I will focus this article on two parts; on the one hand, the generation of solar thermal electricity and on the other, the incidence of this solar energy in the calculation of the thermal load, which is extremely high in tropical countries.
by Camilo Botero*
I recently acquired the book Solar Thermal Electricity. Success story of the research, which has been tremendously motivating for me that in Colombia and other Latin American countries (in most of which there is a great intensity of solar radiation) we concentrate on the use of renewable energy.
Nowadays the generation of electrical energy, starting from solar energy, represents in Spain a considerable percentage of the total energy consumed (approximately 5%).
Solar thermal electricity is experiencing a moment of great interest in the concert of nations, finally its takeoff has occurred and our Ibero-American countries can not be oblivious to this challenge that represents a great opportunity to introduce us, in a significant way, in the use of this renewable energy.
Spain already gives us the example categorically, since it is one of the pioneer nations and perhaps is at the forefront of the issue.
Institutional support for these developments must be resolved as soon as possible, involving scientific, academic and governmental institutions with their knowledge resources and above all financial support for initiatives, since solar thermal energy will undoubtedly have a very important role in the energy system of the future, which will surely be more decentralized and diversified.
For example, I read in the magazine Futura that this type of energy is being used in oil wells to generate the steam required by the process and thus managing to commercialize the gas that was used for that purpose; this will make the rational use of energy more efficient and supportive.
In Colombia it would be a great alternative for the interconnected system, because when there are droughts, conventional thermal plants of very low efficiency and great capacity for deterioration of the environment are used.
Some considerations regarding Colombia
(Taken from Man and Machine No.37, July-December 2011 UAO)
The Energy Mining Planning Unit (UPME), in partnership with the Institute of Environmental Studies (IDEAM), published the Atlas of Solar Radiation, which is the official document of this energy resource in the country.
There are presented, registered, the values of the energy resource for the development of solar energy systems for Colombia. In this work, measurements are recorded that contrast with values of the official publication, which indicates the great energy potential existing in some regions.
Solar Radiation Atlas
The annual solar radiation map made by the IDEAM of Colombia and the UPME, shows that the isolated zones or Non-Interconnected Zones (ZM) to the system present average values of 4 to 4.5 kWh /m2 of radiation per day, which is suitable and very motivating for the development of new programs for the application of photovoltaic systems, given that in countries where photovoltaic solar energy has been developed, similar radiation values are used.
In the case of southern Spain, with the highest radiation and the largest solar plants and platforms in the country, an average daily solar radiation of 3.8 to 4.5 kWh/m2 of radiation per day is recorded.
The country is characterized by the regions: Andean, Atlantic, Pacific, Orinoquia and Amazonia.
The intensity of solar radiation in the Colombian Andean region shows that the areas of Valle del Cauca and Magdalena have the greatest potential in this region and as you ascend to the tops of the mountain ranges, that potential gradually decreases, with the exception of some areas called altiplanos, where a greater solar potential is observed compared to that of the slopes and valleys.
It can be observed, according to the conventions, that for most of the Colombian territory that has an incidence of global solar radiation, it has averages between 4 and 4.5 kwh / m2 per day, especially over much of the Amazon and the Andean region. Colombia, due to its geographical position, is favored with a great availability of the solar resource.
Measurements made at another point in Valle del Cauca contrast with the values obtained from the official document. Thus, in Lake Calima, municipality of Darién, in Valle del Cauca, where there are no known weather stations that report solar radiation, a digital pyrometer was used and solar radiation values exceeding 1,000 W /m2 were measured.
As for photovoltaic solar energy values, values higher than 1,200 W/m2 were measured at the Autonomous University of the West in Cali, which is quite high and promising for generation.
The impact of solar radiation on the calculation of thermal load
As stated in the previous article, solar radiation is one of the three modes of transferring heat and is done by means of electromagnetic waves.
When the calculation of the thermal load is carried out in order to determine what the size of the equipment would be in tons of cooling, this mode of heat transfer is a preponderant factor, especially if there are large domes and windows that are exposed to such radiation.
The information that comes in the American or European texts or software and in the excellent manuals of the main equipment firms regarding the intensity of solar radiation in our region, is not correct and even when we already have local information, it is not presented in the way that is required in a process of calculating the thermal load to calculate the radiation at peak hours. We must work on organizing this information from our guilds.
What is evident is that the load by solar radiation through translucent materials in a tropical country, is determinant of the capacity of the central systems, with the aggravating, in some cases, that the temperature condition can be met, but because it is a phenomenon of electromagnetic waves causes thermal discomfort in a very marked way if the adequate shade is not provided.
* Camilo Botero is the current Secretary of the Federation of Ibero-American Associations of Air Conditioning and Refrigeration - FAIAR; he was president of ACAIRE and is president of Camilo Botero Ingenieros Consultores Ltda. He has worked as a teacher in several Colombian universities, guilds and currently in ACAIRE in diploma courses of air conditioning projects, energy efficiency in air conditioning and refrigeration, cogeneration and trigeneration, applied psychometrics, thermodynamics, fluid mechanics, heat transfer and turbomachinery.
