Home Solar Energy Storage Systems

The standard solar power system used to provide electricity today consists chiefly of two components: PV (photovoltaic) panels and a storage system. The PV (photovoltaic) panels generate the electricity and the storage system stores any excess for later use when there isn’t enough sunlight to power all your needs.

Storage systems usually consist of a large number of batteries stored in a vented, safe location such as a basement or specially constructed room. Batteries are optional but in order to be completely ‘off grid’ some kind of storage system is needed and batteries are almost universally used to power these systems.

There are two basic kinds of batteries used in most systems: lead acid and nickel cadmium.

Lead acid batteries are by far the most common due to their lower cost. They are very similar to lead acid car batteries although there are some interesting differences which are discussed below. The batteries have positive and negative terminals (to which leads are attached) and contain metal plates that connect to the terminals. The plates sit in a chemical solution, typically sulfuric acid.

The chemical reaction between the lead plates inside the housing and the sulphuric acid mix produces electricity. When these substances chemically combine, they generate free electrons that flow through the terminals and down the attached leads to your home outlets. PV (photovoltaic) solar panel-generated electricity drives the chemical reaction backwards, (re)charging the batteries.

The same principles apply in the case of nickel cadmium batteries with some interesting practical differences. NiCad batteries are more expensive than lead acid but the price is justified by the fact that the latter delivers more value. They last much longer than other batteries and discharge more current before they need to be recharged.

Both types are known as deep-cycle batteries. Car batteries supply a lot of current for a short period of time – just long enough to start your car. Then the motor takes over to power the electrical devices – these are shallow cycle batteries. Solar power system batteries however are designed differently because they have to deliver a smaller current over a much longer period of time. These deep cycled devices work during the night when the PV (photovoltaic) panels are not delivering electricity to run the home or charge the batteries.

Charge Controllers

Draining a battery completely (or overcharging it repeatedly) would drastically shorten its lifetime; charge controllers are a device that is part of the system and stops this from happening.

When the battery reaches a certain level; the controller cuts of any drain to prevent the stored charge going below a designed-in level. It also cuts off once the battery reaches a pre-set stored charge level. Most are designed to allow lead acid batteries to discharge no more than 50% of capacity to ensure a long life.

PV (photovoltaic) panels will last for 20 years, but even good batteries may last no more than 10 years, often less. Extending their lifetime of the batteries is a key factor in keeping the overall investment in the system as low as possible.