Solar Roof Tiles – Bringing Photovoltaic Technology into Roof Shingles
by Jenny Griffin
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 may be placed 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.
However, the recent introduction of photovoltaic roof tiles offers an ingenious alternative to bulky photovoltaic panels for harnessing energy from the sun.
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. 
How Photovoltaic Shingles Work
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. 
Installing Solar Roof Tiles
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.
Types of Photovoltaic Roof Shingles
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.