Performance Testing And Monitoring Shape PV Optimization


The performance of PV systems will be driven not only by the quality of manufacturing processes and equipment, but also by the reliability of testing procedures and increased attention to performance monitoring, panelists stressed at the SolarTech Performance Symposium, held last month at the Intersolar North America Conference in San Francisco.

According to Doug Rose, vice president of technology strategy at SunPower Corp., improving manufacturing quality requires building quality into the process steps, including knowing the effects of every change made to each piece of equipment or process step. This due diligence goes beyond obtaining certification, he noted.

‘Certification does not equate [to] high quality and reliability – though it is a necessary hurdle to be able to sell,’ he said. In order for reliability testing to be a meaningful indicator of performance, he added, it must be extremely accurate.

A ubiquitous challenge in the industry, therefore, has been the uncertainty – and often inaccuracy – of performance predictions. Predictions of how modules respond to low irradiance can be off by as much as 10%, thus affecting the comparisons among different modules, Rose explained.

Michael Quintana, technical project lead for Sandia National Laboratories, also acknowledged this problem and stressed the urgent need to address it – and to do so in a cost-effective manner.

‘Predictions – that's everybody's challenge,’ he said. ‘We can't wait 20 years to figure out if it works or not. We have to look into the future and be able to predict. We have to do that with very low cost – we can't spend all our hard-earned dollars trying to figure out whether we can increase reliability and performance without increasing costs.’

Unreliable performance predictions affect not only product selection, but also payment of expected-performance-based incentives. Unlike performance-based incentives, which are paid based on the actual amount of energy produced, this payment method relies heavily on these prediction tools.

Molly Tirpath Sterkel, project supervisor at the California Public Utilities Commission, noted that the expectations are, naturally, higher for systems utilizing performance-based incentives, because this type of incentive drives design optimization.

‘When policy focuses on performance – and it incentivizes performance – the systems will perform,’ she stressed.

System monitoring will continue to play a key role in performance optimization, the panelists agreed.

‘We are equally interested in monitoring from the standpoint that we believe there are still opportunities for optimization of systems out in the field – understanding what those systems are capable of and understanding what those systems are actually producing,’ Rose said.

Monitoring provides the obvious benefits of quantifying energy production and identifying performance issues, but customers must be made aware of the availability of monitoring services, explained Smita Gupta, senior energy consultant with Itron Inc.

According to a phone survey conducted by the California Solar Initiative, only 25% of California's residential systems and 44% of the state's nonresidential systems are monitored. For third-party-owned systems, the rate jumps to 50%.

Of the customers who were not told that their system could be monitored, just 1% ended up seeking out the service themselves, Gupta noted.

‘Awareness [of] monitoring had the biggest impact on its adoption, and the system with more financial vested interest tended to be more monitored,’ she concluded.

System monitoring is currently required only for systems larger than 50 kW. According to Tirpath Sterkel, the obstacle to making it a requirement for all systems is the uncertainty of what it really costs. She cited a survey of monitoring-services providers in which half of the companies could not specify how much their monitoring services would cost.

‘As a policy-maker, how can I require your product if you won't even tell me how much it costs?’ she asked.

Gupta agreed. ‘If you don't know how much it will cost, how can you require it? Everybody knows the benefits of monitoring, but it's the end customer who's actually making the purchase,’ she said.

Nevertheless, 10 years from now, all systems will be monitored, Tirpath Sterkel predicted. However, she recommended that the monitoring remain uncomplicated.

‘We want to require the simplest, most basic – is it on, is it off, what's it performing – form of monitoring,’ she added.

Otherwise, SunPower's Rose warned, the requirement may end up acting as a deterrent.

Ultimately, effective monitoring not only leads to system optimization, but also to customer satisfaction, Gupta said. When customers see that their system is effectively producing energy, they will portray solar in a positive light, leading to more systems being built – and that means proliferation of the industry.

(Please address all comments regarding this article to Jessica Lillian, editor of Solar Industry, at

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