29 thoughts on “Weekend reflections

  1. Kevin Cox, you say “It is obvious that if it costs less energy to produce than it generates then solar cells will save green house gas emissions.”

    That statement contains an “if” and that was the essence of my post. I was wondering if a solar panel costs less or more energy to produce than it generates over its lifespan. I was also pointing to the need to add in transport and distribution costs and obsolesence or decommissioning costs. I was not stating an answer either way. I was simply stating that the obvious “comon sense” assumption that solar panels save on C02 emissions needs to be tested.

    It is certainly the case that a number of scientists (Pimentel is one) question the value of biofuels because they have calculalated energy inputs and energy outputs from biofuel production and use.

    “”There is just no energy benefit to using plant biomass for liquid fuel,” says David Pimentel, professor of ecology and agriculture at Cornell. “These strategies are not sustainable.”

    Pimentel and Tad W. Patzek, professor of civil and environmental engineering at Berkeley, conducted a detailed analysis of the energy input-yield ratios of producing ethanol from corn, switch grass and wood biomass as well as for producing biodiesel from soybean and sunflower plants. Their report is published in Natural Resources Research (Vol. 14:1, 65-76).

    In terms of energy output compared with energy input for ethanol production, the study found that:

    corn requires 29 percent more fossil energy than the fuel produced;
    switch grass requires 45 percent more fossil energy than the fuel produced; and
    wood biomass requires 57 percent more fossil energy than the fuel produced.
    In terms of energy output compared with the energy input for biodiesel production, the study found that:

    soybean plants requires 27 percent more fossil energy than the fuel produced, and
    sunflower plants requires 118 percent more fossil energy than the fuel produced. “”

    Full article at;

    In other words, biomass fuels are an “energy sink” not an “energy tap”. I am concerned, similarly that solar panels might be a “energy sink” rather than a net energy source.

  2. Ikonclast – a quote from the US office of Energy Efficiency and Renewable Energy:

    “Typically, the energy payback time (i.e., the time it takes for a PV system to generate the same amount of energy that it took to manufacture the system) for PV systems is 2 to 5 years. Since a well-designed and maintained PV system will operate for more than 20 years, and a system without moving parts will operate for close to 30 years, PV systems produce far more energy over their useful life than we use to manufacture them.”

    This quote, plus links to technical papers on this question, are at:

  3. They have probably done their homework (ie. empirical tests) so I will accept that. I would like also to see the research of an incisive researcher like Pimentel on PV solar panels.

    The PV energy return is quite modest. Two to five years just to get the energy back is rather mediocre in my book. And it does not even appear that they have counted transport, installation and decommissioning (dumping, recycling) energy costs.

    It seems quite likely that those energy costs could double the situation to four to ten years to get back energy inputs.

    How long does it take to get back the energy input into manufacturing a diesel generator I wonder? (Assuming for the moment that the diesel fuel is free like the sunlight is free.) I would wager that it is much less then 2 years. I suspect a few hundred hours of operation would do it easily.

    This illustrates one of the problems of transition to renewable power with a low return rate like PV solar panels. A large energy investment is required up front and this energy investment is only slowly recouped. The large up front energy investment is subsidised as it were by fossil fuel use until the solar investment is paying its own way by generating enough power to manufacture all future PV needs plus meeting other power needs.

    If we are not careful we will be caught in an energy “bind”, a severe energy shortage, where not enough renewables have come on stream to meet needs and fossils are declining severely. Whilst we currently waste enormous amounts of energy and could probably live nearly as well on half the energy we could still have an energy crunch where failure to secure energy security then impacts on food security and the need to run urban infrastructure.

    I don’t need to sketch out what happens to populations facing food shortages and collapsing urban infrastructure.

  4. In find the discussions on energy efficiency very interesting. The type of questions Iconoclast raises are assumed to be answered when a economic theoretician writes down, in an abstract way, “production possibilities” and checks for “resouce feasibility” in an intertemporal model of an economy with finite life. (Sometimes I gain the impression that Economics, concerned with the material welfare of humans, will survive outside Economics and Commerce Faculties.)

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