Step 1 - What is the required load?
First, we need to work out what the total energy requirements are over a 24-hour period in watt-hours (Wh).
Watt-hours = Watts (power consumption of the appliance) x Time (how long each appliance will run for at its rated capacity).
Example:
4 x 14W Energy Saving Lights on for 6 hours/day = (4 x 14W) x 6hrs = 336Wh
1 x 200W TV on for 3 hours/day = 200 x 3 = 600Wh
1 x 2000W Kettle on for 1/2 hour/day = 0.5 x 2000 = 1000Wh
1 x 200W Fridge/Freezer on for 24 hours/day = 4800Wh
Total Energy = 6736Wh
Step 2 - Take into account efficiency losses
A significant amount of power is lost during the conversion processes, which takes place from DC to AC power. Please note, the below is an approximation for this exercise.
Solar Charger = 98%
Inverter = 90%
Lithium Battery = 90%
Total energy required including system losses = 6736Wh ÷ (98% x 90% x 90) = 8526Wh
Step 3 - What us the required PV array size?
Calculate the minimum size PV array needed to power 8526Wh from the available hours of sunlight in a day for your location (the UK average is 6 hours).
Total solar array in Wp required = 8526Wh ÷ 6hrs = 1421Wp
Choose your panel/size and divide into the required total Wp = 1421Wp ÷ 300W = 4.7
The required number of panels is therefore, at least 5 x 300W
Step 4 - Sizing the battery bank
To size a battery bank, we first need to calculate the total required capacity (Ah).
Total energy required for a 24-hour period is – 8526Wh
Choose the battery chemistry and DOD (Depth of Discharge), for this example we are using Lithium
Choose the system voltage, for this example we are using a 48VDC system
Required energy x DOD of the battery ÷ System voltage = 8526Wh x 80% DOD ÷ 48V = 222Ah
A battery bank of at least 222Ah @ 48V would be required providing 24-hours autonomy.
Step 5 - Sizing the inverter
Any inverter will need to be big enough to cover the peak AC load required (the sum of all the appliances running together). It is important to consider the efficiency of the inverter in order to calculate this accurately.
Peak load = 336W + 200W + 2000W + 200W = 2736W x 90% Efficiency = 3040W
An inverter with a power rating of at least 3kW is required.
N.B. The hours of sunlight in the UK vary dramatically from season to season so a back-up source of generation or generator would be needed for the winter months.