Batteries are used for storing energy and are critical for off-grid and hybrid solar power types as back up storage when there is no supply of solar power energy at night or during blackout. They are characterized by some of the important parameters in choosing a good battery for your solar power system like capacity, Depth of Discharge (DoD), Round-trip efficiency and battery life.
- Capacity is the amount of energy that the solar batteries can store, typically measured in kilowatt-hours (kWh).
- Depth of Discharge (DoD) of a battery is the amount of battery’s capacity that has been used. A higher DoD means better as you will be able to use more of the battery’s capacity, represented by a percentage. One shall recharge a battery when the power is 10% if the DoD is 90%.
- Round trip efficiency is the amount of energy that can be used as a percentage of the amount of energy it took to store it. A high round-trip efficiency is better for a battery.
- Battery life is also important as batteries are naturally degrading as time goes by and with multiple cycles of charge and discharge were performed. Measured in years or number of cycles with percentage of the original capacity. For example, one battery has a warranty of 1,000 cycles or 10 years at 80% of its original capacity.
Generally, the industry has batteries with three main chemical compositions that are used for storing energy generated by the solar panels. We have (1) Lead Acid, (2) Lithium-ion, (3) Saltwater.
- Lead Acid are the most usual and tested batteries for off-grid power systems. Relatively cheaper than other types, it also has shorter lifespan and lower DoD percentage. With its cheap cost, it is typically used for storing a lot of energy.
- Lithium-ion may be the best option for the current battery storage industry. With its lighter and more compact form, along with high DoD percentages and longer lifespan, cost is relatively higher than the lead acid.
- Saltwater is the newest in the battery industry. Without heavy metals, it uses saltwater electrolytes. It is considered to be the most environment-friendly as heavy metals have to be disposed properly and with special processes. It still needs to be tested as it is new in the industry.
| Lead Acid | Lithium-ion | Saltwater | |
| Cost | ✅✅✅ | ✅ | ✅✅ |
| Battery Life | ✅ | ✅✅✅ | ✅✅ |
| Depth of Discharge | ✅ | ✅✅ | ✅✅✅ |