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7ЭКОЛОГИЧЕСКИЕ АСПЕКТЫ ИСПОЛЬЗОВАНИЯ АЛЬТЕРНАТИВНОЙ ЭНЕРГЕТИКИ, ЭКОЛОГИЯ МЕГАПОЛИСОВ, МАЛЫХ ГОРОДОВ, ДЕРЕВЕНЬ
ECOLOGICAL ASPECTS OF ALTERNATIVE ENERGY AND ECOLOGY OF MEGAPOLISES, CITIES AND VILLAGES
THE GLOBAL STATUS OF RENEWABLE ENERGY TECHNOLOGIES
K. J. Touryan
NREL
1617 Cole Blvd. MS 1635 Golden, CO 80401 Phone: 303-275-3009; fax: 303-275-3040; e-mail: [email protected]
Kennel J. Touryan, Ph. D., Manager, NIS Country Programs, Chief Technology Analyst
As part of the NREL Technology Transfer Team, Ken Touryan manages a variety of technology transfer activities, including NREL's Initiatives for Proliferation Program (IPP). Ken created the IPP program at NREL and has managed this multi-laboratory effort for the past nine years. The IPP program was initiated in 1994 to control and reduce the global threat represented by nuclear, chemical and biological weapons. IPP aims to identify and develop non-military applications for defense technologies and create high-tech commercial employment opportunities for weapons scientists and engineers. Under Ken's leadership, this program has created many successful partnerships between U.S. firms and former weapons scientists, provided synergies with NREL's applied research, and established a unique link between NREL's technical expertise and global security.
The inability of fossil fuels to keep up with the rapidly increasing demand for energy, especially in developing countries, is making imperative the search for alternate energy sources. Renewable technologies, including the use of hydrogen, offer new hope of meeting this increasing demand in significant ways. To this end, we review the status of several of these renewable energy technologies and their readiness to compete in the energy market, in the immediate future.
Introduction
As we enter the 21st century, all indications are that the world will run out of fossil fuels much sooner than past predictions. In fact, most forecast point to the time frame of 2010—2015 when oil production world wide, will peak, and 2020, when natural gas production will peak (Fig. 1). Coal may last until the end of the century, but subject to stringent environmental controls. In fact, there are five global trends that are converging, to make the introduction of new energy technologies, such as renewable energy and hydrogen, viable options to replace a significant portion of the increasing global energy demand. These five are: 1) Increasing environmental awareness specially as it pertains to the emission of green house gases; 2) The availability of new technology options, such as energy from wind, solar, biomass and hydrogen from renewable resources; 3) World energy demand growth, specially in Asia;
4) Increased security risks, with terrorists attacking power oil/gas pipelines, refineries and large power plants, plus uncertainties in the availability of fossil fuel resources caused by political unrest,
Millions of barrels per day (oil equivalent)
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Fig. 1. Source: John F. Bookout (President of Shell USA), "Two Centuries of Fossil Fuel Energy". International Geological Congress, Washington DC; July 10,1985. Episodes, Vol. 12. P. 257-262 (1989).
Статья поступила в редакцию 11.11.2005. The article has entered in publishing office 11.11.2005.
and 5) Increasing business interest in the energy field, with the potential profitable markets for introducing new sources of energy.
It is important to note, that renewable energy RE technologies (RET), including the proposed hydrogen economy, are well poised to respond to the above five challenges. RETs are environmentally far more benign than fossil fuels. Unlike oil and gas resources, they are evenly distributed throughout the world and are available to every country, and they are easier to protect against terrorism, because by their very nature they operate as distributed systems.
Renewable energy resources include: wind, solar, biomass, geothermal, hydro and ocean energy. Because of lack of space, in this paper we will focus on wind, solar and biomass, and only touch upon geothermal, hydro and marine sources of energy. We will also cover briefly, the use of hydrogen as the fuel that can meet future global transportation needs.
Resource Assessment
In order to estimate the viability of using a given renewable energy technology, one needs to gather data on the availability of the resource itself, whether it be wind, solar, biomass, etc., In fact, there are certain minima below which the new technology will not be competitive with fossil fuel sources. For example, at today's cost of electricity, at 4—10 cents a kWhr, wind will become economical only if it is available at 300,000 kWhrs/ year, or more (Fig. 2).
Same goes for the solar insolation. One needs over 2000 solar hours/year, before one can use solar hot water or photovoltaic (PV) power to replace fossil fuels. For each location, careful measurements must be taken, over a period of least a year, plus using meteorological data, covering a period of 10 years, before consideration is given for the use of wind turbines or solar PV panels. At the National Renewable Energy Laboratory (NREL), computerized mapping techniques exist, based on GIS and meteorological data that can be used to obtain global, mesoscale or microscale distribution of winds and/or solar insolation for any country in the world. In addition, NREL has developed software (VIPOR, HOMER and Hybrid 2) that can evaluate the economic feasibility for the use of any renewable technology, in any location, based on input data that includes the local energy resource, the fossil fuel price (or cost of electricity), the availability of a power grid, etc.
Wind Energy
Of all the RETs, wind energy is the most competitive in the present market and has made the widest penetration, to date; 40,000 MW world wide. In 2003, wind provided 15 billion kWhrs of energy world wide at an average cost of 5—6 cents/Whr. Germany is the lead country in the use of wind
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Fig. 2. The costs of diferent forms of renewable energy
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energy, followed by Denmark, Spain, the UK and the USA. The new trend for installing wind farms is the use of very large machines, 1-5 MW per unit, and moving the wind farms, off shore, to conserve space. In addition to larger machines, future innovations include: advanced blade materials and manufacturing, low speed direct drive generators, custom power electronics, feedback control of drive train and rotor loads and more flexible structurally. The target O&M cost for the next generation turbines is 3 cents/kWhr. As far as their environmental impact is concerned, the only issues are the aesthetics of large wind farms near populated areas and bird-kills, especially along bird migration paths.
Solar Thermal Energy
Along with wind energy, the use of solar thermal power for hot water is commercially available and in wide use in temperate climates, such as Israel and Cyprus. Not so for space heating; too costly for Northern climates. The main emphasis these days is on electric power generation using solar energy to heat a working fluid, convert it to steam and run engines or turbines. Three types of concentrating solar power technologies are under development: single-axis tracking parabolic trough systems, dual tracking dishes, or flat plates with Fresno lenses, and power towers (Fig. 3). Trough technology is the most advanced of the above three systems. It has 354 MW of commercial power generation in operation in South West California (Kramer Junction) It operates in a hybrid mode with natural gas, using organic Rankine cycle for power generation. Plans are to install 1000 MW systems by 2010, reducing O&M costs from 12 cents/kWhr to 4 cents/kWhr.
The dual tracking dish systems employ Bray-ton or Sterling cycle engines at their focus, and come in 25-30 kW units. The receiver and generator are integrated into a single assembly that is mounted at the mirrored dish. To reduce the cost of reflectors, glass is replaced by thin reflective polymer membranes stretched across each receiver section, with another membrane stretched on the back, creating a partial vacuum that in turn forms spherical shapes that are ideal for the dish concentrator. Even the Fresno lenses are made of poly-
acrylic material rather than glass, providing up tot 300 sun concentration. Dish concentrator systems are well suited as distributed power generators. The third dual tracking system is the power tower. The Solar Two, 10 MW systems, with 400 heliostats is operational at Dagett California, using molten salt for storage, which is then used to boil water and run a steam turbine. As with the parabolic trough system, power towers can operate in a hybrid mode as solar/fossil plants.
Solar Photovoltaic Energy
Direct conversion of solar energy to electricity, with no moving parts, and no intermediate steps, makes solar photovoltaic technology (PV) the most desirable energy conversion system. Mono-crystalline or poly-crystalline silicon (c-Si) cells represent over 90 % of commercially available PV systems. World PV Cell/module production exceeded 1 GW in 2004 and is growing at the rate of 30-40 % per year. Shortages in the availability of solar grade silicon has led to the development of thin film solar cells such as amorphous Si (a-Si), cadmium telluride cells (CdTe), and gallium indium di-selenide cells (CIGS), Also a new effort is underway for using thin film crystalline Si cells (<100 microns). Of these thin film cells, a-Si cells have the widest commercial application at present. The third type of PV cells is the gallium indium phosphide/GaAS, multij unction cells that operate under 500 suns, with efficiencies approaching 40 %. The most efficient crystalline Si cells are at 25 % and the most efficient thin film cells are closer to 19 % (CdTe cells). Finally, research activities are underway to use organic materials, such as polymers to generate the PV effect. The key parameters for thin films are: high efficiency, availability of abundant, non-toxic materials that are durable and stable.
Because demand of solar cells has always exceeded production (Fig. 4), the cost of cells, per peak watt has remained in the 3-5 cent range. Costs will come down to competitive levels with wind energy, when continuing improvements of cell efficiencies are accompanied by mass production of the solar cells. Another major effort is an innovative mounting system for PV panels that could be
Fig. 3. Three types of concentrating solar power technologies
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□ Rest ofWorld 3 4 4.7 5 4.6 4.4 5.6 6.35 9.75 9.4 18.7 20.5 23.4 32.6 40.7
■ Europe 6.7 7.9 10.2 13.4 16.4 16.6 21.7 20.1 18.8 30.4 33.5 40 60.7 86.4 112
□ Japan 12.8 14.2 16.8 19.9 18.8 16.7 16.5 16.4 21.2 35 49 80 129 171 255
□ United States 11.1 14.1 14.8 17.1 18.1 22.4 25.6 34.8 38.9 51 53.7 60.8 75 100 113
■ Total 33.6 40.2 46.5 55.4 57.9 60.1 69.4 77.6 88.6 126 155 201 288 390 520
Fig. 4. World PV Cell/Module Production in Megawatts (1988-2002)
used for roof or faced mounting, retrofit, or new build. One such integrated system consists of flexible a-Si modules that are mounted onto the tiles thus constituting both a roofing material and power generation unit for the building.
PV cells are energy intensive in their production, Thus, one important consideration for the use of photovoltaics, is the energy payback. For example, for a 20 % efficient cell, the payback in the sunbelt region is 2.5 years and in the northern regions, closer to 5 years. Just for curiosity, in order to generate the entire electric power needs of the USA (3.3 TW) using PV arrays, with 10 % system efficiency at the consumer, one would need an area of 400 by 400 km (four times the size of Belgium).
Energy from Biomass
The traditional use of biomass has always been direct burning of wood and agricultural wastes as fuel. The next two most common approaches are that of gasifying wood (syngas), or biogas production from organic material. The next level of sophistication is the production of ethanol by fermentation of sugars. The most common feedstocks are corn and sugar cane. The obvious advantage of biomass is that it can be converted into transportable fuels; gas or liquid. To that end, the feedstock available for conversion is: trees, grasses, bio-product crops, agricultural crops, agricultural residues, animal wastes and municipal solid wastes.
The conversion processes can be: enzymatic fermentation, gas/liquid fermentation, and acid hydrolysis fermentation, and gasification, product synthesis from syngas, combustion and co-firing. The end products are then: fuels such as ethanol, methanol, hydrogen, electricity, heat and chemicals (plastics, solvents, etc.).
Finally, bio-diesel can replace fossil fuel based diesel, using vegetable oils, mixed with methanol. In the US, 1 % of all commercial trucks run
on bio-diesel, with little or no engine modifications.
Hybrid systems
Renewable resources such as wind, or solar energy, are intermittent or diurnal. When used in a stand-alone mode, they require storage. Storing energy from wind and solar, in batteries, flywheels, pumped hydro, are expensive and cumbersome. A more practical approach would be to connect the wind turbine or the PV array to the electric grid, allowing the utility to 'purchase power' when it i. e. being generated through wind or solar energy. Another approach is to use hybrid power systems, with diesel generators as back up. The advantages are many. They include: use of local renewable resources; can range in size from small household systems (100Wh/day) to ones supplying whole areas (10's of MWhrs/day), and combine many technologies to yield power, tailored to the local resources and the community. Potential components include: PV, wind micro-hydro, river-run hydro, biomass, batteries, and conventional generators (Fig. 5). Under funding from the USDOE, NREL has developed several models for conducting options analysis on any hybrid system,
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Fig. 5. Wind/Diesel/PV hybrid system
in any location to determine the economic viability of the system. These models can be found on the website, under www.nrel.gov (Homer, Viper and Hybrid 2). Using these codes, NREL has sized a number of hybrid systems for villages in all parts of the world...
Life Cycle Analysis
Because renewable resources are diffuse, intermittent and diurnal, it is very important to ensure that the life cycle of the system is a net energy producer, with a reasonableenergy payback. The formula to be used for this analysis can be given by:
Q(net) = Q(rate of production) -- [Q(energy consumed in operation) + E/T],
where E is the energy invested in its production and T is the lifetime.
A series of life cycle assessments (LCA) have been conducted at NREL on biomass, coal, and natural gas systems, including hybrid modes, in order to quantify the environmental benefits and drawbacks of each (Fig. 6). The results show quite clearly that overall, biomass power provides significant environmental benefits over conventional fossil-based power systems, and they consume very small quantities of natural resources and have a net energy balance.
There are four major tracks in the development and use of hydrogen as the replacement fuel for transportation. production, transport, utilization and storage. Developmental work is under way on all four tracks, simultaneously. The traditional source of hydrogen has been from methane, using the steam reform process. The future lies in hydrogen production from renewable resources. These include: photoelectrochemi-cal production from water; photobiological production from algae; from biomass (steam reform process using methane from biomass); solar thermal hydrogen production, and co-production of electricity and hydrogen from renewable technologies, such as wind/PV — electrolysis (Fig. 7).
Fig. 6. A series of life cycle assessments
Benefits of a Hydrogen Economy
As with ethanol and methanol, hydrogen would be a key transportation fuel, which roughly constitutes 1/3 of the world energy consumption. For example, if the US makes full use of hydrogen, from renewable sources, its dependence on oil will be reduced from 20 million barrels a day to 11 million a day. It will give us feedstock diversity, and the power generated can be decentralized, thus meeting a countries energy security requirements. Environmentally, greenhouse gas emissions will be removed, and there will be an improvement of the local air quality. Finally, hydrogen will reduce the balance of payments for country, like the US that imports over 55 % of its oil.
Fig. 7. Wind/PV — electrolysis
Hydrogen, transportation will most probably utilize the existing natural gas pipelines. As for utilization, intense R&D efforts are under way to develop PEM (Proton exchange membrane) Hydrogen fuel cells. These cells combine hydrogen with oxygen to produce electricity, heat and water. The potential benefits of fuel cells are significant; however, many challenges must be overcome before fuel cell systems will be a competitive alternative for customers. Cost, performance and durability of fuel cell components are key areas that need to be addressed.
These components include the PEM membrane, the catalyst, and the bipolar plates. The latter for example should be lightweight, gas impermeable and amenable to mass production.
Significant improvements over currently available hydrogen storage technologies are required if hydrogen is to become a viable energy carrier. Compact, lightweight carbon adsorbent materials have become interesting for possible use in a hydrogen storage system. Of particular interest are the na-nostructure carbons, such as carbon single-walled and multiwalled nanotubes (SWNT and MWNT) that can store significant amounts of hydrogen at room temperature (8—10wt%). These nanotube stacks would then replace the bulky, 5000 psi storage tanks and provide adequate storage in existing auto fuel tanks, replacing gasoline with hydrogen.
Other Renewable Technologies
The renewable energy technologies that we have not talked about are; geothermal energy; small hydro and various marine renewables, such as tidal waves, tidal current turbines and ocean thermal gradient generators.
Work on geothermal energy is ongoing, worldwide. By its very nature, however, geothermal is highly localized, primarily in regions around the Pacific rim, and in other volcanically active regions. Today, 8000 MW electricity is being produced from geothermal power, in 21 countries. There are four types of geothermal resources: hydrothermal; geo-pressurized; hot dry rock, and magma. To extract geothermal power, economically, one needs the overlap of three key parameters. These include high permeability strata, and water saturation at high temperatures (above 120 °C). Limited space here will not allow for a detailed treatment of geothermal source of energy. Suffice it to say that costs in cents per kWhr, has decreased form 10—16 cents, down to 5—8 cents. Work is being done to improve the technology, reduce drilling costs and expand the resource base.
Hydro-power plants represent a mature technology. Work is now being concentrated on the modernization of small hydro power plants, ranging from a low of 100 kW, to 2 MW. These systems use either the run-of-the river resources or submersed dams across the river. The key improve-
ments lie in the production of new turbines with 88—90 % efficiencies. The small hydro potential in Asia, is estimated to be 80,000 MW.
Marine Renewable: tidal waves, ocean currents, ocean waves and ocean thermal gradients are all less developed technologies. England has been lead- R ing the development of oscillating wave generators ^ and tidal current technologies, with other European * countries, Australia and Japan, following suite. = Much work was done in the 70's and 80's using ^ ocean thermal gradient energy conversion, both off- 1 shore and on-shore. These temperature gradients ^ are small, about 20 °C, thermodynamic efficiencies 5 are very low, requiring very large structures for £ generating power. Component tests on these sys- g tems have been done, primarily by the Japanese, but @ they do not constitute a major investment at this time (unlike oscillating wave energy converters).
Concluding remarks
Increasing demand for oil by developing countries, such as China and India, are placing great stress on the world demand for oil. In fact, new predictions place the peak oil production date, closer to 2015 and the peak natural gas production at 2020. It is imperative that world emphasis on the use of renewable technologies and conservation measures be given a careful consideration. As mentioned in the Introduction, five converging factors have made renewable technologies attractive for expanded use, with a reasonable target of 20 % use, globally by 2020.
