Autonomy, reliability and price...
There are still a few years, we frequently saw solar batteries banks for a week of autonomy in domestic installations. Today, the ay materials cost and the demand explosion has multiplied several times the price, often turning full autonomy in a luxury out of reach.
A solar battery is by far the most fragile component and sizing error or connection can quickly become fatal. We must therefore find the best compromise between the level of maintenance, the life (number of cycles) and the price of the battery we choose.
Maintenance, obligatory ?
The first criterion is by far the level of service that we can provide on site, it is essential to have a person responsible for the maintenance and monitoring of the entire system and batteries in particular. This person must have a minimum of electrical skills or should be formed at the time of installation.
As an installer, we saw all kinds of errors, some benign, some fatal... As put mineral water in batteries (certain death), use solar batteries for other purposes such as vehicle start (dead + or - slow), amend the installation schematic, not to complete the level electrolyte (quick death)...
So if you're not there and connot verify yourself the maintenance, or do not have a person competent enough, we advise you to use maintenance free solar batteries or AGM batteries or gel batteries that not require the addition of distilled water.
Wich batteries to choose ?
For very small applications, simple lighting kind, you can use car batteries, they will last less time but are much cheaper than solar batteries, so it is difficult to tell the difference. Nevertheless take good quality batteries. Knowing that the best is the enemy of the good buy initially the battery you can afford.
For capacities ranging from 100Ah-12V to 800Ah-48V, it is possible to work with 12V batteries. The rule is not to exceed 4 batteries in parallel. Learn how to connect the batteries by clicking on this link ! (building)
So for banks which are more than 800Ah-48V, the batteries must pass elements 6V or 2V industrial type. These are by far the batteries last longer but they have the disadvantage of taking up much space, to be very heavy and cost more.
However, if you are considering a consistent system with skilled personnel for maintenance, these batteries usually last very long because they have a high number of cycles.
The battery sizing comes after the consumption sizing.
How to size your batteries ?
Once your power consumption made, you choose how many days you want to reserve (autonomy) in your batteries. In Madagascar and Africa in general, the rate of sunshine is such that there is no need to have many days of autonomu, usually one or two is enough. Depending on the energy that you want to store then you can choose the type of battery that best suits your needs.
Example : Daily consumption = 1 200Wh x 2 autonomy days = 2 400Wh that you need to store.
Batteries store amps, we must transform watts in amps by dividing the power (watts) by the voltage (volts). According to the famous formula
P = U * I so I = P / U
It is 2400/12 (12 is an example of tension) = 200Ah
When you have got it, you must apply a loss coefficient due to the chemical transformation of electricity, between 30 and 20% depending on the quality of batteries considered
200 Ah + 20% = 240 Ah
When you have got this figure, you must add a maximum discharge rate, because uou cannot discharge a battery to 100%. Typically a value between 30 and 40% of the energy does not harm too much the battery's life.
X x 30 / 100 = 240 so 240 / 30 x 100 = 800 Ah
To store 2400Wh, 800Ah-12V is needed. You can obtain it by using four 200Ah-12V batteries in parallel. The ones who have problems with serial and parallel lift a finger !... I see... Little reminder...)
How to wire your batteries ?
The parallel results is adding the amperage by connecting + to + and - to -.
Two 100Ah-12V batteries in parallel give 200Ah-12V.
The series has the effect of adding the voltages between them, two 100Ah-12V batteries in series will give 100Ah-24V.
Increase the voltage by putting batteries in series has the advantage to reduce the amperage and thus the connecting cables and components (fuses, regulators, ...).
But a 12V system has the advantage of being simple and to be able to connect directly to 12 volts applications (lighting, radio, TVs, solar fridges,...)