Medium temperature solar thermal energy is used in applications that require temperatures between 100 and 400 degrees Celsius. Solar thermal energy is a renewable energy source that converts solar energy into thermal energy.
In general, flat collectors are used in low temperature solar thermal energy systems. However, for temperatures above 80 degrees Celsius, flat collectors practically no longer have any performance and other solar concentration systems must be used.
Medium temperature thermal energy harvesting systems are mainly used for industrial applications. On the other hand, low temperature systems are used to obtain domestic hot water and high temperature systems are used to produce steam and generate electrical energy.
Types of medium temperature solar collectors
The two types of medium temperature solar thermal energy collectors are:
1. Vacuum tube solar collectors
Vacuum solar collectors are a set of linear tubes through which a heat transfer fluid circulates in the center. In the space between the conduit through which the fluid circulates and the external layer of the tube, a vacuum is generated to prevent heat transmission by convection to reduce losses and obtain better use of solar energy.
The heat transfer fluid is maintained in a closed circuit and transfers thermal energy through an external heat exchanger.
The vacuum collectors allow temperatures of up to 120º C to be reached.
Advantages of vacuum tube collectors
The main advantage over flat collectors is their better thermal insulation.
In flat collectors there are thermodynamic losses due to convection, while in tubes, being vacuum insulated, these losses are reduced to values around 5%. Compared to flat solar panels, these losses are up to 35% less.
1. Concentrating solar collectors
Concentrating solar collectors are a type of solar collector that, thanks to its shape, concentrates the solar radiation received on a surface at one point.
There are different types of concentration collectors, but the operating principle is based on an arrangement of mirrors that reflect all the solar radiation received onto a point or a glass tube located along the focal line of the mirror.
At the focal point is the absorbing surface in contact with the heat transfer fluid. This arrangement between the absorber and the fluid aims to reduce convection losses.
Optical procedures with lens devices are enormously expensive. The most developed concentrators currently are those with reflection using mirrors, which for this temperature range correspond to linear concentrators with a parabolic trough reflective surface.
Uses and applications of medium temperature systems
Medium temperature solar thermal systems are used in a variety of applications that require higher temperatures compared to low temperature solar systems, but not as high as those required in high temperature solar systems.
Some of the most common uses include:
- Water Heating : Medium temperature solar thermal systems are ideal for heating water used in residential, commercial and industrial applications. This includes domestic hot water in homes, swimming pools and space heating systems and underfloor heating in commercial buildings.
- Industrial processes : In industry, these systems are used to provide heat in processes that require moderately elevated temperatures, such as sterilization, pasteurization and cooking in the food industry, as well as in drying and heating applications in manufacturing.
- Electricity generation : Some medium temperature solar thermal systems are used to generate electricity by producing steam, which then drives a turbine connected to a generator.
- HVAC and Cooling : In commercial and residential applications, these systems can also be used for HVAC, providing heat or cooling on demand.
- Water desalination : In arid regions, medium-temperature solar thermal systems are used for the desalination of seawater, which helps supply drinking water to areas with limited water resources.
- Agriculture: In agriculture, they are used for greenhouse heating, drying of agricultural products and irrigation applications.
These systems provide a renewable and sustainable energy source for a wide range of applications, contributing to the reduction of energy costs and the reduction of carbon emissions. Their versatility and efficiency make them attractive to a variety of sectors.