Primary to final energy, how much do we waste?
Imagine making 3 cups of coffee, throwing 2 away and drinking the third. Then repeating that process everyday.
Sounds absurd but it’s effectively the global energy system as it’s designed today. The world takes chemical energy stored in fossil fuels, burns it to create thermal energy which spins turbines to create mechanical energy that creates the electrical energy we send down the lines to convert it back to heat for the 3 cups of which we’ll throw away 2.
Now imagine you have a new coffee machine that produces just 1 cup of good coffee without wasting two. According to the IEA, BP’s annual statistical review and other publications, you would classify this as three in order to compare it to the broken machine.
So the first issue is how to define waste?
For fossil fuels, waste is usually defined in terms of waste heat which can’t be used in the conversion to electricity.
A ton of coal has an energy density of approximately 25 GJ (23.7MMBTU, 6944kWh) of which it can convert 32% of the heat into electricity (latest heat rate from EIA, 10551). Lose another 6% on transmission and the efficiency of the kettle in converting electricity back to heat is about 80% which means you actually spill 3 cups to make 1.
Trying to use clean coal makes the situation worse. If you switched to coal with 90% carbon capture (CCS), you lose an extra cup (efficiency 27%, heat rate 12507) although would that be considered waste as technically you’re using the energy to clean up the initial mess?
And as an interesting tidbit, for a ton of coal, if you placed a giant kettle on top of the power plant it would produce 278,000 cups of coffee (1kWh makes 50 cups X 6944kWhX 80% kettle efficiency). Make the equivalent at home and you can only make 84,000 cups after the energy conversion losses.
Switching from coal to gas, and the heat rate improves to 7732 or 44% efficiency. So we waste less to make coffee and this is where we need to drink a lot of it because it gets confusing.
Because… not all heat is wasted. A lot is used in industrial processes as well as heating homes and commercial buildings. But how to measure it?
Unfortunately, there is no simple answer and the closest you’re going to get is a footnote in everyone’s favourite sankey diagram, LLNL’s energy flow charts.
Efficiency by end use in USA / (Rejected)
Residential 65% (35%)
Commercial 65% (35%)
Industrial 49% (51%)
Transport 21% (79%)
And finally, driving between all those power plants. Transportation using petroleum products wastes 80% or throwing 4 cups of coffee away to drink 1.
Which roughly works out to be two thirds wasted in the USA, and a further study showed about 72% globally.
How does this compare to renewables?
BP solved the reporting problem by assuming renewables are as inefficient as fossil fuels.
But the reality is, it’s difficult to define waste from renewables when there is no by-product. If anything, using the capacity factors (difference between theoretical maximum and actual electricity output) would identify the inability to convert solar and wind into useful energy but it’s not quite the right proxy for waste.
Current capacity factors are in the order of the following:
Solar PV 24% / (76% unused)
Wind 34% / (66%)
Do we accept waste as ok?
Throwing two cups of coffee away to make one is a lot of waste. Unfortunately, it’s also historically been cheaper than other alternatives and we shouldn’t forget that a lot of the world has benefited from cheap wasteful energy.
Here maybe a little navel gazing both figuratively and literally is in order. For those looking at their not so small belly, maybe we should focus on the final form of wasted energy and that is over-consumption. Did we need all that energy in the first place?
Do you agree? Or at least only make 1 coffee while thinking about it.
