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SolarTown Learning

Solar Electronics and Battery Chargers

Category: Solar Electronics

Never be Stuck without Power Again

With solar powered electronics, you can rest assured that even in the most remote circumstances, you do not necessarily have to be cut off from civilization-so long as you've got solar to power your electronic devices. With solar portable chargers, you can free yourself from the inconvenience of the electric grid!

While there are many products on the market today with built-in solar battery chargers, such as those found on watches and calculators, stand-alone gadgets are making solar battery charging more versatile than ever before. Portable solar battery chargers allow you to recharge anything from laptops with a portable solar laptop charger, to Blackberries, to iPods, to small appliances.

Many electronics are now built with solar collectors as well, including radios, flashlights, headlamps, GPS devices, and more, all with the free, renewable power of the sun. They are ideal for those who enjoy camping, hiking, RVing, boating, and other outdoor adventures, but they are equally practical for business people on the go. We summarize some of the major outdoors applications of solar products in our learning section on solar outdoors. In this article, we summarize how solar electronics work and how much you can realistically expect to get by on a solar charge.

How Solar Electronics and Battery Chargers Work

Whether a solar collector is built into an electronic or is a portable add-on, the general principles of energy generation are the same. How much power you get from a particular solar portable charger will largely depend on several factors, including the amount of sun the collectors receive, the charge control built into the system, electronics usage patterns, and power ratings of the charger.

Charge Control

By and large, most solar battery chargers now available have some type of charge control built into their systems which determine when the charger will cease to provide power. This is useful for protecting batteries from being over-charged. When making a selection of a solar electronics product, you should choose based on several factors, including the type of charge controller that will work best for you. Here are the most common types of charge controls:


  • Simple charger: Using the simplest charging technology, these solar portable chargers use a constant rate of DC power to charge batteries. The power output does not change based on time or the charge of the battery, which means there is a risk of over-charging with this type of charger.
  • Trickle charger: Most rechargeable batteries will gradually lose their charge over time, especially NiCd and NiMH batteries, but with a trickle charger a battery's power will be replenished at the same rate as self-discharge. A trickle charger will keep a battery at full capacity until you are ready to use it. Although this is the slowest way to charge a battery, it is safe to leave a battery in a trickle charger indefinitely.
  • Timer-based chargers: With this option, batteries will be charged for a pre-set amount of time regardless of the size of the battery. This can therefore result in over-charging lower capacity batteries and under-charging higher capacity batteries.
  • Intelligent charger: Using more sophisticated technology, intelligent chargers produce output current based on the state of the battery's voltage, temperature, and/or time it has been charging. Once the battery has been fully charged, the charger shuts itself off.
  • Fast charger: These are desired most when you require a quick recharge, which will require more amps from your charger.

Usage Patterns

How you use your electronics will also play a role in the type of solar portable charger you choose. If you want a charger that will charge your cell phone overnight, you'll need a charger with an energy storage system. Similarly, if you are looking for a solar battery charger that will allow you to use your laptop while it is being charged, you will require a charger with higher amperage.

Available solar energy is also an important consideration. Most people assume that solar battery chargers require bright, direct sunlight in order to work, but this not the case at all. As long as there is some sunlight, the charger will be able to replenish a battery. The brightness of the sun does, however, affect how much energy the collectors are able to absorb. Direct sunlight is ideal, while cloudy days will offer a lower potential for solar energy collection.

Calculating Solar Power Potential

To choose a battery charger, you will need to determine the size of your battery, which is expressed as the amp hours that it can store. You can calculate how long it will take to charge a given battery by dividing the amp hour rating of the battery by the charge rating, and then adding 10% (to account for the time it takes to completely charge a battery).

The output for most solar battery chargers is rated in watts, with 15 watts generally delivering 1 amp per hour in direct sunlight. Most solar battery chargers can accommodate up to 26 watts, which is sufficient to power most Apple and PC laptops, even those that are not ENERGY STAR certified. In this section, we review some of the basic uses for a solar battery charger, how much time it will take to recharge the batteries using solar energy, and how much time that will give you on certain electronic equipment. This is the formula we use:

Formula: average charge per hour with solar (assuming solar charger produces 26 watts in direct sun)

15 watts = 1 amp-hour (Ah)

26 watts generated hourly ÷ 15 watts to produce one Ah = 1.73 Ah with one hour of charging

Formula: charge time

(Ah ÷ 1.73 Ah) + 10%

Using this formula, we look at how much time it would take to charge the battery needed to power a Macbook while it is turned on and while it is turned off.

Macbook Pro 15"

Battery capacity: 5500 mAh (milliamp-hour or 5.5 Ah)

Ideal battery life: 5 hours per charge

Charge time (off): Charging the battery with solar energy while the laptop is off

(5.5 Ah ÷ 1.73 Ah) + 10% = 3.5 hours

Conclusion: 3.5 hours of charging just the battery could ideally give you 5 hours of run time.

Charge time (running): 12 watts used while running, leaving 14 watts for charging

(26 watts generated hourly - 12 watts used to run the laptop) ÷ 15 watts = 0.93

      (5.5 Ah ÷ 0.93 Ah) + 10% = 6.5 hours

Conclusion: 6.5 hours of charging with solar energy while running the laptop could give you an additional 5 hours of run time.

We can use the same formula to estimate how long it would take to charge regular batteries using solar.

Rechargeable Duracell AA batteries

Battery capacity: 2650 mAh (or 2.65 Ah)

Ideal battery life: 500 photos per charge

Charge time (from dead): Charging the batteries with solar energy after they've been totally drained.

      (2.65 Ah ÷ 1.73 Ah) + 10% = 1.7 hours

Conclusion: 1.7 hours of charging will give you 500 photos.

Advantages of Powering-Up Electronics By Solar Energy

Using solar to power your laptop, cell phone, PDA, flashlight, radio, or GPS system ensures that you're never without power for these useful devices. Solar energy for electronics is also cost-effective, saving you money on electricity you would otherwise use to charge these devices. Of course, using solar for providing power for electronics is also a green choice since it will reduce the amount of energy you spend to remain plugged in and wired up.