Yesterday millions of people across the U.S. experienced the first total solar eclipse visible from coast to coast in 99 years. In honor of that event, this week’s #TechTuesday is dedicated to a Photovoltaic System.
Solar cells, also called photovoltaic (PV) cells by scientists, convert sunlight directly into electricity. PV gets its name from the process of converting light (photons) to electricity (voltage), which is called the PV effect. The PV effect was discovered in 1954, when scientists at Bell Telephone discovered that silicon (an element found in sand) created an electric charge when exposed to sunlight. Soon solar cells were being used to power space satellites and smaller items like calculators and watches. (NREL)
PV cells come in many sizes and shapes, from smaller than a postage stamp to several inches across. Solar cells are often less than the thickness of four human hairs. In order to withstand the outdoors for many years, cells are sandwiched between protective materials in a combination of glass and/or plastics to make a PV module.
In order for the generated electricity to be useful in a home or business, a number of other technologies must be in place:
- Mounting Structures
PV arrays must be mounted on a stable, durable structure that can support the array and withstand wind, rain, hail, and corrosion over decades. These structures tilt the PV array at a fixed angle determined by the local latitude, orientation of the structure, and electrical load requirements. To obtain the highest annual energy output, modules in the northern hemisphere are pointed due south and inclined at an angle equal to the local latitude. Rack mounting is currently the most common method because it is robust, versatile, and easy to construct and install.
Inverters are used to convert the direct current (DC) electricity generated by solar photovoltaic modules into alternating current (AC) electricity, which is used for local transmission of electricity, as well as most appliances in our homes. PV systems either have one inverter that converts the electricity generated by all of the modules, or microinverters that are attached to each individual module. A single inverter is generally less expensive and can be more easily cooled and serviced when needed. The microinverter allows for independent operation of each panel, which is useful if some modules might be shaded.
Advanced inverters, or “smart inverters,” allow for two-way communication between the inverter and the electrical utility. This can help balance supply and demand either automatically or via remote communication with utility operators. Allowing utilities to have this insight into (and possible control of) supply and demand allows them to reduce costs, ensure grid stability, and reduce the likelihood of power outages.
Batteries allow for the storage of solar photovoltaic energy, so we can use it to power our homes at night or when weather elements keep sunlight from reaching PV panels. Not only can they be used in homes, but batteries are playing an increasingly important role for utilities. As customers feed solar energy back into the grid, batteries can store it so it can be returned to customers at a later time. The increased use of batteries will help modernize and stabilize our country’s electric grid.
Advantages of Solar Energy
- Renewable: Solar energy is a renewable energy source. This means that we cannot run out of solar energy. We will have access to solar energy for as long as the sun is alive – another 6.5 billion years according to NASA.
- Abundant: The potential of solar energy is beyond imagination. The surface of the earth receives 120,000 terawatts of solar radiation (sunlight) – 20,000 times more power than what is needed to supply the entire world.
- Sustainable: An abundant and renewable energy source is also sustainable. Sustainable energy sources meet the needs of the present without compromising the ability of future generations to meet their needs. In other words, solar energy is sustainable because there is no way we can over-consume.
- Environmentally Friendly: Harnessing solar energy does generally not cause pollution. However, there are emissions associated with the manufacturing, transportation and installation of solar power systems – almost nothing compared to most conventional energy sources. It is clear that solar energy reduces our dependence on non-renewable energy sources. This is an important step in fighting the climate crisis.
- Good Availability: Solar energy is available all over the world. Not only the countries that are closest to the Equator can put solar energy to use – Germany, for example, has by far the highest capacity of solar power in the world.
- Reduces Electricity Costs: With the introduction of net metering and feed-in tariff (FIT) schemes, homeowners can now “sell” excess electricity, or receive bill credits, during times when they produce more electricity than what they actually consume. This means that homeowners can reduce their overall electricity expenses by going solar. Data from One Block Off the Grid reveals that adding solar panels to your home can bring in monthly savings of well above $100 in many states. In Hawaii, residents save on average $64,000 after 20 years. Nowadays, most homeowners choose leasing or power purchase agreements to finance their solar panels. This drastically reduces, or in some cases completely eliminates, the upfront costs of a solar panel system, and allows homeowners to start saving money from the first day.
- Many Applications: Solar energy can be used for many different purposes. It can be used to generate electricity in places that lack a grid connection, for distilling water in Africa, or even to power satellites in space. With the introduction of flexible thin-film solar cells, solar power can even be seemingly integrated into the material of buildings (building integrated photovoltaics) – Sharp, a solar panel manufacturer with headquarters in Japan, recently introduced transparent solar power windows.
- Silent: There are no moving parts involved in most applications of solar power. There is no noise associated with photovoltaics. This compares favorable to certain other green-techs such as wind turbines.
- Financial Support from Government/State: Government and state rebates have become available both on utility-scale and for the majority of homeowners. This means that the effective costs of solar panels are much less than what they used to be. In some cases, the price of a residential photovoltaic system can be cut more than 50%.
- Low Maintenance: The majority of today`s solar power systems do not required a lot of maintenance. Residential solar panels usually only require cleaning a couple of times a year. Serious solar manufacturers ship 20- or 25-year warranties with their solar panels.
- Technology is Improving: Technological advancements are constantly being made in the solar power industry. Innovation in nanotechnology and quantum physics has the potential to triple the electrical output of solar panels.
Disadvantages of Solar Energy
- Intermittent: Solar energy is an intermittent energy source. Access to sunlight is limited at certain times (e.g. morning and night). Predicting overcast days can be difficult. This is why solar power is not our first choice when it comes to meeting the base load energy demand. However, solar power has fewer problems than wind power when it comes to intermittence.
- Energy Storage is Expensive: Energy storage systems such as batteries will help smoothen out demand and load, making solar power more stable, but these technologies are also expensive. Luckily, there`s a good correspondence between our access to solar energy and human energy demand. Our electricity demand peaks in the middle of the day, which also happens to be the same time there`s a lot of sunlight!
- Associated with Pollution: While solar power certainly is less polluting than fossil fuels, some problems do exist. Some manufacturing processes are associated with greenhouse gas emissions. Transportation and installation of solar power systems can also indirectly cause pollution. The bottom line is this: There’s nothing that’s completely risk-free in the energy world, but solar power compares very favorably with all other technologies.
- Exotic Materials: Certain solar cells require materials that are expensive and rare in nature. This is especially true for thin-film solar cells that are based on either cadmium telluride (CdTe) or copper indium gallium selenide (CIGS).
- Requires Space: Power density, or watt per square meter (W/m²), is essential when looking at how much power can be derived from a certain area of real estate of an energy source. Low power density indicates that too much real estate is required to provide the power we demand at reasonably prices.
The largest PV systems in the country are located in California and produce power for utilities to distribute to their customers.
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Aerial photos show photovoltaic power generation in Zibo, east China's Shandong Province. (Photo/Xinhua) pic.twitter.com/AnQL1LWkLs
— People's Daily,China (@PDChina) August 19, 2017