The above diagram represents a portable solar system that could be used to spend a few days in any place without power supply.
Price: £80 approx.
Weight: 5 kg approx.
It could be used for:
- Lighting a small area such a medium-sized camping tent, a mountain refuge, or a little cave 😉
- Recharge mobile phones, photo cameras or any device that can be charged via a USB port;
- Listen music with a MP3 with speakers that need power supply;
- Charge a car or motorbike flat battery (you would need to plug the solar panel directly into the battery using crock leads and leave it charging for a while).
1. Charge controller. This is the brain of the system. Its two main purposes are to bring the electricity produced by the solar panel into the battery for storage, and to take that storage electricity from the battery into the USB port for music or charging devices, and into the bulb for lighting.
In top of this to main functions, the charge controller also avoids electricity going from the battery into the solar panel (which would otherwise happens at night) and avoids the battery going flat or overcharged, so prolongs the lifespan of the battery.
The charge controller I have chosen has got to outputs, which I think it is very useful, as one can be used for the USB ports, while having the other one permanently set for lighting.
It is a 10 Amperes (A) charge controller. That means that it could work with a solar panel (producing a direct current of 12 Volts) of up to 120 Watts (remember Watts=Volts*Amperes, or W=A*V, so 120=12V*10 A). Feeling like back at school with your physics, aren’t you? J
Well, the system could be used without a charge controller, by plugging everything directly into the battery. That would save some money and weight, but it would mean plugging and unplugging all the time, and probably devices would get damaged.
2. Solar panel. This is the piece that puts power into the system. It transforms sunlight to electric power. This one produces direct current (DC) with a voltage of 12 Volts, and has a power of 5 Watts. It is a quite small one, but I believe It will produce enough energy to have lighting for a small place, charge small electrical devices and listen music for some hours.
To design a solar system you need to keep in mind how many hours of sunlight the solar panel is going to be exposed to. In this particular case, the system has been designed to work in south Spain around summer season, which means no less than 6 hours per day. So, if the panel were 100% efficient (quite improbable), it would provide 6*5=30 Watts of power, or put in a different way, it would charge the battery with 2.5 Amperes (W=V*A; 30W/12V=2.5A). I hope I am right here!
3. Battery. I have chosen a 7 AH one. AH means amperes per hour. So, the battery would be able to deliver 7 Amperes in one hour, 3.5 Amperes in two hours, and so on. The device consuming more energy will be the bulb, a 3 Watts one, that needs 0.25 Amperes (3W/12V=0.25A). So if the light is on for 4 hours it would drain 1 Ampere out of the battery, letting power to charge any small device or listen to music, and still the battery would be far from being discharged to its 50% storage capacity.
4. Lighting. As mentioned above, the systems includes for lighting a bulb that works with direct current of 12 Volts and consumes 3 Watts of power. It has also a bulb holder with a switch control included. In the beginning I thought about using a fluorescent light, but after some reading, it seems that LED lights are more efficient.
5. USB port. I couldn’t find a USB portal that can be connected directly into a battery, so I have decided to use a car lighter plug. The amount of combinations and things you can charge from a USB port are just endless.
Please do keep in mind that I am not an expert in these matters, and this post is more like a personal reflexion and a way to put in paper what goes floating around in my head. I also hope that somebody will spot the mistakes and will be willing to share them, so I can amend it before the whole think explodes in my face! J
Also, remember that working with electricity can be dangerous, even when the amperage in this system is very low, and to consider polarity in devices before plugging.
After finishing the design, I started thinking that it was like a human body, with the solar panel being the digestive system feeding in sun; the battery being our fat reserves; the lights and the charging capacity our muscle power ( among other things); and the charge controller , the brain:
Or probably it is more like a plant. A solar panel is like a leave, transforming sunlight into energy; the battery is like potatoes that plants use for energy reserves; the system has lights and charging power, plants have flowers and fruits:Ok, ok…I think I am going to leave it here…J
See you Later.