Navitron Renewable Energy and Sustainability Forum

Energy/Electricity Storage and Use/Grid Connection => Off-Grid, Batteries & Inverters => Topic started by: Stuart_M on October 09, 2013, 03:46:26 PM

Title: Tiny off grid project
Post by: Stuart_M on October 09, 2013, 03:46:26 PM
Hi All,

I have a part interest in a smallholding where we breed mostly chickens but also some ducks and geese too. As winter approaches and they days get shorter we could really do with some lighting in the barn and covering the area where the birds are shut up overnight.
Wed be looking for a max usage of an hour a day and it struck me that this would give me an opportunity to test out the world of being off grid.

The vague plan I have involves a solar panel + charger + battery to run 4 of the 10 watt floodlights (of the type available from a well know auction site).
As I have a tendency to over-engineer most of what I build some guidance from the experts on here would be much appreciated!

Unfortunately the budget rules out a generator so I was considering a 40 watt panel to mount on the shed roof, a cheap charger and a leisure battery. Keeping the system DC would be cheaper and simpler for now with 12V being the preference as at some point I could add a second panel and a split charge system to run an second battery for some electric fencing.

Questions so far are:
1)   Does it sound like this would work given the expected demand?
2)   Will a 10 solar controller really work or is it just a box with some terminal block in it?
3)   Im assuming with batteries bigger is better?
4)   Do I need to the possibility of the battery being fully charged and the panel generating on a system this small?
5)   Anything else I need to consider?



Title: Re: Tiny off grid project
Post by: Tiff on October 09, 2013, 03:58:23 PM
How long would you expect the floodlights to be on for? 1hr or all night long? - Makes a big difference.

Your plan sounds perfectly reasonable, my first PV off grid system was pretty much the same thing - cheap charge controller, PV and battery to power some security lights on the garage.

Also bear in mind that your demand for light will at its highest when the PV output is at its lowest. December can be very gloomy....

Title: Re: Tiny off grid project
Post by: Stuart_M on October 09, 2013, 04:18:07 PM
Hi Tiff,

The birds take about 30 minutes to put to bed and about 45 to get out in the morning so if we rounded it up to 1 1/2 hours then that should give us some contingency. Chances are that at least one visit per day will be in daylight anyway and we may only need the lights once a week.
We've lived without anything for several years but having spent too much time on the forum this year I'm itching to try something!


Title: Re: Tiny off grid project
Post by: Tiff on October 09, 2013, 04:40:03 PM

So that works out to 3.3AH a week.

In Dec a 40W panel giving aprox 0.05kWh = 4.1Ah a day.

Provided my maths is correct then it should work nicely.

Title: Re: Tiny off grid project
Post by: martin on October 09, 2013, 04:40:38 PM
Oh lordy........... ;D
I fully sympathise with your chomping at the bit to "have a go", but feel that a few caveats may not come amiss....... First of all there's "the law of sod" - the time you need most extra light is the time of year when pv panels are gathering least-  often the "boring way" is the most sensible (for your use a couple of old but good car batteries and a mains car charger would look the easiest, simplest and cheapest way-  just charge the batteries, take one and connect to the lights, and swap it for the other battery every day, or every other day, and charge the batteries at home)
A few quick very rough sums to help you out - if you want to use 40w of lights for 1.5 hours, that's around 5 ampere hours per day -rule of thumb says you'd ideally want a battery at least 10 times that capacity (50 amp hours)-  or for 2 days, double that.......... Then you have to "fill it up again", and ideally you need to reckon to be producing an excess of charge so as to keep the battery topped well up - a 40 w panel should on average produce it's "face value" per day in the depths of winter - so very roughly, an hour's-worth of lights (minus losses) per day - (you don't want to let the battery charge ever get too low)
An el cheapo "PWM" (pulse width modulation) controller will probably do the job well (look for the magic PWM label)-  and you're right, bigger is generally better with batteries....
Good luck!

Title: Re: Tiny off grid project
Post by: biff on October 09, 2013, 04:51:25 PM
Pulse modulation really works better than the bog standard one,
                                           If it were me,and I would maybe find some reason to dally longer than an hour,I would over spec the batts and get my hands on a few big 100ah Yousa,A 40watt pv panel gives out a surprising amount of power daily and you need to have the batts to capture it.
    There is nothing like a bit in reserve,

Title: Re: Tiny off grid project
Post by: Stuart_M on October 09, 2013, 05:30:02 PM
Unfortunately the field we have is the wrong side of one that gets pretty boggy during the winter so Id mentally ruled out the 2 battery option as it would involve more carrying than Id really like! Also the second battery (assuming new) could cost around the same as a panel + controller.

It sounds like it might be worth a go although I think taking a battery + light up the field first might be a good plan to make sure I havent completely underestimated our requirements.

Will look at PWM controllers too. Are all the imports from the Far East in this price range of similar standard or should I be looking for a particular brand?

Title: Re: Tiny off grid project
Post by: martin on October 09, 2013, 06:27:52 PM
I think they're probably all pretty similar (and may well use similar innards) - you can pick them up for around a tenner for a 10 amp job (so will safely cope with up to 110 watts or so of solar panel) -  even if I was only going to use a 40w panel, I'd still go for a 10 amp one, then you can add panels without spending more.......
You'll probably find that you'll get a confusing pidgin-English destruction book with the controller, which if you can decipher it points to umpteen different "functions" available from the output terminals by use of various button presses of the function button - very useful if you want a light to switch on automatically a certain time after sun down etc., but otherwise blessed confusing..... ;D

Title: Re: Tiny off grid project
Post by: Sprinter on October 09, 2013, 10:31:11 PM
I understand the need to tinker, however if its only an hour or two per day for the humans not the birds then how about a couple of cheap rechargeable fishing head torches at a tenner a pop from fleabay

charge them overnight on cheap electric and use them for a week between charges, job done, I use mine for 8 to 10 hours between charges

unless you really want solar of course

Title: Re: Tiny off grid project
Post by: Stuart_M on October 10, 2013, 09:44:29 AM
For some reason I'd forgotten about the head torch I've got. Using a normal one is a pain but a head torch gets round the problem of needing both hands free so could work well.
Unfortunately the need to build something got the better of me so I've ordered a panel and controller last night on the basis that it will be learning experience.
It also makes a nice warm up project before looking at panels for home and modifying my heating system. This forum has a lot to answer for.!


Title: Re: Tiny off grid project
Post by: biff on October 10, 2013, 10:23:51 AM
                "This forum has a lot to answer for"

Title: Re: Tiny off grid project
Post by: Tiff on October 10, 2013, 10:46:59 AM
Sometimes its good to do something like this as a 'hobby project' or just as a learning experience. There are other benefits - i.e. the enjoyment of building something and the knowledge gained.

Some people build model boats, some modify cars, some keep pets, others spend their time in the pub or watching X-factor. They don't have to jusify their actions, they do it for enjoyment.

I would say that 'doing renewables' as a hobby project has far greater benefits for all of us then the multitude of other things we could spend our time and money on.

Go for it Stuart, have some fun and keep us updated with progress and any questions you may have.