the Agile or Cosy tariff and will summarise in a few months. Regards, Toodles. 

Posted by: @tim441

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Octopus and some energy Co will pay for exports even if not signed off by MCS

Tried 3 times, same answer NO. Even if they did, because I don't have a working smart meter they only pay about 4p. Plus if you want to be accepted on the scheme you have to pay them a bunch of money. Good marketing reality slightly different. Either way for 4p per kWh not worth the effort.

@johnmo That is a bummer.😒  We have a SMETS1 meter that was apparently ‘updated’ on-line by either EonNext or Octopus (we weren’t able to establish who carried out the operation) the result is that OE can read our SMETS1.5 meter; for all that we do get occasions where missing data delays the final billing. Checking with one app [Octoprice] we currently have some 12 days or more with much missing data! Regards, Toodles.

@johnmo sorry to hear that and hope a way can be found. 

I had fun and games with smart meter due to poor signal but got there in the end. They put in an extra antenna for one thing. 

Getting paid for exports also helps when SavingSessions are run and dump to grid.

Posted by: @tim441

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They put in an extra antenna for one thing. 

We are in Scotland and its all via a radio signal and additional antenna don't work - you are either in signal area or out, tried with BG and Octopus same result. Somewhat resolved to being on either standard or E7 tariff.

@toodles the Sunamp Thermino (which I know nothing about!) brings into play an interesting question on solar diverters. I decided against having one... partly as quite expensive to install... but also....

If one has an ashp (I do)... then heating DHW at efficiency SCOP of say 3 then it's likely to cost between 3p (ave cheap rate say 10p/kwh) and 5p kwh (ave solar export "lost" rate say 15p/kwh).

Also I have batteries to help store excess pv production.

So using a diverter and heating hot water via an immersion is strictly "costing" 15p kwh if one is on Octopus fixed exports and losing that income. Or more correctly a net 10 - 12p.

I hope I've got that right! That's my thinking anyway ..

Posted by: @toodles

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Sunamp Thermino uses approx. 3- 3.5 kWh per day for DHW

Posted by: @tim441

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heating DHW at efficiency SCOP of say 3

This morning our cylinder heated via the heat pump, it's a 210L UVC. It took 1 hour and we used 1.7kWh, but it will also most likely heat at 2 pm this afternoon (no solar today) and it seems to use about another 1.5kWh. I did have it set to heat when ever it wanted based on temperature, but it would heat 3 times a day using around 1.3 to 1.5kWh each time, so quickly moved to more control and set two heating slots.

So really I am using similar amounts of energy as the Sunamp, assume it's heating once per day.  So next question is do I need the cylinder to heat twice per day?

If I run out of water or the water is not hot enough for odd time showers and washing up the wife gets upset, so a trial is difficult - so monitoring is in order. I did do a period of heating the cylinder only by immersion and it seemed to go ok, but have managed to loose or delete costs. But I think I gave it a one hour window to heat, so no more than 3kWh. So may try that and monitor if I need the heat pump to add additional heat and see how my consumption goes before we get in to heating season.

@tim441 I follow your thinking and regard the solar energy as a negative cost of 15 pence if exported but any of that that I use is a positive cost of 15 pence; I prefer to pay the lower cost of 11.2 pence available to me for a total of 8 hours per day on Cosy during which time, my MyEnergi Eddi and the Tesla apps import for me to use later. I say use later as the Sunamp Thermino is a heat storage device through which our cold water passes to become hot water in a similar manner to a combi boiler.

My Eddi has been known to allow the Solar PV to power the Sunamp but most of the time, I use the programming functions on Eddi to use cheapest Cosy rate to charge Sunamp. At one time, I was getting a much lower payment for my solar export and the Eddi then used solar for the Sunamp charging. The Eddi is also used to switch on the dual fuel towel rail in the evenings for a few hours via the optional Relay Board that we had fitted to ours.

The reason we chose the Sunamp in the first place was due to MCS inflexibility; there are two of us living in a ‘4 bedroom’ house (even though one bedroom is less than 7 foot square) and they dictate that 210 litre tank is the minimum capacity for such a house. We had room in our airing cupboard for a 99 litre hot water tank and that served us very well (used the gas boiler to heat water at that time) but do not have accommodation anywhere for a 210 litre tank plus the myriad of pipes, sensors and attached ‘boxes’ that most HP powered tanks bristle with. The Sunamp units are approx 25% of the volume of an equivalent capacity conventional tank; we have 210 litre capacity in a box smaller than our 99 litre tank was - and still have an airing cupboard we can make use of! Regards, Toodles.

@johnmo Yes, the Eddi powers the Sunamp starting at 04:00 and by 05:15 or so, it has ‘reached maximum temperature’ and then holds sufficient energy to heat some 210 litres of water that we regulate via a tempering valve. Another good feature of the Sunamp is that it is very well insulated and total loss in 24 hours is typically 0.75 kWh or less. Regards, Toodles.

Just been looking at things DHW. So cylinder heated this morning for 1hr, it also reheated at 2pm, both are timed slots with a thermostat controlling. Total electricity used 2.7kWh. The cylinder thermostat has a 2 Deg hysterisis, a target temperature of 50. At 12pm the cylinder temp was reading 49.

As an experiment I have deleted the timed slot in the morning for ASHP heating and instead replaced with immersion heating for 1hr. So will in theory use 3kWh, have the immersion thermostat set to max temperature so it's not getting in the way. Will have a look first thing tomorrow and check the temperature it has settled too. But also check if it reheats in the afternoon heating slot.