Edmund Becquerel- The photovoltaic effect was first noted by a French physicist, Edmund Becquerel, in 1839, who found that certain materials would produce small amounts of electric current when exposed to light. At the age of 19, in the acidic solution, he placed silver chloride (AgCl) and illuminated with different types of light, including sunlight – while connected to the platinum electrodes, which ultimately produced some voltage and current. When the electrodes were coated with AgCl, which was a sensitive material and the light shining was ultraviolet light, then the best results were produced – most electric current and voltage was produced.
Bell Laboratories- Later in 1954 Bell Laboratories finished the creation of the first practical finished silicon solar cell, with a low-efficiency percentage of 6%. However, the efficiency may have been low, but the creation of the solar cell (“solar battery”), was just the starting, as the solar cells would improve as would technology overtime, leading to a sustainable limitless energy source of the sun – renewable energy, with the help of more efficient solar cells.
Albert Einstein- The G.O.A.T., Albert Einstein back in 1905, proposed that electromagnetic radiation acts as both a particle and a wave, which answered all the questions for the photoelectric effect, which classical physics could not explain, but modern physics could. He proved that light is a particle (photons – packets of light which carry energy) and the flow of the photons is a wave. Einstein’s quantum light theory (photons) suggests that a beam of light must have a frequency (f) which must consist of individual photons which will have some energy (hf), and the energy of the photon is proportional to its frequency (f). So, the higher the photon’s frequency, the higher its energy greater (Ek of electron), vice versa, as long frequency is greater than the threshold frequency (f0). Wavelength is inversely proportional to the frequency of the wave. Thus equally, the smaller the photon’s wavelength, the greater its energy (greater Ek of electron), vice versa, as long wavelength is smaller than the maximum wavelength (0). He stated that height of the oscillation frequency is the photon energy (hf) and the number of photons is dependent on the intensity of the light. His observations were that electron needs to absorb a certain amount energy before it can fly off the metal plate. The energy arrives all at once, as a photon, rather than gradually, as a wave, which explains why there is no time lapse between the shining of light ad liberation of electrons. One photon will only collide with one electron in the metal plate. Every material has a different work function , which is the minimum required energy that an electron must absorb to set free, and – any remaining energy turns into kinetic energy (Ekmax) for the electron (Ekmax = E – ). The photons must have a higher energy than the work function of that specific material. The energy of a photon depends on the wavelength of the light, a long wavelength will not be able to liberate the electrons. While light with a small wavelength (big frequency) will be able to free the electron from the metal plate, as long the wavelength must be smaller than the maximum wavelength (0). The smaller the wavelength, the greater the Ekmax imparted to the escaping electrons by the collisions. He noticed if the wavelength of the light is smaller than the max wavelength , then an increase in light intensity will result in more photons, however, the amount of energy (hf) a photon consists of does not change. If the wavelength of the light is greater than the max wavelength, then increasing the light intensity will have no effect on emitting electrons as no electrons will be emitted.
Energy of a photon (hf) could also be expressed in terms of wavelength () by using the equation: E= hc
Silicon Doping- Elements from a different group will make up different semiconductors, and which are usable, but in today’s technology Silicon from group 14 has proven to be the best material in photovoltaic cells, because of its availability and moderate cost. Different materials will have different band gaps (Eg), which is essentially the amount of energy required by a photon to emit an electron from the p-n junction. Silicon has a very low band gap of 1.14eV which means that even the longest of infrared wavelengths will be able to knock and electron free. However, the element Germanium is found to have the lowest band gap of any material of 0.67eV, which means that the majority of the light coming will be able to emit electrons and conduct electricity, with the highest efficiency, however Germanium is a rare and expensive element, thus it is not used in solar cells, but rather in rockets and spacecrafts.
Silicon is the second most abundant element on earth and is commonly used in solar cells (Photovoltaics) as a semiconductor because of its atomic structure and because it can handle much higher temperatures than germanium while in use. Silicon shares properties of metals and of an insulator, thus making it a great use in solar cells. The silicon atom has a total of 14 electrons, with the first two shells full which hold 2 and 8 electrons. And with the third shell holding 4 electrons which is only half full, thus it needs 4 more electrons in the valence shell to gain sustainability. Therefore, the silicon atom will share four bonds with 4 other silicon atoms to form a stable silicon crystal with 8 electrons in the valence shell. This creates the crystalline structure which is used in photovoltaic cells. However, pure crystalline is a bad conductor because absolutely none of the electrons are able to move around. In order to make it a good electrical conductor, the silicon in the solar cells have impurities, where there are different atoms mixed in with silicon, causing the process called, doping. In order to change the silicon crystal’s electrical properties, therefore doping must occur which is the process of creating N-type and P-type semiconductors, by introducing foreign atoms such as boron and phosphorus as impurities to the silicon. Electricity is created by the flow of free electrons which carry current within the cell’s electric field. For the silicon atoms, equilibrium is easily attainable as each atom needs 4 electrons for a valence shell which could be done by sharing its 4 electrons.
Phosphorus is an element used as a doping agent, which has 5 valence electrons and is introduced to the silicon crystals as impurities, which begins to normally share electrons to gain a valence shell, however, there is still one electron that remains unbounded. When energy is introduced to the crystal, then the electron gets dislodged from the atomic shell, causing it to be negatively charged. This is called the N-type semiconductor, where N stands for negative.
Boron is an element used as a doping agent, which has 3 valence electrons and is introduced to the silicon crystals as impurities, which begins to normally share electrons to gain a valence shell, however, there is a lack of electrons, thus holes are formed. Therefore, this crystal will carry the positive charge because it needs extra electrons to fill the hole left thus making it a P-Type Semiconductor where P stands for positive. The holes move around seeking to be filled just as the free electrons move around looking for holes to fill.
The combination of both the N-type and P-type semiconductors make a solar cell. An electric field is made when these two semiconductors are in contact with each other, which is a must for electricity to flow in the solar cell. On the N side, there are free electrons which are attracted to the holes formed on the P side, however, at the point of contact, there is the junction of both the semiconductors. A barrier is formed by the mixture of electrons and holes preventing the free electrons on the N side from reaching the holes on the P side. The barrier turns into an electric field which is separating the two sides when in equilibrium. The barrier acts as a diode allowing the flow of electrons in one direction, from the P-type semiconductor to the N-type. In order to create electricity, sunlight is required which will beam onto the solar cell, causing electrons to get emitted and thus generating a flow of electrons through a certain pathway within the electric field and then through an external circuit which will then force the holes and electrons to reunite together and create an electric current. This process is recurring whilst sunlight is available, thus it will keep producing electricity.
Different materials have a different band gap energy (Eg). The thin layer on top of the cell becomes doped giving its p-n junction with its particular bandgap. The bandgap energy is the amount of energy required to emit an electron from the p-n junction. A photon will hit onto the solar cell and the photon either be reflected and heat will be produced or the photon will be transmitted into the cell. If the photons (hf) energy is less than the band gap (Eg) of the absorber material, then an electron-hole pair won’t be created, so their energy is not converted to a useful output, and will only generate heat. Whereas, if the energy of the photon (hf) is greater than the band gap (Eg), then an electron will be emitted, generating an electron-hole-pair. Both the holes and electrons will move towards their respective sides.
Light has dual properties of both a wave and particle, the light come in packets of energy called, photons and the flow of the photons is a wave. More than likely a single visible photon, even with a long wavelength will be able to able to supply energy (hc ) to emit an electron when it hits the solar cell by providing enough energy to overcome the band gap (Eg) of the silicon which is 1.14 eV and a fraction of remaining energy will be turned into kinetic energy (Ek) for the dislodged electron and excess kinetic energy through the phonon interactions will be lost in heat. The shorter its wavelength the greater the energy of the photon (measured in eV or J), vice versa. And the more intense the light, the more electrons emitted, one photon dislodging one electron, as long as the wavelength is smaller than the max wavelength (0).In dislodging an electron, a hole will be created instantaneously, the barrier allows the flow of electrons to the N-side only, and the hole will be sent down towards the P-type semiconductor, whereas the electron will be sent upwards to the N-type semiconductor. Since, silicon is a semiconductor, it will act as an insulator and will maintain the imbalance created by the emitted electron in the equilibrium (stability), therefore, the dislodged electron will want to return to the P-side, in order to settle back into equilibrium. The electron is unable to travel through to P Side from the N-Side because of the p-n junction and the created electric field. Thus, in order for the electrons to travel back to the P-side, an external path is built, which results in a current through the recurring movement of electrons through the circuit.
Silicon Cells- A solar cell is a photovoltaic cell which is a device that generates electricity directly from visible light by means of the photovoltaic effect, in which an electron gets emitted to form a current and thus electricity. Around 85% of the photovoltaics around the world are made from silicon variations. The main difference between most solar panels is the purity of the silicon, as the more perfectly aligned the silicon molecules are, the better the solar cell will be at converting solar energy (sunlight) into electricity. The efficiency of solar panels goes hand in hand with purity, but the processes used to enhance the purity of silicon are expensive. Most people’s deciding factors in buying solar panels are the panels cost and space-efficiency.
Amorphous Silicon (Thin Film)- Thin-Film Solar cells are made by depositing thin layers of photovoltaic material on a substrate. Film solar cells may use silicon or other substances as the active material. The photovoltaic substance that is used varies and multiple combinations of substances have successfully and commercially been used. Currently, the four most known materials used in thin-film cells are: Cadmium telluride (CdTe), Copper indium gallium selenide (CIGS), Amorphous silicon (a-Si), Organic photovoltaic cells. The silicon material is not structured or crystallised on a molecular level, as many other types of silicon-based solar cells are. The availability in New Zealand seems to be very minimal as these solar panels are still currently in development in order to go up against mono and polycrystalline solar panels. The price per watt is around 0.8$/ W NZD, which is the most expensive in New Zealand, just due to its rarity and small mass production in New Zealand.
Advantages- Amorphous silicon can be deposited onto substrates at temperatures below 300°C, which makes the technology a good candidate for flexible substrates and roll-to-roll manufacturing techniques. Amorphous Silicon is much more simplistic and thus, cheaper to make as the substrates can be made out of inexpensive materials such as glass, stainless steel and plastic. Amorphous silicon is a direct-bandgap material, and therefore only require about 1% of the silicon that would`ve been used to produce a crystalline silicon-based solar cell. They are much more flexible, light in weight, and also have a low thickness, making it easy to install on different rooftop structures such as curved surfaces. They still work well even in the shade and in poor lighting conditions. Amorphous Silicon can handle up to high temperatures of 50 degrees Celsius and its electrical efficiency won’t be affected, whereas both poly and mono reduce in efficiency at temperatures of 25 degrees Celsius, and take a major blow at 50 degrees Celsius.
Disadvantages- These panels actually have a shorter life cycle than both mono and poly. Thin-film is a relatively new technology and different materials are used in the production of solar cells for these panels. The efficiency of amorphous silicon solar cells that are manufactured in high-volume processes ranges from 8% to 10%. This problem is partially solved by “stacking” several amorphous solar cells on top of each other, which increases their performance and makes them more space-efficient. However, thin-film solar technologies are still in a development process, and we are probably going to see huge improvements in this solar technology in the near future. Thus, you would have to cover a larger surface with amorphous silicon solar panels than crystalline-based solar panels for an equal output of electrical power. The total cost of setting up thin-film solar panels that produce a useful amount of electricity can rise significantly because up to 4 times more space and equipment are required to install thin-film panels than monocrystalline panels that can produce the same amount of electricity. This also levels the cheaper price of thin-film panels.
Polycrystalline Silicon Cell- Unlike monocrystalline-based solar panels, polycrystalline solar panels do not require the Czochralski process. Raw silicon fragments are melted and poured into a square mould, which is cooled and cut into perfectly square wafers – these wafers are cleaned and then doped. A single 12 volts, 150-watt Polycrystalline Solar Panel costs around on average $270NZD. However, panels are slightly bigger with dimensions of 1473mm x 670mm x 35mm, than monocrystalline and are less efficient, with an efficiency percentage of 13-16%. In New Zealand, there plenty of availability of Polycrystalline solar panels, with the watts mainly ranging from 100W to 250W for residential housing.
Advantages- The process used to make polycrystalline silicon is simpler and cost less. The amount of waste silicon is less compared to monocrystalline. Cheaper per watt of 0.60 $/ W and good for households with large surface rooftops. Less silicon waste in the production process. Polycrystalline silicon solar cells also have a long-life time of 25years, which is the same as monocrystalline silicon cells. Since, polycrystalline is less resistant to temperature than monocrystalline, buyers think that this will result in a major difference in electrical energy produced, however, this is not the case the difference is very minor, and shouldn’t be taken into account.
Disadvantages- The efficiency of polycrystalline-based solar panels is typically 13-16%. Because of lower silicon purity, polycrystalline solar panels are not quite as efficient as monocrystalline solar panels. Because there are many crystals in each cell, there is less freedom for the electrons to move. Thus, lower space-efficiency. You generally need to cover a larger surface to output the same electrical power as you would with a solar panel made of monocrystalline silicon. However, this does not mean every monocrystalline solar panel perform better than those based on polycrystalline silicon. Polycrystalline silicon cell is less temperature resistant than monocrystalline silicon. The area required for 1kWp by a polycrystalline silicon cell is 8-9m^2, which is 2m^2 above monocrystalline on average. Since polycrystalline is less efficient than monocrystalline, therefore greater surface area needs to be covered in order to attain the same amount of energy as monocrystalline panels. When the temperature gets higher than 25 degrees C, crystalline solar panels start to produce less energy.
Monocrystalline Silicon Cell- Monocrystalline solar cells are made out of silicon ingots, which are cylindrical in shape. To optimise performance and lower costs of a single monocrystalline solar cell, four sides are cut out of the cylindrical ingots to make silicon wafers- these wafers are cleaned and then doped. The Silicon waste from the sawing process can be recycled into polysilicon. A single 12v 150w Monocrystalline Solar Panel costs around $360NZD. The panels are 1460mm × 664mm × 35mm, which makes them a tiny bit smaller than polycrystalline solar panels, however monocrystalline is more efficient, with an efficiency percentage of 15-20%. Monocrystalline solar panels are considered to be the first generation of solar panels and have been known for more than 50 years, and thus is widely available across the whole of New Zealand with a larger variety of watt panels.
Advantages- Monocrystalline solar panels have the highest efficiency rates since they are made out of the highest-grade silicon (high-purity silicon). The cell is composed of a single crystal, therefore the electrons that generate a flow of electricity have more room to move. Thus, the efficiency rates of monocrystalline solar panels are typically 15-20%. Monocrystalline solar panels produce up to four times the amount of electricity as thin-film solar panels. Monocrystalline silicon solar panels have the highest power outputs, they also require the least amount of space. And they also outperform most other types of panels, other than Amorphous silicon panels in low-light conditions. Monocrystalline silicon panels have a long lifetime. Manufacturers usually offer a 25-year warranty for these solar panels.
Disadvantages- Since a lot of silicon crystalline is used in these solar cells, thus the cost of buying monocrystalline panels is expensive. From a financial standpoint, a solar panel that is made of polycrystalline silicon (and in some cases thin-film) can be a better choice for some homeowners. If the solar panel is partially covered with shade, dirt or snow, the entire circuit can break down. Consider getting microinverters instead of central string inverters if you think coverage will be a problem. Micro-inverters will make sure that not the entire solar array is affected by shading issues with only one of the solar panels. When the temperature gets higher than 25 degrees C, crystalline solar panels start to produce less energy.
Solar Energy as a Future Source of Renewable- In the NZ, there is a strong focus on green energy and especially solar cells, which can contribute to lowering CO2 emissions in everyday life. Solar energy is the best source of renewable because obviously, it is a sustainable source of energy as long as the sun is still alive. Dam and turbines, although they do not pollute the environment, however, they change the eco-life and habitats of organisms within the area, whereas photovoltaic cells just need to be set up on a rooftop and sunlight needs to be available to produce electricity. Unlike biofuel and wind turbines, sun power does not create pollution or noise. Fossil Fuels make around 60% of New Zealand energy production, this is disastrous for mother planet earth because of all the pollution being released into the atmosphere and causing the rising crisis of global warming. Unlike wind turbines, solar panels don’t require spacious areas, and don’t create any disruptive noise. The initial electricity gathered by wind turbines actually quite cheap, however, the maintenance required is much more than solar cells. Once installed, little maintenance is required because of its long life and a good durability, with a minimum guarantee by companies of 20years. Solar panels are versatile and solar energy can be created anywhere in New Zealand, even in the regions that don’t seem possible to be able to produce electricity. There is one disadvantage of solar energy, which is that energy is only produced when sunlight is available, in order to emit electrons and create a current. But many solar panels still are able to create electricity in cloudy weather, because of the new improvements in technology. Any excess electricity can be sold back to the national grid, which is a bonus, however, the upfront cost is a dagger because people need to borrow money at an interest which further increases the price of solar energy. The NZ government has been handing out incentives to change solar energy from fossil and others, to the most sustainable and environmentally friendly energy source. Another disadvantage of solar energy is that is seasonal compared other sources, as in NZ there are periods of limited sun, therefore if your solar system doesn’t produce enough, then a solution would be to be grid- connected, which means that any electricity needed in winter season could be bought directly from the national grid, but this will result in extra costs. Geothermal is restricted as is relies on being close to the tectonic plate, whereas solar panels are effective anywhere in NZ. For the future of renewable energy, I would personally recommend monocrystalline solar panels to be used in the solar system. Because monocrystalline has been in the industry for over 50years and been showing promising advancements over polycrystalline with higher efficiency ratings ranging between a 1-2% increment each year, thus sooner or later monocrystalline will be able to become very space-efficient and produce enough electricity even in cloudy weather, without the need to buy electricity from the grid. Also, in 10 or years these panels will become very cheap because of their high mass production due to their popularity.
Improved Solar Cell Technology- 1st Gen- The first generations of solar cells, were mainly built with silicon wafers. Multi and single crystalline silicon solar cells gave around an average efficiency of 15-20%. Residentially these solar cells are very popular on rooftops as they have been around for around 50 years and the costs have dramatically dropped. This solar cell technology has brought to the table high stability, good performance, however, they still need a lot of energy in production to output electricity. Specialists are looking into ways to improve the impactfulness of these cells by increasing their efficiency through an increase in a variety of wavelength absorbance by the silicon semiconductor. Crystalline solar cells have dominated in the solar energy industry and look to further dominate if the efficiency is improved, thus resulting in more households using solar cells because of their major improvements in technology and price drop because of bulk production.
2nd Gen- The second generation is the thin film which is currently based on these materials which are Cadmium telluride (CdTe), Copper indium gallium selenide (CIGS), Amorphous silicon (a-Si), which have efficiency percentage of 8-14%. The material usage is much less because silicon wafers are voided in thin film, thus it possible to reduce the cost of thin film, and make them cheaper than the first-generation solar cells when mass produced. They are much more flexible, light in weight, and also have a low thickness, making it easy to install on different rooftop structures such as curved surfaces. There is a large energy consumption in the production of these solar cells, as the solar cells still include vacuum processes and high-temperature treatments. Also, the second-generation solar cells are made from elements that are scarce, thus the price is limited at a certain cost. These aren’t that impactful as they have a very low-efficiency rating, thus this technology hasn’t had made much of an impact on the use of the solar cells, because crystalline is more affordable, reliable and more efficient.
3rd Gen Organic materials are used within the third-generation solar cells such as molecules and polymers. Therefore, polymer solar cells are a subcategory of organic solar cells. The third generation holds the record for most efficient (36-40%) solar cells because it’s the high-performance multi-junction. Thus, the use of multiple semiconductors allows absorbance of a wider range of wavelengths from the electromagnetic spectrum, thus giving out a higher efficiency conversion of sunlight to electrical energy. These organic solar cells have very expensive production costs thus they are not residentially used, but rather commercially used in businesses. However, polymer solar cells also have many benefits such as they are quick, simple and moderate priced in mass production of those solar cells and the materials used are widely available and are not the most expensive of materials used in solar cells. This improvement in solar cell technology has been the most impactful, however, the use of these solar cells is limited because they are still in development and are more expensive than traditional crystalline solar cells.
Solar Energy Available in NZ
The sunlight reaches NZ with a maximum intensity of 1000Watts per square metre. If the housing in NZ had solar panels filling the whole of their rooftop areas, than twice as much energy as the national energy use would be produced. Because an average New Zealand household annually uses 11,500kWh thus they use 960 kWh per month, and the daily average Hastings sun hours are 5.85hours because Hastings receives annually 2100 hours of sunlight, therefore you can calculate the AC rating by: 960 kWh per month/ 30days/ 5.85hours = 5.5kW AC Equation AC rating= kWh per month/ 30days/ sunlight hours a day
Because photovoltaic cells aren’t always as good as what they are said to be by the manufacturer, they tend have a derate factor 0.8 (usually between 0.8-0.85), therefore the DC rating: 5.5kW AC/ 0.8 derate factor = 6.9 kW DC
Equation DC rating= AC/ derate factor
The most common panel rating in New Zealand in 250Watts (0.25kW) thus in order to calculate the number of solar panels required by a New Zealand household = 6.9 kW DC/ 0.25 kW Panel Rating = 27.6 panels. So, roughly around 28 panels of 250Watts (28 250 = 7000W = 7kW) Equation for number of panels = DC rating / panel rating
Therefore, a New Zealand household would need 7kW DC system (7kW DC 0.8 derate factor 365days 5.85hours = 11, 960 kWh in a year). Energy Online charges 22.24cents per kWh, thus $0.2224 = $2560 annually, a typical solar system and the installation for a 7kW system costs around $28,000, which will take around 11 years to break-even because you’ll be saving the on the foregone yearly $2560 energy bills. There will be an excess of 460 kwh which could be stored on a battery, however most NZ houses don’t buy batteries as they cost a lot and because the excess energy could be sold back to the national grid at a buy back rate of 8¢ / kWh, thus [(460 kWh 0.08) = $42.32 back into your pocket yearly].