When you harvest energy using solar panel or wind mill you definitely want to know how much you get of it. The obvious way is to use power and energy meter. deba168 have installed a small 10V solar panel plant at his living place in order to light LED bulb when power goes off. After his setup he decided that he wants to monitor energy outcome of it. So he started another project where he monitors power and energy of his plant.
He have chosen Arduino which is pretty easy to get going. Measuring power and energy is a matter of measuring current, voltage and time. Then all parameters can be calculated. Voltage measuring is easy by feeding it to analog input. Since voltage may get a bit higher that Arduino power supply, there is a resistive voltage divider used. Current could be measured by using current sense resistor, but deba168 used current sensor module ACS712 which works by using hall principle. The last parameter – time is measured using Arduino library. Having this he was able to calculate output voltage, current, power and energy data to LCD. He also attached Ethernet shield so he could log data to xively.com and SD card as well.