Plug in solar

TroubledTarts

https://forums.moneysavingexpert.com/discussion/comment/81994949#Comment_81994949

You won't be able to store a good days solar production with that size battery.

With a two panel system we can fill 2 x 2kwh batteries and run our not small baseload of 135wh

So with only one of those you are potentially wasting 2kwh a day to the grid on a good producing day as your storage will be full. So it's not really 1000kwh pa useable generation.

Plus who really pays 25p kWh with TOU, fixed tariffs etc. our figure for comparison is 15.6p kWh as that was our average price last year on Agile and if I am honest more like 13p kWh during the summer months with this year expected to be cheaper with the new formula taking 3.5p kWh off even with the issue in the straight of pitta meze.

Realistic savings might be £60-£100 a year for the average personal? Unless you really work hard at it.

Don't get me wrong those German kits are great value and with the warranty do mean they pay for themselves but not at a rate of £250 a year.

Conversely someone on say Octopus go their daytime rate is much higher than 25p kWh so they could make an even greater saving. I guess it's down to your tariff and how much you can store and use at to what the savings may be.

QrizB

With a two panel system we can fill 2 x 2kwh batteries and run out not small baseload of 135

That might be true on good summer's days, but for a lot of the year you'll struggle to fill a single 2kWh battery with 2x 500 watt panels and a 135 watt base load.

My year-round average for my rooftop panels is about 2.6 kWh/kWp which would be 2.6kWh/day from a 1kWp array (950kWh/yr).

If your 135w base load is taking 1.6kWh from the system during 12 daylight hours, the "average day" will only have 1kWh spare to add back into the battery. And the battery will be flat again by dawn.

Of course, with the plug-in system set to cover a 135w base load then any day where you generate more than 3.2kWh will see some electricity exported (or wasted). April to September you'll see most wasted power; looking back to 2025s generation data, I think our hypothetical 1kWp / 2kWh system with a 135w base load would be wasting maybe 150kWh over that period.

(On the flip side, in December and January I'm happy if my system makes 1kWh/kWp per day, on average.)

But if it's notionally capable of generating 950 kWh a year and you waste 150 of those, that's still 800 kWh usefully saved.

At the SVT (and many people are still on the SVT) that's £200 a year of savings.

TroubledTarts

Absolutely yes the filling two batteries was a good sunny day indeed @QrizB

I was just pointing out you can't use all 1000kwh predicted at the very best for a two panel system and in fact good days (not sure how many there are as it's our first summer with this system) with just a 2kwh battery you won't be able to capture it all. Then you have losses of an inverter from DC to AC.

I just don't want people blindly going into it thinking they will get £250 a year payback and it all does depend on how efficient they are at using it, for example today I could see the connected battery filling up during a sunny spell at 800w and I was funnelling 150w into the house so being a particularly chilly day upped the input into the house to 750w, put the 600w small electric fan heater on then fell asleep with the dog for an hour then changed the setting again (not everyone has the luxury of doing that and not wasting energy back into the grid for example)

I take your point most are on the svt and with these kits gaining traction they may well be picking up many customers paying SVT and not on boards like these paying much less for their electricity.

So there are many caveats and no one saving fits all I guess is the answer it's dependent on many factors.

Still that Lidl Germany deal is an absolute bargain I do hope we see things like that turn up in the UK soon.

QrizB

Ok, the Lidl battery isn't quite as good a deal as I thought (although it's still an excellent price for what you get).

Folk on the 'net (even in that German-language link I shared on the previous page) think it's a rebadged Marstek B2500. One of these:

https://marstek.de/en-eu/products/saturn-b2500-d

Marstek are selling theirs for €399 too, but looking at the configuration diagrams it looks as though the battery is entirely DC; it doesn't include the grid-tie microinverter.

Marstek will sell you one for €109, so the total cost (excluding solar panels) is €508. Which is £440 at current exchange rates.

Still a cracking deal if you ask me!

tfhnota

The "battery" has solar input but output is 800W DC, so this is equivalent to a charge controller plus battery plus some wiring to make it compatible with a plug and play microinverter (which has its own charge controller and solar inputs) so some redundancy in this set-up.

Martyn1981

https://forums.moneysavingexpert.com/discussion/comment/81994978#Comment_81994978

Hi, no need to store it all, so to speak, as the OP said - "even with ideal generation and perfect usage patterns."

Hence I was working on the basis that 1kWp would generate ~800W max at ideal generation which will be consumed (not exported) (but even at 900W, the battery could store the excess).

I thought ~25p/kWh was a roughly fair price for leccy these days? Like you, I pay less, my average is very close to 7p as ~98% is cheap rate. But that doesn't seem the right figure to use in an example for plug-in-solar, and an 'ordinary' house, for whom TOU tariffs won't be a benefit. Even with a large(ish) PV array of 5.58kWp, TOU didn't work for us, until we got an EV. Larger PV and batts also make the shift viable, but that doesn't seem appropriate in this PnP example.

Martyn1981

https://forums.moneysavingexpert.com/discussion/comment/81995010#Comment_81995010

Regarding the 1,000kWh, that would be output after AC conversion. In the UK, a well orientated PV system in southern UK can manage that per kWp. Maybe 1,100kWh/kWp if ideal, such as coastal with cooling winds. And again, just to be clear, I'm not saying you would get that, nor save £250pa, I was specifically responding to the claim that you won't get an ROI "even with ideal generation and perfect usage patterns."

That statement suggests to me, ~1,000kWh pa (I won't go with 1,100kWh), and the usage pattern to consume ~800W/hr, or something in the 400W+ range, that will use the generation fast enough, before the battery is full, and generation is clipped (if demand is less than 800W).

Again, please be assured, I'm not blindly saying that you could save £250pa*, I also don't think that the vast majority of folk could, but I was responding to the conditions set out, which appear(?) to work out at ~£250pa.

Also, That's based on 2kWh storage, double it to 4kWh, and you have about 5hrs of ideal generation storage, even without any consumption on the AC side. So clipping would be minimal. That's another £350, but allows for more normal (rather than perfect) usage patterns.

We shouldn't, I agree, push nor suggest the income/savings levels from ideal situations, but we also need to avoid blanket denials of their potential economic viability.

Hope that makes sense.

TroubledTarts

https://forums.moneysavingexpert.com/discussion/comment/81995279#Comment_81995279

Absolutely makes sense I think I like to be a pessimist these days and work on the worse case scenario for payback on purchases like this so anything over that is a bonus.

I do agree with what @QrizB and yourself have said that many of these systems will be installed by customers on the SVT so that 25p kWh savings is a real benchmark and they are really going to notice the difference off their energy bills.

In any case these are interesting times for the hobbiest and I can't wait for the legislation to finally come out and to see all the people coming on and sharing their savings, their installs and asking questions.

Martyn1981

https://forums.moneysavingexpert.com/discussion/comment/81995307#Comment_81995307

Yes, as QrizB will know, I usually take a more modest view, and caveat my posts up the whazzoo. It's just that on this occassion, the comparison was to best case.

In reality, I'd guess at 600kWh/kWp being easy(ish), so 700 to 900 being a not unreasonable target, if you have somewhere suitable to place the panels.

It also occurred to me, that having a decent sized battery*, might allow you to move from SVR to TOU, using the battery from AC side charging in the winter. But then I got a headache! Your savings from the PV and battery would be lower, but only because the battery opened the door to TOU, and lower bills …… so the battery is still responsible for the savings IYSWIM, but becomes a rather complicated and circular issue to square in my head (pun intended).

I think this is a fun topic, and do hope, like Germany and many before them, that the UK can make use of PnP solar. It seems to be a topic/issue that the US is now adopting or looking to adopt. They have better generation than us (though some in the NW corner of Washington State (rainy Seattle) may disagree. Also, their PV install costs are roughly double those of the UK/Aus, as they have lots of permitting and marketing costs. So low cost PnP PV could be a monster hit. [LOL, I naturally fell back into caveating with the word 'could'. CYA]

*Going to depend on house and circumstances, but probably 6kWh+ useable, as a rough guess.

JKenH

I bought an EcoFlow Powerstream “plug in”solar system and connected it to 700w of solar panels in 2022. It was ground mounted on wheeled pallets that could be manoeuvred to optimise generation. On a good day in summer I saw over 9 Os (5.4 kWh). Being ground mounted it suffered badly from shading much of the year and after I got bored with wheeling it around the garden I left it in the optimal single position and found it generated around 550kWh p.a. at best.

These are definitely units for the “hobbiest”. Unless you are really into solar, you don’t want 2 great big solar panels in your garden (or on your balcony). Even then, while you might like them, your partner might not. The grandchildren, though, probably will, as the panels make a good goal for football. My set up is now parked, disconnected, out of sight in the field. My average import cost is just over 5p/kWh (although I do get 12p for export) 550kWh (from the EcoFlow app) so it’s not a great earner for me. If I were to reconnect it on sunny days it would push up the voltage and given that I already regularly experience multiple over voltage shutdowns on my Solis inverters on sunny days it would probably now cost me more than it would earn/save.

I am not saying don’t get one; they are much cheaper now, they can be fun (for some of us), and in some situations will significantly help with electricity bills but bear in mind the aesthetic impact for the non believer. I am expecting loads to be appearing used on eBay.

On the subject of efficiency, while I don’t have EcoFlow batteries, I do have several Bluetti power packs and I have found round trip efficiency (AC/DC/AC) is only around 70%. If using purely for DC/AC applications (using solar input only) then that might improve to 85%.