When you first start looking at solar panels, all the available information might seem overwhelming but figuring out what solar panels you need is actually a simple process.
As a general rule, divide your home’s hourly energy requirement in watt-hours by the solar panel’s wattage to calculate how many solar panels you will need.
The most important consideration that influences every component you will need for a solar system is knowing how much power you will need for the appliances connected to the system.
List out every appliance
The first step in figuring out what size solar system you will need is to list all the appliances that will connect to your solar system.
You need to list all of them , even your cellphone and laptop charger.
Example list of electric household appliances
- Small electric stove
- Extendable convection oven
- Microwave
- Kettle
- Refrigerator
- 4 x LED Lights
- Fan
- Geyser
- Cellphone charger
- Laptop charger
Now that you have the list of appliances that will connect to your solar system, we will add more information to that list in the next step.
Find the power consumption rating
The power consumption label on each device is a label that can be printed on the device itself, or it can be a label that is stuck on the device or the device charger.
You are looking for the output rating that can be either in watts or volts and amps or milliamps.
On the power consumption label of the convection oven, you can see the output as rated at 1300W. You need to note down that number for each device.
If the output on the label is in volts and amps you can use the following equation:
Watts = volts x amps
If the output on the label is in milliamps and volts you can use the following equation;
Watts = (milliamps x volts)/1000
Using our list of appliances, we can then add the power consumption of each device in watts.
| Small electric stove | 2200 watt |
| Extendable convection oven | 1300 watt |
| Microwave | 1200 watt |
| Kettle | 1200 watt |
| 4 x LED Lights | 20 watt |
| Fan | 15 watt |
| Geyser | 2200 watt |
| Cellphone Charger | 0.8 watt |
| Laptop charger | 0.8 watt |
| TOTAL | 8136.6 watt |
The total watts of all the appliances listed above is 8136.6, which is a high number that will need a big solar system with many solar panels and the resulting high cost. There are ways to bring this number down by a significant amount, and one solution is to eliminate unnecessary appliances or switch to using gas for some appliances.
By switching to a gas geyser as well as gas stove as well as using a kettle on the gas stove this number can be reduced by 5600w, thus giving us a lower total of :
8136.6watt – 5600w = 2536.5watt
By reducing this number, you can reduce your total power requirement and the number of solar panels you will need.
How long will you use each device?
The next step is to figure out how long you will use each device per day and note that figure down. If you use your cellphone charger for 2 hours per day, you write down 2 hours. If you use your microwave for 30 minutes per day, you write down 0.5 hours.
Go down your list of appliances and try to be as accurate as possible with the duration of use of each appliance. After this is finished, we can move on to the next step.
Calculate the total watt-hours
| APPLIANCE | WATTAGE | HOURS | WATT-HOURS |
| Extendable convection oven | 1300 | 0.5 | 650 |
| Microwave | 1200 | 0.2 | 240 |
| 4 x Led Lights | 20 | 6 | 120 |
| Fan | 15 | 3 | 45 |
| Cellphone charger | 0.8 | 3 | 2.4 |
| Laptop charger | 0.8 | 3 | 2.4 |
| TOTAL | 1059.8 |
The total watt-hours required is 1059.8, and now we have a fairly accurate estimate of the amount of power we will need from our solar system.
6 x 200 Watt panels will give you a total of 1200 watts which will be sufficient for the power needs of the appliances in our example.
Battery bank sizing
When it comes to battery bank sizing for your solar system it depends on the following factors;
- Total watt-hours per day required.
- Amount of days you want to have storage for the battery bank (without sun)
- The lowest temperature that the batteries will be exposed to
In our earlier example, we have shown the fairly simple process of calculating the watt-hours required to power all the appliances in your home.
The next step is the number of days you will want to have power from the battery bank without the sun.
2 Days will be on the lower end of the spectrum, with 7 days being the longest duration; one can have power from a modestly sized battery bank while keeping costs in mind.
The last step in battery bank sizing is keeping in mind the lowest temperature that the batteries will be exposed to, as too low temperatures ( >20 degrees) will affect the performance of the batteries.
Another factor that should keep in mind is that most batteries can not be discharged more than 50% without damaging the battery. With newer technology like lithium-ion batteries, which can achieve a discharge rate of 80%, lithium-ion batteries come at a premium price compared to normal solar batteries.
Battery size is measured in amp-hours, and as a rule of thumb, 1000 – 1500 amp hours of batteries will be sufficient for the appliances listed above with about 2 days of storage.
Charge controller sizing
Your charge controller is the link between your solar panels and your batteries, and the first step in sizing the charge controller is to calculate the average amount of hours that your solar panels will have sun. Most areas have an average of between 4 to 6 hours of full sun per day.
The next step will be to calculate the amount of current (amps) that your charge controller will have to be able to handle coming from your solar panels. In the above example, we have 1200 watt of solar panels, and if you have a 24-volt system, the calculation is the following:
1200 watt / 24 volt = 50 Amp
Thus, your charge controller will have to be able to handle 50 amps of current flowing between the solar panels and the batteries.
