How Much Energy Is Needed for a Solar Panel to Charge a Laptop Battery?

So you want to use a solar panel for charging your laptop batteries? Perhaps you want to be working in the great outdoors, where power sockets are out of reach. Or maybe you want to save electricity bills by making energy on your own. It can be hard to start without knowing how much energy is required for a solar panel to charge a laptop battery. You can use a solar laptop charger, but if you already have solar panels, you can use to charge a laptop battery directly, you may need to calculate.

Knowledge is the key to setting up your solar panels to charge your devices. Here are the things you need to know:

Voltages Needed Laptop Batteries

There’s a maximum voltage that you need to fully charge a battery, and it must be equal to the maximum rated output voltage of the battery. A typical voltage for batteries in small laptops is 11.1 V or 14.8 V, depending on the number of cells. This can be between 10 to 15 volts. For bigger or standard-size laptops with three lithium-ion cells, it usually needs 19 volts, but it can vary from 14 to 23 volts.

All laptops come with an internal input regulator so that they can take a range of voltages. Sometimes, if the voltage is too low, it will not turn on while charging. Once the battery is charged, the laptop will come on.

How Many Watts Does a Laptop Use?

To know how much energy is needed by your laptop, you have to discover how much watts it consumes. For sure, it consumes less electricity as compared to other household appliances and a desktop computer. The electric consumption of a laptop depends on different factors: screen size, type of laptop (whether it’s a basic, general, high-end, or gaming laptop), usage, CPU power, graphics card, or adapter wattage.

Generally, a laptop consumes 30 to 90 watts per hour. However, it varies depending on the factors stated above. If you use your general laptop for gaming or use any other high-end laptop, it can consume even more than that. Some models may go a lot more than 100W per hour, which is the reason why the laptop becomes very hot.

If it has a low-grade CPU or processor, it needs more power to provide your laptop with a good enough performance. Also, the higher the performance of your graphic card, the higher the power consumption.

Solar Panel Basics

Now that you have an idea of how much power a laptop uses, here are some of the things you need to know before using solar panels.

Voltage Ratings

Solar chargers are typically designed for 12 VDC, but there are 24-volt panels. Typically, when 24 volts or greater is needed, solar panels are wired in series.


A solar charge controller acts like an on and off switch to allow power to pass or to cut it off when needed. When using a solar panel with more than 5 watts rated output, it is recommended to use a solar charge controller. It can help prevent overcharge, improve charge quality, and prevent battery discharge in low-light or no-light situations.

In most cases, when using a 6-watt or larger solar panel, a charger controller is highly recommended.

Output Conditions

Solar panel ratings are calculated in bright and direct sunlight. Partial shade, overcast, and indirect sunlight can decrease the power output. These conditions often occur, so oversizing the size of your solar panel or array is often recommended.

Typically, there’s an average of 6 hours of usable sunlight during the summer and four hours of usable sunlight in the winter. There may be exceptions to these averages, but you can build a more reliable solar power system by erring on the side of caution.

Solar Panel Size

When it comes to solar power, it’s all a matter of numbers – the power you need vs. the power the panel can generate. Before getting started, you need to know how many watts or amp hours you will need to produce in hours.

First, determine how much electricity your laptop will consume in a specific time period. Then, figure the amount of direct sunlight that the solar panel will receive in that period of time. Calculate the total amount of watt-hours needed.

The power generation a solar panel can provide is commonly given in watts. To calculate the energy it can supply your laptop battery with, divide the watts by the voltage of the solar panel. For example, you have a 120 W solar panel with 18 V. Then, 120 W / 18V = 6.6 Amps.

How to Understand Watts, Amps, and Volts

The power consumption of a laptop is given in watts. To calculate the energy you need to harvest for use in charging your laptop battery, just multiply the power consumption by the hours of use. For instance, a 60-watt device used over 4 hours needs 240 watts.

The energy in watts is equal to the voltage in volts multiplied to the electric charge in amps. Simply put, Watts = Volts x Amps.

If your device doesn’t have the watts stated on the label, then it must at least have the input volts and the Amps AC it draws. From there, you can use the Watts equation: Volts x Amps. To convert watts to amps, you simply divide watts to volts.

How to Figure Out How Much Solar Power and Inverter Needed for Charging Laptop Battery

  1. Measure how much power your laptop actually uses using a wattmeter. Let the laptop discharge fully and then recharge it while the meter measures it. Record the number and how long it took to recharge it. Let’s assume it took 90 watts and two hours to charge, so 90W x 2 hrs = 180 Wh.
  2. Determine how much usable sunlight you have. The sun may be up for 12 hours a day, but you will need an insolation map to check how much usable sunlight you have in your area.
  3. Take the watt-hours you need and divide the number of hours of usable sunlight. Let’s say the sun shines in your area for 5 hours. So, 180Wh / 5h = 36W.
  4. You will need an inverter to convert the DC power from the panel into AC, so the laptop charger can convert it back to DC. Inverters have losses, so divide the watt-hour by 80%. So, for a 180 Wh, you need at least 45W of solar panel, and that assumes a perfectly clear day. But that doesn’t happen all the time – perhaps you have some clouds or even rain. You’ll either have to do without under those conditions or add extra panels. How much will be up to you.
  5. Your device might draw 90W, but you’ll want to add a little more to be safe. Choose an inverter that can supply at least 120% of power, so you need one with at least 108 watts.