Frequently Asked Questions (FAQS)
What is PV?
PV is an acronym which stands for 'photovoltaic', a way of producing electricity from light. More properly, the photovoltaic effect is an aspect of the photoelectric effect, and may be defined as the conversion of electromagnetic radiation to electrical voltage by a material.
The photovoltaic material that almost everybody has seen is the silvery amorphous silicon solar cells in solar powered calculators.
What is a PV module?
A photovoltaic module is typically a group of solar cells assembled in a commercial unit ready for installation in a system. It is the form in which most power systems are purchased. Usually the PV module has a specified power rating and guaranteed lifetime (commonly ~20 years).
What is the history of PV?
Highlights:
In 1839, Edmund Becquerel of the famous French physicist family, discovered the photovoltaic effect. The material used was copper oxide in an electrolyte.
In the 1860's, Willoughby Smith discovered the photoconductive properties of selenium.
In the 1870's, W.G. Adams and R.E. Day investigated the photovoltaic properties of selenium.
In 1874, Charles Fritts made the first solar cell from selenium and gold. The efficiency was less than 1%.
In 1887, H. Hertz discovered the photoelectric effect in metals.
In 1904, Albert Einstein published his monograph on the photoelectric effect. His theory utilized Max Planck's idea of quanta.
Notice that for almost a hundred years, from 1839 until the development of quantum theory in the 1920's and 1930's, there was no satisfactory scientific theory of solid state physics to explain the photovoltaic effect. It was an anomalous phenomenon, which some scientists considered a hoax.
In 1954, Gordon Pearson discovered the photovoltaic properties of silicon. Later Pearson with Charles Fuller and Darryl Chapin work to improve the efficiency of the silicon solar cell. The efficiency was 4% to 6%.
In the late 1950's, NASA determined that solar cells were an ideal energy source in space and serious funding of PV research began.
In the late 1970's, the OPEC inspired oil embargo startled the first world nations into funding many forms of alternative energy research, including PV.
In the late 1990's, with rising worries about the future energy supply, interest in photovoltaics again began to rise.
What is the photoelectric effect?
The photoelectric effect may be defined as changes in electrical characteristics of substances due to electromagnetic radiation, usually in the form of light. Radiation of a sufficiently high frequency impinging on some substances (usually metals, but not always) cause bound electrons to be released.
The photoelectric effect has two principle aspects - photoconductivity (change in conductivity due to light) and photovoltage (change in voltage due to light).
What is the photovoltaic effect?
The conversion of electromagnetic radiation (photons) to electrical voltage by a material.
What is the photoconductive effect ?
Photoconductivity may be defined as changes in conductivity (the inverse of resistivity) due to electromagnetic radiation (usually light). Conductivity is a measure of the ease with which electric current flows in a material.
It was the photoconductive properties of selenium which led to the discovery of its photovoltaic properties.
What materials show the photovoltaic effect?
In general the photovoltaic effect is demonstrated by semiconductors. The first solar cells were made with selenium and gold. Nowadays a wide variety of semiconductor materials are used, as well as a few exotics which may never escape the lab.
How do I figure out what size of system I need?
First there are questions of type to consider.
- Is the system going to be Standalone or Grid Connected?
- Are you going to use standard AC or will DC do?
- Are you using the system at night?
Presumably you will know this immediately.
Then there are several other basic pieces of information you need to know or find out.
- How much energy do you use on a day to day basis?
- How much sun do you get at your location?
To find out how much energy you use on a day to day basis, you can look at your grid utility power bills for the last year or two. An energy audit will enable you to track down where every watt goes.
To find out how much sunlight you get at your location, consult any one of the several available insolation databases.
When you know if you are using the system at night, and how much energy you use daily, the question of storage capacity can be dealt with.
The New Solar Electric Home by Joel Davidson has a good discussion of sizing a PV system.
The Solar Electric House by Strong and Scheller has a chapter about system types and a good discussion of energy audits.
Who makes PV modules?
As with cells, There are many manufacturers of PV modules. A look through a business index would be useful.
magazines , books , newsgroups , associations , the WWWeb , mailing lists , as well as other PV FAQs .
Your local librarian is your friend. ;-)
Other questions or comments?
Please contact us online or call us.
