Solar panel and battery for garden lighting

highdef

Hi, I'm developing a new piece of land and am making it into garden with pathways, a pond and a couple of social spaces. I was going to just install mains 240 or 12 volt lighting however I have been thinking about going mains free and install a solar panel in an area of the garden that gets plenty of direct sunshine. This would be connected to one or more 12v car batteries via a charge controller and other associated bits and pieces. Would this be a good idea?

Panel wise, I was looking at something like this - http://www.outdoor.ie/solar-lights-accessories/271-solar-panel-50-watt.html however I may be able to get a 175w one for a decent price so can I assume that the bigger, the better?

With regards to how much power I can have fed from it to the battery, the panel shown in the link says a max ouput of 50w. How does that correspond with regards to charging a 12v car battery, say of 70AH?

Then, with the 70 AH battery, how much lighting could be fed from it - say 10 x 5w LED bulbs (12v) - how long would they stay lit in any one period of time on a full charge?

Finally, would it be possible to power some mains devices via an inverter as well as the lighting - say a beer fridge and/or maybe a hifi stereo or something like that? I'm guessing it would be a bit much for one car battery.

If I got the 175w solar panel and got either bigger capacity car batteries or else had more than one (I reckon more than one battery would make more sense), could the above be doable, resulting in zero running costs? I'm guessing that the 175w panel could charge several batteries at a half decent rate, sunshine/daylight permitting of course!

highdef

I'd go 24v for the simple reason you can get 24v 250W solar modules for the same price as a 12V 150W.
Design the system to 10% or less discharge per day. With 50% Wp PV to your average daily Wh load.
Eg. 450Ah @ 24v will comfortably run an average load of 1kWh per day for which a 500Wp PV array can cater for.

Car batteries are not suitable for solar. They'll die in the first year of commissioning.
Leisure batteries are generally garbage too.
6V motive batteries are best for low budget, Crown or Trojans are very good.
If you spec it right zero running costs is entirely possible. Keep the beers outside and cool them naturally from November to January and turn off the fridge so you don't hammer the batteries with reduced solar gain.

The appliances you listed can all be found in 12v or 24v models which will save you a lot of energy by not running an inverter. Avoid absorption and thermoelectric fridges though, they're woeful, compressor versions are most efficient.
Aim for 10% discharge a day.

highdef wrote: »

With regards to how much power I can have fed from it to the battery, the panel shown in the link says a max ouput of 50w. How does that correspond with regards to charging a 12v car battery, say of 70AH?

70Ah @12v = 840Wh expecting a 50W module will recuperate 150Wh most days so ~ 2 days to recharge the battery from 50% discharge to 90%, another day to get to 95% and a week to get to 100%.
That's if you don't run any loads in the meantime.

highdef wrote: »

Then, with the 70 AH battery, how much lighting could be fed from it

4 x 5W LED bulbs for 4 hours to 10% discharge

highdef wrote: »

- say 10 x 5w LED bulbs (12v) - how long would they stay lit in any one period of time on a full charge?

8 hours to 50% charge (going lower than this wrecks the battery...16 hours if you want to deplete it but it'll never recover full capacity afterwards)

{EDIT:}

highdef wrote: »

Panel wise, I was looking at something like this - http://www.outdoor.ie/solar-lights-accessories/271-solar-panel-50-watt.html

Jaysus rip off merchants!

Don't pay more than €1.20 per watt even that's expensive small modules often are.