One of my solar energy trainees once asked me: if he can use a car battery for solar PV projects. I will address that question in this article. But first, I will give you a general overview of the roles batteries play in a PV system, differences between varying battery-types, and their pros and cons. Your understanding of all these will help you make an informed decision as you buy batteries for your PV system. In conclusion, I will recommend one for you after putting into consideration: energy efficiency, cost-effectiveness, life cycle, and storage capabilities.
Once you start thinking about going off-grid, you are already thinking about how you can store energy generated by your solar panels for use later in the day when there will be no sunlight – at night, cloudy or rainy days. Unfortunately, there’s only one option available to you. BATTERY! Battery in PV system can rightly be compared to fuel in your car tank. The bigger your fuel tank, the farther distance it will take you, the more money you got to spend.
During Sun-Hour, the panels generates solar energy. The charge controller weighs the energy generation from panels against your appliances’ energy use. If there’s excess energy supplied, the charge controller will use that surplus to charge the battery.
If the battery is already charged or full, the charge controller will waste (in some more organized country, the excess energy will return to the national grid) the excess energy without causing overcharging or damage the battery.
At night or when there’s no sunlight, the panels produce little or zero energy. Your appliances will utilize energy stored in the battery to power your house
Here, we are going to focus on Deep Cycle Battery (Solar Battery) as against Starter Battery (Car Battery).
Deep Cycle Battery is the type of battery recommended for use in solar PV system as opposed to Starter Battery (Car Battery). Deep cycle battery is specifically designed for to be discharged to low energy level and rapid recharged or cycle charged and discharged day after day for years.
We have three types of Deep Cycle Battery: Lithium-ion Battery, Lead Acid Battery and Nickel Battery (Nickel battery technology is not common in solar PV applications. so we are going to focus on Lithium-ion and Lead Acid chemistry)
Lithium-Ion batteries use an intercalated lithium compound as the material at the positive electrode and typically graphite at the negative electrode. This newer battery technology is fast becoming more common in solar PV storage system. When it comes to the best in solar batteries, lithium-ion batteries are surely the best if you can afford it.
1. Self-Discharge – They do not lose as much capacity as other batteries when they are idle.
2. Physical Size – they are lighter and smaller in size, saving you mounting space
3. Life Span – last longer than other type of solar battery
4. Depth of Discharge – can discharge 80% of its stored energy.
5. Less Maintenance effort
They are very expensive. In fact, one (1) li-ion battery can buy four (4) of any other solar battery. Take it as we say here: “better soup na money make am”
Lead Acid battery is the most commonly used in solar PV system. Lead acid battery is made from a lead alloy. The only advantage Lead-Acid battery has over Lithium-ion battery is that they are cheaper and readily available in Nigeria market.
Lead Acid Battery has two main types: Flooded Lead Acid and Valve Regulated Lead Acid batteries
These types of solar battery have a liquid electrolyte solution. They are popularly known as water battery in the market. Flooded lead acid battery is one of the most common battery used for off-grid system.
1. Price – they are cheaper than Sealed battery
2. Life Span – they last longer than sealed Batteries
3. They are very reliable
1. They require regular maintenance and monitoring. You need to be adding distilled water regularly
2. Size – They have big physical size, taking much mounting space
3. Corrosion – They are prone to corrosion
4. Leaks – The electrolyte can leak if not installed upright
These are types of batteries we usually refer to as sealed batteries or maintenance-free batteries. They a sealed in the sense that electrolytes in the battery are prevented from leaking out, but they have pressure release vents.
1. Zero Leaks – electrolyte cannot leak since they are sealed. Therefore, you can tilt them if your installation demands
2. Less Maintenance Effort – You don’t need to add distilled water
3. Less Corrosion
1. Costlier than Flooded Battery
2. Less Life Span than Flooded Battery
Lead Acid Battery has two main types: AGM and GEL.
AGM (Absorbent Glass Mat) Battery holds the electrolyte in a special designed glass mat.
1. AGM charges faster than Gel battery.
2. It also has instant high load current on demand.
3. It’s cheaper than GEL batteries.
AGM has its own drawbacks when compared with GEL batteries.
AGM works best as a mid-range battery with capacities of 30 – 100 Ah. That means that it’s less suitable for large PV system. GEL
Gel battery contains a silica type gel that holds the electrolyte in a paste.
1. Gel batteries performs better than AGM in higher temperature.
2. It’s more suitable for large PV system.
3. They are more durable than AGM.
The drawbacks of GEL battery are: They are costlier than AGM and they charge slower than AGM.