Should I go off-grid?

HertsLad

Wow, thank you very much to all who have made great suggestions so far. It leads me to think I may be over optimistic. I am shocked that some of you with such  a large number of panels are only getting very low watt hours on some days. I know from a 100w panel I have, that the difference in output between sunshine and cloudy conditions is like night and day.

I will probably generate a lot of warnings that I have chosen the wrong path when I say I will be using lead acid batteries (and not lithium ion) in conjunction with each pair of solar panels. The panels are rated 330w and about 36v. So I will wire each pair of panels in parallel so I have the same voltage but twice the current. This power will then be fed into a charge controller, 24v inverter and 4 lead acid batteries, each being 12v, 70aH. 2 of the batteries will be wired in series to give 24v with two more behind to double the capacity. The first two panels will be placed in the garden to enable me to move them around to have them facing the sun for a much greater period than if they are all in a fixed position on my house roof.  This first sub system will send power to my kitchen, say, to power the fridge 24/7 (can it even do that?), a propagator heat pad (supplying warmth to plants in my freezing cold house) and some low energy LED lights at night. That's about it. I decided I will only operate many appliances when the sun is shining, e.g. steam iron, and almost never use my microwave oven, electric kettle or freezer again.

The other panels will go on the house roof, facing south east. Two of the panels on the roof will go to a further 4 lead acid batteries, a second charge controller and inverter. The original idea was for that to power the desktop PC and LED monitor which I am using to type now. It uses about 150w. But I now think I should place the PC/monitor on my list for making hay when the sun shines. I can use my phone for checking emails and web sites, on cloudy days, just like I do when travelling every day. The phone can be recharged from power banks. The power banks can be kept topped up from relatively small solar panels which I use when travelling.  So the first two panels on the roof only need to power my video doorbell, 4G router and night time LED lights (all very low power), and my electric blanket (for 20 mins per day in winter, 100w). Because the demand is so low, I was hoping it may be achievable. 

The final two panels and perhaps several more to consider adding will also be on the roof. The power from these extra panels will be used to catch up with things like using this PC/Monitor, steam iron and dehumidifier. But only for hours when the sun is shining. I thought perhaps I can simply use power as available. I doubt if many UK homes have batteries but perhaps their grid tie inverters work in a different way. I now understand it is problematic not to have batteries, so I figured I could add a few £35 car batteries from Euro Car Parts when they have 45% off, just to make my kind of system work with a very small buffer by way of the batteries.

I chose lead acid batteries because they seem to last a long time if not abused. Even assuming you can use only 40% or 50% of the 70AH, they still seemed good value compared to lithium ion.

Conclusion: I don't know as much about solar PV as I do about how to keep warm in an unheated house.

Verdigris

I chose lead acid batteries because they seem to last a long time if not abused. Even assuming you can use only 40% or 50% of the 70AH, they still seemed good value compared to lithium ion.

An off-grid-ish friend in France bought some big lead acid batteries. After I pointed out the advantages of LiFePo batteries he realised he'd made a mistake and sold them on, for half price, and ordered some LiFePo batteries from China and a BMS more locally. You can get 95% DOD (depth of discharge) and more than 6000 full cycles from LiFePo.

QrizB

You seem to have given some thought to your proposal, which is a good sign.

If you have six panels at 330W each, that's 2kW total. Located carefully that would see you through 9 months of the year.

Rather than three separate systems, have you considered one big system? Six panels in series would give a ~2kW, ~200V string that would match well with one of these (cheaper equivalents are available from auction sites) and an array of lead-acid batteries to give you off-grid power throughout your home.

That style of inverter will integrate with a mains supply or generator to supplement your power if you don't have sufficient solar or battery, but doesn't allow export to the grid.

jimjames

HertsLad said:

QrizB said:

solar PV tends to generate too much energy in the summer and not enough in the winter, and there's no cheap way to store electricity for periods of weeks or months....Running a generator for 3kWh/day through the winter months is likely to cost more in fuel than paying the annual standing charge plus buying power from the grid, even without the capital and operational costs of the generator.

What I need to find out is whether I can generate enough power through just 6 PV panels to provide most of my 3kWh per day needs. I may be able to reduce power consumption if I stop using my small freezer, for example. At least I can keep using electricity if this is all proved wildly optimistic.

We have 14 panels rated 3kWp and get up to 21kWh per day over the summer but some days well below 3kWh in winter so with less panels you'll get even less in winter.

You can see the number of days below various thresholds here:

http://solar-panels-review.321web.co.uk/index.php/yearly-comparison-of-solar-pv

For example in 2021 we had 126 days below 5 kWh and 61 below 2kWh. That's with 14 panels that are pretty much optimally orientated and total 3kWp so 6 panels might be double each of those number of days.

In December you can see that some days the lowest output was 0.12kWh. That would be hardly enough to do anything.

http://solar-panels-review.321web.co.uk/index.php/solar-power-month-by-month/12-monthly-data/12-monthly-uk-solar-panel-electricity-output-for-december

In essence I don't think 6 panels will get you enough, even double that will give over 2 months where you don't have sufficient generation to meet 3kWh per day.

HertsLad

QrizB said:

Rather than three separate systems, have you considered one big system? Six panels in series would give a ~2kW, ~200V string'

I hadn't discovered units like the inverter/controller which you flagged up, thank you. I think it shows the advantages of exchanging ideas at a forum like this. Others were even more expensive but that inverter is still a higher price than my collection of inverters and controllers. Also, if one single component failed in that inverter then everything would come to a halt. Whereas with multiple "1000w" inverters, I can hedge my bets. The 200v DC voltage also seems higher risk than working with 36v. I may be wrong but that's why I decided on separate systems. 

Going back to my thread title and original idea, I fear it will be very difficult to achieve, to go off-grid with electricity. But the largest saving is only by getting rid of the standing charge - soon to be £140 per year in my case. So it is still my target, somehow.

It is interesting that nobody has commented on solar thermal so far. It's like the time for solar thermal has passed and relatively few people are interested these days. One large UK manufacturer, Kingspan, closed down. I still think it has potential but only if you can buy panels pre-owned for a low price.

HertsLad

theoretica said:

Would you generate enough excess power over the summer that the export back to the grid would cover the standing charge?  If so, no point going off grid.

I didn't want to have a 'proper' system installed by 'accredited' installers because the costs seem far too high, with a payback period longer than my likely lifespan. For example, EON solar quoted £9000. I think it's only by using installers that you can hook up to the grid. A few years ago the feedback tariffs made it attractive but not these days. I think it's probably better to use batteries to store surplus energy for your own use.

2nd_time_buyer

HertsLad said:

theoretica said:

Would you generate enough excess power over the summer that the export back to the grid would cover the standing charge?  If so, no point going off grid.

I didn't want to have a 'proper' system installed by 'accredited' installers because the costs seem far too high, with a payback period longer than my likely lifespan. For example, EON solar quoted £9000. I think it's only by using installers that you can hook up to the grid. A few years ago the feedback tariffs made it attractive but not these days. I think it's probably better to use batteries to store surplus energy for your own use.

That price from EON sounds like it includes a battery.

If you went for a 4kW solar only install. You should be able to get something for under £5k.

It sounds like you are prepared to put in the work to minimize cost (good on you!)... With careful use of energy and monitoring the weather and perhaps a small DIY battery, with a 4k grid-tied  system, I think you would be close to meeting your needs for the vast majority of the year. At current energy prices (with Octopus Agile Export*), I think it would be feasible for you (but not necessarily a "normal" consumer) to have a net zero energy bill.

*Agile export has been averaging over 10p per KWh over the last year (around 20p this winter)

HertsLad

2nd_time_buyer said:

That price from EON sounds like it includes a battery.

If you went for a 4kW solar only install. You should be able to get something for under £5k.

It sounds like you are prepared to put in the work to minimize cost (good on you!)... With careful use of energy and monitoring the weather and perhaps a small DIY battery, with a 4k grid-tied  system, I think you would be close to meeting your needs for the vast majority of the year. At current energy prices (with Octopus Agile Export*), I think it would be feasible for you (but not necessarily a "normal" consumer) to have a net zero energy bill.

*Agile export has been averaging over 10p per KWh over the last year (around 20p this winter)

Thank you so much for flagging up Octopus Agile Export. I had no idea anyone was offering 20p or even 10p per kWh, so I will check it out. Does anyone recommend a good value supplier of that type of grid tie system? 

Yes, the EON quote included a 8 kWh battery. 

2nd_time_buyer

HertsLad said:

2nd_time_buyer said:

That price from EON sounds like it includes a battery.

If you went for a 4kW solar only install. You should be able to get something for under £5k.

It sounds like you are prepared to put in the work to minimize cost (good on you!)... With careful use of energy and monitoring the weather and perhaps a small DIY battery, with a 4k grid-tied  system, I think you would be close to meeting your needs for the vast majority of the year. At current energy prices (with Octopus Agile Export*), I think it would be feasible for you (but not necessarily a "normal" consumer) to have a net zero energy bill.

*Agile export has been averaging over 10p per KWh over the last year (around 20p this winter)

Thank you so much for flagging up Octopus Agile Export. I had no idea anyone was offering 20p or even 10p per kWh, so I will check it out. Does anyone recommend a good value supplier of that type of grid tie system? 

Yes, the EON quote included a 8 kWh battery. 

Contact Solar, Eco Renewables, and indeed EON. Seem to be reasonable value and install nationally.

A few board members, including myself, have used Eco Renewables and have been happy with the job.

matelodave

Bear in mind that you have to generate enough power during the day to not only supply your daily needs but also to replensih what you've used overnight from the batteries. You only need a day or two of minimal sunshine and you will deplete the batteries but also have no energy available for your daily consumption. 

3kwh at 240v = 12.5amps which translates to 150a/h at 12v or 75a/h at 24v. As lead acid batteries shouldn't be discharged below around 50% you'd need so store at least twice as much as you think you'll use plus you need to take into account all the inefficiencies that are involved. Batteries are only around 90% efficient and so need more energy to charge them than they deliver. Also take into account that an inverter to provide 240v will only have an efficiency of 90% or less.

The size of a solar array and the associated batteries to give you enough of a buffer for several days, or even a week starts to become prohibitive.

Running a generator to deliver enough energy to provide for your daily consumption could well be more expensive than paying your daily standing charge - especially now petrol is around £1.50 a litre and diesel even more and it's not the most efficient way to charge batteries unless you are prepared to run it every time you want some leccy.  Would you neighbours be happy with one clattering away for several hours to recharge the batteries - I dont think so.

I also noticed that you were thinking of using propane the cost of which becomes disproportionally expensive as the cylinder size reduces, so you'd need to contemplate 47kg cylinders to make that viable although it might work out cheaper to use a propane powered generator rather than petrol.

It may sound like fun to try and beat the system but TBH the cost and hassle probably outweighs any advantage that you might gain from not paying the standing charge.

It might be OK if you want to live like a hermit in darkest Wales but not so sure about the in the leafy suburbs.