Thanks for your reply!
I assume your idea will be to run most of your stuff off this all the time, powered from the mains. Then when the mains is off, connect the PV panels to it to extend the run time. And when the mains is back, return the PV panels to the leased inverter.
Well that would work.
Thanks. that's great news!
You could probably automate it as well - a box, suitable relay, some DC connectors, rig it up so that if the mains is off it automatically switches the PV DC connection over. If they come to service the system, just unplug your box and hide it away till they've gone.
Roger that.
BUT, will it actually pay for itself ? You're shelling out £2,200 plug whatever extras (cabling and connectors to connect to the PV system). How many power cuts do you normally get, and how long are they ? And do they tend to happen mostly in summer (long days, lots of sun) or winter (short days, little sun) ?
I need this to have peace of mind. I don't want to have blackout one day, for days when I have solar panels on the roof which could power me for 4, 6 or 8 hours every day, for free. I prefer to have a backup, independent from mains AC provider. That £2200 plus labour and some optional parts, is not much to spend, but a lot to gain.
It's not clear from your numbers whether your usage takes account of the PV generation - are you using 16kWH or 4.5kWH of imported electricity ? Or put another way, are you using 16kWH total, of which 11.5 comes from the PV and 4.5 from the grid; or are you using 27.5kWH of which 11.5 comes from the PV and 16 comes from the grid ?
You got me thinking, yes, my calculations were incorrect, thanks.
I use 16 kWh per day on my meter. But that
excludes energy which flows through the house during the day hours, when PV generates their 11.5 kWh on their meter. I don't pay for that on my meter, PV gives that to me for free. If I don't use it, I see red LED on my meter and electricity is being exported to the grid.
So I must be using 16 kWh (imported) plus up to 11.5 kWh from solar. In reality, almost always I see red light during sunny days, meaning I don't use all solar generation and some of it is being exported. On cloudy days, I don't see red LED, so I must be using all PV generation at the time.
Realistically, I must be using between 25% and 75% of what solar generates. So I am using 16 kWh plus 2.875 or 8.625 = 18.9 kWh up to 24.6 kWh.
I think this is now more accurate number now.
You need to work out :
How long, on average, you will actually be able to run on battery + solar. E.g. if you typically have a 4 hour power cut every week, and they are mostly in the middle of the day, then that's going to mean a daily average of 4/7th of an hour. If we take an "average" day of 12 hours, then you are producing less than 1kW, so you'll actually get to use in the order of 0.5kWH/day of solar via your system.
And what it's going to "earn" from your PV. At current prices, it's going to be in the order of £70 to £90/year. Doesn't seem like a good investment to me.
As I mentioned, I am buying myself backup power source. I can't have PV and not use it, if there is a crisis and there is no power at all. That would be such a waste of solar panels ability to produce electricity. I would like to use it during blackout. And I do have some blackouts where I live and that's a pain. £220 system will give me total immunity from 1-4 hours blackouts.
Of course, if having power through those power cuts is the difference between doing nothing and doing paid work, then you could value the system in terms of how many more billable hours you can do - in which case it might be worth it.
As for "use battery at night, recharge during the day", I suspect that you won't have enough margin of generation over consumption to be able to recharge from the PV most of the time. That will depend a lot on your usage profile. If you use your lecky over (say) a 16 hour day, and then are using little while you're asleep the other 8 hours, your usage is around 1kW average. During summer you may have enough margin to charge for a few hours mid-day, but most of the time you won't. But working all that out really means having a good idea of both your generation and usage profiles so you can work out how long you actually have excess PV production for.
And even if the figures say it'll work, you need something fairly advanced that can monitor your net lecky import/export so that you can charge the batteries at just the rate that will reduce your export to nothing - and use the charge in them to reduce your net import when you don't have excess PV production.
I could imagine that there are products out there that will do it - but I also suspect that they won't be cost effective, especially as you can't integrate your PV panels to your own system. Ideally the system would be one unit with mains, battery, and PV DC connections which manages it all itself - but that would require that you be able to remove the existing inverter.
And on that last bit, is there an option to buy out the lease so that you own the system and can then adapt it ? From what I've seen, these "rent a roof" schemes (which is what I assume you have) are generally not a good deal for the home owner other than not having to find the up-front capital to install the system.
If we assume I use from 18.9 up to 24.6 kWh per day, and solar panels generate 11.5 kWh per day, I need extra 7.4 up to 13.1 kWh per day from battery, to run for entire day.
"UPS 5kW System with 9.6kWh Energy Storage" for £2200 won't cover that completely, but then it will re-charge next day, on average, to full capacity again, using 11.5 kWh which solar panels produce per day (if I don't use any electricity). I will have to cut electricity use drastically and I will, otherwise I won't charge battery at all as you said.
But still, ability to have some of electricity I need, thanks to ~£3k investment, is good enough option. Without UPS System I have 0 kWh to use. With UPS, I enable solar PV to work without mains, and I will have from like 1 kWh (very cloudy day) to 11.5 kWh (average). I'd like that.
For "use battery at night, recharge during the day", I can worry about that later. I will call PV company see what are my buyout options. If there is none, would you say "UPS 5kW System with 9.6kWh Energy Storage" for £2200 is best I can get, taking into account all limitations of this scenario?
Thanks for your time!
