Solar Panel/Battery and Octopus Flux advice sought

JasMcG

JasMcG

JasMcG

Associate
Joined
16 Sep 2023
Posts
6
Location
London
Hi there.

New to this forum and looking for specific advice.

I recently installed 3.2kW of Solar Panels and a 6.5kWh battery.

Just this week I signed up to the Octopus Flux tariff which allows me to import electricity between 2-5am at a cheap rate.
I did this because I reckon that over winter I will get very little electricity from my solar panels and I'd be as well to top up my battery at cheap rates overnight and then source my electricity from there during the day.

Now, my question is: is this the right thing to do?
I ask this because I've noticed that I've been importing more electricity - as you would expect (!) - but wonder if this is the cost-effective thing to do, especially year-round or just during the winter.

Any advice would be appreciated, ta!
 
Check the rates. In my case, importing 2-5am is 18p per unit.
Exporting at other times is 19p per unit. So without a doubt, filling the battery when cheap is the thing to do.

It's better to export any dribble of electricity from the panels during the day, than have that electricity charging the battery.
 
Depends if in the deep winter days you will be using grid during the 4-7pm high price window. Without an EV tariffs are limited..
 
What is your typical house load draw? Battery you basically want to float you through past the 4-7pm period, great if it lasts til 2am again when you can charge for cheap and 3.2kw even on a bad day depending on your home load and orientation/angle should cover the house load at minimum during the day but worst case you will pay a bit on the 31p rate before flux period hits.

My system isnt that much bigger than yours, I am around 3.8 iirc, 425w*9 and my worst day so far has been 5.8kw yield from solar.

My midnight to midnight battery consumption with my house load which thanks to inverter is 80-150w higher than it previously was, energy reporting on Givenergy is crap so I got no idea what my 24hr energy usage for home is anymore, meter data only tells import/export/solar generation and battery charge and discharge and I really cant be bothered to math it all in to try and figure it out works out to the following, before I was using around 13-15kwh a day in home but now its more like 15-18kwh thanks to inverter/gateway/string inverter etc etc, I cant tell wth is drawing what and its frustrating the HELL out of me.

I will pick days without me charging from grid so its literally all battery and ill add in PV Generation for some consistency

16th 8.4kwh PV Generation 9.1
15th 9.1kwh PV Generation 17.7
13th 9.1kwh PV Generation 10.1
12th 10kwh PV Generation 9.1
11th 9.8kwh PV Generation 17.3

Solar has been going this month from ~7:30am to around 6:30pm GENERATION WISE facing nearly directly south, I think I am just a smidge off but at around 5-6pm the sun starts going behind house so I lose the rest of sun :( stupid back garden having a pool covering half of its length.

Here is some graph info of my load draw so you can get an idea of my consumption and battery discharge throughout a 24hr period, ill spoiler it as not to spam thread.

image.png

If you can get solid generation between 4>7pm id stay on flux, me personally I cba changing and battery should be able to get me at least through flux, worst case scenario ill just pay standard rate of 31p til 2am hits but thats no biggie tbh as days with lots of sun increase your leeway between what you can catch up on :D Saturday the clouds kept clipping the sun.

The pool out back has fish in so that has tank at end as filter+uv light, 2 pc's on 24/7 and gaming PC goes on in evening, the spikes in morning graph and evening that go high are fridge freezer kicking on.

You can tell in the spoilered image how much more power gets used over house load thanks to the solar/storage equipment.

Some of the tariffs are for people with ASHP/EV Vehicles but sometimes they don't ask for proof.

If your home usage isn't that high id stay on flux if anything for the export rates, at the very least if the sun comes out you should be charged long before 4pm hits and should start building up funds for when the days go to crap lol

Edit
Looks like from ~7pm-7am when there is no solar, 12hr period I use ~7-7.5kwh from battery when I don't charge it during flux period.
 
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Thank you for your detailed reply, alphaomega16.

I use about 3,000kWh of electricity per annum, so that's an average of just over 8kWh per day, spread out over the year remember.
We have gas central heating (and shower) and electricity for everything else.
During the day we have two TVs which are on for various times, a PC which is on for most of the day and a fridge/freezer which is obviously on constantly.
For cooking we have an electric oven and hob, plus an air fryer - I'd reckon we probably use those for about an hour per day (cumulatively, not an hour each!).
So, not a great electrical load most of the time.

Today my system has generated a meagre 0.8kWh so far - it's cloudy so hadn't expected much different tbh.

Right now I'm importing about 1.5-3kWh per night between 2-5am and that fills the 6.5kWh battery which then discharges to between 50-70% capacity during the day.
I would expect the volume of charging each night to rise during the winter as the nights get longer/days get shorter.
So, buying electricity during the night in winter whilst it's cheap is a good use of my system, right?

What should I do during the warmer (ie lighter) parts of the year when I will get more use of the solar I generate and use to charge the battery?
During summer, solar will be doing much more charging of the battery and I don't know if there's a need to top up from the grid - if I did then I would start each sunny day with a fully topped up battery.
With this scenario I would be exporting more (from solar) but is this the right thing to do?
During summer, should I still charge the battery from the grid at cheap rates? Or is this not cost-effective or a good use of my system?

Apologies if my questions are a bit on the naïve side, my solar/battery system is new and there are so many variations on how best to use it using Octopus Flux.
 
Even with a 13.5kw battery id set it to charge during cheap rate but let it keep going at 100% charge and run off the grid because if it turns out to be nice day anything you generate is extra 1p per kwh so battery just has to last from 5am to 2am :)

Although you will have to keep an eye on your battery to check its running as it should and you don't have any state of charge problems that cause it to drop and prematurely run from grid.

Solcast forecasting is a pretty solid site to check and can give yo a heads up on what to expect for next couple of days but you have to set it up with some info on your system, location etc etc.

It will probably take a couple of years to predict how far you can run on what you got and your routine and whatnot but you get to a fair idea for day to day if you are consistent.

No clue what the weather is usually like in London but if you keep an eye on what the day is like and your generation you can sort of get a feel for best/worst days and make adjustments based on that as well as time of year.

Aside from the cooker which is still gas in our gaff we are pretty much set up like you.

I just thought my battery and usage throughout periods with no sun might give you a fair idea how long yours will last, it sounds like you are around 50% of our usage and battery capacity.

Worst case scenario you draw a few from grid before flux cheap rate starts, best case you draw even on import/export so you only pay Standing Charge during crappy days but that is what summer is for, to bank a few quid for winter :)

I have only had my system since July 19th so im still on the learning curve myself.
 
Hi again.

I had replied yesterday, but obviously forgot to hit the send button . . .

Thanks again for your time and advice, alphaomega16.

Here's my thoughts, and I would welcome any comments.

In winter, I seems clear that it would be a good idea to use the Flux tariff.
I will be getting virtually nothing from the solar so it would make good sense to load my battery with cheap electricity overnight.

It's during summer that I am unsure about.
If I use Flux during summer then my battery will be fully charged come dawn.
From dawn onwards during summer I will be generating electricity from solar and (1) some of that will be used directly by my house, (2) some will recharge the battery as it drains, and (3) some of it will be exported.
So, that begs the question, should I use the Flux tariff during summer?
Why should I buy cheap electricity overnight during summer when my solar/battery combo can handle my needs?

I hope I've worded this clearly enough to make it understandable (!).

Thanks in advance once again for any comments.
 
In Winter I favour Go, as you said, very little export, Go lets me load the battery up for less cost, and I'm not exporting much.

In Spring/Summer Flux should be better.

In my opinion, on both Go or Flux it's worth charging the battery in the cheap off-peak window, for peace of mind.
  • On Go it's currently 9p/kWh import off-peak, and then 8p/kWh export on Go SEG equivalent all the time.
  • On Flux it was 18p/kWh import off-peak, and then 22p/kWh export roughly in the day, with a higher rate 16:00 - 19:00.
In both cases the numbers are fairly close, but bear in mind you do lose some efficiency importing elec from Grid and then using it later on, it's not 100% 1:1 storing it efficiently.

The main benefit here is that your battery is always charged no matter the weather, no need to really think about it or try and predict the solar gain. Less editing of the parameters = more chance it works smoothly.

The negative is that on a sunny day you didn't need to charge as much, but really you're not losing much even in this scenario with either tariff because the import and export costs are similar. If the battery fills up early then the rest just goes to export and you get paid something not far off what the import cost was.
 
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200sols said:
I'm debating agile or flux for winter now, cant get onto go. Currently on svr.
Click to expand...

It's a little cheeky sure, but I got onto Go, they don't seem to validate if you have an EV or not, so I just applied and went onto it.

Intelligent does validate and I would not be able to get that onto that.

Had to contact them when moving off Flux though to switch the Outgoing to SEG, as the default Flux outgoing was preventing the switch taking place properly.
 
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HungryHippos said:
It's a little cheeky sure, but I got onto Go, they don't seem to validate if you have an EV or not, so I just applied and went onto it.

Intelligent does validate and I would not be able to get that onto that.
Click to expand...
You just switched on the website? I could try I guess but dont want to mess anything up after just getting it all working :cry:
 
200sols said:
You just switched on the website? I could try I guess but dont want to mess anything up after just getting it all working :cry:
Click to expand...

I just edited my post above, it does let you but outgoing was an issue, I had to change export tariff with them first and then I could complete the switch to Go online myself.
 
HungryHippos said:
It's a little cheeky sure, but I got onto Go, they don't seem to validate if you have an EV or not, so I just applied and went onto it.

Intelligent does validate and I would not be able to get that onto that.

Had to contact them when moving off Flux though to switch the Outgoing to SEG, as the default Flux outgoing was preventing the switch taking place properly.
Click to expand...
ooo you cheeky bugger :D Nice one.

You got nothing to lose by trying and if you manage to get on even better, was just giving heads up that it could be hit and miss.
 
I just switched to agile yesterday in the end and kept the 15p export. They had me set up by 7pm and I charged battery overnight for about 3p... time will tell, windless winter days will probably be bad but can always move back to flex.
 
I'm still on flux and assume I will stay that way... I'm not sure agile would be manageable for me as it seems like you need several fingers on the pulse....
 
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