Choosing the Perfect Battery for Your Off-Grid System
Deciding on the right battery for an off-grid solar power system is an important factor that will impact the performance and longevity of your system. Here are some factors to consider:
How many days of autonomy (days without solar power) will you need? Being mindful of the devices you will run during this time will help in planning for 1 to 3 days of autonomy, which is typical. Let's say you want one day of battery storage. A generator may be needed in this case to fill the gap when you have to recharge your storage capacity for a longer period of time.
Capacity: The battery capacity is the amount of energy the battery can store, some are measured in ampere-hours (Ah), while others are measured in kilowatt-hours (kWh). You will need to determine your energy need in order to determine the appropriate battery capacity for your system. Here are some ways to determine this:
Amp-hours = 1000 x energy storage (kWh) / Battery Voltage (Volt)
Kilowatt-hours = Amps x Battery Voltage (Volt)
Lead-acid batteries are easily configured for series or parallel. They cost less than comparable lithium batteries. Whether they are sealed, flooded, or AGM, lead-acid batteries have a 50% DoD (depth of discharge) and typically do not last as long as lithium. Lithium, on the other hand, has a higher DoD (around 80%) and is not prone to damage, thus it will last a lot longer. Lithium battery banks can be parallel but can't be put in series easily. This is mainly due to the BMS (Battery Management System) built into most lithium batteries.
Depth of Discharge: As mentioned previously, the depth of discharge (DoD) is the amount of energy that can be safely drawn from the battery before it needs to be recharged. For example, a battery with a 50% DoD can be discharged up to 50% of its capacity before it needs to be recharged. A higher DoD means you can use more of the battery's capacity.
For example, if your needs are 10kWh, then you need to determine the battery capacity DoD would play a part in the battery size you need.
Lead Acid Sizing:
10kWh x 2 (for 50% DoD) x 1.2 (inefficiency factor) = 24 kWh
Lithium Sizing:
10kWh x 1.2 (for 80% DoD) x 1.05 (inefficiency factor) = 12.6 kWh
Temperature: Hot and cold environments also affect battery performance, so it is vital to choose a battery that can operate in the temperature range of your location. Hot temperatures shorten the lifespan of the battery, partly due to the increased speed of the chemical reaction inside the battery. Cold temperatures, on the other hand, drop the internal resistance of the battery, increasing the effort to charge, and thus lowering capacity.
Are you planning on using them in an outside location where temperature control is less likely? Will they be stored in a covered location with adequate ventilation and climate control? These are a few questions to consider.
Maintenance: Some batteries require more maintenance than others. For example, flooded lead-acid batteries require regular topping up with distilled water and equalization, while lithium-ion and AGM lead-acid batteries are more maintenance-free!
Cost: The cost of the battery is an important factor to consider as well. It should not be the only deciding factor. Less expensive batteries may have a shorter lifespan or lower performance, which can end up costing more in the long run. Always look to balance cost and performance for your individual budget.
Overall, it is important to choose a battery that is appropriate for your energy needs, fits your budget, and can provide reliable performance for the lifespan of your off-grid solar power system.
At SanTan Solar, we offer a variety of choices from name brands such as Big Battery, PowerUpESS, Outback Power, Rytenergy, and Generac.
We also have a limited stock of Tesla Powerwall batteries! Contact us for a price quote and availability!
Shop all SanTan Solar Batteries HERE! Call us today for a quote or with any off-grid solar system questions! ☀️
Check out our most recent YouTube video below!
