Energy Possibilities: Windows, Windmills, and Satellites

The well-known correlation between the Human Development Index, an internationally recognized measure of basic human well-being, and annual per capita electricity use as shown in the Figure on page 39 of the April 2002 issue should not be misinterpreted or overrated. Current advances in building technology point toward options for increasing human comfort while diminishing energy consumption. These possibilities are strongly related to advances in materials physics--especially the development of electrochromic materials with optical absorption that can be regulated, reversibly and persistently, by charge insertion and extraction.

Buildings use large amounts of energy for heating, cooling, lighting, and ventilation. Air conditioning has become increasingly important for balancing excessive heat that flows in through glass facades; that excessive heat is a major reason behind the recent energy shortages in California. Architectural trends toward larger glazings--responding to building occupants' wishes for improved indoor-outdoor contact--are likely to lead to even greater demand for air conditioning.

One emerging technology for diminishing the heat load on buildings is "smart" windows, which have multilayer coatings, including electrochromic materials. These windows can regulate the throughput of solar energy and visible light across a wide range of transmittance values by charging and discharging electricity provided by small solar cells. The first of such products has been on the market for a few years, and strong R&D efforts--in the US and internationally--make it likely that less expensive and more durable smart windows will be available within a few years.

Simple estimates show that the energy savings inherent in the smart windows technology are large. In quantitative terms, the lowered electricity demand for air cooling is of the same magnitude as the electricity that can be generated by today's best solar cells, given the same area and orientation as for the smart windows.

The smart windows technology can be less expensive than solar cells. Even more important, the ability to regulate the window transparency alleviates thermal and visual discomfort associated with excessive light inflow while maintaining the primary function of the window: visual contact between indoors and outdoors.

Twenty years after my last physics experiment, I was pleased to read Physics Today's special issue on the Energy Challenge. Having some recent experience with a 300-MW wind farm on the Oregon-Washington border, I would like to add some comments from a utility's perspective to Samuel Baldwin's short treatment of wind energy ( page 62). As the article suggests, the current generation of wind technology can be cost competitive with traditional thermal power plants.

Two issues that vex utilities considering wind power are the variability and the unpredictability of the resource. Power system operators must match demand and generation on a second-by-second basis. Adding to their systems a resource with wind power's characteristics simply makes their jobs more difficult, so the system operators tend to oppose wind power on its face. However, they already deal with vast uncertainties from other generating plants that continually suffer complete and partial breakdowns and loads that fluctuate in significantly unpredictable ways. Demand is not fully predictable, either. Adding small amounts of wind power (perhaps up to 10%) to a larger system adds little to the system's overall unpredictability and, as a practical matter, may hardly be noticed by operators.

Some strong preliminary evidence indicates that a customized mesoscale weather model does a good job of predicting the output of the wind farm on relevant time scales. On the whole, the future for wind power appears very bright.

The articles in the April 2002 special Energy Challenge issue of Physics Today seemed generally thoughtful and well-written. However, I was puzzled that nowhere in that issue, not even in Samuel Baldwin's renewable energy article ( page 62) covering solar power, was there a mention of solar power satellites, lunar solar power, or the other space-based alternatives that, in the long run, can provide us with an astronomically large, completely renewable energy resource--for example tens of terawatts from (admittedly large) satellites in geosynchronous orbit. Considering that these options have, in the past, been advocated primarily by physicists, including Gerard O'Neill, Freeman Dyson, and others associated with the Space Studies Institute,¹ it seems derelict of Physics Today to ignore the current status and future prospects of this energy option.

Fortunately, David Criswell provides an introduction to the lunar solar power option in a recent issue of The Industrial Physicist.² Space-based power has apparently suffered from NASA neglect at least since the 1970s, although an installed base of at least several hundred kilowatts is already in operation, powering satellites and the space station. Of course, there is always a battle for research funding, but the long-term potential usefulness of space-based solar power seems so immense that a more focused effort to develop this technology is long overdue.