What Processes Are Driven By Solar Energy?
Photosynthesis
Photosynthesis is the process whereby plants use sunlight, water, and carbon dioxide to create sugars and oxygen (source). This process converts solar energy into chemical energy that fuels plant growth and provides the base for most food chains on Earth. Photosynthesis is powered by the radiant energy of the sun, which is absorbed by chloroplasts in plant cells and used to split water molecules into hydrogen and oxygen. The hydrogen joins with carbon dioxide to produce glucose and other sugars. Oxygen is released as waste. Through photosynthesis, plants are able to harness the sun’s energy to build carbohydrates that enable them to grow and reproduce. The byproduct, oxygen, makes life possible for many other organisms on the planet.
Nearly all plants, algae, and some bacteria undergo photosynthesis. Common examples include trees, grasses, flowering plants, seaweeds, and phytoplankton. All of these organisms contain chloroplasts and chlorophyll pigments that absorb sunlight and initiate the light-dependent reactions of photosynthesis. The amount of photosynthesis any plant can carry out depends on the intensity and wavelength of available sunlight. Plants adapt to maximize photosynthetic activity, growing leaves to capture more light and opening stomata on hot, sunny days. Photosynthesis allows plants to convert the sun’s radiant energy into the chemical energy they need to thrive.
Solar heating
Solar heating systems use solar thermal collectors to absorb energy from the sun and convert it into heat. There are two main types of solar collectors: flat-plate collectors and evacuated tube collectors. Flat-plate collectors are simple insulated boxes with a dark absorber material inside them. Evacuated tube collectors are made up of multiple glass tubes, each containing a vacuum that helps increase efficiency.
Some common applications of solar heating include:
- Heating water for domestic or commercial use
- Heating the air in a building with an air heating system
- Heating swimming pools
Solar heating offers several benefits compared to other heating methods:
- Solar energy is free and abundant once the system is installed
- Solar heating offsets the use of electricity or gas for heating
- Solar heating systems produce no emissions or pollution
- Solar thermal systems are easy to install and maintain
With over 100 million solar thermal systems installed worldwide as of 2020, solar heating is a mature and proven technology for supplying renewable heat.
Solar Cooking
Solar cooking utilizes the energy of the sun to heat, cook, and pasteurize food and water. There are several different types of solar cookers including:
Box cookers – An insulated box with a glass or plastic lid that traps heat inside the box. The food is placed inside to cook. This is one of the most common and simple designs.
Panel cookers – These have a reflective panel that focuses sunlight onto a cooking pot. The pot sits in a holder and concentrates the sun’s energy.
Parabolic cookers – These use a parabolic dish reflecting sunlight onto a focal point where the cooking pot sits. This design provides high intensity heat to cook food very fast.
Solar cooking works by using the sun’s energy as thermal radiation to heat the food and cookware inside the solar cooker. The cookers are designed to trap this heat energy either in an insulated space or by focusing the sunlight to intensely concentrate the heat. Solar cookers work best in direct sun, achieving temperatures from 200-400°F during peak hours. [1]
Solar cooking has many benefits compared to conventional cooking methods including:
– Significantly reducing fuel costs and use of limited fuel supplies such as wood, charcoal, gas or kerosene. Solar energy is free once a solar cooker is purchased. [2]
– Lowering air pollution and health hazards from indoor cooking fires which is a major issue in developing countries.
– Providing a sustainable cooking method using renewable solar energy.
– Allowing food to be cooked or pasteurized even in off-grid locations without electricity.
– Slow cooking food at lower temperatures results in better retention of nutrients.
– Portable designs allow cooking while camping or for emergency preparedness kits.
Solar Distillation
Solar distillation is a process that uses solar energy to evaporate water and then condense it into fresh drinking water. It is most commonly used for desalination and purifying water in areas with limited clean water resources.
Solar stills work by using the sun to heat saline, brackish or contaminated water in an airtight container. As the water heats up, it evaporates and condenses on the plastic or glass cover of the still. The condensation then runs down the cover into a collection trough, providing clean distilled water.
The simple design and passive operation of solar stills make them ideal for small-scale desalination and water purification. They require no electrical power and have very low operating and maintenance costs compared to other forms of desalination. Solar stills are an eco-friendly way to produce clean water in a sustainable manner.
Solar distillation has several advantages over other water purification methods:
- Removes salts, heavy metals, bacteria, viruses and parasites
- Avoids use of chemicals or filtration membranes
- Passive operation with no fuels or electricity needed
- Low cost and maintenance requirements
- Well-suited for remote or rural areas off the grid
While the yield of solar stills can be modest compared to large-scale desalination plants, they provide an accessible decentralized solution for providing clean water in water-scarce regions.
Solar drying
Solar drying is the process of using sunlight to remove moisture from various materials like food, agricultural products, and clothing. Some key applications of solar drying include:
Drying agricultural products like grains, fruits, vegetables, spices, herbs, tobacco etc. Solar dryers help retain nutrients and color in these products compared to sun drying (Solar Drying overview).
Drying fish, meat and marine products. Solar drying prevents spoilage and bacterial growth in these protein foods (Solar vs sun drying).
Drying clothes and textiles. Solar clothes dryers disinfect fabrics and reduce drying time compared to line drying (Benefits of solar drying).
Solar drying provides many benefits over conventional open sun drying methods:
– Faster drying times – solar dryers can dry foods 5x faster than sunlight. This increases throughput for agricultural products.
– Protection from insects, dust and contaminants during the drying process. This improves hygiene and storability.
– Prevention of over-drying or spoilage due to consistent temperature control.
– Solar thermal energy is free, renewable, and available in abundance in sunny climates.
– Solar dryers take up less space than open sun drying yards. They also protect privacy for drying clothes.
Overall, solar drying provides an effective method to preserve foods, textiles and other materials using clean, renewable solar energy.
Solar ponds
Solar ponds utilize a salt gradient to capture and store solar thermal energy. They consist of three layers – the top layer has low salt concentration, allowing sunlight to pass through. The bottom layer has a high salt concentration, absorbing and storing solar heat. In between is a gradient layer where the salt concentration increases with depth. This gradient setup traps heat in the bottom layer while allowing sunlight through the top layer. The stored solar thermal heat can then be used for applications like power generation and process heating.
The pond operates as a large-scale solar collector. The sunlight passes through the low-salinity upper layer and is trapped in the high-salinity lower layer. This thermal energy can then be extracted and used to generate electricity or provide process heat for industrial purposes. Solar ponds are low-cost but effective way of collecting and utilizing solar energy.
Solar furnaces
Solar furnaces use mirrors and lenses to concentrate sunlight onto a small area to produce extremely high temperatures.[1] The solar furnace at Odeillo in France can reach temperatures up to 3,500°C by using a large parabolic mirror to focus sunlight down to a 10 cm diameter.[1] The High-Flux Solar Furnace at the National Renewable Energy Lab in Colorado can achieve over 1,800°C and up to 10 kilowatts of power over a 10 cm diameter using two parabolic dishes to further concentrate sunlight.[2]
These high temperatures have applications in high-temperature processes like material research, wafer production, and hydrogen production. Solar furnaces allow clean high-temperature processes without generating greenhouse gas emissions from fossil fuel combustion. The highly concentrated sunlight can also be used to test how materials and components perform under intense heat loads.
However, solar furnaces are limited to sunny areas and cannot operate continuously without energy storage. The concentrated sunlight can also cause rapid material failure if not properly controlled. Overall, solar furnaces provide a sustainable way to reach extremely high temperatures for specialized industrial processes.
[1] https://en.wikipedia.org/wiki/Solar_furnace
[2] https://www.nrel.gov/csp/facility-hfsf.html
Solar chemical processes
Solar energy can drive useful chemical reactions through photocatalysis. Photocatalysis uses a semiconductor material to absorb light and generate charge carriers that drive redox reactions. Compared to conventional thermal or electrochemical processes, photocatalysis can enable reactions at ambient temperatures and pressures using just solar energy as the input (Schultz, 2014).
Applications of solar photocatalysis include water splitting to produce hydrogen fuel, CO2 reduction to fuels and chemicals, and organic transformations. Photocatalytic reactions often utilize visible or ultraviolet light, while conventional processes rely on high temperatures from fossil fuel combustion. Photocatalysis can achieve high efficiency and selectivity under mild conditions by tuning the semiconductor bandgap and interface (Galushchinskiy et al., 2022).
Despite the promise of solar photocatalysis, there are still challenges to commercial adoption at scale. Key barriers are the limited light absorption range of photocatalysts and rapid recombination of photogenerated charges. Ongoing research aims to develop new photocatalysts and reactor designs to improve solar utilization for sustainable chemical production.
Solar vehicles
Solar vehicles convert sunlight into motion using photovoltaic cells that transform solar energy into electrical energy (Aptera Motors, 2022). This electrical energy can then power motors to provide propulsion for the vehicle. Solar vehicles are increasingly being developed for applications like cars, planes, boats and more.
Some of the most efficient solar vehicles are purpose-built for solar racing competitions like the World Solar Challenge, where teams compete to design and build the most efficient solar-powered vehicles (CNET, 2022). Vehicles are optimized for maximal solar absorption and minimal energy usage. Many utilize lightweight materials, aerodynamic designs, and high efficiency motors.
Commercial solar vehicles also optimize for efficiency but balance practical considerations like passenger capacity. The Aptera solar car claims to require no charging for most daily use. Major car companies like Lightyear and Sono Motors are also developing solar electric cars for consumers.
Solar boats and planes have also been developed, capable of long distance travel powered purely by the sun. Advancements in photovoltaic efficiency, battery storage, and electric propulsion continue to improve solar vehicle capabilities.
Solar Electricity Generation
Solar electricity generation refers to the conversion of sunlight into electricity through photovoltaic (PV) solar panels or concentrated solar power (CSP). PV panels convert sunlight directly into direct current electricity via semiconducting materials. CSP systems use mirrors to concentrate sunlight to drive traditional steam turbines or engines that generate electricity (SEIA, 2022).
Solar electricity generation has seen tremendous growth worldwide due to improving efficiency and falling costs. As of 2021, global solar PV capacity exceeded 880 gigawatts, providing over 3% of global electricity demand. In the United States alone, total installed solar capacity grew from 2.5 gigawatts in 2010 to over 122 gigawatts by the end of 2021, enough to power 23 million American homes (SEIA, 2022).
The main driver behind the adoption of solar electricity is the precipitous drop in costs. Since 2010, the average cost to install solar has decreased by more than 70% for residential systems and over 90% for utility-scale projects (SEIA, 2022). As solar electricity achieves cost parity with fossil fuels, growth is projected to accelerate. The International Energy Agency predicts global solar capacity will reach over 4,600 gigawatts by 2030, rising to over 12,000 gigawatts by 2050.
