Solar, with no mains supply available

[Harry Bloomfield]

A friend frequents a fishing club, a hut, which is off-grid. The story goes, that the club hut has had solar panels and batteries donated, and installed, but the system cannot be used, because there is no mains supply. Adding a mains supply, would cost £20K, making it not worthwhile. Several specialist have investigated, and come to the same conclusion. Seems daft to me, but are there such systems, and is there a workaround?

 

[StephenStephen]

A friend frequents a fishing club, a hut, which is off-grid. The story goes, that the club hut has had solar panels and batteries donated, and installed, but the system cannot be used, because there is no mains supply. Adding a mains supply, would cost £20K, making it not worthwhile. Several specialist have investigated, and come to the same conclusion. Seems daft to me, but are there such systems, and is there a workaround?

Hard to say without more info about the actual system...
Of course there are solar and battery off-grid systems (boats for example)...
Bimble solar might be able to help...

 

[Why Not Indeed]

Grid Tied vs. Off Grid Inverter. What's the Difference?

Learn the difference between a grid tied and off-grid inverter. Choose the correct inverter for your project. Find Out More.

www.sunstore.co.uk

They need an inverter that is capable of doing this. I can't believe that "several specialists" between them would not have known this, so you're probably not getting the whole story.

 

[hllns]

Does it even need a mains inverter or just a charge controller? What are they powering? Lights? CCTV camera? Mobile phone charging? Off grid solar is all about the power budget.

 

[SUNRAY]

They require, or so I'm told, a 12V to 230V sinewave inverter that is capable of being connected to an AC generator (in this situation a solar sytem etc) and a battery to run it.
The thing about most solar inverters is they monitor and lock to the mains supply, hence the inverter and battery which can then be charged off the solar AC.

Now the nitty gritty, first of all I doubt very much there are no solar charger/inverter systems available capable of working off grid, in fact I know there are some running hill top radio masts etc and caravans/narrow boats etc so it's all a matter of scale. In sunny countries, ie Spain etc they have houses running Air Con and pool heating off grid.

In essence, all that's required is the panels, a charge controller, batteries and an inverter.

I should have thought of the obvious right at the beginning... Ebay

https://www.ebay.co.uk/itm/25583921...+nmtOvCeRZChewd98PQ/mw7A==|tkp:BlBMUMDFkuuqYw

Go down their advert and see they offer advice, explain wht you have and it seems they will offer suitable kit to get it going.


EDIT: Note to self, check for replies before posting... I started this reply about 5pm then phone and dinner before comleting and posting.

 

[ericmark]

I have solar panels, and battery, and today had a smart meter fitted and while the grid supply was disconnected my central heating was running, so clearly it can run without a grid supply, (Islanding) but as to if battery fully flattened over night whether it would kick back in when the sun comes up, never tried.

The grid tie is designed to power down when grid fails to ensure no back feed, and my supply comes from a special part of the inverter and the 4 sockets and FCU are always powered from the inverter, and there is a system to auto disconnect the TN-C-S earth when the power fails.

So I have some thing like this

a small generator may work, or a second inverter, but it needs to run within the permitted voltage and frequency as it is designed to disconnect if it detects loss of supply.

I simply don't know how accurate the supply would need to be, and clearly it could not export any surplus. You are trying to make the inverter do some thing it was never designed to do.

So the system has three parts, the panels, the battery, and the inverter. My panels produce around 250 volt DC, this goes into the inverter which produces two outputs, 230 volt AC at 50 Hz and 50 volt DC, the latter is fed into the battery, but there is some software which one works out how charged the battery is, and stops it charging when full, and two works out how much power so it can charge battery at 2 kW and discharge at 3 kW and the inverter limits the charge and discharge within those limits.

Now with a lead acid battery it is easier to control, but a typical lead acid will take around 8 hours to fully charge, where my battery could be fully charged in 2 hours.

To power my sons inverter (3 kW) in his narrow boat, we had 3 x 140 Ah batteries and really not enough, and with the farm I worked on in the Falklands we had ex-bus batteries Nickel Iron. And we used them at 24 volt DC no attempt was made to get 230 volt.

Many years ago around 1958 I stopped in a caravan site where a DIY wind charger kept the toilet block lit, so I am sure there is a way, but the DIY methods are normally extra low voltage, and use panels designed for extra low voltage.

So if the club is willing to buy a new inverter to connect the panels and battery I am sure it can be done, but one is the price of the inverter, and two some one who knows how to select an inverter to do the job.

 

[plugwash]

I'm no expert but from what I understand.

Off grid is a completely different game to on-grid. In on-grid the grid is responsible for providing a stable mains supply. Your solar and battery just put energy in and out as they wish. The grid deals with all the difficult problems of maintaining a stable voltage/frequency in the face of sudden changes in load. In an off-grid system your battery/inverter needs to do all that work.

In an on-grid system you can just have seperate inverters for your batteries and your panels . It's a bit less efficient but it will work fine and means there are less compatibility concerns. In an off-grid system you really want one combined system with batteries, panels and inverter. There do exist off-grid or backup power inverters that can work in conjunction with grid tie inverters (IIRC the tesla powerwall works this way), but I don't think it's a common feature and it also gives you a bit of a bootstrapping problem.

Afaict off-grid systems also ofteb work at much lower voltages, presumablly because of their history of being derived from marine/travel systems.

The bottom line therefore, is that a pile of donated on-grid solar gear is likely to be of little use for building an off-grid solar system.

 

[Ragnar_AT]

They can certainly use the donated panels and batteries, what they need is a charge controller and off-grid inverter (you can get fairly chunky ones, my work place has a 5 kW one in a vehicle and that‘s nowhere near the largest one that manufacturer offers).