I would strongly suggest a 48V system over a 36V system. The number of batteries determine this. Should you use 2V lead acid batteries, it means that you would need 18 of them in series in a 36V system and 24 of them in series in a 48V system. Systems smaller than 36V are not advisable. Hence, we will focus on a 48V system. To determine battery size required, divide kW by system Voltage, thus 33,000/48 = 687,5 Amps. This is the total Amps (current) that the batteries need to supply in a 24hr window. BUT, lead-acid batteries cannot and must not be fully discharged. They can be discharged maximum to about 80% of their capacity. Hence, you would need bigger batteries than you think. In this case you take 687,5 times 5 = 3437 Amps. This number determines what you need. Now to determine what you have. If you have 24 2V 250Ah batteries, your total Amps will be 24 x 250 = 6000 Amps. But you need to limit it to a 20% discharge, thus 6,000 x 20% = 1,200 Amps. Compare this to the 3,437 Amps you need, and you will see that you do not have enough battery capacity. If you have 24 2V 700Ah batteries, your total Amps will be 24 x 700 = 16,800 Amps. But you need to limit it to a 20% discharge, thus 16,800 x 20% = 3,360 Amps. Compare this to the 3437 Amps you need, and you will see that you now have enough battery capacity. The batteries also need to take the knocks of start-up current requirements of fridges and pumps. If the batteries cannot supply the current needed, you will usually notice the dimming of lights in the evening for a split of a second. It can also happen if the batteries are not fully charged. These extra power needs were not calculated in, but you still need to be considered. Remember that you need as much as possible battery power during the dark hours. So, use most of your high-power appliances during daylight hours. Once Lithium battery prices come down in future, it needs to be considered as an alternative. Lastly, use good quality charge controllers. These will give you an insight into what the solar panels and batteries are doing, as can be seen in the images.

**Johan Swart.**

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