Solar Powered Shed Light

We’ve all seen adverts for these solar powered shed lights and we’ve certainly all seen the solar garden lanterns that everyone has and I thought “I could make one of them and I bet it’s cheaper!”

The main reason for making this is because my girlfriend has a horse which is in a field with a shed used for feed in the middle of nowhere with no electricity. Of course it is quite difficult to make up a bowl of horse chow in the pitch black so I thought I’d show my love in the only way I know how; build her a nerdy contraption!

I decided to keep everything as cheap as possible but still providing a decent amount of light for a decent amount of time.

Components required:
  • Light bulb
  • Rechargeable Battery
  • Solar panel
  • Switch
Here's a quick knocked-up diagram:


I used an actual bulb rather than LEDs because I don’t like how LEDs can be rather directional so a bulb would provide better light but would use up the battery faster. This should be slightly offset by the fact that the light will never really be on for more than 10 minutes a day. Keeping the cost down for a light that would be used for any longer would most certainly require LEDs.

The battery is a standard deep-cycle 12v 1.2Ah battery. These are often found as the backup in burglar and fire alarms for power failures.

The solar panel was very cheap indeed and this is because it is only rated at 125mA in full sunlight. The idea is that because the light will never be on for more than 10 minutes a day the solar panel will keep the battery topped up but would never practically charge the battery if it was completely drained. Using the formula: Charging time (Hours) = 1.2 ~ 1.4 x (Battery capacity (mAh)/Output current in charger (mA))

1.2 ~ 1.4 x (1200/125) = 11.5 hours

Of course the calculation assumes full direct sunlight all day AND night. During the winter there is rarely full sunlight and there may only be 6 or 7 hours of light in a day so realistically the charge time is a whole lot longer.

The bulb is a standard 12v 10w car lamp. I’m not quite sure what kind of car would use this as it’s not a headlight bulb and doesn’t have the double filament like the break lights do.

Using the formula: 10 / 12 = 0.833
1200 / 833 = 1.44 hours
The battery will last 1.44 hours before becoming totally flat.


This is what the lamp and the battery look like after completion


The whole thing; switch, battery, bulb and solar panel

Extras that could be possibly be added:
  • A fuse (Probably should have one anyway!)
  • A circuit to turn the light off automatically when the battery gets low or a timer to turn it off after a specified amount of time.
  • A charging regulator to stop the charge to the battery when it’s full (most useful during summer months)
  • A wind turbine to charge the battery faster or when there is little sunlight. With strong wind (about 20mph+) turbines can output a lot more power than a solar panel.
So there you go if you fancy building your own. All the parts were bought from Maplin apart from the switch which came from an old lamp.

Solar panel: http://www.maplin.co.uk/module.aspx?ModuleNo=98358&doy=10m6 £9.99
Battery: http://www.maplin.co.uk/module.aspx?ModuleNo=27088&doy=10m6 £20.99