Clean and renewable energy technology (CRET) consists of solar (PV and thermal); combined heat and power/cogeneration (CHP); wind; geothermal (heat pumps, energy piles, and earth sheltering); and biomass. The increasing prevalence of electric vehicles (EVs) requires more charging stations, often powered by renewable energy. Currently, 28% – 42% of EVs are charged from rooftop solar power. Soon-to-come wireless induction charged cars will require 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, but there has been a mandate 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, CO2 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 (EIA). 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 increase the supply of fuel by 15%. The debate on food versus fuel is a stretch, as only 25 M acres are used to grow food from the 500 M acres available. Cellulosic ethyl consists of stems, leaves, stalks and trunks of plants. It requires additional processes that break down cellulosic materials into sugars with enzymes. This type of ethanol does not reduce food supply and has a promising future, as the move to energy crops (grass and wood) will increase their supply (Michigan State University). Geothermal uses the stable ground temperature to heat and cool water. If you are willing to spend $7,000 – $30,000 to buy and install a system, you can breakeven in 5 – 10 years.
Wind turbines, $1.2 million to $2.6 million, per MW of installed capacity, are relatively expensive, but have the greatest future.
Popular Science claimed it was 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). The electricity is transferred from a power cable tether to a ground station. This idea seems worth considerable investment. Other ideas include harnessing the motion in waves with Ocean Thermal Energy Conversion (OTEC), which could even help prevent hurricanes.
The future is bright for solar power to power, heat, and cool our buildings, and generate electricity for transport. Hydroelectric dams are the renewable type with the most electricity generated. However, they are rapidly deteriorating, and there are strong reasons not to build new ones.
Many dams are located in the west, where deeper river valleys exist. One of the most famous is the Hoover Dam, located at the lower end of the Grand Canyon, with the Glen Canyon dam upstream. In 2005, there were 75,000 dams in the US.2 A dam is used to control floods, to supply irrigation, and to 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. The three power plants produce 6,809 MW, more than three times the Hoover Dam production of 2,074 MW. In comparison, the Diablo One nuclear plant in California produces only 1,106 MW.
Unfortunately, these tourist attractions, which produce 7% of our energy, have many downsides, and many dams are being blown up.
After 30 years, water begins to erode the limestone and leak underneath the wall. To prevent leaks, costly construction is required. In the 1970s, walls were extended from 80 to 150 feet. Now they have to go 300 feet. At this depth, there are water pockets and additional drilling costs. To counteract the need to drill this deep, the head is reduced to a third of its original amount, but this leads to a reduction in power output. Along with this reduced capacity, the release of water is dangerous for many urban cities built along rivers. The city of Nashville was flooded because they had to release enormous amounts of water. The Teton dam cost $100 million to build, and when it failed catastrophically in 1976, the government paid $300 million in claims for damages, 11 people and 13,000 cattle died, and the total damage was estimated at $2 billion. The dam was never rebuilt.
Many dams need to be reinforced, but the appropriate method is not always straightforward. Although 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. There is a $350,000 engineering study to determine whether it is worth rebuilding the Lake Delhi Dam that failed in 2010. Part of the pre-construction study will determine whether the type of dam is required to be a moderate or high hazard dam. A moderate dam costs $10 million, and another $3 to $4 million is needed for electrical generation equipment. If a high hazard dam is needed, this 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 middle of this arch dam due to the settling of the foundation and the concrete expansion caused by the sun. Contraction joints help, but a novel approach would be to shade the dam wall by an awning of solar panels, limiting its exposure to the sun’s rays. The panels could be a walk-out area extending from the top of the dam. Pumped storage hydropower improves a dam by pumping water to a storage pool above the power plant during low electricity demand. 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 technology, the orientation, shading, and building materials should be selected based on the climate. Cool roofs have a high solar reflectance or albedo and can reflect sunlight on the bottom of a solar thermal water heater system (a box of metal or black piping within a panel) to provide 60% – 70% of the hot water used in a home. The systems most highly rated under the SRCC OG300 protocol have a solar fraction of 90%, and using PV offset for water heating allows a solar fraction of 100%.
Today, the efficiency of photovoltaic solar technology is 12% – 20%. The highest efficiency achieved is 42.8%, supported by the DARPA Very High Efficiency Solar Cell (VHESC) program. DARPA could even achieve efficiencies of 54% in the laboratory and 50% in production. PV cells for an average home cost $20,000 with an 8-year payback period. The capital needed for a cleanroom manufacturing facility is $100M – $1B.