Solar / Battery Storage considerations

I have 20kWh batteries and an ASHP. From end of January when Solar and batteries went in we managed on GO (686 out of 707 in February and 658 out of 700 in March with panels producing 363 and 396 kWhp). February was very sunny for me!

Our ASHP heats 300m2 so has a lot to do. The 12 months is looking like 2800kWh. From following various ‘fora’ I find that good heat pump monitoring makes one aware of issues especially short cycles and keeping the flow temperature as low as possible with a flow return difference of about 5C. I have some issues to take up with the installer.


GE system and Octopus here. When my fuxed rate ends ill do flux. But, when clocks go back, im expecting to go back to Eco7. Why? Well in the winter my batteries power the house and they are mainly charged from grid. In my case at E7 rate overnight. Sunce last November i have imported only 50 standard rate units. Partly because the GE inverter can be slow to respond and feeds via grid rather than battery for first 10 seconds. All this slackness adds up !

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Taking into account the difference in the size of arrays our winter figures are way lower than yours in winter but are broadly comparable for April. This must be down to the shallow angle (10 degrees) of our panels.

In summer the tables should be turned and we’ll get better than normal. In fact for the first 3 days of May we produced as much as the whole of December!

Ho many kw of solar do you have?

This is my earlier reply to you.

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I gave the solar installer the power records from our power bills. It looks like something is drawing power that the solar meter isn’t picking up. We suspect it’s the hot water and they are going to send a sparkie out to check it.

Enphase (our solar system) are bringing out a new battery system (IQ Battery 5), so it will be interesting to see what pricing looks like. It comes with a 10 year warranty with an option for an additional 5 years. I do think though, at best, batteries would save around $1,500 on our power bill per year, so probably still not a very economic solution at this stage.

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For a slight change of emphasis, here’s a picture of happiness from the myenergi app this morning:

The solar PV is generating 7kW (capacity is 8kW)
The car is fully charged to 80% of full
The Powerwall 2 is soaking up 5kW for use later today
The Eddi is diverting 1.5kW of surplus into the hot water cylinder
The house is using 400W

Best regards, BF


Built my own 2.5k for 15.5kw…check out EEL on youtube…they do a rather nice Mk3 kit - very professional.

Wow, impressive

I can dump 11kWh between 4-7pm at 36p/kWh on my tariff. Even in the day they pay 22p/kWh for exports. I buy between 2-5am at 20p/kWh and at other times 33p except at 4-7pm it’s 46p/kWh. Since I started at the end of January, 2052 were bought of which 1962 were at the off peak rate.

You may not have available a tariff geared to solar and battery.


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I think our range of tariffs is similar, though our rates are around half of yours, so its the total cost saving that reduces for a similar level of investment. As tariffs go up, I expect that batteries would look more favourable (depending on how the cost of the batteries trends over time).

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Didn’t quite make the 50 today. Still pleased with that though. I’ve read elsewhere these early months can provide the best days, is that the case or is it really around summer solstice?

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Just heard yesterday that we have a date for our installation of solar and batteries - should be all done by early June :grinning:


Here is something interesting. My mate has just had Solar Panels, solar diverter and Batteries fitted. However his meter is an old type with the spinning disc. He has no idea what will happen, and neither do I. Presumably it means anything he draws from the grid will go back the next day, and will end up with a meter going backwards

That happened to a colleague of mine with his meter going backwards until he had a smart meter (eventually!) fitted

At the moment he is trying to avoid that. I suspect he will gain overall, but of course won’t have access to cheaper electricity in the winter for night time charging

Our neighbour had an old meter at first when he had panels fitted and it went backwards. True story

Not sure if they all go backwards - though I have heard of people for whom they did. Ours doesn’t go backwards when the wind is blowing - not sure if that was engineered deliberately at installation of the turbine

Apparently we are also having our supply split so will be getting a smart meter soon (ish) which fits with the solar installation. Well; if that happens - the scaffolding was supposed to appear today but it hasn’t (though the electrician came for a preview yesterday)

We’ve just changed our Octopus tariffs.

We were previously on Go Faster with a 5 hour nightly rate of 8.25p but a day rate of nearly 40p per KW. We don’t have an electric car which this tariff is aimed at, it’s now actually mandatory but wasn’t when we joined.

I’ve been watching the Agile pricing over the past few months even during the back end of winter and there’s rarely been a day when it would have been cheaper on Go Faster. This is before factoring in that we can move to Agile Outgoing over SEG and increase our export rate to 15p from 4.1p per KW.

It’s looking very encouraging. Yesterday our net bill including standing charge was a princely 34p. Not bad considering the standing charge is 42.77p per day!

We don’t have batteries, just a small 3kw system but it really shows how well solar should work for us during the summer months. Even in winter it was covering our base load on many days.

Fingers crossed Agile doesn’t go through the roof in winter. If it does then we’ll need to switch to a standard variable tariff.

There’s a nice card available in Home Assistant to show the agile rates. I’ve also got it calculating a running total on the Energy dashboard and it’s great to see the amount we have spent coming down each hour as we export more than we use!


Is there one for Agile Outgoing? We are totally self sufficient and exporting 20kWh/ day of which 11 kWhs is at the Flux peak rate of 36p/kWh.

When we want to charge the car it will be while the battery also charges to ensure we have capacity for the high solar generation in the middle of the day.