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PV System Performance

DC monitoring raises the bar for solar power plants

Fortnightly Magazine - July 2011

adhering to schedules and budgets. DC monitoring can reduce that risk, resulting in better financing terms that can offset the cost of the monitoring system itself and reduce the levelized cost of solar energy (LCOE).

Large PV projects have a number of risk variables that must be carefully managed. Dividing the risk among multiple partners is advantageous, but complicated. This is where DC monitoring can play a useful, if not vital, role. Over-allocation of risk can create additional costs if risk bearers are uncomfortable with the scope of their responsibility; this runs contrary to the goal of pushing down LCOE. DC monitoring is a tool that can be used to slice up performance risk to fit in a bucket that each component provider and installation stakeholder is comfortable carrying. By providing data that can be used to quantify component performance at boundaries not easily defined in PV systems without DC monitoring, DC monitoring gives solar stakeholders more information about the risk they’re bearing while simultaneously maximizing energy harvest.

While the attributes of the PV module are well-defined and understood, methods used to predict real-world lifetime system performance are still evolving. It follows that DC performance data can and should be fed back to improve performance prediction models. To do so, this information should be released to the public domain or at least shared as widely available as possible to derive maximum benefit from analysis. The information gleaned from a DC monitoring system can give all parties confidence to stand behind increasingly stronger PEGUs and warranties for future projects—or better yet, inspire faith among end customers and financiers that the understanding and reliability of PV technology is sufficient to render performance guarantees irrelevant or uneconomical.

Additional cost is the objection most commonly heard when considering whether to implement a DC monitoring system. It’s clear that a DC monitoring system will increase the dollar-per-watt cost metric of a proposed project (by perhaps $0.20 per watt), and that increased cost will be passed on to the customer. However, one must also consider that DC monitoring can increase total energy harvest, though the gains realized from enhanced efficiency and reduced downtime aren’t easily quantified in system energy generation estimates. LCOE, though harder to assess, is a more relevant and descriptive metric and should be given equal or greater weight than dollars per watt when evaluating the economics of a project proposal. It would greatly benefit all solar stakeholders to commission studies or research papers that attempt to quantify the effect DC monitoring has on LCOE.

In addition to the supplementary sensors that monitor performance, DC monitoring systems require supporting infrastructure to collect and transmit performance information to internet-connected monitoring systems. Thus, added complexity is another hurdle DC monitoring must overcome. However, added complexity is acceptable if it adds value and improves the efficiency of the installation. Although it doesn’t come close to approaching the same level of complexity found in a coal-fired or nuclear power plant, DC monitoring provides a similarly enhanced level of instrumentation to improve real-world system performance.

Monitoring in the Future

Deciding whether