Muối ăn: một loại gia vị phổ biến trong chế biến thức ăn, gồm chủ yếu là chất vô cơ có công thức hóa học là NaCl, một phần KCl và các khoáng chất khác. Muối ăn có thể được khai thác từ biển, hoặc đôi khi từ mỏ muối. Việt Nam có rất nhiều ruộng muối nằm dọc theo các tỉnh ven biển. | 164 Desalination Trends and Technologies a b c d Fig. 15. Solar concentrating systems a parabolic trough b Fresnel lenses c dish engine and d power tower. reflectors each of which focuses the sun s radiation on a receiver tube that absorbs the reflected solar energy. The collectors track the sun so that the sun s radiation is continuously focused on the receiver. Parabolic troughs are recognized as the most proven CSP technology and at present experts indicate the cost to be 10 US cents kWh or less. Fresnel mirror reflector. This type of CSP is broadly similar to parabolic trough systems but instead of using trough-shaped mirrors that track the sun flat or slightly curved mirrors mounted on trackers on the ground are configured to reflect sunlight onto a receiver tube fixed in space above these mirrors. A small parabolic mirror is sometimes added atop the receiver to further focus the sunlight. As with parabolic trough systems the mirrors change their orientation throughout the day so that sunlight is always concentrated on the heatcollecting tube. Dish Stirling engine systems and concentrating PV CPV systems. Solar dish systems consist of a dish-shaped concentrator like a satellite dish that reflects solar radiation onto a receiver mounted at the focal point. The receiver may be a Stirling or other type of engine and generator dish engine systems or it may be a type of PV panel that has been designed to withstand high temperatures CPV systems . The dish is mounted on a structure that tracks the sun continuously throughout the day to reflect the highest percentage of sunlight possible onto the thermal receiver. Dish systems can often achieve higher efficiencies than parabolic trough systems partly because of the higher level of solar concentration at the focal point. Dish systems are sometimes said to be more suitable for stand-alone small power systems due to their modularity. Compared with ordinary PV panels CPV has the advantage that smaller areas of PV cells .
