Bahawalpur Solar Park test run proves successful

[Edevelop]

BAHAWALPUR: A 100MW unit of the Quaid-i-Azam Solar Park, the first of its kind in the country, had a successful test run, Dawn learnt on Thursday.

According to sources, the solar park unit was run on a trial basis giving 85pc to 87pc of its total targeted production.

Confirming the successful test run to Dawn, Mepco Executive Engineer Dr Khawaja Niaz Ahmed said the solar park had started functioning on experimental basis successfully and it was being expected. He said the power generated by the solar park was being supplied to the national grid under Mepco supervision through its network.

According to Mr Ahmad, the solar park unit was expected to get its total generation target of 100MW gradually.

He said Mepco engineers were at the site to oversee the power generation and its supply to the national grid.

The solar park with a total generation capacity of 1,000 MW had been set up on more than 10,000 acres in Cholistan area with the Chinese support.

In the first phase, a 100MW unit has been set up, installing about 0.4 million solar panels on about 500 acres. Work on 300MW and 600MW units will be undertaken by Punjab energy department later.

Solar park test run proves successful - Newspaper - DAWN.COM



Sea of clean, green energy in the land of the pure

 

[Kompromat]

Outstanding work.

 

[ziaulislam]

well, i am the nonly one who doesnt like solar energy for one simple reason...COST
it was expensive in past too, when oil was soaring around 100, furnace oil and solar were the same cost however our delima was that we lack refineries and thus for some odd reason we are fond of diseal escalting the cost much more than solar.
however these days even diseal is cheaper than solar production.
so unless you want to go green solar doesnt make much sense in our country.
yes if local production kicks up alot then may be we can lower the cost but its too much for now. govt focus should be coal imported or local, hydro and wind
unfortunately hydro has been completed ignored other than PPPP era tarbela expansion fully funded by world bank we see nothing else.
PPPP were much better in this one aspect atleast they completed several small hydro projects

 

[daring dude]

Nice work, But kinda absolute form Solar power generation,.,, As their is more effective methods now for better efficiency in terms of Area that's been used..& 0.4mn or 40lacs of Solar Panels been used and 500 Acres of land been used...We can find or evaluate better sources in terms of it's efficiency and Power generation that is our Dire need.... Please check below Sources,,,, ;

Introducing the Most Efficient Solar Power in the World
It's taken 25 years, but a new solar-thermal plant in New Mexico has finally broken the old efficiency record.
By Cyrus Moulton|Thursday, October 08, 2009


Image: Randy Montoya
In 1986 solar panels were literally ripped from the White House roof. But political will and financial incentives have reignited the search for efficient, affordable ways to harness the sun’s energy. Two new solar thermal technologies—which focus sunlight to create heat rather than convert it directly to electricity, as photovoltaics do—promise to make solar power practical at vastly different scales.

The SunCatcher solar thermal system, developed by Tessera Solar and built byStirling Energy Systems at the Sandia National Laboratories’ National Solar Thermal Test Facility, captures solar energy at 31.25 percent efficiency, the highest ever achieved by this technology. Each of SunCatcher’s 38-foot-wide dishes collects enough heat energy to run a Stirling engine that can then generate 25 kilowatts of electric power. The system will fulfill two of the world’s largest solar contracts, providing a planned 1,600 megawatts to Southern California by 2014. It improved on its predecessor with a new design that makes each dish substantially lighter and cheaper to manufacture.

Meanwhile, a group of recent and current MIT engineering students is working to bring solar thermal to Africa with an off-grid system that operates on a much smaller scale. The team has developed a microgenerator capable of producing 3 kilowatts of electric power plus hundreds of gallons of hot water each day using relatively inexpensive, readily available components such as auto parts. Engineer and cofounder Amy Mueller says that the MIT group’s nonprofit, called STG International, has already set up microgenerators at two locations in Lesotho. A third Lesotho installation is under construction at a medical clinic, where it will provide power for lighting and communications equipment as well as hot water.

discovermagazine.com/2009/oct/08-introducing-most-efficient-solar-power-in-world

Solar Power
(Technology and Economics)
The earth receives more energy from the Sun in just one hour than the world's population uses in a whole year.

The total solar energy flux intercepted by the earth on any particular day is 4.2 X 1018 Watthours or 1.5 X 1022 Joules (or 6.26 X 1020 Joules per hour ). This is equivalent to burning 360 billion tons of oil ( toe ) per day or 15 Billion toe per hour.

In fact the world's total energy consumption of all forms in the year 2000 was only 4.24 X 1020 Joules. In year 2005 it was 10,537 Mtoe (Source BP Statistical Review of World Energy 2006)



Electricity Generating Costs and Domestic Solar PV System Economics



Angle of Incidence below). Similarly the insolation will be reduced as higher latitudes due to the effect of air mass - (See below).

The graph also shows that, in this case, the total received energy over the 10 hours of daylight will be 3.5 kWh.

If the insolation had been constant at 1000 W/m2 the same amount of energy would have been received in 3.5 hours. The Equivalent Hours of Full Sun is a measure of average insolation at different locations. In this case the EHS is 3.5 hours.

The available solar energy and thus the Equivalent Hours of Full Sun (EHS) also depend on the atmospheric conditions of cloud cover and pollution. See Available Energy - Practical Systems below.



The concept of EHS is useful for comparing the potential of solar energy systems when installed at different geographic locations.

[paste:font size="4"]
Capturing Solar Energy
Solar energy can be captured in two forms, either as heat or as electrical energy.

• Thermal Systems
  Thermal systems capture the Sun's heat energy (infra red radiation) in some form of solar collector and use it to mostly to provide hot water or for space heating, but the heat can also used to generate electricity by heating the working fluid in heat engine which in turn drives a generator.
  
• Photovoltaic Systems
  Photovoltaic systems capture the sun's higher frequency radiation (visible and ultra violet) in an array of semiconductor, photovoltaic cells which convert the radiant energy directly into electricity.
  
  
  

The actual solar energy or insolation reaching a solar collector or array depends on its position on the Earth, its orientation and it also varies continuously with time as well as weather conditions.

The amount of energy captured is directly proportional to the area of the Sun's energy front intercepted by the collector.



diagram above.

• At the same time the tilt also changes the path length of the radiation through the atmosphere which in turn changes the amount of the Sun's energy absorbed by the atmosphere. (also shown in the same diagram above).

• The tilt also changes the number of daylight hours.

These factors all work together to reduce both the intensity and daily duration of the insolation during winter months.



As seen from the northern hemisphere of the Earth, the declination in the elevation of the Sun varies during the course of the year between minus 23.45° in the summer and plus 23.45° in the winter.

Taking into account the solar declination, the altitude angle α of the sun is (90 - Θ ± δ) degrees.

The inclination angle of solar collectors from the horizontal for maximum efficiency should therefore be (Θ ± δ) degrees and the collector should be able to follow this variation in declination throughout the year.

• Time

Fortunately as a source of renewable energy the Sun is much more predictable than the wind. It comes up every morning and goes down every night. The intensity of the wind may be extremely variable, but it is available 24 hours per day, while solar power is only available during daylight hours. At least solar power is reliable and is available when it is needed most - during peak demand hours.



Though the insolation is subject to two temporal variations, a diurnal (daily) cycle due to the Earth's rotation and a yearly cycle due to the tilt of the Earth's axis, we know precisely the magnitude of these effects at any time so we can design our solar power systems accordingly. What is less predictable however is the affect of the weather.



Unless they are connected to the grid, systems which must provide energy on demand need some form of energy storage or an alternative source of energy for the hours of darkness.



[paste:font size="4"]Some Meteorology
Unfortunately we have no control over the weather. Overcast skies can severely reduce the energy received on the ground. Obviously solar power generating plants are best located in regions with minimum cloud cover, dust and air pollution. At least we usually have statistics about regional weather conditions to help in choosing suitable locations for solar power plants.



For dimensioning a solar power generating system it is essential to know the number of hours of daylight expected at the site location. This can normally be obtained from national meteorological services and environmental research establishments as well as from NASA in the USA. It helps even more if they are able to provide tables of expected solar energy for the region.

Note: It is important to check the basis of the data. Some organisations quote the solar insolation on a horizontal surface, that is the ground. Others base their data on the insolation of a collector with a fixed angle of tilt corresponding to the latitude of the location.



chart below shows that, in the UK, the available energy from the winter Sun is between one sixth and one twelfth of the energy from the summer Sun depending on the latitude.

• Azimuth Tracking
  Azimuth tracking keeps the collector pointing at the Sun as the Earth rotates.
  
  The insolation varies between zero and its maximum value during the course of every day and remains around its maximum value for a relatively short period of time. Azimuth tracking enables the collector to follow the Sun from East to West throughout the day and brings the most benefits.
  
  Passive systems provide the simplest form of azimuth tracking. They have no motors, controllers or gears and they don't use up any of the energy captured by the collector. They depend on the differential heating of two interconnected tubes of gaseous refrigerants, one on either side of the collector. If the collector is not pointing towards the Sun, one side heats up more than the other and vaporises its refrigerant. The resulting change in weight is used in a mechanical drive mechanism to turn the collector towards the Sun where it will remain when the temperature and weight of the two tubes will be balanced.
  
  Active tracking is also possible by employing temperature sensors and a control system with linear actuating motors taking their drive power from the system.
  
  
  
• Altitude/Elevation Tracking
  Elevation tracking enables the collector to follow the seasonal variations in the Sun's altitude but the economic benefits are less than for azimuth tracking.
  
  Compared with the daily variations in insolation, the seasonal variations are very slow and the range of the variation, due to the solar declination is much more restricted. Because of this, reasonable efficiency gains can be obtained simply by manually adjusting the elevation of the collectors every two months. To avoid the cost and complexity of elevation tracking, it may be more cost effective just to specify larger collectors.
  
  
  
• Dual Axis Tracking
  Combining azimuth and elevation tracking enables the installation to capture the maximum energy using the smallest possible collectors but the systems are complex and many installations get by with just azimuth tracking.
  
  
  

[paste:font size="4"]Definition)



[paste:font size="4"]Solar Energy Available at Different Latitudes

Location

Latitude

Degrees

Altitude
Metres

Tracking

Insolation kWh/m2/Day

June

December

Anchorage, Alaska

61.17°N

35

None

4.5

0.6

2 Axis

6.8

0.7

Quito,

Equador

0.47°S

2851

None

4.38

4.81

2 Axis

6.09

6.62

• 
  Source NREL
  
  
  

Because of cloud cover and pollution, the quoted hours of "full Sun" are substantially less than the actual hours of daylight. In sunnier climes, an average of 33% of solar irradiation comes from diffuse light but for the majority of locations this is typically more than 50%. The equivalent hours of full Sun takes into account the affect of overcast or partially cloudy skies.



hybrid system combining wind and solar power could be the answer.



[paste:font size="4"]Electrical Energy Storage
Because no power is provided during the hours of darkness, the stand alone systems must generate and store sufficient energy during the day to satisfy the peak daily load. The storage should also be sufficient to cover several days when no sunlight is available. Batteries are normally used as a buffer to provide the necessary storage to guarantee short term continuity of supply by storing surplus energy during the day for use during the night and during periods of overcast skies. Unfortunately it is not practical to store the summer's surplus energy for use during the winter. See alternaitive Thermal Storage below



binary cycle in which the heated oil is passed through a heat exchanger to raise steam which is used to drive a conventional turbine and generator in a separate circuit.

To maintain the thermal efficiency of the turbine, the working fluid leaving the heat exchanger should not be allowed to cool down. Solar plants are therefore supplemented by gas-fired boilers which generate about a quarter of the overall power output and maintain the temperature overnight.

Several such installations in modules of 80 MW are now operating and solar conversion efficiencies of between 15% and 23% have been achieved. Each module requires about 50 hectares of land and needs very precise engineering and control. Power costs are two to three times that of conventional sources.



Thermal Energy Storage

The use of molten salts to provide the capture, storage and release of solar energy has recently been demonstrated. (See Alternative Storage). The solar thermal energy may be captured directly by a molten salt which has a high thermal capacity in a "Power Tower" or indirectly in a heat exchanger from the hot working fluids circulating through arrays of solar concentrators. A suitable salt such as potassium nitrate is liquid above 370 °C (698 °F) and acts as a second working fluid. It gives up its heat when required to water in a second heat exchanger to form steam for driving the turbine.

The Solana concentrating solar thermal plant in Arizona which uses molten salt storage can keep delivering power for six hours after sunset.



Small Scale Thermal Plants

Steam turbines are only practical for very large installations. Stirling Engines are often used in small systems to drive the electrical generator.



Balance-of-System (BOS) components including chargers, inverters and controllers to manage the energy flows in order to provide power on demand. This makes the system very expensive. Grid connected systems also need power conditioners and control systems if surplus energy is to be sold back to the utility company.

Efficiencies achieved with small scale systems range from 18% to 23%.



[paste:font size="4"]see below) to generate the electrical energy needed to power the water circulation pumps instead of using mains electricity.

At sunrise, the pump remains switched off until the water reaches its operating temperature at which point the pump is switched on. As the Sun's radiation increases during the morning, the water temperature will rise, but at the same time the solar powered pump will run faster, increasing the water flow and thus transfering heat more quickly from the panel to the hot water storage tank. By suitably dimensioning the pump and the photovoltaic panel, the heat transfer rate from the panel can be matched to the heat absorption rate from the Sun thus maintaining a constant water temperature. As the received Sun's energy wanes in the afternoon the process is reversed, the pump runs more slowly reducing the rate at which heat is extracted from the panel thus maintaining its temperature. Being completely independent of the electricity grid, these systems have the added economic and environmental benefits that no electrical energy is drawn from the grid for running the pumps.

• Temperature Limits

With water as the working fluid, the system is prone to freezing and boiling unless special precautions are taken. Low cost systems allow the water to freeze in very cold and dark environments by using flexible freeze-tolerant, silicone rubber pipework which is sufficient to accommodate the expansion of the water as it turns to ice. The volume of water used in solar thermal panels is very small, typically around 2 or 3 litres and is spread over a very large area to capture the maximum solar radiation. The high received radiation acting on a low water volume enables the water to heat up very quickly but for the same reason makes it susceptible to boiling. Unless there is a constant water flow to a storage tank with the heated water in the panel being replaced by cold water from the tank, the water could reach temperatures of 150 degrees C or more and for this reason the water pumps must be continually switched on. Even so, the possibility of boiling still remains, even with the pumps running, if the system is incorrectly dimensioned. The equilibrium temperature reached will depend on the balance between the solar energy captured by the panel and the thermal energy absorbed in the storage tank, the rate at which it is withdrawn from the tank and the system heat losses. Using a very small panel coupled to a very large tank with high hot water usage will result in a low water temperature in the tank. Conversely using a very large panel with a very small tank could result in boiling, particulaly if the hot water usage is very low. This need not be a disaster since the water content in the panel is very low and system could be designed to allow the steam to vent in case of boiling.

• Efficiency

Energy conversion efficiencies achieved in these pure thermal applications may be three or four times the efficiency of photovoltaic applications though their applications are much more limited.

• Economics

In higher latitudes the available solar energy captured by practical domestic installations may be sufficient to provide hot water for washing and showering but not enough to supply building space heating requirements during the colder months. Back-up heating systems will consequently be needed to cater for the base load to satisfy these requirements. Because the supply of solar energy is intermittent, the conventional heating system must fill in the gaps and there is little opportunity to downsize it. The householder will therefore, most likely have to pay the capital costs of a base load system capable of supplying the full heating load as well as the solar heating system even though the conventional heating system will not be working at full capacity most of the time.

Domestic solar thermal systems may not generate electricity directly but they do contribute to a reduction in the use of electrical energy and its associated costs.

• Example
  Useful Energy Captured
  
  The table above shows that in the UK, the average solar radiation received is about 2.5 kWh / M2 / day. A single solar panel with an area of 3 M2will therefore capture 2.5 x 3 x 365 = 2737 kWh of energy per year. With a system conversion efficiency of around 40% and less than optimal orientation of a typical rooftop mounted solar panel, the maximum usable energy received by a single panel system will be around 1000 kWh. This is roughly equivalent to the energy supplied by a 3 kW immersion heater used for one hour per day. As always however, averages can be misleading. In the summer, the solar panel could deliver an "average" of about 5 kWh of heating energy per day, but in the winter this could be as low as 0.4 kWh per day. The energy captured can of course always be increased by increasing the number of solar panels employed in the system.
  
  Cost Savings
  
  The cost saving will depend on whether the solar system is replacing 1000 kWh of heating energy supplied by a gas or an electric water heating system and the associated tarriff charged for the energy. With UK domestic gas currently costing less than £0.03 per kWh ($0. 045) and electricity costing about £0.10 per kWh ($0.15) the annual savings are likely to be somehwere between £30 and £100 ($50 to $150).
  
  Since typical single panel installations cost around £2,500 or £3,000 ($4,000 to $5,000), unless the systems qualify for a government subsidy or there is a very large increase in energy costs, the payback time for the investment will be measured in decades rather than years. Saving the planet can be quite expensive.
  
  Carbon Footprints
  
  As with wind power, if the investment fails the conventional economic tests, the notion of carbon footprints is often used to jusify the expense, based on the potential for reducing the amount of greenhouse gases emitted by alternative methods of power generation.
  
  
  
  See also Domestic Solar PV System Economics below.
  
  
  

[paste:font size="4"]electronVolts (eV)) infrared photons with high-energy (3.5 eV) ultraviolet photons and all the rainbow of visible-light photons in between. Solar cells, also called photovoltaic or PV cells, are semiconductor devices designed to capture these photons and convert their energy directly into electrical energy.



[paste:font size="4"]How Solar Cells Work
When a photon with sufficient energy impinges upon a semiconductor it can transfer enough energy to a electron to free it from the bonds of the semiconductor's valence band so that it is free to move and thus carry an electric current. The junction in a semiconductor diode provides the necessary electric field to cause the current to flow in an external circuit.

A more detailed explanation of how solar cells work is given in the section on photovoltaic diodes.



Conversion Efficiencies
The typical output voltage of a PV cell is between 0.5 and 0.6 Volts and the energy conversion efficiency ranges from less than 10% to over 20%. An array of cells can therefore generate about 200 Watts of electrical power per square metre when illuminated by solar radiation of 1000 Watts per square metre. The corresponding current density will be about 400 Amps/m2. Because of climatic conditions the intensity of the insolation rarely reaches 1000 W/m2.

Practical cells are also much smaller than one square meter with actual sizes of commercially available cells ranging from about one centimetre square to 15 centimetres square. The corresponding output Wattages for these cells range from 20 milliWatts to about 4 Watts.



Solar PV systems are amongst the least efficient ways of generating electricity, (see Efficiency Comparison Table), but this poor performance is not just due to the low PV conversion efficiency of the cells which is improved year by year by ongoing research and development. It is mainly due to the lack of available sunshine, and no amount of R&D can improve that.



A PV conversion effifiency of 15% may appear to be very low, but it is on a par with the "well to wheel" conversion efficiency of the energy used to power a gasoline/petrol driven automobile.



Irradiance of 1000 W/m2, Cell Temperature 25 °C (77 °F) and Air Mass =1.5

• Air Mass

The receiving surface corresponding to AM 1.5 is defined as an inclined plane at 37° tilt (the average latitude in the USA) toward the equator, facing the sun. In this case, the surface normal points to the sun, at an elevation of 48.81°, its zenith angle, above the horizon.

• Rated Power

Rated Power is defined as the maximum power (Wp or kWp) generated by the cell or module under the Standard Test Conditions.



Alternative PV Cell Rating

The STC laboratory test conditions are not truly representative of typical open air operating conditions and for this reason a more realistic set of test conditions, NOCT, was developed.

• Normal Operating Cell Temperature (NOCT)
  Normal Irradiance 800 W/m2, Air Temperature 20°C (68°F), Wind Velocity (cooling) of 1 meter per second (2.24 miles per hour), with the rear side of the solar panel open to the air flow.
  
• Air Mass and Rated Power similar to STC

Interpretation and Application of the STC and NOCT Ratings.

The following is an example of key data taken from a reputable manufacturer's specification sheet for a 250 Watt solar panel.

• Information provided:
  STC rating 250 Wp
  
  NOCT raring 183.3 Wp
  
  Cell dimensions 156 mm X 156 mm
  
  Number of cells 60
  
  No mention of the area
  
  No mention of conversion efficiency
  
• What does this mean in practice
  • The STC and NOCT ratings are the power outputs achieved under test conditions.
  • The test conditions are designed to represent the maximum solar energy which could be received under ideal conditions.
  • In practice you will never achieve these power outputs from sunlight
    • The STC and NOCT ratings assume a constant high level of irradiance (1000 W/m2or 800 W/m2). These are simply different standard input power levels used for the tests, thus any cell will normally generate a larger output power under STC conditions compared with NOTC conditions.
    • Outside of the tropics, the irradiance from the Sun at ground level on typical solar panels will rarely even approach these test levels.
    • The insolation which is the average effect of the Sun's irradiance, taking into account, the hourly, daily, and seasonal variations as well as latitude and local climate conditions, will be much lower than the test irradiance. The NREL maps on the Going Solar page indicate the expected regional insolation levels.The consequence is that the average solar energy intercepted by the panels will be very small and the corresponding electrical energy output from the panels will also be very small.
    • The actual solar energy captured also depends on the configuration of the solar panels and whether they are able to track the Sun during its path across the sky.
  • What will be the average electrical power output from the above "250 Watt" solar panel?
    It depends on the location and the type of solar array and the conversion efficiency of the solar PV cells. Assuming a fixed solar array located in the North East of the USA, facing South and tilted towards the Sun at an angle corresponding to the latitude of the site, the NREL map shows that the insolation is around 4 kWh/m2/day. In the sunnier South West the insolation will be about 50% more at 6 kWh/m2/day which translates directly into 50% more electrical output power from the same solar panels.
    
    
    
    The 60 cell solar panel has an effective area of 60 X 0.156m2 = 1.46 m2
    
    In the North East this panel will therefore intercept 1.46 X 4 = 5.84 kWh of solar energy per day.
    
    This insolation is equivalent to a constant (average) solar power of 5840 / 24 = 243.3 Watts during the 24 hour day.
    
    The conversion efficiency of the solar cells is calculated from the manufacturer's specified electrical power output achieved from the NOCT specified power input.
    
    The energy intercepted by the 1.46 m2 panel under NOCT conditions will be 1.46 X 800 = 1168 Watts
    
    The specified electrical output power from the panel is 183.3 Watts
    
    Thus the conversion efficiency = 183.3 / 1168 X100 = 15.7%
    
    Applying this conversion efficiency to the actual insolation of 243.3 Watts gives an average electrical power output from the panel of 243.3 X 0.157 = 38.2 Watts (This corresponds to an electrical output of 26.2 W / m2)
    
    
    
    Not bad for a solar panel rated at 250 Watts?!
    

(Tandem) Solar Cells
Better conversion efficiencies are possible by using multiple layers of differing semiconductor materials, optimised for different wavelengths, in a single device. This can raise the theoretical efficiency limit, currently about 30% for a single junction device, to about 45% for a three junction cell.

Efficiencies of over 33% have already been achieved in practical devices.

• Exotic Materials

Materials such as Gallium Arsenide, Copper Indium Diselenide, Cadmium Telluride and Indium Nitride have been employed to provide particular characteristics to optimise solar cells for specific applications.

Gallium Arsenide is used for military and aerospace applications in a variety of cells in combination with other elements because of it's suitability for capturing high energy photons (ultra violet radiation), high potential conversion efficiency and its ability to withstand high temperatures. It is however more difficult to manufacture and cells using Gallium Arsenide can be 100 times more expensive than commercial silicon based cells.

Copper Indium Diselenide and Cadmium Telluride are used in polycrystalline form in low cost thin film cells because of their ease of manufacture and reasonable yields. Efficiencies are however low ranging from 8% to 14%

Indium Nitride is suitable for capturing low energy photons (infra red radiation) making it suitable for full spectrum devices when used in tandem solar cells in combination with other materials such as Gallium Arsenide which capture the high energy photons.

• Electrochemical Solar Cells - Dye Sensitised Solar Cells (DSSC or Grätzel Cells)

Relatively new, these cells are low cost devices which use dye sensitised Titanium dioxide in combination with a liquid electrolyte to generate the current. Up to now they are only available in small sizes with efficiencies between 7% and 10%.



[paste:font size="4"]Solar PV Collectors
Solar cells are usually sold in modules built up from a number of cells arranged in series and / or parallel to provide convenient or commonly used voltages and power ratings.

Solar Arrays

Modules can be similarly interconnected to create larger arrays with the desired peak DC voltage and current.



Concentrators

As with thermal collectors, concentration of the incident energy on to a smaller surface is possible. For very small applications, optical mirrors and lenses are used.



Jacobi's Law). Unfortunately, batteries are far from the ideal load for a solar array and the mismatch results in major efficiency losses.

A typical PV array designed to charge 12 Volt batteries delivers its maximum power at an operating voltage around 17 Volts. Lead Acid batteries are normally charged up to 14 Volts though the voltage quickly drops to 12 Volts as they start to deliver current and lower still as the depth of discharge (DOD) increases.
In its simplest form, charging is carried out by connecting the PV array directly across the battery. The battery however is a power source itself and presents an opposing voltage to the PV array. This pulls the operating voltage of the array down to the voltage of the discharged battery and this is far from the optimum operating point of the array.


The diagram below shows the performance of a17 Volt, 4.4 Amp, 75 Watt PV array used to top up a 12 Volt battery. If the actual battery voltage is 12 Volts, the resulting current will only be about 2.5 Amps and the power delivered by the array will be just over 50 Watts rather than the specified 75 Watts: an efficiency loss of over 30%.
Maximum Power Point Tracking is designed to overcome this problem.

The power tracker module is a form of voltage regulator which is placed between the PV array and the battery. It presents an ideal load to the PV array allowing it to operate at its optimum voltage, in this case 17 Volts, delivering its full 75 Watts regardless of the battery voltage. A variable DC/DC converter in the module automatically adjusts the DC output from the module to match the battery voltage of 12 Volts.
As the voltage is stepped down in the DC/DC converter, the current will be stepped up in the same ratio. Thus the charging current will be 17/12 X 4.4 = 6.2 Amps and, assuming no losses in the module, the power delivered to the battery will be 12 X 6.23 = the full 75 Watts generated by the PV array.
In practice the converter losses could be as high as 10%. Nevertheless a substantial efficiency improvement is possible.



It is not enough however to match the voltage at the specified maximum power point (MPP) of the PV array to the varying battery voltage as the battery charges up. Due to changes in the intensity of the radiation falling on the array during the day as well as to changes in the ambient temperature, the operating characteristic of the PV array is constantly changing and with it the MPP of the PV also changes. Thus we have a moving reference point and a moving target. For optimum power transfer, the system needs to track the MPP as the solar intensity and ambient temperature changes in order to provide a dynamic reference point to the voltage regulator.


High performance MPPT modules may incorporate software algorithms to take account of the variations in insolation and temperature. A typical job for fuzzy logic or a neural network. Alternatively the optimisation can be accomplished in hardware by means of a perturbation signal incorporated in a feedback loop which drives the system operating point to the MPP.

A small dither voltage is superimposed on the PV voltage and its affect on the regulator output current feeding the battery is monitored. If the current drawn by the battery increases when the dither voltage increases, then the operating point has moved towards the MPP and therefore, the operating voltage must be increased in the same direction. On the other hand, if the current into the battery decreases, then the operating point has moved away from the MPP and the the operating voltage must be decreased to bring it back.

[paste:font size="4"]
Large Scale Photovoltaic Plants
Several large scale grid connected PV power plants have been constructed throughout the world, mostly of 300 kW to 500 kW capacity but some as high as 300MW or more. Up to now deployment of large scale plants has been limited to experimental installations because of the high cost of the solar panels. With typical efficiencies of around 15%, a 500 kW plant will need around 20,000 square metres of PV panels costing about $1.00 per Watt as well as large scale inverters capable of handling the full system power output. See an example of a Grid Scale Solar PV System.



Small Scale Photovoltaic Plants and Domestic Applications
The diagram below shows the basic building blocks of a small stand-alone off-grid PV power generating system. A grid connected system would not need the battery and MPPT power tracking system. They do however need alternative capacity to come on stream to carry the load during the hours of darkness.

Photovoltaic System Dimensioning

• Array sizes for Photovoltaic System
  The following example show the array sizes necessary to generate 10 kWh of usable energy with an average daily insolation of 2 kWh/m2/day. Note that the results are heavily dependent on the efficiency assumptions used.
  
  Needless to say the array must not be shaded by objects such as trees or buildings.
  
  
  
  • Example
    Energy received per unit area = Insolation X Solar conversion efficiency.
    
    Thus:
    
    The area required for a given energy capture = Energy required ÷ ( Insolation at the desired location X Solar conversion efficiency)
    
    Using an efficient (expensive) photovoltaic array with a conversion efficiency of 15% the area of the array will be:
    
    10÷(2 X 0.15) = 33.3 m2
    
    Insolation data is usually provided for the energy falling on a flat surface. By tilting the array to an angle corresponding to the latitude of the location, an extra 10% of energy can be captured reducing the area required to 30 m2. See the diagram showing Array Orientation
    
    This advantage will be lost however if the array is to be mounted on a roof which is not optimally aligned towards the Sun.
    
    If the array is free standing on the ground, and not constrained to be used on a roof, a solar tracking system can be used to enable more of the Sun's energy to be captured. A 30% improvement is possible reducing the required array area to about 21 m2
    
    
    
    Note that the PV array output is DC electrical power.
    
    To provide AC power there would be further electrical losses of 10% to 20% in the voltage regulator, inverter and control circuits.
    
    
    
    • Grid-connected Systems
      Assuming 20 % electrical system losses, a fixed PV array with an area of around 36 m2, or a solar tracking PV array of 25 m2 would be required to provide 10 kWh of AC power per day.
      
      
      
    • Stand Alone Systems
      Off-grid systems are subject to the same performance parameters as grid-connected systems however since they also use battery storage they suffer from an extra efficiency loss of up to 30% due to the back emf of the battery.
      
      Unless an MPPT tracking system is used to reduce these losses the array would have to be 30% bigger to compensate. Thus to provide the same 10 kWh of AC power per day in a stand-alone system, the required PV array area would have to be 47 m2 for a fixed installation and 33 m2 for a solar tracking system.
      
      
      
    Electricity consumption in many households in Europe and the USA is 2 or 3 times more than 10 kWh per day, particularly for those willing to invest in solar PV electricity generation. (See Energy Demand Table). This implies that very large PV arrays with areas up to 150 m2 or more, probably larger than the available South facing roof surface, would be needed to satisfy their energy demands.
    
    
    
    All of the above is based on an average insolation of 2 kWh/m2/day, but in northern temperate zones the winter insolation is likely to be less than a quarter of the average for the location. See the table for Energy Availability and Energy Capture above. Thus the available energy will be only 2.5 kWh/day during the winter months or the systems would need to be four times bigger in order to supply the same 10 kWh/day of electrical energy in the winter.
    
    
    
  Standard Test Conditions of 1000 W/m2 insolation. It would generate 52.8 kWH (52.8 Units) of electricity per day if the Sun was directly overhead and shining constantly day and night. But the table above shows that the average insolation in the UK is only about 2.5 kWh/m2/day. This is equivalent to 2.5 hours of full Sun (see EHS above) per day, not 24 hours. Thus the actual electrical energy output from the PV system in the UK will be about 5.5 kWh per day or 2,000 kWh per year.
  
• Payback
  Buying 2,000 kWh of electrical energy from the local utility company would cost £200 ($300) with the curent costs of electricity at £0.10 ($0.15) per unit. Ignoring maintenance costs, this gives a payback period of sixty years.
  
  Fortunately, many governments provide generous grants to subsidise the installation and/or operation of solar power systems thus reducing the capital outlay and decreasing the investment payback time.
  
• Selling surplus energy back to the utility company
  The average UK household consumes about 5,000 kWh of electrical energy per year or around 14 units per day. The likelihood of a domestic installation as described above having regular surpluses is quite remote.
  
  Furthermore, feeding electrical energy back into the grid involves the obligatory installation of additional, costly metering and safety systems as well as synchronisation electronics so that this option is only economically justifiable for installations with relatively large surplusses.
  

Electricity Generation from Solar Energy, Technology and Economics

What Are the Different Methods of Solar Power Generation?

General Reference (not clearly pro or con)

Natural Resources Defense Council
National Renewable Energy Laboratory (NREL)
Massachusetts Executive Office of Energy and Environmental Affairs
The International Renewable Energy Agency (IREA) stated the following in its June 2012 working paper, "Renewable Energy Technologies Cost Analysis Series: Concentrating Solar Power," available at irena.org:
"Concentrating solar power (CSP) is a power generation technology that uses mirrors or lenses to concentrate the sun’s rays and, in most of today’s CSP systems, to heat a fluid and produce steam. The steam drives a turbine and generates power in the same way as conventional power plants…

CSP plants can be broken down into two groups… Line-focusing systems include parabolic trough and linear Fresnel plants and have single-axis tracking systems. Point-focusing systems include solar dish systems and solar tower plants and include two-axis tracking systems to concentrate the power of the sun…

The parabolic trough collectors (PTC) consist of solar collectors (mirrors), heat receivers and support structures. The parabolic-shaped mirrors are constructed by forming a sheet of reflective material into a parabolic shape that concentrates incoming sunlight onto a central receiver tube… A heat transfer fluid (HTF) is circulated through the absorber tubes to collect the solar energy and transfer it to the steam generator…

Solar tower technologies use a ground-based field of mirrors to focus direct solar irradiation onto a receiver mounted high on a central tower where the light is captured and converted into heat. The heat drives a thermo-dynamic cycle, in most cases a water-steam cycle, to generate electric power."

What Are the Different Methods of Solar Power Generation? - Alternative Energy - ProCon.org

 

[VelocuR]

Thanks to China engineers

 

[Donatello]

Wow! That is one excellent project. We have abundance of Solar radiation and cheap and large land area. Should use it to generate Wind and Solar to supplement the grid, along with electrification of towns/villages that are not feasible to be connected by grid.

 

[Mujahid Memon]

Is this a photovoltaic or Solar Thermal Plant ?? can anyone answer

 

[Faiez]

Is this a photovoltaic or Solar Thermal Plant ?? can anyone answer

it's clearly a PV.......

 

[Ammyy]

Congrats Pakistan for this achievement.

So when will they complete work of entire 1000 MW project?

 

[Danish saleem]

Congrats Pakistan for this achievement.

So when will they complete work of entire 1000 MW project?

Bro

The complition of 600 MW 1st Phase will be 30th December 2016.(In sha Allah).

 

[Muhammad Omar]

Congrats Pakistan for this achievement.

So when will they complete work of entire 1000 MW project?

100 MW completed 900 MW work will start after Chinese President come on Monday