Solar energy is quite expensive and difficult to maintain at large scales but at small scales it is not only cost effective but also the small scale power requirements can be fulfilled by constructing simple solar circuits. These can be used in the decorative items.
Small Solar panel:
The first thing required to create these simple solar circuits is of course a device which will collect the sunlight. You can use a small solar panel made of monolithic copper indium diselenide. These are available in the market and will cost you about 3 to 4 dollars.
Two solderable terminals marked with polarity will be there on the back side of the panel. The specifications of the panels are given on it. Usually with that price, the panels may produce 4 to 5 V.
Direct circuit i.e. direct circuit using the sunlight to run some device:
If you want to use this solar panel directly for producing electricity then connect the load with the terminals of the solar panel. You can run small motors like the motor of the CD player or small bulbs like high power (50 to 90 mA) blue led. If you connect light of greater power then it may be damaged by this amount of current. If you place that circuit near some lamp or in sunlight, it will immediately start working.
This direct usage will not store the energy. Small interruptions in sunlight with suspend the system. This may lead to the blinking of the load connected to this type of direct circuit.
Direct device interrupted with resistance:
For working of solar circuit without interruption, superconductors may be adjusted within the circuit. It will provide current during small interruptions. Capacitors should be added in series if more than one capacitor is needed as to match correct energy out put.
One path of current is complete; this type circuit will take 30 seconds to one minute to get it started. This will work for 0ne or two minutes even when the sunlight is not available. This is quite effective for the light applications.
Addition of battery will make the solar circuit to work in dark:
Addition of capacitor will only make the circuit to work with interruption in sunlight and it will not provide adequate energy storage. If you attach a rechargeable battery (like NiMH rechargeable battery) then this type of circuit will not only provide electricity in the presence of light but also in the dark. This type of solar circuit will charge the battery which will provide the electricity in absence of light.
One important thing is to keep in mind that the battery will not only take up electricity but also transfer some part of acquired electricity back to solar panel. It is advisable to connect a reverse diode in between the two. By doing this you can save 50mA of electricity going back to solar panel. NiMH batteries and sealed lead-acid batteries are most suitable batteries for such type of unmonitored system. The charging should be kept below 130mA.
Dark detector LED driver Circuit:
The dark sensor is device is very easy to incorporate in your solar circuits. By the help of this your solar circuit will automatically sense the dark and it can also be used as infrared phototransistor.
PNP transistor can be used to perform switching and it is controlled by the output voltage of the solar panel. In this circuit yellow LED can be connected which will turn on in dark as the transistor will allow current to flow through it. The panel’s output is high in the sunny environment which will turn off the transistor. Red or yellow LED can be driven by this type of solar circuit. This circuit does not have sufficient voltage which is required to drive blue or white LED.
Solar circuit for garden:
By adding Joule Thief voltage in the above type of circuit, the design of the solar circuit can be improved and it can be used in solar garden lights. This circuit needs to be enclosed in very tough and water resistant casing.
The voltage used in light detector can be used in more effective device like AVR microcontroller. This is a very efficient and low current device. This device will save the power by controlling the running of LED all the time. Joule Thief style of booster can be driven by microcontroller which can run white LED.
This type of circuit can be used to run two red LED outputs. Many funky lanterns can be made lit with the help of such solar circuits.
A word of caution:
In above discussion, many minute details are not included intentionally as they are not important in such small scale products. But these can be critical if you are working on large scale.