Monitoring, Solar

Module Level Management Emerges from the Shadows

Issue 1 and Volume 1.

A major market development of module optimisation technologies in recent years has brought down the cost of electronic technologies for providing real-time monitoring data at the module level. Some products also offer additional functionality such as theft deterrent, and module switching and isolation for fire safety. What is their value to the market and what is their justification?

In the wake of a massive PV market expansion and a corresponding growth in opportunity, technology entrepreneurs have been inventing innovative value-added technologies all around the PV infrastructure sector, from large engineering solutions to software.

It’s in the nature of the 21st century technologist to find a technical solution to a known problem; equally, it’s in the nature of the same innovator to find a problem to fit a neat technology. The issue for the customer is finding value solutions.

In the past two years, in particular, balance of systems (BoS) technologies have emerged to add value by providing better information and better performance for photovoltaic installations. In an industry where billions of investment dollars are being spent on improving conversion performance by 1%-2%, the BoS technologies are focusing on 20%-50% improvements by ensuring PV systems are producing close to 100% of their designed capability.

So where a balance of systems developer is selling an extra 10%, 20%, or even a 50% improvement in performance, what they are actually saying is that the customer is not yet getting the full capability of the investment, and this new product will help him get there.

Balance of System Challenges

The challenge for all of these technologies has been to find a technology that adds value but that does not add significant cost, in a market driven by cost reduction. Furthermore, any such technology must not erode the healthy margins of the major players that support a 20-year-old architecture which works OK.

While feed-in tariffs stand at as much as 55 euro cents to encourage the development of a new industry base, the project attitude has been quite complacent. Business plan return on investment (ROI) targets will be achieved even if some of the technology is not working. But as governments start to rein in and reduce tariffs – as recently witnessed in several European countries for example – achieving maximum performance becomes far more critical and any technology that can (at worst) guarantee and maintain target levels of performance, is worth considering.

In the 1970s and 1980s when Europe was under severe oil price pressure from OPEC, European automotive manufacturers were forced to increase efficiency, which led to the development of engine efficiency technologies. Core engine architecture did not change, but the use of measurement and information at the lowest component level by engine control units (ECUs) provided small percentage improvements to aspects such as timing and ignition, which over time has provided massive returns in fuel efficiency.

Similarly, as PV feed-in tariffs fall and pressure is put on project margins, it is essential that PV arrays achieve optimal performance – and the lowest practical technology level to obtain the necessary performance management information is the module.

Module level Technology Development

For many years performance tuning technology has been limited to a core function of the centralised inverter (MPPT). The only monitoring has been either from the inverter or other centralised data loggers, so the lowest level of management was at the string level.

So, for instance, in 2009 module optimisers such as SolarMagic, Tigo and SolarEdge appeared that use module level MPPT optimisation dynamically to counter shading and other material inconsistencies. The same year also heralded the ‘second coming’ of the module level inverter/AC module — from players such as Enphase and Enecsys — to overcome the limitations of the centralised inverter and series/paralleled PV arrays.

Last year then saw the cost of module level monitoring and control technologies come down. Technologies such as TwentyNinety Active Array work on the premise that performance degradation can be random and can be caused by many external factors that would never be detected and could even be masked by a string monitor/inverter. If a module suffers 10%-15% degradation from dirt or faulty materials, a string monitor would not detect that degradation; the lower performance would be blended and invisible to the user.

These module level technologies also provide a simple solution to a major concern of many of the world’s firefighters: the fact that during daylight hours, anywhere downstream of a classic dumb module — between the module and the DC isolator — is live and therefore capable of carrying very high DC current.

By designing in sensors at the module level, some new systems such as Tigo, TwentyNinety Active Array and SolarEdge can also provide a degree of fire safety control. These systems can shut off/isolate the individual module, either through wireless or wired switching systems.

Performance Benefits Quantifiable?

All the new BoS technologies advertise anything up to 50% improvement on current performance. But the higher claims come from optimisation technologies that achieve their claims in a shaded environment by normalising output and optimising MPPT.

But what about systems unaffected by shade, which form the vast majority of installations? As with any electronics technology, a solar module will experience a standard bell curve of component and material failure. When that device is placed in harsh external conditions, additional factors such as heat and dirt increase the likelihood of performance degradation.

Long term studies of PV installations show that some modules will perform optimally for long periods while others will lose as much as 25%-30% of their capacity through environmental factors such as heat, dirt, and snow or external factors like wiring. With dumb modules, a 10% degraded module will then produce a disproportionate degradation to the overall performance of the string and could remain undetected for a long time.

While automatic module optimisation will improve the string performance without fixing the root problem, module level monitoring solutions are designed for this classic fault scenario. Simple software alerts identify symptoms such as a lower output than an adjacent module, increased temperature or increased string resistance, allowing the customer to repair or replace immediately.

Are Manufacturers Ready?

Key to any technology acceptance by early adopters is the value created by the product and its price. Many major manufacturers are taking module level technology very seriously because of the need to demonstrate confidence in their product in the face of low-cost competition. But at the same time they are also being driven to reduce costs and consequently this market will develop. Initially the manufacturers will market a premium product. But, as in the automotive industry, simple low-cost key management data will become an essential optimisation tool for plant operators.

Sidebar: Microinverters for Module Management

Unlike a central, or string inverter, a microinverter converts DC power from a single module to AC. When connected to a central inverter, modules are typically connected in series; when they have micro-inverters, the modules are connected in parallel.

Advances in electronics made them commercially viable, enabling manufacturers to address some of the challenges associated with standard central inverters. Manufacturers are also offering smart monitoring as part of their package to customers. The changes in the size and sophistication of these devices, and consequently the overall improvements in solar system performance, helped bring about the convergence of energy and information technologies.

Previously, Raghu Belur, Enphase’s marketing VP, explained to REW how the firm came to develop its micro-inverter. “All entrepreneurs go looking for a problem; the harder the problem, the better it is. Our CTO and co-founder, Martin Fornage, installed a solar system on his property and during that time recognised the limitations of a traditional inverter solution.” Continuing, he said: “Other people had worked on micros before but had been unable to make the technology commercially viable. Our approach, with its digital design and development of custom semiconductors made the micro-inverter commercially viable and attractive,” adding, “We were able to address the issues of efficiency, reliability and cost for the first time. We didn’t think of it simply as a piece of hardware, but instead as a system, which means embedding computing technology and monitoring for operations and maintenance purposes. And a lot of that comes from the founders’ backgrounds. I came from Cisco Systems, which has a very system level approach to all its activities.”