Value chain · CLM-1308
In plain terms
"Energy payback time" and "energy return" are two views of one calculation and can be converted only when the lifetime and counting method are known. Neither says how much of the sun's or the fuel's energy a system uses up; that is a separate measure.
The claim as recorded
The guidelines relate the two PV metrics as EROI_PE-eq = T / EPBT, where T is the system lifetime and the energy payback time uses the same 1/G primary energy factor; a payback time therefore converts to an EROI only on the primary energy convention and only with the lifetime stated. EROI describes the whole life, while EPBT says only when the investment has been repaid. The guidelines also state that EROI leaves out the primary energy taken from the resource, so it measures how little extra energy a system needs, not how efficiently it uses primary energy; for efficiency they point to the LCA metrics CED and nr-CED. For systems whose investment comes up front, as with PV, EROI computed over time starts below the whole-life value, and EROI at whole-industry scale is discouraged.
Evidence behind this: T3: an IEA-PVPS Task 12 methodology guideline with named authors. It recommends and does not mandate; not the normative-instrument (T1) case, as ruled for SRC-187 on 2026-09-11.
Scope and limits
The 1.21-year figure is this register's arithmetic, not the document's. The relation holds only for a single system with a defined lifetime; the document discourages it at industry scale, which is the scale of any SBSP build-out. It is our inference, not the document's statement, that payback figures such as CLM-1038's cannot be read as EROI without T and the conversion convention.
What it assumes
No assumptions are recorded against this claim.
Where it comes from
PDF p.17 Eq. 5, EROI_PE-eq = T / EPBT, with EPBT = Inv / ((Out_el / T) / G); EROI_PE-eq covers the whole life while EPBT covers only the time to return the invested energy (paraphrase); Eq. 6: net output positive when t > EPBT. PDF p.13 footnote 3: EPBT and non-renewable EPBT differ by the mix used (paraphrase). PDF p.20: "the primary energy directly harvested from the PES (i.e., PE) plays no part in the definition of EROI"; two systems with the same EROI may need very different total primary energy (paraphrase). PDF p.21: CED and nr-CED measure efficiency, EROI measures effectiveness, and EROI does not normally separate renewable from non-renewable inputs (paraphrase). PDF p.20 Table 1 (repeated as Table S-1 on PDF p.5): EROI has a short-term perspective, CED and nr-CED a long-term one. PDF p.24: with up-front investment, EROI(t) is first below the integrated value and then rises above it (paraphrase). PDF p.25: at industry scale there is no system lifetime and use of the term EROI "it is therefore here discouraged"; a Net Power Output measure is suggested instead (paraphrase). Our arithmetic on the CLM-1307 worked example: EPBT = 30 / 24.8 = 1.21 years; the page states no EPBT for that example.
Basis: EROI_PE-eq = T / EPBT, T in years; dimensionless ratios
Related records
- Answers question
- QST-008 not published in this releaseQST-021 not published in this release
Cite this
energyaperture.com/c/clm-1308
CLM-1308, Energy Aperture, as of 2016-01.
Connected records
Other published records linked to this one. A list, not a judgement.
- Also from SRC-646
- CLM-0316In 2009 three researchers guessed that, once the energy to deliver and use it is counted, an oil-based fuel must return at least about 3...CLM-1307An "energy return" figure for solar power can be stated in two ways, counting the electricity itself or counting the fuel a power station...CLM-1309A fair energy-return comparison of SBSP with ground solar counts the same things for both: the energy to build, run and scrap each...CLM-1310The 2016 guidelines recommend default lifetime, wear-out and performance numbers for a ground solar energy-return study, and list 16 facts...