MULTIPLE EFFECT DISTILLATION OF SEAWATER WATER USING SOLAR ENERGY - THE CASE OF ABU DHABI SOLAR DESALINATION PLANT - Energy Research Developments: Tidal Energy, Energy Efficiency and Solar Energy - page 44

with summer months experiencing larger drops than winter months due to the sandstorm
prevailing mainly in summer months.

5. Control of heat collecting operation

The solar collector field is operated by the solar controller which uses a solar cell to
switch the heat collecting pump on and off depending on the solar radiation. The solar
radiation condition for pump startup, I on (kcal/hm 2 ), and shutdown, I off (kcal/hm 2 ), are
determined from the measured values of the heat accumulator outlet temperature, T w1 ( o C)
and the ambient temperature, T a ( o C) according to the relations:

I ≥ 5 × ( T − T ) − 25

on w 1 a

(44)

I < 5 × ( T − T ) − 10

off w 1 a

6. Heat collection amount from solar collector field

The heat collection efficiency is defined as the amount of heat collected divided by the
amount of solar radiation falling on the absorber plates of the solar collector field and is
expressed by the following formula:

2

η = α + β . x + γ . x (45)

c

where η c is the collector efficiency, α,β,γ are constant parameters and x is a variable defined
as:

1

− ( T + T ) − T

c 1 c 2 a

2

x = , T c1

'

I

t

and T c2 are the collector field inlet and outlet water temperature and I' t is the solar radiation
on the absorber plate.
The rate of heat collected, Q c , from the solar field is obtained from the equation:

'

Q = A . η . I = m . C .( T − T )

(46)

c c c t c p c 2 c 1

Using Eqs. 34 and 35 the collector outlet temperature can be obtained as follows:

2
2

− C − C − C C

2 1 3

T c =

(47)

2

C

1