Exiom Solutions, a photovoltaic manufacturer, is interested to know if their photovoltaic panels are safe to touch even in the hot summer operating conditions. In the extreme conditions, these PV solar panels are exposed to up to 1000 W/m direct sun radiation. Based on previous measurements, it was found that about 9% of the solar radiation is reflected back to the sky when it touches the solar panel surface. The rest of the solar radiation is absorbed into photovoltaic cells. The efficiency of the cells is about 14.5% and the rest will turn into heat (spec. sheet and figures are attached on the next page). To consider the worst case scenario, an assumption is made that the back of the panels might be placed on a surface that does not transfer heat (assumed insulated) so all of the wasted heat has to be dissipated from the top surface of the solar panel. In a hot summer day, ambient air temperature might get to 110F (43.3c) while effective sky temperature is around -20C. Emissivity for the surface of this collector can be assumed 0.8. If the temperature all over the panel or panels can be assumed uniform under steady state operating condition, and neglecting natural convection effects, answer the following: a) On a very calm day (no breeze), what would be the temperature of the surface of this solar panel if only one panel has been mounted? b) is the safe-to-touch temperature of 65C violated? c) If wind is blowing with a velocity of 4 m/s on the surface of the panel, find the surface temperature (find it for both conditions if the longer side is alongside the wind direction vs. the shorter side and report two temperatures). d) If wind is blowing with a velocity of 8 m/s on the surface of the panel, find the surface temperature (again report two temperatures for both orientations). e) If 25 panels are attached to each other in a 5 by 5 arrangement without spacing (see figure), with 4 m/s wind velocity, what will be the surface temperature (both orientations)? f) is constant surface temperature a better assumption for this problem or constant heat flux? B)(bonus 70 points) This is in addition to 100% of the points. li.e. 910 points + 70 points) (In other words, ever without solving part 'g' you can get 100% in this exam). What will be the heat transfer coefficients and temperatures for parte if you want to repeat the calculation with constant heat flux assumption? Will you report different temperatures for leading edge vs. trailing edge? Where do you think the maximum temperature happen? On the leading edge, trailing edge or somewhere in the middle of the plates? Note: For each of the above parts, if the information you have is sufficient, calculate the desired variable. If the information is not sufficient, make the necessary but reasonable assumptions and proceed with your calculations to find them. Exiom Solutions, a photovoltaic manufacturer, is interested to know if their photovoltaic panels are safe to touch even in the hot summer operating conditions. In the extreme conditions, these PV solar panels are exposed to up to 1000 W/m direct sun radiation. Based on previous measurements, it was found that about 9% of the solar radiation is reflected back to the sky when it touches the solar panel surface. The rest of the solar radiation is absorbed into photovoltaic cells. The efficiency of the cells is about 14.5% and the rest will turn into heat (spec. sheet and figures are attached on the next page). To consider the worst case scenario, an assumption is made that the back of the panels might be placed on a surface that does not transfer heat (assumed insulated) so all of the wasted heat has to be dissipated from the top surface of the solar panel. In a hot summer day, ambient air temperature might get to 110F (43.3c) while effective sky temperature is around -20C. Emissivity for the surface of this collector can be assumed 0.8. If the temperature all over the panel or panels can be assumed uniform under steady state operating condition, and neglecting natural convection effects, answer the following: a) On a very calm day (no breeze), what would be the temperature of the surface of this solar panel if only one panel has been mounted? b) is the safe-to-touch temperature of 65C violated? c) If wind is blowing with a velocity of 4 m/s on the surface of the panel, find the surface temperature (find it for both conditions if the longer side is alongside the wind direction vs. the shorter side and report two temperatures). d) If wind is blowing with a velocity of 8 m/s on the surface of the panel, find the surface temperature (again report two temperatures for both orientations). e) If 25 panels are attached to each other in a 5 by 5 arrangement without spacing (see figure), with 4 m/s wind velocity, what will be the surface temperature (both orientations)? f) is constant surface temperature a better assumption for this problem or constant heat flux? B)(bonus 70 points) This is in addition to 100% of the points. li.e. 910 points + 70 points) (In other words, ever without solving part 'g' you can get 100% in this exam). What will be the heat transfer coefficients and temperatures for parte if you want to repeat the calculation with constant heat flux assumption? Will you report different temperatures for leading edge vs. trailing edge? Where do you think the maximum temperature happen? On the leading edge, trailing edge or somewhere in the middle of the plates? Note: For each of the above parts, if the information you have is sufficient, calculate the desired variable. If the information is not sufficient, make the necessary but reasonable assumptions and proceed with your calculations to find them
