tailieunhanh - Green Energy and Technology - Energy for a Warming World Part 6

Kỹ thuật năng lượng mặt trời thụ động bao gồm các định hướng một tòa nhà về phía Mặt trời, lựa chọn vật liệu có khối lượng nhiệt thuận lợi hoặc tài sản ánh sáng phân tán, và thiết kế không gian lưu thông không khí tự nhiên. | 86 4 Intermittency Buffers The principle of energy storage in compressed air is really quite simple. Anyone who has done some school chemistry will be familiar with Boyle s Law of gases 6 which states that for a gas of constant mass the product of its volume and its pressure is proportional to its temperature. Consequently for a gas in a chamber which is being compressed by the movement of a piston the gas pressure exerts a force on the piston. This force newtons is equal to pressure pascals times the area of the piston m2 . In overcoming this force to move the piston work in joules must be done which for small movements is equal to the force times distance moved. By Boyle s law the change in volume and the increase in pressure will produce an increase or decrease in temperature and the storage of some heat in the gas. The first law of thermodynamics then dictates by conservation of energy that the applied work on the piston must equate to an increase in heat stored plus the stored elastic energy in the compressed gas. Usually the change in temperature can be assumed to be small isothermal operation in which case the stored energy in the gas can be readily calculated 7 . For example if 1000 m3 of air at X 105 Pa is compressed at constant temperature so that its volume is reduced by 60 then the elastic energy stored in the gas will be GJ or MW-h. Larger cavity or chamber volumes will produce proportionally larger stored energy levels. Very large storage volumes of the order of 500 000 m3 with air at pressures in the range 7-8 MPa have been proposed to procure energy storage levels in excess of 500 MW-h. However the only practical way of storing volumes of this magnitude is to use impermeable underground caverns at depths of 700-800 m. Technology Required An electricity supply plant operating with a compressed air facility as back-up would function as follows 8 . A compressor a small version of which is to be found in every fridge freezer draws power

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