How to choose a solar panel

The most commonly asked questions when purchasing solar panels for charging electronics are how to calculate the number needed and what size is best. By conducting some quick research and performing simple calculations, you can determine the correct size, type and number of solar panels needed.

Step 1 : Daily Power Consumption

The first step in finding the right solar panel is determining how much power you use -- or need, in watts, on a daily basis. Determining your watt-hours usage is a critical component of obtaining an accurate estimate of how many watts of solar panel producing capacity you'll need.

Suppose you have:
  • Satellite phone that needs 12-watt hours per day
  • iPod that uses 3 watt-hours per day
  • Camera that uses 6-watt per hour per day on average
You will need a total 21 watts on a daily basis

If you need to fully charge these devices every day; would need a solar panel capable of generating that amount of power.

Step 2 : Isolation

Isolation is a term used to describe the total number of hours a day that your solar panel will be able to generate its rated voltage.

In other words, you'll want to figure out the average number of hours of peak sunlight you get per day. Keep in mind, that when the sun is low in the sky -- as it is in the morning and late afternoon/early evening, it won't produce as much energy as it does at noon. The sun's rays may not be a strong in the middle of January as it is in July.

Therefore, make sure you're calculating peak hours of sunlight to be conservative. In a nutshell, isolation hours vary by month and location, so be sure to take that into consideration when calculating your peak sunshine hours.

To estimate the average amount of sunlight hours, take the average sunlight hours for each season, add them together and divide by four.

For example, if your area receives five hours of sunlight in the summer, four hours in the spring and fall and three hours in the winter, your year-round daily average of sunlight is four. There are also online solar calculators that can provide you with average daily sunlight estimates for your location.

Step 3 : Number of Panels Needed

Now that you know the power consumption average usage and the average daily sunlight received, you're ready to calculate the number of solar panels needed.

To begin, divide the total watts daily usage by the average daily sunshine you receive. The result will tell you the watts amount that you'll need to generate in one hour.

In the above example, we calculated 21 watts daily usage and four hours of average daily sunshine, which gives you 5.25 watts of power needed. In this case, a 7-watt solar power rating or 10-watt solar power rating will do the trick.

Things to Consider….

Charge controller are a good idea to use on any panel that is over 10 watts rated output. A charge controller acts like a switch allowing power to charge the battery when needed, stopping power once the battery is full.

Other benefits of a charge controller are preventing overcharging and battery discharge. We high recommend the MorningStar SS-6, 6 amp, affordable, simple to use and perfect for solar panels rated up to 70 watts.

Solar panel rating are based on optimal conditions; bright direct sunlight. Overcast, shade or indirect sunlight decreases power output from the solar panel.

Tip: Over-sizing the size of your solar panel will help compensate lost of power in less then ideal conditions.

Tip: You can run/charge your device straight from your solar if your device is not sensitive to voltage variations. We recommend adding a battery component for energy storage, this will enable you have a constant, stable source of power.


Knowing how to pick out the right solar panel is essential in meeting your power expectations.