Hello there. You've probably found this Instructable to gather ideas about making a portable solar power supply yourself. I've always been interested in electronics with this project being my latest idea to come wandering out of my head, why not make a portable box on wheels, that I can plug basically anything into, thats powered by the sun? So therefore I thought I'd share this Instructable with the rest of the world.
Step 1: Start thinking...
The first thing to do is to think of what you will be wanting to power via the sun, the whole house would be nice, but that's a tad too expensive and not very portable. Our family go away camping many times during the year so I knew what I had in mind. Some 12 volt energy efficient lightbulbs, a 15 inch LCD TV with a free-to-air digital receiver, some sort of radio/CD player would be nice too, a way to charge our mobile phones/sat navs and being able to inflate our air-beds, one which is 12 volts DC and one which is 240V AC.
With all of that in mind I started looking at prices of components on websites such as Ebay and Maplin as price is a very important factor in designing a solar system. Our LCD and receiver draw 2.2 Amps DC on 12 volt, energy efficient lighting draws just under 1 Amp for a 12 watt bulb whilst the phone/GPS chargers draw very little power. Using the TV for say, 3 hours a day max would equal 6.6Ah consumed, lighting used for 4-5 hours a night would consume roughly 4Ah while all the charging of portable devices would be around 2Ah while pumps for air-beds wouldnt run for long so maybe only consuming around 1Ah, totalling 13.6Ah. Deep Cycle batteries shouldn't be discharged below 50% of their rated capacity, the smaller the discharge cycle, the longer the battery will last, therefore a battery of 30Ah would suffice. The UK receives on average 6 hours of sunlight during summer, which is the time of year we go camping and replacing 13.6Ah into a battery would take a 50W solar panel roughly 5 hours to recharge.
(Watts = Voltage x Amps)
(Average solar panel voltage at max power = 17 Volts)
(50 watts/17 volts = 2.94 Amps)
It's easier to draw power from a battery than to replace, requiring usually 10% more power to recharge than what was consumed, therefore:
(14Ah / 2.94 Amps = 4.76 hours of direct sunlight)
In a real world situation this will never happen due to too many different factors such as;
Solar panel shading,
Size of wiring,
Therefore it's safer to use a larger battery bank, where power can be used up repeatedly if weather conditions the day after aren't suitable for efficient solar charging to completely recharge the battery.