Not sure if this equates, but by Solis 4G Inverter quotes the following figures. Dont think I can prove that though.
SolarEdge report a higher inverter output than the net meter. That is where the 95.5% comes from in my case. I’ve averaged the figures. The net meter is probably accurate to 1-2%.
I also found a US government energy site talking about 80% round trip efficiency for lithium batteries in general.
Phil
If I remember you don’t have a battery so all solar is converted and used either in the home or by the grid. Conversely home use in excess of Solar available results in drawing from the grid
The SolarEdge app gives me approximate figures for home consumption direct from solar or the battery, and grid import or export. So I can apply different efficiencies but I’m not convinced I am given sufficient information. The crude implication is that battery efficiency may be even lower.
I’m surprised no one with batteries is concerned about the efficiency of batteries. I suppose there is payback nonetheless!
Phil
I think a concern will be is whether the inefficiencies are included in calculations given by solar/battery salesman. Certainly when I’ve done calculations, even with current high fuel costs, I cant make batteries viable, with payback not coming until year 11 for a 6KWh battery. That’s assuming 100% efficiency, then you need to consider when they might need replacing, and to me it seems a lot of extra hassle for no big gain. Of course all houses are different
FYI Panel payback looking like just over 6 years, so very pleased with that
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It will depend on the tariff you are on. Octopus have several worth looking at if you have a battery (using it for load shifting).
I’m on Flux. Last winter Agile would have been 30% cheaper as on most day there wasn’t enough left to export without having to buy some before the next cheap rate. From May to October I can export 10kWh/day with some import judging the likely solar.
For the last 12 months I have paid £25/month to cover about 4K miles and heat with an ASHP supplemented by a wood burner in the evening. It a 300m2 home so big and fully heated to 18/20c apart from the cold spells.
Not dissatisfied but no one told me the battery round trip would be 80%. In fact the blurb implies 95%.
Phil
I pay 7.5p per unit at night and have ( as well as an EV) 19kWh of home batteries. Plenty to run all day in the dark winter months.
My PV export gets me 15p per unit.
Battery storage works for me. I tend to dump the battery each day before the 7.5p rate kicks in too.
My import from the grid is at 7.5p for about 99% of the time.
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Last year, once I take into account my FIT payments, my whole electricity bill was a net £220, so it would need a big negative bill to make Batteries work for me. (Remember I do also use a solar diverter for 95% of hot water which covers washing machine, disk washer, and free kettle for various things including weed killer). What I am waiting for is Car to Home/Grid In an EV vehicle - but no rush for that quite yet.
So is a big negative bill happening for people?
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I don’t think the net bill is as important as the cost of the energy you would have used. So £300/year net disguises £3000 at least for me. It’s a much better return than savings account and is better for the planet.
Phil
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Not sure I understand what you mean. In my case (and of course we all have different loads), to get a return on batteries in a lowish number of years, I would want more than a £220 annual savings.
You said last year your net bill was £220. That does not say much about what it used to be before the solar.
To illustrate my then and now converting the consumption then to current costs the bill for electricity, gas and diesel (current mileage) would be £3000 ish, but with the changes to electric only, I paid £300 for the year. So I have £2700 to set against the outlay. It will probably take 10 years or more to recoup, but it doesn’t really matter. I also don’t know what future prices will be.
Perhaps you can explain yours better.
Phil
Hi Phil,
I don’t know the precise round trip efficiency, though it would be useful to know.
Best regards, BF
Does your MyEnergy kit monitor the PowerWall? I find it reasonably good. If you get a report on the PW for a longer period then it shows totals for both directions. Round trip is just the ratio of export to import.
Phil
No, they don’t appear to connect.
Looking at the Powerwall’s lifetime energy flow figures, the Powerwall reports 9.3MWh of charging and 8.2MWh of discharging over about 2.5 years, which gives a ratio of 88.1% but it doesn’t say whether this is the dc in to dc out, or ac in to ac out. In other words, it doesn’t say whether the ac-dc and dc-ac conversion losses are taken into account.
I hope this helps, if only in part.
Best regards, BF
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Roundtrip losses i estimated to be about 75% ( or more precisely a loss of about 25%). This includes heat lost/generated by the inverter as well as battery.
My current inport tarrif is 7.5p/ unit, with export at 15p/unit. So still worth be topping batteries each night, and discharging in the evening.
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Well last year I export 2,248KWh to the grid, and that generated a £365 FIT Payment, so already a pretty good payment.
Moving to an EV with car-to-grid and/or car-to-home would allow me to squeeze a little more out of that and give me all the benefits of a Home Battery without the cost of one. I do realise that feature isn’t available quite yet, but my move to EV wont happen for a couple of years assuming I can squeeze a little more life out of my current car
FYI, I did once have a look around at getting a battery added, and struggled to find anyone that would do that. Most of these companies that sell these want to sell them as a package, which is where you get the discounts.
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FiTs is a bonus. No subsides now. The 12 months from 1 June 2023 was 2667. I get paid a few pence less than Standard rate for exports between 4-7pm but pay less than half for imports between 2-5am. So the grid is a means to recover 80% approximately of the solar surplus. But if I go off Octopus Flux there is a single rate for export like Roberto.
How much electricity do you use per year whether solar or from the grid? Did you estimate approximately 50% of solar used?
Phil
I have an Emporia energy monitor. If you just want clamps on the tails it easy to install yourself at a cost of £80-100. The Emporia 3 model is better.
I have this feeling the solar apps adjust the figures to suit their narrative. I have a net meter on the inverter circuit and that reads approximately 4.5% less than the app reports. The difference is probably the energy consumption of the inverter itself. Similarly I’m not sure whether the app reports panel energy prior to the micro inverters or after. They draw power as well.
I think the PW2 is AC in and out. The PW3 is about to be launched in the UK and is designed to compete with other solar/battery systems by offering DC from panels as well. I think there is a case for certification for systems a bit like vehicle emissions.
Phil
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4,657 Was generated by Solar:
931 of Solar energy was used by the house
1,478 of Solar energy was diverted to Hot Water and a 2KW heater in the hall
2,248 Was exported to the grid
1,434 Was imported from the grid
So yes, about 50% gets used by me.
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Can I ask a question. Some battery systems offer emergency power i.e Givenergy all in 1 and Tesla Powerwall. In event of grid outage it cuts in within milliseconds. Would that be quick enough to keep Naim kit alive. Hardly ever get power cuts so wondering whether the backup gateway is worth it