Second International Conference on Electrical Engineering

25-26 March 2008

University of Engineering and Technology, Lahore (Pakistan)

978-1-4244-2293-7/08/$25.00 ©2008 IEEE.

Efficient Utilization of Solar Energy for

Domestic Applications

Noor M. Sheikh

Department of Electrical Engineering

University of Engineering & Technology, Lahore, Pakistan

deanee@uet.edu.pk Abstract: Shortage of energy is dangerously affecting the

economic growth of the developing countries. Oil, gas

and coal reserves are being depleted rapidly and are

affecting the environment. Embargo and safety

requirements limit the development of nuclear energy.

Renewable energy resources need to be embedded with

the conventional generation. A lot has been said and

done on solar energy. However emphasis has been on

the conversion to electricity using photovoltaic cells. In

the present work, it is proposed that efficient use of

solar energy would be to utilize it for direct heating and

cooling. Solar chillers based on solar heating coupled

with gas firing are proposed for urban houses. Solar

pumps for irrigation in the rural areas should be used.

This would reduce the demand of electricity hungry air

conditioners and diesel hungry tube wells.

Key words: solar energy, solar cells, solar

chillers

Introduction:

Per capita utilization of energy is a strong indicator

of development in a country. Energy divide between

developed and developing countries is widening. The

conventional sources of energy in the form of oil, gas

and coal are being quickly depleted and are becoming

costly. The hydel energy, though cheaper, is not

being harnessed due to geo political reasons and the

seasonal availability of water. Nuclear energy has

serious concerns regarding safety. The developing

countries do not have easy access to nuclear energy.

Contribution from renewable resources of energy is

gradually increasing both in developed and

developing countries for reasons of environmental

protection and shortage of conventional resources.

Wind and solar [1] energy has a great potential as

renewable energy options. In Pakistan metrological

studies have indicated a potential of wind energy in

the belt from Karachi to Hyderabad and along the

Mekran coast. Alternative Energy Development

Board (AEDB) in Pakistan has started with a 100

MW unit near Karachi [2]. Low duty cycle of wind

energy may not be able to

meet the peak requirements. Solar energy is a blessing

for the developing countries. Pakistan is lucky in this

regard. A lot of efforts have been put in this direction.

Main focus till now has been using solar cells for

generating electricity. The cost and availability of solar

cells is still prohibitive. The efficiency of conversion is

also low. A major utilization of electricity in domestic

and commercial applications in urban areas is for air

conditioning. In rural area a key application is to draw

underground water using tube wells running with

electricity. For these applications, a direct use of solar

energy is more efficient. It is suggested that solar

absorption chillers be used in such applications in urban

areas. In rural areas stand-alone DC supply is a better

choice. This would also enable water pumping during

the day without the requirement of storage batteries. In

the present paper a case study for a domestic cooling

and a rural irrigation illustrates the economical use of

solar energy. The incentives from the government in

this regard would further enhance the contribution from

renewable resources

2. Budget of Electrical Energy in Pakistan

The situation of supply and demand of electrical

energy in Pakistan is quite alarming. The total

generation capacity is presently around 17000 MW.

This includes a hydel capacity of 6500 MW which is

around 38%. The new hydel projects would require a

decade to be matured. The thermal generation is of

the order of 10,200 MW, half of which is provided by

private sector IPPs and around 5000 MW is delivered

by generation companies under the control of

WAPDA resulting in a total thermal component of

60%. Nuclear contribution is 301 MW contributing

2% of the total.

The peak demand in summer is around 19,000 MW

resulting in a shortfall of 2000 MW. A significant

contribution to this peak is the air-conditioning load

from domestic and commercial sector. As a result

load management has to be enforced resulting in a

decline in the economic activity and discomfort to the

public.

Alternate Energy Development Board (AEDB) was

set up in 2003 to take measures for developing

renewable energy resources in the country. The board

has initiated projects for exploiting wind energy from

Karachi to Hyderabad and along Mekran coast where

abundant wind energy is available. A pilot project of

100 MW is in the construction stage. The board is

also exploiting solar energy in the interior areas of

Sind and Punjab.

Solar power technology has been primarily

dominated by use of solar cells. Arrays of

photovoltaic cells convert light from sun to

electricity. The cost of solar cells is still prohibitive.

Isolated use of solar cells for emergency phones

along freeways and unattended repeaters is quite

common. However the use of photovoltaic cells has

expanded dramatically in recent years.

Grid connected applications are being

encouraged through preferential feed-in tariffs and

financial public incentives [ 3].

Since cooling is a significant cause of peak in the electric

load profile, alternate ways should be analyzed to flatten

the peak. Cooling through solar energy is a viable option.

The deficit energy in bad weather and evening hours can

be provided by natural gas. The tariff for the natural gas

is still favorable and justifies the use of gas for cooling.

The absorption chillers using lithium bromide-water

solution are commercially available [4]. Lithium bromide

is used as absorbent and water as refrigerant. The

ammonia water system could also be used. It is well

known that absorption chillers are less efficient as

compared to vapor compression refrigeration [5]. The

efficiency of absorption chillers can be increased by

increasing the number of stages [6]. Cost is the limiting

factor. For domestic applications a single stage

absorption chiller is a cheap solution in view of the free

availability of solar energy and cheaper gas tariff. In the

present study a lithium bromide single stage chiller is

proposed for typical domestic applications. For

commercial and industrial applications a three stage

absorption chiller could be used. Additionally hot waste

gases could be used for efficient heat recovery.

In a simple domestic arrangement a fixed collector solar

pre-heater may be used. In order to increase the

efficiency, a tracking arrangement with stepper or

switched-reluctance motors operated through solar cells

can be used. For a typical three bed house a comfortable

cooling can easily be achieved resulting in a saving of 5

kW electric equivalent.

3- Solar Chiller for Domestic Application

A typical house would has a load pattern indicated in

Table 1.

Table 1. Utilization Pattern for a typical house.

Total Area

500 sq.ft. (one kanal)

Covered Area

3000 sq.ft.

Connected Load

Air conditioning

Lighting

Refrigeration

Appliances(including

Vacuum cleaner, electric

iron, kitchen

accessories, pumps and

PCs)

5 kW

2 kW

1 kW

2 kW

Total connected load 10 kW

photovoltaic array with solar absorption chillers.

In order to reduce the electrical burden other measures of

more efficient utilization of electricity is required. In

lighting load, light emitting diodes with broad spectrum

should be used. Insulation of house should be properly

controlled both for electric air conditioning as well as

absorption chillers.

A typical application in a rural environment is a pump for

irrigation using underground water. Presently these

pumps are operated using electricity or diesel engines.

Solar energy is an attractive option. It is however

suggested that the motor should be operated directly

using DC supply instead of converting it to AC. Further

the cost of batteries could be eliminated. The pump

would operate the day over facilitating irrigation with a

silent night. Such pumps are operative in Punjab and

result in reduction of load to grid and strengthening of

Assuming a load factor of 0.6, the load on the

distribution network is 6 kW.

A lithium bromide chiller of 6 ton capacity is used for

the same house [6]. The capital cost for the chiller is

Rs. 6, 00,000.

If electrical air conditions are used with the same

installed capacity the capital cost is Rs. 2,00,000.

However the running cost for gas chiller with a 50%

solar mix is Rs. 2000 per month whereas the

differential cost of electricity is Rs. 10,000 per month

resulting in a saving of Rs. 96,000 annually which

means a pay back period of differential cost is four

years.

For an equivalent solar system the economics would

be about 400% capital investment and payback period

of 6 years. Unless there is a financial incentive from

the government, total electric solar system is not

economically feasible. Hybrid system could also be

used combining the

rural economy.

4. Conclusions:

There is great potential in using solar energy in Pakistan.

It is proposed that instead of converting solar energy into

electricity and using electrical air conditioners, it may be

more economical to use solar absorption chillers for

domestic applications. This would result in reducing the

peak load of the utilities. DC solar pump is an option for

rural irrigations.

References:

[1] http://www.pv.unsw.edu.au/School of Photovoltaic and

Renewable Energy Engineering

[2] http://www.aedb.org/Altenate Energy Development Board,

Pakistan

[3]http://www.energy.ca.gov/ClifoniaEnergy Commission

[41http://www.broad.cont/english/products/pro_bj.asp

[5] http://www.solar2006.org/presentations/forums/ f01-henkel.pdf

[6] http://www.newbuildings.org/downIoads/

guidelines/AbsorptionChillerGuideline.pdf