storage. That is, they can store the heat in molten salt and continue to operate—and generate electricity—so as to match up with peak loads.
Meanwhile, a concentrated solar project on a much grander scale has been envisioned for North Africa. The project, called Desertec, is far from generating any electricity. Yet the idea is to build huge solar farms in the Sahara Desert and transmit the power produced across the Mediterranean Sea to markets in Europe. The ambitions are huge. So is the price tag. Financing such a vast project is a major hurdle, so is the fact that concentrated solar still costs much more to produce than traditional forms of power. Uncertain politics will also be a very big hurdle.
In general, concentrated solar plants face key constraints: land, access, transmission—and cost. They can be used only in hot sunny areas. The typical design can also use substantial amounts of water, which can be a problem when the places most suited to concentrated solar projects are hot and arid.
Nonetheless, recent years have seen a land rush in the California desert for sites to build either concentrated solar plants or utility-scale arrays of solar panels. These expansive solar plants have run into what might strike some as a surprising obstacle: the opposition of environmental groups that are determined to protect the sparsely settled desert regions against development.24
GRID PARITY?
What many believe is now in sight, whatever the technology, is the prospect of grid parity. The concept emerged around 2000–2001. It holds that solar will eventually be able to compete head to head with electricity from the local utility and come out cheaper, or at least equal. Yet calculating grid parity is not easy, since it’s not really a one-to-one comparison. Indeed, it’s not altogether clear how one ought to compare a one-time investment—with free electrons thereafter—to a monthly bill from the local utility.
Calculating grid parity is complicated because the math has to account for the cost of manufacturing the solar cells, installation costs, and present and future power prices. And, of course, of critical importance is the issue of sunlight: that is, how much sunlight is delivered to that particular region in the various seasons and, thus, how many hours a year can the solar panel operate. Italy has about twice as many hours of sunlight a year as Germany, and this factor alone will affect grid parity.
There is another complication: PV are not dispatchable power that one can count on, as is the case with electricity dispatched from a power plant. Like wind, PV are intermittent. They do not generate much electricity on cloudy days or any at night. The advantage that they have over wind, however, is that they can deliver on hot, sunny days when electricity demand spikes upward, and thus can offset utilities’ need to build peak capacity that is used only at times of heaviest demand.
This intermittency affects the investment requirements. A gigawatt of installed PV capacity is not the same as a gigawatt of coal or nuclear capacity because the PV installation does not operate at night or when the sun is not shining. That is why, when talking about PV, as with wind, one must distinguish between installed capacity and electricity actually generated. Tower-based concentrated solar, however, does hold out the promise of dispatchability.
Some express concern that the concept of grid parity looks only at the direct costs for the consumer and not at the total cost to the entire system—the additional investment in backup power and additional transmission investment necessitated by intermittency, as well as subsidies and incentives. The result is to add another layer of cost and complexity to the power system. The fuel—the sun (or wind)—may be free, but the full cost in some way “must be covered by the market and ultimately ratepayers,” according to one study.
Grid parity is linked to another concept: net metering. This allows a power customer to deduct the amount of electricity it puts into the grid, owing to its solar generation, from the amount it receives from the grid. In some markets, where electricity prices are high, grid parity, at least looking at it from the viewpoint of the consumer, may be near, but it has not yet arrived. “All gridconnected markets are subsidized,” observed Paul Maycock, who ran the government’s solar program under President Carter. “If you are getting this subsidy, the market is not yet real.”25
ALL THE ROOFS?
Hans Ziegler was the passionate proponent of photovoltaics who in 1958 championed the solar cells aboard the Vanguard