Clean Energy

Selecting Right Solar Backup System for Your Home/Office

Sizing and designing Solar Backup System is simple, as simple as choosing right laptop, right motor bike for you.To help you understand and size right Solar Backup System,I have tried my best simplifying it, avoiding tech jargon with thumb rules and plain illustrations. If you really think that “technical things just go above my  head ”, then you will love to learn this.
Step 1:  List out what appliances you want to use with solar backup system
First, you need to know your daily energy demand, Like average Nepalese family, I also have following appliances in regular use.
  •    CFL lights
  •   21″TV with LED display
  •   Laptops
  •  Internet Router
  •   Refrigerator
  •  Water Pump


Step 2: Find out what is the wattage rating of each appliances.
Different appliances have different power consumption.To find out exact watt rating of appliances, refer to the user manual /catalog of appliances or  search in internet to know precisely. Some of the appliances have inconsistent power consumption characteristics, for example, water pump consume twice the rated power in first few seconds and runs uniform rest of the time. Whereas CFLs consume more power as they are heated.But we need take their uniform power consumption rating to size solar backup system.
Step 3: Note down how long you want to use above appliances.
 The size of Solar Backup System (SBS) equally depends on rated watt of appliances and time of use. The size of SBS increases with the increment on time of use while investment increases with the size of backup systems. So, we should try to be more precise on time of use and note it down on basis of  past experiences.
Step 4:  Find out daily energy consumption of individual appliances by multiplying total wattage with time of use
Step 5: Sum up total watt hour to find out your daily energy demand
The total watt-hour shown in the table is the total energy consumption daily. We will be able to find out  the size of solar panel, battery backup and inverter with the above figure, by simply using some thumb rules derived from mathematical calculations.
Sizing Solar Panel
 Divide total watt- hour with 3. It is thumb rule for sizing solar panel by considering that you get 5 hours of sunshine daily in average.
Sizing Battery Backup
The size of battery backup needs to be equal to the size of Panel. This thumb rule considers two days autonomy for battery backup which means you can run all your appliances in normal condition also if there’s no sun for two days. However, there’s a trend to keep size of battery backup a bit high while reducing size of panel, especially in case of solar – grid hybrid system to reduce upfront investment on solar panel.
Sizing Inverter


It is first necessary to find out total wattage use at a time i.e. sum of individual watt of all appliances times quantity of appliances. Then select inverter which has power rating double the total wattage (Not watt-hour). Average inverters found in Nepalese and Indian market have only 75 % efficiency. If you are going for standalone system then I strongly suggest you to get inverters with high efficiency like Sunny boy, Outback etc which are costly in the beginning but perform trouble free. Using less efficiency inverters in standalone system will result heavy loss of power due to inverter and the total system runs out of power.

Prakash Acharya is an entrepreneur from Nepal, passionately working to substitute fossil fuels with clean energy technologies. He co-founds Mukti Energy, a solar energy company providing a one-stop solution in the sector. He is also a big believer in change so he advocates and works for creating impact in society. His topics of interest spans from sustainability, zero energy, poverty reduction, sociology to smart city. He graduated from Institute of Engineering, Thapathali Campus on Industrial engineering. He is also a former assistant lecturer in IOE, Thapathali . Prakash is a fellow for Social Entrepreneurship Outreach Program 2014, Social Entrepreneurship Forum Sweden.

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