Sustainable Energy Technologies

Comparative Review of Sustainable Energy Sources Energy Storage:

Energy Density of Some Materials (KHW/kg)

 Gasoline  --------------> 14
 Lead Acid Batteries ----> 0.04
 Hydrostorage -----------> 0.3 (per meter3)
 Flywheel, Steel --------> 0.05
 Flywheel, Carbon Fiber -> 0.2
 Flywheel, Fused Silica -> 0.9
 Hydrogen ---------------> 38
 Compress Air ------------> 2 (per meter3)

Energy density storage drives the choices that can be made. Technology helps to drive this. At present energy storage in batteries is not sufficiently high to solve the basic problem.

Hence The Advanced Battery Consortium

For the future our choices are:

• Invest in discovery of new oil reserves (e.g. Off-shore, shale oil)
• Invest in Clean Coal Technology as 20% of the worlds supply of Coal is in the US
• Invest in Renewable Energies

Every form of energy generation has environmental fall-out. Can we pick the best one globally and or locally? As long as the decisions are driven by "voodoo" economics (i.e. heavy subsidy), intelligent decisions are not likely to occur.

Most forms of alternative energy genearation require much less of an organizational infrastructure. This means that a shift to alternative energies means a loss of jobs. This is undesireable to most politicians.

What happens if we try to be objective and evaluate our choices via some standard considerations, such as:

Evaluation Criteria for Alternative Energies:

• Capital Costs
• Operating Costs
• Efficiency
• Is it renewable?
• Energy Storage Requirements
• Pollution
• Environmental Modification
• Levelized cost to the consumer
• Feasibility on Large Scale
• Individual Homeowner Independence
• Unit Capacity
• Loss of Jobs

Comparative Table

Evaluation	Solar Thermal	PV	Hydro	Wind	OTEC	Tidal	GEO	Biomass
Capital Costs	Large	Large	Enormous	Moderate	Enormous+	Enormous	Small	Small
Operating Costs	Moderate	Moderate	Neglegible	Small	Unknown	Neglegible	Small	Moderate
Efficiency	15%	5--10%	80%	42%	7% +	25%	100%	25%
Renewable	Yes	Yes	Yes	Erratic	Yes	Yes	NO	Maybe
Storage	Not Needed	Unclear	Built-IN	Essential	Not Needed	Unclear	Not Needed	Not Needed
Pollution	None Really	Waste Heat	None	Visual	None	None	Steam Plumes	Particulates; CO
Levelized Costs	25 cents KWH	16 cents KWH	4 cents KWH	3.5 cents KWH	Unknown	Unknown	Low	Unknown
Environmental Impact	Moderate	Large	Enormous	Small	Unknown	Outrageous	Small	Moderate
Large Scale	Too Expensive	Possible but Expensive	Proven already	Very Possible	The Solution	Discrete Locations	Discrete Locations	Net Energy Gain?
Small Scale	NO	Difficult	Low Head --> Legal	Definitely	NO	NO	NO	Absolutely
Unit Capacity	1000 MW	Depends on Acreage	2000-6000 MW	Highly Variable	As large as you need	250 MW	1000 MW	50-100 MW
Employment Opportunties	Few	Few	Few	Few	Lots to build it	Some	Few	Many

What about Energy Storage?

Options:

• Battery Farms:
  • Acres of batteries; charged by transmission lines during periods of low demand
  • Returned to transmission lines during periods of high demand
  • Designed for load levelling
  • One Acre could store about 400 MW-hours of energy and deliver 40MW of power (for 10 hours)

  We need better batteries period (also for electric vehicles): US is investing in this

• Pumped Hydro:
  • Not many locations lend themselves to this
  • Process is 64% efficient which is pretty good

• Flywheels:
  • Need to optimize energy-to-mass ratio which is material dependent
  • Fused Silica has 25 times the energy storage per kg than lead-acid batteries
  • Flywhees are promising

• Hydrogen
  • Very high energy density storage per kg
  • No naturally occuring sources
  • Separate H from H₂0 is energy intensive
  • Not economically viable unless shipped large distances from point of production

• Compressed Air
  • Thermodyanimcs tells you that when you compress air the temperature goes up melts the pressure containment vessel
  • Have to cool the air as its compressed energy intensive
  • Not very practical

Bottom line(s):

Wind energy coupled with advanced battery design has real promise.

OTEC provides a truly large scale solution

Solar PV does not look economically viable on the large scale.