Monday, August 21, 2017

Steam solar updraft tower

Drought and fires and heat: Recently there have been reports of fires and heatwaves in Nigeria, Kuwait city, California, etc. When the ground absorbs solar radiation it heats up and heats up the air above it, making the whole area hot. If you shade the ground with solar air heaters, mirrors, and so on and transfer this heat to water or air, you can move the heat away from the ground to higher regions where it dissipates. So you could use mirrors to reflect solar energy onto a container of water and feed the steam produced into a solar updraft tower or you could heat air with solar air heaters and feed it into the tower, or do both. The process of rain making with evaporation at ground level (cooling) and condensation high up (producing heat of condensation) moves heat from the ground to higher altitude (a well known ocurrence explained in physical geography books and so on). When clouds form,  they can reflect solar energy back to space, reducing solar energy to the ground by 50% or so. People have been advocating solar updraft towers, but so far not much has been done. They can be used for energy supply and convectional rain formation. The design usually mentioned has a greenhouse at the bottom providing hot air. My concern is that air does not come into intimate contact with hot surfaces with a greenhouse, and if the hot air is not transferred quickly, there will be heat losses through the glass of the greenhouse and so on. 
Air is not heated much by radiation, but it is heated efficiently by direct contact with hot surfaces. I therefore propose that solar air heaters be used for the "base" of the solar updraft towers, rather than greenhouses. With greater efficiency one would not have to have such a large area (the greenhouse needs a huge area). Also, with solar air heaters, the heaters can be mounted vertically, saving huge space. See photo.
President Trump is trying to save oil, gas and coal jobs and so on, so it seems oil is here to stay for a while, in the US anyway. If one could use oil and gas at night to heat water and feed moist air or steam into the solar updraft tower, one could increase the chances of convectional rain. With gas and oil to heat water, the tower could become a steam method electricity generator and rain maker at night. One could heat seawater if one is close to the sea. Trees could be grown in the deserts using this method, making it fairly "green". 

I did some calculations as to ground surface temperatures with and without shade. I used the following for my calculations:
          1) Solar absorptivity of sand/soil  0.5
2) Emissivity of sand/soil 0.75
              3) Convective coefficient (calm day) 12 W/m^2.K
            4) Effective sky temperature 0 deg C
5) Air temperature 35 deg C
6) Solar radiation onto soil/sand (direct and diffuse) 900 W/m^2 without shade and only 200 W/m^2 (diffuse radiation) with shade
ANSWERS: Without shade the ground temperature is about 52 deg C and with shade the ground temperature is about 32 deg C (assuming the ground insulates fairly well).

CONCLUSION: The shading by mirrors, solar air heaters and so on will make a big difference to ground and surrounding air temperatures.
For solar heater information see

No comments:

Post a Comment