Solar Power World

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by Uli Schoettle, Molex Incorporated

While solar panel manufacturing continues along a trajectory of decreasing costs and industry reaches grid parity – i.e. aligns with conventional energy prices – new quality and performance metrics are emerging as OEMs and system integrators shift focus to differentiate their products for an increasingly more sophisticated customer.

In the early days of the solar powered energy industry, the key focus for OEMs was to produce a photovoltaic (PV) panel with the highest energy conversion rate. As these solar crystalline-based technologies reached maturity, the industry split – some PV panel manufacturers continued with the solar technology and looked into ways to increase manufacturing efficiency and reduce associated productions costs; others diversified by looking into developing new solar technologies, such as thin-film, that promised significantly cheaper manufacturing costs but initially yielded lower efficiency levels.

Solar Junction Box Developments

Regardless of the solar technology being used and the installation type, whether it is residential or commercial rooftops, utilities, public buildings or solar farms, the solar junction box is among the most critical components of every solar panel and, obviously, a key concern for panel manufacturers. Junction boxes provide the electrical interface between the conductor ribbons on the panel and the DC I/O cables; they must comply with the relevant IEC, VDE and UL/CSA standards, and must undergo separate investigations to evaluate such factors as flammability, resistance to ignition, thermal endurance, and electrical properties of critical components. Other key measurements include assuring minimal current leakage and resistance to temperature, humidity, water spray and impact testing.

Next-generation junction boxes are a two-point design with a current rating comparable to the much larger products of the past, with integrated safety mechanisms. Bypass diodes, for example, are used to protect the PV panel from reverse current and overheating of the cells during hours of darkness, partial shading, or when the panel is covered by leaves or other debris.  So, while they must be sealed to protect against the ingress of water and other elements to avoid the risk of arcing, they must also be resistant to overheating due to temperature build-up from cycling of the bypass diodes.

Metallic enclosure materials have the benefit of increasing heat dissipation properties in solar junction boxes, but they can add more expense to the product and must be electrically isolated to protect the electronics from accidental exposure to high voltage. Non-metallic housing materials have become de rigueur; in particular moulded PPO (Polyphenylene Oxide), which is a field-proven light-weight plastic material that is easy to manufacture, whilst being resistant to variations in temperature and UV-resilient.

In addition to ease of manufacture and assembly of the two-part, plastic junction boxes, ease of field repair or replacement in the event of damage or wear are also key factors for consideration – to address this the bypass diodes and DC cable connections are housed in a removable top cover. As security in the field is another important factor – the top cover and base are secured together with a locking mechanism to prevent accidental exposure of high-voltage contacts.  Internal locking mechanisms protected by latch guards prevent accidental or unauthorised decoupling of connectors. Touch-proof safety features also protect against electrical current even when connectors are unmated.

Spring terminals are used to connect the base of the junction box directly to the PV ribbon conductors, without the need for retention clamps or clips.  Molex-patented Solder Charge™ technology can also be used to facilitate high-speed assembly and eliminate the need for hand-soldering of the ribbon, significantly cutting assembly costs, as well as reducing user error and process variations that may cause future problems.

The latest addition to Molex’s junction box line-up is the SolarSpec Smart Junction Box, which makes it easy for panel manufacturers to provide their products with module-embedded safety and monitoring functions. This system is based on the original two-part design, which comprises a base attached directly to the solar PV panel and a removable cover assembly. It is within these interchangeable covers that Molex has embedded a SolarEdge chipset that provides varying levels of ‘smart’ electronic integration. Functionalities include system safety, shut-off and arc detection, security monitoring and theft protection, performance tracking on output levels and panel efficiencies, remote diagnostics and power optimisation.

DC Connector Enhancements

Interconnection quality is critical to ensure PV module performance and reliability – poor electrical connections can contribute to a fire in the junction box or other related problems that may not even surface until several years after being put into service. Investments in research and development have yielded a comprehensive range of DC interconnect products that adhere to stringent industry standards.

When converting direct current (DC) from the PV array into alternating current (AC), solar inverters are often subjected to extreme environmental conditions, including moisture ingress, corrosion, connector reliability, loss of grounding, and bypass diode failure. Here rugged, crimp terminal pin (male) and socket (female) DC Connectors have been designed for direct connection to solar junction boxes, field installations and photovoltaic (PV) grid wiring and, more recently, panel-mount DC connectors for solar inverters.

SolarSpec DC Connectors feature a simple snap-lock mating, which allows for quick and easy field assembly with an audible click to ensure successful mating.  The innovative touch-proof safety design ensures that installers and maintenance engineers are protected from electrical current even during mating and decoupling operations. In addition, moulded ribs on the housing surface allow for secure gripping, especially while wearing work gloves.

The DC connectors are IP67-sealed to protect against the ingress of dust and water, and the housing body is resistant to UV and ozone damage. They remain fully-sealed when mated and have an enhanced strain relief design to avoid cable overstressing and ensure the integrity of the cable sealing. Because the high electrical current involved at these two points, the solar industry stipulates compliance to NEC 2008 (690.33) and NFPA 70 standards which require a locking mechanism to prevent accidental or unauthorised decoupling of the DC connector during service in the field. In the SolarSpec DC Connector design, this locking mechanism is protected by latch guards and therefore no additional protection sleeve is needed.

As there is a growing trend for a higher number of panels with increased efficiencies in a solar grid array, Molex is also developing DC connector solutions for higher voltage and amperage applications.

Ancillary Product Innovations

Standard products, that are tried and tested in harsh industrial environments, but not developed specifically for the solar industry, are already used in solar applications; these include antenna solutions for wireless communication and user interface-membrane/capacitive switches.

Looking to the Future

The biggest challenge currently facing the solar energy industry is developing systems that can produce energy at a scale and cost that is comparable to traditional energy sources.  To help reach that goal, the solar industry is leveraging interconnect products that have track records in other industries for offering proven durability and performance.  They are finding numerous high quality connectivity solutions available for solar arrays, trackers, concentrators, and solar inverters.  To reach critical mass and realize economies of scale, leaders in the photovoltaic solar industry must continue and strengthen efforts to improve system durability and manufacturing efficiency – in order to drive down the cost per watt of solar energy produced.  And, as the journey progresses, electronics industry leaders will be there to help.

Uli Schoettle is an industry marketing manager at Molex Incorporated, a global leader in the design and manufacture of electronic, electrical and fiber optic interconnect systems.  For more information, visit Molex at www.molex.com.