How Many Batteries for 2kW Solar System?

How Many Batteries Do You Need for a 2kW Solar System?

Knowing how many batteries you will need for your solar system can be daunting, and it is. Because there are a number of factors that must be taken into account.

Including batteries type and capacity, the voltage of the system, and the amount of backup energy you want to store.

Do you have a 2 kW solar system? And looking for the correct battery capacity? Well, the following article explains an easy way to estimate how many batteries for 2 kW solar panels.

How much energy does a 2kW solar system produce?

The energy production of a 2 kW solar system is mainly depends on the amount of sunlight that the system receives. And the amount of sunlight that the solar system itself depends on 4 basic variables, which are the location (the climate), the season and the orientation of panels and its tilt angle.

In general, the power generated by a 2kW solar panel system at a particular location can be calculated by multiplying 2 kW by the total peak sun hours per day at that location.

For example, if the solar panels receive a total of 5 hours of sunlight the energy production will be 10 kWh (= 2 kW x 5 hours). Note that the system can produce up to more than 10 kilowatt-hours per day in the summer months.

However, to correctly size your battery bank, you must do so according to the time when the panels receive the least amount of sunlight so that you can fully charge your batteries even in the winter months.

How Many Batteries 2kW Solar System Can Charge?

As stated above, on average, a 2kW solar system will generate approximately 8 kWh per day.

When calculating how many batteries for 2kW solar system, the first thing to consider is the type of batteries that you will use exactly. Will you use lead acid batteries or lithium-ion batteries, this is important because each type has what is known as the depth of discharge (DOD), a percentage of the amount of stored energy you could consume.

So, to store 8 kWh and reach it, you will need - at least - the volume of batteries with a capacity of 10 kWh of lithium-ion batteries (you only use 85% of the battery’s capacity to prolong its life), or 16 kWh of lead acid batteries (you only use half of the battery’s capacity).

Batteries come in different voltages, in our case we can use 24V or 12V batteries because they are the most practical for small PV systems.

For example, with Li-Ion batteries you will need 8 12V-100Ah batteries, or 4 12V-200Ah batteries, or 4 24V-100Ah batteries, or any combination as long as the battery bank capacity is not less than 9 kWh.

Battery Bank Capacity (in kWh) = Battery Capacity x Number of Batteries
Battery Capacity (in kWh) = Battery voltage (V) x Battery amps (Ah)
Battery types and capacity
Lead Acid Batteries
Lithium-ion Batteries
12V-100Ah12V-200Ah24V-100Ah12V-100Ah12V-200Ah 24V-100Ah
How many batteries required for 2kW solar system
14 7 7 4 4

This is the maximum number of batteries that a 2 kilowatt solar system can charge in a day. and this is the appropriate number for you if you need 8 kWh of electricity after sunset.

In general, this is not the best method for the size of your system. The number of batteries you will need is not related to the size of the solar panel system, but rather depends on how much energy you use at night.

Calculate the Number of Batteries for 2 kW Solar Using the Nightly Consumption

Find out what your energy needs are at night

First, you should know how much electricity consume each device you will use at night and for how long it will be used.

You will need to review each device and check its power consumption, you can find a sticker on the back of each device that states its wattage.

For example, we will prepare a list of examples of some home appliances:

Load (watt)Duration of use (hours)Energy consumption (kWh)
300 watt fridge121.8
1000 watt microwave11
4x 10 watt light bulbs 
80 watt TV
7
4
 0.3
 0.3
Total 3.1 kWh

Doing this step can be a bit tedious, but it is very important in correctly determining how many batteries for 2kW solar system.

Sizing The Battery Bank

If your solar system produces much more than you normally consume during the day, the exact calculations for sizing your battery system will depend on your nightly energy use and the type of battery.

Here are example battery banks for both lead acid and lithium, if you use 5 kWh at night:

Lead Acid Sizing:

5kWh x 2 (for 50% depth of discharge) = 10 kWh

Lithium-ion Sizing:

5kWh x 1.15 (for 85% depth of discharge) = 5.75 kWh

    For Lead Acid, 10 kWh is equal to:        For Lithium-ion, 5.75 kWh is equal to:     
900 amp hours at 12 volts
500 amp hours at 12 volts
450 amp hours at 12 volts
250 amp hours at 12 volts

Calculating the Number of Batteries for 2 kW Solar System Using the Total Daily Consumption

If your energy consumption at night is variable, sizing your battery bank to store at least 70% of the total energy consumed daily is a good way to ensure a sufficient amount of electricity is available during the night.

Battery Bank Capacity (in kWh) = Daily Power Consumption × 0.7

For example, based on usage of 8 kWh per day.

The solar battery for this scenario needs to store 5.6 kWh (= 8 kW x 0.7).

In this case, the formula to calculate the number of batteries needed would be:

Number of Batteries = Battery Bank Capacity / (Battery Capacity x DoD)

Number of batteries = (8kWh x 0.7) / (12V x 100Ah) x 0.50 (for lead acid battery) = 9.33 

Therefore, you would need 10 12V-100Ah lead acid batteries for your solar PV system.

Days of Autonomy

How Many Batteries for 2kW Solar System?

If your 2 kW solar system usually produces more electricity than your daily consumption, you can increase the size of your battery bank to store enough energy for times when your solar panels is not exposed to sunlight due to clouds or rain. All you have to do is multiply your daily consumption by the required number of days.

Typically, days of autonomy could be between 2 to 5 days.

In this case, the formula to calculate the number of batteries needed would be:

Number of batteries = Daily power consumption x Days of autonomy / (Battery capacity x DoD)

Conclusion

A 2kW inverter would require a minimum 24V-200Ah LiFePO4 battery. Alternatively, you can get two separate LiFePO4 batteries of 12V-100Ah that would power the system.

It is important to note that the number of batteries required for your 2 kW solar system can vary depending on your specific power needs and not on the solar size array.

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