One of the trickiest parts of maximising efficiency in a solar installation is dealing with variations in power output among panels and strings of panels in the same system. SolarEdge is a company that has developed a unique solution to the problem of irregularity in solar panel array output. It uses a solar system architecture that utilises per-module maximum power point tracking (MPPT) to tackle system efficiency from a holistic design perspective, providing an ingenious balance of system strategy for solar system efficiency and energy savings.
Centralised MPPT inverters
In order to explain the innovative inverter technology that SolarEdge specialises in, it is first essential to understand how conventional solar system inverters function.
System losses can sometimes be attributed to the nature of industry-standard crystalline solar panels themselves, which are susceptible to partial shading and overheating, and sometimes attributed to the nature of conventional inverters, which do not perform MPPT for individual modules.
There are many potential reasons for variation amongst panels in an array: natural variance in a solar panel’s rated capacity is typically +/-3% of rated output, shading can happen on some parts of the array but not others, the array can heat up unevenly, and strings of panels on different sides of the same roof can generate different amounts of electricity at different times of day.
In a system with a centralised-MPPT, single-input inverter, total solar system array output will be limited by the panel that is producing the least amount of power–the weakest link is where the chain breaks. If an inverter has only one input for one ‘string’ of panels, you may have to deal with losses on a regular basis, or buy more than one inverter to improve the overall system efficiency.
Some inverters support MPPT at a string level, which does help to minimise losses, but the inverter still cannot ‘see’ into a string to monitor and control what individual panels are doing. This means that your system is not taking full advantage of all the power produced by your panels, which in turn means higher cost per watt of your system and extended payback periods for your solar investment.An example of partial shading in a conventional multi-string inverter system (Image via pvsolarchina.com)
So in summary, the current industry standard multi-input inverter design approach, while much more efficient than inverter systems of the past, still only addresses the efficiency problem on a string level. Even when the inverter itself is functioning efficiently, output variation between the panels within the array limits the potential overall system efficiency, and therefore, its usable electricity output.
SolarEdge Solar Power System Architecture
SolarEdge provides an end-to-end distributed solar power harvesting and PV monitoring solution, maximizing the power generation of residential, commercial and large-scale PV system installations by up to 25%, for a faster return on investment.
The SolarEdge three-fold architecture consists of power optimizers which perform module-level MPPT, a highly reliable solar PV inverter, and a portal for module-level PV monitoring and yield assurance. The power optimizer is connected by installers to each PV module or embedded by module manufacturers, replacing the traditional solar junction box.
SolarEdge technology benefits:
–Up to 25% increase in power output compared to single- and multi-input inverter system arrangements
–Superior inverter efficiency (up to 98%) – peak performance in both mismatched and unshaded conditions
–Flexibility in system design options: SolarEdge system architecture allows parallel uneven length strings, panels of different wattages and from different manufacturers (more inventory options); installation involves fewer components and less wiring, which means faster installation and better roof space utilisation than conventional systems
–Interactive, ‘from anywhere’ monitoring offers a new world of opportunities with regard to system troubleshooting maintenance
-The power optimizer (MPPT tracker) can be embedded into any module as a certified junction box–possible on-site or factory-based integration into solar modules
–Superior safety for installers and firefighters: Electric arc detection and termination features; safe module voltage when disconnected or off. Read more (pdf)
-SolarEdge ‘Inverter Configuration Tool’ software means immediate installation feedback for quick system commissioning
How does SolarEdge distributed inverter technology work?
The SolarEdge System: Holistic system design for efficiency, cost-savings, and ease of monitoring. (Image via SolarEdge.)
Three components form the balance of system in SolarEdge’s ‘system architecture’.
-Module-embedded power optimisers, which monitor and regulate the power output of all the individual modules in an array, in order to maximise overall system output–these can be installed on-site, or may be pre-assembled in solar module factories of companies that are in a partnership with SolarEdge,
-A smart inverter, which inverts the DC power of all modules to grid compliant AC, and
-A monitoring system, data from which is accessible via the Internet.
SolarEdge System Overview:
The inverter uses a highly-optimised algorithm to constantly track the maximum power point (MPPT) of each module individually, preventing power loss even under panel mismatch or partial shading. In fact, even panels from different manufacturers can be used simultaneously in the same array. (This offers intriguing possibilities for future applications in Building-Integrated Photovoltaics (BIPV); solar windows, solar walls, and rooftop solar arrays could all be routed through one inverter.) The algorithm also allows the system to react more effectively to changes in irradiance and temperature, a big benefit on cloudy days.
Highly Efficient DC-DC Conversion
Each power optimiser performs a DC-DC power conversion (peak 99.5% efficiency) that allows it to boost or buck output voltage of modules in the array to ensure a fixed string voltage.
Fixed String Voltage
The voltage of a string is held constant at the optimal point for DC to AC conversion, regardless of the number of modules in a string, or external factors such as weather or shading. This feature means that there are fewer limits to system design and panel location, greater inverter efficiency and reliability, and lower installation costs.
A range of module-by-module status indicators (current, voltage, etc) are continuously measured and communicated by the power optimisers. Data are transferred through the existing DC power lines, meaning that there is no need for extra wiring. For ease in monitoring all the goings-on within the system, the inverter houses a LAN- and wireless-capable communications hub, enabling the owner or operator to view system performance in detail on a remote monitoring server from a computer or other even hand-held devices.
Performance data being recorded on a remote monitoring server also means that the system owner or operator can quickly identify and troubleshoot problems with your system, should any arise, minimising or eliminating the need for site visitations and associated travel charges.
SolarEdge product range and spec sheets
For residential applications: P300 – P350 – P405 – P500 (click to download pdf specsheet)
For commercial applications: P600 – P700 (click to download pdf specsheet)
Single-phase inverter: SE2200-AUS – SE6000-AUS (click to download pdf specsheet)
3-phase inverter: SE5K-AUS – SE17K-AUS (click to download pdf specsheet)
Founded in 2006, currently engaged in partnership agreements with module manufacturers and integrators in Europe, USA and Japan, which provide SolarEdge technology alongside their current services.
Global headquarters: Hod Hasharon, Israel
Other offices in USA, Germany, and elsewhere in the Asia-Pacific region
© 2013 Solar Choice Pty Ltd
James holds a Master's degree in Environmental Management from the University of New South Wales. and an undergrad degree in philosophy from Bridgewater State University in his native Massachusetts. He has a keen interest in developments in the renewable energy field, with a focus on distributed solar and energy storage.
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