What Is Solar Energy
What is Solar Energy?
Solar energy is radiant light and heat from the sun that is harnessed using a range of technologies such as solar heating, photovoltaics, and solar thermal energy to generate electricity and provide heating/cooling for homes, businesses, and industry (Solar energy – Encyclopedia Britannica). Sunlight is converted into electricity using the photovoltaic effect, where photons from sunlight excite electrons in a solar cell to generate electric current.
The idea of harnessing solar power dates back to the 7th Century B.C., but it was not until 1883 that the first solar cells capable of converting sunlight into electricity were created by Charles Fritts. Modern solar cell technology advanced rapidly starting in the 1950s as solar adoption expanded for residential and commercial uses (About Solar Energy – SEIA). Today solar energy is one of the fastest growing and most promising renewable energy sources worldwide.
Different Types of Solar Energy Technologies
There are several technologies that utilize solar energy, the most common being:
Photovoltaics (PV)
Photovoltaic panels, commonly known as solar panels, convert sunlight directly into electricity using semiconducting materials. Solar panels are composed of photovoltaic cells made from materials such as crystalline silicon or thin-film semiconductor material. When sunlight hits the cells, the absorbed energy knocks electrons loose, allowing the electrons to flow and produce electricity (NREL).
Solar Heating & Cooling (SHC)
Solar heating and cooling systems use solar thermal collectors to absorb and convert sunlight into heat energy. This heat can then be used directly to provide hot water and space heating or used to drive an absorption cooling system for air conditioning (DOE). Common SHC technologies include solar water heating systems, solar air heating, and solar absorption cooling.
Concentrated Solar Power (CSP)
Concentrated solar power systems use mirrors or lenses to concentrate sunlight onto a small area, generating high temperatures that are used to produce electricity through a steam turbine or heat engine. CSP technologies include parabolic trough, linear Fresnel reflector, power tower, and parabolic dish/engine systems (NREL).
Passive Solar Building Design
Passive solar building design utilizes solar energy by the strategic placement and design of windows, walls, floors and roofs to maximize heating, cooling and lighting without the need for mechanical systems (DOE). Techniques include south-facing windows, thermal mass and insulation.
How Solar Panels Work
Solar panels convert sunlight into electricity through the photovoltaic effect. They are made up of photovoltaic cells, which are made from semiconductor materials like silicon. When sunlight hits the solar cell, the energy from the photons of light excites the electrons in the semiconductor material, causing them to flow and generate an electric current.
The photoelectric effect refers to this process of electrons being emitted from a material when it absorbs light. The amount of current generated depends on the intensity and wavelength of the sunlight. For solar panels, the optimum wavelength is visible light which has enough energy to produce electricity efficiently.
Solar panels are composed of many solar cells wired together. Each cell contains positive and negative charged layers that create an electric field. When sunlight excites the electrons, this electric field forces the electrons to flow in one direction, producing direct current (DC) electricity. An inverter then converts this to the alternating current (AC) used for appliances.
Silicon is commonly used in solar cells, which can be amorphous, monocrystalline or polycrystalline. The purity and crystal structure affects how efficiently it can convert sunlight into electricity. Other materials like gallium arsenide are also used for higher efficiency.
References:
https://www.iop.org/explore-physics/physics-around-you/sustainable-building/solar-panels
https://pickmysolar.com/how-solar-panels-work/
Solar Energy Storage
Solar energy is an intermittent resource, meaning it is not available at all times. As a result, storing the energy generated by solar technologies is an important consideration for utilizing solar power effectively. There are several ways to store solar energy, with batteries, thermal storage, and pumped hydro storage being among the most common methods [1].
Batteries are one of the most widely used storage methods for solar power systems. Batteries like lithium-ion and lead-acid allow generated electricity to be stored and discharged when needed, such as at night. Batteries provide short-term storage, from a few hours up to a day [2]. Thermal storage involves heating up a material or substance during sunlight hours and utilizing the trapped heat after sundown. This allows solar thermal systems to continue operating when the sun is not shining. Thermal storage mediums include molten salt, water, rock beds, and phase change materials [2].
Pumped hydro storage is a large-scale grid energy storage method ideal for solar power. During peak solar energy production, excess electricity is used to pump water uphill into a reservoir. When energy is needed, the water is released back downhill to turn turbines and generate electricity again. Pumped hydro can provide longer-term storage than batteries [1].
Advantages of Solar Power
Solar energy has several key advantages that make it an attractive renewable energy source. First, solar is a completely renewable resource that reduces dependence on finite fossil fuels like coal, oil and natural gas. Sunlight will continue shining on Earth for billions of years, making solar a sustainable long-term energy solution.
Solar energy also provides cost savings over time. While the upfront installation costs are still high, homeowners recoup these expenses through lower or eliminated electricity bills. Many local and federal incentives also help offset the initial investment. Once installed, the fuel itself – sunlight – is free.
There are also environmental benefits to going solar. Solar panels generate clean power without any harmful air or water pollution. Widespread adoption would significantly cut greenhouse gas emissions that contribute to climate change and improve public health.
With no moving parts and minimal maintenance needs, solar PV systems can operate for decades with a lifespan of 25-30 years. They are extremely reliable, durable and require little ongoing costs other than occasional panel cleaning.
Disadvantages & Challenges of Solar
While solar energy has many benefits, there are some notable disadvantages and challenges to be aware of. One of the major drawbacks of solar energy is intermittency – solar power relies on sunlight so energy production declines or stops altogether when it’s cloudy or at night. This can cause issues meeting energy demand if solar is relied on too heavily in a region. Storage solutions like batteries can help address intermittency but add significant cost.
High upfront costs are another key disadvantage of solar power. Installation of solar panels and related infrastructure is very capital intensive for homeowners or utility companies (https://www.nachi.org/disadvantages-solar-energy.htm). The costs of solar panels have gone down substantially but are still prohibitive for many adopters.
Solar projects can also face land use constraints and meeting regulatory requirements. Large solar farms take up significant amounts of land which could have alternative uses or value (https://www.constellation.com/energy-101/energy-innovation/solar-energy-pros-and-cons.html). Roof top solar on homes has space limitations as well. There are also limitations around effectively transporting and storing solar energy from remote solar farms to demand centers.
While great progress has been made, these challenges continue to limit more widespread solar adoption. However, falling costs, policy support, and technology improvements are helping address these issues over time.
Solar Energy Adoption & Capacity
Solar power capacity has grown rapidly in recent years as costs have declined and more countries adopt policies to accelerate renewable energy deployment. As of 2020, the world had over 760 gigawatts (GW) of total installed solar PV capacity, up from around 40 GW in 2010 [1]. The top countries for total installed solar PV capacity in 2020 were [2]:
- China – 253 GW
- United States – 96 GW
- Japan – 71 GW
- Germany – 54 GW
- India – 45 GW
In terms of solar energy penetration as a share of total electricity generation, the top countries in 2020 were [3]:
- Honduras – 17%
- Australia – 16%
- Chile – 16%
- Israel – 15%
- Germany – 12%
Global solar PV capacity is expected to continue growing over the next decade, potentially reaching over 5,000 GW by 2030 according to projections by the International Renewable Energy Agency [4]. Key factors driving growth include improving cost-competitiveness, supportive government policies, and the need for clean energy to combat climate change.
Notable Solar Power Projects
Some of the world’s largest and most notable solar power projects and installations include:
The Bhadla Solar Park in Rajasthan, India covers an area of 56 square kilometers and has a total capacity of 2,245 MW, making it one of the largest solar parks in the world [1].
The Topaz Solar Farm in California, USA is one of the largest solar power plants in the world with a capacity of 550 MW [2]. It covers an area of 25 square km.
The Villanueva Solar Park in Coahuila, Mexico is the largest solar plant in the Americas with an 828 MW capacity [3]. It covers over 5,000 acres of land.
The Benban Solar Park in Egypt has a capacity of 1.6 GW, making it one of the largest solar parks worldwide. It is located in the Sahara desert near Aswan.
The Tengger Desert Solar Park in Ningxia, China with 1.5 GW capacity is one of the biggest PV solar farms in the world. It covers an area of 43 square km.
The Kamuthi Solar Power Project in Tamil Nadu, India has a capacity of 648 MW and covers an area of 10 square km. At the time of its completion in 2016, it was the largest single-site solar plant in the world.
Solar Energy Policy & Incentives
Governments at the federal, state, and local levels have implemented a variety of policies and incentives to encourage solar energy adoption. These include subsidies, tax credits, solar mandates, and net metering policies.
The federal government offers a 26% tax credit for installing residential solar energy systems. This credit applies to both solar panels and other equipment like inverters and battery storage. Many states also offer additional tax credits and rebates for going solar.
Some states like California, New Jersey, and Nevada have renewable portfolio standards that mandate utilities to source a certain percentage of their electricity from solar. Over 30 states also have net metering policies that allow solar panel owners to sell excess electricity back to the grid.
Local governments may also provide property tax exemptions, rebates, and permitting incentives for residential solar installations. Overall, federal, state and local solar incentives aim to make the economics of solar more favorable for homeowners and businesses.
Future Outlook for Solar Energy
The future outlook for solar energy is positive, with projections for substantial growth in the coming years and decades. According to the International Energy Agency (IEA), global solar PV capacity is projected to reach over 5,500 gigawatts by 2040, a nearly 10 fold increase from 2022 levels https://www.iea.org/reports/world-energy-outlook-2022/executive-summary. The IEA’s stated policies scenario predicts that solar PV will provide over 15% of global electricity by 2040. This growth will be driven by continued cost declines and supportive government policies.
Emerging solar technologies like perovskite solar cells and organic PV could enable greater efficiency and flexibility in solar applications. With continued research and development, these new solar technologies have the potential to greatly expand the role of solar energy. Additionally, improvements in energy storage technology will help address the intermittency issues associated with solar and make it more feasible for solar to meet a higher share of energy demand.
According to an analysis by the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL), solar PV and concentrated solar power (CSP) together have the technical potential to provide up to 40% of the nation’s electricity by 2035 and up to 45% by 2050 https://www.nrel.gov/docs/fy12osti/51946.pdf. Realizing this potential would require substantial solar deployment along with investments in complementary technologies like energy storage and transmission infrastructure upgrades. With supportive policies, continued cost reductions, and technology advances, solar appears poised to become a major pillar of the global energy system this century.
