How To Size Your Solar Power System

Before decide how big your solar system is, 3 things need to be considered:

1.How much total watts of your appliances
2.How big size is your battery bank
3.How much energy of the solar panels can be generated to your battery bank

How much total watts of your appliances

First you need to list out all the appliances that you wish to use over a period of time or no. hours per day.

For Example: Use 40w fluorescent lights for 4 hours, 40w x 4 hrs = 160WH from the battery.
You may repeat the calculation for all your other appliances, then add the total consumption and you will know how big size of your battery bank needed.

To know more about appliances in wattage, you can check the Appliance -Wattage listings here

To find out the approximate amperage of electrical devices, you can use the Ohms Law formula:

Amps= Watts divided by Volts.
For example: A 1,800watt appliance at 240v would be 7.5 amps
To calculate your daily power usage, you can eventually based on your last 12 monthly electrical bills and calculate your average kilowatt hour (kWh) usage per month.

For examples : Monthly electrical bill consumption 1000kWh :

1000 kWh divided 30days = 33.33kWh per day

1 – Calculate Daily Power Used:

To do this, get your last 12 monthly power bills and calculate your average kilowatt hour (kWh) usage per month. The reason we use 12 is because our power consumption fluctuates with the seasons. But if you do not have all your power bills, then simply use last month’s one.

Then divide your monthly usage by 30 (the average number of days in a month, to get your daily power used.

– So for example: If you have a monthly power consumption of 800 kWh, then your daily amount is 800/30= 26.7 kWh per day.
– Now if you want to only halve your power bill then you need to produce 26.7 / 2 = 13.4 kWh of solar panel watt power per day.

2 – Calculate Total Solar Panel Watt Needs:

To do this, you first need to determine how many usable hours of sunlight your area receives per day. This is where a solar insolation map comes in handy – you can view one from our original article on our website.

Once you know your daily sunlight hours, go back to your daily kilowatt hours needed and divide it by the daily sunlight hours, then multiply it by a factor of 1.25 (takes into account energy losses from the solar panel watt wiring, battery , and inverter)

– Continuing from our example 1 – Calculate Daily Power Used:

To do this, get your last 12 monthly power bills and calculate your average kilowatt hour (kWh) usage per month. The reason we use 12 is because our power consumption fluctuates with the seasons. But if you do not have all your power bills, then simply use last month’s one.

Then divide your monthly usage by 30 (the average number of days in a month, to get your daily power used.

– So for example: If you have a monthly power consumption of 800 kWh, then your daily amount is 800/30= 26.7 kWh per day.
– Now if you want to only halve your power bill then you need to produce 26.7 / 2 = 13.4 kWh of solar panel watt power per day.

Our solar panel watt needs equal:
13.4 kWh / 5.5hrs x 1.25 = 3.045 kW or 3045 Watts per day.

This means we need solar panels with the capacity to produce at least 3045 Watts of power.

3 – Calculate Solar Panel Watt Costs:

This step will help you work out the cost of the solar panels needed to make 3045 Watts of power. At the moment the highest average cost for solar panels in the US is \$4.85 per Watt.
– In our example: It will cost us at the most 3045 x 4.85 = \$14,768 to install solar panels to halve our power bill. And that’s before wiring, charge controllers, batteries, inverters, and electrician costs.