Humans have been utilizing renewable energy sources longer than most people realize. As early as the 7th century BC, people were using magnifying glasses to intensifying the rays of the sun to make fires.
In modern times, solar energy is harnessed on a much larger scale. There is an extensive history behind the technological advances that have brought us to the solar cells we use today. Although standards for the solar wire used in these applications are relatively new, they have already had quite a progression of their own. Before reaching today's solar cable and solar cable standards, humans needed to work up to modern solar technology — the technology needed to harness electrical power via the sun’s rays.
A Brief History
In 1839, French scientist Edmond Becquerel discovered the photovoltaic effect: the creation of voltage or electric current in a material upon exposure to light. For the next century, scientists experimented with the concept and photosensitive materials like selenium. In 1908, William J. Bailey of the Carnegie Steel Company invented a solar collector with copper coils and an insulated box, which became a blueprint for the modern solar cell.
By 1950, three engineers at Bell Telephone Laboratories created the first solar cell powerful enough to convert energy from the sun to run standard electrical. Since then, scientists have continued to work to improve the conversion rate, equipping us to power special cars, aircraft, and even entire buildings with the use of modern solar arrays.
The Different Solar Power Cables
For a long time, THHN wire was the solar power cable used in these arrays. Thermoplastic High Heat-resistant Nylon-coated (THHN) wire is a general-purpose building wire. It is used in a wide range of industries and applications, and its heat resistance properties made it more suitable for solar applications than other types of wire and cable. Historically, UF, SE, and USE wire were also used in various components and covered in sections of the National Electrical Code pertaining to photovoltaic systems. As of 2008, the NEC only lists PV Wire and USE-2 Solar Wire (commonly dual-rated as RHH/RHW-2 wire) as acceptable options. They are safer, sturdier, and more efficient than their predecessors.
PV Wire meets the current UL standard, UL 4703. The photovoltaic wire is rated to 90°C in wet conditions and 150°C in dry conditions, and to 600, 1000, or 2000 volts. It is known for its use as an underground service entrance cable and can be used in either grounded or ungrounded arrays. It is often used in exposed applications and has thick insulation and jacketing, better sunlight resistance, flame resistance, and flexibility at low temperatures.
Use-2 cable is regulated by the UL 854 standard. According to UL experts, it is popularly chosen for underground applications, although it is also appropriate for exposed use according to Sec. 690.31 (B) of the NEC. USE-2 wire is rated to 90°C in wet and dry conditions, is rated to 600 volts, and is more crush and impact resistant than PV wire.
Solar Power Today
Although USE-2 and PV wires have been developed specifically for modern solar power cable applications, other wire types used in the past can still be useful in the solar power industry. Wires like THHN can still be used in certain PV functions where it is safe to do so. However, it should never be used to replace PV or USE-2 wire where they are specified, as it does not include all of the specialized features incorporated into PV and USE-2 wires, which could lead to failures.
The history of solar power and solar power cable is rich, despite the relatively short time cabling standards have had to develop. As we continue to refine solar energy processes and the materials we use in the building of arrays, it is certain that our standards will continue to evolve. To learn more about the current uses of popular solar cables, watch our PV Wire vs. USE-2 Wire video.