One of my longtime hobbies has been building mini power generation systems. Usually these are based on solar, but I’ve also experimented with thermoelectric power generation. If there’s one thing I’ve learned in all my projects, it’s that power, and specifically electricity, is actually rather difficult to make.
Normally, we plug stuff into the wall and it just works. We might notice that our MacBook charger is rated to 85 watts, or our iPad needs 10 watts, but what does that mean? Obviously the MacBook requires about 8 times more power than the iPad, but it’s hard for us to conceptually understand how much 85 watts really is.
First, I’ll “science” a little bit and say that a watt is defined as volts x amps. So your typical home wall outlet, supplying 120 volts, would need to draw roughly 0.7 amps to power your 85 watt MacBook. This explains the MacBook’s 85 watts mathematically, but we still don’t really know how hard it is to generate 120 volts, or how the 0.7 amps factors in. Getting a feel for that is difficult because we typically only experience the consumption of power, not the generation of it.
To make things easier, I’ll round up our MacBook to 100 watts. This could also be expressed as 0.1 kilowatts. What would generating that power look like? Well, most people have seen solar panels, so a 100 watt solar panel would be roughly 0.5 square meters of surface area using the densest, most efficient panel available. A 100 watt wind turbine would have blades about 0.5 meters long and would require a sustained wind of about 20mph to produce the full 100 watts.
Hopefully, that helps get you started thinking about what generating 100 watts looks like. It’s not easy. In terms of things we use, 100 watts is a bit on the low side. Things like microwaves, electric stoves, hair dryers, and air conditioners, all easily draw over 1000 watts on average. Lighter appliances like fans, refrigerators, televisions and large desktop computers fall in the 100-750 watt range, while personal electronics including laptops, cell phones, and anything battery-powered fall in the sub-100 watt range.
For what they do, computers (including smartphones and tablets) are actually extremely power efficient. When running on limited battery supplies, they have to be. The most inefficient part tends to be converting the 120 volt AC power from the wall to the 12 volt DC internal components tend to require. The Mac mini is still one of the most power efficient desktops you can buy. The newest models consume roughly 10 watts at idle, and when power requirements burst, they’re able to ramp up the power quickly and then bring it back down just as quickly. Even my 2007 model only draws 15-20 watts.
If you want to know more about power consumption of devices at home, I highly recommend P3 International’s Kill-A-Watt meter. In addition to being a watt and watt-hour meter, it can also measure amps, voltage, power factor and more. It’s definitely helped me get a better understanding of how much power my Mac mini consumes, and if I ever want to build a bigger power generation system, I’ll have an idea of exactly how much I’ll need.