1
Seat No.: Enrolment
GUJARAT TECHNOLOGICAL UNIVERSITY
ME SEMESTER II EXAMINATION WINTER 2018
Subject Code: 2722108 Date: 12-Dec-2018
Subject Name: Solar Energy Engineering
Time: 02:30 PM To 05:00 PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
Q.1

A combined solar and fuel system is used to meet the energy requirement for the society. The proposed collector having area 50 m2 will cost Rs.11,00,000/- and will be 90% financed over 20 years at an interest rate of 9%. The energy generated by solar system so as to reduce fuel purchase by 56%. The first year's fuel cost for a system without solar would be Rs.1,25,500/-. Fuel costs are expected to rise at 10% per year. It is expected that the equipment will have a resale value at the end of 20 years of 40% of the original cost. In the first year, extra insurance, maintenance, and parasitic energy costs are estimated to be Rs. 11,000/-. Extra property tax is estimated to be Rs. 22,000/-. These are expected to rise at a general inflation rate of per year. Extra property taxes and interest on mortgage are deductible from income for tax purposes; the effective income tax rate is expected to be 45% through the period of the analysis. Calculate the life cycle for this process over a 20 year period if the market discount rate is 8%. Use Present worth method to calculate the present worth of solar saving.
09

Calculate the reflectivity and transmissivity for the angle of incidence 75° on the solar pond surface. Take a refractive index for water relative to air =1.33.
05
Q.2

A water-heating flat-plate collector operates at a mean plate temperature of 70° C. Determine the time by which it will reach this temperature if there is no useful heat gain till that time. The following data is given: length of absorber plate 1.6 width of absorber plate 1.0 Number of covers overall loss coefficient 7.2 W/m2 combined convective and radiative top loss coefficient from absorber plate to glass cover 6.4 W/m2 combined convective and radiative top loss coefficient from glass cover to atmosphere 22.8 W/m2 for plate and tubes 4.5 for insulation 2.0 for glass cover 16 Volume of water in collector 2.1 liters, Mean plate temperature at 7:00 a.m. 14.9137 C.
07
2
Flux incident on
Average transmissivity
Ambient
Time
collector
absorptivity product
temperature
(a.m.)
IT

Ta
7 8
175
0.50
15.0
8 9
380
0.70
16.0
9 10
555
0.86
18.0
10 11
700
0.89
20.5

Derive the expression for the useful heat gain from the solar air-heater.
07
OR

Explain the testing procedure proposed by the National Bureau of standard and American Society of Heating, Refrigeration and Air-conditioning for Engineers for the liquid flat plate collector.
07
Q.3

Explain the concept of central receiver tower. In a central receiver tower, the height of the tower is 150 the rim angle is 50º and the diameter of the mirrors is 4.5 m. Find the size of the image formed by the outermost mirror at the receiver, the area of the absorber and the corresponding concentration ratio. Assume that mirrors are flat, and, dished. Take fraction of ground area covered 0.38 and total angular error 0.002 radians. Calculate the useful heat gain and number of reflectors for the following parameters: Average temperature of absorber tube 600° Ambient air temperature 30° Beam radiation 600 Average tilt factor for beam radiation 1.023, Overall loss coefficient 14.5 W/m2K, Transmissivity of receiver 0.89, Reflectivity of reflectors 0.87, Absorptivity of receiver 0.94.
08

Explain the working of solar dehumidifier with neat and clean sketch. Also state the advantages and disadvantage.
06
OR
Q.3

Explain in brief the concept of halocline for solar pond. Derive the expression to calculate the minimum concentration gradient to maintain the given temperature gradient at particular level in solar pond. Also draw the concentration and temperature variation along the length of solar pond.
08

Explain the working of Stirling cycle solar thermal power generation system with neat and clean sketch. Also state the advantages and disadvantage.
06
Q.4

Explain the various thermochemical energy storage reactions and the concept of double conversion of salt pair for the solar application. Also, explain with neat layout basic oxide hydroxide storage concept.
07
3

A researcher wants to calculate incidence angle for surface tilted at 30o with horizontal from the data available for horizontal surface in northern hemisphere Angle of incidence for horizontal surface 45.6o, Surface facing 10o East of South at location, Date 23rd December (Non leap year), Standard time of location: 12 p.m. Day length for horizontal surface: 10.7 hrs.
07
OR
Q.4

Explain the modeling and performance of natural solar water heater (NSWH). Calculate the useful heat gain form the NSWH for the temperature rise of 10 oC, collector area 4 m2, overall loss coefficient 4.2 m2 oC, collector efficiency factor 0.91, inlet water temperature 30 oC, ambient temperature 15 oC and solar radiation absorbed by collector 780 m2.
07

Explain the total solar radiation falling on earth surface.
Explain an attenuation of beam radiation in earth atmosphere with neat sketch.
03
04
Q.5

Explain the tracking requirement for the compound parabolic collector. Derive an expression for the solar swing angle with reference to equatorial plane.
07

Derive an expression of useful heat gain for compound parabolic collector.
07
OR
Q.5

Calculate the overall loss coefficient Ul for the receiver of a cylindrical parabolic concentrating collector system. The receiver consists of a selectively coated absorber tube with one glass cover around it. The following data is given: Absorber tube inner diameter 7.5 cm, Absorber tube outer diameter 8.1 cm, Glass cover inner diameter 14.4 cm, Glass cover outer diameter 15.0 cm, Emissivity of absorber tube surface 0.15, Emissivity of glass 0.88, Mean temperature of absorber tube 170° Heat transfer coefficient from glass cover to atmosphere 20.75 W/m2 Ambient air temperature 25° Wind speed 4 m/s.
09

Explain the term concentrator, receiver, aperture, concentration ratio and Optical efficiency for the cylindrical parabolic collector.
05