Batteries

Batteries are applied to store energy for times of little or no sunlight. They are the most sensitive component of any photovoltaic system and require a certain amount of care. They are not easygoing like batteries in cars.

Only lead-acid batteries are used in the field. They come in different types: 

 

• Automotive batteries (regular type, used in cars, also called SLI batteries)

-   very short service life, high maintenance, only shallow charging

+  very low price, good availability

 

• Automotive batteries (heavy- duty type, used in trucks and buses)

-   short service life, medium maintenance, shallow discharging

+  low price, good availability

 

• Solar batteries (different designs)

-   medium discharging, limited availability, medium price

+  better service life, limited maintenance

 

• High-quality batteries (diff. designs)

-   expensive (4-6* autom. battery price)

+  high service life, low maintenance, rather deep discharging

 

Regular batteries have to be filled up with distilled water in certain intervals. A few are maintenance-free. Only those of the gel-type are suitable in solar systems.

Automotive batteries are unsuitable if any alternative exists. Heavy-duty ones may be used in smaller systems with severe budget constraints or if others are not available. High-quality, deep-cycle batteries are optimal for solar applications. Solar batteries are a compromise between quality and costs.

 

The service life of batteries, which is expressed in cycles of charging and discharging periods, increases with: 

• the quality of the battery,
• the quality of the charge controller,
• low temperature,
• a low depth of discharge and
• careful operation and maintenance.

 

The depth of discharge (DoD) is that portion of the battery capacity which is removed during discharging. The capacity is indicated in ampere hours (Ah) or sometimes in days of autonomy. This is the number of days a fully charged battery can satisfy the energy demand.