Energy: Units of Energy in our Everyday Life
In this blog post, I'll try to visualize how much energy we handle in our everyday lives. It's not rocket science but it's important to be able to relate quantities of energy to ones everyday life.
The SI unit for energy is 1 Joule. Lifting an apple of 100 grams one meter corresponds to one Joule.
One kilowatt hour corresponds to 3,6 megajoules. Like a 1 kW heater running for one hour.
Comparing One Day of Manual Work with Buying Energy
An adult of good fitness can sustain some 50-150 watts when biking one hour. 100 watts for one hour corresponds to 0,1 kWh. The efficiency of human muscles is some 20%, so the input energy of 0,5 kWh will give an output mechanical energy/work of 0,1 kWh.
Eight hours of manual work consumes four kWh of input and generate 0,8 kWh of mechanical work. If one would instead choose to work at an office for 8 hours, that person would be able to earn some 1300 SEK after taxes (140 USD or 130 EUR). That money will buy almost 83 liters of diesel. With an energy density of 9,77 kWh per liter, 83 liters of diesel correspond to 833 kWh. With an energy efficiency of 40%, the output will be some 333 kWh mechanical work. Instead of working manually, one can buy almost four hundred times more energy.
If one would buy electric energy instead, the price would be 0,8 SEK/kWh. 1300 SEK would buy some 1625 kWh of energy. With an energy efficiency of 88%, that corresponds to 1430 kWh mechanical work.
Lots of numbers here, but the options are:
ASSUMPTION: Since energy is (currently) super-cheap compared to time, it may seem to make sense to be time-aware and spend energy. But the supply of cheap energy is limited and I will elaborate on that in a future blog post.
Comparing a 100 km Bike Ride to a 100 km Car Ride
Biking 100 km (5 hours) would consume some 4 kWh. Using a car in the middle class (Sverigecykeln) that consumes 6,6 l/100 km, gives an energy consumption of 64 kWh. With an average of 1,2 persons per car, the energy consumption per person is 53 kWh.
ASSUMPTION: Energy consumption isn't the only cost when deciding how to transport one-self. Most of the time, there is a compromise between the travel time and the cost of transport. Since the energy consumption isn't properly reflected by the price, it is (from a selfish point of view) currently a good idea to waste energy to save time.
Reducing costs in terms of money, where one hour is worth hundreds of SEK and one kWh is worth 0,8 SEK up to 1,57 SEK, the options are:
CONCLUSION: Clearly, the least energy consuming option will be the most expensive option. This paradox is causing individuals to waste energy to save time.
The SI unit for energy is 1 Joule. Lifting an apple of 100 grams one meter corresponds to one Joule.
One kilowatt hour corresponds to 3,6 megajoules. Like a 1 kW heater running for one hour.
Comparing One Day of Manual Work with Buying Energy
An adult of good fitness can sustain some 50-150 watts when biking one hour. 100 watts for one hour corresponds to 0,1 kWh. The efficiency of human muscles is some 20%, so the input energy of 0,5 kWh will give an output mechanical energy/work of 0,1 kWh.
Eight hours of manual work consumes four kWh of input and generate 0,8 kWh of mechanical work. If one would instead choose to work at an office for 8 hours, that person would be able to earn some 1300 SEK after taxes (140 USD or 130 EUR). That money will buy almost 83 liters of diesel. With an energy density of 9,77 kWh per liter, 83 liters of diesel correspond to 833 kWh. With an energy efficiency of 40%, the output will be some 333 kWh mechanical work. Instead of working manually, one can buy almost four hundred times more energy.
If one would buy electric energy instead, the price would be 0,8 SEK/kWh. 1300 SEK would buy some 1625 kWh of energy. With an energy efficiency of 88%, that corresponds to 1430 kWh mechanical work.
Lots of numbers here, but the options are:
| Option | Input | Efficiency | Output |
|---|---|---|---|
| Manual Work | 4 kWh | 20% | 0,8 kWh |
| 1300 SEK diesel | 833 kWh | 40% | 333 kWh |
| 1300 SEK electricity | 1625 kWh | 88% | 1430 kWh |
ASSUMPTION: Since energy is (currently) super-cheap compared to time, it may seem to make sense to be time-aware and spend energy. But the supply of cheap energy is limited and I will elaborate on that in a future blog post.
Comparing a 100 km Bike Ride to a 100 km Car Ride
Biking 100 km (5 hours) would consume some 4 kWh. Using a car in the middle class (Sverigecykeln) that consumes 6,6 l/100 km, gives an energy consumption of 64 kWh. With an average of 1,2 persons per car, the energy consumption per person is 53 kWh.
ASSUMPTION: Energy consumption isn't the only cost when deciding how to transport one-self. Most of the time, there is a compromise between the travel time and the cost of transport. Since the energy consumption isn't properly reflected by the price, it is (from a selfish point of view) currently a good idea to waste energy to save time.
Reducing costs in terms of money, where one hour is worth hundreds of SEK and one kWh is worth 0,8 SEK up to 1,57 SEK, the options are:
| Option | Energy Cost | Fuel Cost | Time | Total Cost |
|---|---|---|---|---|
| Biking | 4 kWh / 3400 kCal | 3 Big Mac & Co (200 SEK) | 8h (1350 SEK) | 1550 SEK |
| Car | 53 kWh | 85 SEK | 1,5h (250 SEK) | 335 SEK |
| Train | 100 SEK | 100 SEK | 1,5h (250 SEK) | 350 SEK |
CONCLUSION: Clearly, the least energy consuming option will be the most expensive option. This paradox is causing individuals to waste energy to save time.
In future blog posts, I will discuss flow of cheap energy and what I fear will happpen when the energy supply is reduced.
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