Solar Power for Community Hut

Catbells

Can anyone tell me what the best solar energy system would be for a community hut which is off grid?
The size of the hut is 30ft x 15ft.

I understand we will need the following components. Is this correct?

• Solar Charge Controller
• Battery Bank
• DC Disconnect (additional)
• Off-Grid Inverter
• Backup Generator (optional)

At an estimate we use the hut for events at weekends so about 100 days a year. The energy is for lighting, heating, tea urn, refrigerator. Thanks for any suggestions.

Cardew

That list of equipment will cost a fortune.


You must bear in mind that to heat a hut(in winter), power a tea urn, lights and refrigerator will require a huge battery bank, and much of the time the solar panels will contribute very little.


Surely it would make more sense to have a portable generator and paraffin heaters.

Catbells

Thats helpful. Thanks. How much is a fortune? We are looking at various forms of electricity and laying a power cable from the street a hundred yards away is the other alternative but would be against our ethos.

We don't want to use paraffin for safety reasons. Wouldn't a generator need to get electricity from somewhere to relay it to us and we are off grid?

Martyn1981

Catbells wrote: »

Can anyone tell me what the best solar energy system would be for a community hut which is off grid?
The size of the hut is 30ft x 15ft.

I understand we will need the following components. Is this correct?

• Solar Charge Controller
• Battery Bank
• DC Disconnect (additional)
• Off-Grid Inverter
• Backup Generator (optional)

At an estimate we use the hut for events at weekends so about 100 days a year. The energy is for lighting, heating, tea urn, refrigerator. Thanks for any suggestions.

Hiya Catbells.

Lots to consider here, but number one will be the amount of energy you need to store.

Heating will be a major issue. So putting that aside, would you be able to meet requirements from a few large batteries transported to site? This would allow cheap and economical charging from the mains, or even from a domestic PV system.

After that and scaling up you'll need to work out the max(ish) sort of stored energy you'll need, so hours of light and lighting power (obviously go for something very low like LED's). Then the energy needed to heat the water in the urn to required temp etc.

At that point you probably want to double the figure, if using lead acid batts as you want them to last, so don't want a DoD (depth of discharge) of greater than 50%. Also allow for system losses of 10% to 20%, so perhaps batt storage of 220% of expected consumption.

From there you can work out the solar input you need. Here you have an advantage that 'only' using the site on weekends gives you longer to charge up the batts, and avoid bad days. The longer the period, the more average PV generation becomes.

You can use PVGIS to estimate generation, and size system towards the worst month(s). If you're happy to add a gennie, then you can size for average, rather than worst case scenario - this will reduce the size of batts and panels you need.

I suspect the PV part will be the simplest, and possibly cheapest, just 4 panels could supply between 1kWh and 4kWh per day on average (could also supply between 0 and 7kWh depending on weather), so that would give you around 7kWh to 28kWh per week.

Play with PVGIS as you'd probably want to further maximise winter generation (at a small loss to summer gen) by installing panels at a steep pitch (50d to 60d).

I chatted last year with an off-gridder who gave me loads of useful costs for setting up a household system. But this kit would be a bit oversized for what you need, for instance

Hybrid solar inverter charger grid interactive off grid 3000w 48v PV 4.5kw max

Petrol battery chargers

Heating will be a pig! You can of course use leccy and batts, but they will need to bigger, and you also need to consider the amount of load you will be drawing from them. If it's a high sustained load, then they won't last as long, or you need a bigger system. this is separate to the DoD this is the C rating (I think) which relates to rate of discharge in hours, a C10 (10 hour) discharge will give a smaller number of life cycles, than the same amount of energy spread over C20 or C100.

If it's a safe location, and you want to get really serious, then this link was also given to me:

DC air con and heat pump

I believe DC units cost a bit more as they have to be designed so as not to overpower the power supply on start up, when such units can have a short but high demand.

If heating (and perhaps cooling) is essential, then cost wise it might be worth investigating insulation, depending on the hut structure. 'Fluffy' (loft insulation) is relatively cheap, but something like PIR (Kingspan, Celotex etc) is much better, and costs could be reduced by sourcing from an off-cut/damaged supplier. Consider floor and ceiling too. This may economically reduce the investment cost in batts and panels.


That's the long(ish) and not particularly helpful answer. The shorter answer would be to suggest you start chatting on a friendly renewables or off-grid site. I find Navitron great, but there are others.

So, thoughts?

Mart.

Martyn1981

Just a thought, but whilst a refrigerator might not have too high a demand, it might be better to just transport ice, or chill packs with you and a good chiller box. You might find that an old chest freezer (sourced from a local tip?) plus adequate ice would do you, and you could super insulate it with any left over PIR insulation.

Mart.

EricMears

Afraid I agree with Cardew. Solar panels would be very useful in the summer months but you probably wouldn't need much lighting or any heating at that time of year and might even prefer cold drinks to tea.

But in the winter such a system would probably struggle to keep a fridge running 24/7 never mind building up a surplus in the batteries to run the various heating appliances described.

Nothing intrinsically 'unsafe' about paraffin but you might consider bottled gas 'safer' - and it's certainly more convenient for cooking appliances & fridge.

A generator generates electricity ! It certainly wouldn't need a grid connection. Small generators usually run off petrol - which could be considered 'unsafe' although storing the fuel in a locked cupboard and filling & using the generator outdoors would make it less unsafe. Larger generators (and if you were considering electrical heating you'd need a large one !) usually run on diesel fuel which is a lot safer to use than petrol (although anyone regarding paraffin as 'unsafe' would probably have similar reservations about DERV).

Still worth considering an electrical connection though. Electricity boards would charge an arm and a leg for digging a hundred yard trench and laying cable in it; however, if the community organisation own all the ground in between, it would be a perfectly acceptable alternative to build a small meter box on the boundary and have that connected to mains but use voluntary labour to dig a fairly shallow trench for a cable between meter box and hall.


I also agree with some of Martyn's points. You probably only need a fridge for keeping milk cool between different tea making sessions. Why not just take home any left over milk and bring it back next day ? Lighting would work perfectly well on a 12V circuit and batteries can be taken home for charging

Martyn1981

For fun(?) you could also build your own evaporative cooling fridge. Just google for loads of info, varying from as simple as two large clay pots, one inside the other, to the more hi-tech:

Solar Fridge Invented (Again) by UK Student


Also for info, it took my 3kW kettle about 45s to boil a large mug's worth of water. So that works out at about 40Wh. So every 25 mugs of tea you want, will require ~1kWh of leccy.


Lastly, you mentioned an inverter, but could you run everything on DC, that might simplify things a bit and save some system (conversion) losses?

Mart.

Ectophile

You forgot the solar panels on your list!

So long as security isn't too big an issue, bottled gas is likely to be more practical for many of the things you list. You can get gas-fired urns, gas heaters and gas fridges.

Owain_Moneysaver

Catbells wrote: »

We are looking at various forms of electricity and laying a power cable from the street a hundred yards away is the other alternative but would be against our ethos.

A power cable from the street would be the eco-friendly option. The embedded energy and carbon in solar panels, batteries etc may be more than ever would be saved by using 'renewable' energy.

Cardew

Martyn1981 wrote: »

For fun(?) you could also build your own evaporative cooling fridge. Just google for loads of info, varying from as simple as two large clay pots, one inside the other, to the more hi-tech:

Solar Fridge Invented (Again) by UK Student


Also for info, it took my 3kW kettle about 45s to boil a large mug's worth of water. So that works out at about 40Wh. So every 25 mugs of tea you want, will require ~1kWh of leccy.


Lastly, you mentioned an inverter, but could you run everything on DC, that might simplify things a bit and save some system (conversion) losses?

Mart.

So your advice to the OP would be that solar is a practical proposition?

Martyn1981

Cardew wrote: »

So your advice to the OP would be that solar is a practical proposition?

It will depend on their needs and budget, what the alternatives are and the cost of a grid connection (which may be many £,000's plus the annual bills).

The description is of a 'community hut' so you also have to consider who will be using it, and the purpose, so solar may be an environmental and educational aim too.

Surely it's better to discuss the issues with the OP, and answer the questions raised, rather than you trying to turn yet another G&E thread into an anti PV rant.

Mart.