Epileptic power supply has become a problem associated with most third world countries. This condition reduces productivity generally and in most cases increases the cost of production. Most people/institutions have sought to install backup power system in their homes/offices to help mitigate the adverse effect of this power unreliability but in turn, they are mostly faced with problems of deciding what they need as quality information are not readily available in the public domain. This information gap is what I intend to solve by this series.

Sizing is a very important part of energy solution reliability. An oversized system leads to having idle resources in the system. This increases cost. It is very important to size the system such that you don’t have too much wastages. In determining system size, the first thing to do is to calculate the load you intend to power with the system. This is done by adding up the wattage of all appliances in the house. For example, in a house that has 1 unit of 1.5Hp AC, 10 Light bulbs of 10watt each, 1 Refrigerator of 200watt, a Television set of 300watts. The total load in this case is 1,346watts, this implies that any inverter you choose must be able to output 1346watts at a go. It is advisable to leave margins for expansion. In the case above, I will recommend a 2KVA inverter, this can output a total of 1600watts. (Considering a power factor of 0.8, 2000 X 0.8 =1600) So even at peak load, it can serve the house. It is worth noting that a time when all the loads will be on at same time might never happen. At best you might be using 80% of your appliances at peak periods. Notwithstanding, it is always better to assume peak load in choosing inverters. Inverters do not generate power, it basically converts electrical power from DC to AC so the power you are using is what is available within the system. There are different types of inverters, checking out their technical specifications and other components of your energy system you can determine which of the inverter types that will be suitable for your need. Check out my detailed write up on inverters in this series to gain an insight into what you need to check out for in deciding on a particular inverter based on what you want to achieve.

The next thing to do is to choose the number of battery(ies) you want to use. It is worth knowing that battery doesn’t generate electric power. All it does is to store and give back at the time it is called into action. So basically, the power you get out of a battery depends on what you stored on it and this largely depends on the battery’s capacity and the charging capacity of the inverter as well. Assuming you use 2 units of 200AH,12V Batteries, at full charge the total power available for you will be 2x200x12 =4800Watts. If the DOD of the battery is 80%, then you have a total usable power of 3840Watts. Assuming you are consuming at an average of 384Watts per hour. At full charge, you will have 10hours that you can run on the battery. Things you should know about batteries before choosing includes the cycle, DOD, C rating, Current and Voltage ratings, Temperature rating and type of cell. Check out for the write up on batteries under this series, it will help you understand in full.

Power for charging batteries can be gotten through mains (I refer to power from both Generator set and any power company as mains) or through renewable sources. For this I am looking at solar panels. In determining the number of panels you will install, you have to check out your energy needs, storage capacity and irradiation level in the environment of interest. Generally, a solar PV panel rated at 300Watts should ideally supply 300Watts per hour. So if you have an energy need of 1200Watts You should be needing 4 of it. Check out details explanation of SOLAR PV CELLS in our series, this will enable you choose the type of panel that will best fit your environment and the implication on sizing.

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