“Reality has a well-known liberal bias.” – Stephen Colbert
Harnessing primary fuels to perform work is a relatively modern phenomenon. For ages, humans scratched out a living with little more than their brains, hands, and muscles. A person’s capacity for labor is finite, and the development of tools that could ease survival’s burden was a constant ambition. Homesteaders were faced daily with important allocation decisions: how much of their personal energy should be spent working on existing critical tasks versus investing in projects that could deliver durable energy dividends over the long run? Like any investment, the initial expenditure, payback period, and total return were critical parameters.
Consider the waterwheel, a circular device that converts moving water into mechanical work. Should personal energy be invested in constructing one or would expanding the farm’s planting area make more sense? Both require significant upfront labor and yield results that leverage renewable energy from the sun long after the initial work is done. The decision is complicated by the different forms of energy created by each project – the farm produces all-important food, whereas mechanical energy from the waterwheel could make processing that grown food much easier. Ultimately, those who consistently made smart energy investments thrived, whereas those who chose poorly struggled.
Things are very different today. Thanks to the miracle of fossil fuels, the harnessing of atomic energy, and the ability to use those energy inputs to manufacture all manner of powerful machines to do our work for us, vast swaths of people live incredibly fulfilling lives while doing practically no physical labor whatsoever. To be sure, there are plenty of people doing important, physically taxing work, but integrated across society that constraint has largely been removed. As a result, society has collectively decided to organize around the constraining factor of minimizing CO2 emissions. This is a constraint imposed by a fear of the potential impacts of climate change – a choice that we suspect much of the developing world will soon relieve themselves of, preferring to roll the dice on managing the consequences if and as they arise. (The complete flop of the recently concluded COP27 summit seems to validate our hunch.)
Regardless of your views on climate change, harnessing the power of the sun is an incredibly seductive potential solution to the CO2 emissions problem. The sun bombards the earth with 173,000 terawatts of power on a continuous basis, whereas the total continuous power consumed by humans across all energy sources averages out to roughly 15 terawatts. (Note: watts are a measure of instantaneous power, whereas watt-hours are measured as the integral of power over time.)
Said another way, all of humanity’s needs can theoretically be met by harvesting only 0.009% of the sun’s energy bounty. If machines could be built to capture a meaningful amount of the sun’s energy without emitting significant amounts of CO2 during their construction, the possibility of a clean energy future becomes more viable. We perennially argue that the simplest and best answer is to make nuclear power the centerpiece of our energy strategy, but the vast potential of solar energy is simply undeniable.
The big “if” in the previous paragraph is tied to the amount of CO2 emitted during the production of solar photovoltaic (PV) panels compared to how much energy is generated by them in operation, and much ink has been spilled trying to estimate how quickly this massive upfront investment of energy is paid back. The answer is as important as it is heatedly debated since the energy needed to create solar panels comes predominately from fossil fuels. If it takes 10 years or more for the upfront energy to be paid back, PV technology will be condemned to nothing more than a niche contributor to our collective energy future. If the payback period is a year or less, and the problem of intermittency can be solved, things get more interesting.
Given the trillions of dollars of government subsidies at stake, it is no wonder that the energy return on energy invested (EROEI) calculation for PV is a controversial figure. Hundreds of peer-reviewed “scientific” papers can be found which use a dizzying array of assumptions to arrive at totally orthogonal answers to this seemingly basic question. No matter how complex and scientific-sounding the language used in such papers is, they are most often a sophisticated expression of the authors’ pre-determined biases. How should non-experts interpret this situation, what are the true drivers of the EROEI for PV, and what is our admittedly biased estimate for this all-important number? Let’s dig in.