Atmospheric Vortex Engine

Frequently Asked Questions

5. Solar Chimney

5.1 What is a solar chimney / solar tower?

A solar chimney (also known as a solar tower) is a solar thermal power plant wherein heated air rises in a tall chimney.  The inflowing air is heated in a greenhouse with an open rim surrounding the base of the chimney and a turbine at the base of the chimney turns a generator to produce electrical power.

The following diagram illustrates the basic elements of a solar chimney:

Solar updraft tower

Additional information on solar chimneys can be found on the AVE - Links page, "Solar Chimney" section.

5.2 What is the Manzanares solar chimney?

The Manzanares solar chimney was a prototype built in Spain in the early 1980's. The experimental chimney was financed by the German and Spanish governments and operated successfully for 7 years.

The chimney had a diameter of 10 m and a height of 200 m. The base of the chimney was surrounded by a 200 m diameter greenhouse with an open outer rim. The transparent plastic roof of the greenhouse was 2 m above the ground. A vertical axis turbine consisting of a rotor similar to a helicopter rotor drove an electrical generator. The greenhouse increased the air temperature 20°C above ambient. The maximum electrical power output was 50 kW. The power output was steadier than that of conventional wind turbines. The solar chimney would start automatically shortly after sunrise, synchronize and connect to the Spanish electrical grid. The chimney was supported with guy wires. Unfortunately the chimney was eventually blown down in a wind storm.

The Manzanares chimney demonstrated the feasibility of solar chimney technology. The prototype cost $5 million. A solar chimney of the Manzanares size is not economical since the power output of a solar chimney is proportional to the height of the chimney and to the area of the collector.

5.3 What is the Enviromission solar tower?

In the early 2000's, the Australian company EnviroMission proposed building a 200 MW capacity solar chimney in Mildura south west Australia. The chimney was planned to have a height of 1 km and a diameter of 130 m. The solar collector would have a diameter of 7 km. The estimated cost of the Australian solar chimney is $800 million.

The power output of the proposed Enviromission solar tower would be 4000 times the power output of the Manzanares solar chimney for several reasons: the tower is five times higher than Manzanares chimney, the area of the collector is 700 times larger, and because exit kinetic energy losses are a smaller portion of the ideal work.

enviromission 5.4 What is the purpose of the chimney? Why does the chimney need to be so tall?

The purpose of the chimney structure is to prevent the warm buoyant air inside the chimney from mixing with the surrounding cooler ambient air outside the chimney via entrainment. Without the chimney, the warm rising air from the solar collector would quickly mix with the ambient air which would rapidly reduce its buoyancy.

The maximum efficiency of a solar chimney is proportional to its height;  the taller the chimney, the more work can be captured by the turbine.

vortex chimney Higher resolution version of the above figure - PNG (398 KB) 5.5 What are the advantages of the AVE (Atmospheric Vortex Engine) compared to a solar chimney?

The thermodynamic basis of the AVE (Atmospheric Vortex Engine) and the solar chimney is virtually identical. However, the AVE has some significant advantages

1)  A tall chimney is not required. The atmospheric vortex engine replaces the chimney with centrifugal force of a vortex to generate a "virtual" chimney.  The construction of an extremely tall chimney (1 km as in the Enviromission proposal) is not required.

2)  The height of a virtual "vortex chimney" could extend much higher into the atmosphere compared to a physical chimney structure.  As the height of the vortex increases, the temperature of the cold source drops which increases the overall Carnot efficiency of the process.

3) A large solar collector is not required.  Waste heat can be obtained from various sources such as from thermal power plants, waste heat from various industrial processes, or simply ground level heat from solar radiation received at the earth's surface in its unaltered state.

4) The chimney and the solar collector represent over 90% of the cost of a solar chimney power plant. The cost of an atmospheric vortex engine power plant could be 5% of the cost of a solar chimney power plant with the same capacity.

5) The condensation level of dry surface air is typically well over 2 km. Therefore the release of the latent heat of condensation which cannot play a role in the solar chimney due to physical chimney height limitations.  However, release of latent heat can come into play in an atmospheric vortex engine due to the height of the vortex which would easily extend well beyond 2 km.  Even negatively buoyant air can become buoyant when raised beyond its condensation level due to the release of additional latent heat.

5.6 What is the minimum surface temperature required for a solar chimney and for an AVE?

The temperature differential at the base of Manzanares solar chimney was typically 20°C. A solar chimney 5 times as high (1000 m high) would need a temperature differential of 4°C to produce the same power. The frictional losses in the Manzanares chimney were less than 10% of the ideal work and could be kept to the same level by a slight increase in chimney diameter. The temperature of sandy soil during periods of insolation can be 30°C higher than the temperature of the air at the 10 m level. The temperature of air at the 0.3 m level can be 15°C higher than the temperature of the air at the 10 m level. The temperature of the air rising in dust devils can be 5°C higher than the temperature of ambient at the 10 m level. Dust devils can reach heights of 2000 m or more. Naturally heated air rising in a 2000 m solar chimney or in a dust devil could produce as much work as air heated in a greenhouse can produce in a 200 m solar chimney.