Traditionally, solar installation designers and engineers have had only two main options for converting DC to AC power: string inverters or microinverters. Both present significantly different benefits and disadvantages for installers, with installation expenses varying up to 20% depending on the inverter selection. Both solutions have pros and cons in regard to convenience, performance and maintenance. But a new third kind of inverter aims to combine the simplicity of installation offered by a string inverter with the intelligence of a microinverter, while reducing installation, cabling and activation costs by 75%.
Micro Parallel Solar iInverter
This option is known as a micro-parallel inverter. This new emerging class of inverters is aimed at solving the biggest problem hindering solar energy production: its cost. With the largest expense associated in PV applications being installation and maintenance by a factor of 2 to 3 over the panels, framing and other associated expenses, a new solution is needed to bring down costs for residential and small/mid-sized commercial projects.
The micro parallel inverter (MPI) is designed around the concept of easing ergonomic burden of installation, diagnostic and maintenance. MPI’s exploit the new features available from the new electronic controllers and communications modules. The result is an inverter that combines the installation simplicity of a string or central inverter with the intelligence, ubiquitous data display, remote control and energy harvest efficiency of a microinverter. This new emerging class of inverters has a plug-n-play modular design, allowing one inverter to control multiple 300-W solar panels, without the shading dropout or maximum power point tracking inefficiency typically associated with string inverter configurations. Combiner boxes, DC optimizers and DC GFCI’s are eliminated by low-voltage AC. System design is simplified to common 240-V single or 3 phases residential or small to mid-commercial wiring and design techniques. Geared primarily for the residential and smaller commercial markets between 5 kW and 200 kW, the MPI can be used for off-grid, grid-tied and grid-tied with emergency backup applications.
MPI’s reduce the inverter installation and commissioning time by 75% when compared to either microinverter architecture or a string inverter with DC optimizer architecture. PLCC Communications bandwidth is also improved by 4 times. Their new features include:
• Remote control of energy generation or termination
• A self-launching public or private web site
• An auto mapping capability that automatically maps the physical location of each panel and inverter to their location in the web sites map of the installation
• A thermal survival mode that increases energy harvest by throttling energy production down when the electronics begin to overheat and then throttles it back up after they cool down
• Automatic generation control to prevent exceeding a systems licensed production allotment
The micro parallel inverter can be mounted on the back of a panel, racking or directly onto the roof via simple one-handed installation, with low-cost quick connect and low-voltage AC terminals leading each of the four inverter channels to a 100-W to 300-W solar panel. Each inverter unit is then quick-connected to a cost effective trunk cable, allowing 4 inverters (16 panels in total) to be routed as AC directly to the breaker panel- without the need of DC combiner/optimizer boxes. The MPI’s lightweight AC cabling supports 16 panels per trunk cable, with just one disconnect at the breaker, unlike the 16 separate disconnects required by micro inverters. The array is then auto-mapped by a self-mapping system that maps each inverter location to their physical location in the grid just by switching on the breaker, eliminating the time-consuming and costly practice of hunting the field for panel identification, both in initial set up and for troubleshooting failures.
Micro Parallel inverters calculate the individual MPPT tracking for each panel, and throttle generation based on a thermal survival circuit that constantly throttles the generated power from the circuitry providing the maximum energy harvest for the system’s panels. The parallel inverter channel design and power sharing allows for graceful degradation, with the inverter remaining operational with as few as 1 panel, on any channel generating DC power as opposed to the loss across the total string due to shading of a single panel experienced by string inverter systems.
MPI Setup Diagram
Intelligent web-based monitoring relays system performance health and status via power line communication (PCL) to an energy and monitoring controller (EMC), which updates a self-launching website for remote viewing and data extraction. Alerts emailed to the maintainer/owner isolate failures to the system, panel, or inverter level, only alerting for serious failures to reduce unnecessary truck rolls. Each channel is easily serviceable in the field thus reducing troubleshooting time and costs of repair.
Unique remote power output throttling capabilities allow the micro parallel class inverters thermal protection against heat-related failures, scalability for meeting grid-base allotment requirements, and remote activation/de-activation control over installations. The EMC software architecture in micro parallel inverters allows for remote upgrades for future sustainability against obsolescence. All of this is done with a ¼ less units to install, and ¼ less units to monitor via PLCC, as one micro-parallel inverter can control 400 kW to that of the 100- kW micro inverter.
With increased focus on installation time and materials as the key to reduce costs for solar farm systems, the micro parallel inverter class makes a sizeable 75% gain in savings on installation cost and maintenance ease for systems up to 200 kW.
Find out more about this new class of inverter offered by Technology Research Corp. here.
Contributed by Technology Research Corp., a subsidiary of Coleman Cable.