Installed capacity, sometimes termed peak installed capacity or rated capacity, describes the maximum capacity that a system is designed to run at.
If for example, a solar farm has an installed capacity of 24 megawatts, the system will have the ability - the components and hardware - to produce a maximum of 24 megawatts with optimal sun exposure.
If a system with an installed capacity of 24 megawatts has optimal sun exposure for one hour, it will produce 24 megawatt hours of electricity in that time.
Installed capacity relates mainly to calculating the cost of solar panels. Looking at how many watt hours an installation will generate produce is used for assessing how many solar panels are required - comparing solar energy production to existing electricity usage.
Similarly, wind turbines use installed capacity to describe how much electricity may be generated by a turbine in optimal wind conditions - describing how many watts of electricity the turbine hardware can possbily produce.
As of 2012, the Montalto di Castro solar park was the largest photovoltaic power station in Italy, producing more than 40,000 MWh of electricity per year... Let's explore!
The solar park was developed and is operated by SunRay Renewable Energy, and its modules produced by SunPower.
The solar park was completed in the winter of 2010, then sold to a consortium of investors.
Montalto di Castro uses sun-tracking technology - changing the angle of the solar panels with the sun for optimal radiation exposure.
The park contains 80,000 modules, with a peak installed capacity of 24 megawatts.
It's located located around 100km from Rome, in the Lazio Region of Italy.
The construction of the Montalto di Castro solar park took place in 4 stages. It took eight months and approximately 250 workers.
According to the SunPower website, the solar park avoids 22,000 tons of CO2 annually and produces enough solar generated electricity to power 13,000 homes.
SunPower. Largest Solar Power Plant in Italy Completed. Retrieved from http://us.sunpowercorp.com/about/newsroom/press-releases/?relID=23297
Wikipedia. Solar Power in Italy. Retrieved from http://en.wikipedia.org/wiki/Solar_power_in_Italy
SMA. Solar Park Montalto di Castro. Retrieved from http://www.sma.de/en/products/references/solar-inverters/isolator/solar-park-montalto-di-castro.html
Solar roof tiles are an ingenious alternative to bulky photovoltaic solar panels... Let's explore what they are and how they work!
Solar energy is typically harnessed through the use of photovoltaic solar panels made of crystalline silicon, which are attached to a roof or other structure.
These panels are positioned facing the sun (south in the northern hemisphere, north in the southern hemisphere) or on a solar tracking system that follows the sun.
Because silicon solar panels are bulky, they can be unsightly, and are also prone to damage in areas that experience strong winds.
Photovoltaic roof tiles are either made from regular crystalline silicone-based materials, or from thin-film solar cells, manufactured from layers of very thin semiconductor materials, such as amorphous silicon, or from other materials such as cadmium telluride, or copper indium gallium diselenide (CIGS).
The latter are thin, flexible, and durable, and ideally suited for use as a roof tile substitute that offers a protective roof cover, while drawing energy from the sun to provide your home with power. 
Photovoltaic shingles work on the same principal as regular crystalline solar panels. Photovoltaic literally means 'light energy'.
The semiconductor photovoltaic cells absorb energy radiated from sunlight, which is then transformed from light (photo) energy into electric (voltaic) current. When energy from sunlight strikes the semiconductor material in the photovoltaic cells, a photon of light energy is absorbed, releasing an electron, which produces an electric current.
The current produced is direct current (DC), but as homes and business run on alternating current (AC), this needs to be converted by an inverter for domestic use. Once the current has been converted to alternating current, it can be connected to the main power board of a building to provide power locally, or it can even be connected to the electricity grid to provide power further afield. 
A regular solar panel typically consists of 40 photovoltaic cells that are installed in arrays of between 10-20 panels in a typical home system.
The panels can be installed onto an existing roof structure, or placed anywhere on the property to take optimal advantage of available sunlight. Photovoltaic roof tiles on the other hand, form an integral part of the roof structure, replacing regular roof tiles to serve a dual purpose of both repelling water, snow, hail, and wind, while absorbing the energy of the sun as a source of power.
While replacing existing roof tiles with photovoltaic tiles may be rather costly, when constructing a new home this may be quite cost effective in the long term, as it saves on the cost of roof tiles, and offers dramatic savings on energy costs.
Photovoltaic roof shingles are available in silicon or thin-film solar materials.
With energy efficiencies as high as 20.3% attained by silicon photovoltaic cells , silicon roof tiles, like silicon solar panels, are more energy efficient than thin-film solar tiles, but they are expensive, and take a long time to install.
Thin-film solar tiles are a recent innovation that are more affordable than silicon roof tiles, as they are cheaper to produce.
They are easy to install, cutting the installation time down by half – to around ten hours, which offers a further cost saving in terms of time and labor.
With ongoing research and development, thin-film photovoltaic roof tiles are catching up in terms of energy efficiency.
A new record of 19.9% efficiency has been attained for CIGS thin-film solar cells by researchers at the U.S. Department of Energy’s National Renewable Energy Laboratory .
This improved energy efficiency, together with the affordability and ease of installation, may make thin-film photovoltaic roof tiles the photovoltaic option of choice for solar power installations in the very near future.
 National Renewable Energy Laboratory. Learning About Renewable Energy: Solar Photovoltaic Technology.
 ExploringGreenTechnology.com: How Solar Panels Works.
 National Renewable Energy Laboratory. Record Makes Thin-Film Solar Cell Competitive with Silicon Efficiency.
The energy game has changed. And this change has given birth to a number of major, fast growing, and innovative solar energy companies.
These companies will play a big role in bringing clean power, improving access for developing nations, and driving the energy future.
Below we look at some of the top solar energy companies today.
Suntech was one of China’s first solar energy companies and is now the world’s largest silicon solar panel producer.
The company has grown quickly since its establishment in September 2001 and now has a presence in 80 countries worldwide and a dynamic research and development team spread across five countries.
One of the company’s key milestones was winning a contract to supply the solar panels for the revolutionary Bird’s Nest 2008 Olympics Arena in Beijing - a 130 kW solar installation.
The business has also successfully penetrated the western market by establishing its first U.S. factory in Arizona on January 2010.
Suntech’s technology now ranks among the best in the world after attaining a photovoltaic conversion efficiency of 19% for mono crystalline solar cells and 17% for polycrystalline photovoltaic cells in 2009 and attained the 2 GW (gigawatt) mark in 2011.
Since its inception in 1999, First Solar has grown such that now powers 2,864,816 homes and displaced nearly 4 million Metric Tons of CO2 (as of April 2012) .
Through continuous research and development, the company has won several awards for ground breaking work in the solar energy industry.
They’ve balanced efficiency and cost to develop the lowest cost solar panels per watt - with the price of less than 1$/watt.
Although First Solar uses cadmium tellurium (Cd-Te) panels, which are less efficient than the crystalline panels, they have been able to consistently set world records for efficiency of the Cd-Te panels, first at 13.4% and now at 14.4% .
The First Solar power systems are particularly attractive because they have the fastest energy payback time when compared to all other photovoltaic PV systems in the market.
Sharp Solar is a subsidiary business of the Japanese electronics giant, Sharp.
The company has been developing solar power solutions for more than 50 years and has secured a large consumer base and is well trusted in the industry.
Sharp Solar was the first of all solar energy companies to achieve 2 GW of solar cells.
They have repeatedly broken world records for solar cell conversion efficiency achieving 14.4% for polycrystalline photovoltaic module in 2008 and 35.8% for triple junction compound solar cells.
The company’s development has been greatly supported by the fast growth of the local Japanese solar market.
Cheap production costs are a common characteristic of most Chinese manufacturing companies.
Yingli Green Energy Company has taken advantage of these cheaper labor and material costs to focus on innovation in order to maintain a competitive edge.
The company develops products across the entire photovoltaic value chain.
These products include poly silicon material, ingots, wafers, solar cells and photovoltaic modules. In this way, the company has been able to serve a wide range of clients and offer a variety of solutions to each.
Significant growth in the Chinese solar energy Industry has caused the prices of solar panels to drop worldwide and the latest reviews have it that seven out of the ten top solar energy companies in the world are Chinese .
Recent trends show that whereas Chinese solar companies are growing exponentially, some major American companies have exhibited the opposite result.
In the USA, two major solar companies which in 2009 had been among the top in the world, Solyndra in California and Evergreen Solar in Massachusetts  , filed for bankruptcy in 2011 .
Solyndra was a champion of the innovative Copper Indium Gallium Selenium (CIGS) solar panels, with a focus on rooftop modules. Solyndra was able to attract investors and governmental support, with sales contracts reportedly worth over $1 billion .
With the drastic drop in costs of solar panels over the last 3 years, Solyndra's business model became unfeasible and the company could no longer compete, despite further government support through the US Energy Department's loan guarantee program .
 Green World Investor – List of World’s Major Solar Energy Companies (February 2011): http://www.greenworldinvestor.com/2011/02/18/list-of-worlds-major-solar-energy-companies/
 First Solar – About: http://www.firstsolar.com/Corporate/About
 Sharp – Sharp Solar: http://www.sharp-solar.com/en/
 Suntech – About: http://am.suntech-power.com/about.html
 Yingli Solar – About Us: http://www.yinglisolar.com/us/about-us/
 Financial Times – China’s Rush Into Renewables: The Way The World Turns (28 November 2011): http://www.ft.com/intl/cms/s/0/0502a28a-15c9-11e1-a691-00144feabdc0.html#axzz1nmZeqJQF
 Green Tech Media – Top Ten Solar (April 2009): http://www.greentechmedia.com/articles/read/top-ten-solar-companies-3794/N4/
 Financial Times – Energy; Sun Sets on Solar Power Group Solyndra: http://www.ft.com/intl/cms/s/0/0ee052e8-d3f7-11e0-b7eb-00144feab49a.html#axzz1p7ZX6YEL
 Bloomberg – Clean-Energy Advocates Urge Overhaul as Aid Shrinks 75% by 2014 (April 2012): http://www.bloomberg.com/news/2012-04-18/clean-energy-advocates-urge-overhaul-as-aid-shrinks-75-by-2014.html
Hydroelectric energy is the world’s most used renewable power source today.
This article looks at how it works, some of the advantages of hydroelectric energy, and what history has told us about some of the disadvantages.
About 20% of the world’s electricity is currently generated from hydropower with China, Canada and Brazil leading in installed capacity respectively .
Some countries, like Paraguay, Zambia and Norway, generate between 98 –100% of their electricity from hydroelectric power .
Hydroelectric power production has a rather simple working principle. A modern hydroelectric power system consists of three parts.
Basically, water under pressure is directed to turn a turbine which drives a generator to produce electricity.
The amount of water flowing through the system as well as how far the water drops determines the amount of electricity produced .
The main forces involved are gravity and air pressure; the effects of seasons on weather patterns also influences hydropower generation e.g. the freezing and thawing of ice due to winter.
The capacity and styel of dams and water-channels determine the amount of power that can be generated from a hydroelectric power system.
Ancient societies used the running force of a river to turn water wheels that turned grain grinders and pumped water.
People historically put hydroelectric power turbines near naturally occurring waterfalls.
In this way, the first hydroelectric plant was set up and powered by the Niagara Falls in 1879.
Later, in 1882, power operators set a plant on the Fox River in U.S.A to power two paper mills and a house.
Technological advances and increase in electricity demand sparked the construction of man-made waterfalls and dams throughout the 1900’s but the use of hydroelectric power quickly took a back seat to fossil fuels in the 1940’s.
Nevertheless, the extreme dominance of fossil fuels was short lived because interest in electricity generation from hydropower was revived in the 1970’s when fossil fuel prices skyrocketed.
Hydroelectric power is very popular for a number of various reasons.
Hydropower’s lifespan is one major advantage as electricity can be generated consistently for decades without using up any raw materials.
Hydropower’s load factor of between 40 – 60% is very attractive for electricity generation especially when compared to the 15 – 40% obtained from Wind and Solar Energy.
Often, lakes form behind the dam which can also be used for irrigation, leisure, tourism, water sports.
Storing water behind dams has a unique advantage of positioning hydropower as support of Solar and Wind Energy systems which are naturally intermittent. Hydropower doesn’t need to be used at full capacity all the time, but can be ramped up at times when other methods aren’t working or when demand is high.
One of the most relevant characteristics of hydroelectric power today is that there are no carbon emissions when the systems are run to generate electricity. Hydroelectric systems do have “embodied energy” consumption, in terms of the energy-use and emissions that come during construction, but they don’t produce a quantity of toxic by-product for every hour of power produced.
There are however, certain serious disadvantages that have limited the full exploitation of the world’s hydropower potential.
The main disadvantages of hydroelectric energy is that they have a big impact on the local environment and eco systems. Furthermore, some dams have experienced major, fatal, disasters.
The dams create large reservoirs or lakes in areas where they would not otherwise occur. This causes destruction of the natural environment and endangerment of resident species often families and whole communities are forced to relocate permanently.
The change in river flow can cause destructive flooding and effects fish and other marine life behaviour.
There have also been cases where dams have collapsed under the weight of the water and lives lost in the ensuing floods, such as the Situ Gintung dam in Indonesia and Shakidor dam in Pakistan .
One of the major determining factors of hydroelectric power stations is the high investment cost. In addition to these high investment costs, the hydropower schemes have a long gestation period of around 5 – 10 years, making them impractical for private investors.
Mainly for scale and cost reasons, hydroelectric projects are generally only undertaken by governments or large power companies – rather than private parties.
For a more indepth discussion, visit our article on the advantages and disadvantages of hydroelectric power.
China’s Three Gorges Dam is the world’s largest dam in terms of installed capacity . Built on the Yangtze River, the dam rises to 185 meters and is 2.3 Kilometres wide and has an installed capacity of 22,500 MW.
However, the Itaipu Dam on the border between Brazil and Paraguay is known to be the largest dam in the world in terms of annual electricity generating capacity .
With an installed capacity of 14,000 MW, Itaipu Dam was able to generate 94.7 TWh and 91.6 TWh (Terra Watt Hours) in the year 2008 and 2009 respectively compared to the 80.8 TWh and 79.4 TWh produced at China’s Three Gorges Dam in the same corresponding years .
 National Geographic – Going With The Flow: http://environment.nationalgeographic.com/environment/global-warming/hydropower-profile/
 Energy Resources – Hydroelectric Power: http://www.darvill.clara.net/altenerg/hydro.htm
 Alternative Energy – Hydroelectric Power: http://www.altenergy.org/renewables/hydroelectric.html
 Technology Student – Advantages and Disadvantages of Hydropower: http://www.technologystudent.com/energy1/hydr2.htm
 Green World Investor – Hydroelectric Energy Advantages and Disadvantages: http://www.greenworldinvestor.com/2011/04/04/hydroelectric-energy-advantages-and-disadvantages/
 Nation Master – Energy Statistics: http://www.nationmaster.com/graph/ene_hyd_pow_pro_of_tot-energy-hydroelectric-power-production-total
 Wikipedia – Itaipu Dam: http://en.wikipedia.org/wiki/Itaipu_Dam
 Department for Environment: Food and Rural Affairs (UK). Delivering benefits through evidence: Lessons from historical dam incidents. Retrieved from http://publications.environment-agency.gov.uk/PDF/SCHO0811BUBA-E-E.pdf
 Associated Press. 54 killed in Pakastan dam burst. Retrieved from http://www.guardian.co.uk/world/2005/feb/11/pakistan
 The Jakarta Post. 22 still missing from dam Situ Gintung dam collapse. Retrieved from http://www.thejakartapost.com/news/2009/03/27/22-still-missing-dam-situ-gintung-dam-collapse.html
 International Rivers. Three Gorges Dam. http://www.internationalrivers.org/china/three-gorges-dam
 USGS. Itaipu Dam: The world’s largest hydroelectric plant. http://ga.water.usgs.gov/edu/hybiggest.html