Solar panels and battery - any real world reccomendations?

[HungryHippos]

Solcast predictions definitely aren't perfect, at best it's an idea but I've seen it be pretty wrong. The day ahead value is the only one you can really rely know for forecasting.

If you could guarantee say 20kwh of generation per day, then you could be in a scenario where charging fully overnight then leads to excess export. The cost for that is the difference between import and export prices.

I'd like to see Givenergy adding an option to dynamically charge battery based on the day ahead solcast figure, as it would potentially be a little more efficient.

Alternatively if SEG paid properly it should at least match the Go off peak import pricing, then it wouldn't really matter anymore.

 

[Mercenary Keyboard Warrior]

The grid electricity I will be using is not extra electricity, the idea is that if I don't have enough power to make it through the night, I turn the battery off between 4 and 7 and use grid units then, rather than leaving the battery to go flat later and use the grid overnight. So should be the same number of units imported, just that it happens between 4 and 7 rather than from the early hours of the morning through till sunrise.

I'm not on Go or similar so paying a fixed 34p per unit at all times.

Are you saying you have batteries but you are not on a cheap charging tariff?

 

[Mercenary Keyboard Warrior]

I think generally it makes sense to charge the batteries on a cheap tarrif at night regardless? If the days ends up being good you just export, or do LOTS of washing! It'll still work out cheaper than not having solar at all in either case - unless you're being particularly careless.

I think for probably 6-7 months of the year yeah full charge no matter what, somewhere around sept-march you just lock in your benefit of batteries by off peak charging.

 

[Tavis75]

Does anyone here use SolCast?



Came across it the other day and it's now integrated into my givenergy dashboard:



I thought that was quite cool - shame you can't see it on the app and that you have to log into the solcast website to access the graph - but useful for planning energy usage / battery charging etc... It might help with @Tavis75 point that you can plan your cheap night rate charging for poor weather days meaning you can use battery power when you get the bonus scheme going?

That looks interesting. I've been messing about with some Javascript on my home automation system (Athom Homey) to allow me to automate some stuff on my GivEnergy battery and one thing I was considering for the summer months was trying to create something that would try and toggle charging on and off, so that it would try and do all charging for the day in the cheapest Agile Export periods whilst exporting to the grid at the higher paying times (but still charging enough to reach 100%). This is something I've experimented a little bit with doing manually before.

So, factoring in expected generation including a weather forecast could help, though as has been said not going to be entirely accurate, so how well it would actually work I don't know, but figure that with a bit of a safety margin and recalculating through the day it might be able to get something that worked OK (unless it suddenly and unexpectedly clouded in late in the day, right when the charging had ended up scheduled for)

 

[Tavis75]

Are you saying you have batteries but you are not on a cheap charging tariff?

Yes, no EV so Go isn't an option (and would then miss out on Agile Export), Agile Import was pretty horribly priced until recently (I've been considering switching now, but worried the current reasonable prices may just be a blip) and last time I looked the Economy 7 tariff seemed to have a higher night rate than I was paying on my standard tariff, although don't think I've checked it since the last price cap change, so maybe should check again.

edit - Hmm, looks like the Economy 7 rate is better than I thought, at about 16p overnight, so maybe worth switching. Anything I should be aware of with that? I don't believe it prevents you using Agile Export like Go does, so that should be OK. Only issue is a bit more management of the system as really need to avoid the day rate prices.

 

[Mercenary Keyboard Warrior]

Yes, no EV so Go isn't an option (and would then miss out on Agile Export), Agile Import was pretty horribly priced until recently (I've been considering switching now, but worried the current reasonable prices may just be a blip) and last time I looked the Economy 7 tariff seemed to have a higher night rate than I was paying on my standard tariff, although don't think I've checked it since the last price cap change, so maybe should check again.

You can get on go with no EV. I had just assumed you were on go so makes sense you may want to try to game the system.
Might be worth trying to get on go however

Go average units work out about the same as the cap, more expensive during the 20 hours but the 4 hours being it back down.
Plus of course if you can charge batteries in the go window you should be quids in.

 

[Mikolos]

Just checked the Octopus website and it looks as though Octopus Agile has been pulled for new customer from 22/10.

Anyone got any other recommendations on decent time of use tariffs?


Still not got my solar installed yet as having a game with quotes but hopefully soon.

 

[redfist]

Just checked the Octopus website and it looks as though Octopus Agile has been pulled for new customer from 22/10.

Anyone got any other recommendations on decent time of use tariffs?


Still not got my solar installed yet as having a game with quotes but hopefully soon.

Have you called them? Might be a case of just not showing it on their website at the moment.

 

[Freefaller]

I still think this is a good deal if you have solar and batteries (and don't have an eV).

 

[gpuerrilla]

Do you have an electric car or a water tank you can heat?

 

[HungryHippos]

Group - with a PV array east/west with a total of 9.5kwh, is it worth investing in 2x 9.5kwh Givenergy batteries - Can I actually realistically charge them in the Summer and will Eco7 have enough time to actually charge them in winter? I use roughly 16kwh a day.

Eco 7 version should more or less be able to charge them even from flat. At the G1 charge rate of 2.6kw, with 7 hours, you can charge 2.6 * 7 = 18.2 KWH.

I would say the first battery of the 2 is likely to make the most difference.

If you have 7 hours of cheap electric anyway, then you only need to worry about the battery lasting as much of the remainder as possible. That leaves 17 hours.

If your 1st battery gets most of the way through that, the 2nd one is only going to save you the delta, which at most will be very little.

 

[Northwarks]

Do you have an electric car or a water tank you can heat?

Yes I have a water tank, that was also part of the plan - EV potentially towards the end of 2023/early 2024

 

[gpuerrilla]

OK then as many panels as you can and the batteries should compliment it well.

 

[Hawk Tuah]

That Economy 7 is what I'm on.

I'm shifting as much as I can to happen overnight now, as well as charging the EV. Dishwasher, washing machine, dehumidifier etc. Which I'm sure is entirely the point of making it available to all and discounting the night rate a bit more than it was previously.

I do like how adding the word 'Reduced' to the title makes you think you're getting a good deal.

 

[Northwarks]

Eco 7 version should more or less be able to charge them even from flat. At the G1 charge rate of 2.6kw, with 7 hours, you can charge 2.6 * 7 = 18.2 KWH.

I would say the first battery of the 2 is likely to make the most difference.

If you have 7 hours of cheap electric anyway, then you only need to worry about the battery lasting as much of the remainder as possible. That leaves 17 hours.

If your 1st battery gets most of the way through that, the 2nd one is only going to save you the delta, which at most will be very little.

Really useful info thanks - want to get the battery spec right, but not wanting to over spec and never or rarely use the spare capacity - Defiantly getting 1x 9.5 just questioning the 2nd etc. Thanks !

 

[Northwarks]

OK then as many panels as you can and the batteries should compliment it well.

Filling both roofs to the max, as many on here have pointed out the scaffolding/labour is a significant chunk, rest is at ground level.

 

[HungryHippos]

It is indeed a good course of action but you may find you will over-produce with so many panels.

Winter will be dire even if you have a lot of them.

Your ROI above 5 or 6kwp is likely going to be based on exporting a lot more than real time usage.

 

[Mercenary Keyboard Warrior]

Really useful info thanks - want to get the battery spec right, but not wanting to over spec and never or rarely use the spare capacity - Defiantly getting 1x 9.5 just questioning the 2nd etc. Thanks !

FWIW I did calcs and for me even an extra 5.8 didnt make sense over the 11.6 I am having installed. I know its spreadsheet modelling and all that but I found iirc that the third would only be in use around 4-5 months of the year, ie the very depths of winter from Nov-Feb
The rest of the year the majority of the days the solar generation plus 10.6 usable battery would cover it when charged over night.
My usage was based on 19.5kwh summer months to 21.5 in the depths of winter as well (extra allowance for some extra oven meals, more lights etc)
My system is projected to produce 3900kw from solar on a 5.4kw array.

I doubt a second battery would have an ROI of less than its warranty period for you which is basically what I found.
Oh those were based on go prices at 7.5p/40p vs capped 34p. Of course if the cap shoots up the ROI may fall on the next battery.

 

[Northwarks]

FWIW I did calcs and for me even an extra 5.8 didnt make sense over the 11.6 I am having installed. I know its spreadsheet modelling and all that but I found iirc that the third would only be in use around 4-5 months of the year, ie the very depths of winter from Nov-Feb
The rest of the year the majority of the days the solar generation plus 10.6 usable battery would cover it when charged over night.
My usage was based on 19.5kwh summer months to 21.5 in the depths of winter as well (extra allowance for some extra oven meals, more lights etc)
My system is projected to produce 3900kw from solar on a 5.4kw array.

I doubt a second battery would have an ROI of less than its warranty period for you which is basically what I found.
Oh those were based on go prices at 7.5p/40p vs capped 34p. Of course if the cap shoots up the ROI may fall on the next battery.

Think you have nailed it for me in this one - Used only in the depth of winter when its charged at cheap rate and possibly offset by really low dependence on the grid in peak summer. I'm fortunately in a position where ROI is clearly important but not a high priority and I guess if its not stressed by deep cycles will last well after the 10yr expected performance?

 

[HungryHippos]

If money is no object then yes 10KWP of panels and 2 x 9.5KWH battery is basically set for a long, long time. It will also be less tied into your own efficiency.

But if ROI matters then I think around 6KWP of panels 1 x 9.5KWH of battery makes more fiscal sense, and will get you the vast majority of the way there with savings.

Not sure if some additional compromise can be made with the battery for a middle ground, for example 1 x 9.5 and 1 x 5KWH battery instead giving 15KWH capacity, but the cost for that may not be hugely different from 2 x 9.5KWH.

I use about 16 KWH per day as well, and on GO I am more or less covering it pretty well up to now with 4.8KWP panels and 1 x 8.2KWH battery. GO is a very important part of the strategy here though, it's reducing my costs a lot when I get weaker solar days.