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Solar Energy 82 (2008) 799–811

CDM potential of solar water heating systems in India

Pallav Purohit a,*, Axel Michaelowa b

a International Institute for Applied Systems Analysis (IIASA), Schlossplatz 1, A-2361 Laxenburg, Austriab Institute of Political Science, University of Zurich, Muhlegasse 21, 8001 Zurich, Switzerland

Received 30 November 2006; received in revised form 19 December 2007; accepted 25 February 2008Available online 18 March 2008

Communicated by: Associate Editor S.C. Bhattacharya

Abstract

The Clean Development Mechanism (CDM) provides industrialized countries with an incentive to invest in emission reduction pro-jects in developing countries to achieve a reduction in CO2 emissions at lowest cost that also promotes sustainable development in thehost country. Solar water heating systems (SWHs) could be of interest under the CDM because they directly displace greenhouse gasemissions while contributing to sustainable development by reducing local pollutants. However, there are only three solar water heatingprojects under the CDM so far. An attempt has been made to estimate the CDM potential of SWHs in India in this study. Our estimatesindicate that there is a vast theoretical potential of CO2 mitigation by the use of SWHs in India. The annual CER potential of SWHs inIndia could theoretically reach 27 million tonnes. Under more realistic assumptions about diffusion of SWHs based on past experienceswith the government-run programmes, annual CER volumes by 2012 could reach 4–9 million and 15–22 million by 2020. This wouldrequire that the government sets the subsidy level for SWHs at a level that allows them to become viable with the CER revenue. Froma macro-economic point of view this makes sense if the sustainability benefits are deemed sufficiently high to warrant promotion of thisproject type.� 2008 Elsevier Ltd. All rights reserved.

Keywords: Clean development mechanism; Renewable energy; CO2 emissions; Solar water heating systems; India

1. Introduction

India has experienced several changes in its energy usepatterns during the past few decades (CMIE, 2001). Thisis due to the population growth, increased economic activ-ity and development and changes in lifestyles. The biggestchallenge of the energy sector of the country is to reliablymeet the demand for energy services of all sectors at com-petitive prices. The Integrated Energy Policy (IEP) of theIndian government aims that the lifeline energy needs ofall households must be met, even if it entails directing sub-sidies to vulnerable households. Further, this demand mustbe met through safe and clean forms of energy at the least

0038-092X/$ - see front matter � 2008 Elsevier Ltd. All rights reserved.

doi:10.1016/j.solener.2008.02.016

* Corresponding author. Tel.: +43 2236807 336; fax: +43 2236807 533.E-mail addresses: purohit@iiasa.ac.at, pallav1976@yahoo.co.in (P.

Purohit), axel.michaelowa@pw.unizh.ch (A. Michaelowa).

cost in a technically efficient, economically viable, and envi-ronmentally sustainable manner (GOI, 2006). The house-hold sector is one of the largest users of energy in India,accounting for about 30% of final energy consumption(excluding energy used for transport) reflecting the impor-tance of that sector in total national energy use (Reddy,2003).

The 60th round of National Sample Survey (NSS)reports that 92.2% of the households in the urban areasof India have access to electricity, which they use as theirprimary source of lighting whereas the corresponding fig-ure for rural areas is 53.5%. As a result, an estimated 78million households (23.4 million un-electrified householdsbelow the poverty line and 54.6 million un-electrifiedhouseholds above the poverty line) still do not have accessto electricity (GOI, 2006). A similar situation exists withthe access to clean cooking energy, which can be used as

1 A Kyoto Protocol unit equal to 1 metric tonne of CO2 equivalent.Certified Emission Reductions (CERs) are issued for emission reductionsfrom CDM project activities.

800 P. Purohit, A. Michaelowa / Solar Energy 82 (2008) 799–811

proxy for water heating needs. Only 9% households in ruralarea and 56.4% households in urban areas use liquefiedpetroleum gas (LPG) as their primary source of cooking(http://mospi.nic.in/nsso_test1.htm). As a result, almost69% (137 million) households, including both rural andurban, use non-commercial fuels (coke, coal, firewood,dungcake, etc.) as their primary source of cooking. Thisis excluding 5.3% (approximately 10 million) householdsin India (4.3% in rural areas and 7.8% in urban areas),which do not have any cooking arrangement (TERI,2006). This coupled with the fact that a significant partof all household energy needs stems from cooking andwater heating requirements, presents a strong case for thepromotion of clean cooking fuels.

Efforts are being made to meet the domestic energyrequirement through renewable energy in India. The coun-try receives solar radiation amounting to over5 � 1015 kW h per annum (MNRE, 2007) with the dailyaverage incident energy varying between 4 and 7 kW hper m2 depending on the location (Mani and Rangarajan,1982). Solar radiant energy can be used through thermalas well as photovoltaic routes. Over the last two decadesa wide variety of solar energy technologies have been devel-oped through research and development, demonstrationand large-scale promotion during the eighties and nineties.As a result, some of these technologies have reached matu-rity and a user-friendly status and are suitable for decen-tralized applications. One of the most widespread uses ofsolar thermal technology is solar water heating. Solar waterheating systems (SWHs) have now been used for more thansixty years (Hottel and Woertz, 1942; Kalogirou, 2004;MNRE, 2007). In many countries, which include China,Israel, USA, Japan, Australia, South Africa and Cyprus,SWHs are very popular for their use in community, com-mercial and industrial applications (Noguchi, 1985; Bhat-tacharya and Kumar, 2000; Kaldellis et al., 2005;Nieuwoudt and Mathews, 2005; Zhiqiang, 2005; Chowet al., 2006; Houri, 2006). SWHs find wide application inlarge establishments such as hostels, hotels, hospitals,industries (textile, paper, food processing, etc.) besidesheating of domestic water and swimming pools. SWHs,particularly simple domestic systems, offer a number ofadvantages which include (a) simplicity to construct andinstall, (b) very small maintenance and running cost, (c)possibility to retrofit to most of the existing houses withoutrequiring additional space, and (d) absence of local pollu-tion due to substitution of fossil fuel/electricity operatedconventional water heating systems.

In the past two decades, considerable efforts have beenmade towards the development and dissemination ofSWHs in India. As per the norms of Bureau of IndianStandards (BIS), the quality of solar water heating equip-ment is quite high (www.bis.org.in). In the household sec-tor, most systems consist of a basic thermosyphon designwith glazed flat plate collectors. Some vacuum tube collec-tors have been introduced, but these imported systems areconsiderably more expensive than domestically-made flat

plate systems. The Government of India launched a dem-onstration program during the 1980s’ for promoting SWHsin the country (MNRE, 2007). In order to promote the useof SWHs, a variety of financial and fiscal incentives havebeen offered to the end users. These include capital subsidy,low interest loan, accelerated depreciation related benefitetc. However, the total collector area of SWHs reportedlyinstalled in the country so far (1.66 million m2 till 31st Jan-uary 2007) is below the expected levels of penetrationwhich is due to a multitude of barriers. These generallyinclude high up-front system costs compared to conven-tional alternatives, unwillingness of banks to providefinancing, and a lack of awareness about the favorable life-cycle economics of solar water heating technology visa visconventional water heaters.

The Clean Development Mechanism (CDM) is anarrangement under the Kyoto Protocol allowing industrial-ized countries (Annex-I) with a greenhouse gas (GHG)reduction commitment to invest in projects that reduceemissions in developing countries as an alternative to moreexpensive emission reductions in their own countries. Italso assist developing countries (Non-Annex-I) in achiev-ing sustainable development by promoting GHG emissionreduction projects that generate emission credits (CERs1)for Annex-I countries. Small-scale renewable energy pro-jects have significant local environmental and socio-eco-nomic benefits. However, due to the small CER volumesgenerated, such projects may not be able to cover theirtransactions costs, even under the simplified modalitiesand procedures developed by the CDM executive board.There is tremendous interest among Indian project pro-moters, financing institutions, and other stakeholders inthe opportunities emerging out of the CDM. The CDMproject pipeline now contains 2783 CDM projects (exclud-ing the 46 rejected and the 9 withdrawn projects) tillNovember 2007. 859 of the projects are now registeredand a further 149 are in the registration process. 295 pro-jects out of these are located in India (cdm.unfccc.int).The amount of CERs issued is 94.4 Million CERs whereasthe average issuance success has increased to 91.9%(www.cd4cdm.org). SWHs become relevant for the CDMbecause they directly displace GHG emissions while con-tributing to sustainable development (Pokharel, 2007). Asper the environmental point of view the use of these sys-tems can play an important role to save the environment(Kalogirou, 2004). The installation of these systems willcreate employment due to the use of locally manufacturedsolar water heaters and savings in the cost of energy. More-over, the introduction of these systems will replace coal-generated electricity that will reduce emissions of sus-pended particulates, SOx and NOx (Kalogirou, 2004;Ardente et al., 2005). We assess the theoretical CDMpotential of SWHs in India before discussing whether at

P. Purohit, A. Michaelowa / Solar Energy 82 (2008) 799–811 801

the current market situation such projects could becomeattractive.

The paper is set out as follows. Section 2 briefly presentsthe detail of a solar water heating system. Section 3 pro-vides some salient features of the Indian programme onSWHs. Section 4 presents a method for the estimation ofthe potential number of SWHs. The discussion how theCDM could mobilize SWHs and the estimation of theCDM potential of SWHs is discussed in Sections 5 and 6,respectively. Section 7 presents the forecast diffusion levelsof SWHs under an optimistic CDM and business-as-usualscenario. Section 8 concludes.

2. Solar water heating system

A solar water heater consists of a collector to collectsolar energy and an insulated storage tank to store hotwater (Fig. 1). An active type domestic water heating sys-tem utilizes a pump to circulate water from the insulatedstorage tank (normally located inside the home at groundlevel) to the solar collector (usually located on the roof)and back to the tank. The pump is required as the densityof the hot water in the solar collector is less than that of thecold water in the storage tank (and thus the water in thestorage tank will otherwise remain in the solar collectoritself). The pump is activated (by a suitable control device)when the temperature of water in the solar collectorexceeds that of water in the storage tank by a pre-specifiedmargin. In a passive type solar water heating system, nor-mally referred to as a ‘thermosiphon solar water heatingsystem’, the insulated water storage tank is located abovethe collector. When the water in the collector is heatedand becomes less dense than the water in the storage tank,it rises naturally into the tank as the water from storagetank flows into the bottom of the solar collector.

A most critical element of any solar water heating sys-tem is the solar collector (or absorber panel). The perfor-mance of a flat plate collector depends upon its designparameters viz. type of absorber plate (Patil, 1975), coatingon absorber plate (Bhide et al., 1982; Cindrella, 2007),thickness and type of insulation (Whillier and Saluja,1965), number and type of glass covers (Akhtar and Mul-lick, 2007), anti-reflective coating on glass cover (Hsiehand Coldeway, 1974), arresting convective movement

Fig. 1. Schematic diagram of a solar water heating system.

between absorber and glazing by transparent insulatingmaterial (Hollands, 1965), spacing between absorber andinner glass and successive glazings (Nahar and Garg,1980), and evacuated space between the absorber and innerglass. Besides these, the performance also depends upon cli-matic and operational parameters (Nahar, 2003). Thoughthe use of concentrating type and tank type collectors havebeen, at times, considered for water heating, it is the flatplate solar collector which has been extensively used inSWHs all around the globe. Flat plate solar collectors aregenerally best suited to applications below about 80 �Csuch as domestic, commercial and (some) industrial waterheating applications. The cost of the solar water heatingsystem would critically depend upon the type of the solarcollector used. A flat copper plate has water tubes attachedto the absorber plate. As solar energy falls on the copperplate and is absorbed, the energy is transferred to waterflowing in the tubes. The absorber plate is mounted in acasing that has a clear covering and insulation to protectthe absorber plate from heat loss.

3. Programme on solar water heating systems in India

To harness the enormous potential of solar energy, theMinistry of New and Renewable Energy (MNRE) is imple-menting a variety of programmes in the country. The mainobjectives of the solar thermal programme of ministry areto develop and promote the use of these technologies inorder to meet the heating energy requirements in domestic,institutional and industrial sectors in the country and alsoto generate electricity in an environment friendly manner.For the widespread utilization of the technology, theMNRE has been operating an interest subsidy schemethrough Indian Renewable Energy Development Agency(IREDA) and seven designated banks. This helps offsetthe high initial cost of the systems, providing an acceptablepay back period to various end users to stimulate the mar-ket, resulting in establishing a strong manufacturing baseand after-sales service network. In India, both the technol-ogy and the manufacturing base for solar water heating arenow well established. These systems are now commerciallyavailable in the market and can effectively supplement theconventional heating systems based on coal, furnace oilor electricity.

The banks have been authorized to finance solar waterheaters without any upper limit to the capacity of the sys-tems. The soft loan scheme has been expanded and is avail-able through all implementing banks (such as CanaraBank, Bank of Maharashtra, Andhra Bank, PunjabNational Bank, Syndicate Bank and Punjab and SindBank). Union Bank of India operates the scheme throughtheir designated branches. The banks provide 85% of thecost of the project as soft loans repayable in 5 years(MNRE, 2007). The subsidized rate of interest is 5% tothe domestic end users and 7% for commercial applica-tions. Housing co-operative societies and developers of realestates have also been made eligible for soft loans for

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1992-93

1993-94

1994-95

1995-96

1996-97

1997-98

1998-99

1999-00

2000-01

2001-02

2002-03

2003-04

2004-05

2005-06

Year

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ulat

ive

coll

ecto

r ar

ea o

f do

mes

tic

sola

r w

ater

heat

ing

syst

ems

(mill

ion

m2 )

Fig. 2. Cumulative installed capacity of SWHs in India (Source: MNES annual reports).

802 P. Purohit, A. Michaelowa / Solar Energy 82 (2008) 799–811

installing solar water heaters in bulk at an interest rate of5%. However, all borrowers taking loans at 5% interest rate(except individuals) are required to give an undertakingthat no accelerated depreciation benefits2 would be availedof. The ministry has been pursuing with state governmentsthe proposal for making solar assisted water heating man-datory in certain categories of buildings through amend-ments in the building by-laws. To encourage localgovernments to notify the mandatory provision for SWHs,Central financial assistance of 9000 €3 to municipalities and18,000 € to municipal corporations is provided for training,study tours, awareness creation, demonstration, prepara-tion of brochures/manuals and creating infrastructure forimplementing the mandatory provision. Thane in Maha-rashtra and Rajkot Municipal Corporation in Gujarathas modified the building bye-laws during the year 2004–2005. The technical potential of solar water heaters in thecountry has been estimated to be 140 million m2 of collec-tor area (MNES, 2002). An aggregate collector area ofabout 60,000 m2, has been financed by IREDA and banksduring the year 2004–2005 under the interest subsidyscheme. In addition, another 100,000 m2 collector area isestimated to have been installed in the country throughdirect sales by manufacturers during 2004–2005. Fig. 2 pre-sents the cumulative installed capacity of SWHs in India. Atotal collector area of about 1.66 million m2 has beeninstalled in the country so far (MNRE, 2007).

4. Potential of solar water heating systems in India

The potential of SWHs essentially depends on availabil-ity and accessibility of solar radiation, affordability of the

2 The strong expansion of Indian wind power is due to the possibility fordepreciation of wind turbines in the first year of operation. This has led tomany companies investing in wind definitely to reduce their tax bill.

3 1 € = Rs 53.73 as on January 17, 2006.

user to invest in solar water heating system, and accessibil-ity of solar radiation to the households. Using the abovementioned factors, the total potential number of SWHs(Nsh) can be estimated as

N sh ¼ n1

Xn

i¼1

N in2ui

" #n3u ð1Þ

where Ni represents the total number of households in theith state, n1 the fraction of households living in the geo-graphical areas with adequate solar radiation availability,n2ui the fraction of households living in the urban areasof the ith state, and n3u the fraction of households in theurban areas having a piped water supply in the householdpremises.

Sufficient solar radiation is necessary for a solar waterheating system. In this study, only the areas with daily solarradiation greater than 4 kW h/m2 have been considered forpotential estimation of SWHs. Ideally, detailed solar radia-tion data for each location should be used in evaluating thepotential of solar energy technologies. However, to makean initial macro level assessment, broad solar radiationavailability characteristics readily available in literature(Mani and Rangarajan, 1982) are used. On a macro level,seven north-eastern states and the northern states of Jammuand Kashmir, Himachal Pradesh and Uttaranchal can begiven low priority in the process of identification of nicheareas for installation of SWHs. It may be noted that duringcertain periods (primarily rainy season of the year), a solarwater heating system may be rarely used (Nahar, 2003).However, it is assumed that the user may be motivated toinvest in such system if it can be used during a major partof the year. Most of the locations in India have more than275 sunny days in a year (Mani and Rangarajan, 1982).

As per 2001 census there are 54 million urban house-holds in the country. Out of 54 million urban households,37 million urban households have piped water supply whilethe remaining use hand pumps. Out of 37 million urban

Table 1Input parameters used in the financial analysis of a solar water heating systems

Parameter Symbol Unit Value

Annual operation, repair and maintenance cost (as a fraction of capital cost) of solar water heating system CMsh fraction 0.02Annual operation, repair and maintenance cost (as a fraction of capital cost) of electric water heater CMeg fraction 0.02Capital cost of the solar water heating system Co € 372Capital cost of the electric water heater Cnew, T € 74Discount rate d fraction 0.10Electrical transmission and distribution losses l fraction 0.22Efficiency of the electric water heater geg fraction 0.90Transaction cost Ctc €/t CO2 0.15Useful lifetime of the solar water heating system tsh years 10Useful lifetime of the electric water heater T years 10

Source: Kandpal and Garg (2003); Krey (2005); Purohit and Michaelowa (2006, 2007, 2008).

Table 2Estimated potential of solar water heating systems in India

State Number of households inurban area of India (million)a

Number of householdsusing SWHs (million)

Andhra Pradesh 4.6 2.3Assam 0.6 0.3Bihar 1.4 0.7Chhattisgarh 0.8 0.4Delhi 2.5 1.3Goa 0.2 0.1Gujarat 3.6 1.8Haryana 1.1 0.5Jharkhand 1.1 0.5Karnataka 3.5 1.8Kerala 1.8 0.9Madhya Pradesh 2.9 1.5Maharashtra 8.3 4.2Orissa 1.2 0.6Punjab 1.5 0.7Rajasthan 2.2 1.1Tamilnadu 6.4 3.2Uttar Pradesh 5.4 2.7West Bengal 4.5 2.2

Total 26.7

a Source: http://www.censusindia.net/.

P. Purohit, A. Michaelowa / Solar Energy 82 (2008) 799–811 803

household, 27 million urban households (i.e. 50 % of thetotal urban households) have tap in their premises, eightmillion urban households have tap water just outside thepremises, two million urban households have tap within100 m (http://wc.worldwatercongress.org:5050/pdf/urban.pdf). Therefore, the maximum penetration of theSWHs should be 27 million, which would increase in thefuture with further households being linked to the pipedwater supply. Table 1 presents the input parameters usedin the estimates presented in this study. Using Eq. (1)and based on the input parameters given in Table 1 the esti-mated potential of SWHs in India has been estimated to be27 million (Table 2). It is estimated that out of the total 54million urban household in India (www.censusindia.net) 27million households can use SWHs4. The state of Maha-rashtra has a highest potential of SWHs (4.2 million) fol-lowed by Tamilnadu (3.2 million), Uttar Pradesh (2.7million), Andhra Pradesh (2.3 million) and West Bengal(2.2 million), respectively.

5. How the CDM could be applied to the diffusion of solarwater heating systems?

Small-scale renewable energy projects are helping toalleviate poverty and foster sustainable development. How-ever, the low emission reductions per installation are mak-ing it difficult for such projects to derive value fromparticipating in the CDM. Negotiators of the MarrakeshAccords of November, 2001 (UNFCCC, 2002) as well asthe CDM Executive Board recognized this problem andadopted simplified CDM modalities and procedures forqualifying small-scale projects defined as (a) renewableenergy project activities with a maximum output capacityequivalent of up to 15 MW, (b) energy efficiency improve-ment project activities which reduce energy consumptionby an amount equivalent to 60 GW h per year, and (c)other project activities whose emission reductions are lessthan 60 kt CO2 per year.

4 The potential of solar water heating systems has been estimated usingEq. (1). Incidentally, the potential number of households that can usesolar water heating systems is the same as the number of households havetap in their premises.

The thresholds for the latter two categories wereincreased by decision of the Conference of the Parties tothe UNFCCC in November 2006. The CDM was slow totake off as after the Marrakech Accords of 2001 it tookanother three years to define the bulk of the rules. TheCDM Executive Board (EB) which is the body definingthe CDM rules surprised many observers by taking a rigor-ous stance on critical issues such as baseline and addition-ality determination. Once the key rules were in place, a‘‘gold rush” happened in 2005 and 2006. Over 1500 pro-jects were submitted with an estimated CER volume ofabout 1.5 billion. However, the volume share of renewableenergy projects has been less than expected due to the highattractiveness of projects reducing industrial gases andmethane from waste. Out of the 2838 CDM projects sub-mitted to the EB (including 46 rejected and 9 withdrawn),859 projects had been registered by the EB till 4th Decem-ber, 2007. Fig. 3 shows the number of different project size

0

100

200

300

400

500

<11 t

o 5

5 to10

10 to

20

20 to

50

50to

100

100 to

500

500 t

o 100

0

1000

to50

00

5000

to10

,000

>10,00

0

Size (000, CERs)

Nu

mb

er o

f p

roje

cts Submitted

Registered

Fig. 3. Size categories of submitted and registered CDM projects (average 1000 CERs p.a. until end of 2012).

804 P. Purohit, A. Michaelowa / Solar Energy 82 (2008) 799–811

categories of the 2738 CDM projects submitted until 1stweek of December 2007 in which only three projectsnamely CDM solar hot water project of Emmvee SolarSystems Pvt. Ltd. and Bagepalli CDM solar hot waterheating programme are in India and Kuyasa low-costurban housing energy upgrade project, Khayelitsha inCape Town at South Africa involves SWHs.

5.1. Baseline

The quantification of climate benefits of a project – i.e.the mitigation of GHG-emissions – is done by means ofa ‘‘baseline”. A baseline describes the (theoretical) emis-sions that would have occurred in case the CDM projectwas not implemented. The amounts of CERs that can beearned by the project are then calculated as the differenceof baseline emissions and project emissions. A solar waterheating system usually replaces electricity (Chandrasekarand Kandpal, 2004; Purohit and Michaelowa, 2006). Toestimate the CDM potential of SWHs in the country thesmall scale methodology IC ‘‘Thermal Energy for theUser” in its version of 23 December 2006 (UNFCCC,2006) has been used. It allows that for renewable energytechnologies that displace technologies using fossil fuels,the simplified baseline is the fuel consumption of the tech-nologies that would have been used in the absence of theproject activity times an emission coefficient for the fossilfuel displaced. IPCC default values for emission coefficientsmay be used. For renewable energy technologies that dis-place electricity the simplified baseline is the electricity con-sumption time the relevant grid emission factor.

5.2. Additionality

To maintain the environmental integrity of the KyotoProtocol, CDM credits are given only for activities that

would otherwise not be expected to occur. Even in thehypothetical case an off-grid situation where lifecycle costsof the solar water heating system would be cheaper than allother alternatives, the high up-front investment cost to auser in acquiring a solar water heating system would stillbe a high barrier to widespread market penetration. Mostof the SWHs so far disseminated in India are sold with asubsidy.

5.3. Monitoring

Monitoring under small-scale rules consists in an annualcheck of all systems or a sample thereof to ensure that theyare still operating. Since the installations of SWHs areoften widely dispersed, monitoring costs could makeCDM participation prohibitive if each user with a systemis visited. Simple and efficient sampling procedures aretherefore required. There are two variables that need tobe monitored and verified in order to correctly establishemission reductions from SWHs according to small-scalemethodology IC: (i) number of systems operating (evidenceof continuing operation, such as on-going rental/lease pay-ments could be a substitute); and (ii) annual hours of oper-ation of an average system, if necessary estimated usingsurvey methods. Annual hours of operation can be esti-mated from total output and output per hour if an accuratevalue of output per hour is available.

6. CDM potential of solar water heating systems in India

The useful energy provided by a solar water heating sys-tem (and consequently the amount of conventional energysaved by it) depends on the design of the SWHs, size of thecollector, solar radiation availability and ambient condi-tions (ambient temperature and wind speed) besides theoperating temperatures required. Moreover, the actual

P. Purohit, A. Michaelowa / Solar Energy 82 (2008) 799–811 805

amount of fuel/electricity saved by the use of the solarwater heating system would depend upon the efficiency ofutilization of the fuel/electricity for water heating and thecalorific value of the fuel. As a consequence the monetarybenefits of a solar water heating system to the end userwould depend upon the location (which affects solar radia-tion availability and ambient conditions), water tempera-ture required (which affects the thermal efficiency of solarwater heating system), the design of the system and themonetary worth of the fuel substituted to the end user.Also, there are seasonal variations in the useful output pro-vided by the solar water heating system.

Through the demand of hot water may vary from house-hold to household in India, a domestic water heating sys-tem with a capacity of one hundred liter per day (lpd)have been most frequently disseminated in the country(Chandrasekar and Kandpal, 2004). The cost of commer-cially available 100 lpd systems varies between 335 € and465 € for indigenous systems. One reason for this lower-than-average price is a robust manufacturing base in Indiathat is the direct result of an ambitious effort by the MNREto boost the solar water heating industry. Moreover, gov-ernment subsidies in the form of low interest loans arehelping to increase the systems’ affordability for middleclass buyers (IREDA, 2006). The amount of conventionalfuel saved by a solar water heating system can be estimatedin the following manner:

The annual useful energy, AUEsh, (in MJ) delivered bythe SWHs can be estimated as

AUEsh ¼ 365CUFshV shqCpðT o � T iÞ ð2Þ

where CUFsh represents the capacity utilization factor ofthe SWHs, Vsh the capacity of the SWHs (in litre), q thedensity of water (in kg/m3), Cp the specific heat of water

Table 3Estimated period (months) of SWHs at different locations in India

Locations Elevation(in meters) msl*

Latitude(N)

Ahmedabad 55 23�040

Allahabad 98 25�270

Bangalore 921 12�580

Bhavnagar 5 21�450

Chennai 12 11�400

Goa 55 15�290

Hyderabad 545 17�270

Kolkatta 6 22�390

Mangalore 102 12�550

Mumbai 14 19�070

Nagpur 310 21�060

New Delhi 216 28�350

Port Blair 79 11�400

Pune 559 18�320

Trivandrum 64 8�290

Vishakhapatnam 3 17�430

Source: IMD (1999); Chandrasekar and Kandpal (2004).

(in MJ/kg �C), To the outlet water temperature (in �C),and Ti the inlet water temperature (in �C).

Hot water requirement for domestic purposes wouldessentially depend upon the prevailing temperatures ata location (Kandpal and Garg, 2003). One of the pri-mary uses of hot water in the Indian households is fortaking a bath in the early mornings or late evenings(in some locations). In the present study, the case ofmorning baths have been considered as majority ofIndian households prefer early morning bath (5–7a.m.). Though the water temperature required for takingthe bath would vary with individual preferences, watertemperatures in the range of 32–35 �C is reportedly pre-ferred by majority of households. Chandrasekar andKandpal (2004) estimated the number of months in ayear when hot water will be required by households fordifferent locations in India using the temperature dataavailable from the Indian Metrological Department(IMD, 1999). In this study, it is assumed that if the aver-age temperature between 5 and 7 a.m. is less than a pre-specified temperature (Tspc), the household would requirehot water for taking a bath. As the value of Tspc wouldalso vary from person to person, the analysis has beenmade for three different values of Tspc (such as 20, 22and 24 �C). One of the important issues in the estimationof the amount of the fuel substituted by the SWHs is thecapacity utilization of the system during the year. Table3 presents the data on the solar radiation along with cli-matic parameters for selected location of India. FromTable 3 it is clear that due to seasonal change in therequirement of hot water in many areas of the country,the effective utility of SWHs to some users may be lim-ited (3–6 months of winter season only).

The annual amount of fuel saved by the use of a solarwater heating system, AFSsh, can be estimated as

Longitude(E)

Number of months in a year withtemperature less than (during 5–7 a.m.)

20 �C 22 �C 24 �C

72�380 4 6 681�440 5 6 677�550 7 9 1272�110 3 4 580�180 – 1 473�490 – 2 578�200 4 6 988�270 4 5 574�530 – – 672�510 3 3 579�030 4 6 777�120 4 5 692�420 – – 173�510 5 7 1076�570 – – 483�140 2 3 3

806 P. Purohit, A. Michaelowa / Solar Energy 82 (2008) 799–811

AFSsh ¼365CUFshV shqCpðT o � T iÞ

CV igi

� �ð3Þ

where CVi represents the calorific value and gi the efficiencyof utilization of ith fuel.

The annual CO2 emissions reduction can be estimated asthe product of the annual amount of fuel(s) substituted bySWHs and the CO2 emission factor for respective fuel(s).For e.g. in case of electricity substitution in the baseline(as discussed above), the annual CO2 emissions reduction,CEsh, can be estimated as

CEsh ¼365CUFshV shqCpðT o � T iÞ

3:6gegð1� lÞ

" #CEFe ð4Þ

where CEFe represents the CO2 emission factor for electric-ity, l the electrical transmission and distribution losses, andgeg the efficiency of electric geyser.

There are five regional grids within the country viz.Northern, Western, Southern, Eastern and North-Easternand different states are connected to one of the five regionalgrids. The CO2 emissions mitigation potential throughSWHs in India is estimated on the bases of the regionalbaseline. With respect to CEFe the range of regional gridaverage emission factors in India ranges from 450 g CO2/kW h in the North Eastern grid to 1040 g CO2/kW h inthe Eastern grid (CEA, 2006).

What is now the financial attractiveness of solar waterheating system based CDM project? The monetary benefitsassociated with a solar water heating system depend uponthe monetary value of electricity saved which is the productof annual electricity savings and the price of electricitysaved and the difference in investment costs between thecommon electric water heater and the solar water heatingsystem. There are many studies in the literature dealingwith the financial/economic feasibility evaluation of solarwater heating systems. Houri (2006) presented an economicfeasibility evaluation of SWHs is Lebanon. The simplifiedinitial estimates indicate a payback period of 4–5 yearswhile advanced mathematical models (RETScreen) indi-cate that the most advanced evacuated tube technologyhas a payback period of less than 9 years at current marketprices. Smyth et al. (2004) have undertaken a detailedtechno-economic evaluation of an integrated collector/storage solar water heater, for colder climates. The pay-back period was 8 years for substituting natural gas anddomestic heating oils thus shows financial unattractivenessof these systems in Northern Ireland. Kalogirou (2004)analysed the pollution caused by burning of fossil fuels fol-lowed by a study on the environmental protection offeredby the two most widely used renewable energy systems,i.e. solar water heating and solar space heating. The resultsindicate that by using solar energy, considerable amountsof greenhouse polluting gasses are avoided. For the caseof SWHs, the saving, compared to a conventional system,is about 80% with electricity or diesel backup and is about75% with both electricity and diesel backup. Ardente et al.

(2005) assessed the energy balance between the energy con-sumed and energy saved during the life-time of the solarthermal collector in Italy. Over and above the monetarysaving accruing from displaced grid electricity, the SWHscontribute to a healthier environment. Similarly, Taborian-ski and Prado (2004) observed that the electric showerheadconsumes the most electric power and emits the most pol-lutants during its life cycle. Though, the financial feasibilityanalysis of the energy and environmental performances ofa solar thermal system should include a comparativeassessment of impacts during the lifecycle and the energysaved during the operating time in this study the financialfigures of merit have been estimated to analyse the financialadditionality of SWHs based CDM project.

The monetary value of the annual electricity saved(MVes) by the solar water heating system can be expressedas

MVes ¼365CUFshV shqCpðT o � T iÞ

3:6geg

" #pe ð5Þ

where pe represents the market price of electricity (in €/kW h).

The difference between the cumulative present value of thebenefits (due to the substitution of the commercial fuels andthe avoided costs of annual repair and maintenance as well asof electric guyser replacement at the end of its technical life-time, if this ends before the end of technical lifetime of thesolar water heating system) and the costs (i.e. capital costand annual repair and maintenance cost) is the net presentvalue (NPV) of the investment on the solar water heating sys-tem. Therefore, the present value of net benefits (NPV) of aninvestment in the SWHs can be expressed as

NPV ¼ ðMVes � ðCMsh � CMegÞÞð1þ dÞtsh � 1

dð1þ dtsh

� ��

�Co þCnew;T

ð1þ dÞT

( )#ð6Þ

where CMeg represents the annual repair and maintenancecost of electric water heater, CMsh the annual repair andmaintenance cost of solar water heating system, Co the cap-ital investment cost of solar water heating system, Cnew, T

the cost of new electric water heater to be installed in theTth year, d the discount rate and tsh the useful lifetime ofthe SWHs.

Table 4 presents the financial performance indicators ofan investment in SWHs using the input parameters listed inTable 1. The financial figures of merit have been estimatedfor different resource-technology combinations and prices.It may be noted that except higher prices of electricity, nat-ural gas and kerosene the use of SWHs is financially notfeasible. In India, the electricity tariff is different in differentstates. Therefore, for the financial attractiveness of theSWHs the price of electricity has been taken to be 0.05 €per kW h and 0.09 € per kW h. Krey (2005) observed thatspecific transaction costs of a CDM project depend, to a

Table 4Financial figures of merit for an investment on solar water heating system

Fuel Unit Calorific value(MJ/Unit)

Efficiency ofutilization

Unit price offuel (€/unit)

Annual fuel saving Financial figures of merit

SPP (years) B/C NPV (€)

Electricity kW h 3.6 0.9 0.06 1167 6.5 1.0 -18kW h 3.6 0.9 0.09 1167 3.7 1.6 249

LPG kg 45 0.6 0.30 140 10.9 0.6 -162kg 45 0.6 0.47 140 6.5 1.0 -18

Kerosene kg 45 0.4 0.19 210 11.8 0.6 -178kg 45 0.4 0.37 210 5.3 1.2 62

Fuelwood kg 16 0.1 0.03 2363 6.4 1.0 -13kg 16 0.25 0.03 945 19.7 0.4 -256

Natural gas m3 39 0.6 0.34 162 8.0 0.8 -85m3 39 0.6 0.47 162 5.5 1.1 44

Source: Kandpal and Garg (2003).

P. Purohit, A. Michaelowa / Solar Energy 82 (2008) 799–811 807

large extent, on economies of scale in terms of total amountof CERs generated over the crediting period. An empiricalsurvey of CDM projects in India indicate that transactioncost range from 0.07 to 0.47 $US/t CO2. However, in thisstudy an average value 0.15 €/t CO2 has been taken to ana-lyse the financial attractiveness of the SWHs based CDMproject. We observe in Table 5 that under the scenario withcurrent electricity price (i.e. 0.05 € per kW h) the NPV ofan investment in the solar water heating system is notattractive, thus showing additionality for the CDM. Thebreak-even prices of CER would have to be 3.5 € (Table5). The use of solar water heating system requires a smallamount of subsidy (5% of the capital cost of the system)to become financially viable. This however, does notinclude other barriers to project implementation such asthe fear of users not to receive maintenance in case ofbreakdown and the unfamiliarity of the technology. Itmay be noted that with the electricity price of 0.09 € perkW h the use of solar water heating system is financiallyfeasible. However, the high capital cost of solar water heat-ing system is one of the major barriers in the disseminationof the technology.

Using Eqs. (1) and (6) the theoretical maximum CO2

emissions reduction potential of solar water heating sys-tems, CEsw, can be estimated as

CEsw ¼ n1

Xn

i¼1

N in2ui

!n3u

" #

� 365CUFshV shqCpðT o � T iÞ3:6gegð1� lÞ

" #CEFe;j ð7Þ

Table 5Financial attractiveness an investment on solar water heating system in India

Indicators Unit Electricity price (pe)

pe = 0.05 €/kW h

Simple payback period Years 6.45Benefit to cost ratio – 0.96Net present value (NPV) € �17.72Cost per CER € 3.50

where CEFe,j represents the CO2 emission factor for elec-tricity in the jth regional grid.

The use of the framework presented in the above sec-tion(s) requires detailed data on a variety of input param-eters. However, due to unavailability of required data aninitial exercise towards estimation of CDM potential andidentification of niche areas has been undertaken on thebasis of the proposed framework. Table 6 presents theannual electricity saving potential of solar water heatingsystem in India. It may be noted that the use of SWHs inIndia annually could save 31 TWh electricity. The theoret-ical CO2 emissions reduction potential of SWHs in India isalso presented in the same table. The CDM potential ofSWHs has been estimated at about 27 million CER annu-ally. Table 6 also gives a breakdown according to states. Itmay be noted that the state of Maharashtra has a highestCO2 emissions reduction potential (4.3 million tonne) fol-lowed by Tamilnadu (3.2 million tonne), West Bengal(2.7 million tonne) and Uttar Pradesh (2.5 million tonne),respectively.

7. Diffusion of solar water heating systems in India

In the literature, studies on the process of diffusion ofnew technologies provide a useful framework to examinethe acceptance of solar systems. ‘‘Communication and dif-fusion of innovation” theories suggest that the acceptanceof innovations is influenced by the characteristics of theinnovation and also the process by which the communica-tion takes place in the community. The acceptance of anidea by an individual usually follows a process of aware-

depending on electricity price and subsidy rates and CER revenues

and subsidies

pe = 0.09 €/kW h pe = (0.05 €/kW h + 5% subsidy)

3.68 6.131.60 1.00

249.12 0.00– –

Table 6Theoretical annual CO2 emissions reduction potential of solar water heating systems in India

State Region Emission factor*

(kg CO2/kW h)Annual electricity saved(TWh)

Annual CO2 emissions reduction potential(million CERs)

Andhra Pradesh Southern 0.86 2.7 2.3Assam North Eastern 0.45 0.4 0.2Bihar Eastern 1.04 0.8 0.9Chhattisgarh Western 0.89 0.5 0.4Delhi Northern 0.75 1.5 1.1Goa Western 0.89 0.1 0.1Gujarat Western 0.89 2.1 1.9Haryana Northern 0.75 0.6 0.5Jharkhand Eastern 1.04 0.6 0.6Karnataka Southern 0.86 2.1 1.8Kerala Southern 0.86 1.0 0.9Madhya Pradesh Western 0.89 1.7 1.5Maharashtra Western 0.89 4.8 4.3Orissa Eastern 1.04 0.7 0.7Punjab Northern 0.75 0.9 0.6Rajasthan Northern 0.75 1.3 1.0Tamil Nadu Southern 0.86 3.8 3.2Uttar Pradesh Northern 0.75 3.1 2.3West Bengal Eastern 1.04 2.6 2.7Total 31.2 27.0

* Source: http://www.cea.nic.in/planning/c%20and%20e/Government%20of%20India%20website.htm.

808 P. Purohit, A. Michaelowa / Solar Energy 82 (2008) 799–811

ness, knowledge and action. The information providedfrom different sources creates awareness and knowledgewhich may lead to adoption. The product characteristicsare also indicated to affect the rate at which diffusion takesplace. The relative advantage of the innovation over itssubstitutes is an important influence on its acceptance(Rogers, 1995).

The diffusion of a technology measured in terms of thecumulative number of adopters usually conforms to anexponential curve (Islam and Haque, 1994; Iwai, 2000).The exponential growth pattern may be of three types –(i) simple exponential, (ii) modified exponential, and (iii)S-curve. Out of these three growth patterns, the simpleexponential pattern is not applicable for the disseminationof renewable energy technologies, as it would imply infinitegrowth. The modified exponential pattern (with a finiteupper limit) is more reasonable but such a curve may notmatch the growth pattern in the initial stage of diffusion(Martino, 2003). Empirical studies have shown that in avariety of situations the growth of a technology over timemay conform to an S-shaped curve, which is a combinationof simple and modified exponential curves. Moreover, Gru-bler (1998) points out that the analyses on the developmentof many technologies confirm the S shape description. TheS-shaped curves characterized by a slow initial growth, fol-lowed by rapid growth after a certain take-off point andthen again a slow growth towards a finite upper limit tothe dissemination (Purohit and Kandpal, 2005). In thisstudy, logistic model is used to estimate the theoreticalcumulative number of SWHs at different time periods.The logistic model (or logistic growth curve) is continuousin time. The growth curve of a technology growing accord-ing to logistic growth is typically characterized by three

phases: an initial establishment phase in which growth isslow, a rapid expansion phase in which the technologygrows relatively quickly, and a long entrenchment stage inwhich the technology is close to its limiting potential dueto intra-species competition.

As per the logistic model, the cumulative number,N(t), of the SWHs disseminated up to a particular period(tth year) can be expressed as (Purohit and Kandpal,2005)

NðtÞ ¼ MeðaþbtÞ

1þ eðaþbtÞ

� �ð8Þ

where the regression coefficients a and b are estimated by alinear regression of the log–log form of Eq. (8).

Fig. 4 represent the projected time variation of thecumulative number of SWHs using the logistic model con-sidered in the study. Two cases such as standard scenario(SS) and optimistic scenario (OS) are presented. The valuesof the regression coefficients using logistic model have beenestimated by regression of the time series data for theinstallation of SWHs (Fig. 1) extracted from the annualreports of the MNRE (MNRE, 2007). In the optimistic sce-nario it is assumed that, in the past, if the diffusion ofSWHs would have been driven by the market forces insteadof subsidies then the cumulative number of installation ofSWHs would be three time more than the actual level(Purohit and Michaelowa, 2007). Our results indicate thatin India, even with highly favorable assumptions, the dis-semination of SWHs is not likely to reach its maximumestimated potential in another 25 years. But all these timeperiods are not relevant for the CDM whose current end-point is 2012 and which may only be able to live longerif post-2012 negotiations retain an emission target based

0

3

6

9

12

15

18

21

24

27

1990 2000 2010 2020 2030 2040 2050 2060

YearCum

ulat

ive

num

ber

of d

omes

tic s

olar

wat

er h

eatin

g sy

stem

s

(mill

ion)

SS

OS

Fig. 4. Time variation of cumulative installed capacity of the SWHs in India using Logistic model in the standard scenario (SS) and optimistic scenario(OS).

P. Purohit, A. Michaelowa / Solar Energy 82 (2008) 799–811 809

policy regime. However, CDM could be used as a tool tofoster the dissemination of SWHs in the country. It couldaccelerate the diffusion process.

0

5

10

15

20

25

1990 1995 2000 20

Ye

Cum

ulat

ive

num

ber

of C

ER

s (m

illio

n)

SS

OS

Fig. 5. CER potential for SWHs in India until 2020 in th

Table 7Projected values of the cumulative number of solar water heating systems and

Year Projected values of the cumulative numberof SWHs (million)

Projected values ofthe use of SWHs (

SSa OSb SS

2008 1.35 3.85 1.582012 3.60 8.90 4.202016 8.34 15.99 9.732020 15.27 21.90 17.81

a SS: standard scenario.b OS: optimistic scenario.

Table 7 presents the projected values of the cumulativenumber of SWHs and likely CER generation using thelogistic model while Fig. 5 shows the development over

05 2010 2015 2020

ar

e standard scenario (SS) and optimistic scenario (OS).

associated CER generation

the annual electricity saved byTWh)

Projected values of the annual CERgeneration (million)

OS SS OS

4.49 1.36 3.8610.38 3.61 8.9318.65 8.37 16.0425.55 15.32 21.97

810 P. Purohit, A. Michaelowa / Solar Energy 82 (2008) 799–811

time. It may be noted that with the current trend of dissem-ination of SWHs in the country more than 3.6 millionSWHs could be installed up to the end of first crediting per-iod in the SS scenario whereas in the OS scenario around 9million SWHs could be installed. Upto the year 2020, morethan 21 million SWHs are expected to be installed thatwould generate more than 22 million CERs in the OSscenario.

8. Concluding remarks

Our estimates indicate that, there is a substantial theo-retical potential of CO2 emissions reduction by the use ofSWHs in India. SWHs are closest to commercial viabilityand would be attractive with current CER prices underthe CDM. While prices are 5–15 € per CER only 3.5 €per CER are needed to make SWHs viable. The potentialnumber of SWHs has been estimated at 26.7 million. Theannual CER potential of SWHs in India could theoreticallyreach 27 million tonnes. Under more realistic assumptionsabout diffusion of SWHs based on past experiences withthe government-run programmes, annual CER volumesby 2012 could reach around 3.6–9 million and by 2020,15–22 million. The projections based on the past diffusiontrend indicate that in India, even with highly favorableassumptions, the dissemination of SWHs is not likely toreach its maximum estimated potential in another 25 years.CDM could help to achieve the maximum utilizationpotential more rapidly as compared to the current diffusiontrend if supportive policies are introduced.

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