Energy storage either balances generation with demand or provides portable supply
Pumped storage hydroelectricity balances supply & demands by moving water between reservoirs.
Low demand: excess power pumps water to high reservoir;|
High demand, water flows (back) thru turbine generating power.
|TVA pumped storage facility at Raccoon Mountain.||Green: power consumed in pumping; red: power generated.|
|Examples of stored
energy in home: home heating and hot water. |
Figure shows how cost of hot water can be reduced by sequence of strategies
|A-hrs||0.7||1||1.5||1.6||24||22||100 F||2500 F|
|NiMHi=nickel-metal-hybrid; SLA = sealed lead acid;|
Time proven: peat, wood, biomass, geothermal
Coming: solar, wind, municipal solid waste (MSW)
Out there, oil shale, tidal/wave, ocean thermal, marine current energy.
Distribution: superconductors, hydrogen
What about: fission
Peat is a soil type with high proportion of dead organic matter that is not decomposed (due to lack of oxygen in waterlogged earth). Formation is slow process, taking 10 years for 1 cm of peat to form.
Major user is Republic of Ireland with 6 peat-burning power stations: 10% of total energy; 40% in oil 1960's oil crisis. Growing economy and rising cost of imported energy, spur greater use.
World reserves are 2.71 M sq-km (~1 M sq-miles); about 1/3
in Russia; 1/2 in Europe. Canada and US have vast "estimated"
Tiny actual production: 17.4 Gtonne; esp., Belarus-2.1; Finland-6.8; Ireland-2.2; Russia-2.8.
Wood. In 1999, 1.4 B tonnes produces 470 mtoe (million tonnes of oil equivalent), about 5% of total energy -- little smaller than nuclear energy, but vastly larger than other renewal sources. Note: 30% of world's land is wooded.
|Africa||N Amer||S Amer||Asia||EU||Oceania|
|Note: Africa and Asia currently overconsume resources.|
Biomass (other than wood) is poorly documented energy source. The lack of data hampers sound decision making. Additional municipal solid waste is omitted (see below).
Note: current world energy use: 410 EJ.
Common estimates of biomass use for energy per person: rural 15 GJ, urban 7.5
GJ. Given the 6 billion people, roughly half-half rural-urban, this
works out to about 70 EJ or 17% of total energy consumption!
Let us assume biomass now supplies 20% energy.
Tendencies favor increasing interest in biomass.
Geothermal energy the natural heat of the earth. Source is radioactive decay of subsurface and is renewal. In addition emission of carbon and sulfur oxides are few percent of other resources and that can be reduced with gas injection.
|Design when water heated above 150 C. When between 100 and 150 C, modified design uses heat exchange to a secondary fluid with lower vaporization temperature than water, e.g., ammonia.|
Current use is small: electricity 0.19 GJ and direct use 0.18 GJ. The 0.35 GJ total is less than 0.1 %! Iceland is exceptional: 48% geothermal, 18% hydropower, 32% oil and 2% coal.
WIND capacity is doubling every 3 years since 1990.
|Danish electricity: 12% from wind.|
Technology. Land turbines are typical 1 MW, offshore 3 MW. Wind turbines use 3 glass-reinforced plastic blades; power train is low-speed shaft, step-up gearbox and induction generator. Variable speed using AC/DC/AC system have several advantages: (i) in low winds rotor turns slower (less noise); (ii) reduced rotor loading; (iii) can deliver current at any specific power factor. Towers are usually tubular steel.
Operation. Wind power increases as third power of its speed, requiring limit on power output in high winds. This limit is achieved by either pitch-controlled blades or fixed, stall-controlled blades. Both have technical trade offs so that they are used equally.
Costs have declined steadily. In US, installed onshore farms are $ M/MW; offshore 60% more. In UK, wind and oil are about 5 cents/kW-hr. In US, nuclear is 7, wind 6, coal 4 cents/kW-hr (in 2005).
Environment. Noise at cut-off is comparable to turbine engine; wind farms needs to be 500 m from residential area. Birds & visual effects are subjective and soluble. Integration into supply networks. Experience: integration is straight forward until wind accounts for 20% of total. Then needed adjustments do not seem to limit increased use of wind.
Solar. Each year the sun supplies the equivalent of 19 Ttoe (toe=ton of oil equivalent) while current consumption is 10 Gtoe. That fact drives the continuing work on solar energy. [19 Ttoe= 800,000 EJ, whereas 10 Gtoe=420 EJ.]
But the pace has been slow. In 1952 Paley Commission estimated 13 million solar homes by early 1970s. DOE plus industrial support built two solar towers and stopped. Spain built a third. Australia solar tower might generate 200 MW at cost of $500-750 M. Private investors are reluctant due to 10+ years to get return on investment.
Photovoltaic cells are more successful, with worldwide sales of $B+/year growing at 30%.
Buildings are most obvious place to concentrate attention in integrated designs using solar panels. So far best examples use 44 KWh/sq.m versus 172 for conventional buildings.
Moving from isolated examples to worldwide applications requires society as a whole to give support. We will need cohorts of solar scientists and engineers, environmental scientists, entrepreneurs, architects and, finally, politicians and public servants informed, courageous and determined.
|Best examples shown. No good date worldwide.|
Municipal solid waste is hard to categorize: