Efficiency factors – what you measure is what you get

    While primary energy factors (PEF) of energy resources within the fossil fuel categories (oil, gas, coal) and nuclear have remained static for the past few years, the PEF of renewable energies (solar, wind, hydro, biofuels) has increased at a rapid pace. Consequently, the overall energy efficiency has changed as well.

    For one thing, fossil fuels have been optimized for more than a century and have reached very high factor values, proof of efficient resources-to-energy transformation. It is also true that these achievements are approaching a ceiling with only small room for improvement. By contrast, renewable energies, especially solar and wind, are only starting to advance in technological development. As a result, they are scoring ongoing higher efficiency factors, with the benefit of no or only minor outputs of CO2. 

    As a follow up to our post on reserves vs resources (where we outlined when fossil fuels will finally be used up), we investigate in this blog post whether the primary energy factors of renewable energies are already comparable and competitive to conventional sources.  Therefore, we will have a look at primary energy input compared with the equivalent electricity output of the most significant energy sources there are.

    For renewable energy sources, most of the reviewed studies present a conversion factor of 1. This 100% efficiency factor results in the source being inexhaustible and with all the energy generated from renewable sources consumed immediately. By contrast, fossil-fired power plants often are regulated and shut. To have a better overview, we consider technical efficiency factors for renewables.

    The current default PEF in the EU is 2.5. This implies that each unit of electricity requires an input of 2.5 units of primary energy to be produced. Hence, all power generation (independent of source) in the EU is considered to be only 40% efficient. However, this value is outdated, having been established in 2006. Due to the ongoing energy transition and evolving technologies within the energy industry, this value today should be closer to 2.0 due largely to the renewable energies’ conversion factor set at 1 within this discussion.

    The table below describes commercially available PEF of power plants in operation versus  theoretical values currently in development: 

    SourceOperation FactorTheoretical Factor
    Solar PV6 – 40%[1]47.1%[2] (achieved) limit at 90%
    Hydro80 – 90%90%[3] (limit achieved)
    Wind35 – 40%59.6%[4]
    Gas20 – 60%80%[7]
    Nuclear33 – 37%45%[9]

    The energy conversion factors outline huge potential for solar PV and seem to indicate a trade-off between baseload energy and high efficiency rates. While nuclear power is providing constant energy levels with nearly zero fluctuations, its efficiency upside is somewhat limited. Solar and wind energy, on the other hand, provide plenty of headroom for future technological potential while these energy sources aren’t capable of providing baseload electricity. 

    Older technologies like coal, hydro and gas are capable of providing constant power output with a surprisingly high theoretical efficiency factor for gas as an additional bonus. 

    [1] http://publica.fraunhofer.de/documents/N-73521.html

    [2] https://ieeexplore.ieee.org/document/8231134

    [3] https://www.sciencedirect.com/topics/engineering/hydro-power

    [4] https://greenliving.lovetoknow.com/Efficiency_of_Wind_Energy

    [5] https://www.powermag.com/who-has-the-worlds-most-efficient-coal-power-plant-fleet/

    [6] https://www.epa.gov/sites/production/files/2015-12/documents/electricgeneration.pdf

    [7] https://www.energy.gov/fe/how-gas-turbine-power-plants-work#:~:text=A%20simple%20cycle%20gas%20turbine,of%2060%20percent%20or%20more.

    [8] https://www.energinorge.no/contentassets/e86a4dc8771845dfb03fee35c1d0f45d/2013-02-15–conversion-factors-for-electricity.pdf

    [9] https://energyeducation.ca/encyclopedia/Nuclear_power_plant


    1. The author of this article is ignorant of the limitations imposed on renewable energy by physics. Solar energy is not a new technology. There have been continuous efforts to improve efficiency since it was first developed over 60 years ago. There has been little improvement for the last 30 years, as there are fundamental limits on conversion efficiency for silicon. Compound semiconductors exhibit the higher efficiency quoted here, but are much more complicated to manufacture and use more exotic materials.

      Wind energy conversion, too, is limited by exotic materials – the need to use rare earth metals in the generators to obtain the highest efficiency. These same materials are also used in electric cars, Since CO2 generation from transportation now exceeds electricity generation contributions, we need to prioritize use of these materials, requiring wind generation to use less efficient generators. Wind energy is also limited by availability of wind. large wind farms show decreased capacity factors, particularly on the leeward side.

      The efficiency of a CCGT power plant is determined primarily by the input temperature, which is limited by the materials used in the gas turbine stage. These have been continuously improved, and research continues on higher temperature ceramic materials, which will provide further efficiency improvements. Higher operating temperatures will also improve nuclear power plant efficiency.

    2. Hi Robert, thank you for the feedback. We have checked the facts again and can confirm that several sources approve of the stated values above without any ignorance applied. Please have a look at the Journal for Physics https://iopscience.iop.org/article/10.1088/0022-3727/13/5/018/pdf.
      Besides, we didn’t argue that solar was a new technology – if you want to learn more about it you could have a glimps on our earlier posts on solar, e.g. https://electrifying.world/2020/04/23/solar-photovoltaic-pv-milking-the-sun/

      Happy to discuss further.

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