Solar Power Storage Systems

Solar Power - Home 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. A storage system stores any excess for later use when there isn't enough sunlight to power all your needs.

Batteries

That 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 needed and batteries are almost universally used.

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 because of their much lower cost. They're very similar to lead acid car batteries with some interesting differences discussed below. 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, typically sulfuric 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. 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, though there are some interesting practical differences. NiCad batteries are much more expensive. But 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 of time, enough and long enough to start your car. Then the motor takes over to power the electrical devices. They are shallow cycle batteries.

But solar power system batteries have to deliver a smaller current over a much longer period of time, hence they are designed differently. During the night when the PV (photovoltaic) panels are not delivering electricity to run the home or charge the batteries, these deep cycle devices do their job.

Charge Controllers

Draining a battery completely (or overcharging it repeatedly), though, would shorten its lifetime drastically.

So, there's a device that's part of the system that keeps that from happening. They're called charge controllers.

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.

PV (photovoltaic) panels will last 20 years, but even good batteries may last no more than 10 years, often less. Replacing them increases the cost of the system, so extending their lifetime is key to keeping the overall investment as low as possible.