Clean and Renewable Energy Technology (CRET) consists of solar (PV and thermal); CHP (combined heat and power/cogeneration); wind; geothermal (heat pumps, piles, and earth sheltering); and lastly, biomass. The increasing prevalence of EVs (electric vehicles) requires more buildings include charging stations which are often powered by renewable energy. Currently, 28% – 42% of EVs are charged from rooftop solar power. Soon-to-come wireless induction charged cars will necessitate further changes. Advancements in technology have created smart homes and Intelligent Transportation Systems (ITS).

Renewable energy in California generates about 32% (2020) of the state’s electricity at the moment, but there has been a mandate put in place to increase that amount to 50% by 2030.

By using renewable energy CO2, CO, NOx, and VOCs can be reduced from the ozone. “From 2000 to 2009 carbon dioxide levels fell in the US, among the front runners were Texas, New York, and Delaware. However, 13 states experienced an emissions increase with Nebraska and Colorado as the leaders” ( The different types of renewable energies are biofuel, geothermal, solar, wind, Ocean Thermal Energy Conversion (OTEC), and hydroelectric. One common type of biofuel is ethanol.

The amount of renewable energy accounts for only 11% of the total energy in the US (2020) up from 6% in 2006. With fossil fuels accounting for 81%.

Adding ethanol to fuel can significantly decrease CO2 emissions and add to the supply of fuel by at least 15%. The food versus fuel debate is a stretch since of the 500 M acres available for growing food only 25 M is currently used.  Also, if cellulosic ethanol, made from the stems, leaves, stalks, and trunks of plants is employed then food production is not affected. This has a promising future since moving toward energy crops (grass and wood) will increase their supply (Michigan State University). Geothermal is using the ground, which stays at a constant temperature during extreme cold and hot weather, to heat and cool water. If you are willing to spend $7,000 – $30,000 to purchase and install a system then you can breakeven in 5 – 10 years.

Wind turbines, $1.2 million to $2.6 million, per MW of capacity installed are relatively expensive but have the greatest future.

Popular Science claimed it has been limited due to the FAA’s desire to keep the airspace clear for planes. The high initial cost of a stationary wind turbine has started a shift to flying wind turbines (airborne wind turbines). This energy is transferred to a ground station through a power cable that also functions to tether the aircraft. This idea seems worth considerable investment. Other ideas are still in its infancy, such as harnessing the motion in waves or OTEC. OTEC could even help to decrease or prevent hurricanes. The two remaining renewables are solar and hydroelectric. The future is bright for solar for powering and heating or cooling in homes and office buildings and even generating electricity for cars and airplanes. Hydroelectric dams are the type of renewable with the most power generated, however, they are rapidly deteriorating and there are strong reasons for not building new ones.

Many dams are in the west where deeper river valleys are present. One of the most famous is the Hoover Dam located at the lower end of the Grand Canyon with the Glen Canyon dam upstream. As of 2005, there were 75,000 dams in the US [2]. A dam is used to control floods, provide irrigation water, and generate power. The Itapua Dam on the border between Brazil and Paraguay produces 12,600 MW. The largest hydroelectric plant in the US is the Grand Coulee Dam. Its three power plants produce 6,809 MW and the Hoover Dam produces 2,074 MW. For comparison, the Diablo One nuclear plant in California only outputs 1,106 MW.

Unfortunately, these tourist attractions that produce 7% of our energy have many downsides and many dams are being blown up.

Over 30 years water begins to erode the limestone and leak underneath the wall. To prevent this from leaking and getting worse costly construction is needed. In the 1970s, walls were extended from 80 to 150 feet. Now they must go to 300 feet. At this depth, there are water pockets and additional costs for drilling. To counteract the situation, the head has been decreased to one-third of the original amount which makes the dam less efficient. Along with this diminished capacity, releasing water is dangerous to the many urban cities built along rivers. Many people do not realize that the city of Nashville was flooded because they had to release large amounts of water. Another instance, the Teton dam cost $100 million to build, and when it failed catastrophically in 1976 the government paid $300 million in claims, 11 people and 13,000 cattle died, and the total damage was estimated at $2 billion. The dam was never rebuilt.

Many dams are needing their foundation reinforced but the appropriate method is not always clear. Even though dams only impound 17% of rivers, leaving room for future development, the risk of flooding caused by a dam failure is not worth further development. For example, the Lake Delhi dam in Iowa failed in 2010. Currently, there is a $350,000 engineering study to see if it is worth rebuilding. Part of the pre-construction study will determine if the type of dam needed will be a “moderate” or “high hazard” dam. A moderate dam costs about $10 million with another $3 million to $4 million needed for electrical generation equipment. If a “high hazard” dam-type is needed, that increases the cost by $2 million.

The El Atazar dam, near Madrid, Spain was chosen to supply water and not electricity. A crack developed in the center of this arch dam due to the foundation settling and concrete expansion caused by the sun. Contraction joints help but a novel approach would be to have an awning of solar panels shade the dam wall, limiting its exposure from the sun’s rays. The panels could be built as a walkout area extending from the top of the dam. By adding a pump the current status of dams can be improved. Pumped-storage hydroelectricity works by pumping water, during low electricity demand, to a storage pool situated above the power plant at a higher elevation. This increases the pressure head for times of high demand and there is excess energy to operate the pump during low demand, a technique called load balancing.

Before considering solar, the orientation, shading, and building materials should be chosen to keep the home cool in a hot climate or warm in a cold climate. Cool roofs have a high solar reflectance, or albedo, and can reflect sunlight onto the bottom of a solar thermal water heater system (a box of metal or black piping within a panel) to provide 60% – 70% of a home’s hot water used.  The systems most highly rated under the SRCC OG300 protocol have a 90% solar fraction and using PV offset for the water heating allows a 100% solar fraction.

Photovoltaic solar technology has been increasing efficiency steadily and is now 12% – 20%. The highest efficiency achieved is 42.8% spurred along by the DARPA Very High-Efficiency Solar Cell (VHESC) program. However, Darpa may reach efficiencies of 54% in the lab and 50% for production. PV cells for an average home cost ~$20,000 with an 8 year payback period. So how do we encourage people to buy more solar electricity and justify the venture capital of $100M – $1B needed for a cleanroom manufacturing facility? Right now, there is a trend factor that is being pushed. Similar to when Californians lived in ranch-style houses with exterior windows and a pool, it is now becoming popular to have panels on your roof. Solar electricity systems work best at temperatures below 90 °F and if temperatures exceed 110 °F, the solar power output can be reduced by 10% – 25%. Biosolar roofs combine a green roof with solar PV. This is an excellent idea, as the two function in symbiosis, with vegetated roofs creating a cool microclimate around the panels via evapotranspiration.


  1. Markham, Derek. “MIT Professor: Power Your House With 5 Liters of Water Per Day”.
  2. “Hydrolytic Power Water Use.” USGS. Water Science School.
  3. “With Cellulosic Ethanol, There Is No Food Vs. Fuel Debate”. Science Daily®. Science News. Michigan State University. 2007.
  4. “State-Level Energy-Related Carbon Dioxide Emissions, 2005-2016.”

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