Solar panels

Solar panels (a solar panel is an array of solar cells) were until recently almost exclusively used in spacebourne applications. Nowadays, rapid technological advances and a sharply risen public environmental awareness have propelled solar panels to the centre stage in humanity’s search for clean energy. The solar industry has exploded, with the photovoltaic industry reporting a combined global revenue of $37 billion over 2008. European countries have taken the lead in the installation of solar powers, with Spain and Germany accounting for almost 75% of the world’s newly installed solar capacity in 2008. In the United States, the country where solar power was invented, solar power capacity grew by 342 Megawatts, which accounts for approximately 6% of the world total growth. Thanks to rapid price drops combined with generous government incentives, the worldwide future for solar panels is starting to look brighter and brighter.

Solar panels in the United States

In 2006, solar power was reponsible for only 0.1% of total electricity generation in the United States. In recent years, solar power has however been growing rapidly, with the U.S. total solar capacity growing by 17% in 2008. The eight-year extension of the 30% solar tax credit has further brightened the future. Due this regulation, it is expected that by the end of 2016, a total of 28 GW of solar capacity will be added. As a result of this and due to the expected enactment of more stimulus bills, solar power is expected be the most affordable form of energy to US consumers by 2016.

The profitability of solar panels depends strongly on local climate, e.g. a solar panel in southern California will likely produce more electricity than its ‘brother’ in Vermont. The image below will give you a rough estimate of the expected solar radiation per square meter of solar panel per day. You may click the image for a large, more detailed version.

PV solar radiation per square meter of solar panel per day

As expected, consumers in the northern states will have a harder time to break even on their initial investment, although government incentives in these states might make such easier. For example, a recent program allows less wealthy Connecticut homeowners to take on low-interest loans, effectively letting the state absorb the upfront cost of the panels. The relatively high energy price in Connecticut further works in favor of solar power, since it narrows the cost offset between solar and grid power. The ability to buy solar power at a price at or below the price of grid power is called grid parity. Today, only sunny states like Hawaii have achieved grid parity (note: also due to high electricity prices!). It is however expected that by 2015, most of the United States will have achieved solar grid parity.

Types of solar panels

There are three main types of solar panels:

Other types exist (gallium-arsenide, CIGS, etc.), but these are generally still way too expensive for the consumer market.

Derating your panels; what affects your system?

Solar panels are often sold listing their capacity in watt-peak. A solar panels power in watt-peak represents its peak output under standardized test conditions (25&Deg;C temperature, 1.5 airmass, 1 kW/m2 intensity). In practice, such conditions are almost never reached, since many factors influence the performance of a solar panel. The following list is a sampling of these factors. See the article on solar cell efficiency for a more in-depth discussion on factors affecting slar panel efficiency:

The process of quantifying the effect of these degrading factors is called derating. For modern solar panels, a derating factor of 0.75 to 0.8 is commonly applied. Thus, a 1kWp solar panel system has an effective power of 750 to 800 watts. When calculating the profitability of solar panels, it is important to make sure you properly derate your solar panels.

How it’s made: solar panels

The video below is a short documentary outlining the processes involved in manufacturing a solar panel.