Fabrication and Characterization of a Prototype Steam Storage System and Generator for Power Production

Abstract

Use of solar energy on a large scale is mainly limited to the sun duration hours, weather conditions and inadequate solar thermal storage technology. A means of addressing this problem using local materials is provided. A pressure storage tank was designed using auto cad, fabricated using materials found in common Kenyan hardwares i.e. black sheets and cotton wool for lagging and tested to find out whether solar power availability can be assured throughout despite overcast conditions and at night using locally available technology and materials. The standards that were used during testing were ASME boiler and pressure vessel code at a small scale. Locally made heat transfer oils were used to carry solar thermal energy that produced steam. The steam storage was designed such that flashing of steam was utilized to keep the supply pressure constant. This ensured that the low density of the solar flux was compensated for by pressurization of steam and power availability was guaranteed during no sun hours. The steam store operated between 1.0 × 106- 1.0× 106 Pa. Its charging duration was twenty minutes and would discharge at the rate of 50 liters per hour continuously after full charge when there was 800 W/m2 of solar irradiance. Length of complete discharge for the heat transfer oils each in turn was: sunflower oil – 4.4 hrs, Rina vegetable oil – 4.6 hrs, water – 5.0 hrs, unused engine oil 5.3 hrs, used engine oil 4.8 hrs, 2M sodium chloride solution – 5.8 hrs, 4M sodium chloride solution 6.3 hours and 6M sodium chloride solution 6.9. hrs. The power output for the heat transfer oils were as follows: sunflower oil - 87.9 W, Rina vegetable oil – 89.7 W, unused engine oil – 95.4 W, used engine oil - 92.8 W, Water - 99.7 W, 2M sodium chloride solution – 104.1 W, 4M sodium chloride solution – 116.3 W and 6M sodium chloride 121.7 W. The steam store was found to have an efficiency of 93.5 % and a thermal capacity of 4.54× 103 kJ. The efficiencies available are for industrial applications whose efficiency range between 20 % and 90 %. This system presents a means of storing solar energy during low demand and its conversion to power during high peak demand throughout the day depending on the size of the storage and application and hence addressing the problem of variability and low density of solar power.