ities are, by their nature, the main consumers of energy for dwellings, factories, public buildings, public services (such as water and wastewater treatment plants and pumps), streets lighting, public buildings lighting, electric trains and subways, trams, and to power thousands of electronic equipment such as computers, printers, copying machines, etc. In some cases energy is produced in the city using coal, oil or gas to fire boilers that generate steam for turbo-generators and/or diesel fuel to operate prime movers. This is energy in form of electricity, but there is also need of energy in form of fuels to power cars, buses, diesel trains, trucks, etc.

Two centuries ago, energy requirements were modest; a city had little energy needs other that gas lamps, candles made from animal fat, and coke for heating, but nowadays, life would be impossible without energy, since it permeates all aspects of our existence.

There are several forms by which a city can get the necessary electric energy, which is usually taken from a national grid, and perhaps generated hundreds of kilometers away. In this context, a city can get energy not only through the electric plants, but too from nuclear, hydro or solar, wind, or sea wave's sources. The same applies to fuels used in cars, trucks and factories. From this point of view a city is energy dependent on the energy availability of the grid, which sometimes can be greatly reduced by abnormal conditions, for instance a very cold winter or a very hot summer that implies the massive use of electric equipment that have high energy consumption.

Mankind is facing at present the threat of an oil shortage in not a very long time, but even if new oil and gas fields were found and with a high yield, this is not the solution for our thirst of energy. The reasons are two folds: a) we need to save the remaining oil resources for generations to come and b) we can't continue in polluting and contaminating the earth environment with noxious discharges produced by fossil fuels.

Which is then the solution? There are many options available, like:

•  Research to develop nuclear fusion energy, which will be inexhaustible and producing no pollution. This research is now decades old but until now the energy produced using plasma for instance, is much less than the energy needed to generate it. For this reason a gigantic international effort is taken place at present to built a US$ 10 billion International Thermonuclear Experimental Reactor (ITER) in Cadarache , France.

•  Large installation using sea tides have been built in France and Canada . It is interesting to learn that there are not many suitable places to use this type of source, and one of those few places is located in Argentina , in the Valdez Peninsula.

 •  Energy using sea waves. There are already operating installations in Scotland .

 •  Solar energy, in the form of ‘dishes', or mirrors, collecting sun rays and directing then to a tower where a fluid is superheated and then used to boil water, producing steam to power steam turbine-generators. There are several installations of this type around the world, mainly in California and in Spain . See picture of the San Lucar plant near Sevilla.

San Lucar Plant -
A: Tower receiving the reflected sun energy
B: Mirrors tracking the daily movement of sun and reflecting in the tower

•  Photovoltaic energy, that is the use of solar rays to directly produce energy using the photovoltaic effect. There are many installations of this type around the world, and Germany is the country with the largest percentage of installations

•  Wind energy. The most promising source of energy. There are thousands of installations around the world. The most advanced country in developing this technology is Denmark , and Germany has the largest wind installations in the world. The picture shows a wind farm, in Jaisalmer, West India

Wind farm in Jaisalmer- West India

•  Using small hydro units in those places where the steep terrain allows for rapid water flows. This is one of the oldest forms of energy generation.

•  There are large compact plants using one of the most promissory sources of energy: Hydrogen, in the so-called fuel cells. This is the same principle used in some experimental cars and in some buses that have been operating in Canada and Spain for more than five years now, using hydrogen as a fuel. Therefore, albeit it appears to be the solution of most of our problems, unfortunately it is not so. The discharge of a fuel cell is only pure hot water, which of course is good; however, there is a problem: the fuel.

•  Hydrogen is not like other chemical elements or products such as copper, coal or gas, which can be found alone. Hydrogen has to be produced, usually from sea water, but, to do so, energy is needed. Therefore, the problem lies in the fact that to produce that energy we need fossil fuels such as coal, oil or gas. True, but not quite. If the needed energy is generated through renewable sources such as any of the above mentioned, then, we will be able to run our cars and trucks, light our houses and run some factories with a very clean energy.

Of course, this is extremely important in cities, which are the most polluting entities in the world. The following figure sketches the principle of a fuel cell

Diagram of a fuel cell (PEM)

•  Biomass: Using any natural residues such as bark, sawdust, organic matter found everywhere, human and animal wastes, etc. methane can be produced (which is generated in a natural way anyway). We can use this methane to produce electricity burning it for instance in reciprocating engines. Landfills are responsible for a very large amount of methane produced naturally in earth by the breakdown of organic matter (paper, cardboard, grass, trimmings, food, etc, which constitute the highest percentage of the matter deposited in a landfill), through anaerobic bacteria.

This also has a tremendous advantage. By collecting methane from a landfill and burning it, we are contributing in decreasing the greenhouse effect, because methane, together with carbon dioxide, is one of the main (in reality methane is the most important because its effects in the upper atmosphere, and several times more harmful than carbon dioxide), producers of global warming to which is attributed the melting of the poles and climate change all over the world. This procedure is already followed in many cities around the world, albeit, of course, it could be better, as it is said in other paper, not to produce methane at all by eliminating landfills, through reducing consumption, reusing and recycling.

•  Biofuels: Fuel obtained from biomass. They have the advantage that reduce air pollution in a high percentage, because they do not add carbon dioxide to the atmosphere. Main biofuels are ethanol (in reality and alcohol), and biodiesel. The first one is obtained by the process of fermentation of biomass using sugar cane or barley as feedstock, and is used blended with gasoline.

Biodiesel is obtained by a different chemical process which combines methanol with recycled restaurant grease, or new and used vegetable oil - for instance soybean oil - and animal fat, and can be used as a fuel or mixed with others. When biodiesel is burnt alone it can reduce carbon dioxide emissions in a 75 % regarding a fossil fuel engine

The purpose of this summary of information about energy is to show that we need to change our way to generating energy, and that there are many options other than fossil fuels and most important, that a city at global scale can contribute to energy saving by adopting one or several of the alternatives above indicated. However, probably the most important thing is missing in the sense that everyone in a city must be energy conscious in reducing energy consumption, at home, in the office, in the trip to work and in the factory. There are several measures when a citizen can mark a difference, because it is the coordinated effort of everybody which helps in saving electricity. Some of these simple but effective measures are:

•  Changing light bulbs at home for more efficient types
•  Buy only electrical appliances with the following label

Energy Star Label
Source: U.S. Environmental Protection Agency – U.S Department of Energy

And using the following Guide when purchasing appliances:

•  Estimated energy consumption on a scale showing a range for similar models
•  Estimated yearly operating cost based on the national average cost of electricity.

Energy Guide Label
Source: U.S. Department of Energy – Energy Efficiency and Renewable Energy

•  Upgrading street lighting. That is replacing the old lamps by more modern devices, and with improved design of light poles to take maximum advantage of light produced. According to Phillips (2007)

“The potential for both energy savings and cost savings for Europe 's municipalities are very significant. Figures show cost savings of more than a billion euros per year are possible by upgrading to new street lighting. The savings also offer environmental benefits and help meet Kyoto commitments for CO2 emission reductions. This is yet another example where economic and ecological interests have merged

•  Programing cloth washing a home in order to maximize the load in the washer and dryer
•  Taking shorter showers which will contribute to save energy in water heating and water
•  Lowering the temperature of the air heater at night
•  Putting off lights when leaving a room
•  Installing movement detectors in hallways and corridors in your apartment building in order to get light only when it is necessary
•  Using automatic disconnecting devices in the office and at home when computers are left without action for a certain period.
•  Stopping the practice of leaving the lights on in public buildings and offices an nights and during week ends.
•  Using cars in a sustainable manner, that is carpooling
•  Using parking lots in train or subway stations to board a train or a subway, instead of driving to downtown.
•  Developing plans at schools to teach children the importance of energy saving

As a bottom line, energy is a complicated issue that can be effectively managed at City Hall level, but for that it is essential people's collaboration. Every single watt saved is worth the effort.

References:

Source: Phillips (2006) – Press Release
Title: European Cities are installing new generation of energy efficient Street Lighting