The power of the sun
The sun is by far the most important source of energy on earth. The amount of solar radiation that strikes the earth’s surface is more than 10000 times the worldwide energy need, including all types of energy consumptions such as for transportation, industry and residential use.
From all the solar radiation emitted by the sun, only a small fraction is intercepted by the earth, and even this fraction is filtered by our atmosphere, creating the perfect conditions for life on our planet.
Just to give an idea of such a power, the temperature on the sun’s surface is estimated around 5800 ºC, whilst on earth, even in the warmest places of the world, the temperature is rarely above 50 ºC.
Over the centuries, the populations around the globe discovered many uses of this remarkable solar potential, for many purposes. Firstly for seasonal gathering and hunting while most tribes were still nomads, and later for agriculture and food processing, including basic methods such as meat and fruit drying when the first populations started living in the same region for longer periods.
The earth position and rotation around the sun creates the different seasons and climates. The wind formation and raining cycles are all connected to the incident solar irradiation on earth, which heats huge amounts of air mass as well as producing the evaporation of water from lakes, rivers, and oceans, creating a dynamic atmospheric cycle, mainly perceived by us in the form of clouds and rain.
All living beings depend on the sun for survival. The photosynthesis process, for instance, responsible for the plants’ growth, is based on the absorption of solar radiation in small densities over a period of time. The plants then fix carbon dioxide from the atmosphere and use nutrients from the soil for their own growth.
The sun strongly influences the way we live. Cold and warm areas and the seasonal variations over the year are directly related to the position of the sun during that period. In regions close to the equatorial line, more even hours of sun occur throughout the year, whereas in places with high latitude as in northern Europe and the south and north of the Americas, daily lengths can be as short as few hours a day during the winter, and as long as more than 20 hours a day during the summer. Due to this high variation, it is important to understand how the sun affects our lives in order to adapt our way of living to the existing conditions.
Houses, for example, can be built with larger or smaller windows in order to increase or reduce the sun’s influence on the ambient temperature. The position of the house in a cold region can be optimized to absorb a larger fraction of the solar energy during the day.
New technologies in construction and materials were developed in the last century to take advantage of the solar potential for natural illumination, passive cooling or heating, water heating and lately for electricity generation.
This development coincides with the fast growth of the world population and the increasing demand of energy in many forms. In the past decades, a great effort has been undertaken by many nations to provide cleaner technologies for energy production. Solar technologies are already being used and can provide the necessary alternative to fossil fuels. The range of applications is rather vast, from solar heating technologies that can provide temperatures from 30 ºC up to more than 2000 ºC when using concentration of the solar irradiation, to solar cooling systems that use the heat provided by the sun to drive an absorption chiller. Water treatment and desalination can also be performed only using solar energy. The so called solar fuels, such as hydrogen, can be produced using solar energy and are a promising alternative to substitute fossil fuels in various applications.
The most simple and cost effective alternative in relation to the use of conventional electricity or fuels is the implementation of domestic water solar heaters. This type of system is already popular and there are many alternatives available for every kind of budget. The savings in places with a good solar resource can go up to 40% of the electricity bill by replacing the electric heaters used with solar collectors.
The solar technology that is gaining fast popularity in the last years is the photovoltaic panels, also called PV panels. These panels use a special material called semiconductors to generate electric current using the sun light. This technology is the most promising for household applications and many countries are already implementing programs to promote its use. The commercial options have efficiencies between 15 to 20%, but most companies and research centers around the world are working to increase these numbers and reduce the production and installation costs. The use of batteries can be an alternative for areas not connected to the national energy grid, considering that the sun shines only during the day, and these regions don’t have the grid as backup.
Another promising group of technologies regarding the use of solar irradiation to produce electrical energy is the concentrated solar power (CSP). This family of technology uses different types of mirror shapes and tracking systems to focus the solar irradiation into a focal point, reaching high temperatures that can produce steam and this steam can run conventional turbines to produce electricity. Projects from 50 MW to more than 300 MW are already in operation in many countries, the majority are installed in Spain and the USA. The storage of this produced heat can also be done and some plants were built to produce electricity 24 h/day during the summer with a 15h of storage.
The concentrated solar energy can also be used to provide heat for the industry. I am currently working on a project researching this application and there is a great potential worldwide. The temperatures produced can go up to 400 ºC to generate steam, hot air or hot oil, depending on the client’s demand. The energy consumption in the industry represents around 20% of the total energy demand, a sector that solar energy can strongly contribute to reducing the dependence on fossil fuels and mitigate climate change.
There is still a long way to go towards the assessment and use of solar energy, but the future is already pointing our direction to an obvious source for our energy needs.
