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Solar energy refers to energy from the sun. It is renewable, widely available, and can be captured in various ways to provide heat, electricity, and light. With global energy needs rising and countries trying to shift away from fossil fuels, solar energy has emerged as a promising alternative and an important component of a sustainable energy future.

According to the Solar Energy Industries Association (SEIA), solar energy accounted for 3% of total U.S. electricity generation in 2020, up from just 0.1% in 2010 (Solar Industry Research Data | SEIA). With costs continuing to fall and efficiency improving, solar power is poised for tremendous growth as a mainstream energy source in the coming years. The solar resource is virtually limitless and harnessing even a tiny fraction of it could meet our energy needs many times over. Converting solar energy into usable forms like electricity and heat has the additional benefit of producing little to no greenhouse gas emissions.

In summary, solar energy is vital for building a clean energy future and mitigating climate change. With abundant potential and rapidly improving economics, solar promises to play a major role in powering the world this century.

Types of Solar Energy

There are three main types of solar energy systems: photovoltaic, solar thermal, and passive solar.

Photovoltaic Solar

Photovoltaic (PV) systems directly convert sunlight into electricity through solar cells made of semiconducting materials like silicon. When sunlight hits the solar cell, electrons are knocked loose from the atoms in the semiconductor material, creating an electric current that can be captured and used as electricity. PV systems produce clean, renewable electricity from the sun.

According to the U.S. Department of Energy, “PV technologies can be used to convert sunlight into useful energy for a variety of applications: generating electricity for homes, businesses, and industry; charging batteries; providing power to off-grid locations;and much more.” [1]

Solar Thermal

Solar thermal systems use sunlight to directly heat water or spaces. There are two main types of solar thermal technologies:

  • Low-temperature solar thermal collectors are flat panels that use sunlight to directly heat swimming pools or provide hot water for domestic or industrial use.
  • Concentrated solar power (CSP) uses mirrors to concentrate sunlight and convert it into high temperatures to produce steam to drive a turbine and generate electricity.

According to Planet Energies, “Solar thermal power has some major advantages over solar PV technology, including the ability to store energy and availability overnight.” [2]

Passive Solar

Passive solar building design utilizes windows, walls, and floors to collect, absorb, distribute and retain solar energy to heat spaces. Properly designed passive solar structures require little external power input for heating and cooling. Key elements include large south-facing windows, thermal mass to store heat, and shading to block unwanted solar gain in summer.

Photovoltaic Solar

Photovoltaic (PV) solar panels work by converting sunlight directly into electricity through the photovoltaic effect. PV cells contain materials called semiconductors such as silicon that absorb photons from sunlight and release electrons. The released electrons create an electric current that is captured and turned into usable electricity.

PV panels are made up of many individual solar cells wired together. The more solar cells a panel has, the more electricity it can produce. Solar panels are mounted on rooftops, ground mounts or solar canopies to maximize sun exposure. Tracking systems allow panels to follow the sun’s movement to optimize energy production.

For residential systems, the direct current (DC) electricity generated by solar panels is fed into inverters that convert it into alternating current (AC) electricity for household use. Any excess electricity can be fed back to the grid through net metering programs. Large solar farms feed electricity directly into the grid to supply power on a utility scale.

Source: https://www.energy.gov/eere/solar/how-solar-panels-work

Solar Thermal

Solar thermal energy involves capturing heat from the sun and using it for water heating, space heating, or electricity generation (source). There are several major applications of solar thermal energy:

Water Heating

Solar water heating systems use solar collectors and a water storage tank to heat water for domestic or commercial use. This allows for significant energy and cost savings compared to conventional electric or gas water heaters (source).

Space Heating

Solar space heating systems use solar energy to heat indoor air or water that moves through radiators, floor heating systems, or forced air systems. This can offset a significant portion of conventional heating fuel (source).

Concentrated Solar Power

Concentrated solar thermal plants use mirrors or lenses to concentrate sunlight to heat a receiver containing a heat transfer fluid. This is used to generate steam to drive a turbine for electricity generation. Solar thermal power plants can provide utility-scale renewable electricity.

Passive Solar

Passive solar design refers to the use of the sun’s energy for heating and cooling living spaces without the use of mechanical and electrical devices1. It relies on building orientation, window placement, thermal mass, and landscape features to collect, store, and distribute solar energy. The key aspects of passive solar design include:

Building Orientation – Orienting the building to face true south (in the northern hemisphere) allows for maximum exposure to the winter sun while minimizing the summer sun. Properly orienting windows, walls, and floors can maximize solar gain in the winter and minimize it in the summer2.

Apertures – South facing windows allow sunlight to enter and heat up the building. Strategically sized and placed windows can optimize solar gain and minimize heat loss.

Thermal Mass – Materials like concrete, masonry, tile, and water can absorb heat from sunlight during the day and release it slowly at night when the temperature drops. This regulates indoor temperatures3.

Proper passive solar design can reduce the need for mechanical heating and cooling, lowering energy usage. However, solar heat gain needs to be balanced properly based on climate and building needs.

History of Solar

The history of harnessing solar energy dates back thousands of years. As early as the 7th century BC, magnifying glasses were used to concentrate the sun’s rays to make fire [1]. Solar technology continued to advance through the 18th and 19th centuries as researchers developed more efficient ways of harnessing the sun’s energy for heat and steam power.

Some key innovations in early solar technology include:

  • In the 1760s, Swiss scientist Horace de Saussure built the world’s first solar collector, which was used to heat water and cook food.
  • In 1839, French physicist Edmond Becquerel discovered the photovoltaic effect while experimenting with metal electrodes in electrolyte solutions.
  • In 1868, Auguste Mouchout used a parabolic trough to produce steam for the first solar steam engine.

These early solar devices were expensive and not widely adopted. But in the 1950s, scientists at Bell Laboratories developed the first practical photovoltaic cell, which was used to power space satellites. This paved the way for broader commercialization of solar photovoltaics [2].

As solar panel technology improved in efficiency and costs declined dramatically in the late 20th century, solar energy adoption accelerated. Continued enhancements in solar cell efficiency, manufacturing, and economies of scale have further reduced costs, making solar energy more economically viable and accessible.

Solar Potential

Solar energy has enormous potential globally according to the Global Photovoltaic Power Potential by Country study by the World Bank Group, which mapped solar irradiation around the world. The study found that many countries, especially those near the equator, receive abundant levels of solar irradiance that could be harnessed for solar power generation. For example, countries like Brazil, China, India, Mexico and Saudi Arabia have “exceptionally high” potentials for solar PV generation. Specifically, the study states China has an average solar PV potential of over 4.5 kWh/kWp and India over 5 kWh/kWp.

The growth projections for solar are also very promising. Solar power capacity has been growing exponentially in the past decade, with an average annual growth rate of over 30%, according to the International Renewable Energy Agency (IRENA). IRENA projects global solar PV capacity to reach over 8,500 GW by 2050 under their ‘Transforming Energy Scenario’, meeting over 15% of global electricity demand. With supportive policies, technological improvements and falling costs, solar is poised to keep growing rapidly in the coming decades.

Benefits of Solar

Solar energy has several important benefits that make it an attractive renewable energy source. First, solar energy is completely renewable and sustainable. The sun provides an endless supply of energy that will not run out for billions of years (1). Harnessing solar energy does not deplete resources or damage the environment like fossil fuels.

Using solar energy also significantly reduces greenhouse gas emissions and air pollution. Generating electricity from solar panels produces no direct carbon emissions, in contrast to burning coal, oil, and natural gas (2). Widespread adoption of solar would help mitigate climate change and improve public health through better air quality.

Solar energy enhances energy independence and national security. With more distributed solar, countries rely less on imported fossil fuels and are insulated from global oil and gas price shocks. Solar diversifies and decentralizes energy production (3). Rooftop solar also makes the grid more resilient to outages by providing local backup power.

(1) https://www.energy.gov/energysaver/benefits-residential-solar-electricity

(2) https://www.enelgreenpower.com/learning-hub/renewable-energies/solar-energy/advantages-solar-energy

Limitations of Solar

While solar energy has many benefits, there are some limitations to be aware of [1]. The biggest limitation is intermittency – solar energy relies on sunlight to produce electricity, so it can’t be generated at night or when it’s cloudy. This means solar often needs to be paired with energy storage or a backup power source [2].

Solar energy also has high upfront costs. While solar panels can generate electricity for decades, installing a solar system requires a significant initial investment. This can deter some homeowners and businesses from choosing solar.

In addition, solar energy storage using batteries can be expensive. Storing solar energy for use when the sun isn’t shining adds to the overall cost of a solar system. Advances in battery storage technologies may help address this limitation over time.

Future of Solar

The future of solar energy looks bright, with predictions of strong growth and exciting new developments on the horizon. According to the Solar Energy Industries Association, total solar capacity in the United States is forecast to more than double from 2022 to 2026, increasing from 140 GW to over 400 GW. [1]

One major focus in solar technology is improving efficiency. Researchers are exploring advanced materials and designs to absorb more sunlight and convert it to electricity more effectively. For example, perovskite solar cells have potential to reach over 25% efficiency, compared to around 16-22% for today’s commercial silicon solar panels.[2] Multi-junction cells with multiple layers tuned to absorb different wavelengths of light are also being developed.

In terms of new technologies, floating solar farms placed on bodies of water are gaining steam, providing greater efficiency by keeping panels cool. Solar microgrids that can operate independently are becoming more popular as well. One futuristic concept is space-based solar power, with solar collectors in orbit that can beam energy down to Earth via lasers or microwaves.[3]

With solar already among the cheapest sources of electricity generation, projections point to it supplying up to 20% of U.S. electricity by 2030 and 45% by 2050. As technology improves and costs continue to fall, the future looks very bright for solar energy.

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