How big should your solar system be?
How big should your solar system be?

How big should your solar system be?

The first step in building a solar power system is determining the size of the solar power system. We will help you answer questions such as:

– How big should the solar PV capacity be?

– What size solar panels should you buy?

– How big should the inverter/battery be?

Not sizing your solar system correctly can cause you to not install the right type of solar system.

The components of a solar photovoltaic system

To size a solar PV system, we need to understand the different components of a solar PV system.

The different components of a solar photovoltaic system are:

– photovoltaic solar module

– Solar inverters

– Charge controller

– Battery

photovoltaic solar modules (solar modules)

Solar panels contain solar cells that convert incident sunlight into direct current (DC). To get the desired voltage and current, group the modules in a larger row (photovoltaic array). Connect the solar panel of the photovoltaic modules (Learn how to connect series vs parallel here) to generate the desired voltage or current.

Solar charge controller

It controls the output voltage and current from the solar panels to the battery. Helps prevent overcharging and over-discharging.

Solar inverters

Solar inverters convert the direct current output of solar modules into usable alternating current (AC).

Solar inverters


They store the energy generated by the solar modules in the form of direct current (DC).


These are the devices that use the electricity generated by the photovoltaic system or electricity from the grid.

Energetic efficiency

Before doing the solar design, you should think about how you can make the system more efficient. Increasing efficiency by implementing energy efficiency measures. This reduces the solar energy output of the photovoltaic system. Some of the measures to increase the efficiency of the system are: use of efficient equipment and, where possible, use of natural resources such as sunlight, wind, etc. This reduces dependence on fossil fuels. It also reduces energy costs. At this time, it is important to check your energy consumption and reduce your energy needs as much as possible. This is true for any system, but is especially important for home and smelter systems, as the cost savings can be substantial. First, identify large and/or variable consumers (such as water pumps, outdoor lighting, electric stoves, AC refrigerators, washing machines, etc.) and try to turn them off or consider alternatives such as propane or DC models . The initial cost of DC devices is usually higher than AC devices, but you avoid the energy losses in converting DC to AC, and DC devices are usually more efficient and last longer. Replace light bulbs with fluorescent bulbs whenever possible. Fluorescent lamps provide the same lighting with less power. If you cannot do without a large consumer, you should only use it during the main hours of the sun or only in the summer.

Solar photovoltaic systems design

How big is the roof area, facade or outdoor area?

Most houses have roofs on which solar panels can be attached. However, if your roof has windows, dormers, chimneys or a vertical vent, it could reduce the space for a solar system.

The bearing capacity of the roof

Make sure your roof can support the weight of the chosen system. The weight of a single module varies from brand to brand, but the standard 60-cell solar panels used in most home systems and smaller weigh around 18kg-20kg. Most houses have roofs that can easily support this weight. An installer will determine this as part of the initial inspection and check if work is needed to strengthen the roof.


The components provide the connections and standard safety features required for each electrical system. These include: generator junction boxes, appropriately sized cables, fuses, circuit breakers, switches and meters.

Solar module load

Determine the average power consumption requirement. Then calculate the total hourly power per day. For this purpose, average watt hours consumed by the various devices per day are measured. Then calculate the total power hours per day that will be provided by the solar modules. Multiply the total hourly power per day by 1.3 (energy lost in the system). In addition, there is a solar calculator which can help you estimate how many portable solar panels for your home you need based on the power and duration of each electrical appliance. This results in the total power to be supplied by the solar panels. Depending on the size of the photovoltaic modules, a different amount of energy is generated. Therefore, create a list of the devices and/or consumers you want to operate with your PV system. Determine how much energy each device consumes during operation. Most devices have a label on the back that indicates the power. Other sources of information are data sheets, local equipment dealers and product manufacturers, or internet information about devices.

AC and DC loads

These are the devices (such as lamps or radios) and components (such as water pumps and microwave amplifiers) that consume the electricity generated by your PV system.

Solar photovoltaic module

In the previous step, we calculated the total hours of power that the solar modules must deliver per day. Now calculate the average daily maximum hours of sunshine at your location. Divide the total power that will be provided by the PV system at the peak hours of the day. This gives the approximate system size in KWh. Divide this value by the efficiency of the solar modules to get the power output of the solar modules. To calculate the number of modules needed: Divide the total watt-hours to be produced by the rated power of the PV modules. This results in the number of photovoltaic modules required.

Installation of solar modules

The modules are connected in series and/or parallel to generate the required voltage and current values ​​for your needs. The system is usually mounted on a metal structure and oriented towards the sun. There are many brands of solar panels, and each brand has slightly different sizes. Some brands of solar panels have a higher capacity and therefore require a smaller roof area. A solar panel consists of a series of small photovoltaic (PV) cells that are connected together. Most systems use solar panels that contain 60 of these cells. A complete system (also called an array) consists of a series of solar panels that are usually placed next to each other.

Solar inverters

The solar inverter converts the DC power of the solar modules or battery into usable AC power. Therefore, the sizing of the solar inverter is important for the conversion to take place correctly. The power of the inverter is given in watts. The power of the inverter must be equal to or greater than the power of the inverter solar powered generator system. For devices such as motors, the size of the inverter should be at least three times the power of these devices. This is necessary to deal with the surge current when turning on this type of devices. In the case of a grid-connected system, the input power should match the power of the PV system to ensure safe and efficient operation.

Solar charge controller

Although charge controllers can be purchased with many optional features, their primary function is to keep batteries in the correct state of charge and protect them from overcharging. The solar charge controller is designed with amp and volt capabilities. Choose a solar charge controller that matches the voltage of the PV system and batteries. Make sure that the solar charge controller has the capacity to process the electricity provided by the PV system.

PV system

Battery size

With a grid connected solar system, no battery is required. It is required in the case of an off-grid solar system or a hybrid solar system (a mixture of off-grid and off-grid solar system). Choose one lifepo4 battery with a capacity at least as high as that of the solar panels. Battery capacity is measured in ampere-hours. Determine watt-hours by multiplying amp-hours by battery voltage.

For example, for a 40AH 10V battery, the number of watt-hours is 40(X) x 10(Y) = 400 WH(Z).

This means that the battery should provide 400 watts for 1 hour or 200 watts for 2 hours, meaning the more power you use, the faster the battery drains. However, you cannot get all the power from the battery. As soon as the voltage drops below the voltage of the device to be powered, the battery can no longer power it.

To calculate battery size, select the multiplier below that corresponds to the average winter ambient temperature your battery will be exposed to.

Ambient temperature multiplier:

25ºC at 1.00 am

21ºC 1.04

16ºC 1.11

10ºC 1.19

5ºC at 1.30 am

-1ºC 1.40

-7ºC 1.59

Overview of different devices and powers*

Below are the most used devices with an indication of average powers:

Coffee pot 200

Coffee machine 800

Loaf of bread 800-1500

Mixer 300

Microwave oven 600-1500

Hot plate 1200

Automatic washing machine 500

300 washing machine manual

Standing vacuum cleaner 200-700

Vacuum cleaner Hand 100

Sewing machine 100

Iron 1000

Electric clothes dryer 400

Gas heated tumble dryer 300-400

Water pump 250-500

Ceiling fan 10-50

Table fan 10-25

Electric blanket 200

Blow Dryer 1000

Shaver 15

Laptop computer 20-50

Computer PC 80-150

Printer for computer 100

Typewriter 80-200

25″ color TV 150

TV 19″ Color 70



CD Player 35

Stereo system 10-30

Clock radio 1

Satellite dish 30

Radio CB 5

Electric clock 3

Lighting: 100W bulb 100

Lights: 25 W compact fluorescent lamp 28

Lights: DC 50W 50 incandescent lamp

Lights: 40W DC Halogen 40

Lights: 20 W compact fluorescent lamp 22

Compact fluorescent lamps: 40 watts equivalent 11

Compact fluorescent lamps: 60 watts equivalent 16

Compact fluorescent lamps: 75 watts equivalent 20

Compact fluorescent lamps: 100 watts equivalent 30

1/4″ 250 drill bit

1/2″ 750 drill bit

1 inch 1000 drill bit

9″ 1200 Disc Grinder

3″ 1000 Belt Sander

12″ 1100 Chainsaw

14″ 1100 Bandsaw

7-1/4″ 900 circular saw

8-1/4″ 1400 Circular Saw

Refrigerator/freezer 20cf 1.8Kwh per day (15 hours) 540

Refrigerator/freezer 16cf 1.6Kwh per day (13 hours) 475

Freezer 14cf (15 hours) 440

Freezer 14cf (14 hours) 350

Freezer 19cf (10 hours) 112

Most devices have a label on the back that indicates the power. Other sources of information include local equipment dealers and product manufacturers.