(CNN) -- The sun, we are frequently told, is the best source of energy there is -- so much so that in just one hour it can provide the earth with all the energy its inhabitants demand in a year. Not only can the sun provide us with all of our energy needs (10,000 times over in fact, according to Greenpeace) but it can also apparently do this without any of those unpleasant side effects that you get from fossil fuels such as air pollution or ozone depletion. And best of all, this resource will never run out -- or at least, not in the next 5 billion years or so.
A warehouse covered with solar panels in Germany, the world's biggest solar energy producer
As a resource, solar energy has many useful functions -- predominantly the generation of heat and light, but it can also fly our planes, drive our cars and desalinate our water. When doing a like-for-like comparison with the resources we usually draw on to fulfill these roles, the argument for solar energy becomes even more compelling. According to the U.S.-based Union of Concerned Scientists, for instance, the energy we get from all of the world's reserves of coal, oil and natural gas can be matched by just 20 days' supply of sunshine.
But if you equate the level of seriousness with which world governments treat solar power with the actual amount of solar energy generated globally, the figures aren't that reassuring. According to the BP Statistical Review of World Energy 2007, solar, wind and geothermal combined only account for around 1 percent of the world's electricity generation, with the International Energy Agency (IEA) putting solar power's contribution to the global energy supply at just 0.039 percent. In the United States, solar power meets less than 0.01 percent of electricity needs, according to the Los Angeles Times.
Even Germany -- which, according to the Washington Post, supplied around 50 percent of the world's solar power-generated electricity last year -- doesn't use a whole lot of it at home. Solar makes up a relatively small proportion of the 7 percent that renewable energy contributes to the country's energy needs.
Solar power comes with many complex issues that suggest it may not necessarily be the panacea it seems at first glance.
The first obvious problem, some say, is that when it comes to power generation, photovoltaic (PV) cells (i.e., solar panels) can only work efficiently when the sun is shining. And that means certain parts of the world are supposedly more suitable for mass-scale PV plants than others. That being said, the world's leader in solar energy production is none other than Germany.
In order to tackle the problem of how to maintain a solar energy supply sun or no sun, there have been developments under way to store existing solar energy in a way which can get round the problem of unpredictable weather. According to PlanetArk.com, the Anglo-German utility company E.ON AG has, for example, has developed a battery with the power of 10 million standard AA batteries. The battery is capable of producing 1MW of electricity for four hours -- electricity that has been previously harnessed from the sun (or wind), and stored.
Another problem, some argue, is space. A recent study by the Rockefeller University in New York found that for solar energy to meet current U.S. electricity needs for just one year, it would require PV cells covering an area of 150,000 square kilometers.
Critics of the study retorted: In a country the size of the U.S. -- at 3.7 million square miles -- how big a deal is 150,000 sq km?
The issue concerns the amount of land which is actually available for such an endeavor -- without creating added harm to the environment (destroying forests to make way for solar plants, for example, wouldn't make much sense). Keeping in mind ongoing population growth with increasing urbanization and the increased adoption of land for farming (particularly with the growing interest in biofuels), the amount of space available for a large-scale project such as solar plants gets much smaller.
Making a comparison of solar and nuclear energy, the Rockefeller report says that to match the power-producing capabilities of one liter of fuel in the core of a nuclear reactor, for example, would take one hectare's worth of PV cells.
Sunshine and space is more of a problem to some countries than others, so many assume that only countries with an extensive land mass and guaranteed good weather are worthy bases for solar power generation. But according to Greenpeace, the small and often overcast United Kingdom could meet two-thirds of its electricity needs with solar panels -- on roofs of existing buildings, negating the need to find space for solar plants.
But there is one area of the world, some are saying, which does meet solar power's two basic needs of sunshine and lots of space: The Sahara Desert. According to the United Nations Environment Report, released in 2006, an area of 640,000 square kilometers could provide the world with all of its electricity needs (the Sahara is more than 9 million square kilometers in size).
The IEA has also said that if just 4 percent of the world's deserts were covered with PV installations, the world's main energy needs would be met. Opponents to such a centralized supply of energy, however, have one key objection: it would be too easy a target for terrorists.
There are also those who are even suggesting that solar energy could be more damaging to the environment than the end benefits it would provide. The Rockefeller report points out that installing such ambitious new energy infrastructure would require "a massive infrastructure, including steel, metal, pipes, cables, concrete, and access roads."
Building massive solar plants would also require large amounts of resources such as silicon and plastic. And this is where perhaps the biggest problem constraining the development of solar power lies. A strain on depleting resources -- such as silicon and plastic (ie oil) -- is pushing up costs, which is hindering growth, and ultimately putting them out of reach for the average consumer, even in rich countries.
Homeowners in the developed world have been reluctant to pay for solar panels to be installed on their buildings while costs remain so high. And according to a report by Greenpeace and the Chinese Renewable Energy Industry Association, China exports a staggering 90 percent of its PV cell solar output -- because its citizens can't afford to use it.
Ultimately businesses only invest in products that make economic sense, so while costs remain high, investment in solar energy will reflect that (as Exxon Mobil's head of public affairs told The Economist in an interview, "Exxon was a big investor in solar in the 1970s. We got out of it because we couldn't make any money out of it.").
However, according to Friends of the Earth, the solar Photovoltaic industry is now the fastest growing renewable energy technology on earth, showing a market growth of 60 percent between the years 2000-2004.
The future may still be bright. The World Bank believes the global market for solar electricity will be worth $4 trillion in 30 years. And a recent report by Greenpeace and the European Photovoltaic Industry Association (EPIA), believes that solar power will be able to power 2 billion people's lives by 2030. E-mail to a friend
(Sources: The Guardian; Union of Concerned Scientists; Greenpeace; LiveScience.com; Reuters; New York Times; Los Angeles Times; Washington Post; Food and Agriculture Organization of the United Nations; Znet; The Economist; BP Statistical Review of World Energy 2007)