Why do we calculate daily energy consumption?
Daily energy consumption is an important figure when DIY an off-grid solar energy system.
It directly determines the battery capacity and the number of solar panels, as well as the cost of the entire off-grid power system.
Calculation of battery pack capacity
Your average daily energy consumption is 3 kWh and you need to design a 24V off-grid system and want it to be able to independently support 2 days of household energy consumption in case of power outages.
Then battery capacity = (3kWh x 2)/24V = 250Ah
That is, you can use 8 LiFePO4 battery cells of 3.2V 230Ah and BMS to form a 24V 230Ah battery pack.
Or you can use 8 3.2V 280Ah LiFePO4 battery cells to form a 24V 280Ah battery pack.
Calculation of the number of solar panels
Let’s take a 24V 280Ah battery pack as an example to see how many solar panels you need.
Suppose you live in the California area and the average peak sun hour is 5 hours per day.
Energy of the battery pack = 24V x 280Ah = 6.72kWh
Total energy of solar panel = 6.72kWh / 5 = 1.34kWh
If you plan to use solar panels with a power rating of 200W, then the number needed is
1.34kWh / 0.2kWh = 6.7
So you need at least 7 solar panels.
* If you don’t know the Peak Sun Hour for your location please see here.
Once you confirm the capacity of the battery system and the number of solar panels, You can roughly estimate their costs.
The price of 8 x 3.2V 280Ah LiFePO4 batteries with shipping is $1462 (slow shipping) ~ $1842 (fast shipping).
An 8S 24V 100Ah BMS is $80.
200W 24V solar panel is about $200, the price of 7 pieces is 7 x $200 = $1400.
So in this off-grid solar energy system, the price of the battery and solar panel will be $1462 + $80 + $1400 = $2942(slow shipping)
Or $1942 + $80 + $1400 = $3422(fast shipping)
How to calculate daily energy consumption
Daily energy consumption is usually measured in “kWh”. And the power of household appliance is usually rated in “W”.
The energy consumption formula is
Energy consumption (kWh) = rated power (W) x usage time (h)/1000
There are 5 daily used appliances, their power consumption and usage time are as follows.
- Appliance 1, 300W, 2 hours
- Appliance 2, 20W, 4 hours
- Appliance 3, 1000W, 15 minutes
- Appliance 4, 10W, 1 hour
- Appliance 5, 100W, 30 minutes
Then daily energy consumption is
300W x 2h/1000 + 20W x 4h/1000 + 1000W x 0.25/1000 + 10W x 1h/1000 + 100W x 0.5h/1000 = 0.99kWh
Alternatively, you can use our prepared daily energy consumption calculator.
Energie Panda Daily Energy Consumption Calculator
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