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Impact of Snow and Ground Interference on Photovoltaic Electric System Performance


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Assessing snow-related energy losses is necessary for accurate predictions of photovoltaic (PV) performance. A PV test platform with seven portrait-oriented modules placed at four tilt angles (0°, 15°, 30°, and 45°) was installed in Calumet, MI, USA, to measure the energy loss in this snowy climate. As a best-case snow-shedding configuration, similar to a carport or a plain sloped roof, three of the test modules were rack-mounted high enough to prevent surface interference. The opposite effect of maximum surface interference, similar to many commercial rooftops, was introduced by mounting the other four modules at grade. The platform was monitored for one year beginning in October 2013. The snowfall that winter was normal: 5.3 m (209 in). Snow-related annual energy losses ranged from 5% to 12% for the elevated unobstructed modules, with the steepest tilt angle experiencing the least amount of energy loss. For the obstructed modules, there was little angular dependence on lost energy, with annual energy losses ranging from 29% to 34%. This relative three- to sixfold increase in lost energy when ground interference is present points out the importance of minimizing obstructions and prompt snow clearing for portrait-oriented PV. Depending on the breadth of an inverter's operating voltage limits, these results suggest that landscape-oriented array layouts and perhaps snow-clearing mechanisms may be advantageous in snowy climates.
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Preprint: Heidari, N., Gwamuri, J., Townsend, T.,Pearce, J.M. (2015). Impact of Snow and Ground Interference on Photovoltaic Electric System
Performance. IEEE Journal of Photovoltaics 5(6),1680-1685, (2015). doi:10.1109/JPHOTOV.2015.2466448
AbstractAssessing snow-related energy losses is necessary for
accurate predictions of photovoltaic (PV) performance. A PV test
platform with seven portrait-oriented modules placed at four tilt
angles (0, 15, 30, and 45 degrees) was installed in Calumet,
Michigan to measure the energy loss in this snowy climate. As a
best-case snow-shedding configuration, three modules were
elevated high enough to prevent surface interference. The opposite
effect of maximum surface interference was introduced by
mounting the other four modules at ground level. The platform
was monitored for one year beginning in October 2013. The
snowfall that winter was 5.3 m (209 inches). Snow-related annual
energy losses ranged from 5% to 12% for the elevated,
unobstructed modules, with the steepest tilt angle experiencing the
least amount of energy loss. For the obstructed modules, there was
proportionately less angular dependence on lost energy and
annual energy losses ranged from 29% to 34%. This relative 3- to
6-fold increase in lost energy when ground interference is present
points out the importance of prompt snow clearing for portrait-
oriented PV. Depending on the breadth of an inverter’s operating
voltage limits, these results suggest that landscape-oriented array
layouts and perhaps snow-clearing mechanisms may be
advantageous in snowy climates.
Index Terms Electricity; Energy loss; photoelectricity;
photovoltaic cells; power systems; solar energy
Solar photovoltaic (PV) technology is a technically viable
and environmentally beneficial solution to society's future
electrical needs [1,2]. However, to optimize both the
environmental [3-5] and economic [6-9] outcomes, including
financing of PV systems, [10,11] accurate prediction of system
yields is critical and requires in-depth accounting of all loss
mechanisms [12,13]. PV technology is increasingly being
deployed in areas with low annual irradiation, like Northern
Europe [3], and in regions that regularly experience snowfall,
such as Germany, Japan, Canada, and the northern U.S. The
accumulated snow on the modules affects the performance of
the system and decreases the output power [14]. Previous
studies indicate that annual snow losses for a low tilt angle
system can easily reach or exceed 15%. Even for an
unobstructed, higher-slope (28 degree) roof mount system in
N. Heidari is in the Department of Electrical & Computer Engineering,
Michigan Technological University, MI (e-mail:
J. Gwamuri is in the Department of Materials Science & Engineering,
Michigan Technological University, MI (e-mail: )
T. Townsend is in the Renewables Advisory Solar department, DNV GL,
San Ramon, CA (e-mail: )
Germany, the losses, while smaller, could still range from 0.3-
2.7% [15-22]. As more of the better sites for PV are claimed
(e.g., unobstructed rooftops and high-rack ground mounts),
lesser-grade sites such as those subject to frequent snows will
become more popular. To quantify the snow loss effect, a test
site has been designed and deployed in a heavy snow location
to investigate PV electricity generation losses as a function of
tilt angle and snow sliding obstruction geometry.
A system has been developed to investigate the effects of snow
on the performance of photovoltaic modules as a function of tilt
angle and degree of ground interference. The system was
deployed at the Keweenaw Research Center (KRC) located in
Calumet, MI USA, and webcam archived images are freely
available to the public [23]. The study has been conducted on
seven 140 W Kyocera (KD140) poly-Si modules. Four modules
are mounted at ground level at angles of 0, 15, 30, and 45
degrees, with no ground clearance. Three other modules are on
a raised rack with a ground clearance of 1.5 m, at angles of 15,
30, and 45 degrees. To simulate the effect of the modules being
in a large array, a 30 cm border of blue metal shielding was
applied around each module. The layout of the test site is shown
in Fig 1. It should be pointed out that only one module at zero
degree tilt angle is needed, as the same snow losses are expected
for a well-bordered horizontal module that is either elevated or
mounted close to the ground.
Each PV module was monitored for temperature (T) with an
accuracy of +/-0.9 °C and for short-circuit current (Iexp(T)) with
an accuracy of +/-1%. All measurements were carried out at 15-
minute intervals. Solar irradiance (Psun) was measured using
four LI-COR Li-200SA pyranometers mounted on individual
panels for each angle. The pyranometer uncertainty is ±5%
[24,25]. The parameters
, and TC are
obtained from the module manufacturer’s data sheet [26]. The
short-circuit current data for the seven PV modules was
recorded for the year starting in October 2013 and analyzed for
the entire year and also over a subset of it encompassing just the
Fall 2013 and Spring 2014 snow season (November 2013
May 2014). The total snowfall recorded for this period was 209
inches [27]. The 2013-14 snowfall of 209 inches was 15%
above the past 5-year average, but 4% below the 40-year
J.M. Pearce is in both the Department of Electrical & Computer Engineering
and Department of Materials Science & Engineering, Michigan Technological
University, MI Corresponding author: 601 M&M Building, 1400 Townsend
Drive, Houghton, MI 49931-1295 (e-mail:
Impact of Snow and Ground Interference on
Solar Photovoltaic Electric System Performance
N. Heidari, J. Gwamuri, T. Townsend, J.M. Pearce, Member, IEEE
Preprint: Heidari, N., Gwamuri, J., Townsend, T.,Pearce, J.M. (2015). Impact of Snow and Ground Interference on Photovoltaic Electric System
Performance. IEEE Journal of Photovoltaics 5(6),1680-1685, (2015). doi:10.1109/JPHOTOV.2015.2466448
average. The recorded amount can be viewed as typical, since
it fit well within the long-term standard deviation of ±25% for
annual snowfall at this location as seen in Table I.
Annual snowfall
5-year avg
181 ±34
40-year avg
218 ±54
40-year low:
40-year high:
Townsend and Powers developed equations to calculate
monthly energy loss as a function of climate and array geometry
[15]. Others, including the authors above, have attempted to
correlate snow-related energy loss on shorter hourly or daily
time scales, with significant limitations. The focus of this study
is on monthly results, though individual measurements are
recorded on 15-minute intervals. Here power is not directly
measured, but is estimated. This is done by relying on
pyranometer and temperature data in the first case, and in the
other case, by relying on short-circuit current and temperature
data. In both cases, the field measurements must be
supplemented with manufacturer’s specifications for the
module and the pyranometers (in this case, Kyocera 140 W
poly-Si type modules, with 36 cells in series, and LI-COR Li-
200SA pyranometers).
The power from each snow-exposed module at each 15-minute
interval was calculated as:
(( )) (1)
By considering the flash-tested power rating of the modules and
the irradiance obtained from the pyranometers at each angle, the
potential clean-module power that can be extracted at each tilt
angle is then determined using equation (2) below:
= (
1+(  )) × (())
 (2)
In the equation above, either the reference irradiance of 1,000
W/m2 or the measured irradiance should be corrected for
temperature. As the reference irradiance is normally viewed as
a constant, here the measured irradiance is adjusted to see what
it would have been under the same conditions that the reference
irradiance was measured at, 25°C. The module power, however,
is sought for the field temperature, not the reference
temperature, so that temperature adjustment is the same as the
one done for the snowy module. The energy loss due to snow is
calculated as the difference in energy without snow, Pc, versus
the energy obtained from snow covered modules, Pm:
×) (3)
A. Abbreviations and Acronyms
α: Temperature Coefficient of Current, module [1/C]
: Temperature Coefficient, pyranometer [1/C]
C: Temperature Coefficient of power, module [1/C]
Eloss: Energy loss [kWh]
Iexp(T): Short-circuit current measured at experimental
temperature [Amps]
: Short-circuit current at Standard Test Condition
Pc: Power that can be extracted from each (hypothetical) clean
module (without snow) [Watts]
Pm: Calculated output power of snow-exposed module (at
various angles and heights) [Watts]
Psun: Irradiance obtained by pyranometer (at various angles)
: Maximum power of flash-tested modules at STC,
nominally 140 W [Watts]
T : Experimental Temperature [Celsius]
: Temperature at Standard Test Conditions (STC) 25oC
t : Time Stamp, (15 minutes was used for this test) [Hours]
Fig. 1. 7-module snow test platform at the Keweenaw Research Center
Fig. 2 below shows the yearly energy loss for the seven
module positions, while Fig. 3 presents the same results, but
limited to the snow season months of November-May. Fig. 2
shows that as the tilt angle increased from zero to 45 degrees in
the unobstructed cases, the yearly energy loss decreased from
34% to just 5%. However, in the case of obstructed modules,
that trend is not apparent, as the losses appear to be similarly
clustered in the 29-34% range. At low angles, the obstructed
case results are similar to the unobstructed case, and at zero tilt,
are deemed to be identical. Measurement error obscures some
of the true trend, but even at 45 degrees, the loss percentage
remains very high. Even though snow readily slides off the
Preprint: Heidari, N., Gwamuri, J., Townsend, T.,Pearce, J.M. (2015). Impact of Snow and Ground Interference on Photovoltaic Electric System
Performance. IEEE Journal of Photovoltaics 5(6),1680-1685, (2015). doi:10.1109/JPHOTOV.2015.2466448
steeply tilted module, if it remains piled up at the base it will
still cause a near-100% loss of power as long as even one cell
in the 36-cell string is shaded.
Fig. 2. Yearly energy losses due to snow for obstructed and unobstructed
photovoltaic modules located in Calumet, MI.
Energy loss for the 45 degree unobstructed module was
5.2%, while the loss for the obstructed module with the same
tilt angle was 31.3%. This represents a six-fold worsening of
lost energy (a 26.1% absolute annual loss) for this extreme
obstruction geometry. At the 30-degree tilt, the loss
magnification is less severe, just a three-fold difference, but still
represents an additional absolute annual loss of 18.8% (10%
and 28.8% for the unobstructed and obstructed cases,
respectively). Results for the 15-degree tilt were about the same
as for the 30-degree situation, and the worst-case loss of 34%
occurred for the zero-tilt case, as expected.
Fig. 3 shows that energy losses during the snow season
follow the same relative trend as for the yearly energy losses
depicted in Fig. 2. However, on a fractional basis, the energy
losses in the snow season (November - May in the Upper
Peninsula of Michigan) are higher due to the reduced winter
solar resource. The error for the measurements was small and
can be attributed to dust or snow accumulation on the
pyranometer. This error would bias the reported energy losses
to be slightly lower than they actually were. Finally, daily
energy losses in kWh from mid-October 2013 to mid-October
2014 for each module have been plotted, and the results for the
worst case (obstructed with the tilt angle of 45), and the best
case (unobstructed with the tilt angle of 45) are presented in
Figs. 4 and 5, respectively.
Fig. 3. Snow season (November to May in the Upper Peninsula of Michigan)
energy losses for obstructed and unobstructed solar photovoltaic modules in
Calumet, MI.
Fig 4. Daily energy loss, in kWh, for the obstructed module with the tilt angle
of 45 degree throughout the year in Calumet, MI.
Figures 4 and 5 show the daily effect of module snow cover
on PV system electricity generation capacity. It can be observed
by comparing the obstructed and unobstructed modules of the
same angle that the power for the unobstructed module (Fig. 5)
rapidly returns to full power after each snowfall event. Fig. 4,
on the other hand, shows significant and persistent losses
through the entire snowy season, especially in February and
March, as the module rarely became clear enough to deliver full
Fig 5. Daily energy loss, in kWh, for the unobstructed module with the angle
of 45 degree
Since the accumulation of snow on the modules has such a
strong effect on the performance of the modules [14], the proper
assessment of energy losses have become important for
improving the electrical performance of the system and
understanding its economic performance [21]. Many of the
studies that have investigated snowfall have been in less snowy
areas or have been conducted during low-snow periods. For
example, in [21], 70 modules with different technologies
oriented at different angles were monitored for two winters near
Toronto, Ontario, Canada to obtain energy losses. Yearly losses
ranged from 1-3.5%, which is small in comparison to the
present study, which finds yearly losses ranged from 5-34%,
Preprint: Heidari, N., Gwamuri, J., Townsend, T.,Pearce, J.M. (2015). Impact of Snow and Ground Interference on Photovoltaic Electric System
Performance. IEEE Journal of Photovoltaics 5(6),1680-1685, (2015). doi:10.1109/JPHOTOV.2015.2466448
indicating that energy losses in the Michigan UP region are
significantly higher than other regions with typically half of the
normal snowfall, like Toronto. It should be noted the years for
the Ontario study were abnormally warm and had little snow.
Townsend and Powers conducted a study in Truckee,
California, which receives about 200 inches of snow annually.
Data were obtained at three tilt angles for pairs of modules, one
of which was kept clean and one which was allowed to gather
and shed snow as prevailing weather conditions dictated. The
snow-exposed modules were mounted about 0.5 m above grade,
so pile-up interference happened often, but not always [15].
Data were also available for a similarly oriented system located
just 3 km away, but which had no ground interference. The
annual losses were found to be 6% for the no-interference, 35-
degree tilt system. These losses increased to 13%, 17%, and
26% for the test station’s angles of 39, 24, and 0 degrees,
respectively. These values are in agreement with the results
from the current study. Other studies found that annual snow
losses for a low profile system can easily reach or exceed 15%.
Even for an unobstructed, higher slope (28 degree) roof mount
system, the losses, while smaller, could still range from 0.3-
2.7% [15-22].
In order to improve performance of the PV systems in snowy
climates like this region, obstructed PV systems should not be
used, unless heavy snow-related losses are viewed beforehand
as acceptable or a method of clearing them is deployed. This
will, for example, limit some rooftop applications, as in this
area they can result in a yearly energy loss of 30% even for high
tilt angles. The results of this study also indicate that the
physical orientation and electrical stringing of the modules is
important. For example, when the modules are partially covered
with snow (as the obstructed modules are on the right of Fig. 1),
the current was decreased by a much larger percentage than the
percent of module area that the snow covered. In this study, the
modules were all oriented in portrait layout, resulting in the by-
pass diodes becoming ineffective during periods of partial
shading. This affected the output power of modules giving the
worst case scenario of power loss of up to 92% (or more,
depending on the thickness of snow cover) [28]. This problem
could be partly alleviated by orienting the modules in landscape
format. Landscape format enables bypass diodes to nominally
skip one-third of the obstructed cells at a time, and if the micro-
inverter or string inverter can operate at a reduced dc input
voltage, the system can operate. However, this study was not
constructed to quantify this more shade-tolerant geometry and
future work is needed to quantify this loss. [29].
At the KRC site, the pyranometers were heated to help melt
off the snow, and technicians were available to clean the
pyranometers after a snow event. The data were screened to see
if there were occasions when the pyranometers were covered
with snow. This was done by comparing readings of sun-facing
pyranometers (located at 0, 15, and 30, and 45 degree modules)
with the readings of a downward-facing pyranometer (from the
back of the elevated 45 degree module). The main purpose for
this pyranometer is to serve as a quality check against irradiance
measurements made on the sun-facing front sides of the frames.
The rear-facing module is shielded from snow and during
daylight hours should always read a small positive number. If
the down-facing pyranometer had a higher value than the
readings of a sun-facing pyranometer, it was likely because the
sun-facing pyranometer was being affected by snow. In order
to compare the readings, whenever the reading of the sun-facing
pyranometer was less than 90% of the reading of the
downward-facing pyranometer, then the sun-facing
pyranometer was assumed to be covered with snow. The hours
that pyranometers were covered with snow in the winter were
found to be 2, 13.5, 12, and 1.5 hours for pyranometers located
at the 45, 30, 15, and 0 degree modules respectively. There were
also times that pyranometers were covered with snow for 15
minutes or half an hour during snow fall events and were then
either cleaned or self-cleaned by wind, but these brief, low-to-
zero irradiance periods were of trivial numerical impact on the
analysis and were not considered among the total hours that the
pyranometers were deemed to be covered with snow.
Future work is also necessary for investigating how snow
affects low-concentration systems, which have been proposed
[30]. In these setups, a reflector is attached from the back top of
one row of modules to the front bottom of the next. Normally
all reflectors are flush. If the reflectors are utilized at the back
of the modules to enhance system electrical generation [31,32],
they will need to be spaced out far enough from the modules to
allow for snow to slide off.
Finally, all systems could benefit from an active method to
clear snow. Thus future work is needed to quantify the
effectiveness of different forms of cleanings such as melting off
the snow [33,34], chemical coatings [35], using squeegees [36],
and tennis balls divots to catalyze clearing [37] to reduce the
snow-related energy losses. This work involves experimental
and economic analysis of these snow removal techniques.
In this paper, energy losses of PV systems with different
architectures and tilt angles were quantified for a test site
located in Calumet, Michigan. It was seen that energy losses
due to snowfall are significantly dependent on the tilt angle and
the degree of ground interference. The study indicated that
annual energy losses decreased dramatically, from 34% to 5%,
as tilt angle increased from zero to 45 degrees for unobstructed
systems. For obstructed systems, annual energy loss hovered in
the 30-34% loss range, regardless of tilt angle. This suggests the
role of ground interference varies from no impact on flat-tilt
systems to a six-fold worsening for 45-degree tilt systems. This
one-year study (2013-14) showed that snow-related energy
losses ranged from 5% to 12% for three elevated modules and
from 29% to 34% for comparably tilted modules mounted next
to the ground. The 2013-14 snow season was slightly higher
than the 5-year average preceding it but slightly lower than the
40-year average, so future losses for this location should be
roughly comparable to this study’s findings. Current results
serve to inform PV system design and optimizations in this and
other locations with similar weather patterns. The study is still
ongoing to better home in on long-term expected performance.
It was found that proper assessment of energy losses due to
snowfall can significantly improve understanding of system
economics and also highlight possible ways to improve
performance by actively cleaning the modules. It can be
surmised that in this region, higher tilt angles of around 45
degrees and unobstructed snow shedding geometries are
Preprint: Heidari, N., Gwamuri, J., Townsend, T.,Pearce, J.M. (2015). Impact of Snow and Ground Interference on Photovoltaic Electric System
Performance. IEEE Journal of Photovoltaics 5(6),1680-1685, (2015). doi:10.1109/JPHOTOV.2015.2466448
recommended in order to keep annual energy loss to an
acceptable level.
The authors would like to thank the generous support of the
Keweenaw Research Center and DNV GL for materials and
labor to perform this work.
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Preprint: Heidari, N., Gwamuri, J., Townsend, T.,Pearce, J.M. (2015). Impact of Snow and Ground Interference on Photovoltaic Electric System
Performance. IEEE Journal of Photovoltaics 5(6),1680-1685, (2015). doi:10.1109/JPHOTOV.2015.2466448
Negin Heidari received her bachelor’s
degree in Electrical Engineering from
Azad University of Kerman.
She is currently a Master student at
Michigan Technological University.
Her research activities include the
investigation of impact of snow and
ground interference on the performance of PV systems, liability
of greenhouse gas emissions, energy production calculation for
large scale PV systems, modeling and simulation of micro-
grids, wind turbines, and batteries.
Jephias Gwamuri was born in Lupane,
Zimbabwe, in 1970. He received his
B.S. degree in Physics and Electronics
from ISP “Enrique Jose Varona”, Cuba,
and his M.Sc in Lasers and Applied
Optics from NUST, Bulawayo in
Zimbabwe in 2004. He is currently
pursuing his Ph.D. degree in material
science and engineering at Michigan Tech, Houghton, MI.
From 2006 to 2012, he was a lecture at the National
University of Science and Technology, Bulawayo, Zimbabwe.
Since 2012, he has been a PhD research fellow with the Material
Science and Engineering Department, Michigan Technological
University, Houghton. His research interests include novel thin
film PV devices, renewable energy technologies, energy
efficiency and sustainability.
Mr. Gwamurir was a recipient of the SPIE best student
poster presentation and OSA student award. He also received
the Fulbright Science and Technology award PhD fellowship
in 2012.
Tim Townsend received his B.S. in
thermal & environmental engineering
from Southern Illinois Univ.-Carbondale
and his M.S. in mechanical engineering
from the Univ. of Wisconsin-Madison.
He performed O&M and monitoring for
over a decade at the landmark PVUSA
utility-scale PV demonstration project in
Davis, CA, authoring several conference
papers stemming from that project. He
has provided PV training for over 2,000 journeyman
electricians, and contributed (as principal author) the PV
Systems chapter of the Handbook of PV Science and
Engineering (2nd ed., Wiley & Sons, 2011). In 2005, he
established today’s common style for PV Independent
Engineering (IE) analysis and reporting, including applying
PVsyst as the preferred modeling platform for aiding investor
decision-making. Part of his recent and ongoing IE work has
included designing a PV snow loss experiment at Truckee, CA;
this resulted in the first and still sole model for predicting
monthly PV snow loss [15] and was the impetus for this paper
with MI Tech.
Joshua M. Pearce received his Ph.D. in
materials engineering from the
Pennsylvania State University.
He then developed the first
Sustainability program in the
Pennsylvania State System of Higher
Education as an assistant professor of
Physics at Clarion University of
Pennsylvania and helped develop the
Applied Sustainability graduate
engineering program while at Queen's University, Canada. He
currently is an Associate Professor cross-appointed in the
Department of Materials Science & Engineering and in the
Department of Electrical & Computer Engineering at the
Michigan Technological University where he runs the Open
Sustainability Technology Research Group. His research
concentrates on the use of open source appropriate technology
to find collaborative solutions to problems in sustainability and
poverty reduction. His research spans areas of electronic device
physics and materials engineering of solar photovoltaic cells
and systems, and 3-D printing, but also includes applied
sustainability and energy policy. Dr. Pearce is the author of the
Open-Source Lab: How to Build Your Own Hardware and
Reduce Research Costs (Elsevier, 2013).
... If modules with different measurements are used, the design can be adjusted to meet specific module requirements. The proposed racking design has a height of approximately 1.8m above the ground, ensuring a 500mm ground clearance-sufficient for snow sliding, even in the most extreme northern atmospheres [61]. A case study is presented where the racking structure is specifically designed for London, Ontario, with a latitude and longitude of 42.9849° N and 81.2453° W. 4 ...
Full-text available
The prohibitive costs of small-scale solar photovoltaic (PV) racks decreases PV adoption velocity. To overcome these costs challenges, an open hardware design method is used to develop two novel variable tilt racking designs. These are the first stilt mounted racking designs that allow manual change of tilt angle from zero to 90 degrees by varying the length of cables. The racks are designed using the calculated dead, wind and snow loads for Canada as conservative design for most of the rest of the world. Structural capacities of the wooden members are then ascertained and resisting bending moment, shear force, tensile force, and compressive force for them is calculated. A structural and truss analysis is performed to ensure that racking design with-stands the applicable forces. Moreover, implications of changing the tilt angle on the wooden members/cables used to build the system are also determined. The systems offer significant economic savings ranging from 1/3rd to 2/3rd the capital expenses of the commercially available alternatives. In addition, the racking designs are easy-to-build and require minimal manufacturing operations, which increases their accessibility. The stilt-mounted designs can be employed for agrivoltaic settings while allowing farm workers shaded ergonomic access to perform planting, weeding, and harvesting.
... If modules with different measurements are utilized, the design can be adjusted accordingly to meet the specific module requirements. The racking design proposed has a height of approximately 2m above the ground thus ensuring a 500mm ground clearance, which is enough to ensure snow sliding in even the most extreme northern atmospheres [98]. The structure is designed for Kelowna, Okanagan Valley, British Columbia, with a latitude and longitude of 49.8880˚N and 119.4960˚W. ...
Full-text available
Using a trellis to plant vegetables and fruits can double or triple the yield per acre as well as reduce diseases/pests, ease harvesting and make cleaner produce. Cultivars such as cucumbers, grapes, kiwi, melons, peas, passion fruit, pole beans, pumpkins, strawberries, squash, and tomatoes are all grown with trellises. Many of these cultivars showed increased yield with partial shading with semi-transparent solar photovoltaic (PV) systems. To further increase the efficiency of trellis-based growing systems, this study investigates novel low-cost, open-source, sustainable, wood-based PV racking designs for agrivoltaic applications. Design calculations are made to ensure these racks exceed Canadian building code standards, which with snow loads surpass those of most of the world. A complete bill of materials, fabrication instructions, and proof-of-concept prototypes are provided for three system topographies (sloped, T-shaped and inverse Y) along with economic analysis. In addition, to being cost competitive, the designs can act as trellis supports and be used for irrigation/fertigation purposes. The results indicate that these racking structures have enormous promise both agriculturally and energetically. If employed on only grape farms inside Canada, 10 GW of PV potential is made available, which is more than twice the total current installed PV in Canada.
... Hotspot When the electrical properties of series-connected modules or cells of PV strings become mismatched, a phenomenon known as a hotspot occurs in PV cells and modules (Mellit et al. 2018). Hotspot fault is caused by a long-term hotspot (Wendlandt et al. 2010;Gwamuri et al. 2015;Davarifar et al. 2013a;Appiah et al. 2019). ...
Solar energy as a source of clean and renewable energy generation has gained traction over the years as an alternative to conventional fossil fuels. This is as a result of the search for permanent and effective solutions to the environmental issues such as environmental pollution, global warming and greenhouse gas emission affecting our planet. Solar photovoltaic sys‐ tem is one of the technologies developed to harness solar energy which is in abundance across the globe. This technology however, has operational and maintenance setbacks and requires close and constant monitoring to maintain highly effective generation of energy. Engineers, researchers and other stakeholders in the field have over the years proposed and developed various operation and maintenance strategies designed to help solar photovoltaic systems maintain high generation efficien‐ cies. The current study is an elaborate review of various strategies and methods proposed in literature and the effects of these strategies on overall system performance. It examines common solar photovoltaic system faults and the strategies or methods proposed by experts to mitigate these faults. The reviewed methods are organized in groups based on their functionality and the manner in which they detect faults in solar photovoltaic system operations.
... Though the authors address the power outage issue of the energy system, this study is mainly related to the large scale/regional power system and didn't comprehensively assess the energy storage's role in response to potential power outages that may occur with diverse duration and frequency. Various studies experimentally investigated the relationship between snow-related events and energy loss under the diverse solar panel architecture and tilt angle scenarios [36][37][38]. The studies revealed that the impact of severe weather events could be reduced with increased tilt angles. ...
The power supply from solar and wind generators is not only inherently variable but also prone to failure due to rare-weather related events, i.e., hailstorms, icing. Current system sizing strategies often consider system reliability or resilience but rarely consider them simultaneously. Here, we proposed a sizing approach for an off-grid power system to supply a minimum power threshold (L th) during power disruption events. The L th concept ensures blackout avoidance and enough dispatchable stored energy during power outages. We developed several scenarios with 4-to 24-hour simulated outage events occurring multiple times per year. After sizing a system, designs are tested by simulating the systems' operation based on data containing stochastic outage events. The resulting lost load is recorded to assess system reliability and resilience. Results showed that, regardless of outage frequency, total annual stochastic outage durations up to 32 h did not affect the optimal capacities of system components while ensuring the same reliability level. However, system capacities increased by up to 90% when the annual outage duration increased to 144 h. Meanwhile, introducing a minimum power threshold, Lth = 0.97, further increased the renewables generation and storage capacity up to 50% and 7%, respectively. Systems' resilience tests showed an 80% chance of a system designed with the Lth approach to withstand the prolonged stochastic power disruptions, while this value is only 25% for the systems designed using the conventional approach.
... 3 For sub-optimally designed systems, snow has been shown to result in annual losses up to 34% in an exceptionally snowy area (on an island in the Upper Peninsula (UP) of Michigan in the middle of Lake Superior). 4 Another study in the UP region found single digit losses of the annual generation. 5 Despite the fact that most such studies are conducted in some of the snowiest regions on Earth, 6-8 snow losses generally represent less than a 10% annual energy loss. ...
Full-text available
Snow loss estimations of solar photovoltaic (PV) systems in northern latitudes are important as project financing requires highly accurate energy generation estimates to provide long-term performance guarantees. As the climate changes, annual snowfall is changing. This study quantifies the losses to potential PV electricity generation due to snow, for all areas of the Northern Western Hemisphere now and for 2040, 2080 and 2100 for climate change scenarios SSP126 and SSP585. Results show in 20 years even in the most optimistic SSP126 scenario many areas in the northern U.S. and southern Canada will be reduced below 5% snow losses. In the more pessimistic SSP585 scenario, heavy snow regions become nearly snowless. Overall, climate change is substantially reducing snow losses for PV systems over most of North America. As such the time dependent reduction in snow losses for a PV in northern latitudes should be included in modeling of the life cycle performance.
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In this project, intended photovoltaic installations on the campus area of Luleå University of Technology are cost–estimated, designed and mapped based on solar power in northern conditions. An increased precipitation of snow and low solar angles are the main factors influencing the energy yield from PV installations in northern conditions. The reduced irradiation during winter results in a power production corresponding to only a few percent of the production during summer. Snow shading can lead to a 30% annual production loss and is strongly correlated to module tilt and placement. The roof surfaces selected for the installations have shown good potential regarding yearly irradiation based on modeling, simulations, solar mapping and photography. The modules selected in the project are monocrystalline moduls in half–cell design from Trina Solar, Longi Solar and Q–cells. Placement has been made in a landscape position with southern orientation. Simulated production for the A–house installation was 260 MWh, B–house 200 MWh, C–house 190 MWh, E–house 310 MWh, F–house 450 MWh and Polstjärnan 80 MWh. Total annual production for the campus has been calculated to approximately 1,5 GWh. The total cost for the installation of each building was estimated for the A–building 1,4 MSEK; B– and C– building 1,1 MSEK; building 1,7 MSEK; building 2,4 MSEK and Polstjärnan 0,4 MSEK. The total cost for all the installations was estimated to 8,1 MSEK with a payback time estimated at 10 years. The most feasible case in terms of produced solar power in relation to total investment cost is the modules from Q–cells. The priority order for the construction of each installations in descending order is: A–house, F–house, E–house, C–house, B–house and Polstjärnan based on availability and profitability. Simulated production in relation to the buildings’ electricity demand shows that storage and feedback to the electricity grid is not relevant for the roof–mounted installations in the project. To cover the electricity demand with self–produced solar power, additional ground–mounted installations and improved conditions for roof installation in the event of new constructions and renovations are recommended.
The U.S. Department of Energy Zero Energy Ready Home program has been nudging builders toward net zero since 2013 and > 9700 homes are now certified. Measures chosen by builders to hit net zero with all-electric homes include framed 2×6 24 inch on center or SIP walls and central heat pumps. Builders achieved DOE ZERH certification at an average added cost of $10,500 without PV or $25,000 with PV over code homes. Many all-electric homes achieved net zero with a net gain to homeowners where the added cost to build a ZERH is outweighed by the monthly energy savings; in some cases the net gain is > $200/month over a 30-year mortgage. A calculated example of PV payback in cloudy Burlington, Vermont, USA, shows for a 2000-ft2 home with an oversized PV system and no credits, the 10.5-kW PV + 28.8-kWh battery pays for itself in just 19.4 years.KeywordsNet zero energyNet zero carbonResidential constructionElectrificationSolar battery storage
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Invisible power generation by natural and artificial light enables sustainability by onsite‐power deployment, lower cost, and minimal burden on the built environment. However, dark, opaque photovoltaics limit light utilization in a transparent way. Herein, it is proposed that the active energy window (AEW) invisibly features power production, providing higher freedom for onsite power generators in window objects without limiting human vision. The AEW has a transparent photovoltaic (TPV) for onsite power and a transparent heater (TH) to remove the effects of shadows from snow and recover the power lost. Moreover, a heating function is applied to remove the effects of weathering related to snow. The proposed prototype integrates a TPV‐TH, offering ultraviolet (UV)‐blocking, daylighting, thermal comfort, and onsite power with a power conversion efficiency of 3% (AM1.5G). Field‐induced transparent electrodes are applied to the TPV‐TH and designed considering the AEW. Owing to these electrodes, the AEW ensure a wide field‐of‐view without optical dead zones, ensuring see‐through vision. The first TPV‐TH integration is performed into a 2 cm²‐window that generates onsite power of 6 mW and has an average visible transmittance of ≈39%. It is believed that light can be utilized with comfort through the AEW in self‐sustainable buildings and vehicles.
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The use of low optical concentration with planar reflectors represents a relatively simple method for improving solar photovoltaic (PV) specific efficiency. A coupled optical and thermal model was developed to determine the effects on yearly performance of a planar concentrator on array-scale solar PV installations. This model accounts for i) thermal, ii) angle of incidence, iii) reflectivity, and iv) string mismatch loss mechanisms in order to enable informed design of low optical concentration systems. A case study in Canada is presented using the model and the simulation results show that a planar reflector system installed on a traditional crystalline silicon-based PV farm can produce increases in electrical yield from 23-34% compared to a traditional optimized system and thus represents a potential method of achieving practical gains in PV system yield.
Technical Report
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This report summarizes the uncertainties associated with the prediction of long-term photovoltaic (PV) yield. The report addresses mainly uncertainties facing large-scale PV developers, although some of the conclusions may also be applicable to small systems. The uncertainties facing developers include factors such as expected yield, government policies and decisions, issues related to permitting, siting and grid connection, cost, availability and quality of equipment, and financing and legal matters. They can differ depending on the type of installation planned (large or small) and the kind of mounting structure (ground-mounted or building integrated). Uncertainties can be reduced, for example, by providing more clarity in policies regarding PV systems and grid connection (e.g. feed-in tariffs, domestic content, municipal taxes), and simplifying permitting requirements or making them more uniform across local jurisdictions.
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Photovoltaic systems are often installed in climates with considerable amount of snowfall and freezing rain in winter. It has been observed that the snow accumulation on a solar panel affects its performance and decreases the energy output. Snow on solar panels should be cleared as soon as possible to generate the maximum power. A low cost method of snow detection on solar panels found on field tests is proposed in this paper. The designed system is based on a low cost open-source Arduino Uno microcontroller that measures voltage and current output of a solar panel, and output of a LDR representing the irradiance. Arduino is also connected to a WIFI network and can send messages over the internet. Based on the sensors data, an algorithm is designed to accurately detect snow on solar panels and notify the owner via twitter about the current status. The designed low cost and very low power system has been tested in St. John’s, Newfoundland, Canada (47°34'28.9"N 52°44'07.8"W) for three months of winter 2014. This paper presents detail of the designed low cost alert system, algorithm and its performance results.
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The accurate prediction of yields from photovoltaic systems (PV) is critical for their proper operation and financing, and in northern latitudes the effects of snowfall on yield can become significant. This work provides methods for identifying snowfall effects from commonly collected performance data, and recommends a model to allow for prediction of these effects based solely on meteorological time series. The model was validated with data from two large-scale (>;8MW) operational PV plants. For the low tilt angles most affected by snowfall, this analysis was able to accurately predict both daily and mean values of snow effects. This methodology will enable system operators to utilize performance data to accurately identify and predict snowfall losses, and will assist system designers to optimize for the effects of snowfall on new system designs.
Conference Paper
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By-pass diodes are frequently used to minimize the effects of shading on PV module power generation. However, the functionality and effectiveness of these diodes depends on proper installation of a module with respect to potential shade sources. The lack of general manufacturer guidelines for proper module installation paired with the current level of technical knowledge held by many general contracting firms, may often lead to compromises in the electrical output of a photovoltaic system. The current produced by a single PV cell is directly proportional to the amount of solar irradiation that it is exposed to. However, in power modules many cells are wired in series allowing current flows to be limited by the most shaded cell. Testing of various module types with and without bypass diodes were performed in accordance with the experimental protocols developed at Rowan University's Center for Sustainable Design (CSD). I-V curves were obtained for a wide range of load impedances using a digital electronic load for both portrait and landscape modalities. Multiple test runs were performed at each shading increment for a single row of cells and the average I-V curve was calculated. Cell row shading was varied from 0-100% in 20 percent increments of cell row height. The study was conducted on multiple modules, covering the primary manufacturing types including: mono-crystalline, poly-crystalline and amorphous silicon. The results of this experimentation showed that the performance efficiency and functionality of by-pass diodes is highly dependent on the orientation of the PV modules. The circuital configuration of PV modules must be taken into consideration when designing a PV array. Depending on the orientation, bypass diodes can be rendered completely ineffective to the point that single cell row shading can reduce power output of the module by as much as 92% and also result in permanent damage to the PV modules.
Conference Paper
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With snowy locations becoming common for large photovoltaic (PV) installations, analytical models are now needed to estimate the impact of snow on energy production. A generalized monthly snow loss model is introduced here. The model was calibrated using ongoing measurements that began in December 2009 for three panel orientations at a BEW test station in Truckee, CA. Supplemental data for a fourth orientation from a nearby municipal PV system were also used to calibrate the model. Overall, the energy prediction error for the four panel orientations has been just 2% RMS on an annual rolling-average basis. Short-term errors are higher, a consequence of the variable nature of snowfall timing, quantity, and quality, and its complex interaction with temperature, wind, humidity, and ground interference. Despite these limitations, good quality, unbiased monthly loss estimates can now be used as inputs to the simulation programs PV investors rely on for decision-making. Loss profiles for three sample cities with prominent PV markets are provided. The samples have not been validated, but are included to show what the model predicts for other climates.
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Limited access to low-cost financing is an impediment to high-velocity technological diffusion and high grid penetration of solar photovoltaic (PV) technology. Securitization of solar assets provides a potential solution to this problem. This paper assesses the viability of solar asset-backed securities (ABS) as a lower cost financing mechanism and identifies policies that could facilitate implementation of securitization. First, traditional solar financing is examined to provide a baseline for cost comparisons. Next, the securitization process is modeled. The model enables identification of several junctures at which risk and uncertainty influence costs. Next, parameter values are assigned and used to generate cost estimates. Results show that, under reasonable assumptions, securitization of solar power purchase agreements (PPA) can significantly reduce project financing costs, suggesting that securitization is a viable mechanism for improving the financing of PV projects. The clear impediment to the successful launch of a solar ABS is measuring and understanding the riskiness of underlying assets. This study identifies three classes of policy intervention that lower the cost of ABS by reducing risk or by improving the measurement of risk: (i) standardization of contracts and the contracting process, (ii) improved access to contract and equipment performance data, and (iii) geographic diversification.
Scientific American is the world's premier magazine of scientific discovery and technological innovation for the general public. Readers turn to it for a deep understanding of how science and technology can influence human affairs and illuminate the natural world.
Subsidy programs, such as feed-in tariffs, designed to make renewable technologies cost competitive with fossil fuels in electricity generation, have been effective in a number of nations. However, these subsidies can become very costly and they raise questions whether there are fair conditions for competition for different energy sources. As a result even effective programs face an uncertain future, changes in political support following the financial crises in Europe and the United States have demonstrated. In the case of solar photovoltaic energy, cost declines resulting from market-expansion schemes and the overall reductions in the price of photovoltaic cells have been significant particularly over the past decade. Yet, they have still left solar power up to 50% more expensive than conventional options. As an alternative in this paper we describe a financing tool based on a pollution abatement methodology. In developing this levelized cost of electricity framework we build a methodology to examine, and then utilize, the social costs and impacts of energy generation technologies. We find that as a means to bridge the cost gap between current conventional energy process and retail solar energy, a program based on a Property Assessed Clean Energy (PACE) loan program would, in the short-term, be an effective tool to accelerate grid parity between solar and conventional energy generation and in the long-term provides a theoretically and financially sound alternative to subsidy-based incentives.
Photovoltaic (PV) power generation plays an important role in future sustainable energy mixes due to its high reliability, yield predictability and capacity for electricity production during peak demand when the electricity price is usually high. But still today, the economic viability of this technology depends on the subsidies usually granted by public authorities and electricity consumers. In the past, some subsidy schemes were inadequately generous, resulting in unsustainable PV growth rates that resulted in high public allowances. This study investigates the actual cost situation of the PV power generation for European countries, giving a perspective of the profitability until 2020 and identifies scenarios for which the technology can be financially self-sufficient without any subsidies. The study showed that the first grid parity was achieved in the Southern European countries. In Northern Europe, the PV cost-effectiveness depends highly on the national electricity price level and solar resources.