Any solar power system that is used to provide electricity consists of two main components.
These are the photovoltaic panels, which generate the electricity and a system to store excess generated energy for later use.
Solar energy storage systems are required so that you have a continuous supply of electricity during the hours of darkness or when there is insufficient sunlight to power all of your needs, as on a cloudy or overcast day.
Solar Energy Storage Batteries
A solar electricity storage system is usually in the form of a large array of batteries stored in a vented, safe location, such as a basement or specially constructed room. Though batteries are optional, in order to be completely ‘off grid’ some kind of storage system is required and batteries are almost universally used.
The two main types of batteries used for solar energy storage are lead acid and nickel cadmium.
Lead acid batteries are by far the most common because of their much lower cost. They are very similar to lead acid car batteries, with some interesting differences. They 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, of distilled water and sulphuric acid.
Electricity is made available by a chemical reaction between the lead plates inside the housing and the sulphuric acid mix. When they chemically combine, they generate free electrons that flow through the terminals and down the attached leads to your home outlets. Photovoltaic solar panel-generated electricity drives the chemical reaction backwards by charging and recharging the batteries.
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The same principles apply in the case of nickel cadmium batteries, though there are some interesting practical differences.
NiCad batteries are much more expensive, although they earn that higher price by delivering more value. They last much longer, and they can discharge more current before they need to be recharged.
Both types are what are known as deep-cycle batteries.
Car batteries supply a lot of current for a short period, enough and long enough to start your car. Then the motor takes over to power the electrical devices. They are shallow cycle batteries.
Solar power system batteries have to deliver a smaller current; over a much longer period, hence they are designed differently. During the night, when the photovoltaic panels are not delivering electricity to run the home or charge the batteries, these deep cycle devices do their job.
Solar Energy Storage Battery Charge Controller
Draining a battery completely, or continuously overcharging it, would shorten its lifetime drastically. To prevent that scenario, an integral device called a charge controller is employed.
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 level of charge stored. Most are designed to allow lead acid batteries to discharge to no more than 50% of capacity. That ensures a long life.
Photovoltaic panels will last up to twenty years, but even the best battery may last no more than ten years, often less. Replacing solar energy storage batteries increases the cost of the system, so extending their lifetime of is key to keeping the overall investment as low as possible.