A gazebo in the countryside, a hut on the edge of the forest or a cottage by the lake are great things. Just like camping holidays with your own caravan. But as beautiful as the nature-loving recreation is, there is often a lack of the important basic supply of electricity and water. When it comes to the water supply, you can easily get by with drinking water from canisters and rainwater for watering.

Unfortunately, when it comes to the power supply, things are not that simple. However, this does not mean the construction and wiring of a 12 V solar system. The installation of a photovoltaic system (PV system) can be done quite easily and without much effort by technically gifted people.

Rather, it is about determining the right components for your own photovoltaic system so that the consumers to be operated can also be reliably supplied by the system.

For this reason we have put a solar calculator or a solar system planner for 12 V island photovoltaic systems online for you. If you enter the number and power of your consumers, as well as the operating time per day, the program calculates the required components for your system. The calculation limit is 800 Wp for solar modules and 1200 Ah for electricity storage. This means that the right components should still be found even if the power consumption is high.


Solar system planner

The solar system planner presented here is only suitable for PV systems that work as isolated solutions. With an island solar system, the solar power generated is loaded into a solar battery. The connected consumers are then later supplied with electrical energy from the battery.

In order for the system to function reliably, the individual components such as the solar module, solar battery and charge controller must be electrically perfectly matched to each other. In addition, the size of the system must be geared to the energy requirements of the consumers.

Calculate the photovoltaic system correctly

 In order to be able to calculate and determine the components of a PV system as an isolated solution, you have to work from “back to front”.

In plain language, this means that the performance of the respective electrical devices must first be determined and the operating times must be defined. The size of the required solar battery depends on the determined values.

In order for the energy drawn from the battery to be recharged in a timely manner, the solar module must be of the optimum size. Once the size or the power of the solar module has been determined, the appropriate MPPT solar charge controller can be selected.

The Best Solar Calculator in 2022

Below we have explained the individual steps for the calculation of a solar system in more detail for you. By the way: The online calculator we provide works according to the same scheme.

Determine the power requirement of the system

At the beginning of the planning of your own solar system is the determination of the power requirement. To do this, the power of the consumers to be operated must first be determined. The power in W (Watt) is given either on the device or in the technical data sheets.

In some cases, instead of the power, the current consumption is given in mA (milliampere) or A (ampere).

If neither the performance nor the current consumption is specified, the current must be measured using a multimeter or a clip-on ammeter. We have explained how to do this on our advice page for multimeters.

If a current of 0.5 A is measured at a voltage of 12 V, the power (P) can be calculated using the following formula:

P = U x I (12V x 0.5A) = 6W


The lower the power of the consumers to be operated, the smaller and cheaper the solar module required. For this reason, it makes sense to use economical 12 V LED lamps instead of lossy 12 V halogen lamps. Because an LED reflector lamp with a power consumption of just 4.6 watts generates almost the same luminous flux as a halogen lamp with 35 watts.

Consumers should also be selected that can be operated with 12 V direct current. An inverter is also required for 230 V devices.

The Best Solar Calculator in 2022

LED lamps with low power consumption

A notice:

With loads such as radios and amplifiers, the current power consumption depends on the volume. At room volume, the power consumption is significantly lower than the maximum power specified in the technical data.

A little more information about refrigerators:

Calculating the energy requirements of a refrigerator is problematic since the compressor for cooling does not run continuously. The relationship between run and pause times depends on many factors such as ambient temperature, set cooling temperature, insulation, and degree of filling. Added to this is how often and for how long the refrigerator door is left open.

When operating a 230 V refrigerator via a 12 V inverter, you should note that when the compressor is switched on, the power consumed by the refrigerator is approx. 10 times higher than the continuous power during operation. Not every pure sine wave inverter is designed for such high inrush currents.

Determine the operating time of the consumers

Of course, the operating time is just as important as the power consumption of the consumers. Because it plays a major role whether a consumer needs to be supplied with electricity for 30 minutes or 3 hours. Especially when the consumer needs a lot of electricity. The information on the operating time is included in the calculation of the required energy requirement (see following paragraph).

Calculate energy demand 

Once the performance and operating times are established, the actual energy demand can be calculated.

With different consumers and/or different operating times, the value for the energy requirement must be calculated separately and the results then added up.


In our calculation example, we assume that 2 lamps, each with 6 W, should be lit for two hours in the evening and 1 lamp with 10 W should be in operation for 30 minutes. In addition, there is a 12 V television with 30 W, which has to be supplied for one hour.

2 x 6W = 12W x 2h = 24Wh

1 x 10W = 10W x 0.5h = 5Wh

1 x 30W = 30W x 1h = 30Wh

The required electrical work for all consumers is therefore 59 Wh (watt hours). If necessary, other consumers are determined using the same scheme and the result is added to the 59 Wh.

Determine battery capacity

In a solar system with a 12 volt lithium battery, the energy requirement of 59 Wh corresponds to a battery capacity of 59 Wh: 12 V = 4.92 Ah (ampere hours). This means: In order to be able to supply all consumers over the specified period, the power storage unit must have a capacity of 4.92 Ah.

The Best Solar Calculator in 2022


So that the battery is not discharged too deeply and thus falls into cycle operation (complete discharging and recharging), the capacity drawn should be a maximum of 20% of the battery capacity. In this case, the solar battery must have a capacity of at least 24.6 Ah.

Determine module size 

The manufacturers always state the maximum peak power (Wp = Watt Peak) in the technical data for the solar modules. However, this value is only reached when the sun shines with full force on the module at a 90° angle. As soon as the irradiation or the angle is not right, the module output drops. In practice, it has been found that a solar module delivers about 45% of its peak output over a period of 8 hours on an average sunny summer day.

In order to recharge the battery with the energy required from the sample calculation, the solar module must be calculated as follows:

(59Wh : 8h) : 0.45 = 16.39W

The solar module must therefore have a peak output of 16.39 Wp or more.

Our practical tip: placement depending on the position of the sun

Due to the position of the sun, a solar module has to be at a steeper angle in spring and autumn than in midsummer. For this reason, an adjustable bracket for the solar module is a good idea. If this is not possible, then the module should be positioned steeper so that the best possible yield (harvest) is achieved in spring and autumn. In midsummer, the angle that is too steep is compensated by the longer duration of sunshine.

Determine charge controller 

When selecting the charge controller, the module current is the most important selection criterion.

Because when the solar battery is fully charged, the charge controller disconnects the solar module from the battery and creates a conductive connection (short circuit) between the module connections. This prevents the voltage generated by the solar module from becoming too high and damaging the solar module as a result.

The module current of the charge controller must therefore be equal to or greater than the short-circuit current of the solar module used. If several solar modules are connected in parallel in a PV system, the sum of the short-circuit currents of all modules is decisive.

In some cases, the agm battery charge controllers also take over the consumer monitoring. If a consumer discharges the solar battery too deeply during a rainy period, the controller disconnects the consumer from the battery in good time.

Our practical tip: Choosing the charge controller

If you plan to expand your PV system later, you should not save on the charge controller and rather choose a model with a higher module current. In this way, you can later connect another solar module or an additional power storage unit without having to change the charge controller.

When wiring the charge controller, a cable with the largest possible cross-section should be selected. As a result, the line losses for the solar power can be kept as low as possible. If necessary, the technical data for the charge controller can be used to find out which cable cross-sections the connection terminals are designed for.


Solar panel calculator is in principle quite simple. You just have to follow the steps outlined above. Setting up and commissioning a photovoltaic system is just as easy. After that, the topic of electricity costs is no longer relevant for you. Because the solar-generated electricity is free of charge and ongoing operating costs are no longer incurred with your photovoltaic system. Those are really good reasons to opt for solar power.



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