From remote villages in Africa to skyscraper office buildings in New York City, solar panels are seemingly everywhere these days. Improvements in our ability to harness the sun’s energy for our own use have been amongst the most exciting innovations in recent years, with everything from high-tech solar cars and aircraft to rooftop solar tiles, enabling individuals to produce their own solar power and transmit this back into the energy grid.
Solar technology is nothing new, with its roots in the Industrial Revolution more than 100 years ago. But it has fought an uphill battle against government support in favor of fossil fuels ever since. Its pioneers’ efforts weren’t in vain, however, and as the world faces the prospect of dwindling fossil fuel resources, their innovations have been re-ignited and fused with modern developments.
So how did solar get to where it is today and what’s in store for the future?
The History of Solar Tiles
While solar energy may feel like a modern revelation, its history dates way back to the mid-19th century when a group of visionaries were questioning an industrial economy based on non-renewables and just how the world would cope once they were exhausted. Solar was the focus of many of their efforts as they sought new and innovative ways to capture the sun’s radiation to power machines of their era.
A mathematics instructor at the Lyce de Tours, Auguste Mouchout, was one of the first to convert solar radiation into mechanical steam power using a glass-enclosed iron cauldron. Incoming solar radiation was trapped and the rays were transmitted to heat water. Although the steam produced was minimal at first, Mouchout discovered that by adding a reflector he could create additional radiation and, therefore, more steam. In 1865 his apparatus was capable of operating a small steam engine and Emperor Napoleon III funded his development of an industrial solar motor for France, before being deployed to the country’s protectorate of Algeria to work on a larger solar steam engine.
When he returned to exhibit his redesigned invention at the Paris Exposition in 1878, he coupled the steam engine to a refrigeration system, with the steam from the solar motor being routed through a condenser and cooling a separate insulated compartment. Despite impressing his audience as a technical achievement, it was deemed by government commissioners to be a practical failure and couldn’t compete with the dropping price of coal. While Mouchout’s discovery wasn’t efficient, it proved that light could be harnessed as an energy resource, without the need for heat or other moving parts.
At the same time, deputy registrar for the English Crown in Bombay, India, William Grylls Adams was coming up with a solution to the costly and unwieldy metal reflector of Mouchout. He decided that a reflector of flat silvered mirrors could be arranged into a semicircle and used to track the sun’s movement – a setup that would be cheaper to construct and easier to maintain. While his invention was impressive, most engineers were doubtful that it could compete with coal or wood as a primary energy resource. Having proved his design, Adam’s didn’t pursue its feasibility, but even today it is considered one of the best configurations for large-scale, centralized solar plants, known as the Power Tower concept.
Further developments were made by French engineer Charles Tellier and Swiss-born American John Ericsson, and by the end of World War I, many of the solar thermal conversion methods used today were already on the table. But in a world hungry to develop fossil fuels, their technical innovations and designs went largely unsupported.
It wasn’t until 1953 that a cell was created that could produce electricity efficiently enough for small electrical devices to be powered. Led by Calvin Fuller, Gerald Pearson and Daryl Chapin, this innovation was hailed by the New York Times as “the beginning of a new era, leading eventually to the realization of harnessing the almost limitless energy of the sun for the uses of civilization.”
Three years later and the first solar tiles were commercially available, with their relatively high cost seeing them mostly used in small toys and radios. But by the late 1960’s, both the USA and Soviet Union’s space-bound satellites were powered by solar tiles.
The early 1970’s saw the cost of solar tiles drop from $100 per watt to around $20 per watt, resulting in their spread across the globe. As the environmental movements gained momentum, energy efficiency and renewable resources came to the fore and solar technology underwent somewhat of a revival. They were implemented in remote regions to power homes and transport water, as well as being used to expand telecommunication capabilities, and solar engineers began re-experimenting with ways to satisfy our need for energy using the power of the sun.
Drawing on the work of their forefathers, contemporary solar engineers took on the challenge of finding cost-effective solutions that were easy to maintain. But again, many lacked the government support needed to go ahead. Los Angeles-based Luz Co. was one of the leaders in solar technology during the 1980s, but in the words of their chairman, Newton Becker: “The failure of the world’s largest solar electric company was not due to technological or business judgment failures but rather to failures of government regulatory bodies to recognize the economic and environmental benefits of solar thermal generating plants.”
After more than a century of research and development, the only limitation to solar becoming a competitive energy resource to conventional means is financial support. We have solar powered cars and aircraft, screen printed solar cells and solar shingles to install on rooftops, with prices that are within the budget of many. It’s an inexhaustible and low-maintenance energy resource that is one of the most promising available to support our current and growing energy needs.
How Solar Tiles Work
Photovoltaic cells are the building blocks of solar, converting sunlight directly into electricity and being connected electrically into frames known as solar tiles. They are made from semiconductor materials (with silicon being the most common currently in use) which absorb light energy and use it to knock electrons loose, allowing them to flow freely. If electrical conductors are attached to the positive and negative sides, these electrons are forced to flow into a directional current by one or more electric fields, which can then be harnessed by placing metal contacts on the top and bottom of the photovoltaic cell. It’s this current (together with the cell’s voltage) that determines the wattage of power that the cell can produce.
Multiple solar modules can be wired together into an ‘array’, resulting in the production of more energy. These can be connected in either series or parallel arrangements to produce different voltage and current combinations. Most photovoltaic devices use a single junction to create semiconductor electric fields, meaning that only photons whose energy is equal or greater than the band gap of the material can free electrons into the electric circuit. In multi-junction cells (also known as “cascade” or “tandem” cells), more than one band gap and junction are used and more of the energy spectrum of light can be converted into electricity. They are stacked in descending order of band gap, with the top cell capturing high-energy photons and passing on the rest to be absorbed by lower band gap cells.
Solar Tiles and Biomimicry
As solar engineers tweak the technology we currently have in place, nature is providing inspiration in many ways, with its redesign being modeled on biological processes in what is known as biomimicry. Solar technology bio-mimicry is being utilized in the adjusted layout of heliostats (field of mirrors or large lenses used to concentrate sunlight), by adopting the spiral formation seen in sunflower florets. Nature has designed what is known as the Fermat spiral for the plant or flower to maximize its gains from the surrounding environment and be as efficient as possible. By copying this model in solar technology, a greater amount of energy can be produced, while at the same time reducing the amount of land required.
Butterfly wings have provided another inspiration, being incredibly delicate but able to harvest solar irradiation efficiently to help the animal stay warm. Electron microscopes were used to discover that overlapping, elongated rectangular scales comprised the structure of a butterfly wing, with openings that led to an underlying layer. The steep-walled ridges of the scales were found to absorb sunlight at higher wavelengths, while the openings acted as a filter so that only lower wavelengths of sunlight reached the lower layer, maximizing the amount of sunlight retained and stored by the butterfly. Understanding the principles of heat collection relating to butterfly wings have enabled researchers to apply this to the development of thin-film solar tiles. In addition to providing an insight into how we can efficiently gain heat, it has also highlighted ways to improve the energy storage capacity of solar tiles, ensuring that they are not just viable when the sun is shining.
New Advancements in Solar Technology
Researchers are constantly striving to improve the efficiency, cost-effectiveness and appeal of solar cells to make them a more viable and widespread source of energy. With current solar cells only being around 15% efficient (meaning that around 85% of sunlight reaching them is not converted into electricity), finding technologies which can harness more sunlight is at the fore.
A new type of light-sensitive nanoparticle, known as colloidal quantum dots, was recently unveiled at the University of Toronto, using n-type and p-type semiconductors that can function outdoors and increase radiant light absorption by around 8%. At the same time, researchers at the Imperial College University in London have discovered a new material known as gallium arsenide that they believe could make photovoltaic cells three times more efficient. These “triple junction cells” can be chemically altered to optimize the capture of sunlight, while using “light pipes” that guide sunlight into the system.
Another area of focus for solar scientists is how to store energy more efficiently after it is produced by photovoltaic systems, with energy currently lost if it’s not used immediately. Batteries on the market that are capable of storing this energy do so inefficiently, and are generally very expensive and with a short shelf life. Novatec Solar has recently unveiled a molten salt storage technology which uses inorganic salts to transfer photovoltaic-produced energy into solar thermal using heat transfer fluid. This would enable solar plants to operate at temperatures in excess of 500 degrees Celsius and have a higher power output, lowering the cost of solar power storage significantly. In doing so, utility companies could use solar as base load plants, rather than just to meet peak demand during daylight hours.
Tesla is also working on the aesthetics of solar, creating solar tiles in a variety of colors and textures that create a more attractive product than the solar panels currently used. The aim is to create not only a better looking roof, but a roof that has a reduced installation cost, lasts longer and provides better insulation.
The Future of Solar and Fossil Fuels
While the costs of solar are decreasing rapidly, innovations and developments are on the increase, with solar showing promising potential to eventually replace fossil fuels. In many markets around the world, unsubsidized solar is already cheaper than fossil fuels and nuclear power, while lithium ion batteries to store photovoltaic energy are also seeing a rapid increase in efficiency and reduction in costs.
Some project that globally installed solar capacity will reach 56.7 terrawatts (TW) within the next 15 years, which is the equivalent of 18.9 TW in conventional baseload power. With a projected world energy demand of 16.9 TW at that time, this would comfortably power the entire world. But there still remains substantial challenges, with governments protecting coal, nuclear, oil and gas generating stations through subsidizations. As has been the case throughout solar’s history, there needs to be a shift in thinking and our approach to energy generation if the full potential of solar is to be achieved.