The basic definition to describe photovoltaic cells would be "devices that convert sunlight into electricity using the photoelectric effect". Photovoltaic cells are also referred to as "solar cells", and they are not brand new technology as some people think they are. In fact, first photovoltaic cell was constructed by Charles Fritts in the 1880s so we are definitely not talking about something that is brand new technology. The first significant application where solar cells were used was as a back-up power source to the Vanguard I satellite more than 50 years ago, back in 1958.
Photovoltaic cells are made of semiconducting materials similar to those used in computer chips. There are many different types of photovoltaic cells, and it is difficult to tell which technology will prevail at the end, among those that are currently mostly used are thin film, monocrystalline silicon, polycrystalline silicon, and amorphous cells.
Concentrating photovoltaics also belongs to new methods of electricity generation from the sun. Photovoltaic cells that are designed to operate with concentrated sunlight are built into concentrating collectors that use a lens to focus the sunlight onto the cells. This is not the ideal solution because the lenses must be pointed at the sun so the efficient use of concentrating collectors is really limited to the sunniest locations. But on the other hand concentrating photovoltaics have an edge when it comes to costs because they use very little expensive semiconducting materials.
Solar cells despite obvious technological development in the last few decades still haven't reached the levels of high efficiency. An average photovoltaic cell has an efficiency of 15%, which means that less than one-sixth of the sunlight striking the cell actually generates electricity. The low efficiency of commercial solar cells is the main reason why solar panels are still connected with high costs because in order to achieve the desired efficiency you need larger arrays.
Therefore, if solar energy wants to become competitive with fossil fuels it will have to produce inexpensive and highly efficient photovoltaic cells. Some of the latest research work was really positive, and this should give us hope that science is ready to come up with some breakthrough discovery that would make solar cells cheaper and much more efficient.
Building-integrated photovoltaics (BIPV) are by definition photovoltaic materials that are used to replace conventional building materials. What this means is that photovoltaic materials actually become an integral part of the building, and in most cases they are planned together with the object as its integral part though they can be also built later on.
The global interest in the building integration of photovoltaics is constantly growing, and in the last couple of years BIPV are being increasingly incorporated into the construction of new buildings as a principal or ancillary source of electrical power. Some energy experts even argue that BIPV is currently the fastest growing segment of the photovoltaic industry.
A Building Integrated Photovoltaics (BIPV) system's main concept consists of integrating photovoltaics modules into the building envelope such as the roof, skylights, or facades. This means that BIPV not only serve as power generator but also as building envelope material, which in the end results in both savings in materials as well as reduced electricity costs.
A complete BIPV system consists of photovoltaic modules, a charge controller, a power storage system, inverter and other power conversion equipment, backup power supply, and different supporting equipment.
BIPV systems can either be interfaced with the already available utility grid or they may be designed as stand-alone, off-grid systems. BIPV may to many people sound as brand new technology but photovoltaic applications for buildings have been used for more than three decades, and began appearing in the 1970s, though it took the 1990s for BIPV technology to become commercially available.
It also needs to be said that BIPV systems require very high level of expertise in architecture as well as civil and photovoltaic engineering. These projects are costly and only technical experience and knowledge can guarantee the best possible results because poorly designed BIPV systems need redesign and repair, which dramatically increases the total costs.
Some countries (like France) even offer additional incentives for building-integrated photovoltaics in addition to the existing feed-in tariffs for stand-alone solar systems. In China, for instance, qualified BIPV projects are entitled to receive a subsidy equal to 50% of the total investment of project.