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| FAQs - PV Inverter SITOP solar - Siemens | 11/23/2008 6:24 PM | ||
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FAQs
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| What
means photovoltaics?
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| Photovoltaics (Greek: Photo = Light and Volt = measure for electrical voltage) is the direct, physical transformation from sunlight into direct current energy with solar cells. |
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| What
is a solar cell? |
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| Solar cells are specially prepared, square-cut
semi-conductors
(called Wafers); they mostly consist of silicon (raw material for
silicon is quartz). There are poly crystalline, mono crystalline and thin-layer cells, depending on the process of manufacturing and raw material. They differ in the expenditure of material in manufacturing and in the degree of efficiency. This means the demand of surface to produce the same amount of electrical voltage can vary. At the front- and backside of a cell are contact ribbons, which lead off the produced energy. |
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| Which kinds of solar cells are available? |
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| Mono crystalline solar cells consist of pure
silicon. The degree of efficiency is about 14-18%. Poly crystalline cells are mostly cut out of a found silicon block. Advantage: easier to manufacture and a less refuse during the production. The degree of efficiency lies currently at 12-16%. Mono crystalline und poly crystalline solar cells are the majority of the actually used solar modules. Today for thin-layered cells there are different semi-conductor materials in use. Very promising half layered cells are amorphous (non crystalline) silicon, copper-indium-diselenid (CIS) und cadmium-tellurid (CdTe). These semi-conductors strengthened by an carrier material (glass), will promise greater economizing of costs in future, because this method only needs 10 percent of the semi-conductor material. Because of the lower degree of efficiency (ca. 6-8%) they aren't very widespread, yet. |
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| What
is a solar module? |
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| In a module there are many single solar cells
on a ground layer and connected with so called circuit paths. For protecting these, they are fasten between a glass- and a tedlar layer. For stabilising modules they are mostly set together in a metal frame. |
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| Of
what consist a photovoltaic installation? |
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| First the solar module, in which a certain
amount of solar cells is electrically switched together. Some of them are combined to a solar generator. The generated direct current has to be transformed in an inverter to a net conforming alternating current. The electric power in grid-connected installations flows through a counter into the public energy supply and is compensated by the energy supplier. In addition to these components the mounting system for fastening the solar modules and the cabling are important parts of the PV installation. |
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| What's an inverter? |
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| The inverter, transforms the produced direct current energy from the generator to net conforming alternating current. In addition it is important to control the system and cuts off at interruptions the connection to the energy net on power failures. | |
| What does the efficiency factor kWp mean? |
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| kWp, called Kilowatt-Peak This value gives the efficiency, of an solar module at full sun insolation (under fixed conditions). A unit, which has become standard in photovoltaic technologies. |
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| How is energy generated from sunbeams? |
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| If sunlight strikes a photovoltaic cell, electrons and small holes (so-called: p-holes) are generated in the silicon and separated by an electrical field. Electrons circulate to the negative pole and the p-holes to the positive pole. Connecting the contacts across a electric gadget like a bulb, the electrons move around the external electric circuit backwards to the negative pole - direct current arises. | |
| How long lives
a pv-installation? |
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| Because of the lucrative payment in
Germany a photovoltaic installation is economic. Good solar modules will generate electrical power longer than the projected 20 years. PV-installations are extremely low-maintenance and reliable. The high dependability and longevity was proved in many applications - this is possible because solar panels exist without any expendable parts. There aren't any kind of moving parts on a PV installation, so almost no mechanical abrasion. |
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| How many power can be generated by a pv-installation? |
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| The efficiency of the plant depends on
the optimal orientation of the modules towards the sun (south,
30° incline.) Shadows on the modules (also if they appear only at certain times of day) reduce the gain and should be avoid. In Central Europe gain of 800 to 1000 kWp per year is possible. This means, a 2.5-kWp-standard installation can produce power amounting to between 900 and 1100 Euro per year. On a clear sunny day the insolation in Germany is around 1000 watt per m². This is equivalent to the power rating of a hot plate. A module of 1 m² achieves around 120 watt with these conditions. |
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| How efficient is a photo cell? |
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| One singular cell with dimensions of 10
x 10 cm generates at full sunlight illumination about 0.5 voltage
and 2.4 ampere electrical power, so producing 1.2 watt
efficiency. With those small amounts, it's hard to start doing
something with it. For this reason you typically interconnect more solar cells to a solar module and laminate them to protect them from environmental influences between a glass- and a tedlar-panel. |
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| What happens
at cloudiness? |
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| PV modules use not only the direct sunlight, which only appears on clear sky, but rather the so-called diffuse light rays from the clouds. The brighter it is outside, the more efficient the modules do their job, if the sun can be seen or not. In Central Europe the diffuse amount brings up about 50 percent of the insolation. | |
| Where should a pv-panel be installed? |
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| Generally PV panels can be installed at
any place, where enough light impinges. An economic gain
guarantees a
south orientated surface with an incline of 30°. Deviations to south-west or south-east or inclines between 25° and 60° reduce the benefit only minimally. Clouding from adjoining buildings, plants and so on should however be avoided. |
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| How
large should be a pv-installation? |
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| The allowance conditions define that,
the whole generated solar power has to be fed in the public power
supply; this does not mean that the dimension of the installation
depends on the personal energy consumption. At grid connected
installations the dimensions are dependent on the available roof area. A PV construction with a rated output of 1000 watt (1 kWp) needs 8 to 10 sq. m roof area. Another factor certainly is the amount of money, that should be invested. Other components like inverters, counter and so on are relative small and easy to install. A ductwork or a shaft for duct cables is advantageous. |
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| How can I use the produced energy? |
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| At grid connected installations the
whole generated energy should be fed into the public power supply
and sold to the facilities based carrier, because of the high
commission. For your home requirements you can use alternative energy which is also available on the free market. |
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| How much cost a pv-installation? |
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| Nowadays prices between 6000 and 8000
per kWp output incl. VAT and installation are mentioned. Operators of a grid connected solar installation make profits and its legitimate that they claim the VAT from the tax authorities. Details should be discussed with a tax accountant. The price per kWp on larger constructions is as a rule cheaper than smaller ones. |
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| Must I feed my generated solar energy in the
public power supply? |
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| No, the electric power can be used in
the own household too - and only the surplus is fed into the grid. Economically more interesting is to feed the whole solar energy into the public power supply, because of the actual commission. |
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| Is the technology today ready to use? |
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| Photovoltaic has proved its reliability over a long period of time and in many applications. This technology first was developed for space travelling, where the demand on reliability is very essential. Today's usual technology is very reliable, efficient and does not harm our environment. In Germany already thousands of installations are in use. Only in Berlin are about 300 grid connected PV systems in use. |
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| What is the degree of efficiency? |
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| The degree of efficiency tells you how many percent of the power of sunlight will be transformed into electrical power. It only tells you if you need more or less area for a fixed amount of installed output. Decisive for the need of area is the module degree of efficiency. This one lies for mono crystalline modules between 11% and 14% and for poly crystalline modules between 9% and 13%. |
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| I'm interested in such a pv-installation, which
are the next steps? |
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| The way to an own photovoltaic installation should go over a experienced trader. There you'll
get good advice for the suitability of the planned
position for the panel, for the most favourable furtherance and also a first planning for free. From our traders you will get a very good consultation and more information about the Siemens inverters.  LINK |
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| What is a string? |
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| This means modules combined several in one row. | |
| Are there differnt kinds of inverters? |
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| In the ten years the prices of PV-installations have dropped by 50 percent, the efficiency and reliability have increased. To reduce the cost-to-efficiency ratio, new inverter designs have appeared in the market, which have their ad- and disadvantages; depending on their applications. The most important classifications are: Central inverters: They are commonly used in large-scale PV-installations, with a power range of 50 kW up to the mega watt region. The PV-rows are combined in parallel strings. The DC-AC-conversion takes place in one common inverter.
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String inverters: The string inverter-concept is based on a modular integration of a master- and a slave device. Each string has its own inverter. The output of the slaves are fed into the master, which transfers the total power.
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Module integrated inverters: In this solution every single module has an own inverter.The benefit of this installation is that with every single module energy is produced. But this installation above is very cost-intensive.
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a pv-installation?
