I am trying to design a fuel cell that can provide enough energy for 1 day's use a maximum capacity but I am having trouble sizing the fuel cell because I need a better understanding of kilowatt hours.
I found online that the average power consumption of a house is about 8,900 kW-hr per year which amounts to approximately 24 kW-hr per day.
If I wanted to design a fuel cell, would it be considered a 1 kW fuel cell? I am trying to size it.
The reason I ask is that I read an article and it said "A 3 kW fuel cell …" so i was wondering if I could just consider this a 1 kW fuel cell and then size it based on that assumption
Best Answer
A joule (J) is a unit of energy. If you lift a one kilogram weight one meter, you have done 9.8 J of work, because the weight of a kilogram is 9.8 Newtons, and a force of one Newton over one meter is a Joule of work.
A Watt measures work intensity or power: how much energy is transferred per unit time. One Joule of work done in one second is a watt. If you lift one kilogram by one meter, and you do it in one second, you need 9.8W of power. A Watt is a Joule per second, J/s. If you want to do the same lift in half a second, you need 19.6W: twice the power.
A kilowatt-hour is a unit of energy again, like a Joule. We are taking Watts (energy per time) and multiplying them by time, so the time cancels out, leaving energy. A hour is 3600 seconds. So a kilowatt-hour is 1,000 J/s * 3,600 s = 3,600,000 J. If work is being done, or energy being transferred at a power of 1000W, and this is done for one hour, that is a kWh. Or 100W over 10 hours, et cetera. A 100W bulb lit for 10 hours consumes 1 kWh.
A food calorie (the big calorie, or the kcal) is 4200J. So a 1 kWh is 3,600,000J / 4,200J/kcal = 857 kcal. This is about the energy in two double cheeseburgers from McDonald's.