Solar-powered systems utilize one of most available renewable energy sources where photovoltaic panels convert solar energy into direct electricity. The generated energy is stored in suitable solar batteries via solar charge controllers to power the solar systems at night. Lead acid batteries or lithium batteries are used commonly in solar-powered light units.
Storage capacity of a solar battery is usually measured in Ampere Hour. An ampere hour (abbreviated as Ah or sometimes amp hour) is the amount of energy charge in a battery that will allow one ampere of current to flow for one hour. An ampere is a unit of measure of the rate of electron flow or current in an electrical conductor. Almost all the modern solar street lights use lithium-ion or LiFePO4 batteries to store the energy and the Ampere hour of solar batteries can range anywhere from 10 Ah to more than 1000 Ah.
To understand the battery needs, manufacturers and dealers use a standard calculation for power requirement.
How to calculate the AH of a battery?
The formula to calculate AH is:
Amp Hours (Ah) = Watt Hours/Volts
Watt hour is a unit of energy to measure the amount of electricity an item consumes over a period of time and Volts is a unit to measure voltage
The battery capacity of a 12 Watt Solar Street Light is 9.6 V and 57.6 Watt Hours.
Amp Hours(AH) = 57.6/9.6 = 6 AH
With 50% DoD rate (depth of discharge), a 100 Ah battery is capable of delivering 0.3 kWh of direct current power on a daily basis. The depth of discharge rate of LiFePO4 batteries is as high as 80% which means the battery capacity can be utilized more. The most reasonably-priced all in one solar street light used to illuminate residential or private properties have batteries with Ampere hours starting from 10 Ah and solar street lights used to light up highways, streets, parks or other public spaces use batteries with a higher Ah.
Solar street lights use MPPT or PWM controllers and one needs to be certain that the controller has enough capacity to handle the current from the panel. The charge controller used in solar lights is rated against Amperage and Voltage capacities. Choose the solar charge controller that matches the voltage of the solar panel and batteries and then pick out which type of controller is correct for your application. The lithium batteries used in today’s solar lights are very efficient when compared to the lead acid batteries and are more energy efficient and have a longer lifespan.