Advice for off-grid project.

[daveywb]

This might sound a bit mad, but bear with me...

I currently have a shed under some trees but some space on a flat roof that could accommodate some panels. I want to generate a bit of energy to give it some background heat and power some other small items. It seems crazy to be spending money to heat it on a sunny day (it's cold due to the shading.)

So my idea is to have a small off-grid system. But also thinking of the possibility of expanding it and making it on-grid in the future.

After looking at some off-grid kits, it seems much more efficient to design your own... Would something like this work? I'm prepared to be told that this combination of items is ridiculous...!

2 x 400w solar panels
https://www.cityplumbing.co.uk/p/longi-solar-400wp-full-black-pv-module-lr5-54hib-400m/p/634021
1 x 800w charger/inverter
https://uk.eco-worthy.com/products/...id-system?currency=GBP&variant=41219755081877
1 x 100Ah lithium battery
https://uk.eco-worthy.com/products/lifepo4-12v-100ah-lithium-iron-phosphate-battery
Any advice would be appreciated!

 

[intheshire]

https://diysolarforum.com/
Try diysolar

Just to point out the above-mentioned forum is U.S.A. based, so all prices are in $, and they have different terminology and regulations than here in the U.K. (Not to mention more sunshine)

 

[intheshire]

It's totally achievable, if you're going Lithium theres a long return on investment.

If you shop savvy , can be well worth the money

 

[johnb2713]

Its unlikely to be very efficient at heating, 800w is a woefully low amount of energy for heating, the panels at 800w will never produce that amount of energy in reality. You need to seriously revise the energy requirements or the design of the system. Use one of the online calculators mentioned in other threads on here to calculate your system production etc.

 

[Richard-the-Ninth]

daveywb, may I suggest before you spend any money you calculate your energy needs and figure out will your "desired parts" be able to cope. It's not as hard as it sounds.

Example: (Using your initial parts)

Items required for generation
Solar panels x 2 Output 400 watts each
Battery 12v Capacity 1,000 Amp hour
Inverter. Output 800 Watts

(Assumed) Items wanted and wattage
3 x lamps (6 watts each)
Phone charger (say 5 watts)
Small kettle to make tea/coffee (1kw)
Small blow heater (2kw )

Total watts 3,300 (18+5+1000+2000 =3,300)

Looking at the above, the inverter can only supply 800 watts, your demand is 3,300 watts, you have lost before you start, BUT you have spent £0.00
Also, your solar panels are rated to 400 watts each, but that is maximum, you may get it on a bright day, but this is the UK, so maximum output is not going to happen everyday. People that have solar for their houses (etc) cover the best facing side of the roof with as many solar panels as possible, this not only gives them a greater maximum output, it also means if it's not very sunny they will still be generating a reasonable amount of electricity to charge the batteries.

The main "problem" with your project is the heater, all electric heaters use a lot of electricity (in the kw range) and to use just lights in the day would be expensive. You are not alone, I looked into a tiny solar project (Mostly for fun) 2 solar panels, all singing all dancing inverter, big battery, it would work no problem at all, but the payback would have been 10+ years, so it was quicker, easier and cheaper to run the project from the mains.

 

[johnb2713]

daveywb, may I suggest before you spend any money you calculate your energy needs and figure out will your "desired parts" be able to cope. It's not as hard as it sounds.

Example: (Using your initial parts)

Items required for generation
Solar panels x 2 Output 400 watts each
Battery 12v Capacity 1,000 Amp hour
Inverter. Output 800 Watts

Thats a very BIG battery

 

[Richard-the-Ninth]

Yes, an extra 0
As you say it should have been 100 Ah.

 

[daveywb]

Thanks all for your replies.

Sorry, I should have been more specific...!
I currently am using an 40w tube heater for a bit of background heat and to protect from frost, then a 350w infrared panel heater for ~3 hours when needed. Plus a couple of lights.

So:
350+40+6+6 = 402w. would be max load.

If the background heater was on 24h and the panel and lights for 3 hours, that would be 2046w in 24 hours.

 

[bladerunnerpv]

Which direction is the 'best shed roof' facing? It sounds restricted by trees so you should do a shading assessment too.

If you have space it sounds like a ground mounted array would work better from the info you've advised.

 

[daveywb]

It faces South East and there is no shading on this part.

I think I could possibly fit 4-6 panels there eventually, but want to start with 1 or 2 as a prototype

 

[Richard-the-Ninth]

As you have a tube heater and an infra-red heater I guess you already have mains in this shed?

I have made some approximate* calculations. (NO extra 0's)
The kit will cost £760
You said 3 hours/day
Electricity 40p /kwh
To break even, you will need to run it for 20+ years

Is it worth it?

Don't get me wrong, it's a great project, but does not make financial sense.

* Some figures were rounded up, some figures were rounded down, I also assumed 6 hours/day not 3 hours/day to allow for any discrepancies. VAT and shipping are NOT included, as is new battery as chosen battery is expected to last 10 years

 

[binky]

Ok, most points covered well above so I would add that lighting is very achievable for your project, an odd socket for lower powered items, maybe a small kettle is also achievable. Heating is another matter. Probably better off spending some money on insulation or a little pot bellied stove to burn scrap wood.

 

[poni]

that would be 2046w in 24 hours.

You said 3 hours/day

£760 for the kit,
2.046Kw per day
£0.4 per Kw
I think that's more like just over 2.5 years
but I could be very wrong, I wait to be corrected

 

[binky]

£760 for the kit,
2.046Kw per day
£0.4 per Kw
I think that's more like just over 2.5 years
but I could be very wrong, I wait to be corrected

Correct, assuming shed used 365 days per year.

Lead acid batteries are good for 3000 charge cycles I think ( might be wrong about that), so should last about 8 years depending on how much they get used. So roughly 5.5 years at around £300 gives a total saving of approximately £1600, plus any inflation on energy.

 

[poni]

Lead acid batteries are good for 3000 charge cycles I think

the correct number but the wrong battery type it should read lithium battery "Eco-Worthy's 100ah LiFePO4 battery contains 3000+ cycle times", and could run for more than 10 years ( this is battery in the first post) but I have read that Lead acid are much the same anyway

maybe you could answer one, maybe two question's ,How long would a 100Ah battery last with a 0.402 Kw load ?, would it last a full 3hrs or would it even last all night in the winter with a 0.04Kw load?

 

[binky]

the correct number but the wrong battery type it should read lithium battery "Eco-Worthy's 100ah LiFePO4 battery contains 3000+ cycle times", and could run for more than 10 years ( this is battery in the first post) but I have read that Lead acid are much the same anyway

maybe you could answer one, maybe two question's ,How long would a 100Ah battery last with a 0.402 Kw load ?, would it last a full 3hrs or would it even last all night in the winter with a 0.04Kw load?

Should last around 3 hours allowing for inefficient inverters 100a at say 14v is roughly 1.4 kw of energy. You don't really want to flatten the battery if possible. I did a little ioff grid nstallation for a stable block a few years ago. 2 solar panels and a small wind turbine to cover long dark winter days. Lights were all 12v gear off Amazon , so no losses, and had a pure sine wave inverter for charging battery tools, boiling a kettle once or twice a day. Customer seems very happy with it.

 

[daveywb]

Thanks all for your input. I've come round to the fact that it might be better to use the flat roof space for something small (2-4 panels) linked to mains to make the most of the energy. Thanks again!