mercury

The storage of energy generated by solar or wind power is usually done in banks of batteries: expensive to build and whose capacities diminish with use, and environmentally toxic as trash but difficult to recycle. An alternative arrangement that instead stores the energy as mechanical potential which can be converted back to electricity whenever required, such as the Firedrake mercury turbine, has obvious advantages but is not much done in practice. As far as the author is aware, the idea of turbines driven by ambient-temperature mercury—a non-reactive liquid metal whose heft, rendering the driving impulse proportionally higher, could potentially result in a compact, low-maintenance, and long-lasting alternative—is original to ASH WEDNESDAY. “Mercury turbines” as understood today are something different: not part of a mechanical energy storage system but instead components of a thermodynamic power cycle, with the mercury vaporized. The Firedrake system is to employ electricity from solar cells to pump mercury up which is released as needed to flow down again through a power-generating turbine, analogous to hydroelectric plants.

The other Firedrake technology—heat sinks for thermal energy storage, as in the Devil’s Dance Canyon—has been implemented on a minor scale in a handful of locations, although usually the energy is delivered to the storage as electricity from solar panels. In the fictitious Firedrake system, it is instead delivered directly as solar heat, without the complexity, expense, and inefficiency of conversion to electricity for transport and then reconversion back to heat for storage. We tend to underestimate the power of the Sun because its heat is quickly dissipated in the surrounding atmosphere. Consider a car left out on a clear day, too hot to touch, and then imagine that if instead of surrounded by air it was surrounded by a transparent insulator: the heat would keep going in but little would be released, and so it would get ever hotter. This is the idea of the Firedrake heat system: the exposed surface is heated, then transfers that heat by conduction to a high-specific-heat storage medium that is insulated: the heat streams in but little is released, concentrating it to the point that it can melt rock, as in ASH WEDNESDAY. But how to turn it into a practical system?

There is a hundred-and-forty-year-old operating template for how this could be achieved: the steam system that underlies Manhattan. This grid, paralleling the electrical grid, carries energy in the form of heat, as steam (this is why steam is so often seen rising from curbs and gratings in New York City, as in the accompanying photograph taken by the author of the Queensboro Bridge approaches, where it mysteriously emerges from an otherwise apparently purposeless pipe). The use of steam as a relatively safe heating system (virtually fireproof) is plain enough, but what is less intuitive is that many apartment buildings also use steam to power their central air-conditioning. Some buildings even have their own electricity generators, driven by steam, and are completely off Consolidated Edison’s electrical grid.

In New York City, the steam is generated in fossil fuel-fired plants, but this could at least be augmented, if not wholly replaced, with heat sinks of suitable design.