Analytical-Diagnostic Monitoring of Solar Arrays with Proxy Irradiance Data
A resource to enable checkups on performance of solar sites without sensors & instrumentation
Steve Yang, P.E.
Energy Performance in every building or PV array is serious business for Wattminder. We believe there is tangible relationship between everything to everything else, especially in the context of internet-of-things. Having a full picture of a solar power site and its history of environmental parameters and performance data will enable ready and precise assessment of its current performance, or diagnostics.
We advocate for web monitoring of solar power sites, or for that matter, every home or building should have energy monitoring also, as the cost of instrumentation, local networking and web interface become affordable, with product offering like Arduino, Raspberry Pi, and other industrial component become widely available at reasonable price. Driven by the prolife ration of smartphones, people expect to access information with their smartphone on everything !, besides doing more and more chores with it, through its local and web connectivities.
Wattminder has efforts underway to take advantage of smartphones, or similar informational devices, both as a source of information and as the primary web-access devices, for anytime anywhere.
It is not well publicized, but a real pain for PPA, or Lease solar energy providers, that is unknown, or only learned after the fact, from monthly utility bills and PPA statements. My own personal observations over hundreds of solar projects show half of solar arrays under perform by 20 - 30%, from their practical capacity, nominally pegged at 77% of maximum DC rating, or PTC rating for California. Further evidence comes from the fact many projects are oversized by 10 - 30%, as a cushion against penalty clauses in PPA contracts. In terms of dollars these unrealized energy production amount to $5B for all installed arrays by end of 2011. These long term contracts with performance guarantees present unknown risk for investors and owners of these assets.
Our analytical tools, and diagnostic capability being developed will address these waste and help detect and quantify performance deficiencies in real-time, or via web machine to machine data links on few times a day basis to keep a vigilant watch over the solar generator sites performance. PVwizard is a platform that combines desciplines of physical & computer sciences, knowledge of photovoltaic data engineering in a synergistic meshing of sensor instrumentation, database tables, algorithmic and inference engine, inter-server communications and advanced web features to deliver critical information to help maintain optimal operation of solar power generators everywhere.
What's unique about PVwizard?Key features of our PVWizard analytical capabilities are: Comprehensive mathematical model, adapted from Sandia Labs, and expanded to include fault sources
Low-cost hybrid analog and digital sensor signal preprocessor that captures the minute changes in solar array strings.
Advanced machine-learning diagnostic algorithms with heuristics that learns to gain better and better accuracy and confidence in its diagnostics.
Both on demand web-interactive(free) and in-the-background, including real-time access of analytical and diagnostics, alerting, warning, and alarms are available.
We listened to solar contractors and monitoring companies, and arrived at these features. In the first place, the sensors and instrumentation are focused on the DC characteristics aimed at being able to perform diagnostics based on electrical changes that are reflective of system conditions and responses to fault sources.
What's unique about PVwizard
Layman's ExplanationsPVwizard evolved from our original PV Performance Benchmark calculator web page deployed as pvmonitor.net, back in Nov. 2007.
We were motivated to create this tool to help average Joe the solar power array owner checkup on the performance of their precious investment. Since on the surface, things may look normal, and the power meter is spinning backwards.Question is how well is the array doing in transforming Sun's light energy into electricity? We found that mathematical model developed by Sandia Laboratory provides a basis for our tool. We had abstracted the dozens of equations into one simple equation that can be computed easily.
In order to apply our model with actual values of parameters in the equation, you need to consult the datasheet that maybe provided to you by your contractor, usually in a binder that includes spreadshet analysis of financials and system design, component list, documentation, and warranties. You should have no trouble identifying the parameters needed for our equation. Your smartphone, coupled with our free PVwizard App, can be a valuable resource in automating much of the site parameter determination, and making it a fun experience to checkup on your solar array.
In plain English, what our three analytical functions can do for you:Performance Benchmark, a calculator that assimilate parameter values about your solar array, along with environmental conditions and compute what your solar array should be producing, under no-fault condition in Watts. (It also works with energy values from power meters, or web page displays.) Two key environmental factors are local irradiance and cell temperatures (derived from ambient temperature). When these two parameters are not precisely known, we provide a table of variability, so that you may see what range of output values may apply for the current operating condition.
Performance Check, as a registered user, when you can access your array's output in KW, our calculator can tell you how well your array is producing; given the current set of operating condition. So having sensors for irradiance, and cell temperature would appreciably increase the confidence level of our assessment.
Degradation Assessment, as a registered user, after you've accumulated a history of recorded measurement (everytime you ran a Benchmark, or Performance Check, you have the option to record the output value into our database); you can request for an assessment of how much had your array degraded (in apparent performance, including all factors impacting your array), in Watts, also in percentages.
Application of PVwizard FeaturesOur primary goal is to assist solar power owners and operators to keep an eye on their systems performance, regardless if they are being monitored by other providers. In reality, most new projects configured as PPA, or lease contracts are equipped with instrumentation and web monitoring. However most monitoring providers do not offer analytics, much less diagnostics on the over-all performance of the array.
Our Benchmark calculator may also be used as a corrolary tool for site analysis, and planning purposes. You'll gain additional insight with PVwizard, when compared with other site assessment tools, since our tool works instantly, and is available on-demand, without need to download and install software.
Work-in-Progress & Future EnhancementsThe primary thrust of our current development is our DOE grant sponsored Web-Based Hotspot detection and diagnostic engine for solar arrays, demonstration platform now being constructed at CMU-SV campus on the grounds of NASA Moffett Field. (see Word's most instrumented solar array). By adopting the latest system on chip technology from Cypress Semiconductor, our diagnostic enginer running on a database server, will be able to detect and diagnose hotspot, or partial shading condition occurring on solar array being monitored with our 1-chip, all inclusive sensor signal conditioning, instrumentation, pre-processing, data convertion, and TCP/IP streaming from remote sites into our web server and performing diagnostics in near real-time. The NRE cost of this technology is expected to be at .25?/Watt, which is orders of magnitude lower than all current sensor instrumentation & data gateway offerings by monitoring service providers.
Easy and open API for enabling a suite of advanced analytics delivered through SOAP services by our diagnostic engine is being readied to allow in the background, machine to machine communications for a range of analytical, diagnostic services on any web-monitored solar power site. These could be once a day, or any number of sampling per day, hour, minute using measurement records. When a full set of site parameters are available, as well as some historic data on a site, our analytics will be able to crunch the numbers and arrive at qualified assessment of performance at time of measurement.
Also in development are smartphone apps that enable interesting and engaging user experience for applying our tools for anytime anywhere access. Longer term projects include international language, semantic web-natural language interface, such that each encounter with our PVwizard becomes an educational lesson. We are also building a skeletal framework to leverage the power of the crowd, or community in growing knowledge about solar arrays in operation. A few more advanced features are also being investigated.
References:Performance analysis of photovoltaic installations in a Solar America City, Photovoltaic Specialists Conference (PVSC), 2009 34th IEEE 7-12 June 2009 Author(s): Gostein, M. Atonometrics, Inc., Austin, TX, USA Hershey, R. ; Dunn, L. ; Stueve, B.
