Using electricity as an energy transport to do work has many benefits over combustion (heat) engines. The conversion of electrical energy to mechanical energy is efficient and does not have the inherent losses of heat engines due to the Second Law of Thermodynamics. Generating electricity from heat sources with systems that efficiently utilize thermodynamics and then transporting the electricity is a "doing more with less" approach.

Clean and cheap electricity is the starting point to change our dependency on fossil fuels. Electricity can easily replace the fossil fuels being burned in stationary locations and it is relatively easy to move rail transportation to electricity. In heavy equipment, there are many situations where the equipment could be converted and directly powered and the electric motor and battery technology found in ships and submarines can be used much more readily in heavy equipment than passenger vehicles. In passenger vehicles there are some recent enhancements in batteries and implementations of electric cars such as Tesla Motors. They are building an electric car that goes 0-60 mph in 4 seconds and has curb appeal, but having someone else burn fossil fuels to charge the batteries isn't economical, convenient, environmentally friendly or even more efficient than using existing fossil fuel engines. Electric passenger vehicles can be a major contributor to renewable and clean transportation, but the infrastructure to supply the electricity needs to be corrected for the electric car to be viable.

There are only two major energy sources that are being used by society, solar and nuclear. All of the energy transport media products whether they are fossil fuels or manufactured media like biofuels and hydrogen have their energy source in either solar or nuclear.

Hydrogen is clean burning, but there are difficulties in transport and storage of pure hydrogen.

Biofuels are great ideas for direct replacements for fossil fuels, but the problem with biofuels is the effect that relatively cheap fossil fuels and technology have had on agriculture in the last 60 years. Until around 1940, the world was fed without the use of fossil fuels. It was very labor intensive and employed a large portion of the population. Fossil fuels changed farming methods and urbanized society. The continual decline in agricultural profitability, fossil fuel based fertilizer and larger farm equipment caused farms to become larger to be able to support fewer owners. Renewable and portable energy products like Ethanol and BioDiesel now take more fossil fuels to produce and deliver than if the the consumer burned the fossil fuel directly. Although it is relatively easy to convert existing transportation to biofuels, the solar conversion efficiency of traditional crops used for biofuels isn't very high: ~0.02% of the solar isolation on a corn or wheat field actually gets converted into ethanol or biodiesel. The ease of conversion of the transportation industry offsets this and there is a lot of work going into more efficient feedstock, but the massive amount of fossil fuels consumed by modern society makes it very difficult to produce these products on a scale that will affect fossil fuel consumption. This opinion is by no means meant to be negative regarding biofuels, it is focused on improving the efficiency of production of biofuels.

Agriculture needs to be fixed before these products can actually lower the fossil fuel dependency, and there is no way to move society back to the farming methods that fed us prior to fossil fuels. If agricultural energy inputs were moved towards renewable sources, the amount of fossil fuel required for consumer BioDiesel and Ethanol could be reduced. With common technology that is found in locomotives, electric drive mining trucks and the battery technology used in submarines, electric farm equipment could be built. Hydrogen powered farm equipment is also a simpler conversion than passenger vehicles due to the low travel speed and high weight tolerance. A high pressure hydrogen tank on a farm tractor and the hydrogen conversion of internal combustion engines is relatively easy, but the efficiency of hydrogen electrolysis from water and the energy required to compress hydrogen are areas that need further development.

The major engineering, usability and economic challenge in building large electric farm equipment is around battery cost and the charging system. The high torque at low rpm characteristic of electric motors allows the powertrain to be much simpler than in diesel systems and due to to low travel speed, high weight tolerance and low traveling distance from the farmyard, many of the obstacles in consumer electric vehicles aren't an issue in electric farm equipment. Converting agriculture to electricity would be difficult, but it is a simpler approach to produce Ethanol and Biodiesel with electricity and use those products in existing consumer vehicles than to convert the consumer vehicles to use electricity directly.

It is also possible to extract hydrogen from water with electricity rather than obtain it from natural gas. A more efficient method is to produce bio-gas methane and crack the hydrogen. Anhydrous ammonia and nitrogen fertilizer can be made without fossil fuels. If there was local, cheap and clean electricity, agriculture would move away from fossil fuels. If the agricultural non-renewable energy inputs lowered, Ethanol and BioDiesel production would become feasible and carbon balanced.

Direct solar systems do not leverage an existing feature of nature like hydroelectric or wind. This means that direct solar energy systems scale in a linear fashion and to increase output additional collectors are required.

Solar Photovoltaics and are improving, but the high energy input of semiconductor manufacture, high technology "clean room" factory cost and daytime only operation make the EROEI very poor. The high electrical input of manufacture, daytime only operation, linear scaling and the low conversion efficiency makes the EROEI of Solar Photovoltaics more in the class of energy transport media than solar conversion systems. It takes many years of operation in high solar isolation locations to recover the input energy of manufacture. Solar Photovoltaics eventually degrade and need to be discarded completely at the end of their lifetime.

The very low maintenance of no moving parts, ease of installation and ability to integrate into existing power systems makes them very suitable for remote power systems and supplementary electrical generation.

Concentrated Solar Plants, Solar Stirling and other attempts at solar thermal power generation  have had success in specific high isolation arid locations. The largest solar plants in the world are trough solar steam systems, but they are very location dependent. There is a relatively large amount of electrical power in California and other locations generated from direct solar thermal power plants (SEGS). These plants perform well in arid locations and usually use natural gas for night and cloudy operation. FPL Energy and others operate several SEGS plants in the Mojave Desert.

Google Map location of Kramer Junction SEGS Power Station.

A document on some of the attempts at solar steam plants from 1890's forward explains some of the historical feasibility issues of direct solar steam plants.

Traditional CSP plants do not utilize a feature of nature and scale in a linear fashion. They currently are very location limited to arid high isolation locations.

Nuclear energy is the only major power source that isn't active or passive solar collection. It has a high initial cost, waste disposal problems and no one wants it in their backyard. We already have a nuclear source in the sun and that is probably as close as anyone wants to live to a nuclear power plant.

Wind turbines are the largest growth area in renewable energy. Taking advantage of daytime heating and natural wind lowers the EROEI and wind systems have very good feasibility. The lack of reliability of natural winds limits the usage to supplementary power generation unless an energy storage system is incorporated.

Among other projects there is an electrical generation project at Chena Hot Springs outside of Fairbanks Alaska that utilizes a modified commercial heat pump to generate electricity from a lower temperature geothermal source. They also use an absorption chiller powered by the geothermal source to keep their Ice Museum from melting in the summer months.

Hydroelectric dams leverage natural rainfall and are reliable and suitable for base load electrical generation. They have a very high capital investment, numerous environmental impacts and are not location independent. Most of the available waterways that are not in extremely remote locations have had hydroelectric power dams built and it is very difficult to get environmental approval to build new dams.

OTEC was first proposed in 1881 with the first experimental plant being constructed in 1930 in Cuba. OTEC involves pumping 40 degree F water from ocean depths (up to 1 km) to the 80 degree F surface, similar to the conditions in the Gulf of Mexico. The plants extract the energy from the flow of heat between the warm surface water and cold ocean water by vaporizing warm water or other fluid to turn turbines. Unlike the varying heat flux used in traditional solar power stations, the heat in the ocean is always there and not dependent on weather conditions, offering base load electricity similar to conventional power plants. In addition, the fuel for the plant is free and essentially limitless. The main drawback is that OTEC plants are very location dependent only being feasible in warm ocean surface locations and even then due to evaporation, the "hot" water isn't very hot. There have been several pilot plants and experimental facilities built around this technology, but it hasn't proven to be feasible for power generation.

Natural wind and water are about the only implemented clean and renewable technologies that use passive solar collection. These concepts aren't exactly on the cutting edge and they have many issues with the environment, are limited to specific locations and wind isn't reliable. Wind Farms are a nice pet project, but wind generation isn't going to go anywhere towards replacing fossil fuels for a large portion of the world. There have been some new ideas and attempts to use passive solar collection methods that improve reliability over natural wind and some of these "controlled wind" concepts are updraft Solar Towers and Water Spray Down Draft Energy Towers.

The Solar Updraft Tower is an active solar collection idea to build large glass air heating collectors connected to a tall chimney. A pilot plant was built in Spain in the 1980's and there has been a commercial attempt recently in Australia. It has numerous problems including requiring a really hot sunny climate, daytime only operation and requires hectares of glass plate collectors and a chimney 1 km high before it is efficient. These drawbacks and the cost of construction and electrical transportation don't make this a universal solution. Due to the arid location dependence, this scheme is competing directly with Solar Steam systems and hasn't shown comparable efficiency to Concentrated Solar Steam plants that have been in commercial operation for many years.

Another idea was the Water Spray Down Draft Energy Tower as patented by Phillip R. Carlson in 1975 and recently advocated by Professor Dan Zaslavsky of Israel. It uses the idea of pumping sea water up a tower in the desert, spraying it to cool the air and the cold air creates wind down the tower which is used to drive a turbine. At first glance, it is amazing that you can pump water that high and create any sort of positive energy output and the idea also would not work in sub-zero temperatures or high relative humidity. Using this idea directly isn't an option anywhere but in the desert near an ocean, but it is at least a new idea.

At the basic level, the water spray down draft tower is transferring heat from the hot desert air into the cold ocean and converting some of this heat into electricity. It does this by pumping the ocean up a 1000' tower. This doesn't seem to be the most efficient way to transfer heat from the air into the ocean and pick up some mechanical energy on the way. Imagine filling a 5 gallon pail with water (~50 pounds) and carrying it up a 1000' tower and then throw it in to cool of the air. It doesn't seem very efficient and it isn't. In the best case it only captures ~2.8% net energy from the hot air.

The good thing is that there is lots of sea water and lots of hot air in the desert. The major negative is the low efficiency and the construction of waterways to get the input water into the desert. There is also the long term humidity effect of dumping this much water into the local climate and the environmental damage that is possible from salt water spray droplets. The cooling effect is due to evaporation of water, so if the relative humidity goes up, the tower loses efficiency. This idea is very location dependant and isn't suitable for non-arid regions and anywhere that has freezing temperatures. The original patent was filed in 1975 and Professor Zaslavsky obtained USPO patent 6,647,717 and was trying to get one built in Isreal. It isn't going to be a solution for moderate or humid climates.

The additional problem with this design is that although spraying water into dry air lowers the temperature it also increases the absolute humidity. Water vapor is less dense than air at ~ 0.8 kg/m³ (air is ~ 1.2 kg/m³) and adding water vapor to the air to cool it also makes it less dense. Apparently the evaporative cooling compensates for this, but adding moisture to dry air makes it less dense than cooling it by other means.

Seasonal Thermal Storage

Drake Landing Solar Community

Original material, images and other documentation on this page and website are copyright ©Robert J. Rohatensky 2006, 2007
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