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Much has also been written about a reverse manifestation of exponential change, about the impressively declining cost of solar photovoltaic cells leading to near-miraculous breakthroughs in solar electricity generation. The latter claim has been particularly popular: I encourage you to check those breathless reports of constantly and rapidly falling photovoltaic (PV) cell prices, and you will see how, if they were the only determinant of the actual cost of PV generation, we would soon be arriving at almost the same place where nuclear generation claims began in the mid-1950s, with solar generation being too cheap to meter, indeed, being absolutely a free give-away. In reality, detailed US data for residential PV systems (twenty-two panels) show that the module cost is now only about 15 percent of the total investment. The rest is needed to cover structural and electrical components (panels must be mounted on supports on roofs or on prepared ground), inverters (to change the direct current to alternating current), labor costs, and other soft costs. Obviously, none of these components, from steel and aluminum to transmission lines, permitting, inspection, and sales taxes, is tending to zero, and hence the overall costs of installation (dollars per watt of direct current delivered by the panels) show a distinctly declining rate of improvement: between 2010 and 2015 they fell by 55 percent, between 2015 and 2020 by 20 percent. And these costs do not include the additional outlays that will have to be made with the increasing share of intermittent sources (solar and wind) in overall electricity generation.
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