A solar kit usually comprises of a solar panel, solar battery and a charge controller. Each of these devices perform unique functions that the other cannot. Although we know a solar PV system must be connected to a solar panel, is it possible to use a charge controller without a battery?
A charge controller is not a battery bank. It’s main purpose is to regulate the amount of voltage flowing to the solar battery from the solar panel. Although some small solar system can work without this two components, it is better if your solar PV system has both.
To find out the main reason why your solar PV system must have a charge controller, keep reading this guide.
What is the operation of a solar charge controller?
Solar batteries or what is termed as deep cycle batteries have usually operate by constantly discharging and recharging. Sometimes the solar panel sends high current to a solar battery. If this charge exceeds the rated voltage, the battery might get damaged.
To prevent that from happening, a charge controller should be installed into your solar PV system.
A charge controller also known as regulator main purpose is to regulate the amount of current being passed to the battery. Since a solar battery has many discharge and recharge cycle, if the large amount of current reach the same battery in a long time, the battery loses its efficiency.
These devices detect the amount of voltage needed by a battery to fully charge, and allows the same amount to be passed. When the solar battery is almost fully charged, the regulator stops anymore current from reaching the battery. The battery then charges to capacity using a technique known as float charging.
Sometimes like during the winter, solar energy is unreliable. If the voltage output in a home is higher than the current input, the solar battery might get over discharged. A solar battery attached to a charge controller will retain some amount of charge for a long period.
Therefore if you want to use the solar battery efficiently, pair it with a high-quality charge controller.
Can you use a solar charge controller without a battery?
There are two types of solar PV installation: Off-grid and Grid-tied system.
In the grid-tied system, the solar panel and the charge controller are connected to an existing grid without a solar battery. The charge collected during the day is used to power appliances. At night, you use electricity to power your residence.
On-the grid method is easy to install. However, you will incur some electricity bills that could be avoided if you used solar energy.
Off-grid system requires complicated installation.
You will need to connect a solar panel, charge controller, and solar battery. Installation is not done blindly, as you must calculate the amount of power needed to power your house. You then need to match a solar battery with the charge controller.
There are two types of charge controllers that are used with a solar battery; Maximum Power Point Tracking (MPPT) and Pulse With Modulation (PWM). These two charge controllers perform the same function however, they differ in size and capacity.
PWM charge controllers are used in small solar PV system. They balance the current and voltage of a solar battery and solar panels. For example, if a solar battery needs 12V to be fully charged, the PWM will allow 12V to reach the solar battery.
When the solar battery is fully charged, PWM stops any more current from reaching the solar battery. PWM cannot pass charge less than 10V to a solar battery.
MPPT charge controller on the other hand also allow current from the solar panel to charge a solar battery. These charge controllers do not balance the current and voltage of the two components. If the solar battery is almost depleted, they allow more current to pass for faster and for efficient charging.
MPPT charge controller prevents over charging and over discharging of the solar battery at the same time. Therefore, even though you don’t think it is important if you had one.
What does a solar panel controller do?
Solar energy is not only a clean form of energy, but also the most cheap alternative for electricity. As more people are embracing use of solar energy, the need for large power storage system is emerging. This is where solar batteries come in.
How a solar PV system works is:
- A solar panel collect solar energy from the sun during the day.
- The solar panel lacks the capacity to store the charge to be used during the night when the sun is not available.
- A solar battery with the capacity to power your home when the sun is down is then installed.
- During the night, your home and appliances draw their power from the solar battery.
- The solar battery is then recharged again during the day when the sun is available and the cycle repeats.
Due to this regular discharge and recharge cycle, you will need to protect your battery from excess current. Furthermore, if you own a solar PV system, you know how expensive solar batteries are.
To ensure the right amount of current reach the solar battery every time it is charging, you will need a charge controller.
A charge controller regulates the amount of current reaching the solar battery at all the time. If the sun is too hot, the charge controller reduces the voltage being passed until it matches with the voltage needed to fully charge the solar battery.
Regulating the amount of charge reaching a solar battery is not the only importance of a charge controller. They also;
- Protect the solar battery from overcharging
A solar panel cannot detect if the solar battery is full. It continues sending more current to the battery. If the battery keeps receiving more charge, it might end up overcharging which might lead to overheating. Overheating can cause fire.
A charge controller detects when a battery is fully charged and stops more current from flowing into the solar battery.
- Blocks reverse current
Solar panels sends current in one direction when charging. At night when the sun is not available, the solar panel might start to draw charge from a solar battery. However, in presence of a charge controller, no charge can flow out of the solar battery. Thus, the battery cannot be over discharged.
- Control set point Vs. Temperatures
Solar batteries operate at specific temperatures. When the temperatures of the solar battery are low, the battery might discharge faster. Some charge controllers have am inbuilt temperature detector. If the sensor detects low temperatures of below 17°C, it raises the set point for compensation.
Control set point Vs. Battery type
Different types of solar batteries operate at different temperatures. Due to the constant change in the voltage entering the batteries, the sealant plates might get damaged. To prevent this from happening, a charge controller detects any voltage change and adjust the set point accordingly. You should therefore use a charge controller specifically made for your type of solar battery.
- Display and metering
Without the proper equipment for measuring the voltage of your solar battery, you might get some frustrations. Luckily, most charge controllers displays the amount of voltage available in your solar batteries.
Charge controllers also send signals in form of light or sound to indicate when your solar battery is fully charged or nearly drained.
A charge controller also prevent overload which might cause fire.
A charge controller is a very important part of a solar PV system. However, it should be connected to a solar battery for it to work.
The guide above explains all the importance of having a charge controller in your solar PV system.
Eng. Matthew Joseph Nandirio is the Founder of walkingsolar.
After graduating from the University of Houston in 2002, matt started working as an electrical and electronic engineer for several multi-national solar energy companies.
He has a wide range of experiences including solar system requirement analysis, planning, maintaining, debugging and even solar device development through research.
He now shares his 20 years of expertise through his articles on the walkingsolar website.
Further, he is also the author of two books on Solar Technology, “Solar Power for Villages” and “DIY Solar System for Dummies”.