Home Find out how many batteries you need for an off-grid solar self-sufficient home

Find out how many batteries you need for an off-grid solar self-sufficient home

12 April 2024 11 gies: 54
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Find out how many batteries you need for an off-grid solar self-sufficient home
Photo: Disclosure/MJ

Are you thinking about cutting ties with utilities and generating your own energy? The off-grid solar energy system is the ideal solution for those seeking energy independence. But the question arises: how many batteries are needed to sustain this autonomy?

Have you ever thought about no longer depending on electricity companies and having the ability to generate your own energy at home? This is possible with an off-grid solar energy system, which allows you to produce and store your own energy, without being connected to the public electricity grid. This option is becoming increasingly popular among those who want greater energy independence and a more ecological option.

But how does an off-grid system work? Basically, it captures the sun's energy through solar panels, transforms that energy so it can be used in your home, and stores the surplus in batteries for use when the sun isn't shining. The big question that arises, then, is: how many batteries are needed to keep my home running without interruptions?

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Understanding off-grid solar energy system

First, it is important to understand the basic components of an off-grid solar energy system. Solar panels are responsible for capturing sunlight and converting it into electricity. The inverter transforms this direct current electricity (generated by the panels) into alternating current, which is the type of electricity used in your home. Batteries store unused energy immediately, allowing you to use it at night or on cloudy days.

Determining energy consumption

First of all, you need to know how much energy your home consumes. This consumption is measured in kilowatt-hours (kWh). For example, if you determine that your home uses 100 kWh per month, that will be the starting point for calculating how many batteries your system will need.

Once the monthly consumption is known, the next step is to adjust this value to compensate for system inefficiencies. Inverters and batteries do not operate at 100% efficiency — generally, they operate between 80% and 90%. Therefore, if your consumption is 100 kWh, in practice, you will need to generate more than that to cover system losses.

By dividing the adjusted monthly consumption by the number of days in the month, you obtain the required daily consumption. In our example, this would be about 4,63 kWh per day, which would be 138 kWh (a little extra to cover the loss). System runtime refers to the number of days you want your solar power system to provide energy without needing to be recharged. The greater the desired autonomy, the more batteries will be needed.

Choosing and Sizing Batteries

Battery capacity is a crucial point for better use of solar energy. Lead acid batteries are common because of their cost-effectiveness and reliability. They are evaluated on their ability to amp hours (Ah), which tells us how much charge they can store. Knowing the daily energy required, it is calculated how much storage capacity is needed to cover your daily use with a safety margin, considering the recommended discharge depth of 30% — that is, we will only use 30% of the battery's total capacity to prolong its useful life.

After calculating the total capacity required, you must configure your batteries in series and parallel to achieve the required voltage and capacity. For example, if each battery has 12 volts and you need 24 volts, two batteries will be connected in series. If you need more capacity, add more batteries in parallel.

How to calculate the number of batteries needed

Using the example of a house with a daily consumption of 4,63 kWh, we will calculate the number of batteries needed for a autonomy of one day, considering a discharge depth of 30% (this means that we only use 30% of the total battery capacity). battery to extend its useful life).

First, we calculate the total capacity needed to store enough energy for one day. If we are only planning to use 30% of the battery's capacity, we need a total capacity that is at least three times greater than our daily consumption to compensate for this. That is, 4,63 kWh / 30% = 15,43 kWh.

To convert the required capacity from kWh to amp-hours, we divide it by the number of volts in the system. Assuming a 24 volt system, we have 15,43 kWh * 1000 (to convert kWh to Wh) / 24 V = 643 Ah.

If we use a lead acid battery with a capacity of 220 Ah, we need to calculate how many of these batteries are needed. To do this, we divide the total capacity required by the capacity of a single battery: 643 Ah / 220 Ah ≈ 3 batteries.

So with 220 Ah 12 volt batteries you will need 3 sets of 2 batteries connected in series (totaling 6 batteries) to satisfy the needs daily energy consumption of the house with an autonomy of one day. The price varies a lot from place to place and also depends on the type of battery used, but that's a conversation for another day.

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