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Einleitung

Täglich scheint die Sonne auf die Erde herab. Die Energie in den Photonen der Sonne kann in elektrische Energie umgewandelt werden. Der Fachausdruck für diesen Prozess nennt sich fotovoltaischer Effekt.

Seit dem ersten öffentlich erhältlichen Sonnenkollektor im Jahre 1960 wurden Forschungen zum Thema photovoltaische Energie(insbesondere durch Pratt & Schaeffer 51) betrieben und Theorien stehts weiterentwickelt. Die konstante Forschung auf diesem Gebiet brachte stets verbesserte und effizientere Wege hervor und machte Sonnenkollektoren erschwinglicher für die breite Masse, auch wenn der Preis doch relativ hoch ist. Heutzutage geht die Forschung nach neuen Wegen für die Fotovoltaische Energie weltweit weiter. Da die meisten von uns keine Studien zu diesem Thema auf dem Niveau von atomischen Reaktionen betreiben, gibt es andere alltägliche Wege um zu helfen- indem man Sonnenenergie versteht und dieses Wissen mit Anderen teilt und indem man anderen Interessierten dabei hilft auf Solar- oder Fotovolatische Systeme zuzugreifen.

Dieser Artikel befasst sich mit den Komponenten von Fotovoltaischen Systemen, erläutert ihre Rolle und Signifikanz und dient als erste Anleitung für diejenigen, die an Solarenergie interessiert sind und auf diesem Gebiet investieren möchten.

Komponenten von Fotovoltaischen Systemen

Zelle
Dünne Quadrate, Disken oder Streifen aus halbleitendem Material, welches elektrische Spannung generiert sobald es dem Sonnenlicht ausgesetzt wird.
Kollektoren
Anordnung von fotovoltaischen Zellen die mit einer klaren Substanz (Lasierung) und einem verkapselndem Substrat beschichtet sind.
Solarmodul
Eine oder mehrere Kollektoren die unter einem bestimmten Spannungsgrad miteinander verbunden sind.
Ladungsregulierer
Reguliert Batterieladung und kontrolliert die Höhe der Spannung für Batterien.
Wiederaufladbare Batterie
Eine Art von Batterie die auf einem hohen Kapazitätsgrad ab- und wieder aufgeladen werden kann ohne dabei der Batterie selbst zu schaden.
Umkehrer
Konvertiert Gleichstrom zu Wechselstrom.
Ladung
Elektrische Komponente in einer Leitung, die Energie aus dieser Letung hervorbringt.
Die meisten Ladungen könenn an und abgeschaltet werden, so wie z.B. Glühbirnen.
Ladungen kommen entweder in Form von Gleich- oder Wechselstrom.
Schutzschaltungen und Sicherungen
Zwei Arten von Schutz vor Überladung.
Wenn eine Leitung eine bestimmte Stromstärke überschreitet öffnet sich die Sicherung und lässt keine weiteren Stromflüsse zu. Wenn eine Sicherung "herausspringt", muss diese ersetzt werden und die Schutzschaltung neu eingestellt werden.
Trennschalter
Ein Sicherheitsschalter der die verschiedenen Komponenten einer Solaranlage voneinander trennt für Situationen wie z.B Reparaturen und Wartung.
Eine Sicherheitsschaltung kann als Trennschalter benutzt werden.
Messgerät
Ein Druckmesser, der anzeigt von wo Energie herangezogen wird und wie diese Energie von der Leitung bezogen wird.

Lage der Solaranlage

Sonneneinstrahlung
Sobald die Sonne auf die Erde trifft, nennt sich dieses Phenomen INSOLATION. Insolation kann als Energiestärke beschrieben werden und in Watt pro Quadratmeter ausgedrückt werden (W/m2) und wird, insbesondere in der Fotovoltaik, oft als durchschnittliche Tagesstärke (im Monat) angegeben. So erhalten wir 1,000 W/m2 wenn man 100% vole Sonneneinstrahlung erhält. (Pratt & Schaeffer 56).
Bei der Analyse der Lage einer fotovoltaischen Anlage ist es wichtig zu wissen in welchem Monat die Sonneneinstrahlung am stärksten und niedrigsten ist oder wann der durschschnittliche Betrag der Sonneneinstrahlung am höchsten/niedrigsten sein wird. Diese Information ist wichtig bei der Beurteilung des Neigungswinkels der Solarkollektoren. Bei der Beurteilung des Nutzens einer Solaranlagen, ist es essentiell zu wissen was die durchschnittliche Tageseinstrahlung bei voller Sonneneinstrahlung und bei schlechtem Wetter ist. Die Informationen zur Sonneneinstrahlung helfen dabei einen perfekten Winkel für die Anlage zu finden, so dass das größt möglichste Potential aus dem fotovolaischen System geschöpft werden kann.
Höchste Sonneneinstrahlung
Die höchste und längste Sonneneinstrahlung über einen ganzen Tag gesehen.
Mittagssonne
Die Mittagssonne herrscht, wenn die Sonne den höchsten Punkt am Himmel erreicht und die Strahlen am stärksten sind. Um die Mittagssonne zu bestimmen nimmt man die Zeit von Sonnenaufganz bis Sonnenuntergang und teilt diese durch zwei.

Gathering Site Data

Solar Insolation Data
Determine which month has the least amount of sun on average. This is the month that you want to use if you are building a system that will be used year-round. (if you are only going to be using it for summer or winter, find month with least sun during months that you will use the system.)
PV Array Location
Sun/Clouds: It is important to estimate the sun availability and cloud cover. Sometimes you can obtain this information on the web if it is a large enough town.
Shade: You want to choose a location that is on or near the place where you loads will be. The MOST IMPORTANT thing to consider when choosing a location for your Array is shading obstacles. Shade covering just one PV cell can reduce the current dramatically. A small amount of shade covering the panel can reduce the panel performance by 80%. As a general rule, the array should be free of shade (during each month in use) from 9am to 3pm. This is the optimum timeframe a panel has to receive light and is called the Solar Window.


PV Module

A Photovoltaic panel can be directly wired to a DC Load if the load is needed only when there is sun, and the load is not sensitive to large voltage fluctuations.

Examples include:

  • A greenhouse fan - this is a load that will serve to cool down the greenhouse during the day. The more direct sunlight there is, the more the load will be working and compensating for the heat within the greenhouse.
  • A waterpump - this is a load that does not need to be operational at specific times, and hence, is only operating when there is enough sunlight to power the pump.
Pv 1 panel.jpg

Batteries

Batteries are required for any system that needs some sort of storage capacity. If you will be using your system at times when there may not be sunlight available, a battery will store the energy from the pv array in order to power the loads at a later time.

Pv 2 battery.JPG
Purpose/Importance
  • Batteries allow you to store energy directly from the energy generated by the PV Array.
  • Batteries store DC energy and allow you to utilize the energy during the night, when there is not a sufficient amount of sunlight, or when there is a blackout (if you are connected to the grid).
  • Batteries are an extremely important power supply for critical electrical loads that consistantly require usage. If you are wishing to power a load only during the day, a battery may not be required, i.e. to power a fan on sunny days inside of a greenhouse. Utility grid-connected pv systems do not require the use of batteries, though they can be used as an emergency backup power supply.
Days of Autonomy
  • Autonomy refers to the number of days a battery system will provide a given load without being recharged by the pv array or another source.
  • General weather conditions determine the number of "no sun" days, which is a large variable when determining autonomy.
  • The general range of autonomy is as follows:
    • 2 to 3 days for non-essential uses or systems with a back-up power supply.
    • 5 to 7 for critical loads with no other power source.
Battery Capacity (AH)
  • Batteries are rated by amp-hour (AH) capacity. The capacity is referring to how much energy that particular battery is capable of storing. The capacity of the battery needs to be capable of supplying energy to the load. It is necessary to factor in the days of autonomy in order to determine how much storage capacity is required of your battery. The AH will tell you how many amps you can pull from the battery in one hour.
  • If more storage capacity is required for the pv system than one battery is capable of supplying, batteries can be wired in parallel to add additional storage capacity. Higher voltages are obtained through series wiring.
  • Initially, the battery capacity should be slightly larger than is required by the load because the batteries will lose capacity as they age. But if you greatly oversize the battery bank, it may remain at a state of partial charge during periods of reduced insolation - ultimately shortening the battery life. Determine the battery based on the size of your load.
  • The AH capacity will be listed on the battery.
Rate and Depth of Discharge
  • A battery is charging when energy is being put in and discharging when energy is being taken out. One cycle is considered one charge-discharge sequence, which often occurs over a period of one day.
  • The rate at which the battery is discharged directly affects it capacity. The faster the discharge, the lower the capacity. The slower the discharge, the larger the capacity.
  • The discharge rate refers to period of time at which the battery discharge was tested. For a battery rated at C/20, the discharge C (in Ah) was reached after 20 hours of discharge. For instance a 220 Ah battery, rated at 220Ah/20 would be discharged for 20 hours at 11 Amps continuously.
  • Depth of Discharge (DOD) refers to how much capacity can be withdrawn from a battery. Most PV system batteries are designed for regular discharges of 40 to 80 percent. Battery life is directly related to how deep the battery is cycled; the shallower the cycle, the longer the life span.
Environmental Conditions and Battery Sizing
  • It may be unreasonable to size a battery system that would be capable of providing power during extreme weather conditions, such as three to four weeks without sun. Hence, it may be a better option to size the system according to the average number of cloudy days or to create a design with a hybrid approach adding in a generator or a wind turbine.
  • Battery capacity decreases at lower temperatures while battery life increases.
  • When sizing a battery, you can compensate for the effects of temperature by using a battery temperature multiplier. Multiply the battery capacity needed by the battery temperature multiplier.

Voltage Regulator

Pv 3 v reg.JPG
Purpose/Importance
The Voltage Regulator prevents the pv panel from overcharging the battery by regulating the voltage to always be below a certain limit. The battery will specify that it cannot continue to accept current past a certain charge. The voltage regulator lowers the current as it reaches closer to this limit in order to lessen the amount of current charging the battery.

Low Voltage Disconnect

LVD.JPG
Purpose/Importance
A Low Voltage Disconnect prevents the battery from discharging too deeply.
(LVD) is a feature that can disconnect DC loads from the battery so that is does not discharge to the point of damage.
If batteries are being discharged to a low level, a controller can shut off the current flowing from the battery to the DC load.
The LVD must be capable of handling the maximum amperage, or load current.
Lights or Buzzers on a controller can be used for critical DC loads instead of the LVD. This is important for appliances such as refrigerators that must not be cut off from a power supply without proper warning.

Meters

METER.JPG
Purpose/Importance
A meter acts as a gauge that informs you of where you are pulling your power from, and how much power is being drawn at any given moment.
Volt Meter
  • Battery Voltage (state of charge)
  • Panel Voltage, Current, Power and Total Energy produced over a certain period
  • Load Power and Total Energy used over a certain period

Charge Controller

CCONT.JPG


Purpose/Importance
  • The charge controller functions as a voltage regulator. The main function of a controller is to prevent the battery from being overcharged by the pv array.
  • The charge controller is capable of sensing a battery´s current state of voltage. When a battery is fully charged, the controller will either stop or slow down the amount of current flowing into the battery from the pv array.
  • Charge controllers come in different sizes and must match the pv system voltage.
  • The controller must also be able to handle the maximum pv array current flowing through the controller at any given moment.

Inverter

Inverters convert DC to AC. To power any AC Loads, the current must be converted via an inverter.

Pv 7 inverter.JPG
Purpose/Importance
  • Photovoltaic modules generate only DC power. Batteries can store only DC power. An inverter is used as a "bridge" which converts DC electricity into AC electricity.
  • AC is easier to transport over long distances, this is an important component for many pv systems.
  • AC appliances have become the conventional modern electrical standard, inverters are necessary to power any type of AC load.


Watts Output
  • This indicates how many watts the inverter can supply during standard operation.
  • Choose an inverter that can handle the system´s peak AC load requirements.
Voltage Input or Battery Voltage
  • This indicates the DC input voltage that the inverter requires to run - usually 12, 24, or 48 volts.
  • The inverter input voltage must match the nominal pv system voltage.

Generator

A Generator is an optional alternative source to a power supply for those needing extra assurance that there will be power available to their system in times of need.

Pv 8 generator.JPG
  • Generators may be AC or DC.
  • The diagram above shows how an AC generator can be wired through the inverter to supply DC power to the battery and DC loads. There are only specific inverters that are capable of operating in this way.
  • DC generators can be directly wired to through the charge controller to supply the entire system.

Wiring

Color Coding
Color Coding of Wire
DC Wiring 120 AC Wiring
Red = Positive Black = Hot
Black = Negative White = Neutral
Green or Copper = Ground
Wire Size
  • Ampacity: The current carrying ability of a wire. Hence, the larger the wire, the more capacity it has to carry current.
  • Voltage Drop: The loss of voltage due to a wire´s resistance and length.
  • Wire sizing must be based on the maximum current through and length of the wiring.

Overcurrent Protection

Operating too many loads at once or faulty wiring will cause a fuse failure, which protects the wires and systems from damaging by integrating overcurrent protection into the system.

Fuses
  • Fuses consist of a wire or metal strip that will burn through when a predetermined maximum current passes throughthe fuse, which opens up the circuit to protect wires from damaging.
Circuit Breakers
  • Circuit Breakers, unlike fuses, do not need to be replaced. When the current exceeds a circuit breaker´s rated amperage, the circuit opens and stops the current flow.
Disconnects
  • Every component in the system must be capable of disconnecting from all sources of power. Disconnects can be switched fuses or circuit breakers.
Grounding
  • To ground a wire means to connect to the earth or to some conducting body that serves as the earth.
  • Grounding limits voltages due to lightning, line surges or unintentional contact with higher voltage lines.
  • Grounding stabilizes voltages.
  • Grounding equipment provides some protection from shock.

Sizing a PV System

To size your system requires seven main steps:

  1. Estimating your electrical load
  2. Estimating solar energy available
  3. Sizing an array
  4. Sizing batteries
  5. Specifying a controller
  6. Sizing an inverter
  7. Sizing system wiring and switches

These worksheets from Sandia Labs will lead you through the first four steps, and these will lead you through the last three steps. Here is an example AC/DC residence design.

You can also refer to Photovoltaics: Design and Installation Manuel, by SCI.

Advantages of Photovoltaic Technology

Photovoltaic technology holds a number of unique advantages over conventional power-generating technologies. PV systems can be designed for a variety of applications and operational requirements, and can be used for either centralized or distributed power generation. PV systems have no moving parts, are modular, easily expandable and even transportable in some cases. Sunlight is free, and no noise or pollution is created from operating PV systems. PV panels do not require the use fossil fuels such as coal, oil or natural gas in the energy production process. Alternatively, conventional fuel sources have created an array of environmental problems, namely global warming, acid rain, smog, water pollution, rapidly filling waste disposal sites, destruction of habitat from oil spills, and the loss of natural resources (Solar Energy International 2004). PV modules use silicon as their main component. The silicon cells manufactured from one ton of sand produce as much electricity as burning 500,000 tons of coal (Solar Energy International 2004). PV systems that are well designed and properly installed require minimal maintenance and have long service lifetimes. If properly maintained (cleaned and protected), pv panels can last up to thirty years or longer. Other aspects of the system, such as the battery, have much shorter life spans and may need to be replaced after several years of use.

Solar Energy International (2004) indicates that there are many other benefits to consider when choosing photovoltaic technology:

  • Reliability: Even under the harshest of conditions, PV systems maintain electrical power supply. In comparison, conventional technologies often fail to supply power in the most critical of times.
  • Durability: Most PV modules available today show no degradation after ten years of use. With the constant advancement in solar energy systems, it is likely that future modules will not show signs of degradation for up to 25 years or more. PV modules produce more energy in their lifetime than it takes to produce them.
  • Low Maintenace Cost: PV systems do not require frequent inspection or maintenance. Transporting supplies may get costly, but these costs are usually less than with conventional systems.
  • No Fuel Cost: Since there is no fuel source, there is no required spenditure on the purchasing, storing, or transporting fuel.
  • Reduced Sound Pollution: PV systems operate silently and with minimal movement.
  • Photovoltaic Modularity: Unlike conventional systems, modules may be added to photovoltaic systems to increase available power.
  • Safety: PV systems do not require the use of combustiable fuels, and are very safe when properly designed and installed.
  • Independance: PV systems may operate independant of grid systems. This is a large advantage for rural communities in nations lacking basic infrastructure.
  • Electrical Grid Decentralization: Small-scale decentralized power stations reduce the possibility of power outages, which are often frequent on the electric grid.
  • High Altitude Performance: When using solar energy, power output is optimised at higher elevations. This is very advantagoeus for high altititude, isolated communities where diesel generators must be de-rated due to the loss in efficiency and power output.

Disadvantages of Photovoltaic Technology

Solar energy is a fairly inexhaustible source of energy, but that does not necessarily translate to PV being the same. PV systems are:

  • Expensive- Very high initial cost. System components are expensive to replace.
  • High Tech- Require a skilled labor force to create, although operation and maintenance of PV cells themselves is relatively easy. There are currently no good methods for people to make their own PV systems from local materials. The high tech nature gives a large advantage to scale of production with current technologies.
  • Some PV materials are toxic. E.g. the Cadmium in Cadmium Telluride solar cells. Many authors have argued that in the panel itself the Cd is secure from the environment -- but then it demands careful end of life treatment.
  • Weather- Solar cells only produce electricity when the sun is shining. At night or in bad weather, you need either storage batteries or a secondary power source. (On the other hand, solar panels are excellent for load balancing because maximum electricity usage and peak solar generation both occur on hot sunny days.)

There are two disadvantages often used in the environmentalist camps concerning high tech PV:

  • Production Pollution- Fossil fuels are extensively utilized to extract, produce and transport PV panels. These processes also entail corresponding sources of pollution. This is true of just about any product made today. Fortunately, the life cycle analysis of a PV system is a net positive for the environment because it can offset fossil fuel energy production over its approximately 25+ year lifetime.
  • High energy cost- Require much energy to produce. In the past it was even argued that it took more energy to produce than they consume. This is just wrong. For a detailed analysis of the life cycle energy costs of solar cells see: Joshua Pearce and Andrew Lau, “Net Energy Analysis For Sustainable Energy Production From Silicon Based Solar Cells”, Proceedings of American Society of Mechanical Engineers Solar 2002: Sunrise on the Reliable Energy Economy, editor R. Cambell-Howe, 2002. In this paper they clearly show that the three types of photovoltaic (PV) materials, which make up the majority of the active solar market: single crystal, polycrystalline, and amorphous silicon solar cells pay for themselves in terms of energy in a few years (1-5 years). They thus generate enough energy over their lifetimes to reproduce themselves many times (6-31 reproductions)depending on what type of material, balance of system, and the geographic location of the system.

Education about Solar Photovoltaic Cells

Solar Photovoltaic Open Lectures

References

  • Pratt, Doug & John Schaeffer. Solar Living Source Book. Tenth. NV: Chelsea Green Publishing Company, 1999.

Links

Web sites for current information on PV

Useful government web sites on PV

How to Afford PV Now

Designing Your Own PV system

General Resources

Misc

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