Solar Water Heater efficiency calculations

One Square meter calculations for ABSORBER area of Glass tubes of .047/.037/1.6/1500mm   (In one Sq .m 20 Glass rods are fixed)   
Diameter x Length x Number of tube  ( D X L X N )

• D= Diameter of inner glass rod
• L=Length of inner glass rod
• N=Number of glass tubes

           =  .037 x 1.4 x 20= 1.036 Sq.m2 of Glass evacuated Absorber area                                                                                            
Solar Collector (Glass rod area)performance can further be predicted with set of three performance variables mentioned below but in this assessment values mentioned are based on Absorber area.
Gross area,      = The area based on the outer dimensions of collector
Aperture area             = The area in which the solar radiation enters the collector

Absorber area  = The area which actually absorbs solar radiation and is surface area of                                       
                              inner glass rod
 The three performance variables for the solar collector efficiency are as follows        (for calculations, based on absorber area):

Conversion Factor:     h0 = 0.717 (2)       (Performance variable)
Loss Coefficient: a1 = 1.52 W/(m2K)      (Performance  variable)
Loss Coefficient: a2 = 0.0085 W/(m2K2) (Performance  variable)
Insolation level (G) in Watts/m2,
Ambient temperatures (Ta)
Average manifold temperature ™ are known.
These values give the value of (x)

   
Based on the ambient temperature, average manifold temperature and insolation level, we calculated the value for X.
Ambient temperature of 25oC

Average water temp [(Tinlet+Texit)/2] of 50oC
Insolation level of 800Watts/m2 (252Btu/ft2). . Value of X, therefore , is
x = (50-25)/800 = 0.03125
h(x) = 0.717 - (1.52 x 0.03125) - (0.0085 x 800 x 0.031252)
h(x) = 0.717 - 0.0475 - 0.0066 = 0.663
The solar conversion efficiency for that specific point in time and set of environmental conditions is 66.3%. That is: 66.3% of the energy provided by the sun is actually used to heat the water.

So  800 x 0.663 = 530.4 Watts of energy per m2 of absorber area will be used to heat the water.Solar Water Heater Collector area will provide 530 watts of Heat output
Based on above factors if
(G, Tm and Ta) are stable for a period of one hour, then 800 x 0.663 = 530.4 Watts of energy per m2 of absorber area will be used to heat the water (168Btu/ft2).
530.4Watts is equivalent to 456kcal, which could heat 100L of water by 4.56oC (20 Gallons by 10.9oF).

ANOTHER METHOD  by which Solar Water Heater collector  EFFICIENCY can be  assessed is as follow

All Solar collectors have common energy source,the SunThe performance of any system,therefore, depends on the conversion of Solar radiation into useful Thermal energy and transfers that energy to the hot water system.
The ability to convert Solar energy into Thermal energy is expressed by the optical efficiency of the system(No).
There are two factors (k1)  and (K2)that relates the system ability to transfer the energy gained.
                           N= No – K1 x Delta T/G - K2 x Delta T Square/G.
With above equation again Solar Water Heater Collector Area efficiency can be calculated and is approximately about 65%.for following set of Glass evacuated rod Collector Area

One Square meter calculations for ABSORBER area of Glass tubes of        .047/.037/1.6/1500mm   (With  20 Glass rods in one Sq .meter)