Batteries for photovoltaic systems

Energy produced by photovoltaic modules is stored in batteries to make it accessible when there is a shortage of light.
This is the most critical element of the whole system and the only one which requires maintenance.
Main requirements:

• constant readiness to absorb and supply electrical energy in large and small quantities
• sufficiently large supply of current
• long life in cyclical operations
• low maintenance running
• minimal costs

Of all the batteries sold on the market the lead battery is the most suitable, mainly because of its charging and discharging efficiency and price/performance ratio.

Principal types of batteries
Batteries with positive and negative grid plates
OpzS batteries with positive plates
Block batteries with tubular positive plates
Batteries with solid electrolytes
Nickel-cadmium batteries

Warning!

• If perpetually overcharged --> water breaks up into a explosive mixture and corrodes the plates.
• Deep discharge --> the plates' grids are transformed into lead sulphate, thus reducing the battery's capacity.
• If stored when uncharged --> the active masses of the electrodes form large, hard crystals of lead sulphate which reduce the battery's capacity.
• At low temperatures --> when uncharged the electrolyte may freeze and destroy the container of the accumulator.

Comparison between batteries for solar plants and automotive batteries:

	Solar battery	Traction batteries
Starting current	Small	Large
Efficiency	Large	Medium
No. of cycles	Large	Small
Local action	Small	Medium
Length of life	Long	Medium

Trigger boxes

Perfectly co-ordinate the solar generator and accumulator and optimise the flow of energy.
Used for monitoring the plant.
The dials are important as the user learns to adjust the collection of current to the offer so as to considerably prolong the system's autonomy.