24-hour Availability

Except for geothermal and biomass (which in Hawaii usually means burning garbage - such as at the H-POWER plant on Oahu - or burning sugar cane waste known as "bagasse"), many renewable energy sources aren't "firm" or available all of the time, when you need it. Non-firm sources, such as wind and solar, are called "as-available" resources and must be backed up by firm generation to ensure electricity is available when customers need it -- 24 hours a day, regardless of whether the wind is blowing or the sun is shining. 

NOTE: Solar insolation is the amount of power available from sunlight per square meter of area.