Many people work remotely from their RV’s, boats, or off-grid cabins, which usually requires extensive use of a computer, and although computers aren’t necessarily power-hungry like an air conditioner, if you are working from one for 10 hours a day, it really adds up.  

Learning how to figure out how much power a desktop or laptop computer uses on a day-to-day basis so we can size our batteries and solar appropriately is exactly what I’m going to teach you here in lesson #3 of this Electrical System Sizing Chapter of the EXPLORIST.life Mobile, Marine, and Off-Grid Electrical Academy.

Calculating Computer Power Consumption – VIDEO

Laptop Computers – Plugged in vs Unplugged?

This blog was initially going to be a blog only covering how to figure out how much power a laptop used, but I took a poll the other day on our YouTube channel asking people if they typically:

• Plugged their laptops in only to charge and then used them off of battery power
• Used their laptops while connected to power.

And the results were close enough that I’ve decided to show how much power a computer uses for both use cases, one of which will work for estimating the power consumption of a desktop computer as well, so stay tuned.

How Much Power does a Laptop Use while Unplugged?

When Powering a computer from its internal battery, how much power does it use?

This is going to be very similar to figuring out how much power a phone uses like we discussed back in lesson 2.2 of this academy, but we are going to cover it again, just geared for computers this time.  Here’s the plan:

1: We figure out how big the battery inside of the device is.

2: We convert that to watt hours.

3: We figure out how many times per day we would be recharging the device.

4: Multiply the device’s battery size times the number of times we recharge the device per day.

That’s the plan; and here’s how it looks, starting with Googling the model number of your computer.  Usually, the computer will list the size of the battery in Watt Hours, which in the case of my laptop is 93.48 Watt Hours (https://maingear.com/maingear-vector-pro/)

And there is our answer!  My laptop has a 93.48 Watt Hour battery.  Step #1 complete.  If your manufacturer lists the battery in amp hours, or milliamp hours and volts; these are the formulas to go from those to Watt Hours; which is what we need.

• Amp Hours x Battery Voltage = Battery Watt Hours
• (Milliamp Hours / 1000) x Battery Voltage = Battery Watt Hours

How Many Times Per Day is a Laptop Battery Used?

Now we figure out how many times we are recharging that battery every day.

If I’m charging my laptop overnight, and then using the laptop and draining it to zero, and then recharging it again the following night, the computer is using 93 Watt Hours throughout the day, and then it is taking 93 watt hours to recharge the battery every night from the battery bank in our off grid electrical system.

If you are only using 50% of the battery, the math is the same, just half.

If you are using the battery, recharging, using, and then recharging again every day, you’d just multiply the full battery capacity by however many times you fully recharge it to get its daily consumption.

What if I don’t use my Laptop Every Day?

When we are putting all of this information into a power audit, it would be unreasonable to try to estimate non-daily usage.

For example, if you are a part-time remote butterfly psychologist and only work 2.7 days a week, you unfortunately don’t get to average out your weekly consumption.

This is because we are set to a solar recharging cycle as the sun goes up and down which is generally only once a day outside of any rapture-level events.  In spite of this; we need to just estimate for normal daily usage for when the device is actually in use when talking about an overarching power audit, which we will cover in more depth later in this academy, so consider subscribing.

What if I only use my laptop while plugged in?

Now, if your laptop is like mine and has garbage battery life so it needs to be plugged in all of the time OR if you work from a desktop computer, finding out the daily consumption of it is pretty easy, but you’ll need one of these AC power meters that plugs into the wall and then your computer plugs into it.  They are only like $15 on amazon.

The computer plugs into this meter and the meter plugs into an outlet and you’ll just press the little reset button on it, and then use your computer as normal for the day.  At the end of the day, you can look back and it will tell you how many kWh passed through the meter.

The more days you use the meter, the more accurate your measurements will be.  This is especially true if your computer usage varies from internet browser work one day to video editing and exporting the next.

The other day while I was writing this script, I kept my computer plugged into one of these AC meters and let it run for 4 hours.  At the end of that time, the meter had counted .204 kWh going through it, which converting to Wh is as simple as moving the decimal place to the right three places, resulting in 204 Wh of usage.

If my average work day is 10 hours, I’d just multiply that by 2.5 to get my daily anticipated usage of 510 Watt Hours.

The AC power meter method is definitely the more accurate way to determine the power usage of your computer, and you can use the AC power meter method even if you use the laptop battery part of the time.  Just let the power meter live on the end of your laptop charging cable, and use your laptop as normal for, say, a week and see what the weekly usage is and then divide by 7 to get the daily usage.  
 
There are several different options to get the anticipated daily power consumption of your Desktop or Laptop computer, so you’ll just need to pick the one that seems the closest to your needs.  Or better yet, use multiple methods and compare them to each other and then see if they agree.

Conclusion

Now you should have a good idea of how to calculate the power used by a computer in a mobile, marine, or off-grid electrical system.