Hello Everyone,

I’m an artist working on a project that I would like to add LEDs that are solar powered. This would be completely off grid.

I am planning on using 100 x 0.025 watt LEDs throughout my outdoor sculpture. These are off the shelf sealed “trailer lighting”. Each is individually sealed in plastic with two wires (1” x 3/4”) ready to hook up to a 12v battery. http://www.ledtrailerlights.com/cm-hd34003-mini-clearance-marker-light-3-leds.htm

I would like to have this work every night for a minimum of 7-8 hrs. I am designing and building it therefore I have leeway on the panel size and battery size. It will be south facing with no obstacles. It will be located in Ottawa Canada.

My questions are: Is this even possible? Will I be able to store extra power for cloudy days in a large battery/ies? Would it be better if the lights came on for 5 minutes with a motion sensor and then off for power conservation? What size panel and battery will I need?

Thank you for your help!

 

My questions are: Is this even possible?

Yes, definitely.

Will I be able to store extra power for cloudy days in a large battery/ies?

Yes.

Would it be better if the lights came on for 5 minutes with a motion sensor and then off for power conservation?

Absolutely, as long as this matches your design goals.

What size panel and battery will I need?

Here marks the end of the easy questions! As I understand it, you'll need about 2.5A (not watts) to light all your LEDs. If you want them to stay on for 8 hours, you'll need 2.5A x 8 hr = 20A•h of battery capacity. That's about half of a typical car battery. If you use the motion detector and cut the on-time to an hour or less, this obviously reduces the battery requirement.

But it gets ugly when you try to account for cloudy days in the winter, the worst-case for any solar-powered system. For instance if you want the system to work after a week of snowy, grey days in late December, the battery is going to have to do all the work with little input from the solar panel. A big part of sizing your battery and panel depends on whether you can accept the device going dark during the worst case scenarios.

Then there's a complex tradeoff. A giant panel will provide enough power for the project on even grey days. You'd only need the battery large enough for one night because it would always get fully recharged by the giant panel during every day. It might take six hours on a grey day or only minutes on a sunny day. A smaller panel won't keep up on grey days and you'll need a larger battery to keep going during those times as you wait for a sunnier day to come along.

Whatever calculation you make for what you need, double it. Panel ratings tend to be optimistic and there are various losses and inefficiencies.

If it was me, I think I'd start experimenting with a deep-cycle car battery and a 10W (or so) panel. Just watch it and see how it does with your load (which you could simulate using a single light bulb). Use a commercially available charge controller. They're built for exactly this sort of application.

 

Yes, definitely.
Yes.
Absolutely, as long as this matches your design goals.
Here marks the end of the easy questions! As I understand it, you'll need about 2.5A (not watts) to light all your LEDs. If you want them to stay on for 8 hours, you'll need 2.5A x 8 hr = 20A•h of battery capacity. That's about half of a typical car battery. If you use the motion detector and cut the on-time to an hour or less, this obviously reduces the battery requirement.

But it gets ugly when you try to account for cloudy days in the winter, the worst-case for any solar-powered system. For instance if you want the system to work after a week of snowy, grey days in late December, the battery is going to have to do all the work with little input from the solar panel. A big part of sizing your battery and panel depends on whether you can accept the device going dark during the worst case scenarios.

Then there's a complex tradeoff. A giant panel will provide enough power for the project on even grey days. You'd only need the battery large enough for one night because it would always get fully recharged by the giant panel during every day. It might take six hours on a grey day or only minutes on a sunny day. A smaller panel won't keep up on grey days and you'll need a larger battery to keep going during those times as you wait for a sunnier day to come along.

Whatever calculation you make for what you need, double it. Panel ratings tend to be optimistic and there are various losses and inefficiencies.

If it was me, I think I'd start experimenting with a deep-cycle car battery and a 10W (or so) panel. Just watch it and see how it does with your load (which you could simulate using a single light bulb). Use a commercially available charge controller. They're built for exactly this sort of application.

Thank you so much for your help.
Your information has given me a direction to research and explore!

 

Sounds like a fun project. Be aware that each of those lights consume .3 Watt (.025A x 12V). So you will need to supply 30 Watts per hour.

 

Watts is already a rate of energy flow.

 

100 x 0.025 watt LEDs

The spec says 0.025A, not 0.025 W .