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Our planet consists of an almost isolated system with finite resources that are incapable of supporting increased demand indefinitely. Until now, air, water, energy and food have been regarded as essentially plentiful and nearly inexhaustible, our access to them being limited only by our technological capacity to extract and use them. The necessary transformation into a “zero growth” society characterized by greater frugality in our use of resources, where products must be recycled at the lowest cost possible, is daunting.
The widespread use of fossil fuels beginning with the Industrial Revolution has improved our quality of life, but it has also resulted in a drastic change in our use of water resources, our health and services in general, which must accommodate a demographic explosion the likes of which mankind has never known. This technological development started by the Industrial Revolution has led to a great capacity for altering and attacking the environment which has dramatically endangered the very ecological niche which for hundreds of thousands of years has allowed man to develop.
Water and energy are critical not only to our well-being, but to our survival as a society and a species. Our society’s economic structure, dependent on constant development with endless resources, seems incapable of finding the proper response to the transcendence, urgency and gravity of the situation. The strictly financial objectives shaping a company’s decisions or a political campaign’s four-yearly election goals conceal and cloud the Earth’s most basic needs behind a curtain of peremptory demands which will be handed down to future generations.
The search for solutions must begin with an analysis of the basic schemes for generating, converting, distributing and using energy. The meager overall efficiency of today’s mechanisms and networks point to energy conservation as a first and essential step. We must also consider the planet’s net energy balance so as to identify long-term sources and the available quantities of each, taking into account the needs of the population and existing technologies.
According to estimates, the supply of fossil fuels such as petroleum, coal and natural gas will be exhausted within a few generations. Of note is the enormous amount of energy that is wasted just to process these fuels for consumption: up to 84% in the basic conversion and transportation systems for developed countries. This does not even take into consideration the inefficiency or misuse of the energy by the end user or the specific application.
Within this context, then, it is worth considering that while an input of six units of fuel into the system costs and pollutes the entire six units, only one unit reaches the end user. Simply increasing the efficiency of the conservation system to save one unit would avoid the use and pollution associated with six. The effort to improve energy technology, therefore, is much more worthwhile than the search for new sources.
Life in general, and the human race in particular, has evolved under the sun’s nurturing radiation. The daily, seasonal and yearly changes in the amount of energy received from the sun are responsible for the dynamics in the water, air and carbon cycles on Earth, turning the ancient myths surrounding the four elements into a reality of modern science. Photosynthesis, the complex process by which chlorophyll in organic matter uses the sun’s energy, has a very low efficiency (less than 0.1%) even in comparison to today’s inefficient electrical grids.
The largest source of safe and abundant renewable energy is, without a doubt, direct solar radiation, not only in its sheer quantity in driving all other energy processes, but also in scope since it reaches the planet’s entire surface. Data on our society’s consumption (transportation, residential, industrial) suggest that a fraction of the available solar radiation could satisfy our energy needs if we simply used the technology within our reach.
This is best illustrated by the mere fact that for billions of years, life evolved through the almost exclusive use of the sun’s energy. Perhaps it is time for mankind to turn its eyes skyward once more in search of that energy which has fed its roots since the dawn of time.
Electricity is probably the most flexible conduit for energy known today, due to the ease and efficiency with which it can be transformed for other applications: heating an oven, lighting a bulb, driving an engine, electrolyzing hydrogen for chemical fuel, etc. The direct conversion of solar energy into electricity has been technically feasible for almost two centuries and features efficiencies far above those reached by nature in its synthesis of carbohydrates through photosynthesis in chlorophyll.
In spite of this, the massive use of non-renewable fuels has limited the adoption of this source of energy to a restricted set of marginal applications in which access to chemical fuels or the electrical grid is impossible or impractical: artificial satellites, isolated communications repeaters, remote sensing stations, etc. The photovoltaic phenomenon uses light (ultraviolet, visible and infrared radiation), a semiconductor-metal junction or a junction between two semiconductors (these being the most efficient arrangements) to generate electricity. Commercial solar photovoltaic cells are made using high-purity silicon.
The high demand for silicon in recent years for the generation of photovoltaic electricity has competed with the electronic circuit industry, overwhelming the production capacity of the few factories dedicated to silicon production and refinement. It is imperative, therefore, that research be conducted into alternative materials capable of converting the sun’s energy into electricity using technology that is both efficient and affordable and which, once manufactured, can compete in the marketplace.
The photovoltaic-photoelectrochemical integration in different types of tiles through the use of low cost diode and collector layers and natural raw materials reduces manufacturing costs and yields maximum power through networks of serial and parallel connections. The electrical energy obtained from the electrolysis of water can be stored in a 1-5 kW fuel cell which can then release the energy in the form of electrical current when no electricity is supplied. The result is a casual joining of the ideas of Becquerel, discoverer of the photoelectric effect, and Grove, discoverer of the fuel cell, in the same year, 1839. These two developments combine to yield a solution for self-sustaining energy that is both simple and ideal.
In an electrolytic reaction, the water molecule is separated into its components. The gaseous hydrogen is liberated in the cathode at atmospheric pressure, with small quantities of water vapor and oxygen as by-products. At the same time, a quantity of oxygen gas equivalent to half the volume of the H2 produced is generated in the anode. The process consumes quite a lot of electricity, so it is economically feasible only in those places where electricity is cheap and where the O2 byproduct can be used, with the ensuing added benefit. The H2 resulting from the electrolysis is dried and compressed, and the oxygen impurities are filtered through a catalytic converter.
While the use of hydrogen to power motor vehicles is still in the research and development phase, most automobile manufacturers have developed hydrogen-driven prototypes or concept vehicles which use internal combustion engines in addition to fuel cells. A series of hydrogen-powered vehicles is in the works, as are hydrogen refueling stations which are being installed around the world as part of various projects. Compared to other alternative fuels, hydrogen-powered vehicles are probably the furthest from being marketed. Most manufacturers have shifted their attention from hydrogen-powered internal combustion engines to hydrogen-powered vehicles.
Hydrogen must be stored simply and economically if its use is to be widely adopted. This presents a real challenge compared to fossil fuels due to the low energy density per unit volume of this gas. Hydrogen storage is a common practice in industry, where it is used safely to provide many specific functions. Hydrogen can also be stored easily in vast underground deposits.
The development of hydrogen technologies is following a track similar to that of electricity in the late 19th century. Neither is considered a primary energy source, but rather a mere intermediary in the energy system, whose use requires transformations that reduce the system’s overall efficiency compared to the direct use of the original source directly in the final application. This can complicate matters considerably, making the process costlier and more complex. In spite of this, the technological developments of the 20th century would have been inconceivable without the intervention of electricity as a conduit for the transportation and manipulation of energy, as will probably happen with hydrogen in coming decades.
Although a good portion of the effort going into fuel cell applications have focused on the automotive industry, they could also be quite useful in the residential sector, where they can provide not only energy to heat air or water, but electricity as well. Their silent and pollution-free operation makes fuel cells one of the most appealing systems for providing heat and electrical energy to homes and other buildings, whether public (schools, hospitals, libraries, etc.) or industrial. The waste heat can easily be reused to heat water, and it can even be stored underground or in other tanks, such as those that employ phase change materials.
On a large scale, fuel cells can be used, along with hydrogen generation, to store energy during low-demand periods and to supply that energy when demand increases, as is done now with pumped storage hydroelectric stations. The main obstacle to these applications is price, both of the electrolyzing devices and the electricity for obtaining hydrogen from water, and of the fuel cell to carry out the reverse process.
The direct capture of energy from the sun for storage as heat in the ground or as hydrogen via photovoltaic or electrochemical processes is one possibility within the reach of our current technology which would bring us closer to a generation of self-sufficient buildings.