Solar Power: A popular misunderstanding?

Depictions of our Sun and its ability to provide for both our forests and now our cities has been a staple of countless environmental sustainability and renewable energy campaigns. Simply put: when many people think about renewable energy, they think about solar panels. Yet, even with all of the attention and press that solar receives, misperceptions persist: many people are unaware that there even are other ways than solar panels to harness the energy of the sun. Indeed, there is much more to the world of solar power than meets the eye. This article will act as a brief guide to explain the main types of solar power, how they work, and where we might see more of them in the future.

Photovoltaic Cells

The most widely known form of solar power is the solar photovoltaic cell, otherwise known as the solar panel. Solar panels are characterized by flat surfaces (usually dark blue or black in color) positioned on the ground or the roof of a building and carefully oriented towards the sky. A photovoltaic cell uses the physical and chemical properties of its materials in order to turn sunlight into a usable current of electricity. The process is driven by the energy in the photons (particles of light), and therefore does not use any depletable fuel. Additionally, the process of turning sunlight into electricity does not deplete the solar panel, and so the panel can operate indefinitely, although natural wearing down leads to solar panels lasting a few decades.

As of now, solar panels convert 15-20% of the incident sunlight into electricity, a number that has increased in recent years. Further breakthroughs promise to raise the efficiency of photovoltaic cells even more.

Active Solar Power

Active solar power is usually characterized by a contained fluid (commonly liquid, but sometimes air) that is heated by sunlight and then circulated through the system. The fluid may be contained in an evacuated tube, or in flat plates that are heated by the sun. This system essentially uses the heat absorbing properties of the fluid in order to transfer the heat energy from sunlight to the desired location (usually floor boards or a water heater). In a way, this is similar to how a water bottle left in the car on a summer day will heat up and stay warm for a while. An active solar system makes use of this retained heat!

Active solar systems can be combined with other technologies, such as water tanks, hot water baseboards, radiators, or forced air systems to provide heat and hot water to homes. As with most forms of solar (and renewables in general), different geographic locations will benefit more from active solar systems than others, and the technologies have only gotten better with time.

Passive Solar

Passive solar power is different from the other types of solar that will be discussed in this article. This is because passive solar is not thought of as a system containing parts and technologies to capture, transport, and store solar energy. Rather, passive solar is better thought of as the design principles of a structure (a home or office building for example) that capture, transport, and store solar energy. For example, some effective aspects of passive solar include window orientation, construction materials, roof overhang, and heat distribution (or dispersal) mechanisms. A proper passive solar design will vary depending on the climate in which the building is situated, but if executed correctly, passive solar makes use of natural climate in order to reduce both heating and cooling expenses. There are no maintenance or operating costs specific to passive solar: once built, the structure uses the benefits of the sun on its own. While the efficiency of passive solar will vary depending on the design and surrounding climate of the building, in conjunction with other forms of solar power, it can lead to efficient and sustainable home energy use.

Solar Thermal Energy

The final type of solar energy to be discussed here is solar thermal energy. This form of solar employs an array of solar concentrators (or solar mirrors) to focus sunlight onto a small area, called the receiver. Such energy concentrated on a small area produces extremely high temperatures that rapidly heat up a liquid in the receiver that is circulated in the system. The hot liquid is then used to make steam, which turns a turbine and effectively converts the heat energy into mechanical energy. This is different from an active solar system, because in solar thermal, the energy from the sunlight is used to make steam and then electricity, and is not circulated around a building for heating purposes. Additionally, solar thermal energy is usually on a much larger scale than active solar. Where active solar may be more suited to a home or business, solar thermal energy may be used to power part of an electrical grid. Currently, solar thermal energy is more so utilized in the Western United States, where large arrays of mirrors can be erected in open, flat places that receive ample sunlight. Yet, solar thermal is also possible on a small scale, as some companies have developed solar grills. These small systems use solar thermal energy to cook food and are geared towards areas that are remote (villages in Africa, and American camping grounds alike) and could benefit from the readily available and clean energy of the sun. New technologies have also focused on solar thermal’s ability to supplement other forms of renewable energy, such as in heat driven water separation systems, where solar thermal is used to create hydrogen fuel.

Article written by Eric West, Undergraduate at Cornell University

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