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Welcome to the Tech Corner
The world of technology and its related jargons could be very misleading and frustrating. Please take a few moments to read this section hence this will ease a lot of pain and make decision making process a lot easier.
Please do not hastate to contact us if you have any question.
**see our new Inverter Tutorial and Frequently Asked Questions at the bottom of this page** Solar energy is the source of all life on Earth. Without it, we would not be here today living on such a rich and diverse planet. Most of the energy available to us radiates from the Sun. It provides us with food energy through plant photosynthesis and provides the heat that we need to survive. Trapped solar energy is released when we burn fossil fuel reserves and the sun drives the earth's weather systems which provide renewable forms of energy like wind, solar and wave power. It is now widely recognised that utilising the sun's natural energy can offer real alternatives to burning finite resources of fossil fuels or endangering future generations by relying on dangerous technologies such as nuclear power. Solar energy has long been used for space heating utilising passive solar design, and for water heating through the use of solar water panels but one of the most exciting areas of development has come in the form of the photovoltaic cell which can convert the sun's energy directly into electricity. Did you know?
In half an hour enough of the sun's energy reaches the Earth's surface to meet the World's energy demand for a year.
The sun produces 400,000,000,000,000,000,000,000,000 watts of power. That's 400 x 1012 TW.
The World's average energy consumption is around 14 TW!
Just one square cm of the Sun's surface burns with the brightness of 232,500 candles.
All the Earth's oil, coal and wood supplies would fuel the Sun for only a few days.
Basic Concepts of Energy and Power
Voltage (measured in volts) is a measure of the potential difference between two terminals of a battery or any component of a system. The mains has a voltage of 240v whereas battery systems use a much safer 12 or 24 volts. In the same way as height affects the flow of water, voltage affects the flow of current in a circuit. Current (measured in amperes) is the measure of electrical flow through a circuit. If a circuit is using direct current (d.c) the flow of electricity will only be in one direction - from positive to negative. In an alternating current (a.c) system the direction of the current reverses continuously at a set frequency. Mains electricity is a.c at 50 Hertz which means it is cycling 50 times every second. Batteries can only store d.c current. Power is defined as the rate at which work is done or energy is transferred. In electrical terms this translates into the consumption of electricity. Measured in watts it can be measured by multiplying the voltage by the current.
POWER = VOLTAGE X CURRENT
Watts = Volts X Amps Energy is defined as the ability to do work. However in an electrical sense it is the amount of work done over a given period. Measured in Watt-hours it is obtained by using the following:
ENERGY = POWER X TIME
watt-hours = watts x hours Useful Units kilo (k) = 1 thousand(103) mega (M) = 1 million(106) giga (G) = 1 billion(109) tera (T) = 1 trillion(1012)
Photovoltaic (PV) uses Photovoltaic cells are nothing new. In 1883 a New York electrician constructed one of the first cells from thin wafers of Selenium which eventually came into widespread use in photographic exposure meters. These early cells were very inefficient and it wasn't until the 1950's that research into light upon semiconductors gave birth to the modern solar cell. The first of these new PV cells were used to power space satellites, even though the stringent specifications made them very expensive. Nowadays, most people are familiar with solar powered calculators and watches and as developments over the last couple of decades has brought prices down, we have seen increasingly cost effective applications of this technology. PV systems presently supply electricity all over the world. It has proved to be the most cost effective form of electricity generation in many remote locations around the world where there is no mains electricity. Such examples include telecommunications, lighting for remote dwellings, water pumping and refrigeration in developing countries, and a whole host of consumer products powered by the sun. The caravan, trucking and boating industries have also long used small PV systems to charge their batteries sometimes in conjunction with small wind turbines. Lately, more and more cost effective systems have emerged with PVs now powering whole houses in the form of solar roofs which are linked to the existing electricity grid in case there is insufficient power during low light periods. The Oxford Solar House pictured here was one of the first British grid connected solar houses and over the course of a year actually generates more than it consumes selling the excess back into the national grid. Why use Photovoltaics?  Power from the sun is clean, silent, limitless and free. Photovoltaics release no CO2, SO2, or NO2 gases which are normally associated with burning finite fossil fuel reserves and don't contribute to global warming. Photovoltaics are now a proven technology which is inherently safe as opposed to other dangerous electricity generating technologies. As a result they will leave no legacy for our grandchildren to inherit other than a sustainable energy technology.
How does it work?
The photovoltaic effect was discovered by Edmund Bequerel in 1839 almost by accident while performing experiments on wet cell batteries. It wasn't until the 1950's that the real breakthrough occurred when silicon was found to display light sensitive properties when treated with certain impurities. 'Photovoltaic' literally means electricity from light. Light can be considered as a stream of tiny particles of energy called 'photons' and in a photovoltaic cell, it is these photons that produce a flow of 'electrons' more commonly known as current. Modern photovoltaic cells are made of thin wafers of a semiconductor, usually silicon, 'doped' with different impurities. One layer becomes electron rich, with the other being electron deficient so that when they are combined and exposed to a light source, a voltage is set up across the surfaces due to the movement of electrons across the interface between the two layers. By placing contacts on each layer the voltage set up will drive a current. This effect is mainly caused by the visible spectrum of light and not ultra-violet or infra-red heat which often accompany it. It is interesting to note that photovoltaic cells actually work best when they are cool.
Types of Photovoltaic Cells
Monocrystalline cells are made from polished, wafer thin slices of single crystals of silicon. Originally, all PV cells were made in this way. These tends to be expensive, as the crystals take time to grow, but it does produce the most efficient cells (~16%). These cells have a life span of about 40 years with most manufacturers guaranteeing output for 10 years. Polycrystalline cells are made from slices of ingots cast from raw silicon crystals giving the characteristic flaked appearance. This method gives a better surface coverage than monocrystalline cells and is cheaper than growing large crystals. These cells have the second highest efficiency (~12%) and are fast becoming the most popular form of cell. They also have as long a life span as monocrystalline cells with similar performance guarantees. Amorphous cells are made by spraying the silicon directly onto glass or ceramic in layers. these types of cells are the cheapest to produce but contain impurities, so the overall conversion of light to electricity is low (~5%). They also have a much shorter life span than others and are usually guaranteed for 6 years. Recent developments in this field are constantly improving performance.
Photovoltaic panels and modules
For Mono and Polycrystalline cells the power output of a single cell is quite small (typically about 1.5 watts), so in order to obtain usable amounts of electricity, many cells are interconnected in series and in parallel. They are built into a module, or panel, with an aluminium frame and covered in glass for protection. Modules usually occupy about half a square metre and are virtually maintenance free. Sizes vary, but a typical panel might produce between 40-60W in peak sunlight and comprise of 30 to 40 cells. These panels produce a 'nominal' voltage* of 12, 24 or 48 volts d.c depending on the way the cells are configured within the module. Modules can then be connected together, in an array, to give higher current or voltage outputs. * actual voltage is higher to provide the necessary charge for a battery.
How much and from what size?
On a clear summer day Britain receives almost as much energy from the sun as Africa!( The main reason I am using the example that UK has been the rainy country where Africa is the sunniest place in the world)The problem is that over a year we only receive a fraction of that because of our changeable climate. The amount of electricity which a photovoltaic can produce depends on the angle at which it is tilted towards the sun. It stands to reason that they are most efficient when the sun falls directly on the face of the panel but usually a south facing array is sufficient. The angle of tilt is sometimes varied from winter to summer to meet the angle of the sun. There are tracking devices which will keep the panels facing into the sun though it is generally thought that even though these offer a possible 40% increase in output over the year they introduce moving parts in an otherwise almost fail-safe system.
Designing a PV system
The scale of the system that you choose is very much dependant on what your requirements are. In the simplest form a solar PV can be used to charge a couple of batteries for a cassette player or similar battery powered device .The most practical use in today’s Afghanistan and in a lot of developing countries might be home lighting system , street lighting system ,irrigation systems etc. Please see Y T S product and services pages . In such a case the wires from the PV cell can be connected directly onto the terminals of the battery provided that it is of a rechargeable type. However, in most cases a system needs to satisfy many different requirements and needs some thought when it comes to design and sizing. Whatever the system, an evaluation of the power requirements is first needed. What is the average daily power consumption likely to be (in kWh)? This can be calculated by multiplying the power rating of each light or appliance by the average number of hours that it is used every day. Secondly one has to get some idea of the maximum power requirement at any one time. When undertaking this exercise one soon realises which appliances use the most power and what scope there is for improvement before sizing a system. Low energy appliances and lights should be used and it will become apparent that it is uneconomic to run heating loads from a photovoltaic system because of their huge power requirements. All but the simplest systems will require some form of power storage to compensate for the intermittent nature of solar energy. A battery store is the most common way of storing this energy. Leisure or deep cycle batteries are best used for recharging. Car batteries are not suitable for this type of application. The size of the battery store will generally depend on the charging source, the power requirements and the number of days storage required. The batteries in a system will need to be protected from overcharging which can both shorten their lives and be potentially dangerous. A charge regulator is therefore used which will begin to 'dump' excess power when the batteries approach their fully charged state. The excess energy is usually released as heat from cooling fins. Regulators are often incorporated into a more comprehensive charge control unit which usually has ammeters to show the incoming current and voltmeters to show the charge of the batteries. The system voltage will depend on the end uses. 12Volts is most commonly used because of the large range of appliances on the market. Most PV modules and batteries are of this rating. Some systems will use 24Volts to minimise losses over long lengths of cable however this requires arranging modules and batteries into a 24Volt configuration and using 24V appliances. DC loads can be run directly from the batteries usually via a fuse and distribution box. Standard ac'mains' appliances can be run using an inverter to provide 230Volts a.c. It is therefore possible to run power tools, computers, or any other appliances unavailable in 12 or 24V. However, inverters run at around 85% efficiency so some losses invariably occur. Finally a low voltage disconnect switch can be fitted to prevent the batteries becoming completely drained and therefore prolonging their life. Inverter Tutorial and Frequently Asked Questions:
Q: What is an inverter?
A: An inverter takes DC power (battery or solar, for example) and converts it into AC "household" power for running electronic equipment and appliances.
Q: How is an inverter different than a UPS?
A: A UPS typically includes the battery and battery charger in one stand alone unit. However, there are UPSs that use external batteries, and PowerStream makes inverters with battery chargers, so the differences blurr as features proliferate.
UPSs also can have communication with the equipment that it is powering letting the equipment know that it is operating on standby, giving it shutdown warning, or communicating with the human in the loop. Inverters typically don't have this communication.
Q: Why are they called inverters?
A: Originally converters were large rotating electromechanical devices. Essentially they combined a synchronous ac motor with a commutator so that the commutator reversed its connections to the ac line exactly twice per cycle. The results is ac-in dc-out. If you invert the connections to a converter you put dc in and get ac out. Hence an inverter is an inverted converter.
Q: What if I want a DC output to run such things as a laptop from a car cigarette lighter, or telephone equipment at -48 volts?
A: Then you want a DC/DC converter.
Q: What is the difference between sine wave and modified sine wave?
A: Alternating current (AC) has a continuously varying voltage that swings from positive to negative. This has great advantages in power transmission over long distances. Power from your power company is carefully regulated to be a perfect sine wave, because that is what naturally comes out of a generator, and also because sine waves radiate the least amount of radio power during long distance transmission.
On the other hand, a sine wave is expensive to make in an inverter, and many sine wave techniques use heavy, inefficient transformers. The most inexpensive way to make AC is to switch the DC on and off--a square wave. A modified sine wave is scientifically designed to simulate a sine wave in the most important respects so that it will work for most appliances. It consists of a flat plateau of postive voltage, dropping abruptly to zero for a while, then dropping again to a flat plateau of negative voltage, back to zero for a while, then returning to the positive voltage. This pause at zero volts puts more power into the 60HZ fundamental than a simple square wave does, so it is called "modified sine wave" instead of "square wave."
Q: Can I use a modified sine wave inverter for my medical equipment?
A: For Medical equipment, oxygen generators, etc. talk to the manufacturer of the equipment. PowerStream inverters are never tested or rated with medical equipment, and we don't guarantee that they will work to save your life. For such applications please find inverters that are rated and tested for such applications.
Q: What about square wave inverters?
A: These old-fashioned inverters are the cheapest to make, but the hardest to use. They just flip the voltage from plus to minus creating a square waveform. They are not very efficient because the square wave has a lot of power in higher harmonics that cannot be used by many appliances. The modified sine wave is designed to minimize the power in the harmonics while still being cheap to make.
Q: How do I know if I need a sine wave, or if I can live with a modified sine wave?
A: The following gadgets work well with a modified sine wave: computers, motor-driven appliances, toasters, coffee makers, most stereos, ink jet printers, refrigerators, TVs, VCRs, many microwave ovens, etc.
Appliances that are known to have problems with the modified sine wave are some digital clocks, some battery chargers, light dimmers, some battery operated gadgets that recharge in an AC recepticle, some chargers for hand tools (Makita is known to have this problem). In the case of hand tools, the problem chargers usually have a warning label stating that dangerous voltages are present at the battery terminals when charging. We would like to add to this FAQ any appliances that you have had trouble with, or had success with, using modified sine wave inverters.
Q: Why do I hear buzzing on my stereo when using a modified sine wave inverter?
A: Some inexpensive stereos use power supplies that cannot eliminate common-mode noise. These would require a sine wave inverter to operate noise-free.
Q: Why don't I measure rated voltages when using a multimeter on my modified sine wave inverter?
A. The rated voltage is an RMS (root mean square--they square the value to make sure it is always positive, then average it, then take the square root of the average to make up for having squared it in the first place) measurement. Most multimeters are designed to give correct RMS readings when applied to sine waves, but not when they are applied to other waveforms. They will read from 2% to 20% low in voltage. Look for a voltmeter that braggs about "True RMS" readings.
Q: How should I select the right size inverter?
A: First add up the power ratings of all the appliances, then buy the next larger inverter! At least that is the simple answer. Note, however, that some appliances, such as table saws, refrigerators, and microwaves have a surge requirement. PowerStream inverters are designed to supply such surges, but since every appliance has its own requirements sometimes you will need to get a bigger inverter than you would otherwise think. Note that the inverter isn't the only consideration when you are pondering the mysteries of startup surges. The battery must also be able to supply the surge power, and the cables must be able to supply the increased current without dropping the voltage too much.
Q: How is a microwave rated for wattage?
A: When you buy a microwave oven you want to know how intense the microwave field is, not how much the oven draws from the wall. So a microwave oven that boasts 600 watts on the box, will have 1200 watts on the boilerplate in the back. Don't be fooled!
Q: Are stereo amplifiers rated the same way?
A: Stereo manufacturers are bigger liars than politicians. Some times they use peak output power (milliseconds), sometimes they use power drawn from the wall, but often they just look at the competition's carton front and add 10%. However the truth is available: look at the boilerplate sticker, which has been evaluated by UL.
Q: Why do I need such humongous cables to the battery when a small cord takes the AC output fine?
A: Power is volts times amps (Watts = V x A). So if you have a lot of voltage you don't need many amps. Roughly you need 12 times as much current from the 12 volt battery as you need from the 110 volt AC outlet. Current is what causes cables to heat up, not voltage. That is why they use thousands of volts in power transmission grids. The thing to do when you have lots of current is to lower the resistance of the cable. The larger the wire the lower the resistance. Think of the cable as a water pipe. A big pipe (wire) can carry more water (current or amperage) with less pressure (voltage), and will present less pressure (voltage) drop from one end of the pipe to the other.
Another consideration is how far the cable has to run from the battery to the inverter. Long cable runs are expensive, either in copper or efficiency, or both.
Q: Why would you use a 24 volt inverter instead of a 12 volt inverter?
A. At a given power rating a 24 volt inverter will need half the current as a 12 volt inverter. This makes the entire system more efficient, and since high current transistors are expensive, the inverter will be cheaper.
Q: Should I use a laser printer with an inverter?
A: Only if you must. Laser printers use up a surprising amount of power (due to the heated rollers), and will discharge your battery faster than you expect, even on standby. If you do, make sure the inverter is rated for the power of the printer plus computer plus monitor. It doesn't do any good to have your computer brown out as soon as the the printer starts to print. Ink jet printers, on the other hand, use a surprsingly low amount of power.
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