Hi from Cornwall England.....

[PapaPedro]

Hi Everyone....
Im Pete from the SW of the UK and my son and i are setting up an off grid solar system. Actually only bought the batteries so far and still puzzling over what Inverter/charge controller/panels to buy. We also want to add a generator of some sort as i think there will be many cloudy days thru the winter months.
The batteries we have may be a little or even a lot over the top but weve bought them now so we will use them and hopefully the capacity will be to our advantage in the end??
They are 12x 2v Sonnenschein OP2V 1500 A600 cells. Each cell has C10 capacity rate of 1643 Ah @ 20c.
The home we are supplying is a 40 ft shipping container converted and so the load would be no more than 10 or 12 KWh per day.
My son would be living there most of the time but it could be locked up and unused for 2 or 3 months at a time.
Would it be best to use the batteries in a 12v or a 24v configuration?
Any suggestions on a system design that i could follow would be great as i have tried to educate myself about inverters and charge controllers but there are so many variables i need experienced help to make the best choices....
Off course our appliances here in the UK run on 240v so that would make the math a little different.
Many thanks in advance....

[Mike90250]

24v system is best for the batteries you have on hand. Series wired means all batteries see the same current (amps).

Do you have a 20hr spec for the battery capacity ? (that is a more standard measurement)

House loads - uh oh ! 12kwh daily is going to need a nameplate harvest of about 24kwh daily, or make up for it with a generator. You can gain some improvement by load shifting, to run loads off the solar when the sun is shining, instead of loads at night, and then recharge the battery.
Rounding up, you have a 40kwh battery and can consume no more than 20kwh daily w/out severely affecting battery life

Panel guess, only on a sunny day, in winter, you might get 3 well aimed hours of sun. To recharge you would need a PV array of 8,000w x 3 hours ( or run a generator. )
With 5 hours of good sun, you only need a 5,000w array. More sun = less panels.

While sitting, your cells will self-discharge and need monthly topping off. You could wire 6 in series and use an ordinary auto charger for a couple hours. Then charge the other 6

[PapaPedro]

Thanks for your input Mike....

Do you have a 20hr spec for the battery capacity ? (that is a more standard measurement)

The only info i have is C10 capacity rate of 1643 Ah.....

12kwh daily is going to need a nameplate harvest of about 24kwh daily

not sure i understand the term nameplate harvest but do you mean the KWh estimate is high? it probably is but im sure i read the UK average was around 480 a month?

So yes we do have poor sunlight hours here in winter so the 8000W array would probably be the way to go...

What size inverter and charge controller would match the batteries and 8000 watt panel array?

Thanks again..... Pete

[Mike90250]

You first need to use a solar calculator like https://pvwatts.nrel.gov/

Your area may differ greatly from a site 10 miles away, they are sunny all the time, you are fogged in. Solar Insolation is the data you are looking for

https://photonenergy.co.uk/new-build-solar-pv/solar-map-of-the-uk

[PapaPedro]

We are up the red end of the scale somewhere around 1250 KWh/m2....
but the other one shows just over 1320 KWh/m2 per year....
Average yearly sum of global irradiation per square meter received by the modules of the given system (kWh/m²

[JSchnee21]

Not that it is any of our business, but just curious, implementing an off grid battery and solar solution large enough to run the entire "house" (albeit more of cabin or "little" house) is a rather expensive endeavor. Is the location sufficiently remote that connecting to the electrical grid is not possible / more cost effective? Between the batteries, panels, inverters, and backup generator, you're looking at 10's of thousands of pounds. Some folks in the US do this for hunting cabins, etc. which are often remote and infrequently used. But it sounds like your son will be living there most of the year. Not to mention the fact that the batteries need to be replaced every 7-10yrs or so.

[Raul]

If is a shipping container then probably the location is on a field in the country side where permitted development is very tight regulated. So will be no utilities nearby.
Pete, for cornwal you got 2-3 sun hrs in summer and under 1 in winter. With a yearly averege of 1,5 ish.
Devon and summerset is slightly better with Sussex being on top.
If you really need 12kwh per day then you need at least 15kwp of panels ideally on ground mount. I think you over estimated by quite a bit. Me and her in doors we averege 6kwh per day in west London and live quite comfortable. The biggest hogs we updated some time ago was the fridge freezers to A+++ and a Mille washer that does 3 washed @30 under 1kwh. You can get a LG direct drive inverter washer and does a cycle of wash @40 under 0.4kwh. Of course LED all around and a good Eco Oled tv 37w 50"", bobs your uncle.

[PapaPedro]

Hi JSchnee21 and Raul....

Yes your spot on Raul... bought a field and a container and have water supply and some sun so off we go with the problem of how do we turn it into electricity.
Also correct on my guesstimate of daily KWh i think but not having actually got any appliances yet, we cant really measure what they would use.....
Also no electricity bill to give a monthly figure so maybe should be bringing it down to 5 or 6 KWh per day.
The batteries were pretty cheap so they had to be bought and i know there's a lot of capacity there but surely that's a good thing when the sun don't shine so much.
I have some electrical knowledge but solar is new to me and i need help in deciding what inverter, charge controller and panels will go with a battery bank this size and the obvious lack of sunshine.
Ive been reading up on it on this site but its all a bit over my head for the moment... guess ive gotta keep reading but surely theres a formula that can be applied to come up with the correct size electronics??
thanks for the suggestions on fridge tv washing machine Raul... will deffinately be looking into those little beauties!!

[Raul]

Also Cornwall gets a fair bit of wind. Is worth putting a cheap anemometer on site and log some data for a averege. There is also called wind finder, a site that gives life data of weather in hole EU including UK.
Its very handy for the winter to have a small 500w mill.

[J.P.M.]

Hi JSchnee21 and Raul....

Yes your spot on Raul... bought a field and a container and have water supply and some sun so off we go with the problem of how do we turn it into electricity.
Also correct on my guesstimate of daily KWh i think but not having actually got any appliances yet, we cant really measure what they would use.....
Also no electricity bill to give a monthly figure so maybe should be bringing it down to 5 or 6 KWh per day.
The batteries were pretty cheap so they had to be bought and i know there's a lot of capacity there but surely that's a good thing when the sun don't shine so much.
I have some electrical knowledge but solar is new to me and i need help in deciding what inverter, charge controller and panels will go with a battery bank this size and the obvious lack of sunshine.
Ive been reading up on it on this site but its all a bit over my head for the moment... guess ive gotta keep reading but surely theres a formula that can be applied to come up with the correct size electronics??
thanks for the suggestions on fridge tv washing machine Raul... will deffinately be looking into those little beauties!!

No longer, but back in the '70's I Iived quite comfortably on about 6 kWh/day in a cold climate (~ 7,000 65 F. DD/yr) using nat. gas for heat/hot H2O. Seems like improvements since then would allow me to lower that. Maybe in the warmer climate of Cornwall & environs you can get by with less than that ~ 12 kWh/day.

If you are new to solar, I'd respectfully suggest you consider doing two things if you have not done so yet:

1.) Get a copy of "Solar Power Your Home for Dummies". A good primer.

2.) After you read the book, download PVWatts from NREL. Root around in the help screens and get familiar with it before doing any runs, and use 10 % system losses instead of the 14 % default.

Living off grid is a choice that some would perhaps rethink if they knew upfront what the costs and involvement of supplying power amounted to and/or the likely lifestyle changes and choices required by an off grid life.

Off grid electricity is always an expensive proposition compared to grid power, often by an order of magnitude (at least in the U.S). Then there is the ongoing maintenance necessary to have a decent shot at even minimum reliability. All that means that lowering the load will be a much easier and cost effective scheme than supplying off grid power to a larger load.

Cheers,

[Mike90250]

Living off grid means YOU have become the power engineer, and have to
Maintain all the lines
Insure the backup generator is fueled and ready to go, for when the Inverter dies, or the sun don't shine
check to make sure the PV array is working properly, and troubleshoot it when not.
Battery Health Watch, maintenance, distilled water, cable torque, corrosion prevention

If grid power is available, use it.

[PapaPedro]

Ok thanks for the comments guys and i sense this will not be so simple as i first thought.... the windmill is a great addition i guess as yes we get lots of wind straight off the Atlantic down on the North Cornish coast....
Still searching for ideas about how many panels i need and what type of inverter and controller to use.
With an estimated load of 6 kwh per day
1250 KWh/m2 per year potentially from the sun or as Raul suggested probably close to only 1.5 hrs per day average...
24v battery bank giving C10 capacity rate of 1643 Ah....
Any thoughts on this question would be appreciated....

Thanks... Pete

[J.P.M.]

Still searching for ideas about how many panels i need and what type of inverter and controller to use.
With an estimated load of 6 kwh per day
1250 KWh/m2 per year potentially from the sun or as Raul suggested probably close to only 1.5 hrs per day average...
24v battery bank giving C10 capacity rate of 1643 Ah....
Any thoughts on this question would be appreciated....

Thanks... Pete

Start with the book, then PVWatts for modeled output. Know that array sizing for off grid is not the same as sizing for grid tied and has additional considerations, particularly with respect to minimum expected generation over some (usually) winter sunless days (how many vs. cost/PITA factor, etc.), and things like storage capacity and array orientation, to name a couple.

[JohnyWalter]

When looking at Generatorsa 20KW system with 200AMP disconnect is roughly $5K and a 14KW is $4K. The difference in LP consumption of the 20KW (3.7GPH) to 14KW (2.2GPH) is at full load so you probably would want to install a 500Gal propane tank unless you already have one?

Another option is a 20KW diesel generator, $12K if you heat with oil, it could run off that source. It will take a lot of hours operation to make up the difference of $7K to a propane unit IMO.

[J.P.M.]

When looking at Generators a 20KW system with 200AMP disconnect is roughly $5K and a 14KW is $4K. The difference in LP consumption of the 20KW (3.7GPH) to 14KW (2.2GPH) is at full load so you probably would want to install a 500Gal propane tank unless you already have one?

Another option is a 20KW diesel generator, $12K if you heat with oil, it could run off that source. It will take a lot of hours operation to make up the difference of $7K to a propane unit IMO.

Not questioning that a ICE powered generator is desirable, maybe highly so, but why so big ? Seems to me a 6 kWh daily load scenario isn't likely have a 20 kW or so load imposed on it.