Sizing Your Solar System

Categories: Batteries, Inverters, Off-Grid, Solar Power

Finding the right solar power system for you.

A few main things to determine the right solar power system:

  1. Determine is your Peak KW Power consumption at any given time
  2. Work out the Total KW/Hrs in a 24 Hr period?
  3. What type of system do you would prefer?
  4. Tell us in how many days you want to recharge your Battery bank?


There are two ways you can get your required consumption rating:

  1. Use your utility bill over a 12 month period and find an average daily consumption
  2. Follow the steps below to determine appliances individually


Establish the peak power of your consumption

On all electrical appliances, there is a rating plate that stipulates the power consumption of the appliance itself.

Essentially you want to work with watts, so you may need to convert Volts or Amps into watts. Use this formula to help you:

(Watts = Volts x Amps) / (Volts = Watts / Amps) / (Amps = Watts / Volts).

Once you have the total amount of watts used at any one point, which will be the size of the inverter you would require to provide you with enough power at any one point.

Alternatively, you can use this sheet to work it out by placing how many appliances


What is the total Kilowatt hours you intend to run these appliances in 24hrs?

Not all appliances need to run constantly. For instance, your lights only get used at night for a few hours, or your fridge only turns on when it needs to regulate the temperature.

If you multiply the total watts on each appliance by the time you will get your kilowatt hours that would need to be provided within a 24hr period.

I.e. Fridge is 200w and runs for 12hrs per day = 2.4kwh

You would need to do this for all appliances and add them up in total at the end.

Again you can use this formulated sheet to record your findings.


Establishing the type of solar system you want

  1. Do you want to work directly off the solar array and only use what is provided with no storage?
  2. Do you want to use only solar and not be connected to the grid?
  3. Are you wanting to produce a portion of what you use currently and the rest grid?
  4. Do you want to use a generator for just in case there is no sunlight for a few days?

There are a few options to go, however, we will be working with a hybrid storage system in this example for this seems to be the most popular for households today.

What is a hybrid system? Well, to keep it simple, basically it means that you use both grid and battery storage. Any power that is stored in the batteries is used first thereafter switches over to the utility grid for the rest until there is more energy to be used in the batteries.


How many days storage back up do you require?

The most expensive part of any solar power system is the batteries. Because you can only use a maximum of 50% of your battery per cycle to ensure you don’t damage them and they last longer, you generally need a minimum of 2 x energy requirement in storage space.

For example, if you need 5kwhrs per day, and you want to be able to store 1-day backup in case there may be no sunlight for 24 hrs, you would need:

5kwh x 2 (50% depletion) = 10 kwh x 2 (extra day) = 20 kwh

20 kw hours in battery terms for a 12v battery that is a 250amph would be:

(W = V x A)  = 6.666 batteries required


Finalizing the requirements

Now that you have the totals, you know what size solar power system you need:

Max peak power: i.e. 2000w

Your Daily usage: i.e. 12kwh

Battery storage: i.e. 1 day back up


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