(1) Abundant in supply and generally characterized by renewability, these resources are capable of sustaining perpetual human utilization; for instance, estimated onshore wind resources available for development amount to 253 GW-yet as of 2003, only 0.57 GW had been harnessed. Projections indicate that usable capacity is expected to reach 4 GW by 2010 and 20 GW by 2020; meanwhile, the combined capacity of grid-connected and off-grid solar photovoltaic applications is projected to increase from 0.03 GW to between 1 and 2 GW by 2020.
(2) Characterized by low energy density, their development and utilization require substantial physical space.
(3) Containing little to no carbon, they exert a minimal impact on the environment.
(4) Widely distributed, they are well-suited for small-scale, decentralized utilization.
(5) Characterized by intermittent supply and high variability, they present challenges to the provision of continuous energy.
(6) With the exception of hydropower, the costs associated with developing and utilizing renewable energy sources are higher than those of fossil fuels.
