Each renewable energy technology should be developed to meet the demands most suited to its characteristics. As yet, however, only wind can provide substantial amounts of affordable electricity. High hopes rest with energy crops, although the gasification plant needed for efficient combustion are still being developed. Denmark's "Energy 21" policy paper, one of the few authorative and impartial assessments of future developments around, expects energy crops to take off from around 2005. The waste burning technologies, which are at or near commercial viability, will continue to be exploited, but these resources are limited and are they truly "renewable?" Hydro, in various forms, remains to be exploited, but generally on a small scale. Last, the solar technologies can be competitive when providing heat or off-grid electricity, but commercial grid-connected applications are some way off.