How many watts would the Human body consume if it ran on electricity?

[Elendil_s_Heir]

I really wish you guys would stop talking about this. The Machines are probably reading this thread.

[clairobscur]

@scr4

If we assume the electricity->energy conversion is as efficient as food->energy, you need the equivalent of about 3000 Calories per day. That’s 12,000,000 Joules per day. If you’re hooked up to the wire 24 hours a day, average power is 145 Watt.

@gazpacho

Which averaged over a day is 121.5 W.

I’m not sure whether I should be amazed by this efficiency or badly dissapointed that most of my appliances need more power than me.
Franckly, I would never have guessed we were consuming so few energy. I would have assumed maybe twenty times that or possibly more (by using a comparison with appliances, precisely). Really surprising.

[naita]

@clairobscur

Franckly, I would never have guessed we were consuming so few energy. I would have assumed maybe twenty times that or possibly more (by using a comparison with appliances, precisely). Really surprising.

Are we really particularly efficient? Not many appliances can be replaced by a human, but if we looked at functions that could, such as pumping water or rotating something, would we use less energy?

Or are people forgetting that the highest energy consumption in appliances is heating and that the 100-150W figure for humans is a daily average and that we spend most of a day idling?

Also if you compared the useful work you could get out of a human who ate a particular amount of food with useful work from an electric motor running on power generated by burning that same amount of food, what would come out on top?

[blood63]

I would be interested in a range of power throughout the day if anyone would care to calculate it.
What is the power rating of our body when we are sleeping? walking? standing?
running?

[Machine_Elf]

@blood63

I would be interested in a range of power throughout the day if anyone would care to calculate it.
What is the power rating of our body when we are sleeping? walking? standing?
running?

According to this, a typical human bean in decent shape can provide a steady 200 watts of mechanical power output (professional cyclists can put out a steady 300+ watts).

Because the body is not nearly 100% efficient at converting food energy to mechanical work, we also get pretty warm when we work that hard. This page is a long read, but it suggests a thermal efficiency for a human body working like this is around 10-20%. If we assume the latter figure, then for 200 watts of mechanical power output, you’re also dumping 800 watts of waste heat into the air around you, and your total food-power consumption is 1000 watts.

For sleeping, you’re back down to the ~100 watts that has been mentioned up thread. Probably not much more for standing.

[gazpacho]

Interestingly the thermal efficiency of a car engine is around 20% to 30% which make humans not all that efficient at mechanical tasks.

[Leo_Bloom]

Some of these issues have been covered in the thread How many people connected in series to power a lightbulb?