Author manuscript, published in "Applied Thermal Engineering 29, 8-9 (2009) 1735" DOI : 10.1016/j.applthermaleng.2008.08.005
Accepted Manuscript Distributed generation and trigeneration: energy saving opportunities in Italian supermarket sector
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A. Arteconi, C. Brandoni, F. Polonara PII: DOI: Reference:
S1359-4311(08)00343-8 10.1016/j.applthermaleng.2008.08.005 ATE 2596
To appear in:
Applied Thermal Engineering
Received Date: Revised Date: Accepted Date:
21 March 2008 7 July 2008 13 August 2008
Please cite this article as: A. Arteconi, C. Brandoni, F. Polonara, Distributed generation and trigeneration: energy saving opportunities in Italian supermarket sector, Applied Thermal Engineering (2008), doi: 10.1016/ j.applthermaleng.2008.08.005
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ACCEPTED MANUSCRIPT
Applied Thermal Engineering Manuscript draft Manuscript No.: Title: Distributed generation and trigeneration: energy saving opportunities in Italian supermarket sector Article type: Key words: CHP plant, absorption chiller, supermarket, distributed generation, photovoltaics Abstract: This paper presents an analysis of the potential for introducing distributed
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generation systems in the supermarket sector in the light of Italian legislation (inasmuch as concerns tax incentives and regulations) with a view to arriving at some generally applicable criteria. The energy users in question are characterized by a strong demand for energy for refrigeration for food preservation and for ambient air-conditioning during the summer. This makes supermarkets particularly suitable for trigeneration applications with the prime mover coupled with absorption systems. This study analyses the feasibility of implementing trigeneration systems for the combined production of electricity and ambient heating and airconditioning energy or, alternatively, for the combined generation of electrical energy and refrigeration for the preservation of food. Finally, the hypothesis of combining trigeneration systems with photovoltaic systems aimed at maximizing the energy saving achievable was also considered. This paper analyses the various technologies from a technical, economic and environmental standpoint, enabling advantages and disadvantages to be identified in relation to a real case.
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Distributed generation and trigeneration: energy saving opportunities in Italian supermarket sector A. Arteconi, C. Brandoni, F. Polonara* Università Politecnica delle Marche Dipartimento di Energetica Via Brecce Bianche, Ancona 60100 *Corresponding author: Tel.(+39)0712204432, Fax (+39)0712204770, email:
[email protected]
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Abstract This paper presents an analysis of the potential for introducing distributed generation systems in the supermarket sector in the light of Italian legislation (inasmuch as concerns tax incentives and regulations) with a view to arriving at some generally applicable criteria. The energy users in question are characterized by a strong demand for energy for refrigeration for food preservation and for ambient air-conditioning during the summer. This makes supermarkets particularly suitable for trigeneration applications with the prime mover coupled with absorption systems. This study analyses the feasibility of implementing trigeneration systems for the combined production of electricity and ambient heating and airconditioning energy or, alternatively, for the combined generation of electrical energy and refrigeration for the preservation of food. Finally, the hypothesis of combining trigeneration systems with photovoltaic systems aimed at maximizing the energy saving achievable was also considered. This paper analyses the various technologies from a technical, economic and environmental standpoint, enabling advantages and disadvantages to be identified in relation to a real case.
Key words: CHP plant; trigeneration; supermarket; absorption chiller; photovoltaics
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1.
Introduction The term distributed generation (DG) includes various fossil fuel or renewable energy
generation and/or cogeneration technologies located in the vicinity of the point where the energy is used. Using DG systems offers a number of advantages, such as a reduction in the energy costs for the user and for the domestic and international economies as a whole, fewer losses in transmission, fewer carbon dioxide emissions, a better quality electrical energy generation and a less vulnerable electrical system [1]. Based on data presented by Terna, the Italian national grid owner, [2], the proportion of electrical energy consumption deriving from public and commercial services in Italy amounts to 25% and, according to an investigation conducted by the International Energy Agency [3], supermarkets represent the principal consumer in the commercial services sector. It is consequently useful and interesting to analyze potential energy saving alternatives for this area. A supermarket's energy requirements are characterized by a strong demand for electrical energy, which represents a mean 80% of its total demand, and the need for ambient heating energy that is concentrated in the winter months. Based on research conducted by the Canadian Energy Efficiency Office [4] on energy consumption in supermarkets, Figure 1, the refrigerated food counters are one of the main energy consumers, followed by lighting and the electrical energy needed for air-conditioning in summer.
ACCEPTED MANUSCRIPT The present paper assesses the feasibility of using trigeneration systems to guarantee the generation of electrical, heating and air-conditioning energy. The system analyzed consists of a natural gas powered primary motor, an internal combustion engine or a micro-turbine system, coupled with a lithium-bromide(LiBr)/water absorption system able to cope with the air conditioning load. Using the absorber has a useful boosting effect on the generation of heat and electricity, affording a considerable improvement in the profitability of the system. [5] Given the great demand for refrigeration for foodstuff preservation, as a second solution combining cogeneration systems with absorption systems for refrigerating the chilled food units was considered as well. Ammonia/water refrigeration systems are the only solution capable of guaranteeing low temperatures (0°C to -40°C), but although they are the oldest
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type of refrigeration technology known, they are less widespread and standardized than LiBr/ water systems, and are generally only installed in large-scale industrial plants [6]. This article therefore analyses also the feasibility of replacing the compression refrigerators with the ammonia/water absorption systems for the chilled food units while keeping compressor refrigeration for the frozen food units [7]. Finally, with a view to polygeneration in order to maximize the energy saving, combining trigeneration systems with photovoltaic systems has also been considered. In accordance with the provisions of the EU decision makers (Directive 2001/71/EC [8]), Italy is promoting the generation of electrical energy from solar energy, which is considered strategic for its great potential, especially in consideration of the climatic features of the Country, and southern Italy in particular. The photovoltaic system is assessed on the basis of the "feed-in-tariff" (DM 19/2/2007 [9]), a scheme of trading account incentives for promoting the use of electricity from solar sources that awards an economic incentive as a function of the kWh generated by a plant.
2.
Technical and economic assessment: case study
2.1.
Baseline case
The analysis was developed on the basis of the consumption of a typical supermarket situated in central-northern Italy, characterized by a sales area of 10,000 m². Table 1 shows the characteristic parameters of the energy user in question.
ACCEPTED MANUSCRIPT The electrical energy demand for all the other uses and electrical energy demand for food is characterized by a major demand for electricity for refrigeration, aimed at food preservation (Figure 2), which is almost constant throughout the year, while the demand for central heating is concentrated in the winter months. There is also a clearly evident increment in the electrical energy demand during the summer months due to the need for air-conditioning and to the worse performance of the refrigerators because of the higher condensing temperatures in summer. For a proper sizing of the distributed generation systems, we cannot fail to consider the daily distribution of the energy consumption. Figure 3 shows the results of monitoring daily electrical energy consumption for air-conditioning and refrigerated food preservation in
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various months of the year. There is a clearly different time distribution of the energy consumptions recorded, with the electrical energy demand for air conditioning concentrated during the supermarket's opening hours, whereas the consumption of the refrigerators for food preservation is continuous, around the clock. The present energy procurement system is managed separately, electrical energy being purchased from the national grid, while the refrigeration energy is produced by the vapor compression type refrigerators and the heating energy by a condensing boiler. The parameters for the current management system are given in Table 2. Adopting the methodology presented in [10,11,12], in the present study 4 possible distributed generation solutions for the supermarket in question are analyzed, using for comparison the current energy procurement system. Starting from the energy needs, the ideal solution for each scenario, assessed from a technical and economic point of view, has been identified. The economic analysis was conducted on an existing supermarket, with the baseline system already in operation. The investment costs considered in the analysis consisted therefore in the cogeneration and absorption system to be superimposed on the existing plant. Financial analytical methods [13] were used considering the Net Present Value (NPV) (1) and the Pay Back Period (PBP), based on a calculation of the cash flows, Fk, generated by the use of DG systems. The cash flows (2) take into account the characteristic costs, Ck, incomes, Rek, and cost of interests, Ik, of the single applications. The expenditure for the initial investment, Ek (k=0), was assumed to have been financed completely with third-party capital at an interest rate of 6%.
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N PV
=
n
∑ 1 k = 0 (
Fk + r
Fk=(Rek-Ck-Ik) –Ek
)k
(1)
(2)
2.2. Case 1_Combined generation of electrical energy and heating/cooling for air conditioning purposes The trigeneration system analyzed comprises a methane gas cogenerator combined with a
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LiBr/water absorption system fed with the heat produced by the cogenerator and used for air conditioning. As far as the choice of prime mover is concerned, the dual possibility of installing internal combustion engines (ICE) or micro gas turbine systems (µGT) was considered. As shown in the graph of a typical supermarket's energy needs (figure 2), the demand for electricity is considerably greater than the demand for heat. Cogeneration systems have an electrical/thermal capacity ratio coming between 0.6 and 0.9 [14] so, if we were to size the system on the basis of the electricity demand, following a logic of keeping up with the electrical energy load, this would coincide with an excessive waste of thermal energy, with a consequent reduction in the global efficiency of the system. For the particular type of user analyzed, it is consequently more advisable to follow a logic of covering the thermal load and sizing the cogenerator on the basis of said thermal energy requirement. Reciprocating engines represent the most widespread technology used today for the combined generation of electrical energy and heat from fossil fuels. This is for economic reasons, relating to a limited initial investment and a high performance in terms of the output of electrical energy, thanks to the great reliability typical of a mature technology that has been applied in various sectors for some time [5]. There are ICE available in sizes ranging from a few dozen kWel up to MWel, and that is why they are extremely versatile in a number of different applications [15]. Micro-turbine systems represent nowadays a potential alternative to ICE, particularly in the context of mini cogeneration. These are systems based on the Brayton regenerative cycle and they use high-speed revolving centrifugal turbo machines (at approximately 100,000 rpm).
ACCEPTED MANUSCRIPT The recovery of the hot gases leaving the turbine enables the air to be preheated before it enters the combustion chamber, increasing the system efficiency by approximately 30%. By comparison with ICE, though they have a lower electrical efficiency and a higher initial cost, they are more compact and lightweight, they require less maintenance and they have a longer working life, thanks to a more straightforward architecture. For trigeneration applications, they offer the great advantage of generating a high-temperature thermal energy: the hot gases released can reach temperatures of 250°C, and are therefore directly suitable for powering absorption systems. [16] The absorbers adopted operate on LiBr/water: these systems have a higher COP than ammonia/water systems, coming between 0.7 and 0.8, though they cannot achieve sub-zero
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temperatures like the latter. The presence of a condensing tower is needed to keep the temperature of the condenser low, which is essential to avoid lithium bromide crystals forming and obstructing the heat exchanger piping, causing a deterioration in performance or a machine stoppage [5]. Figure 4 shows the diagram of the equivalent mean thermal capacity (3), Qeq , calculated as the sum of the mean thermal capacity effectively required for heating purposes and the thermal capacity that would result from satisfying the demand for air conditioning with an absorption system having a COP of 0.75. Clearly, if we were to size the cogenerator according to the thermal demand in summer, the cogenerator would have to work under a partial load for the rest of the year with a consequent loss of performance. The optimal choice is therefore to size the system to suit the winter thermal demand, which would mean that a percentage of the refrigeration demand for air conditioning is supplied by compression type refrigerators (this percentage amounts to 27% if the prime mover is ICE and to 19% if it is µGT)
Qeq = Q +
R COP
(3)
The system chosen (Figure 5) comprises a cogenerator which produces 330 kWel and 480 kWth coupled - in summer - with a 300 kWc LiBr/water absorber type refrigerator powered by the heat recovered from the exhausts and from the water used to cool the engine. The heat available for heat recovery in summer operation is 407 kWth because the thermal energy recoverable from oil cooling cannot be used due to its too low temperature (80°C compared to 88°C required to supply the absorption).
ACCEPTED MANUSCRIPT The characteristic parameters of this option are given in Table 4. As for the choice of operating hours, based on the supermarket's opening times (8:0021:00), and on the assumption that the cogenerator is switched off when there is no simultaneous thermal and electrical load, the total number of operating hours would amount to about 4000 per year. The items used to calculate the cash flows and thus assess the investment are listed below.
Capital costs: ¾ initial cost of the cogenerator including the cost of installation and commissioning ¾ initial cost of the absorption system including the cost of installation and
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commissioning
Running costs: ¾ cost of maintenance on the system ¾ cost of purchasing methane gas ¾ cost of purchasing electrical energy not produced by the cogeneration system
Revenues: ¾ revenue deriving from not needing to purchase electrical energy ¾ revenue deriving from the sale of white certificates ¾ revenue deriving from tax deductions on methane gas
The revenue from cogeneration relies on selling, or not purchasing, electrical energy and on the tax benefits established by national legislation. In Italy cogeneration systems defined as "high-performance" enjoy a series of incentives such as a tax rebate on methane gas purchased, dispatching priority and the awarding of Tradable White Certificates, TWC. A cogeneration system is defined as high-performance when it complies with the “primary energy saving index” (PES) and “thermal limit” (Lth) [17] parameters defined by the Italian Authority of Energy and Gas [18]. The PES index (4) enables the primary energy saving obtained with cogeneration to be compared with a separate electric generation/boiler system quantified in relation to a separate management. The thermal limit is the ratio between the thermal power annually produced by the cogenerator and the total useful effect given by the sum of electrical and thermal energy produced. For the power ratings in question, these parameters must be higher than 10% and 33%, respectively.
ACCEPTED MANUSCRIPT PES = 1 −
Lth =
f ⋅ Ki m W Q + ηel,ref ηth,ref
Q W +Q
(4)
(5)
where m f is the flow rate of the fuel delivered to the cogenerator, Ki the net heating value of the fuel used, W the electrical energy generated, Q the useful thermal energy and ηel , ref and
ηth, ref the electrical and thermal reference efficiencies that, for the case in point, are
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respectively 0.4 and 0.9. If PES>0,10 and Lth>0,33 a quantity of methane gas amounting to 0.25 Nm3 per kWh produced is liable to a tax reduction, which is further rebated if the electrical energy is being used for self-supply [19, 20]. It can be demonstrated [5] that if the cogenerator has an electrical efficiency of 40% no fuel tax has to be paid. In the case studied, not all the gas methane used is rebated because the electricity cogeneration efficiency is in both cases lower than 40%. On the gas amount liable of tax reduction, the tax payed is € 0,000135 €/ Nm3 instead of 0,012498 €/ Nm3 . TWC, implemented by some European Union Member (Italy, UK, France), are tradable certificates used to achieve energy efficiency in end-use sector. A TWC scheme involves achieving a mandatory energy-saving target against the “business-as-usual” scenario [21]. TWCs attesting to the saving achievable can be exchanged on the basis of bilateral agreements, or using the market managed by the administrator of the electrical energy market. Each Ton of Oil Equivalent, TOE, of electrical and/or thermal energy that is saved corresponds to a TWC, the value of which has been set, for the purposes of simulations, at 100 €/TOE. The calculation of the TOE has been based on a specific table established by the AEEG. According to current legislation, TWCs are issued annually (subject to an audit on the system's compliance with the PES and Lth parameters) for a period of 5 years as of the first year of its application. It is worth noting here that the mechanism for issuing TWCs is currently under review. The outcome of the financial analysis on the investment is the NPV shown in Figure 6, which shows a Pay Back Period of less than 5 years, demonstrating the potential for applying this solution.
ACCEPTED MANUSCRIPT Figure 6 shows the PBP for the present solution also in the case that no economic incentives are provided (dotted line). As can be seen also in this hypothesis the PBP is a still acceptable value of 5 years and 3 months. Finally, in order to assess the emission reduction from trigeneration it has been calculated the TCO2ER indicator (6) defined by Mancarella and Chicco expressed in terms of emission factors [22,23] and reported in Table 5. Q
TCO2 ER = 1 −
( µCOf )Q f 2 W ( µCO ) SP W 2
Qth ) SP Qth + ( µCO 2
1 W )( )R + ( µCO 2 COP SP
(6)
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This indicator compares the emissions produced from trigenerative plant, which depend on the fuel input, to the emissions produced from separate production systems and gives the percentage of emissions reduction. Q
As suggested in [22, 23] it has been assumed µCOf
2
= 202
W [g/kWh], µCO = 525 [g/kWh], 2
Q
µ
Qth CO 2 =
µCOf
2
η SP,th
[g/kWh], with η SP,th =0.9.
As mentioned previously, the alternative hypothesis of using micro turbine systems as prime mover to be coupled with a direct fumes absorption system was also assessed. The micro turbine systems currently on the market have power ratings coming between 30 and 200 kWel. To assess the technical and economic feasibility of this option, a 100 kWel model was chosen. The ideal solution emerged as an installation with three micro turbines (figure 7) coupled during the summer with three 100 kWc direct fumes absorption systems, the technical and economic parameters of which are given in Table 4. The cost items used to calculate the cash flows are the same as for the ICE systems. The analysis (figure 6) indicates a PBP of 7 years and 6 months, because of the higher initial cost of the micro turbine systems and their lower electrical efficiency, though the systems entail lower maintenance costs and are more reliable (guaranteeing 60,000 hours of operation with maintenance costs of 0.014 €/kWh each). In this case the absence of any incentives (dotted line) give a PBP of 8 years.
ACCEPTED MANUSCRIPT Table 5 shows the PES, Lth and TCO2ER values and the percentage of primary energy saved for the solutions analyzed. Despite their lower PES, due to their lower electrical performance, the micro turbine systems can guarantee a higher Lth because, coupled with an absorber, they can reuse all the heat being generated, which has a high enthalpic content. It is common knowledge that the advantage of using trigeneration systems with natural gas depends strictly on the price of methane gas vis-à-vis the price of electricity. Figure 8 shows the trend of the PBP as a function of said ratio: it is clear that the PBP is strongly influenced by the mutual cost of natural gas and electricity. For the present case the ratio is 0.247. It is evident that for ratios of 0.3 and above the PBP rises sharply, especially for the micro turbine systems, which are characterized by a greater
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fuel consumption. The analysis shows that any feasibility study must keep this ratio’s influence in proper account. Moreover, during the fuel contract negotiation it is of paramount importance trying to obtain a fixed link between cost of natural gas and electricity.
2.3. Case2_Combined generation of electrical energy and refrigeration for chilled food preservation The hypothesis of using cogeneration systems to generate electrical energy and refrigerate chilled food products has been analyzed within the Case 2. At the supermarket under investigation the percentage of refrigeration energy demanded for the chilled food counters amounted to 70% of the total requirement for food preservation. The system hypothesized (figure 9) consists of two micro turbine systems coupled with ammonia/water absorption units. The micro turbine systems are similar to those used in Case 1, while the absorption unit chosen is a small 11 kWc [7]. The technical and economic parameters characteristic of this solution are given in Table 6. Having seen that the demand for cooling capacity for food preservation is constant throughout the year and for 24 hours every day (Figure 3), and since it is known that the profit is maximized when the electrical energy is used for self-supply, the cogenerator and the absorption units were sized so as to guarantee that all the electrical energy generated at night could be used by the supermarket. To reach this goal all the frozen food cabinet are maintained in the compression type refrigeration and part of the chilled food counters as well. As a whole the absorption refrigeration covers the 43% of the food refrigeration load for the supermarket. With this arrangement the operating hours of the system amount to 8000 hours/year.
ACCEPTED MANUSCRIPT The following is a list of the items used to calculate the cash flows needed to assess the investment. Capital costs: ¾ initial cost of the cogenerator including the cost of installation and commissioning ¾ initial cost of the absorption system including the cost of installation and
commissioning Running costs: ¾ cost of plant maintenance ¾ cost of purchasing methane gas ¾ cost of purchasing the electrical energy not generated by the cogeneration system
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Revenue: ¾ revenue deriving from not needing to purchase electrical energy ¾ revenue deriving from tax deductions on methane gas ¾ revenue deriving from the sale of white certificates
The assessment gives rise to a PBP of less than 5 years (figure 10), an extremely worthwhile result for future applications. The PES, Lth and TCO2ER values for the application are shown in Table 5, they are higher than in Case1 since all the energy generated can always be exploited. A problem that cannot be neglected, given the greater number of operating hours involved, is the need to overhaul or replace the machine after approximately 7 years of operation.
2.4. Case 3_Combined generation of electricity and heating/cooling for air-conditioning, associated with electrical energy generation using photovoltaic panels As demonstrated previously, the electrical energy generated by the trigeneration systems does not saturate the demand for electricity so, with polygeneration in mind, we hypothesized being able to exploit the roof of the building for the installation of photovoltaic panels. The PVSOL [24] dynamic simulator was used to design the grid-connected photovoltaic system. Table 7 shows the results of the sizing and the characteristics of the system installed.
ACCEPTED MANUSCRIPT The following is a list of the items used for the economic assessment of the PV system. Capital costs: ¾ initial cost of the system including installation and commissioning
Running costs: ¾ cost of plant maintenance
Revenue: ¾ revenue deriving from not needing to purchase electrical energy ¾ revenue deriving from the 2007 energy account funding for semi-integrated systems ¾ revenue deriving from the sale of unused energy
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Figure 11 shows the NPV for the investment in the solar system and in the solar system associated with trigeneration using ICE. It is worth emphasizing that, having established an extra-maintenance agreement for the ICE that includes a total number of 96,000 operating hours, the investments are compared for a working life of at least 15 years. As it is well known, even if they show great perspectives for the future, PV systems still need Government subsidies to reach profitability. The Italian Government support the production of electric energy from solar source on the basis of "feed in tariff" (DM 19/2/2007 [9]), a scheme of trading account incentives for promoting the use of electricity from solar sources that awards an economic incentive as a function of the kWh generated by a plant. It is interesting to note that the integration of the two distributed energy technologies presents a NPV lower than the phothovoltaic system alone thank to the profitability of the trigenerative plant. Table 5 shows the CO2ER (7) calculated as the sum of TCO2ER and carbon dioxide emission reduction derived from photovoltaics. CO2ER= TCO2ER+CO2ERpv
(7)
2.5. Case4_Combined generation of electricity and refrigeration for chilled food preservation, associated with electrical energy generation using photovoltaic panels Table 5 shows the CO2ER for the solution analyzed, calculated as in the previous case. To hypothesize the investment relating to the combined production of electricity and refrigeration energy for food preservation and of electrical energy by means of photovoltaic panels, one needs to consider the different working lives of the systems. In the cost items used
ACCEPTED MANUSCRIPT for the analysis of the trigeneration system, an item for extraordinary maintenance has been added, which includes the replacement of the micro turbine and absorber systems at the end of their working life. Figure 11 shows the trend of the NPV for the photovoltaic system and the solution combined with trigeneration. Although the need to replace the equipment after seven years induces a delay in the PBP with respect to the previous solution, the Pay Back Period is always lower than the photovoltaic system alone.
CONCLUSIONS
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This article analyses four different solutions for applying Distributed Generation and trigeneration to the supermarket sector, which emphasize an important primary energy saving opportunity. As a first case, the generation of electricity and heating/cooling energy for airconditioning was considered. Using ICE combined with a LiBr/water absorption systems gives a PBP of less than 5 years, whereas using a micro-turbine-system, though potentially interesting, is still not competitive because of the higher initial cost and lower electrical efficiency of the machine. It is important to emphasize, however, that the profitability of the investment strongly depends on the ratio between the prices of natural gas and electrical energy. As a second solution, using trigeneration systems for the combined generation of electricity and refrigeration energy for the chilled food products was considered, which is particularly interesting because the refrigeration energy demand is one of the main cost items for supermarkets. The PBP in this case is less than 5 years, assuming the congenerating equipment has 7 years of operative life. This option enables a PES of 56%. The drawbacks of this solution relate to the difficulty of obtaining indirectly powered ammonia/water absorption systems on the market, and to the high initial outlay. Finally, with a view to maximizing the energy saving, the hypothesis of combining photovoltaic systems with the trigeneration systems was also analyzed. The investments, exploiting the fiscal incentive mechanisms, gave a PBP of approximately 10 years. Out of 4 options, the first two were analyzed both in the case an economic incentive is provided by the Government (the Italian situation has been applied here) and in the case no economic incentive at all is provided. Absence of incentives showed only a reduced penalty in
ACCEPTED MANUSCRIPT PBP, therefore demonstrating that the technology is intrinsically viable not only on energetic terms but also on economic terms. On the other hand, when the PV system is added to the trigeneration, economic incentives still remain a must in order to achieve a reasonable profitability for the investment.
Acknowledgements
The authors are grateful indebted to Inres Coop, Milan, which monitored and elaborated the energy consumptions of the supermarket analyzed. This work has been supported by the Italian Ministry of Environment and by Marche Regional Government (Ancona, Italy) within the the framework of the project "Ricerche energetico-ambientali per l'AERCA di Ancona
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Falconara e bassa valle dell'Esino". The authors thank the anonymous reviewers for their insightful comments and precious advice given on how to improve this paper.
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NOMENCLATURE AEEG
Autorità per l’energia elettrica ed il gas (Italian Electricity and Gas Authority)
C
costs
CHP
combined heat and power plant
CO2ER
CO2 emission reduction
COP
coefficient of performance
DG
distributed generation
E
expenditure
F
cash flow
I
cost for interests
ICE
internal combustion engines
Ki
net heating value [kWh/Nm3]
Lth
thermal limit
m
flow rate [Nm3/h]
η
efficiency
µCO2
emission factor [g/kWh]
µGT
microturbines
NPV
net present value
PBP
payback period
PES
primary energy saving
PV
photovoltaic system
Q
thermal power [kW]
r
interest rate
R
cooling power [kW]
Re
revenue
STC
standard condition
TCO2ER
trigeneration CO2 emission reduction
TOE
ton of oil equivalent
TWC
tradable white certificate
W
electrical power [kW]
Subscripts c
cooling
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ACCEPTED MANUSCRIPT el
electrical
eq
equivalent
f
fuel
k
current year
O&M
operation and maintenance
pv
photovoltaics
ref
reference
SP
separated production of electrical and thermal energy
th
thermal
ACCEPTED MANUSCRIPT References
[1] Gianfranco Chicco, Pierluigi Mancarella. Distributed multi generation: A comprehensive view, Renew Sustain Energy Rev(2007), doi: 10.106/j.rser.2007.11.014. [2] www.terna.it. Energy consumption in Italy_General data (2006) [3] Baxter, V.D. 2005. "Summary of Advanced Supermarket R&D Activities Conducted Under International Energy Agency (IEA) Annex 26," 8th IEA Heat Pump Conference, Las Vegas, NV USA, 2005. [4] Office of Natural Resources, Canada, Commercial and Institutional Retrofits - Guide Saving Energy Dollars in Stores, Supermarkets and Malls, 2003. [5] E.Macchi, P.Campanari, P.Silva, La microcogenerazione a gas naturale, Polipress.pp,
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Milan, 2005, ISBN 88-7398-016-3. [6] Piero Colonna, Sandro Gabrielli, Industrial trigeneration using ammonia–water absorption refrigeration systems (AAR), Applied Thermal Engineering 23 (4) (2003) 381–396 [7] S.A. Tassou, I. Chaer, N. Sugiartha, Y.-T. Ge, D. Marriott, Application of tri-generation systems to the food retail industry, Energy Conversion and Management 48 (11) (2007) 29882995. [8] Directive 2001/77/EC , Promotion of electricity produced from renewable energy sources in the internal electricity market, European Parliament and of the Council, 27 September 2001. [9] Italian legislative Decree 20, 19/2/2007, Criteri e modalita' per incentivare la produzione di energia elettrica mediante conversione fotovoltaica della fonte solare, in attuazione dell'articolo 7 del decreto legislativo 29 dicembre 2003, n. 387. [10] G.G. Maidment, X. Zhao, S. B. Riffat and G. Prosser, Application of combined heat-andpower and absorption cooling in a supermarket, Applied Energy 63 (3) (1999) 169-190. [11] G.G. Maidment, R.M.Tozer, Combined cooling heat and power in supermarkets, Applied Thermal Engineering, 22 (6) (2002) 653-665. [12] G.G. Maidment, X.Zhao, S.B. Riffat, Combined cooling and heating using a gas engine in a supermarket, Applied Energy, 68 (4) (2001) 321-335. [13] Leland Blank, Anthony Tarquin, Engineering Economy, McGraw-Hill, New York, 2006, ISBN 0-07-291863-2. [14] E. Cardona, A. Piacentino, F. Cardona, Part I: Assessing economic and technical potential. Energy saving in airports by trigeneration, Applied Thermal Engineering, 26 (1415) (2006) 1427–1436.
ACCEPTED MANUSCRIPT [15]
Zhi-Gao Sun, Energy efficiency and economic feasibility analysis of cogeneration
system driven by gas engine, Energy and Building 40 (2) (2008) 126-130. [16] P.A. Pilavachi, Mini- and micro-gas turbines for combined heat and power, Applied Thermal Engineering 22 (18) (2002) 2003-2014. [17] Luigi P.M.Colombo, Fabio Armanasco, Omar Perego, Experimentation on a cogenerative system based on a microturbine, Applied Thermal Engineering 27 (4) (2007) 705-711. [18] Deliberazione 42/02 of the Italian Electricity and Gas Authority, Testo coordinato delle integrazioni e modifiche apportate con deliberazione 11 novembre 2004, n. 201/04, e con deliberazione 29 dicembre 2005, n. 296/05. [19] Italian law 448/98. Misure di finanza pubblica per la stabilizzazione e lo sviluppo.
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[20] Deliberazione 16/98 of the Italian Electricity and Gas Authority. Verifica di congruità dei parametri per la determinazione dell’onere termico per il primo trimestre 1997. [21] Luis Mundaca, Transaction costs of Tradable White Certificate schemes: The Energy Efficiency Commitment as case study, Energy Policy 35 (8) (2007) 4340-4354. [22] Gianfranco Chicco, Pierluigi Mancarella, Assessment of the greenhouse emissions from cogeneration and trigeneration systems. Part 1:Models and indicator, Energy 33 (2008) 410417. [23] Gianfranco Chicco, Pierluigi Mancarella, Assessment of the greenhouse emissions from cogeneration and trigeneration systems. Part 2:Analysis Techniques and application cases, Energy 33 (2008) 418-430. [24] PVSol 3.0 - Computer simulation software for design and calculation of photovoltaic systems. The Solar design Company, Albuquerque, NM, 2003.
ACCEPTED MANUSCRIPT Figure captions Figure 1. Electrical energy demand according to end-uses in a supermarket [4] Figure 2. Monthly energy consumption at the investigated supermarket Figure 3. Daily distribution of electrical energy used for air-conditioning and refrigeration Figure 4. Equivalent mean thermal capacity (Case_1) Figure 5. Layout of a cogeneration plant with ICE (Case_1) Figure 6. NPV for Case 1, solutions with ICE and µGT (the dotted lines represent the NPV in
case no economic incentives are provided) Figure 7. Layout of a cogeneration plant with µGT (Case_1) Figure 8. Variation in the PBP as a function of the ratio between gas and electricity prices
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Figure 9. Layout of a trigeneration plant with ammonia/water absorbers (Case 2) Figure 10. NPV for Case 2, combined generation of electricity and refrigeration for chilled
food preservation (the dotted line represents the NPV in case no economic incentives are provided) Figure 11. NPV solution with a PV system combined with a trigeneration plant
ACCEPTED MANUSCRIPT Table captions Table 1: Characteristic parameters of the supermarket under study Table 2: Characteristic parameters of the current energy procurement and separate management system Table 3: Distributed generation solutions analyzed Table 4: Technical and economic parameters of the trigeneration plant with ICE and µGT (case 1) Table 5: PES, Lth and carbon-dioxide emission reduction of the solutions analyzed Table 6: Technical and economic parameters of the trigeneration plant with ammonia/water absorbers (case 2)
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Table 7: Technical and economic parameters of the PV system
ACCEPTED MANUSCRIPT
Other_electrical equipment 16%
Lighting 21%
Bakery 6% Food Preparation 7% HVAC 12%
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Refrigeration 38%
Figure 1. Electrical energy demand according to end-uses in a supermarket [4]
ACCEPTED MANUSCRIPT Thermal energy consumption Electric energy consumption (except for food refrigeration) Electric energy consumption for food refrigeration 400 350
[MWh]
300 250 200 150 100 50
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months
Figure 2. Monthly energy consumption at the investigated supermarket
ic D
ov N
ct O
Se p
ug A
Ju l
Ju n
M ay
pr A
M ar
Fe b
Ja
n
0
ACCEPTED MANUSCRIPT
350 REFR_JUL REFR_JAN
300
[kW]
250 200 150 100 AC_JUL AC_AUG
50 0
0
2
4
6
8
10
12
14
16
18
20
22
24
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hours
Figure 3 Daily distribution of electrical energy used for air-conditioning (AC) and
refrigeration (REFR)
ACCEPTED MANUSCRIPT
Equivalent mean thermal capacity 800
[kW]
600 400 200
Dic
Nov
Oct
Sep
Aug
Jul
Jun
May
Apr
Mar
Feb
Jan
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0
Figure 4. Equivalent mean thermal capacity (Case 1)
ACCEPTED MANUSCRIPT WINTER
SUMMER
HOT FUMES
Qf=907 kWth ICE
HOT WATER COOLING OIL
W=330 kWel
Qth=481 kWth
Heating plant
HOT FUMES
Qf=907 kWth ICE
HOT WATER COOLING OIL
W=330 kWel
Qth=407 kWth
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Figure 5. Layout of a cogeneration plant with ICE (Case 1)
R=300 kWc Abs.Chiller LiBr/water
ACCEPTED MANUSCRIPT
400
ICE µGT
NPV [k€]
200 0 -200 -400 -600
0
1
2
3
4
5
6
7
8
9
years
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Figure 6. NPV for Case 1, solutions with ICE and µGT
(the dotted lines represent the NPV in case no economic incentives are provided)
ACCEPTED MANUSCRIPT WINTER
SUMMER
Qf=990 kWth
Qf=990 kWth
µGT
µGT
µGT W=300 kWel
Heat exchanger H20 /Fumes
Qth=501 kWth
µGT
µGT
µGT W=300 kWel
3 x Absorption chillers LiBr/water
R=300 kWc
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Figure 7. Layout of a cogeneration plant with µGT (Case 1)
ACCEPTED MANUSCRIPT
15
PBP [years]
present situation 10
5 case 1 ICE case 1 µGT case 2 0 0,20
0,25
0,30
0,35
ratio gas-to-electricity [(€/kWh)/(€/kWh)]
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Figure 8. Variation in the PBP as a function of the ratio between gas and electricity prices
ACCEPTED MANUSCRIPT
Qf=660 kWth
µGT
µGT W=200 kWel
Hot fumes T=270°C
Qth=334 kWth
Absorption Chillers ammonia/water 15 x 11 kWc
R=165 kWc
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Figure 9. Layout of a trigeneration plant with ammonia/water absorbers (Case 2)
ACCEPTED MANUSCRIPT
400
NPV [k€]
200 0 -200 -400 -600
0
1
2
3
4
5
6
7
8
9
years
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Figure 10. NPV for Case 2, combined generation of electricity and refrigeration for chilled
food preservation (the dotted line represents the NPV in case no economic incentives are provided)
ACCEPTED MANUSCRIPT
1
PV PV+case 1 PV+case 2
NPV [M€]
0 -1 -2 -3 -4
0
1
2
3
4
5
6
7
8
9
10
11
years
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Figure 11. NPV for the solutions with PV system combined with trigeneration plant
ACCEPTED MANUSCRIPT
Parameters
Sales area [m²]
10,000
Opening days per year [days]
310
Annual electricity consumption [MWh]
5,093
Mean electrical capacity [kW]
828.5
Maximum electrical capacity [kW]
1,050
Annual thermal energy consumption [MWh]
880
Mean thermal capacity [kW]
280
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Table 1: Characteristic parameters of the supermarket under study
ACCEPTED MANUSCRIPT
Parameters characteristic of separate management
Cost of purchasing electrical energy
0.17 €/kWh
Cost of purchasing methane gas
0.4 €/Nm3
Efficiency of condensing boiler
106.6%
Average COP of chilled food refrigerators
2.8
Table 2: Characteristic parameters of the current energy procurement and separate
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management system
ACCEPTED MANUSCRIPT
Energy end-use* Heating Electricity
Air conditioning Food preservation
Case 1 Cogenerator Cogenerator
Case 2 Boiler system Cogenerator
Case 3 Cogenerator Cogenerator/ Photovoltaics LiBr/water Compression LiBr/water absorber refrigerator absorber Compression Ammonia/water Compression refrigeration absorber refrigeration Table 3: Distributed generation solution analyzed
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*Energy end-use is referred to cogeneration system
Case 4 Boiler System Cogenerator/ Photovoltaics Compression refrigerator Ammonia/water absorber
ACCEPTED MANUSCRIPT
ICE
µGT
Electrical capacity [kW]
330
3 x 100
Total retrievable thermal capacity [kW]
481
3 x 167
Thermal capacity of hot fumes [kW]
220
3 x 167
Fuel consumption [Nm3/h]
95
3 x 35
Parameters
Cogeneration
Electrical efficiency 38.9% Initial cost €/kWel
800
1200
7
3 x 1.4
Days of operation per year
310
310
Hours of operation per year
4,000
4,000
Installed cooling capacity [kWc]
300
3 x 115
Available thermal capacity from engine[kWth]
407
3 x 167
Cost of O&M [€/kW-year]
3.3
10
Average COP
0.75
0.7
Initial cost [€/kW]
300
450
Cost of O&M [€/hour]
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30%
Absorption refrigeration
Table 4. Technical and economic parameters of the trigeneration plant with ICE and µGT
(Case 1)
ACCEPTED MANUSCRIPT
PES
Lth
TCO2ER
20%
52%
22%
16%
56%
14%
56%
66%
43%
Case 1 ICE LiBr/water absorber Microturbine LiBr/water absorber Case 2 Microturbine Ammonia/water absorber
CO2ER
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Case 3 ICE LiBr/water absorber Photovoltaics Case 4
/
/
40%
Microturbine / / 60% Ammonia/water absorber Photovoltaics Table 5. PES, Lth and carbon-dioxide emission reduction of the solutions analyzed
ACCEPTED MANUSCRIPT
Parameters
Absorber Number of units installed
15
Unitary Cooling capacity [kWc]
11
Unitary Input thermal capacity [kWth]
22
COP
0,5
Initial cost [€/kW]
813
Cost of O&M [€/kW-year]
57,21
Table 6. Technical and economic parameters of the trigeneration plant with ammonia/water
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absorbers (Case 2)
ACCEPTED MANUSCRIPT
Parameters
Manufacturer
Sharp Corporation
Power rating [W]
125
Performance STC
13.3%
Electrical efficiency
38.9%
Orientation
45°
Inclination
30°
Plant Energy produced Initial cost of plant
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Cost of O&M Guaranteed life
856,000 [kWh] 3.4 M€ 2% of Initial cost of plant 20 years
Table 7. Technical and economic parameters of the PV system
