Compared to oil in the ground, the sun looks like a limitless energy source. Making comparisons of the two by calculating the equivalent of barrels of reserves for a solar project seems like an odd notion.

But experts in reserves accounting say that it can and should be done, and are working on a way to do so. An arm of the United Nations (UN), with support from SPE, is working to adapt the system now used to track reserves of oil and minerals in the ground to apply to renewable power sources such as the wind and the sun as part of a long-term effort to cover other sources of energy.