At AW Electrics, a question we are often asked is, “What size solar battery do I need?” Choosing a solar battery is a big decision, and it is important to consider several factors before making a purchase.
To help inform your decision, AW Electrics have produced the following step-by-step guide to assist you to select the right solar battery for your needs.
To determine the appropriate size of a solar battery, you should consider the following 3 main factors:
Work out your daily energy consumption (in kilowatt-hours, kWh) by adding up the energy usage of all your appliances and devices.
You can calculate your electricity usage by using your smart meter. Alternatively, you can check your electricity bill for a monthly consumption figure and divide it by the number of days in the billing period to get an average daily consumption.
This will help you to understand what battery capacity you will need. For example, if you use 8 kWh a day, you will require a minimum battery capacity of 8 kW to sustain your energy needs for one day.
Autonomy days refer to the number of days a solar power system can operate without any input from the sun or other external energy source.
In other words, it is the number of days the system can continue to provide power using the energy stored in its batteries, even if there is no sunlight to recharge the batteries.
The autonomy days of a solar power system depend on several factors, such as the capacity of the batteries, and the amount of energy consumed daily.
The importance of autonomy days is particularly relevant in off-grid solar systems where there is no connection to the grid.
In these systems, the batteries serve as the primary source of energy, and a longer autonomy period ensures that the system can continue to operate during extended periods of low sunlight or adverse weather conditions.
When you are considering what size battery to opt for, it is important to factor in how many days of autonomy you want.
DoD is the term used to describe the percentage of a battery’s capacity that can be used before recharging is required.
It is calculated by dividing the amount of energy taken out of the battery by its total capacity.
The higher the DoD percentage, the more the battery has been discharged.
For instance, consider a battery with a total capacity of 100 kWh. If 40 kWh of energy has been used from this battery, the DoD would be:
DoD = (Energy Used / Total Capacity) x 100 DoD = (40 kWh / 100 kWh) x 100 = 40%
In this example, the DoD is 40%, indicating that 40% of the battery’s capacity has been used.
Lithium-ion batteries have a higher DoD than lead-acid batteries, meaning they can discharge more before needing to be recharged. However, a deeper DoD can also reduce the battery’s overall lifespan, so it’s important to strike a balance between maximizing energy use and preserving battery life.
So, to calculate the required battery size for your personal use, you can use the following formula:
Battery Size (kWh) = (Daily Energy Consumption x Autonomy Days) / DoD
For example, if your daily energy consumption is 10 kWh, you want 3 days of autonomy, and the battery has a DoD of 90%, the required battery size would be:
Battery Size = (10 kWh x 3) / 0.9 = 33.33 kWh.
Keep in mind that this is a simplified calculation and there may be other factors to consider, such as system efficiency, temperature, and battery degradation over time.
It’s always a good idea to consult with a solar professional to help you choose the right solar battery for your specific needs.
We specialise in solar panel maintenance, repairs, and new installations, and are happy to discuss your solar panel battery needs and options.