Are the alternative energy strategies achievable?

The constraints on penetration of energy technologies are time and information, net energy, and capital cost. As D. Spreng has pointed out, time, energy, and information constitute a triad: energy can be substituted for time, information can be substituted for energy. That energy can save time follows from irreversible thermodynamics, but the principle can be extended to the social sphere. Related to the energy-time exchange is the economic cost of intermittency of energy supply. Renewable energy sources, particularly solar sources, are characteristically intermittent. To eliminate intermittency imposes a cost which must be considered in planning energy futures based on renewable sources. Two other constraints on penetration of energy technologies—net energy and capital cost—are briefly considered. As for net energy, estimates of energy paybacks for solar thermal electric converters differ by factors of three; this introduces large uncertainties in the energy subsidy required for this technology. As for capital cost, the Peterka theory of technological change is shown to place limits on the amount of subsidy required to introduce a new energy technology.