Renewable Energy

In PV systems, battery banks are used for energy storage. Fortunately, batteries can be utilized with almost any type of PV system.

• Grid-Tied with Battery Backup: If the utility grid is available, you can design a grid-connected PV system based on batteries, also known as a battery backup PV system. In this setup, batteries are only utilized when the grid power is interrupted.
• Stand-Alone or Off-Grid: When there is no access to the utility grid, you can design a Stand-Alone or Off-Grid system. In this configuration, batteries are used whenever the PV arrays cannot meet the power demand of the loads, such as during cloudy periods, at night, or when specific appliances are running during the day.

In this section, you will become familiar with the types of batteries used in PV systems. This is an opportunity to learn about their basic structure and characteristics, helping you understand the essential criteria used for selecting battery banks in PV systems.

A charge controller is an electronic component situated between the PV arrays and the battery bank. As you might have guessed, its primary life-long function is to regulate the charge coming from the PV arrays to the battery bank. Charge controllers vary from small units designed to connect a single PV module to a battery, to large-scale controllers designed to link multi-kilowatt PV arrays to massive battery banks.

In all off-grid systems where batteries serve as energy storage, the charge controller is considered an essential component. Its main purpose is to protect the battery from being overcharged by the solar array or excessively discharged. The charge controller regulates the current and voltage entering the battery. Some types of controllers, featuring low-voltage tracking characteristics, also protect the battery from deep discharge by the load.

If batteries are routinely overcharged, their expected lifespan decreases significantly. Charge controllers monitor the battery voltage and stop the charging current whenever the voltage exceeds the limit. This is particularly important for Sealed Batteries, as the water lost during the recharging process cannot be replaced in them.

There is only one exceptional case where a controller is not required: when the charging source is very small or the battery is very large in comparison. Specifically, if the current produced by the PV panels is 1.5% of the battery’s rated current or less, a charge controller is not necessary.

Unlike wind or hydroelectric system controllers, solar controllers can be disconnected from the system when the battery is full without causing any damage to the solar modules. Most controllers can simply open the circuit or limit the current between the battery and the PV modules when the voltage reaches a specified threshold, and switch back on when the battery voltage drops.

This voltage limit is adjustable in some controllers, while in others, it is preset by the manufacturer. Controllers are categorized based on the amount of amperage they can handle. International standards require controllers to withstand a 25% current overload for a limited time. This ensures that the controller is not damaged when solar radiation increases excessively, causing the PV modules’ output to peak. However, excessive current over a long period can damage the controller.

Selecting a charge controller with a higher current rating than currently required allows for future system expansion without incurring significant additional costs.

General Functions of a Charge Controller:

• Voltage Regulation: Controlling the voltage reaching the battery from the solar panels to prevent overcharging.
• Over-discharge Protection: Preventing the battery from discharging beyond safe limits.
• Reverse Current Prevention: Blocking reverse current flow during the night. (Reverse current is the small amount of power that flows back through the panels at night, draining the battery. While this loss is often negligible, it becomes significant in large PV systems. Almost all controllers manage this current automatically).

An inverter converts DC power—produced by PV arrays or stored in a battery bank (in battery-based systems)—into AC power, which is used in homes and businesses. Inverters come in various shapes and sizes. An inverter can be as small as a 100-watt unit used in a car, or as large as a multi-megawatt unit for utility-scale PV projects. If a PV system is used solely to provide power for DC loads, such as certain lighting, water pumping, or small electronic devices, an inverter is not required.

Inverters in PV applications are divided into two major categories:

1. Grid-Interactive (Grid-Tied) : These inverters can connect to the public utility grid. They can send electricity back to the grid through a meter during times of low consumption or draw power from the grid to supply connected loads if the solar system is insufficient.
2. Stand-Alone (Off-Grid) : These inverters are not designed to interact with the public utility grid; their sole function is to supply power directly to the consumers/loads.

Grid-interactive and stand-alone inverters often look similar. If you look at two inverters from the same manufacturer, you might not see any difference in their appearance because manufacturers try to house different types of inverters in the same casing to reduce the number of parts and cut costs. The only way to confidently identify the type of inverter is to check the label located on its side.

Loads are the electronic devices that people wish to use in their homes and offices. You can have DC loads, AC loads, or both; you just must ensure that you provide the correct type of power to each. For example, you cannot use a DC light bulb when AC power is being supplied.