Energy reserves

Renewables reign supreme

A recent opinion piece by Gwynne Dyer in the 4 June issue of the Otago Daily Times mentioned a new (to me) source of geothermal energy that can be extracted from hot dry rock which is omnipresent around 4 km below much of Earth’s surface. The idea is that when water from the surface is brought into contact with the rocks it can be superheated to drive turbines at the surface. It’s renewable in the sense that the water used can be recycled (provided that internal source of energy remains).

While talking about this to my colleague, Ben Liley, he mentioned an update to an energy-availability diagram that I’d talked of earlier.

Here it is. Very nice!

It shows the potential energy available from the Sun (large circle at centre), from other renewable sources (circles at left), and from finite sources including fossil fuels and uranium (circles at right), all compared with 30 years’ worth of global energy assuming full electrification of energy (blue globe at left). The area of each circle is proportional to the corresponding reserve over a 30 year period. The authors note elsewhere in the paper that with the current energy mix, which is dominated by the less efficient burning of fossil fuels, the Earth’s consumption would be about 2.5 times larger than shown here with full electrification.

The amount of solar energy is smaller than their previous estimates because it now includes realistic efficiency factors (typically around 20 percent of the incoming energy is converted to electrical energy in solar panels). It also assumes that ‘only’ 6 percent of the land surface area will be covered by solar energy farms. In reality that is rather a large fraction, though it must be remembered that solar farms could also be located above oceans, or even in space. The amount of winds energy is also smaller than previously for similar reasons.

The diagram shows that, with those assumptions, the amount of renewable energy available exceeds our demands by a factor of 27 and 5 for solar and wind respectively. If our needs were to be met by solar energy alone, around 0.2 percent of the land area would need to be devoted to solar farms.

It also shows that we can’t rely on petroleum. Without renewables, the remaining reserves can meet only 65 percent of our demands over the next 30 years. And after then, what? We can’t rely on nuclear energy either. The amount of uranium available can provide only half our needs for the next 30 years.

The amount of geothermal energy available is sufficient to supply about half the planet’s needs. Coming back to the Gwynne Dyer article I mentioned at the start: that source of energy was considered, but is not included in the figure because it is highly uncertain whether it will come to fruition within that 30 year time scale. In future though, that number could increase. But not by enough to solve our future energy problems.

Whichever way you look at it, renewables will be our saviour.

As the name implies, fossils are dead.

Long live their death.