How to calculate solar power requirement

How to calculate your solar power requirements:

Approach A

1. Choosing the right solar panel for your needs is like choosing a battery.

In the same way that a bigger battery will provide more power for longer, a larger Solar panel will collect more energy in less time.

The right size of panel will depend on variables such as the power required by the appliance, the length of time you want to use it and how much sunshine you get at the time of year

2. There are three things to consider when choosing a solar panel or creating a solar system.

You need to know what appliances you will be using and how much energy they require, how much energy your battery can store and which solar panel will replenish your 'stock' of energy in the battery in line with your pattern of use.

3. How much energy will your appliance(s) use over a period of time?

The power consumption of appliances is given in Watts (e.g. 21” fluorescent light, 13W). To calculate the energy you will use over time, just multiply the power consumption by the hours of use.

The 13W light fitting, on for 2 hours, will take 13 x 2 = 26Wh from the battery.

Repeat this for all the appliances you wish to use, then add the results to establish total consumption.

4. How much energy can your battery store?

Battery capacity is measured in Amp Hours (e.g. 17Ah). You need to convert this to Watt Hours by multiplying the AH figure by the battery voltage (e.g. 12V).

For a 17Ah, 12V battery the Watt Hours figure is 17 x 12 = 204Wh

This means the battery could supply a 13W fluorescent for 15 and a half hours, 204W for 1 hour, or 102W for 2 hours, i.e. the more energy you take, the faster the battery discharges.

5. How much energy can a solar panel generate over a period of time?

The power generation rating of a solar panel is also given in Watts (e.g. STP010, 10W). To calculate the energy it can supply to the battery , multiply Watts by the hours exposed to sunshine, then multiply the result by 0.85 (this factor allows for natural system losses).

For the solar 10W panel in 4 hours of sunshine, 10 x 4 x 0.85 = 34Wh. This is the amount of energy the solar panel can supply to the battery.
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Approach B


SOLAR ENERGY CALCULATION

One single solar panel from type standard 150 Watt / 24 volts can deliver a power of 150 Watt per hour, considering full sunshine.

Knowing that the sun shine vary during the day, the effective sun power of one day is equal from 4 to 6 hours of a maximum measured at midday.

Since this maximum at midday is not the same everyday, it should be taken in consideration, that more or less heavy cloud reduces the possible power.

The electrical power is stored into batteries, similar to the one used in cars.

Example: One solar panel of 150W/24V produce between 150W x 4h = 600 Wh and

150W x 6h = 900 Wh.

One battery of 12V/110Ah has a capacity of 12V x 110Ah = 1320 Wh

For technical reasons, it is not recommended to empty a battery more than 70%. The usable capacity of this type of battery is around 924 Wh, what match to the produced electrical energy of 600Wh to 900Wh.

We are offering 24V-systems, using 2 batteries with 12V/110Ah.

Using an inverter 24V to 230V connected to the batteries, it is easily possible to get a power source of 230V, driving different types of electrical appliances like a fan, energy saving lamps or a television.

But notice: There are different types of inverters. The type of inverter advised has an output of pure sinus. Using them will avoid troubles that can occur on critical devices like television or personal computers. If the inverter has a modified sinus output or (worst case) a rectangular output, a significant part of the stored electrical energy will be wasted, and on long-term running critical devices may damage.

With the stored power of 600 Wh to 900 Wh (one solar panel, see example above), it is possible to use the following devices:

- 4 energy saving lamps 11W, time of use 4-6 hours (4x 11Wx 4h = 176 Wh)

- 1 fan 75W, time of use 3-5 hours (1x 75Wx 3h = 225Wh)

- 1 television 100W, time of use 2-3 hours (1x 100Wx 2h = 200Wh)

Total consumption = 601 Wh

We recommend the usage of two solar panels to get a buffer capacity in case of less sun.

The main thing is to get an idea of the electrical power needed for the devices that are supposed to be powered by solar energy, and also an idea of the duration of use of each device. With this two informations, it is possible to calculate the size of the solar panel required to obtain good results.

On most electrical devices, the power consumption is written on it, and these specifications are based on one hour of usage.

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How to Calculate Amps on a Solar Panel

A solar panel will generate electricity when placed in the sun. Current will flow from a panel connected to an electrical circuit. How many amps of electricity the panel will produce depends on the power of the solar panel, the amount of sunshine falling on the panel and the characteristics of the circuit to which the panel is connected. Calculate the amps produced by the panel making measurements using a digital multimeter.

Step 1:

Look at the back of the solar panel or consult the installation manual and find the maximum rated power of the panel in watts. Look also for the maximum power voltage, Vmp, which is in volts.

Step 2:

Calculate the current produced by the solar panel when it is generating its maximum power. Calculate the current in amps by dividing power in watts by the voltage in volts. For example, if the solar panel is rated at 175 watts and the maximum power voltage, Vmp, is given as 23.6 volts, then calculate the current as 175 watts divided by 23.6 volts, which is equal to 7.42 amps. This is current produced by the solar panel at full power.

Step 3:

Take a digital multimeter and switch the dial to direct-current volts. With the solar panel connected to an electrical circuit, measure the voltage between the positive and negative terminals of the solar panel. Make a note of this value. Disconnect the solar panel from the circuit and switch the digital multimeter to measuring resistance. Measure the resistance of the electrical circuit in ohms and write down this value. Reconnect the solar panel to the circuit.

Step 4:

Calculate the current in amps flowing through the circuit by dividing the voltage by the resistance. This relationship is Ohm's law. For example, if you measured the voltage as 22.1 volts and the resistance of the circuit as 3.2 ohms, divide 22.1 by 3.2 ohms to get 6.91 amps. This is the actual current produced by the solar panel, given the amount of sunshine on the panel and the characteristics of the circuit.