Here’s how they work.Heat in a solar thermal system is guided by five basic principles: heat gain; heat transfer; heat storage; heat transport; and heat insulation. Here, heat is the measure of the amount of thermal energy an object contains and is determined by the temperature, mass and specific heat of the object. Solar thermal power plants use heat exchangers that are designed for constant working conditions, to provide heat exchange. Copper heat exchangers are important in solar thermal heating and cooling systems because of copper’s high thermal conductivity, resistance to atmospheric and water corrosion, sealing and joining by soldering, and mechanical strength. Copper is used both in receivers and in primary circuits (pipes and heat exchangers for water tanks) of solar thermal water systems. Heat gain is the heat accumulated from the sun in the system. Solar thermal heat is trapped using the greenhouse effect; the greenhouse effect in this case is the ability of a reflective surface to transmit short wave radiation and reflect long wave radiation. Heat and infrared radiation (IR) are produced when short wave radiation light hits the absorber plate, which is then trapped inside the collector. Fluid, usually water, in the absorber tubes collect the trapped heat and transfer it to a heat storage vault. Heat is transferred either by conduction or convection. When water is heated, kinetic energy is transferred by conduction to water molecules throughout the medium. These molecules spread their thermal energy by conduction and occupy more space than the cold slow moving molecules above them. The distribution of energy from the rising hot water to the sinking cold water contributes to the convection process. Heat is transferred from the absorber plates of the collector in the fluid by conduction. The collector fluid is circulated through the carrier pipes to the heat transfer vault. Inside the vault, heat is transferred throughout the medium through convection. Heat storage enables solar thermal plants to produce electricity during hours without sunlight. Heat is transferred to a thermal storage medium in an insulated reservoir during hours with sunlight, and is withdrawn for power generation during hours lacking sunlight. Thermal storage mediums will be discussed in a heat storage section. Rate of heat transfer is related to the conductive and convection medium as well as the temperature differences. Bodies with large temperature differences transfer heat faster than bodies with lower temperature differences. Heat transport refers to the activity in which heat from a solar collector is transported to the heat storage vault. Heat insulation is vital in both heat transport tubing as well as the storage vault. It prevents heat loss, which in turn relates to energy loss, or decrease in the efficiency of the system. Heat storage for electric base loads Main article: Thermal energy storage Heat storage allows a solar thermal plant to produce electricity at night and on overcast days. This allows the use of solar power for baseload generation as well as peak power generation, with the potential of displacing both coal- and natural gas-fired power plants. Additionally, the utilization of the generator is higher which reduces cost. Even short term storage can help by smoothing out the “duck curve” of rapid change in generation requirements at sunset when a grid includes large amounts of solar capacity. Heat is transferred to a thermal storage medium in an insulated reservoir during the day, and withdrawn for power generation at night. Thermal storage media include pressurized steam, concrete, a variety of phase change materials, and molten salts such as calcium, sodium and potassium nitrate. Steam accumulator The PS10 solar power tower stores heat in tanks as pressurized steam at 50 bar and 285 °C. The steam condenses and flashes back to steam, when pressure is lowered. Storage is for one hour. It is suggested that longer storage is possible, but that has not been proven in an existing power plant. Molten salt storage See also: Thermal energy storage The 150 MW Andasol solar power station is a commercial parabolic trough solar thermal power plant, located in Spain. The Andasol plant uses tanks of molten salt to store solar energy so that it can continue generating electricity even when the sun isn’t shining. A variety of fluids have been tested to transport the sun’s heat, including water, air, oil, and sodium, but Rockwell International selected molten salt as best. Molten salt is used in solar power tower systems because it is liquid at atmospheric pressure, provides a low-cost medium to store thermal energy, its operating temperatures are compatible with today’s steam turbines, and it is non-flammable and nontoxic. Molten salt is used in the chemical and metals industries to transport heat, so industry has experience with it. The first commercial molten salt mixture was a common form of saltpeter, 60% sodium nitrate and 40% potassium nitrate. Saltpeter melts at 220 °C (430 °F) and is kept liquid at 290 °C (550 °F) in an insulated storage tank. Calcium nitrate can reduce the melting point to 131 °C, permitting more energy to be extracted before the salt freezes. There are now several technical calcium nitrate grades stable at more than 500 °C. This solar power system can generate power in cloudy weather or at night using the heat in the tank of hot salt. The tanks are insulated, able to store heat for a week. Tanks that power a 100-megawatt turbine for four hours would be about 9 m (30 ft) tall and 24 m (80 ft) in diameter. The Andasol power plant in Spain is the first commercial solar thermal power plant using molten salt for heat storage and nighttime generation. It came on line March 2009. On July 4, 2011, a company in Spain celebrated an historic moment for the solar industry: Torresol’s 19.9 MW concentrating solar power plant became the first ever to generate uninterrupted electricity for 24 hours straight, using a molten salt heat storage. In 2016 SolarReserve proposed a 2 GW, $5 billion concentrated solar plant with storage in Nevada. In January 2019 Shouhang Energy Saving Dunhuang 100MW molten salt tower solar energy photothermal power station project was connected to grid and started operating. Its configuration includes an 11-hour molten salt heat storage system and can generate power consecutively for 24 hours. Phase-change materials for storage Phase Change Material (PCMs) offer an alternative solution in energy storage. Using a similar heat transfer infrastructure, PCMs have the potential of providing a more efficient means of storage. PCMs can be either organic or inorganic materials. Advantages of organic PCMs include no corrosives, low or no undercooling, and chemical and thermal stability. Disadvantages include low phase-change enthalpy, low thermal conductivity, and flammability. Inorganics are advantageous with greater phase-change enthalpy, but exhibit disadvantages with undercooling, corrosion, phase separation, and lack of thermal stability. The greater phase-change enthalpy in inorganic PCMs make hydrate salts a strong candidate in the solar energy storage field. Use of water A design which requires water for condensation or cooling may conflict with location of solar thermal plants in desert areas with good solar radiation but limited water resources. The conflict is illustrated by plans of Solar Millennium, a German company, to build a plant in the Amargosa Valley of Nevada which would require 20% of the water available in the area. Some other projected plants by the same and other companies in the Mojave Desert of California may also be affected by difficulty in obtaining adequate and appropriate water rights. California water law currently prohibits use of potable water for cooling. Other designs require less water. The Ivanpah Solar Power Facility in south-eastern California conserves scarce desert water by using air-cooling to convert the steam back into water. Compared to conventional wet-cooling, this results in a 90% reduction in water usage at the cost of some loss of efficiency. The water is then returned to the boiler in a closed process which is environmentally friendly. Conversion rates from solar energy to electrical energy Of all of these technologies the solar dish/Stirling engine has the highest energy efficiency. A single solar dish-Stirling engine installed at Sandia National Laboratories National Solar Thermal Test Facility (NSTTF) produces as much as 25 kW of electricity, with a conversion efficiency of 31.25%. Solar parabolic trough plants have been built with efficiencies of about 20%. Fresnel reflectors have an efficiency that is slightly lower (but this is compensated by the denser packing). The gross conversion efficiencies (taking into account that the solar dishes or troughs occupy only a fraction of the total area of the power plant) are determined by net generating capacity over the solar energy that falls on the total area of the solar plant. The 500-megawatt (MW) SCE/SES plant would extract about 2.75% of the radiation (1 kW/m²; see Solar power for a discussion) that falls on its 4,500 acres (18.2 km²). For the 50 MW AndaSol Power Plant that is being built in Spain (total area of 1,300×1,500 m = 1.95 km²) gross conversion efficiency comes out at 2.6%. Furthermore, efficiency does not directly relate to cost: on calculating total cost, both efficiency and the cost of construction and maintenance should be taken into account.
When you were little you used solar thermal energy to burn a leaf in the garden with a magnifying glass aimed at the sun.
when you were little, you used a magnifying glass to aim the sun and burn a leaf. That is solar thermal energy. It can be used to heat water which will run a steam engine and make electricity
When you were a child you used a magnifying glass aimed at the sun to burn a leaf in the garden. That is solar thermal power. It can be used to heat water which will run a steam engine and make electricity.
“All we have to decide is what to do with the time that is given us.”
—The Fellowship of the Ring, J.R.R. Tolkein
We have reached a critical point in the climate change saga. The global temperature is now one degree Celsius higher than the pre-industrial average, and the latent effect of fossil fuel emissions already in the atmosphere is enough to warm the planet another half degree. This means that we will reach the critical 1.5-degree threshold that portends severe and irreversible climate change even without another iota of emissions.
Add to this the fact that there are no indications that the world is prepared to cut fossil fuel emissions (they are actually going to continue to increase), and it is understandable that those who concern themselves with this subject are beginning to doubt our ability to avoid a full-blown crisis. This doubt has caused some to begin to turn their thoughts towards adapting to what increasingly seems to be the inevitable.
The dictionary defines “adapt” as follows: “to bring one thing into correspondence with another.” In other words, to establish a stable relationship in which tensions are reconciled and a tranquil status quo can be established. Such a modus vivendi is possible, however, only if there is a stable state to which we can adapt.
Unfortunately, it will take the planet hundreds or thousands of years to return to thermodynamic equilibrium, depending on how hard we force the climate with our carbon dioxide emissions. During this time the climate will undergo continuous change, and this means that we will not be able to adapt to it. Instead we will be continuously fighting a rear-guard action, as it were, both preparing for and reacting to ever-worsening conditions.
This will be the new normal, and it will increasingly challenge the ability of individuals and societies to survive. There will be no détente with the forces of nature that we have unleashed. We cannot adapt; we can only extemporize. We will continuously prepare, repair, and relocate.
Let me hasten to add that I am not endorsing a fatalistic do-nothing policy. Of course we need to do our best to prepare for the oncoming crisis. I am merely pointing out that it is misleading to call this “adapting” because mankind will never again be at peace with the climate. That was the Holocene. We are now in the Anthropocene.
Let’s say that you are the mayor of Miami. The sea level is rising. You want to build a sea wall, but how high do you build it? Do you build it for the sea level in 2040, in 2060, in 2100, or beyond? Whatever height you choose, the sea will eventually rise to crest it.
And, how do you react when saltwater begins to permeate the sandy ground that underlays south Florida and begins to invade the freshwater aquifers that provide Miami and other cities in the area with drinking water? You cannot build a wall to contain it. All you can do is pipe water in from farther inland (if it is available) or move. You can call this adaptation if you like, but it seems more like capitulation. We will be doing a lot of capitulating as we defer to mother nature’s increasing hostility.
Now let’s say you are the mayor of Dharan, Saudi Arabia, one of the hottest cities in the world. In a recent heat wave, the city recorded a wet-bulb temperature of 92 degrees Fahrenheit. The wet-bulb temperature is taken with a thermometer wrapped in a wet cloth with air blowing over it. It gives the equivalent dry-bulb temperature at 100% humidity. Weather reports give dry bulb temperatures, but the wet bulb temperature is more important when measuring human tolerance to heat and humidity. When the wet-bulb temperature reaches 95 degrees Fahrenheit, the body can no longer cool itself because it cannot perspire. Humans can only survive for about six hours at this temperature.
As the world continues to warm, heat waves in Dharan will increase in frequency and wet-bulb temperatures will get closer and closer to 95 degrees. Eventually they will begin to exceed it on a regular basis and living in Dharan will become like living in hell. As mayor, how to you adapt to this?
You will need to run air conditioners a lot more. Dharan is home to Aramco, the Saudi Arabian national oil company, so the city should have ample oil to produce electricity to power its air conditioners. But this increases carbon dioxide emissions, which compounds the fundamental problem. Some other things you will also need to do: increase the city budget for energy use, provide for energy assistance to the poor, restrict the use of vehicles to curtail emissions, and issue a climate curfew to restrict outdoor activity during the hottest times of the day.
The growing health hazards of living in such a hot climate and the deteriorating quality of life will eventually force residents to relocate to cooler climes. There will be nothing you can do as mayor to stop it. By the end of the century, climate scientists expect that much of the Middle East will be uninhabitable. This will put tens of millions of climate refugees on the road headed north with frightful social, economic, and geopolitical consequences.
Over the next three decades, droughts, floods, and heat waves will reduce global agricultural production by ten to twenty percent while at the same time we will add another two billion souls to the human family. How do we adjust to this? We can ration food up to a point, but what happens when there is simply not enough food to go around? We can’t adapt to this, and many will die. The poorest among us will be the first, but no one will be spared if the planet continues to warm.
I don’t think that most people have a clear idea of how dramatically conditions will change and how long that change will go on. What we can try to do is coexist with the change, survive the change, struggle to cope with the change, and generally just keep our heads above water (metaphorically and literally). What we cannot do is adapt to the change.
Sisyphus was the life of the party. He was always kidding around and never showed the gods on Mt Olympus much deference. He also liked to play tricks on them, thinking that he was smarter than the lot of them. Zeus became irritated at this arrogance and condemned Sisyphus to endlessly rolling a boulder up a steep hill, only to lose control of it near the top. The boulder rolled back down the hill and Sisyphus had to start the whole process over again and again. Zeus wanted to remind Sisyphus who was boss.
Somewhere along the way we lost our sense of place and purpose in the world – ideas that gave depth and meaning and purpose to our lives. Without them, we are at sea. The disorientation is intolerable, so either we settled for an indolent aimlessness, or we sought substitutes: fame, money, power, influence, friendships, entertainment, recreation, hobbies, and other pastimes and purposes to fill the emptiness inside. But these are inadequate substitutes because they don’t contain or represent a deeper meaning or purpose for us. They are only what they are. So, we pursued them to excess in a futile effort to fill the unyielding inner emptiness, and in the process, began to destroy the world we live in and depend upon. But having lost our connectedness to nature, we had become either blind to or indifferent to the damage we were inflicting.
Comes now Mother Nature, like Zeus, to punish us for our arrogance, our irresponsible waywardness, and our callous disregard for her. She comes to condemn us to endlessly adjusting to a harsh and unstable climate – our version of the Sisyphean fate. But our punishment, unlike that of Sisyphus, will not be eternal. Either we will survive the catastrophe that we created, and the torment will end, or we will not survive and will join the 99.9% of all other species that have ever existed and which have become extinct.
Whether we survive this punishment is a question we cannot answer. What we can say is that, the sooner we get started on serious efforts to curtail fossil fuel emissions, the more we improve our chances.