Page 14 - North American Clean Energy May June 2018 Issue

Sergio C. Gualteros is an Analyst of Research and Innovation at Nergica. Drawing on his expertise in integrating renewables into electric systems, his projects foster the development of innovative solutions for energy e ciency and the transition to cleaner energies.
Pierre Beaudoin is a Project Manager of Research and Innovation at Nergica. He is a specialist in the integration of o -grid renewables, and has been working in the eld for over 25 years.
Matthew Wadham-Gagnon is a Business Development Manager at Nergica. With more than 10 years of engineering experience as project manager, coordinator, and guest speaker, he has acquired leading-edge expertise in his eld of activity.
Nergica is a centre of applied research that stimulates innovation in the renewable energy industry through research, technical assistance, technology transfer, and technical support for businesses and communities. Known until recently as the TechnoCentre éolien, Nergica has been active for nearly 20 years in the eld of renewables, and is an o cial college centre for technology transfer (CCTT) a liated with the Cégep de la Gaspésie et des Îles.
Nergica | www.nergica.com
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North American Clean Energy
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Figure 1: PV system installed at Rivière-au-Renard (Canada)
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solar power
Solar PV Challenges
SOLAR PV SYSTEMS SUBJECT TO EXTREME COLD-WEATHER CONDITIONS
face particular challenges, from the planning stage, to operation and maintenance. Low temperatures, heavy snowfall, freezing rain, and short periods of sunlight are some of the phenomena that may a ect solar PV performance. Due to an ongoing misconception that solar PV systems are not suitable for such conditions, its deployment in colder North American regions remains considerably low.
However, solar PV is the fastest growing renewable energy source worldwide, with an extraordinary 50 percent growth rate in 2016. is unprecedented growth has also facilitated the development of measures to adapt PV systems to harsh environments. Regarding PV systems in cold climates, such measures can be separated into two main groups: (i) design and technologies and (ii) O&M strategies.
Design and Technologies
During planning and design stages, on-site extreme weather conditions must be considered. Snow accumulations on the PV modules can be minimized by using higher tilt angles, and frameless modules, which helps snow to slide o easily. Along with the aforementioned con guration, portrait-oriented PV module installation is an advantage; a longer sliding surface will facilitate snow shedding. If high tilt angles and frameless PV modules cannot be used, landscape orientation is preferred, as snow accumulation at the bottom of the covered modules will tend to cover a single PV cell string, minimizing energy losses. For ground-mounted arrays, if high snow accumulations are expected on site, elevated frames are needed.
Even a light coverage of snow on the module surface can have a large impact on energy yield. Bypass diodes are used to bypass covered PV modules, thus minimizing related losses. anks to recent engineering development, bypass diodes are also included inside the PV modules so that covered PV cell strings can be also bypassed. Proper string/row design can also help reduce coverage losses; the electric connection of a string over two physical rows will produce an undesired combination of covered and uncovered modules, and should be avoided.
Figure 2: Bypass diodes can reduce energy losses caused by partially-covered PV modules
Microinverter-based architectures are superior to string inverters in cold climates. e increased granularity of this architecture leads to better performance monitoring, which reduces the single-point-of-failure challenge, and minimizes the impact of partially snow-covered PV modules.
O&M Strategies
PV systems installed in cold and isolated regions are subject to logistical constraints for O&M, which considerably increases operational expenditures. Reducing system complexity helps minimize required O&M interventions. For example, sun tracking systems, which comprise sensitive equipment and moving parts, are likely to fail due to extreme low temperatures or high wind speeds.
In order to avoid false-alarm situations, the adverse e ect of freezing temperatures on electronic equipment must also be considered. In fact, electronics are highly impacted
by ambient temperature; voltage, current, and temperature readings can drift when sensitive equipment functions outside its operating temperature range. Utilizing hermetic, temperature-controlled enclosures for electronics, or using military-grade electronics, can help reduce this drift in systems with high precision requirements. To avoid false-alarm conditions in small-scale systems, an overall uncertainty estimation is recommended.
One of the most common concerns in cold weather is removing snow accumulations from PV modules. In an e ort to reduce O&M interventions, self snow-shedding and de-icing must be evaluated at each particular site. Snow cover on a PV module can eventually allow some solar radiation to pass through; even partially covered modules can produce electricity and heat, and promote self snow-shedding. Experience and observations gleaned from the rst winter of PV operations should provide su cient information to operators. Cleaning tools for de-icing and snow removal must be carefully chosen in order to avoid damaging PV modules.
Advantages of Solar PV Systems in Cold-Climate Regions Nevertheless, cold-climate regions show an exceptional set of favorable conditions for PV. Silicon-based PV modules perform considerably better in colder temperatures. Module e ciency at 0°C can be up to
12.5 percent higher; snow accumulations surrounding the PV modules can act
as a mirror, increasing both the solar radiation reaching the modules and the energy yield. Similarly, because copper resistance decreases at lower temperatures, electric losses in the conductors are reduced. In fact, ideal conditions for PV modules include high solar radiation, low temperatures, and high ground re ectivity.
In standard conditions, the main
cause of PV module degradation is the heat generated by the incident solar irradiation. Since cold weather helps keep module temperature low, PV systems in cold climates are expected to have longer service lives. In fact, PV systems installed in northern Canadian locations have been operating for more than 35 years with lower degradation rates than expected, and almost no O&M issues reported.
Some cutting-edge technologies remain to be tested in northern locations. Such
is the case for bifacial PV modules, which may pro t from high snow re ectivity, therefore increasing energy yield and promoting faster snow and ice melting. Passive and active melting technologies can also be tested in PV systems. One example of passive technology is the ice-phobic coatings that impede rime or glaze from forming on the PV modules, while reverse ow-current through the modules to generate heat is an active melting technique already used in some European PV systems.
Despite existing restrictions, cold- climate regions represent a bene cial environment for solar energy systems. PV modules are easy to install and operate, have no moving parts, and perform particularly well in cold climates. Indeed, overcast locations are less favorable to solar PV deployment than cold, snowy sites. Furthermore, by combining PV with wind energy in higher latitudes, operators can take advantage of regions where lower solar radiation seasons often coincide with higher winds. With the proper design, solar PV can become a mainstream energy source for northern isolated locations, replacing polluting diesel generators, and improving energy source diversi cation and availability.
Figure 3: Capacity factors for wind and solar PV in Arviat, Canada (N 61° 6.4984', W 94° 3.5971')
in Cold-Climate
Regions
by Sergio Gualteros, Pierre Beaudoin, and Matthew Wadham-Gagnon
26
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