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In this article https://www.sciencedirect.com/science/article/pii/S266711312200002X

the authors show a result of prediction on energy reserves (in particular solar ones) as known in 2015 (Figure 1) and as known in 2022 (Figure 2).

In the first one (Figure 1), they quote result in TWyr/y. For solar, they quote 23 000 TWyr/y.

In the second one (Figure 2), they quote result in TWyr30. For solar, they quote 8300 TWy30. They state "we will refer to TWyr over 30 years as TWyr30".

Since results on estimation of solar energy reserves should not change by a huge factor between an estimation of 2015 and 2022, what mathematical operation should I do in order to translate from one to the other ?

(If I do 23 000 * 30, it will not decrease the result, so it is not the good operation.)

Figure 1 :

enter image description here

Figure 2 :

enter image description here

Fred
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Mathieu Krisztian
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1 Answers1

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To convert from TWyr/y to TWyr30, multiply by 30. This is confirmed in the text under "total world energy consumption":

Depending on the reference, estimates for 2021 global annual TFEC [total final energy consumption] ranges from 18.53 TWyr to 20.13 TWyr. The IEA estimates a middle-range value of 19.11 TWyr that we have retained for this article. Projecting expected [business as usual] 40–50% TFEC growth over the next 30 years, cumulative energy consumption over the period should amount to 660 TWyr30.

Note that 660/30 = 22, in line with the 2015 estimate.

When looking at solar the conversion is not as simple:

Year TWyr/y TWyr30
2015 23,000 690,000
2022 277 8,300

The reason for the drastic change in the estimate from 2015 to 2022 is several important changes in assumptions, which are explained in the section on solar energy (emphasis added):

It's only feasible to cover about 6% of the land with solar:

An important consideration we apply here to properly quantify renewable reserves is an extension of the term ‘reasonable’ underlying RARs [Reasonably Assured Recoverable Reserves] beyond pure extraction/exploitation economics. This consideration is especially relevant to solar since we have in the past reported the total amount of energy impinging annually on the earth's continents. Of course, whereas it would now be economically reasonable to deploy solar (PV) over most of the continental surface area, it would be unreasonable to assume that the entire space would be covered by PV. [...] Retaining the PV deployment assumptions from this article and its associated land-use web app we assume a reasonable upper limit of deployment to each land-use category including an implementation of emerging PV deployment strategies such as floating PV and agrivoltaic. We estimate this upper limit at 6% of the land mass. We did not account for any prospective offshore deployment at this time (a total resource twice as large as the continents’), although the practice may gain acceptability in the future.

Solar panels are only about 20% efficient:

In focusing on the energy available, we had also not accounted for the energy conversion efficiency at hand. While it is likely to increase in the future, we assume here a current state-of-the-art footprint conversion of sunlight to electricity of 20%, an assumption we justified and applied in a recently published article on large scale PV deployment.

Taking this information, we can apply the calculation to the 2015 estimate and confirm it roughly equals the 2022 estimate:

23,000 * 0.06 * 0.20 = 276

Note that in the 2022 chart the units on the finite resources are incorrectly labeled with units of TWyr30. In the body of the paper the correct units, TWyr/y, are used in the discussion.

LShaver
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