Solar panels for remote hut

solar novice

Hi All,

It's a few season's since I scraped through physics, and the baffling array of commercial spin on just what I require for a small solar system for lighting has my head spinning so thought I'd try and source some independent advice!

My wife & kids (& I) have a small remote hut (in New Zealand) and need to run solar lighting.

We're only there for a few weeks a year, and that's generally mid-late April to early May (our fall-early winter), so perhaps not the strongest months for solar.

I'm proposing to run 12 V LED lights, and think we'll need 8 spread around different parts of the hut (there's 3 separate rooms), and run them for an average of say 8 hours a night. I think we'll need 5W bulbs. We won't have them all on at once but don't mind having a bit more capacity.

Any suggestions as to what sort of panel we should looks at, and what size?

What sort of charge controller?

And what sort and size of batteries/ I should look at?

Appreciate any thoughts!!

niel

Re: Solar panels for remote hut

you had me confused for a moment as solar lighting we generally refer to as walkway lights, but i see you are referring to the lights inside as being solar lighting being the lights are to be solar powered. just refer to them as lights as it will lessen any confusion.

as to the system you propose i would go by the worst case and have all lights on at the same time for the 8hr time period. this equates to 5w x 8 lights = 40w draw. at 12v this is 40w/12v=3.34a. doing this for 8hrs is 8hr x 3.34a = 26.67ah. for 2 days use this is 53.34ah. (i list 2 days because not every day has sunshine, but you can opt for more days of autonomy if you like and it will up battery and pv requirements) now one does not want to go beyond 50% dod to save on battery life so a doubling of the ah will represent the ah capacity of the batteries or 2 x 53.34ah = 106.67ah. you will find that this is a fairly common area of capacity for many batteries.

the controller can be a simple pwm type as you won't have a large system here, but you can still opt for a smaller mppt cc if you would like to.

for the pv you need to know roughly the number of hours your area is rated at 1000w/m^2. often this is about 5hrs for most during the sunniest times of the year. i will go with 3hrs (not knowing for sure if applicable to your area or not) so that's 26.67a/3hrs=8.89a required daily for charging. given pv inefficiencies we divide by 77% for 11.55a required from pv. for a 12v nominal pv the voltage on the pv will be approximately 18v for 207.82w stc rated.

now there are a number of ways to approach that pv wattage as you can opt to parallel similar voltaged pvs or get one of the larger pvs rated around 210w with an odd vmp not usually suited for pwm controllers and would require a mppt cc. there are still some 12v nominal pvs out there with that wattage rating too if you find one and that would allow the use of the cheaper pwm cc.

keep in mind this is a worst case that i've run through for you and i'm sure you can make it worse than i just did, but this is quite an undertaking to accommodate a place with lights occupied so very little. it would be possible to run a generator with a good 3 stage charger on a similar battery and use a much smaller pv in the area of 2a or 3a with a vmp in the area of 17.4v to about 18v or so through a cc to keep a float charge on the battery during times you aren't there.