• 4th Grade Introduction to Energy Resources Renewable and Nonrenewable Energy Sources [View Experiment]
  
• Renewable Energy - Pros and Cons [View Experiment]
  
• Pros and Cons of Geothermal Energy [View Experiment]
  
• The pros and cons of nuclear energy [View Experiment]
  
• Energy Experiments: Getting Started [View Experiment]
  
• Solar Irradiance Measurements [View Experiment]
  
• Coal Energy: Lesson Plans, Experiments and Resource Guide [View Experiment]
  
• Experiments with Renewable Energy [View Experiment]
  
• Research Projects in Renewable Energy for High School Students [View Experiment]
  
• Experiment on the Use of a New Source of Renewable Primary Energy for Rendering More Efficient Cogeneration [View Experiment]
  

Primary energy sources

Energy sources are substances or processes with concentrations of energy at a high enough potential to be feasibly encouraged to convert to lower energy forms under human control for human benefit. Except for nuclear fuels, tidal energy and geothermal energy, all terrestrial energy sources are from current solar insolation or from fossil remains of plant and animal life that relied directly and indirectly upon sunlight, respectively. And ultimately, solar energy itself is the result of the Sun's nuclear fusion. Geothermal power from hot, hardened rock above the magma of the earth's core is the result of the accumulation of radioactive materials during the formation of Earth which was the byproduct of a previous supernova event.

Fossil fuels

Fossil fuels, in terms of energy, involve the burning of coal or hydrocarbon fuels, which are the remains of the decomposition of plants and animals. Steam power plant combustion heats water to create steam, which turns a turbine, which, in turn, generates electricity, waste heat, and pollution. There are three main types of fossil fuels: coal, petroleum, and natural gas. Another fossil fuel, liquefied petroleum gas (LPG), is principally derived from the production of natural gas.

Pros

• Because it is based on the simple process of combustion, the burning of fossil fuels can generate large amounts of electricity with a small amount of fuel. Gas-fired power plants are more efficient than coal fired power plants.
• Fossil fuels such as coal are readily available and are currently plentiful. Excluding external costs, coal is less expensive than most other sources of energy because there are large deposits of coal in the world.
• The technology already exists for the use of fossil fuels, though oil and natural gas are approaching peak production and will require a transition to other fuels and/or other measures.

• Commonly used fossil fuels in liquid form such as light crude oil, gasoline, and LPG are easy to distribute.
• LPG can be transported, stored and used virtually anywhere. It does not require a fixed network and will not deteriorate over time. As a result, it is particularly useful in regions which are not connected to fixed energy networks.
• LPG is clean burning and has lower greenhouse gas emissions than any other fossil fuel when measured on a total fuel cycle. In fact, by 2010, all buses and taxis in the Southern Chinese city of Guangzhou will be LP Gas fueled. The city will host the 2010 Asian games and has taken the step in a bid to reduce air pollution in advance of the games. LPG is also non-toxic and will not contaminate soil or aquifers in the event of a leak.
• LPG can be accessible to everyone everywhere today without major infrastructure investment.
• LPG can be up to 5 times more efficient than traditional fuels, resulting in less energy wastage and better use of our planet’s resources.

Cons

• The combustion of fossil fuels leads to the release of pollution into the atmosphere. According to the Union of Concerned Scientists, a typical coal plant produces in one year:
  • 3,700,000 tons of carbon dioxide (CO2), the primary human cause of global warming.
  • 10,000 tons of sulfur dioxide (SO2), the leading cause of acid rain.
  • 500 tons of small airborne particles, which result in chronic bronchitis, aggravated asthma, and premature death, in addition to haze-obstructed visibility.
  • 10,200 tons of nitrogen oxides (NOx), leading to formation of ozone (smog) which inflames the lungs, burning lung tissue making people more susceptible to respiratory illness.
  • 720 tons of carbon monoxide (CO), resulting in headaches and additional stress on people with heart disease.
  • 220 tons of hydrocarbons, volatile organic compounds (VOC), which form ozone.
  • 170 pounds of mercury, where just 1/70th of a teaspoon deposited on a 25-acre lake can make the fish unsafe to eat.
  • 225 pounds of arsenic, which will cause cancer in one out of 100 people who drink water containing 50 parts per billion.
  • 114 pounds of lead, 4 pounds of cadmium, other toxic heavy metals, and trace amounts of uranium.
• Dependence on fossil fuels from volatile regions or countries creates energy security risks for dependent countries. Oil dependence in particular has led to monopolization, war, and socio-political instability.
• They are considered non-renewable resources, which will eventually decline in production and become exhausted, with dire consequences to societies that remain highly dependent on them. Fossil fuels are actually slowly forming continuously, but we are using them up at a rate approximately 100,000 times faster than they are formed.

• Extracting fossil fuels is becoming more difficult as we consume the most accessible fuel deposits. Extraction of fossil fuels is becoming more expensive and more dangerous as mines get deeper and oil rigs go further out to sea.
• Extraction of fossil fuels can result in extensive environmental degradation, such as the strip mining and mountaintop removal of coal.

• The drilling and transportation of petroleum can result in accidents that result in the despoilation of hundreds of kilometers of beaches and the death or elimination of many forms of wildlife in the area.
• Safety measures are necessary in order to use LPG without incident.
• The storage of these fuels can result in accidents with explosions and poisoning of the atmosphere and groundwater.

Biomass, biofuels, and vegetable oil

Biomass production involves using garbage or other renewable resources such as corn or other vegetation, to generate electricity. When garbage decomposes the methane produced is captured in pipes and later burned to produce electricity. Vegetation and wood can be burned directly, like fossil fuels, to generate energy, or processed to form alcohols.

Vegetable oil is generated from sunlight and CO2 by plants. It is safer to use and store than gasoline or diesel as it has a higher flash point. Straight vegetable oil works in diesel engines if it is heated first. Vegetable oil can also be transesterified to make biodiesel which burns like normal diesel.

Pros

• Biomass production can be used to burn organic waste products resulting from agriculture. This type of recycling encourages the philosophy that nothing on this Earth should be wasted. The result is less demand on the Earth's resources, and a higher carrying capacity for Earth because non-renewable fossil fuels are not consumed.
• Biomass is abundant on Earth and is generally renewable. In theory, we will never run out of organic waste products as fuel, because we are continuously producing them. In addition, biomass is found throughout the world, a fact that should alleviate energy pressures in third world nations.
• When methods of biomass production other than direct combustion of plant mass, such as fermentation and pyrolysis, are used, there is little effect on the environment. Alcohols and other fuels produced by these alternative methods are clean burning and are feasible replacements to fossil fuels.

• Since CO2 is first taken out of the atmosphere to make the vegetable oil and then put back after it is burned in the engine, there is no net increase in CO2. So vegetable oil does not contribute to the problem of greenhouse gas.
• Vegetable oil has a higher flash point and is safer than most fossil fuels.
• Transitioning to vegetable oil could be relatively easy as biodiesel works where diesel works, and straight vegetable oil takes relatively minor modifications.
• The World already produces more than 100 billion gallons a year for food industry, so we have experience making it.
• Algaculture has the potential to produce far more vegetable oil per acre than current plants.
• Infrastructure for biodiesel around the World is significant and growing.

Cons

• Direct combustion without emissions filtering generally leads to air pollution similar to that from fossil fuels.
• Producing liquid fuels from biomass is generally less cost effective than from petroleum, since the production of biomass and its subsequent conversion to alcohols is particularly expensive.
• Some researchers claim that, when biomass crops are the product of intensive farming, ethanol fuel production results in a net loss of energy after one accounts for the fuel costs of fertilizer production, farm equipment, and the distillation process.
• Direct competition with land use for food production.

• Current production methods would require enormous amounts of land to replace all gasoline and diesel. With current technology, it is unfeasible for biofuels to replace the demand for petroleum.
• Growth in vegetable oil production is already resulting in deforestation.
• Converting forest land to vegetable oil production can result in a net increase in CO2.
• Demand for vegetable oil used as a fuel may drive up prices of vegetable oils in the food industry
• Costs to modify existing engines may outweigh fuel cost savings

Hydroelectric energy

In hydro energy, the gravitational descent of a river is compressed from a long run to a single location with a dam or a flume. This creates a location where concentrated pressure and flow can be used to turn turbines or water wheels, which drive a mechanical mill or an electric generator.

Pros

• Hydroelectric power stations can promptly increase to full capacity, unlike other types of power stations. This is because water can be accumulated above the dam and released to coincide with peaks in demand.
• Electricity can be generated constantly, so long as sufficient water is available.
• Hydroelectric power produces no primary waste or pollution.
• Hydropower is a renewable resource.
• Hydroelectricity assists in securing a country's access to energy supplies.

Cons

• The construction of a dam can have a serious environmental impact on the surrounding areas. The amount and the quality of water downstream can be affected, which affects plant life both aquatic, and land-based. Because a river valley is being flooded, the delicate local habitat of many species are destroyed, while people living nearby may have to relocate their homes.
• Hydroelectricity can only be used in areas where there is a sufficient supply of water.
• Flooding submerges large forests (if they have not been harvested). The resulting anaerobic decomposition of the carboniferous materials releases methane, a greenhouse gas.
• Dams can contain huge amounts of water. As with every energy storage system, failure of containment can lead to catastrophic results, e.g. flooding.
• Hydroelectric plants rarely can be erected near load centres, requiring large transmission lines.

Nuclear energy

Nuclear power stations use nuclear fission to generate energy by the reaction of uranium-235 inside a nuclear reactor. The reactor uses uranium rods, the atoms of which are split in the process of fission, releasing a large amount of energy. The process continues as a chain reaction with other nuclei. The heat released heats water to create steam, which spins a turbine generator, producing electricity. A relatively small number of nuclear power plants (about 50) has the potential to supply the entire U.S.

Depending on the type of fission fuel considered, estimates for existing supply at known usage rates varies from several decades for the currently popular Uranium-235 to thousands of years for uranium-238. At the present use rate, there are (as of 2007) about 70 years left of known uranium-235 reserves economically recoverable at an uranium price of US$ 130/kg. The nuclear industry argue that the cost of fuel is a minor cost factor for fission power, more expensive, more difficult to extract sources of uranium could be used in the future, such as lower-grade ores, and if prices increased enough, from sources such as granite and seawater. Increasing the price of uranium would have little effect on the overall cost of nuclear power; a doubling in the cost of natural uranium would increase the total cost of nuclear power by 5 percent. On the other hand, if the price of natural gas was doubled, the cost of gas-fired power would increase by about 60 percent.

Opponents on the other hand argue that the correlation between price and production is not linear,but as the ores concentration are becoming smaller,the difficulty(energy , and resource consumption are increasing,while the yields are decreasing) of extraction is rising very fast,and that the assertion that a hear price will yield more uranium is overly optimistic,for example a ruffle estimate predicts that the extraction of uranium from granite will consume at least 70 times more energy then what it will produce in a reactor,seawater seems to be equally dubious as a source. As a consequence an eventual doubling in the price of uranium will give a marginal increase in the the volumes that are being produced.

Another alternative would be to use thorium as fission fuel. Thorium is three times more abundant in Earth's crust than uranium, and much more of the thorium can be used (or, more precisely, converted into Uranium-233 and then used).

Current light water reactors burn the nuclear fuel poorly, leading to energy waste. Nuclear reprocessing or burning the fuel better using different reactor designs would reduce the amount of waste material generated and allow better use of the available resources. As opposed to current light water reactors which use uranium-235 (0.7 percent of all natural uranium), fast breeder reactors convert the more abundant uranium-238 (99.3 percent of all natural uranium) into plutonium for fuel. It has been estimated that there is anywhere from 10,000 to five billion years worth of Uranium-238 for use in these power plants . Breeder technology has been used in several reactors. However, the breeder reactor at Dounreay in Scotland, Monju in Japan and the Superphénix at Creys-Malville in France, in particular, have all had difficulties and were not economically competitive and have been decommissioned. The People's Republic of China intends to build breeders.

The possibility of nuclear meltdowns and other reactor accidents, such as the Three Mile Island accident and the Chernobyl disaster, have caused much public fear. Research is being done to lessen the known problems of current reactor technology by developing automated and passively-safe reactors. Historically, however, coal and hydropower power generation have both been the cause of more deaths per energy unit produced than nuclear power generation. Various kinds of energy infrastructure might be attacked by terrorists, including nuclear power plants, hydropower plants, and liquified natural gas tankers. Nuclear proliferation is the spread from nation to nation of nuclear technology, including nuclear power plants but especially nuclear weapons. New technology like SSTAR ("small, sealed, transportable, autonomous reactor") may lessen this risk.

The long-term radioactive waste storage problems of nuclear power have not been fully solved. Several countries have considered using underground repositories. Nuclear waste takes up little space compared to wastes from the chemical industry which remain toxic indefinitely. Spent fuel rods are now stored in concrete casks close to the nuclear reactors. The amounts of waste could be reduced in several ways. Both nuclear reprocessing and fast breeder reactors could reduce the amounts of waste. Subcritical reactors or fusion reactors could greatly reduce the time the waste has to be stored. Subcritical reactors may also be able to do the same to already existing waste. The only way of dealing this wastes today is by geological storage.

The economics of nuclear power is not simple to evaluate, because of high capital costs for building and very low fuel costs. Comparison with other power generation methods is strongly dependent on assumptions about construction timescales and capital financing for nuclear plants. See Economics of new nuclear power plants.

Depending on the source different energy return on energy investment (EROI) are claimed. Advocates (using life cycle analysis) argue that it takes 4-5 months of energy production from the nuclear plant to fully pay back the initial energy investment. Opponents claim that it depends on the grades of the ores ,the fuel came from, so a fully pay back can vary from 10 to 18 years,and that the advocates claim was based on the assumption of high grade ores(the yields are getting worst ,as the ores are leaner ,for less then 0.02% ores,the yield is less then 50%).

Advocates also claim that it is possible to relatively rapidly increase the number of plants. Typical new reactor designs have a construction time of three to four years. In 1983, 43 plants were being built, before an unexpected fall in fossil fuel prices stopped most new construction. Developing countries like India and China are rapidly increasing their nuclear energy use. However, a Council on Foreign Relations report on nuclear energy argues that a rapid expansion of nuclear power may create shortages in building materials such as reactor-quality concrete and steel, skilled workers and engineers, and safety controls by skilled inspectors. This would drive up current prices.

Pros

• The energy content of a kilogram of uranium or thorium, if spent nuclear fuel is reprocessed and fully utilized, is equivalent to about 3.5 million kilograms of coal.

• The cost of making nuclear power, with current legislation, is about the same as making coal power, which is considered very inexpensive (see Economics of new nuclear power plants). If a carbon tax is applied, nuclear does not have to pay anything because nuclear does not emit toxic gases such as CO₂, NO, CO, SO₂, arsenic, etc. that are emitted by coal power plants.

• Nuclear power plants are guarded with the nuclear reactor inside a reinforced containment building, and thus are relatively impervious to terrorist attack or adverse weather conditions (see Nuclear safety in the U.S.).

• Because of the fear of a nuclear disaster, nuclear safety has become a major issue.

• Nuclear power does not produce any primary air pollution or release carbon dioxide and sulfur dioxide into the atmosphere. Therefore, it contributes only a small amount to global warming or acid rain.

• Coal mining is the second most dangerous occupation in the United States. Nuclear energy is much safer per capita than coal derived energy.

• For the same amount of electricity, the life cycle emissions of nuclear is about 4% of coal power. Depending on the report, hydro, wind, and geothermal are sometimes ranked lower, while wind and hydro are sometimes ranked higher (by life cycle emissions).

• According to a Stanford study, fast breeder reactors have the potential to power humans on earth for billions of years, making it sustainable.

Cons

• The operation of an uncontained nuclear reactor near human settlements can be catastrophic, as shown by the Chernobyl disaster in the Ukraine (former USSR), where large areas of land were affected by radioactive contamination.

• Waste produced from nuclear fission of uranium is both poisonous and highly radioactive, requiring maintenance and monitoring at the storage sites. Moreover, the long-term disposal of the long-lived nuclear waste causes serious problems, since (unless the spent fuel is reprocessed) it takes from one to three thousand years for the spent fuel to come back to the natural radioactivity of the uranium ore body that was mined to produce it.

• There can be connections between nuclear power and nuclear weapon proliferation, since many reactor designs require large-scale uranium enrichment facilities. While civilian nuclear facilities are normally overseen internationally by the IAEA, several countries with such facilities refuse oversight.

• Large capital cost. Building a nuclear power plant requires a huge investment and the costs of safe disassembling (called decommissioning) after it reaches end of usable life must be factored into the full lifecycle budget (see Economics of new nuclear power plants).

• Nuclear fuels are a non-renewable energy source, with unknown high concentration ore reserves. There is a large amount of trace concentration nuclear material in seawater and most rocks; however, extraction from these is not currently economically competitive.

• The limited liability for the owner of a nuclear power plant in case of a nuclear accident differs per nation while nuclear installations are sometimes built close to national borders.

• Waste heat disposal becomes an issue at high ambient temperature thus at a time of peak demand the reactor may need to be shut down or have reduced output

Fusion power

Fusion power could solve many of the problems of fission power (the technology mentioned above) but, despite research having started in the 1950s, no commercial fusion reactor is expected before 2050 . Many technical problems remain unsolved. Proposed fusion reactors commonly use deuterium, an isotope of hydrogen, as fuel and in most current designs also lithium. Assuming a fusion energy output equal to the current global output and that this does not increase in the future, then the known current lithium reserves would last 3000 years, lithium from sea water would last 60 million years, and a more complicated fusion process using only deuterium from sea water would have fuel for 150 billion years.

Wind power

This type of energy harnesses the power of the wind to propel the blades of wind turbines. These turbines cause the rotation of magnets, which creates electricity. Wind towers are usually built together on wind farms.

Pros

• Wind power produces no water or air pollution that can contaminate the environment, because there are no chemical processes involved in wind power generation. Hence, there are no waste by-products, such as carbon dioxide.

• Power from the wind does not contribute to global warming because it does not generate greenhouse gases.

• Wind generation is a renewable source of energy, which means that we will never run out of it.

• Wind towers can be beneficial for people living permanently, or temporarily, in remote areas. It may be difficult to transport electricity through wires from a power plant to a far-away location and thus, wind towers can be set up at the remote setting.

• Farming and grazing can still take place on land occupied by wind turbines.

• Those utilizing wind power in a grid-tie configuration will have backup power in the event of a grid outage.

• Due to the ability of wind turbines to coexist within agricultural fields, siting costs are frequently low.

Cons

• Wind is unpredictable, therefore wind power is not predictably available. When the wind speed decreases less electricity is generated.

• Wind farms may be challenged in communities that consider them an eyesore or view obstructor.

• Wind farms, depending on the location and type of turbine, may negatively affect bird migration patterns and may pose a danger to the birds themselves. Newer, larger wind turbines have slower moving blades which are visible to birds.

Solar power

Solar power involves using solar cells to convert sunlight into electricity, using sunlight hitting solar thermal panels to convert sunlight to heat water or air, using sunlight hitting a parabolic mirror to heat water (producing steam), or using sunlight entering windows for passive solar heating of a building. It would be advantageous to place solar panels in the regions of highest solar radiation. In the Phoenix, Arizona area, for example, the average annual solar radiation is 5.7 kWh/m2/day , or 2080.5 kWh/m2/year. Electricity demand in the continental U.S. is 3.7*10¹² kW·h per year. Thus, at 100% efficiency, an area of 1.8x10^9 sq. m (around 700 sq miles) would need to be covered with solar panels to replace all current electricity production in the US with solar power, and at 20% efficiency, an area of approximately 3500 sq miles (3% of Arizona's land area). The average solar radiation in the United States is 4.8 kwh/m2/day , but reaches 8-9 kWh/m2/day in parts of Southwest.

The monetary cost, assuming $500/meter², would be about $5-10 trillion dollars.

Pros

• Solar power imparts no fuel costs.
• Solar power is a renewable resource. As long as the Sun exists, its energy will reach Earth.
• Solar power generation releases no water or air pollution, because there is no combustion of fuels.
• In sunny countries, solar power can be used in remote locations, like a wind turbine. This way, isolated places can receive electricity, when there is no way to connect to the power lines from a plant.
• Solar energy can be used very efficiently for heating (solar ovens, solar water and home heaters) and daylighting.
• Requires no fuel.
• Coincidently, solar energy is abundant in regions that have relatively largest number of people living off grid - in developing regions of Africa, Indian subcontinent and Latin America. Hence cheap solar, when availabile, opens the opportunity to enhance global electricity access considerably, and possibly in a relatively short time period.

Cons

• Solar electricity is expensive compared to grid electricity.
• Solar heat and electricity are not available at night and may be unavailable due to weather conditions; therefore, a storage or complementary power system is required for most applications.
• Limited power density: Average daily insolation in the contiguous U.S. is 3-7 kW·h/m² (see picture)
• Solar cells produce DC which must be converted to AC (using a grid tie inverter) when used in currently existing distribution grids. This incurs an energy loss of 4-12%.
• A photovoltaic power station is expensive to build, and the energy payback time - the time necessary for producing the same amount of energy as needed for building the power device - for photovoltaic cells is about 1-5 years, depending primarily on location.
• Solar panels collect dust and require cleaning. Dust on the panels significantly reduces the transfer of energy from solar radiation to electric current.

Geothermal energy

Geothermal energy harnesses the heat energy present underneath the Earth. The hot rocks heat water to produce steam. When holes are drilled in the region, the steam that shoots up is purified and is used to drive turbines, which power electric generators. When the water temperature is below the boiling point of water a binary system is used. A low boiling point liquid is used to drive a turbine and generator in a closed system similar to a refrigeration unit running in reverse.

Pros

• Geothermal energy does not produce air or water pollution if performed correctly.
• Geothermal power plants run continuously day and night with an uptime typically exceeding 95%.
• Once a geothermal power station is implemented, the energy produced from the station is practically free. A small amount of energy is required in order to run a pump, although this pump can be powered by excess energy generated at the plant.
• Geothermal power stations are relatively small, and have a lesser impact on the environment than tidal or hydroelectric plants. Because geothermal technology does not rely on large bodies of water, but rather, small, but powerful jets of water, like geysers, large generating stations can be avoided without losing functionality.

Cons

• Geothermal energy extraction is only practical in certain areas of the world, usually volcanic, where the heated rock is sufficiently close to the surface such as to be reached by current drilling technology . Enhanced geothermal technology uses deeper drilling and water injection to generate geothermal power in areas where the earth's crust is thicker.
• Drilling holes underground may release hazardous gases and minerals from deep inside the Earth. It can be problematic to dispose of these subsidiary products in a safe manner.ss

Hydrogen economy

Hydrogen can be manufactured at roughly 77 percent thermal efficiency by the method of steam reforming of natural gas . When manufactured by this method it is a derivative fuel like gasoline; when produced by electrolysis of water, it is a form of chemical energy storage as are storage batteries, though hydrogen is the more versatile storage mode since there are two options for its conversion to useful work: (1) a fuel cell can convert the chemicals hydrogen and oxygen into water, and in the process, produce electricity, or (2) hydrogen can be burned (less efficiently than in a fuel cell) in an internal combustion engine.

Pros

• Hydrogen is colorless, odorless and entirely non-polluting, yielding pure water vapor (with minimal NOx) as exhaust when combusted in air. This eliminates the direct production of exhaust gases that lead to smog, and carbon dioxide emissions that enhance the effect of global warming.
• Hydrogen is the lightest chemical element and has the best energy-to-weight ratio of any fuel (not counting tank mass).
• Hydrogen can be produced anywhere; it can be produced domestically from the decomposition of water. Hydrogen can be produced from domestic sources and the price can be established within the country.
• Electrolysis combined with fuel-cell regeneration is more than 50% efficient.

Cons

• Other than some volcanic emanations, hydrogen does not exist in its pure form in the environment, because it reacts so strongly with oxygen and other elements.
• It is impossible to obtain hydrogen gas without expending energy in the process. There are three ways to manufacture hydrogen;
  • By breaking down hydrocarbons — mainly methane. If oil or gases are used to provide this energy, fossil fuels are consumed, forming pollution and nullifying the value of using a fuel cell. It would be more efficient to use fossil fuel directly.
  • By electrolysis from water — The process of splitting water into oxygen and hydrogen using electrolysis consumes large amounts of energy. It has been calculated that it takes 1.4 joules of electricity to produce 1 joule of hydrogen (Pimentel, 2002).
  • By reacting water with a metal such as sodium, potassium, or boron. Chemical by-products would be sodium oxide, potassium oxide, and boron oxide. Processes exist which could recycle these elements back into their metal form for re-use with additional energy input, further eroding the energy return on energy invested.
• There is currently modest fixed infastructure for distribution of hydrogen that is centrally produced, amounting to several hundred kilometers of pipeline. An alternative would be transmission of electricity over the existing electrical network to small-scale electrolyzers to support the widespread use of hydrogen as a fuel.
• Hydrogen is difficult to handle, store, and transport. It requires heavy, cumbersome tanks when stored as a gas, and complex insulating bottles if stored as a cryogenic liquid. If it is needed at a moderate temperature and pressure, a metal hydride absorber may be needed. The transportation of hydrogen is also a problem because hydrogen leaks effortlessly from containers.
• Some current fuel cell designs, such as proton exchange membrane fuel cells, use platinum as a catalyst. Widescale deployment of such fuel cells could place a strain on available platinum resources. Reducing the platinum loading, per fuel cell stack, is the focus of R&D.
• Electricity transmission and battery electric vehicles are far more efficient for storage, transmission and use of energy for transportation, neglecting the energy conversion at the electric power plant. As with distributed production of hydrogen via electrolysis, battery electric vehicles could utilize the existing electricity grid until widespread use dictated an expansion of the grid.

Source: Wikipedia (All text is available under the terms of the GNU Free Documentation License and Creative Commons Attribution-ShareAlike License.)