THERMAL:  direct heating/cooling OR convert heat to motion (pistons, turbines, electricity)

 Solar: including passive and active; solar for both cooling and heating
  widespread, cheap, most underused resource? not a complete solution but..
    high tech e- generating systems are still expensive, problematic.

 Geothermal: water heated underground, either naturally or artificially
  natural geothermal: hot springs like Yellowstone, Iceland, etc.
        if you want electricity, very limited distribution, often in sensitive areas, parks, etc.
        if you want low grade heating/cooling, could work almost anywhere
  artificial (find hot but dry rock underground, drill hole, pump in water):
        unsuccessful so far.  pipes clog up almost instantly with precipitate minerals

 Ocean Thermal:  OTEC still stuck in the back pages of Popular Mechanics
    Joe has been to the OTEC facility on the Big Island of Hawai'i

 Biomass: burning vegetation and/or organic compounds (refuse, tires...)
  dirty:  lots of greenhouse gases, toxic emissions (dioxins) and fly ash
  inefficient:  few therms/kg.  but wood is widespread, renewable, cheap
  wrong track: deplete soils for gasohol instead of producing food?  dumb

 "Fossil Fuels": generated from long dead plants and animals (e.g. plankton)
   entirely non-renewable, finite.  hi greenhouse gases when burned

      Peat: compressed plants from swamps and marshes = peat bogs
           Black Plague Fuel, so why is cutting edge Sweden using peat???

      Coal: low grade/brown/lignite (semi-peat) to high grade anthracite
           classic killer fuel that refuses to die, still widespread and in demand

      Petroleum: including crude oil and its distillates (asphalt to jet fuel)
           absolutely dominates the Earth in infinite ways: this is PetroPlanet
           burned directly, also used as fuel in internal combustion engines.
           let's import all our petroleum, save ours for when theirs runs out

      Natural gas (methane): associated with crude oil (plus other sources)
           transportation is big problem, NOT a compact fuel (see LNG)

 Nuclear: including classic fission (splitting atoms) and (someday?) fusion
  so many promises: can be built almost anywhere, near population centers
   waste heat could be pumped into cities; let's have one in Ballard!
  so many problems:  storage/"disposal" of H and L LRW biggest negative
   mining U fuel not without drawbacks either: finite resource.  Moon?

HYDROPOWER: derived from "moving water" including rivers, tides, waves
 dominated by Gwatt hydroelectric dams on major rivers around globe
 very clean compared to therms but heavy local impact on river habitats
 small instream (no dam) hydro has big potential in LICs, but not in USA
 wave and tide machines still in Buck Rogers research stage

WINDPOWER:  derived from moving air; need brisk steady winds (rare)
 very expensive with too many technical/mechanical problems; but clean
 

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