The large magnitude of solar energy available makes it a highly appealing source of electricity. The United Nations Development Programme in its 2000 World Energy Assessment found that the annual potential of solar energy was 1,575–49,837 exajoules (EJ). This is several times larger than the total world energy consumption, which was 559.8 EJ in 2012.

Answer this question, if possible (if impossible, reply "unanswerable"): Who estimated the annual potential of solar energy in 2000?
The United Nations Development Programme