1. SOLAR POND TECHNOLOGY
WITH ISOBUTENE HEAT
EXCHANGER
By Okumu Hassid, Michael Odero and Oliver Wesonga

2. INTRODUCTION
• The project partners are Hassid Okumu, Oliver Wesonga and Michael Odero.
• Hassid Okumu is an Electrical and Electronic Engineering student at Jomo Kenyatta University of Agriculture and Technology. He is an Energy System enthusiast
and is keen to explore renewable energy resources in Kenya towards sustainable development.
• Oliver Wesonga is an Electrical and Electronic Engineering student at Jomo Kenyatta University of Agriculture and Technology. He has written a paper on
renewable solar pond technology for Kenya's coastal region for the 5th Africa Engineering Week and 3rd Africa Engineering Conference where he is to present the
same paper.
• Michael Odero is an Electrical and Electronic Engineering student at Jomo Kenyatta University of Agriculture and Technology. He has written a paper on
feasibility analysis on harnessing oceanic resources for power generation for the 5th Africa Engineering Week and 3rd Africa Engineering Conference where he is
to present the same paper.
• The three partners are keen to explore solar pond technology using isobutene as the working fluid with an aim of realizing affordable clean energy.

3. INTRODUCTION
• Solar energy is a form of renewable energy whose exploitation is on the rise given the rise of the fossil fuel prices. Solar is advantageous compared to
most of the other forms of energy since it does not have harmful emissions. There are various ways of obtaining solar energy one of them being the
use of solar ponds.
• A solar pond is a mass of shallow water about 1 to 2.5 meters deep with a wide collection area that serves as a heat trap. The pond has three distinctive
zones and incident solar energy is collected and stored at temperatures of about 80-100 °C. Solar pond can be used for desalination, heating and
generation of electricity.
• For power generation, the heat in the solar pond is extracted through a heat exchanger. Power is then generated through an organic Rankine engine
generator operated by a working fluid. The working fluids currently being used in organic Rankine cycles include toluene, r-236fa, r-236ea and r-
245ca. Isobutene have been used in the binary flash in geothermal plants and can thus be used as a working fluid in solar ponds. Isobutene has a
boiling point of -6.9 °C at a vapor pressure of 39 mmHg.
• Electricity generation using solar ponds is sustainable, operation and maintenance cost is minimal due to its renewable nature.
• There has been an increase in the demand for fossil fuels for power generation and there are worries that the fossil fuel deposits may be depleted in the
near future in case their usage is not monitored. Focusing on renewable energy and hence the solar pond technology will reduce the demand for fossil
fuels as it is derived from natural resources.
• Solar pond technology produces little or no emissions and wastes in the form of carbon dioxide and other chemical pollutants. Using isobutene also
makes the system to be ecofriendly since isobutene is not harmful to aquatic life in case it is accidentally spilled off to oceans for solar ponds located
close to the sea.
• The solar ponds can be used for desalination purposes. There is a vast supply of water in the ocean though its use is limited due to its salinity. Fresh
water can be obtained from the solar pond and thus its utility can be increased mainly when used in coastal regions.

4. PURPOSE
• According to the Least Cost Power Development Plan, the Kenyan policy makers have had a rising interest in solar energy due to the rising prices of fossil fuels.
Solar energy is considered to have low emissions and high efficiency of conversion to electricity. Kenya has a daily average radiation of 6 kwh/m2 throughout the
year in more than 28,000 km2 land and some regions have a global horizontal irradiation (GHI) of 2,400 kwh/m2/year making it a continuous and reliable source
of electricity generation.
• Solar technology have been in the past been harnessed through solar photovoltaic cells and concentrated solar thermal. Solar photovoltaic panels are the most
commonly used and with the M-Kopa initiative have ensured that most Kenyan households use solar PV. Photovoltaic panels are however criticized for their very
low efficiency. The most efficient solar PV is currently around 18-20%. Concentrated solar thermal plants have been criticized for the unchecked impact they
have on the ecosystem mainly flying animals that can be easily burned by the heat generated.
• Solar pond have been used in the past and the most notable one is the one located in Beith Ha’arava in Israel. Solar ponds have been in the past used for
desalination for obtaining fresh water, heating, drying of crops and power generation. In Africa, Egypt have embraced the technology along the Nile River.

5. Direct normal solar radiation in
Mombasa as per LaRC data
MONTH DNR (KWh/𝐦 𝟐
)
JANUARY 5.54
FEBRUARY 5.61
MACHR 4.92
APRIL 4.47
MAY 4.11
JUNE 4.32
JULY 4.33
AUGUST 4.26
SEPTEMBER 4.73
OCTOBER 4.71
NOVEMBER 4.94
DECEMBER 5.28
AVERAGE 4.76

6. EXAMPLES OF SOLAR POND PLANTS
Plant Area (meters
squared)
Power Output Temp
(degrees
Celsius)
Depth Comments
Tabor 1500 6 kW 90 2.0m Decommissio
ned due to
leakages
Ein Baqek 6250 150 kW 73.4 2.55m
Collins and
Frederiksen
2100 20 kW 80 2.1m
Swift, Reid
and Boegli
3355 100 kW 3.0m
Pacetti &
Pricippi
25000 50 kW 4.0m Was meant
for water
treatment
Venegas 1375 10 kW 3.5m
Beith 60000 5MW 4.3m

7. PROJECT DESCRIPTION
The factors that make this project unique are as listed below
• Despite the fact that solar pond technology is a viable source of energy it is unique to Kenya since it is not mentioned
anywhere in the least cost power development plan (LCPDP) and in the generation and transmission masterplan, Kenya. It is
therefore a project that is unique in the country
• The current project that utilize solar pond technology are utilized without the use of isobutene as a heat exchanger.
Isobutene increases the efficiency of the technology a factor that has been used in other technologies such as geothermal
but that has not been utilized in any solar pond project.
The objectives of the project is
• To utilize solar energy available in large supply in a more efficient way than the available technologies
• To incorporate the use of isobutene in solar ponds
• To demonstrate the viability of solar pond technology in the country

8. PROJECT METHODOLOGY
• A solar pond is a shallow body of water which acts a collector of solar energy with integral heat storage capabilities. Solar ponds are mainly of two
types, convective and non-convective solar ponds. Convective solar ponds include shallow solar pond and the deep salt less solar pond
• Non convective solar ponds are of three types, salinity gradient solar pond, membrane solar pond and polymer gel layer solar pond. The salinity
gradient solar pond is made up of a pool of water of about 1-5 m depth and constructed in such a way that the pond contains dissolved salts
• In any liquid, heat is transferred through convectional currents. When sunlight falls on a liquid contained in a container whose bottom is painted
black, the water at the bottom becomes hotter than the rest of the water. This makes it less dense than the rest of the water and it therefore rises to the
top where it is cooled.
• In a salinity gradient solar pond, the water at the bottom of the solar pond is made denser than the rest of the water by the introduction of salts in high
concentration. In this way. When the water at the bottom is heated by the sun it becomes hot but cannot rise to the top of the pond and be cooled since
it is denser. This water therefore continues to absorb heat from the sun
• In addition the water at the bottom is insulated from that at the top and therefore there is very minimal heat loss form the solar pond

9. PROJECT LOCATION
The solar pond can be constructed anywhere since it makes use of the energy of the sun. For efficient operation, the solar pond should be
constructed in a place that has the following properties
1. Be constructed close to the place at which the solar thermal energy is to be utilized this is important to reduce the transmission losses
for the thermal energy
2. The solar pond involves the use of a substantial amount of water. For this reason it is important that the solar pond is located in a place
where there is a lot of water available for flashing
3. The thermal conductivity of the soil should not be too high. A high soil conductivity will mean that the system will lose heat by thermal
conduction
4. The water table in the area that is selected should not be too close to the surface

10. MARKET GAP
The market gap best served by this project is as listed below
• Can be a source of electrical and thermal energy for islands, the rift valley and the coast
• Water heating in hotels and lodges
• Domestic water heating for estates

11. POND CONSTRUCTION
• There are two main types of solar ponds, convective and non-convective solar ponds. The project will be implemented using non convective solar
pond technology. A non-convective solar pond is a large shallow water body with a depth of between 1-5 m deep and built in such a way that the
temperature gradient is reversed from the normal.
• In this way the temperature of the solar pond can be kept as high as 95 0c. One of the ways is by use of a density gradient.
• The area of the pond is determined based on the amount of heat energy needed. A circular solar pond would be perfect because it has a lot less heat
loss. Due to construction complexities it is usually preferred to construct a square pond. For very large ponds, the shape of the pond is not a big
determinant since it does not reduce the heat loss
• The pond is made up of three zones. The surface, gradient and the storage zone are 0.5m 1m and 1m respectively. The surface layer can be reduced
depending on the wind in the area
• The construction of the solar pond construction is similar to that of a water reservoir. The slope of the pond is between 1:1 and 1:3 depending on the
type of the soil. After the excavation is done and the bonding is done one must ensure that there are no sharp objects that can damage the liner when it
is being laid.

12. POND CONSTRUCTION
• A liner is then used to prevent the leakage of the salt. There are cases where the solar pond is not lined because the soil in that area has a low
permeability. Most of the liners used are polymeric liners. After the installation of the liner it is important to have a method of detection of leakages in
the solar pond
• After the liner is installed the pond is filled with water to a depth equal to the thickness of the storage zone and half the gradient zone. Salt is directly
dumped into the pond. The concentration of salt in the storage zone is between 200 and 300kg/m3
• The normal method of introducing the gradient zone is by the introduction of fresh water. The fresh water is introduced at eth interface between the
storage zone and the gradient zone. The fresh water since it is of a lower density rises to the top and reduces the density of the layer above the
injection point.
• More fresh water is added above the gradient zone to introduce an upper mixed layer with a thickness of between 30 and 50 cm

13. OVERVIEW OF SOLAR POND PLANT

14. PROCESS FLOW DIAGRAM

15. POND OUTPUT ENERGY
• The temperature range for the storage region is between 800 and 950 C. The thermal energy absorbed by the system to raise its temperature from the
normal ambient temperature to a temperature of 950 C can be calculated as below
• Thermal energy absorbed by the pond
𝑄 = 𝑚𝑐𝛥𝑇
• M is the mass of the concentrated salty water, C is the specific heat capacity of salty water and 𝛥𝑇 is the change in temperature for the water. The
specific heat capacity of fresh water is 4200 J/kg/K. If the water is made salty, the specific heat capacity reduces. The higher the concentration of salt
the lower the specific heat capacity.
• Taking a mass of 1 kilogram and a specific heat capacity of 3700 j/kg/k for a 10% concentration of sodium chloride we have an energy of
𝑄 = 1 𝑥 3700 𝑥 95 − 30
𝑄 = 240500 𝐽/𝑘𝑔

16. POND OUTPUT ENERGY
• The amount of energy absorbed from the sun is highly dependent on the total amount of water in the pond. The amount calculated above represent the
amount of energy absorbed per kilogram of water in a day if the temperature of water rises from 300C to 950C. Once the temperature of the pond
reaches its maximum the temperature remains constant for a long period of time since it is insulated

17. POND EFFICIENCY
The efficiency of the solar pond is determined from the rise in temperature in the solar pond
If the temperature of the solar pond is raised from 20 -100 degrees celsius the efficiency of the pond would be
1 −
273+20
273+100
= 20%

18. ISOBUTENE HEAT EXCHANGER
Heat is extracted using internal or external heat exchanger. Internal heat exchanger is immersed in the storage zone. Being made of copper or plastic to
eliminate corrosion. However, for large ponds external heat exchangers are more convenient. Being made of stainless steel or titanium. Experiments have
however shown that copper heat exchangers are more reliable
The isobutene fluid flows within the copper or steal pipes used as either internal or external heat exchangers.
The properties of isobutene that make it suitable for use as a heat exchanger include
• It has a low boiling point
• It is not corrosive to the parts of the turbine and the heat exchanger material
• In case of spillages the liquid does not affect aquatic life
The only disadvantage of using isobutene is that it is explosive when exposed to air and therefore care must be taken to protect the system against the
exposure to light

19. SAFETY PRECAUTIONS
1. The solar pond would be completely fenced to prevent human beings and animals from getting into the pond area
2. The liquid isobutene is capable of building up electrostatic charges. The entire system must therefore be adequately grounded to prevent ignition
3. The handlers of the system should have protective gear to prevent eye and respiratory organ irritation
4. Since the liquefied gas is harmful to fish, algae and other water plants it should be properly handled to avoid harming the environment
5. The working fluid should be stored away from heat sources ignition sources, combustible materials, strong acids among others
6. Provision of elbow joints and vents to moderate the highly pressurized isobutene gas working fluid

20. EXPECTED RESULTS
• Based on the designs we expect to be able to design a solar pond that when implemented will produce 0.8 MW of electric energy.
• The power generated should be able to be connected to the national grid

21. CASE STUDY
The largest solar pond to be designed and constructed was on the shores of the dead sea at Beith Ha’arava, Israel. It has a capacity of 5MW
constructed in two phases; the first phase being 40,000 m2 and the second being two 10,000 m2 solar ponds. It has a depth of 4.3 m, a free
board of 0.7 m and a wall slope of 1:3. The wall has a thickness of 2.5 m to 2.8 m. The upper convective zone has a thickness of 0.3 m to 0.6
m and the non-convective zone is kept at a thickness of 1.2 m. The lining of the pond is made of polyethylene, clay and a series of high
velocity, low fluid volume jets for gradient formation and repair. The construction of the pond is estimated to be $7.1/m2.
To suppress wave formation due to wind, wire nets were installed every 10 m.
The heat harvested is used to rotate turbines and produces 5 mw of electric power. The system is coupled to the national electricity grid of
Israel. The annual pond efficiency was determined as 16%.
In Africa, a feasibility study has been carried out in Cairo, Egypt. The researcher considered Cairo as a suitable site due to its annual solar
radiation, land availability and the economic stability of Egypt as a country. The cost of the project is estimated to be between 8-10 million
Kenyan shillings and land is the main reason for the high cost of the project, accounting for more than 90% of the total project. The researcher
concludes that solar ponds are cost effective and simple to construct making it an ideal venture for developing countries.

22. CONTACT INFORMATION
HASSID OKUMU
EMAIL: okumuhassid@gmail.com
PHONE:+254719403099
OLIVER WESONGA
EMAIL: olivererastus@gmail.com
PHONE:+254734911092
PHONE:+254708665358
MICHAEL ODERO
EMAIL: michaelcodero3@gmail.com
PHONE:+254719403099