A deep cycle battery is a special type of battery that discharge electrical energy gradually as we need it, and that can keep working up to 80% use of the charge if you can afford the Lithium-Ion battery. However, choosing the right deep cycle battery for your solar panel system can be intimidating because there are quite a few factors to consider, calculations to make, and more.
Simply put, all of the available options can make this process very difficult. Today we are here to show you how to size battery bank for solar panel based on daily power usage, days of autonomy, depth of discharge, and system voltage.
Nowadays, deep cycle batteries are often used as battery banks to store the extra energy generated by a solar panel setup.
Low cost and maintenance free deep cycle AGM lead acid batteries are ideal for applications which require constant charging and discharging, such as solar panel battery banks in most off-grid PV systems.
5 Steps To Size Deep Cycle Battery Bank
Step 1 - Determine Daily Total Power Usage
Step 2 - Determine The Days Of Autonomy
Step 3 - Determine The Depth Of Discharge
Step 4 - Determine System Voltage
Now you simply need to determine what voltage your system has. The common system voltage is 12V, 24V, and 48V.
Step 5 - Determine The Correct Size Of Battery Bank
Battery Bank (Ah) = ((daily power usage (Wh) x days of autonomy) / Depth of Discharge) / System Voltage
Battery Bank = ((200 x 5/.8)/24) = 8.9 Ah.
4 Factors Determining the Size of Battery Bank
1. Daily Power Usage
On-Grid Load Determination
Get the daily average from annual electric bill
Check power meter reading
Use a Watt meter to measure power usage
For appliances that don’t have wattage written on their product labels (See the LED TV label below) or device without product label, I use my Kuman Electricity Usage Monitor Plug Power Meter to measure their wattage. This handy Kuman watt meter can also measure voltage, ampere, and kilo-watt-hour (No more guessing needed ?).
Off-Grid Load Determination
2 Look up consumption from online specification (Very accurate, fairly tedious)
3 Calculate consumption with online load calculator (Fairly accurate, less tedious)
4 Estimate consumption from an appliance lookup table (Less accurate, not tedious ?)
Read the power label of each appliance
Look up consumption from appliance online specification
This is the recommended way for large appliances such as refrigerator that you can’t easily get to their product label at the back of it or appliances you’re considering. Most of the time the power/energy consumption will be given in kWh per year.
Calculate consumption with online load calculator
Estimate consumption from an appliance lookup table
|Waffle Maker (4 Slice)|
|Toaster (2 Slice)|
|Rice Cooker (1.8L)|
|Jacuzzi (No heater)|
|TV (42 Inch LCD)|
|TV (42 Inch Plasma)|
|TV Cable Box|
|Video Game Console|
|Ethernet Switch (8 Ports)|
|LED Monitor (22 inch)|
Daily Power Usage Worksheet
We have prepare a usage worksheet here so that you can calculate your daily power usage without pulling your hair.
2. Days of Autonomy
Days of autonomy specifically refers to the number of consecutive days where you may not be able to charge the system. A data logging anemometer combined with local weather stats should help you determine how long that battery needs to last for before it requires recharging. This is crucial to keep in mind, especially if you live somewhere that may not get a lot of consecutive sunny days.
3. Depth of Discharge
4. System Voltage
The other factor which you need to be aware of in order to properly size your battery bank is what voltage level your system has. Typically, your system will feature either 12V, 24V, or 48V.
What Battery Size Do You Need?
What is Amp-Hour (Ah)?
The formula to calculate Wh from Ah:
The formula to calculate Wh from Ah:
(Ah)*(V) = (Wh)
Solar Battery Bank Calculator
Calculating the sizing for your deep cycle bank of solar batteries does require some patience in adding things up and a bit of arithmetic, but does not require an advanced degree in science or math. Additionally, sizing calculators on various websites can be a big help.
As a quick recap, to size battery bank for solar panel, start by determining total power usage, then the days of autonomy, then the depth of discharge, and finally the total voltage of your system.
Take all of those values and then plug them into the formula which we laid out in the tutorial above. This will tell you the size of the battery you will need for your solar PV system.
Something that can’t be stressed enough is that you always need to keep safety in mind. Always follow all safety guidelines for working with solar and electrical systems.
Do some research first and be sure to consult a pro if needed. You don’t want to end up damaging your system or causing serious injury because you don’t know what you’re doing. The bottom line is that if you are uncomfortable or confused, it’s probably best to consult an expert.