Are you considering a solar system for your office or home as a backup? Or offset your goal is to offset your electricity usage from the utility?
Depending on the combined power consumption of the appliances you have and plan to run then a 5 kW solar system might be the right solution for you.
A 5 kW solar system is available in several configurations – with varying solar panel capacities (watts), and different battery sizes (Ah), as an off-grid and grid-tie system.
This post answers one of the frequently asked questions about a 5 kW solar system – what type of batteries you can use and how many of them you need.
Battery bank for a 5 kW Solar System
The 5 kW system is available in hybrid, off-grid, and grid-tie versions. The battery setups applicable in the off-grid and hybrid versions provided below are only an example.
You can have a solar system working reliably using different battery capacities and configurations for a battery bank.
How Many Batteries for a 5 KW Solar System?
To work out how many batteries you should use, you need to decide which appliances you’d like to keep running in case of a power outage and for how long.
This will inform how much energy you should store in the batteries (watt hours) and hence the capacity and number of batteries to use.
Therefore depending on the power requirements of the appliances, the battery setup you end up using can be different.
Using Lithium Batteries
If you choose to use the much lighter lithium batteries, you could use 1 x100Ah, 48V LiFePO4 or 2 x 50Ah, 48V LiFePO4 batteries connected in parallel.
This system can store about 4,800 Wh of power from solar panels.
Assuming your location receives between 4-5 hours of sunshine, then you can expect this system to generate an average of 20 – 25kWh of energy each day of which only about 25% will be stored in the battery bank.
Using AGM Batteries
You can also use 12pcs of 12V, 100 Ah AGM batteries to store an estimated 7,200 Wh of energy, about 36% of the daily energy produced by the solar system.
Cost of Batteries
This depends on the type of battery – battery chemistry and can vary from one manufacturer to another.
For example, at current market prices, a 50Ah, 48V LiFePo4 battery from Renogy costs about USD 1,700 while a deep cycle 100Ah, 12V AGM will set you back by only USD 270.
Multiply this cost by the number of units in your battery bank to get an estimated cost of your battery bank.
Do You Need Batteries for a 5 K W Solar System?
Depending on your design requirement, you may not need any batteries (5 kW grid-tie solar system).
Such a system is ideal for situations when you have a reliable grid supply, probably keen on generating your owner energy to save money. Because it does not have a backup storage system, it is a much cheaper system.
Another option available to you is an off-grid solar system that relies on the inverter and battery bank system to run your appliances.
This is ideal for situations when you do not have access to the grid at all and therefore need to generate your own electricity.
Lastly, there is a middle ground option, the hybrid option that has elements of both worlds – a grid-tie and battery bank. This is suitable for situations when you have a fairly reliable grid but are keen to have backup power albeit limited to run your appliances in case the grid is not available.
This is a more affordable solution compared to an off-grid solution however requires more investment than the grid-tie inverter solution.
How Long the Batteries Last
This depends on the design and the quality of manufacture of the batteries. Lithium batteries can last anywhere from 2,000 – 5,000 cycles (estimated), which works out to about 5 – 10 years of daily use compared to the much shorter lifespan of 200 – 500 cycles for AGM batteries.
Note, that all these lifespans are estimates and you should consult the battery documentation for your specific battery.
Suffice to say that Lithium batteries last considerably longer than AGM batteries and in some cases up to 8 times longer.
Ultimately how long a battery lasts depends on the design and quality of manufacture, and battery management -whether it is maintained at the recommended battery voltages or discharged within the recommended limits.
Closing Thoughts
If you plan to acquire a 5 kW solar system, you have the option of a battery-less or grid-tie solar system to one with a battery backup.
If you decide to go with one with a battery backup, size your battery bank according to the power consumption of the connected appliances and how long you expect them to run.
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