Solar Power

 

Sun as a Source of Power

Sun as a source of power has been on our minds for quite some time, but let us skip stories about our ancestors who painted water barrels in black to get them hot by the end of the day, and see exactly when did humans officially resolved solar power mystery and laid out the path for the success we get to enjoy today! Photovoltaic cell generating electric power, known as a solar panel today, was discovered by Alexandre Becquerel in 1839. He noticed that when electrode placed in a conductive solution was radiated by the sunlight an electric current was generated. The first solar power cell, however, wasn’t produced until almost 50 years later by the researcher Charles Fritts in 1883: he built 1% sunlight to power conversion efficiency selenium-over-gold solar panel. For comparison, this year a startup called Semprius demonstrated that its solar panels are able to convert almost 34 percent of sunlight into electricity - that’s a score! Following century, in 1904, Albert Einstein had published the paper about the photoelectric effect explaining the principles behind photovoltaic cell discovery and laid out the path for the future developments. In 1954, Bell Laboratories, now known as AT&T, made the first solar cell out of silicon; later the same company also manufactured solar power units for first satellites.

Evolution and performance

 

The following era of big V8 engines and cheap petroleum of 1950-70s had distracted everyone’s attention from developments in solar power field. Plus, units were still too expensive and inefficient: $250 per Watt produced fewer than 10% efficiency! However by 1973, when computer and semiconductor industry have forced major advances in silicon wafer manufacturing, solar power panels were produced already for $10 per Watt reaching 15% efficiency. By 2010 the price per Watt dropped to $3 and residential installations became common thing; President Obama has ordered the solar power system with hot water heater at the White House. Today, only two years later, companies like Twin Creek Technologies and others are committed to manufacture silicon panels for 40 cents per Watt – Incredible progress!

 

SOLAR POWER

Theory, Construction and Variety

 

Solar power is harnessed to generate either electricity or heat. Generally, when you hear about solar power it’s spoken about electricity; however there is strong and flourishing niche of solar power concentrating heaters designed to generate overheated steam or heat up water. Solar panels allow sun photons to generate electron traffic inside of load carrying member using photovoltaic effect. The load member of a panel can be the top or the back layer of the panel. Most modules have been made of either one: crystalline silicon wafers, silicon thin-film cells or cadmium telluride thin-film cells, interconnected between each other and the system with silver or copper wires. Recently, however alternative rare semiconductors like gallium arsenide and other are being implemented to produce high efficiency solar cells. Reverse currents and overheat are two major problems with these technologies. Reverse currents tend to be generated at night due to the waste of power and heat up of shaded cells; therefore good ventilation must be provided behind the unit.

 

 

SOLAR POWER

Monocrystalline Modules

It’s been thought that modules made out of single crystal are the most efficient, and the most expensive; 23% efficiency is a 2012 arguable efficiency record for monocrystalline modules, but recent developments in other-than-silicon semiconductor field, particularly gallium arsenide, have announced efficiencies of up to 34 percent. Single crystal panels, however, have proved themselves to survive through 30 years of harsh conditions. Among many applications are space satellites, desert and marine installations. You can easily recognize them for their shapes: octagons and "polka dots".

SOLAR POWER

Polycrystalline Modules

 

Polycrystalline and multicrystalline units are not as expensive as their monocrystalline relatives and known for lower efficiencies of around 15%. There is an apparent trade-off here between monocrystalline and polycrystalline panels, and many commercial installations are done with polycrystalline panels because of the cost. They are easy to recognize for their blue sparkling appearance.

 

SOLAR POWER

Rigid and flexible Thin-films (Amorphous cells)

Thin-film, or amorphous, cells are made by depositing ions of semiconductor on the surface of either glass, ceramic or metal. The average efficiency of these panels used to revolve around 7% but because they are much cheaper to make than one-piece silicon wafers there is a market. We see these cells every day in calculators and toys. Recent advancements in thin-film technology, however, have produced higher efficiencies at low cost attracting some serious attention. There are rigid and flexible thin-film modules. Rigid thin-films are made by applying an encapsulant on a glass or superstrate - everything is done on the same production line. Flexible thin-film modules can reach 12% sunlight-into-electric power conversion efficiency and are inexpensive.

SOLAR POWER

Flexible thin-film modules are also one production line process where photoactive layer is deposited over flexible, this time, flexible substrate which can be either conductor or insulator. Compound semiconductor technology has been commercialized since 2008 and it’s going to take little time to prove itself. Efficiencies are slightly under 10%, therefore larger surface installations are required to match the output but the price is a good trade off.

SOLAR POWER

Solar Concentrators for Electricity

Solar power concentrators are optical installations designed to focus sunlight on smaller areas in order to heat up water, produce steam or generate electric power. Solar power concentrators collect light over large areas and focus it onto smaller areas of solar cells. This increases the electrical power obtained from each cell. Solar power concentrators can reduce the cost of energy since more electricity is obtained per solar cell, and smaller cells are needed, affording to employ more expensive and higher quality semiconductors. Intensifying sunlight can easily double the efficiency of a cell reaching impressive 50% in some cases.

SOLAR POWER

Lenses or mirrors are used depending on a scale of a project. Large commercial installations use parabolic mirrors capable of refocusing sunlight power coming from any direction on one spot, while smaller units use lenses which are heavier and more expensive than mirrors.

SOLAR POWER

A startups Alta Devices and Semprius use highly efficient semiconductor called gallium arsenide to reach impressive 34% efficiency on small, button-like cells. Gallium arsenide is more efficient and expensive than silicon but the total area of photoactive layer is this way decreased and the sunlight collecting area is proportionally increased. This method drops the unit cost substantially.

SOLAR POWER

Solar Concentrators (СSP) for Heat

In 2010 Obama administration has ordered the solar power system with hot water heater at the White House indicating that heat generating solar power systems are backed by some reliable and proven technologies. Most CSP technologies use mirrors or lenses to produce intense heat in one small spot. The heat is used to produce high temperature steam or hot water, steam in turn either generates electric power or transfers heat to the heat exchanger. First concentrated solar power plant was built in Italy in 1968; this plant has established the architecture of modern CSP plants. Giovanni Francia had designed a solar power receiver surrounded by the circle of mirrors which redirected sunlight towards the receiver. The plant was able to produce 1 Megawatt of power with steam temperatures reaching 500 degrees Celsius.

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Summary

The spread of solar power technologies over to the residential market indicate the maturity and readiness to dominate the market. Recent advancements allowing producing silicon panels for less than half a dollar per watt indeed turn heads. It is only a matter of installation cost and time for the technology to spread wide. Car roofs, sidewalks, various flat surfaces have become installation targets.

SOLAR POWER

When solar power panel per-Watt cost will be measured in tens-of-cents instead of dollars, it will become an issue of installation cost rather than product price. We need to be ready for this change. Manufacturers need to focus on creating DIY and out-of-the-box packages allowing regular construction guy to perform complete installation under the guidance of residential electrician.

SOLAR POWER

References: Amecosolar.com, Wikipedia and Technology Review

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