Monday, June 18, 2012

Solar Winter Edition Review: measurement of snow loss

Monday, June 18, 2012
In the past, PV modules were mounted installed in snowy climates portion of the small, off-grid array on very steep angle. This is done both to shed snow quickly and to maximize winter issue. Unfortunately this concedes too much be annual energy to a good design strategy for larger contemporary systems.

Systems tend to today's snowy climate PV, angle shallow enough make vulnerable to loss of snow are installed, and how PV plants in snowy locations more widespread analytical models are required, the snow on energy production estimate the impact.

Weather and array design factors influence the amount of snow loss. The quantity and quality (humidity) include snow, the recurrence pattern of storms and the later pattern of temperature, radiation, wind speed, wind direction and humidity weather factors. Array design factors can be essentially on orientation (fixed or track inclination, azimuth and Tracker rotation limits) and the surrounding geometry (open rack or building-integrated). Building features can also either help (e.g. melt) or inhibit (e.g. dam up or drift) natural snow to shed.

Nevertheless, a generalized monthly snow loss model is introduced here which, despite some restrictions will be shown, delivers high-quality, unbiased monthly loss estimates that now programs PV investors for decision making relies can be used as inputs for the simulation.

Lake Tahoe test rig

BEW engineering, Inc - a company of the DNV - set of three pairs of 175 WP poly-silicon Mitsubishi model PV-UD175MF5 PV modules at a fixed angle to 0 ° and 24 ° 39 ° on South side racks in Truckee, California, at the beginning of winter 2009-2010. The module pairs arranged far enough apart to prevent row shading on the winter solstice.

In the vicinity of Lake Tahoe station width is 39 ° and their height is 5900 (1800 meters). The Web site receives an average annual temperature of 200 inch (5 m) of snow.

A module of each pair is manually cleaned and heated thermostatically. The three un camped modules may collect naturally shed or snow and are lined with two feet (0.6 m) of similar material edge effects to minimize.

A data logger stores hourly records of the irradiance for the three angle, short-circuit current and temperature for each module together with air temperature and humidity. In the meantime an hourly webcam shots records snow depth and help with quality checks. A second source of data is a 125 kWP Truckee sanitary district (TSD) system two miles (3.2 km) South of the BEW railway station and in the sitting on the same level.

Losses are for the BEW rig snow measured as the difference between the modules clean and untreated in monthly amp-hours. For the TSD system losses are measured as the difference in the measured and predicted energy for an array always clean snow.

The VLB system is South at a fixed 35 ° tilt, similar to the paired sets of BEW test modules. Six feet (2 meters) above the ground are the lowest edge of 17 feet (5 m) long rows. While the District of this array manually clean it regularly to prevent that accumulate snow snow between the lines themselves plowing. This maintenance was particularly valuable practice because snow is removed from the array, even ground does not occur error. It is as if the array above ground is very high. In fact, the annual loss of energy as site TSD ground led twice errors at the site of BEW.

Calculate winter losses

Depending on the angle winter energy losses of 40-60% and annual losses of 12% - identified 18% in the first year of operation, although the data from the VLB system were not included. The first winter was statistically normal. The lost energy due to the accumulation of snow in the seven month winter season ranged from as little as 25% of the 39 ° inclination to less than 42% of the flat orientation. The project seasonal results to the loss in annual production of 12%, 15% and 18% for the 39 °, 24 ° and 0 ° tilts, respectively.

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