Solar FAQ
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Solar FAQ
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How does a PV cell work? In a photovoltaic cell, light excites electrons to move from one layer to another through semi-conductive silicon materials. This produces an electric current
What is Photovoltaics? Photovoltaics is a high-technology approach to converting sunlight directly into electrical energy. The electricity is direct current and can be used that way, converted to alternating current or stored for later use.
Conceptually, in its simplest form a photovoltaic device is a solar-powered battery whose only consumable is the light that fuels it. There are no moving parts; operation is environmentally benign; and if the device is correctly encapsulated against the environment, there is nothing to wear out.Because sunlight is universally available, photovoltaic devices have many additional benefits that make them usable and acceptable to all inhabitants of our planet. Photovoltaic systems are modular, and so their electrical power output can be engineered for virtually any application, from low-powered consumer uses-wristwatches, calculators and small battery chargers-to energy-significant requirements such as generating power at electric utility central stations (see figure 1). Moreover, incremental power additions are easily accommodated in photovoltaic systems, unlike more conventional approaches such as fossil or nuclear fuel, which require multimegawatt plants to be economically feasible.
To understand the many facets of photovoltaic power, one must understand the fundamentals of how the devices work. Although photovoltaic cells come in a variety of forms, the most common structure is a semiconductor material into which a large-area diode, or p-n junction, has been formed. The fabrication processes tend to be traditional semiconductor approaches-diffusion, ion implantation and so on. Electrical current is taken from the device through a grid contact structure on the front that allows the sunlight to enter the solar cell, a contact on the back that completes the circuit, and an antireflection coating that minimizes the amount of sunlight reflecting from the device. Figure 2 is a schematic depiction of a rudimentary solar cell that shows the important features.
The fabrication of the p-n junction is key to successful operation of the photovoltaic device (as well as other important semiconductor devices). We will assume that the semiconductor material is single-crystal silicon. Although photovoltaic technologists today use many other varieties of semiconductors, crystalline-silicon concepts represent a reasonable compromise for this discussion because they are well known and understood by physics students.
Silicon is representative of the diamond crystal structure. Each atom is covalently bonded to each of its four nearest neighbors; that is, each silicon atom shares its four valence electronic with the four neighboring atoms, forming four covalent bonds. Silicon has atomic number 14, and the configuration of its 14 electrons is 1s22s22p63s23p2. The core electrons, 1s2, 2s2 and 2p6, are very tightly bound to the nucleus and, at real-world temperatures, do not contribute to the electrical conductivity. At absolute zero, as N silicon atoms are brought together to form the solid, two distinct energy bands are formed-the lower, "valence" band and the upper, "conduction" band. The valence band has 4N availability energy states and 4N valence electrons and is therefore filled. Conversely, the conduction band is completely empty at absolute zero. Thus the semiconductor is a perfect insulator at absolute zero.
As the temperature of the solid is raised above absolute zero, energy is transferred to the valence electrons, making it statistically probable that a certain number of the electrons will be raised in energy to such an extent that they are free to conduct electrical charge in the conduction band. These electrons are called intrinsic carriers. The amount of energy necessary to bridge the valence and conduction bands is referred to as the forbidden gap or energy gap Eg, which is 1.12 eV at room temperature for silicon. Even at room temperature, however, the amount of conductivity is still quite small. At 300 K there are 1.6 x 1010 intrinsic carriers per cubic centimeter; thus the material is still a very good insulator compared with a metal, which has approximately 1022 carriers per cubic centimeter.
To modify the conductivity to more useful values, one must introduce small controlled amounts of impurities into the host materials. By substituting, or "doping," the silicon, which is in column IV of the periodic table, with either column-III materials (boron, aluminum, gallium or indium) or column-V materials (phosphorous, arsenic or antimony), one can increase and control precisely the number of conduction band electrons or valence band holes (deficiencies of electrons).
A column-V dopant completes the covalent bond and leaves an additional, loosely bound electron that can be transferred to the conduction band by an energy of about 40-50 meV, termed the ionization energy. Column-III impurities leave the covalent bond deficient of one electron (that is, with a hole). An electron from the valence band can transfer to the empty site and satisfy the bond requirement. In effect the hole moves, because the transferred electron leaves behind a hole. The amount of energy required to thus place the hole in the valence band ranges from 45 to 160 meV.
By varying the density of the doping impurities, one can design the silicon to range from a poor conductor of electricity to a near-metallic conductor. Silicon that has been doped with column-III elements is called a p-type semiconductor; that doped with column-V elements is called an n-type semiconductor.
What are Solar Trackers?Our trackers are available in four standard models. Your selection of a tracker depends on your application, specific PV module and PV array size. Our tracker frames are precisely engineered for strength, are fabricated from structural aluminum and disassemble for ease in shipping and installation.
Types of Custom Trackers
360 degree trackers for polar applications.
Trackers on trailers for mobile applications.
Trackers for your small dish concentrator.
How Does the Wattsun Solar Tracker Track The Sun? Wattsun Solar Trackers utilize a patented, closed loop, optical sensing system to sense the sun's position and track it. The sun sensors, mounted on the controller chassis, feed information to the control electronics about the direct component of sunlight available, the diffuse amount of sunlight, the total amount of sunlight as well as the differential amount of sunlight on opposing sensors. Based on this information, the controller seeks to equalize the sunlight received by opposing sensors for each axis.
The controller circuitry automatically adjusts the tracker sensitivity accordingly. It increases the sensitivity with increased direct sunlight; and decreases the sensitivity with scattered or diffused light as in cloudy conditions. This enables the tracker to eliminate undue hunting in cloudy or overcast conditions when the sunlight is scattered.
It also makes adjustments according to the total amount of light received by the sensors. Since it knows how much light is available, it enables the controller to sense sunset, and return to sunrise position in the evening if connected to a power source at night. When powered directly from the PV modules, it will return to sunrise, at first morning light through the use of its energy integration circuitry which enables the tracker to move with as little as 20ma of available current.
This circuitry eliminates the need for any maintenance points such as batteries in the system. On dual axis models, the controller prioritizes movement of the Azimuth or East / West axis. It will first adjust the E/W axis to be on track, and then adjust the Elevation axis to position.
What Actually Moves The Tracker? The tracker controller sends a signal to the DC gear motor which actually moves the PV array to a perpendicular position relative to the sun's rays. The motors are small, fraction HP, low voltage, gear motors which move the tracker to position. The gearing is designed such that the tracker cannot be back driven by high winds or other forces.
Since the drive motors are DC, one polarity moves them in forward direction and reversing the polarity moves them in the opposite direction. When the controller wants the tracker to move, it sends a signal of the appropriate polarity to the DC gear-motor. Once the tracker has moved to the "on track" position as determined by the controller, the controller electrically "brakes" the motor to stop movement which results in greater tracking accuracy.
The extreme positions of the tracker movement are set by internal limit switches inside the gear motors. When a limit switch is activated, say for example full East position, the gear-motor will be disabled from moving further East and can only move to the West when the controller sends a signal.
There are limit switches for all extreme tracker positions which are factory set. The outputs of the controller are protected by over current limiting and over temperature compensation. You could short the outputs of the controller and the unit will shut down with no damage.
How Much Power Does The Tracker Use? Since rotating the array once per day does not require much work, the energy required to do so is insignificant. The energy required to move the array and power the tracker controller is approximately ½ a watt hour during daylight hours. This equates to about 5 watt hours per day. This is negligible when considering the increased power provided by a solar tracking array.
How Much More Power Will I Get From A WattsunTracked Array? The power output of a PV panel depends on the amount of light falling on the panel. By moving the PV modules so they are always facing the sun, the power output is maximized. The increase in power provided by tracking will depend upon geographic location, season and weather.
The National Renewable Energy Lab publishes a book entitled "Solar Radiation Data Manual for Flat Plate and Concentrating Collectors" which provides solar data for tracked and fixed arrays, by month, for virtually every city in the US. This is a good resource for determining power gained by tracking in your area or ask your dealer for this information regarding your location.
We provide a dozen solar radiation maps in our Resources section.
Other benefits of a tracked array over a fixed mount include providing power early in the morning when your batteries are at their lowest, late in the afternoon and whenever the sun peeks through the clouds on those low power producing days. By tracking the sun and capturing all the power accessible, whenever it's available, at any time of the day, backup generator run time is minimized.
What Affect Does Tracking Have On Solar Water Pumping Applications? For power critical applications such as solar powered water pumping, a tracker provides the extra power needed to start the pump early in the morning and keep it pumping to nearly sunset. PV array direct water pumping requires a threshold of energy to start the pump.
With a Wattsun tracker, the tracker is facing East at minutes after sunrise, providing the pump with it's threshold energy much earlier in the morning. The pump starts pumping much earlier and continues to pump later in the day. The energy received by the pump from the PV array is more evenly matched to the pump throughout the entire day.
This is why a tracking increases the amount of water pumped dramatically. It can double the amount of water produced in the summer, when it is typically needed the most. With a Wattsun Tracker, the water is supplied in a smooth dawn to dusk flow and allows for a smaller pump and less modules in many cases. Our Two Module trackers are specifically designed for the popular small submersible water pumping applications.
What Is The Difference Between A Wattsun Active Tracker and Passive Heat Powered Trackers? PERFORMANCE!
Wattsun Trackers track the sun by sensing light, not by accumulating heat from the sun. Passive trackers rely on heat buildup from the sun to move a Freon based liquid from one edge of the tracker to another. The passive trackers on the market are single axis, Tilt & Roll trackers. Corners of these trackers stick up into the air which can catch the wind and blow them off track. They use shock absorbers to try to dampen the movement induced by wind.
In the cold, heat powered trackers have trouble building up enough heat to operate. Passive trackers also have to wait to heat up in the morning to return to sunrise position. The time to return can vary tremendously depending upon weather conditions. Inherent in the design of passive trackers, the range of travel is also limited.
Typically, passive trackers are made of welded, painted mild steel. These trackers are shipped in large crates making them expensive to ship, hard to transport to the site, and require either a lot of manpower or heavy equipment to install. Passive trackers are offered with various performance enhancing options. There are options to make the tracker return east earlier and options for high wind versions.
These all come at added cost and with other performance detriments. High wind versions take longer to return East in the morning and rapid return options are more likely to catch the wind and allow the tracker to be blown off track.
Wattsun Trackers are actively powered from the PV array and are positively driven to track the sun. They will track to within 1/2 of a degree in normal sunlight. Our azimuth trackers, designed specifically for larger arrays, keep the bottom edge of the array parallel to the ground which reduces the ground clearance necessary and also reduces the torque forces applied to the tracker by the wind. They will follow the sun through its full movement in the sky.
Wattsun Trackers are available in dual axis tracking, which eliminates the need for seasonal adjustments. Our frames are built from quality structural aluminum and disassemble for ease in shipping and installation. Wattsun Trackers are built to operate from -40 degrees C to 105 degrees C. They are not affected by the cold and cannot be blown off track by the wind. All Wattsun Trackers are designed to withstand a minimum of 32 lbs./sq.ft. wind loading (over 90 mph).
Comparison Of Wattsun Trackers V.S. Passive, Heat Powered Freon Trackers Wattsun Solar Trackers
Not Affected by Wind Not Affected by Cold 180+ Degrees E/W Tracking Range 75 Degrees Elevation Tilt Range Dual Axis Available Aluminum Frames Early Morning or Sunset East Return Most Ship up's Accurate to Within 1/2 Degree
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Passive Heat Powered Solar Trackers
Can Be Blown Off Track by Wind Affected by Cold Approx. 90 Degrees E/W Tracking Range 43 Degrees Elevation Tilt Range Dual Axis Not Available Painted, Mild Steel Frames Has To Build Up Enough Heat To Return Most Ship Via Truck Freight + or -10 Degrees in Ideal Conditions, Ambiguous
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Basic Functions In a Solar SystemPV Panels - Photovoltaic panels convert sunlight to DC Electricity. DC electricity is the type used in cars, RV's, electronics.
Charge Regulators - Regulators prevent the modules from overcharging the batteries
Deep Cycle Batteries - Batteries store the electricity produced by the modules. They are similar to car batteries, but they are capable of storing more electricity.
Battery Status Meter - Meters keep track of how much electricity is stored in the batteries. They are like a car gas gauge except the tank is the batteries and the fuel is electric
Product Load - The load is the lights and appliances that you use. The modules must produce more electricity than you use each day to store up reserve in the batteries.
Inverter - Inverters convert DC electricity to AC or "home electricity". An inverter is needed if you wish to use normal AC lights and appliances in your solar electric system.
What Types of PV Technology are available? Types of PV Technology:
Monocrystalline Silicon Cells:
These cells are made from very pure monocrystalline silicon. The silicon has a single and continuous crystal lattice structure with almost no defects or impurities. The principle advantage of monocrystalline cells are their high efficiencies, typically around 15%, although the manufacturing process required to produce monocrystalline silicon is complicated, resulting in slightly higher costs than other technologies.
Multicrystalline Silicon Cells:
Multicrystalline cells are produced using numerous grains of monocrystalline silicon. In the manufacturing process, molten polycrystalline silicon is cast into ingots, these ingots are then cut into very thin wafers and assembled into complete cells. Multicrystalline cells are cheaper to produce than monocrystalline ones, due to the simpler manufacturing process. However, they tend to be slightly less efficient, with average efficiencies of around 12%.
Amorphous Silicon:
Amorphous silicon cells are composed of silicon atoms in a thin homogenous layer rather than a crystal structure. Amorphous silicon absorbs light more effectively than crystalline silicon, so the cells can be thinner. For this reason, amorphous silicon is also known as a "thin film" PV technology. Amorphous silicon can be deposited on a wide range of substrates, both rigid and flexible, which makes it ideal for curved surfaces and "fold-away" modules. Amorphous cells are, however, less efficient than crystalline based cells, with typical efficiencies of around 6%, but they are easier and therefore cheaper to produce. Their low cost makes them ideally suited for many applications where high efficiency is not required and low cost is important.
Other Thin Films:
A number of other promising materials such as cadmium telluride (CdTe) and copper indium diselenide (CIS) are now being used for PV modules. The attraction of these technologies is that they can be manufactured by relatively inexpensive industrial processes, certainly in comparison to crystalline silicon technologies, yet they typically offer higher module efficiencies than amorphous silicon.
Can I afford Photovolatics? That depends on your application. Generally, the cost of PV energy is higher than energy bought from your local utility. However, if you need power in a location not served by a utility, PV may be the cost-effective option. The number of PV system installations is increasing rapidly. As more people learn about this versatile and often cost-effective power option, this trend will accelerate.
You should consider your goals and distinguish between your wants and your needs. Reevaluate your ideas about having electric power available during all kinds of weather - 100 percent availability. Availability has a unique meaning for a PV system because it depends not only on reliable equipment but on the level and consistency of sunshine, and the capability of the energy storage system. Because the weather is unpredictable, designing a PV system to be available for all times and conditions is expensive, and often unnecessary. PV systems with long-term availabilities greater than 95 percent are routinely achieved at half the cost or less of systems designed to be available 99.99 percent of the time. Designing for lower availabilities decreases the size of the PV array and batteries and will save many dollars.
Another way to resolve the availability issues is to design a Hybrid system which will include another energy source.
Although saving money is important you should be determined to design and install a safe system that will last 25 years or more. Quality may cost more initially but will save money in the long run.
Outdoor Solar Lighting FAQ
How does a Solar Outdoor Light work? In principle it is very simple: A solar panel is used as a generator which converts light to electricity. That makes it a "solar generator." The electricity is used to charge a battery while there is daylight--even under cloudy skies. The battery powers the light, at night, turning it on at dusk and turning it off at dawn, or some earlier time if chosen.
It is similar to the generator charging your car battery when the motor is running, and then having enough "charge" in the battery for head lights all night when the engine is turned off. Worried about your car battery going dead? It will, because your car was not designed for all night lighting without having the engine running.
That is why Solar Outdoor Lighting is not quite so simple in reality. The solar generator must have enough capacity to charge a big enough battery to power light all night, every night. And the battery must have enough capacity to run the light even after a string of cloudy days. And the charging and discharging of the battery must be very precisely controlled.
Why use Solar Outdoor Lights? Thousands of Commercial Grade Solar Outdoor Lights have been in everyday use since 1990, lighting residential streets, country roads, traffic and advertising signs, transit shelters, parking lots, national and municipal parks, recreation areas, military installations. These lights are so dependable that a utility has installed them at their own switching center to have light when "electric wired" power fails, and through hurricanes and earthquakes. Remember those giant black-outs?
Why are Solar Outdoor Lights so dependable? Because each light has its own power plant--a solar generator energized by the sun. The generator is guaranteed for twenty years-which keeps an ultra reliable battery charged to deliver lighting power whenever it is needed. There is some charging every day, even when it is cloudy.
Why does Solar Outdoor Lighting compete so well with "electric wired" lighting? Solar Outdoor Lights may seem expensive before the real costs of installing "electric wired" lights are added up for the years of service that are to be expected. Solar Outdoor Lights have no charge for running wires, or trenching, no charge for putting in transformers and meters, and no electric bill.
Where can solar lights be used? As you travel North where there are more clouds and longer nights, larger size solar panels and batteries are required. Properly designed "Northern" systems are just as reliable as "Sun Belt" systems, but they cost more.
Why don't Solar Outdoor Lights go dead? Unlike automobile batteries, Solar Outdoor Lighting batteries provide enough electric storage capacity to keep the light on for many long nights even when the charging rate of solar generators is limited by a string of cloudy skies.
Is that all it takes?
No. In addition to adequate solar generators and big batteries, Solar Outdoor Lights require controllers to regulate the charging process and to ensure that the light will be on when it is supposed to be on, not fooled by passing clouds, automobile headlights, the full moon, etc.
It still sounds simple; why can't anyone produce Solar Outdoor Lights? To produce a light that will last for years and years, that will shine during the longest nights after a string of short and cloudy days, after hurricanes and snow or sand storms, at the customer's location, a product that is safe to install and service, to insure flawless performance, requires meticulously matched customer lighting needs and locations on a "worst case" basis.