Energy fuel stock cam be selected based on a variety of choices which consist of the following 6 points:

• How accessible is the resource to individual humans or regional locations?
• What have been the primary historical uses of this technology?
• What is the energy density of the material of choice in units of watt hours per kg of material?
• What are the principle applications of this technology choice?
• What are the main advantages in terms of increased efficiency, lack of pollution, practicality of use, etc?
• What are the main disadvantages as they relate primarily to damaging the local or global ecosystem.

Wood:

• Generally accessible for all global populations
• First fuel used to heat and cook
• Comprises about 50% of Coal.
• Sufficient energy density to boil water; first fuel-stock for steam engines and trains.
• Widely available; renewable over 100 years than can grow back; harvesting usually causes significant soil erosion and changed local ecosystem
  
  

Coal:

• Available in peat marshes, surface deposits (rare) and underground seams. Major country resources in UK, Germany, USA, China, and Australia.
  
  
• Discovered in Richmond, Virginia, 1701; commercial production in 1748; used to fuel the first train steam engine in 1803; large scale energy source by 1850.
  
  
• 1 coal unit with about a 30% variation depending on the type of coal.
  
  
• Used for coal fired electricity; coal fed steam engines, especially for trains; replaces wood for most all steam generation by 1890
  
  
• Relatively high abundance in many locations; requires a large labor force. Fosters export economy (e.g. UK, Australia)
  
  
• CO2 emissions; change in global ecosystem via atmospheric pollution of CO2; Extremely unhealthy in inversion; Lots of particulate emission leading to acid rain; exploited resource to be exhausted.
  
  

Oil

• Not much surface oil exists, therefore requires drilling for access. Major resources in USA and Middle East.
  
  
• First discovered in 1859 near Titusville PA; immediate transportation fuel. By 1920 in USA there were one million vehicles with corresponding gas stations conveniently located. Oil-fired heating in the early 20th century.
  
  
• About twice the energy density of coal, when it is refined as gasoline.
  
  
• Primarily for transportation; heating and electricity generation are secondary.
  
  
• Relatively high abundance in many locations; requires a large labor force. Fosters export economy (USA first, Middle East later)
  
  
• Principal source of CO2 addition to the atmosphere and change of global ecosystem; toxic waste fields associated with extraction, particularly in South America
  
  

Natural Gas:

• Not naturally available but generally can be recovered from oil well heads
  
  
• Usually co-located with oil discovery, because gas pressure is needed to help force liquid crude up a pipe. 1906-1970 residential use in the US increased by a factor of 50.
  
  
• About 15% higher energy density than crude oil
  
  
• Used for NG-fired electricity and district heating
  
  
• Relatively high abundance in many locations and more easily handled than oil; distribute through gas pipelines; very high energy density
  
  
• Major source of CO2 and strong driver of increased methane (CH4) atmospheric concentration due to direct leakage from the extraction process. Increased methane emissions amplify any CO2 based warming.
  
  

Hydropower:

• Only on flowing rivers
  
  
• Earth dams have been used historically for flood control and irrigation; first hydroelectric dam built in 1881 at Niagara Falls; Large Dam Federal Project in the 1930s in the American Southwest (e.g. Hoover Dam).
  
  
• At 100 m height 1 kg of water has about 35.000 times less energy density than 1 kg of coal; lots of kg of water on any major river is available so can build dams at 2000 MW nameplate, similar to a coal-fired power plant.
  
  
• Electricity generation for entire cities or regions.
  
  
• Zero greenhouse gas pollution associated with generating electricity. Low operating costs and hence cheap electricity for consumers.
  
  
• Regional resource only; strong change in local ecosystem; invasive species; significant transmission line infrastructure required.
  
  

Nuclear Power:

• Requires mined uranium ore
  
  
• First commercial facility built in Arco Idaho, 1955. In 1974 first 1000 MW plant was built; by 1986 the US had 100 plants. Currently there are 107 nuclear facilities in the US and 450 worldwide.
  
  
• Energy density is not meaningful with this technology-- a small amount of uranium can boil a lot of kg of water. Typical nameplate capacity is 1000 – 3000 MW.
  
  
• Electricity generation; 20% of US electricity; 75% of electricity portfolio for France
  
  
• No GHG emissions; high efficiencies; high unit capacities
  
  
• Fuel stock is rare and mined which leads to resource exhaustion; nuclear waste must be stored on site in most cases; takes about 15 years to implement any nuclear power plant.
  
  

Wind Power:

• Available wherever there is reliable surface wind.
  
  
• Used in 500 AD in Persia for pumping water and grinding grain; by 1300 first horizontal windmill appears in Europe; First wind farms appeared in the US in the 1980s.
  
  
• Energy density depends on wind speed. A modern wind farm now has nameplate capacity of 500-1000 MWs.
  
  
• Electricity generation for regional areas (e.g. Germany). In the USA, wind has now slightly exceeded hydro in overall contribution to the US electricity generation portfolio. New generation of large scale offshore facilities came on line starting in 2013.
  
  
• Zero greenhouse gas pollution associated with generating electricity. Low operating costs. Highly scalable
  
  
• Regional resource only; Intermittent source for electricity so energy storage must be built in; build out rate subject to supply chain constraints (Bothun 2018)
  
  

Solar PV Power:

• Available everywhere in daytime.
  
  
• Photoelectric effect discovered in 1902; Southern California Edison installed a 6 MW PV system in 1985.
  
  
• Energy density depends entirely on solar illumination at a particular latitude; best case at equatorial latitudes at noon 2000 watts per square meter. PV panels are generally 5-10% efficient so average generation is about 300-- 600 watts per sq. m for most locations. Requires lots of land and lots of PV panels to achieve even a 10 MW PV facility.
  
  
• Small scale only; local house use; device charging; Rooftop based building electricity for some locations.
  
  
• Zero greenhouse gas pollution associated with generating electricity. Simple installation. Doesn't require water supply. Silicon is abundant.
  
  
• Not easily scalable --highly dependent on availability of materials. Very difficult to make 1000 MW facility for better grid tie-in; chemical etching process in panel construction produces toxicity for local environment.
  
  

Solar Thermal Power:

• Available everywhere in daytime but requires water source.
  
  
• A 10 MW Solar Thermal Tower was developed in Barstow CA demonstration project
  
  in 1982
  
  
• Focusing issues between the heliostats and the tower limit maximum plant size to about 200 MW.
  
  
• In principle, renewable electricity can be generated 24x7 by using molten salts as thermal energy storage.
  
  
• Zero greenhouse gas pollution associated with generating electricity.
  
  
• Not easily scalable; requires water; hard to debug and correct current performance issues at large scale plants (e.g. Ivanpah) that require thousands of heliostats.
  
  

Ocean Wave Energy:

• Available everywhere that has access to ocean coastline.
  
  
• Only pilot projects have been built.
  
  
• Energy density depends on height of wave (squared) and the frequency of wave arrival and this is very location dependent.
  
  
• Few yet: 2.25 MW Wave Farm in Portugal; 1.5 MW Wave Dragon in North Sea
  
  
• Constant 24x7; highly creative devices are being prototyped. Extremely scalable.
  
  
• Very material-intensive in terms of MW generated per ton of material used; grid connection can be problematic if located too far off shore.
  
  

Ocean Current Energy:

• Feasible only in areas of strong tidal flow or where ocean current is near the surface (like Gulf Current)
  
  
• First tidal power Bay of Fundy Nova Scotia 20 MW tidal barrage; largest tidal barrage of 240 MW built in 1966 France. No ocean current generation projects yet.
  
  
• Energy density depends on velocity of flow
  
  
• Provides local tidal electricity. Currents as large as the Gulf Current could potentially power the entire US.
  
  
• None for tidal. The constant flow of Gulf Current could provide 24x7 electricity generation.
  
  
• Extensively damages any tidal estuary ecosystem destroyed; corrosive environment for ocean current flow can damage equipment. Tidal energy is not scalable and has a very low CF as tidal flow is intermittent.
  
  

Ocean Thermal Energy:

• Wide-spread in equatorial waters --about 25% of surface ocean waters can be used for this purpose as this is where a suitable temperature difference exists between surface water and water at depth (500m-- 1km)
  
  
• A 22 KW plant was built in Cuba in 1930; since then variety of pilot plants have been built each limited to < 100 KW capacity.
  
  
• Energy density depends on the rate of warm and cold-water exchange
  
  
• With the development of large scale carbon fiber pipes and the nanotechnology storage of Hydrogen, world electricity for thousands of years can be derived from this resource.
  
  
• This is the only unlimited supply of energy the planet has left
  
  
• Current technological limitations on the sizes of pipes that can be built; high initial expense; challenging infrastructure would be required to export electricity from the middle of the ocean
  
  

Geothermal:

• Very limited accessibility to this resource; requires reliable source of steam produced by water in contact with hot rock
  
  
• A 250 KW power station was built in Larderello Italy in 1913; A10 MW plant was built in California in 1965.
  
  
• Energy density depends on the rate of steam generation. In most locations, cold water is pumped down to hot areas near the surface to refresh the system.
  
  
• Commonly used for heating in Iceland; can use steam to reform methane into hydrogen to be used for a transportation fuel.
  
  
• Most efficient source of energy available as steam emerges on its own.
  
  
• Heat is removed faster than can be recovered at most areas. Geothermal is therefore not renewable but is a mined resource; Hot Dry Rock proven not feasible.
  
  

These choices for sources of energy generation have a variety of different pros and cons as well scalability challenges. Future energy decisions likely require a wisely chosen mixture of various energy generating technologies. Given the scale of our energy use all future choices will have some measure of damage to local and global ecosystems. Human actions currently can alter the energy pathways in our natural systems. The observed increase in ocean heat content is evidence that human industrial processes are changing these natural systems indicating that the Anthropocene is here and that humans are a global geophysical force that can dictate how the Earth system behaves. Knowledge of this should aid in planning for the most sensible future global energy mix. From the physical point of view, humans are in a necessary partnership with nature. Tremendous use of energy has caused an energy imbalance in the Earth system. Climate change is the primary manifestation of this imbalance since the system essentially now has more energy to work with. Restoring energy balance should be targeted as a principal outcome of changing the future global energy mix from its current dominance by fossil fuels.