Solar energy is changing the world, but the transition to photovoltaics (PV) will take time. As reported back in September 2018 in Electronic Design, fossil fuels and nuclear power remain the dominant energy sources in the world today, while large-scale renewable energy installations are growing. Coal continues to decline as a viable energy source of the future, and nuclear power has more or less peaked, depending on the age and location of the power plant. Among renewable energy alternatives, including wind and hydropower, PV production is steadily improving in terms of energy conversion efficiency and market share.
Novel battery technologies, such as organic (carbon-based) and inorganic perovskite, are steadily pushing towards maximum theoretical PV efficiency. Series cells, which can simultaneously utilize silicon and perovskite technologies to independently capture two different regions of the solar spectrum, continue to improve efficiency.
A chart from the National Renewable Energy Laboratory (NREL) shows that PV has been under observers' attention for decades (Figure 1). It demonstrates continuous improvements in efficiency, showing both incremental improvements and significant leaps brought about by new methods.
Figure 1. Photovoltaic cell efficiency as of 2020.
PV cell efficiency is the percentage of power output (kW) per cell area (square meters) under standard lighting conditions, taking into account several other factors such as ambient temperature and the spectral content of the lighting modeled under natural daylight.
Over the past decade, we have witnessed the development of large, powerful solar farms in production worldwide. These units, along with thousands of smaller units in microgrid arrays the size of homes, businesses, or campuses, have successfully supplied real electricity. During peak solar hours, when power exceeds local consumption demand, they can feed PV electricity back into the conventional grid.
Connector requirements
As with any evolving technology, practical problems will continue to be solved, and solutions will continue to be refined. The design goals for photovoltaic panel mounting connectors must include:
• It can quickly connect the various panels together with minimal work time and effort.
• Keyed paired connectors offer the convenience of maintaining polarity.
• Once the forward latch is installed, it will prevent accidental disconnection.
• Minimal or no specialized tools.
• It can accommodate wires of different sizes.
• Safety certifications (UL, IEC).
Materials must comply with global substance restrictions such as EU RoHS and REACH.
• UV resistant and waterproof (IP67).
• Low contact resistance minimizes losses.
Here we show examples of how to implement these design standards and make them available to a growing market.
First connection
Establishing a reliable connection between panels is the first step. Over the past decade or so, different manufacturers have offered several options. Historically, crimp-type connectors (such as PV4) have primarily been used for panel interconnection. More recently, the PV4 series has been upgraded to the PV4-S, whose male and female connectors are rated for 1500 V according to UL6703 and meet the standard IP68 waterproof standard (1 m of water for 24 hours).
To reduce system efficiency, these connectors feature low contact resistance (0.35mΩ). UL's rated current depends on the wire size, ranging from 15 A for 14 AWG (2.5 m²), to 20 A for 12 AWG (4.0 m²), and 30 A for 10 AWG (6.0 m²).
Figure 2 shows the pin and socket pairs. Standard products include complete kits, contacts only, and housing only, in quantities ranging from 100 to 2000 pieces. Specifically, the 2270024-1 pin connector and the 2270025-1 socket connector comply with RoHS and REACH requirements and do not contain brominated or chlorinated flame retardants or PVC.
Figure 2. SOLARLOK PV4-S connector.
Wiring using minimal tools
The SOLARLOK 2.0 DC Plug connector system, developed by TE Connectivity, features Insulation Displacement Connection (IDC) technology (Figure 3). Both the male and female ends integrate the SOLARLOK 1,500-V PV4-S interface for versatility and compatibility with solar PV connectors equipped with standard solar interfaces.
Figure 3. SOLARLOK 2.0 connector: Open and unpaired (a), Closed and paired (b).
Internally, the IDC method uses four rotating blades, providing both cutting edges and contact surfaces. The blade shape is designed to cut double-insulated cables and provide strong conductor compression capabilities without cutting the stranded wires. The anticipated benefit is low power consumption achieved through low contact resistance.
IDC connector assemblies mean no wire stripping is required. This is a significant advantage when installing multiple panels, potentially reducing overall cost and assembly time. The cable, cut to a specific length, is inserted, and the two halves of the connector close. No cable stripping or custom tools are needed.
Outdoor connections are always a reliability concern. The SOLARLOK 2.0 DC plug connector features a unique gel filling. The supplied Powergel is a two-part mixture used at a 1:1 ratio; it cures within two hours at room temperature. Once applied and the IDC connector is closed, the gel seal becomes tacky to adhere to the surface and provides a seal over a wide temperature range of −40 to +90°C. The gel is compatible with standard cable sheath materials and is independent of cable sheath size.
SOLARLOK 2.0 connectors also comply with RoHS and REACH requirements and have low halogen content. They are CE marked and meet IEC 62852 and UL 6703 requirements.
By connecting the panels together, their outputs can be combined to feed a load.
For this, a commercially available junction box can be used. Next, a charge controller is needed to power the battery pack. From there, the inverter converts the battery's DC voltage to the AC voltage used in the local power grid, which is 120V AC in the United States.
