Electricity savings and CO2 emissions reduction in buildings sector: How important the network losses are in the calculation?

Energy 35 (2010) 485–490

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Electricity savings and CO2 emissions reduction in buildings sector: How important the network losses are in the calculation? C.S. Psomopoulos a, *, I. Skoula b, C. Karras c, A. Chatzimpiros b, M. Chionidis b a

Technical Institute of Piraeus, Department of Electrical Engineering, High Voltage Laboratory, P. Ralli & Thivon 250, 122 44 Egaleo, Greece EPTA Ltd – Environmental Consultants Engineers, 15 Olofytou str., 11142 Athens, Greece c EMEK S.A.-Hellenic Metallic Constructions, Megaridos str., 19300 Aspropyrgos, Greece b

a r t i c l e i n f o

a b s t r a c t

Article history: Received 4 May 2009 Received in revised form 8 October 2009 Accepted 13 October 2009 Available online 14 November 2009

The increase of CO2 emissions and the emerging climate change are the most serious environmental problems nowadays and limit economic development. This increase is mainly attributed to the growing world population and the related growth in energy demand, which results in the vast consumption of fossil fuels in the power generation sector. Significant actions for the implementation of energy saving measures have been adopted worldwide for reducing greenhouse gas emissions. CO2 calculators have been developed to evaluate the effectiveness of these measures, relating energy to CO2 emissions. These calculators include in most cases the entire power system. The purpose of this work was to evaluate the role of the electricity networks’ losses in the actual CO2 reduction potential, following the implementation of energy saving measures, in relation to the network’s voltage level in which the infrastructure is connected. Buildings are representative due to their volume and to different voltage levels of power supply. The work presented was conducted in the framework of the Intelligent Energy Europe Programme entitled Bottom Up to Kyoto (BUtK), as a part of an evaluation of the CO2 emissions’ reduction potential through energy savings measures in 6 municipalities of EU’s New Member States. Ó 2009 Elsevier Ltd. All rights reserved.

Keywords: CO2 emissions CO2 calculators Electricity production Energy saving in buildings Electricity network losses

1. Introduction The increase of greenhouse gas (GHG) emissions in the atmosphere is currently the most serious environmental threat, and at the same time a factor that limits economic growth [1,2]. Climate change will cause damaging impacts in the next decades [1] affecting the natural and human systems in many ways [3]. That is why in 1992, in Rio de Janeiro over 150 governments recognised climate change as a common concern of humankind and signed the United Nations Framework Convention on Climate Change (UN-FCCC, or ‘the Climate Convention’), in order to protect the climate system by stabilising greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system [4,5]. At the December 1997 Third Conference of Parties (COP-3) in Kyoto, the industrialized world agreed to reduce emissions of greenhouse gases approximately 6–8% below 1990 levels by 2008–2012 [6,7]. The Intergovernmental Panel on Climate Change (IPCC) in its published assessment report concluded that

* Corresponding author. Tel.: þ30 2105381182; fax: þ30 2105381321. E-mail address: [email protected] (C.S. Psomopoulos). 0360-5442/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.energy.2009.10.016

most of the warming observed over the last 50 years is caused because of human activities [1,8,9]. A country’s CO2 emissions are caused by different economical, social, behavioural, cultural, and technological factors. Analyzing the internal production factors leading to CO2 emissions in an economy is both a pertinent and relevant effort because it helps decision-makers identify those policy measures being most effective in curbing CO2 emission trends [4–14]. The combustion of fossil fuels used in power industry emits to the atmosphere CO, dust suspension and greenhouse gases like CO2, N2O, SO2 and NOx [10,11]. CO2 emissions were the largest contributor to emissions related to climate change, accounting for 82% of total EU greenhouse gas emissions in 2002 [12,13]. Three quarters of the CO2 volume are attributed to human activity and are directly related to the combustion of fossil fuels [7,11,14,15] (35–36% of the global CO2 emissions [14–18] and about 39% of the total EU CO2 emissions are produced from the electricity and heat production [12,13]). These emissions are considered to be the main cause of global warming that will occur in the next 40 or more years [3,18–20]. Energy-related CO2 emissions, which account for example for over 80% of the emissions in the US [17] (USA is one of the largest energy consumers and first in CO2 emissions, Japan and Germany are the second and third within the G-8 [21]), and more than one-

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half of CO2 emissions in Greece [22–28], have been the focal point in many countries that have adopted measures to limit emissions of greenhouse gases [7,29,30]. The relationships between output and energy consumption, as output and environmental pollution, have been the subject of intense research. Most studies focus on testing the nexus of outputenergy or output-pollution separately while no investigation has so far been made to examine these two links under the same framework [21,32,33]. Regarding fossil fuels, the amount of carbon reduced by energy saving measures can be determined from the change in the demand and the carbon content of the fuel. For grid electricity, the amount of carbon abated depends both on the magnitude of the reduction and on which power generation plant produces the last kWh of the decreased demand. The marginal generation plant depends on the total demand on the system at the time that the demand reduction occurs, and on the operation of the system as a whole. The emissions depend on the carbon content of the fuel used and the electrical efficiency of the generation unit [29,32,33]. Development of targeted and efficient emission-mitigation policies in the energy sector is greatly helped if policy makers have the most accurate picture possible of sources of CO2 emissions. Moreover, the energy supply situation in a country not only determines the current level of energy use and CO2 emissions, but also influences the potential for future CO2 emission reduction from the energy sector [7]. The production of energy by combusting fossil fuels generates pollutants and carbon dioxide. Since current electricity production heavily relies on fossil fuels, it is envisioned that expanding generation technologies based on zero carbon emissions and renewable energy sources would dramatically reduce future greenhouse gas (GHG) emissions [34–39]. This paper investigates the role of the electricity networks’ losses in the actual CO2 emissions reduction when energy efficiency measures are applied in the buildings sector. Buildings are essential due to their large number, their significant consumption of electricity and the variety in the networks’ voltage level in their main power feeding point. The purpose of the work was to evaluate the CO2 reduction potential after the implementation of energy saving measures in public buildings of 6 municipalities in the following New Member States: Estonia, Latvia, Poland, Romania and Slovenia. This work was conducted in the framework of the Intelligent Energy Europe Programme entitled Bottom Up to Kyoto (BUtK,) and concerned the above-mentioned countries. 2. Methodology 2.1. Electricity production and network losses All networks by definition have losses in their components during the transmission and distribution of electricity. These losses are caused by joule heating, hysteresis, leakages, etc. The losses in European Networks can be divided in the following components presented in Fig. 1 [39–42]. According to Eurostat [42] and International Energy Agency [41] for the year 2005 these losses for European Union – 27 were 220,735 GWh, when the total electricity production was 3,311,000 GWh, electricity imports were 324,258 GWh and exports were 312,942 GWh. The breakdown of EU-27 electricity data is presented in detail in Table 1. Table 2 represents the losses for the countries under consideration, while these are compared with the EU-27 and EU-15, as these are officially presented in EUROSTAT and IEA databases [41,42] (Fig. 2). Another important parameter that affects the calculation of the electricity losses as a percentage of the electricity demand in a country or region, is the inclusion or not of the imports and

Distribution transformers 25% Conductors and cables 15%

LV Conductors and cables 25%

System Transformers 10% Meters, unbilled consumption, etc 5%

HV Conductors and cables 10% HV Transformers 10%

Fig. 1. Electricity transmission and distribution loss components in European Networks (source [39,40]).

exports, and of course if the net or the gross electricity production is taken into account. As it can be concluded from Tables 2 and 3, imports and exports can significantly affect the result of the estimated percentages, if their differences are high. Fig. 3 presents these percentages of the aforementioned cases:

NL1TOTAL ¼

ELE gEP þ EIMP  EEXP

(1)

NL2TOTAL ¼

ELE nEP þ EIMP  EEXP

(2)

Table 1 Electricity data in European Union – 27 countries for 2005. EU-27 Electricity data

Unit: GWh

Production from: Coal Oil Gas Biomass Waste Nuclear Hydro Geothermal Solar PV Solar thermal Wind Tide Other sources

1,000,829 138,503 663,744 57,332 27,086 997,699 340,846 5397 1491 0 70,496 534 7043

Total production Imports Exports

3,311,000 324,258 312,942

Domestic supply Statistical differences

3,322,316 675

Total transformationa Electricity plants Heat plants Energy sectorb Distribution losses Total final consumption Industry Transport Residential Commercial and public services Agriculture/forestry Fishing Other non-specified

2263 0 2263 344,127 220,735 2,755,866 1,127,359 74,433 798,080 701,767 47,521 262 6444

a Transformation sector includes electricity used by heat pumps and electricity used by electric boilers. b Energy Sector also includes own use by plant and electricity used for pumped storage. Source [41,42].

C.S. Psomopoulos et al. / Energy 35 (2010) 485–490 Table 2 Electricity losses and generation in EU-27, EU-15 and selected EU countries for 2005.

487

Table 3 Electricity losses and generation in EU countries under evaluation for 2005.

Unit

Gigawatt hour

Unit

Gigawatt hour

Year

2005

Year

2005

Product

Electrical Energy

Product

Electrical Energy

Countries Distribution Final energy losses consumption

Total gross electricity generation

Total net electricity generation

EU-27 220,728 EU-15 180,210 Estonia 1103 Latvia 836 Poland 14563 Romania 5844 Slovenia 954

3,310,401 2,848,272 10,205 4905 156,936 59,413 15,117

3,135,445 2,709,512 9114 4714 143,550 55,503 14,149

2,755,978 2,443,911 6023 5701 98,835 39,046 12,742

Countries Distribution losses

Total gross electricity generation

Electricity Imports

Electricity Exports

EU-27 220,728 Estonia 1103 Latvia 836 Poland 14,563 Romania 5844 Slovenia 954

3,310,401 10,205 4905 156,936 59,413 15,117

324,258 345 2855 5002 2321 7234

312,942 1935 707 16,188 5224 7558

Source [41,42].

Source [41,42].

where NLTOTAL is the percentage of the energy losses in the country’s network, ELE are the electricity losses in the network, gEP is the gross electricity production, nEP is the net electricity production, EIMP are the electricity imports and EExP are the electricity exports. 2.2. The CO2 evaluation method considering network losses Typical models evaluating the CO2 emissions from electricity consumption as it was calculated by different tested and proven calculators are simple and usually follow the simple equation (3) as the CO2 calculator of MedClima Project [43].

ECO2 ¼ EFCO2 $EE

(3)

where ECO2 is the total emissions in kgCO2 produced by the electricity consumption or savings EE (kWh), and EFCO2 is the CO2 emission factor (kg CO2/kWh). The emissions are usually expressed in tCO2, thus the results of this equation should be multiplied with the factor 103. The emission factors can be calculated by a methodology proposed by IPCC [1,35], EEA [24], and individual research works focused on countries e.g. for UK [25] and Belgium [26]. The CO2 emission factor, known also as ‘carbon intensity’, provides the quantity of carbon emitted to the atmosphere per unit of electricity delivered (e.g. in kg CO2/kWh). If this factor concerns an isolated power generation plant it can be directly determined from its fuel use and output. In a multiplant generation system,

supplying electricity through a common supply network, the carbon emissions obviously depend at any time on what generation plants exist, and which of them are actually operating at any point in time [1,24–26,35,44,45]. The simplest and most commonly used definition of carbon emission factor is the ‘system-average’ factor calculated by estimating the total carbon emissions from the system during a year, and dividing that figure by the total quantity of electricity transmitted (or delivered, if end-use intensities are being considered). Compared to others, this definition has the advantage that all carbon emissions can be assessed when all end-use sectors are combined. However, if electricity consumption is reduced (or increased), not all power stations are affected equally: the operation of ‘base load’ stations (typically nuclear in the aforementioned countries) is unchanged, while the change in demand is met by reduced operation of other (typically coal-powered) plants. At this point, it must be mentioned that in other countries base load stations use coal as fuel and the decrease to the load is reflected to the operation of gas turbine plants, which have higher operational cost [1,24–26,35,44,45]. In this work, the system average intensity was used to measure the carbon emissions resulting from electricity generation. These values were the typical ones as they were official calculated for each country [1,24–26,35,44,45]. This is also the usual method used by the emissions’ calculators around the world. These calculators based on the system average intensity usually operate with one of the following two types of CO2 emissions’ factors estimation methods:

GWh 160000 Distribution losses

140000 120000

Total gross electricity generation

100000

Electricity Imports

80000

Electricity Exports

60000 40000 20000 0 Estonia

Latvia

Poland

Romania

Slovenia

Fig. 2. Graphical representation of the data presented in Table 3.

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losses components are not available in detail for every country, the European average components presented in Fig. 1 will be used in the calculation of the factor fNL. Thus, since the majority of public buildings in EU is connected to the low or medium voltage network, this factor will have the values 1 for low voltage and 0.75 or 0.5 for the medium voltage depending of the inclusion or not of the distribution transformers’ losses in the calculation [39–42]. The equations (4) and (5) can be written as:

% LOSSES 16,00 14,00 12,00 10,00 8,00

  EsTOTAL ¼ EE $ 1 þ NLiTOTAL $fNL

6,00

This equation approaches the total electric energy savings or consumption from a building or facility including the network losses and the connection point, provided that the electricity savings or consumption (EE) is known.

4,00 2,00 0,00

(6)

EU 27

Estonia

Latvia

Poland

Romania

Slovenia

Ele/gEP

7,01

14,66

12,18

9,28

9,84

6,31

NL1total

6,64

12,80

11,85

9,99

10,34

6,45

NL2total

7,01

14,66

12,18

11,00

11,11

6,90

3. Results and discussion

Fig. 3. Losses’ percentage calculated based on electricity production, imports and exports, by country.

(1) The emission factor that includes the power generation and the electricity grid, which corresponds to the emissions from the power plants up to the connection point of the building in the grid, in the low voltage network. (2) The emission factor estimated based on the multiplant generation system, and which usually not includes the grid parameter, where the electricity losses occur. The evaluation of the errors in the emissions reduction calculation is based on the actual losses that a network presents, as a percentage of the electricity produced including imports-exports. This percentage can be calculated as it is shown above in equations (1) and (2). In the common CO2 calculators, the network location in which the building or infrastructure is connected (meaning low voltage network or medium voltage network), is usually not considered at all. As it is mentioned above, in the two basic concepts of the commonly used ‘system-average’ the position is either not considered or every infrastructure is considered to be connected in the low voltage network. This approach even though simplifies the calculations it introduces by definition an error, whose magnitude depends on the type of the system’s average intensity and the magnitude of the electricity losses [39–45]. Further to this, it is widely accepted that network losses depend on the point of the grid that the consumer is connected. This can be approached by the simple equations:

  EsTOTAL ¼ EE $ 1 þ NLiTOTAL

Using the relations above and the data provided by the Tables 1 and 2, including data from IEA and Eurostat [41,42], it is assessed that the network losses have an impact to the calculation of CO2 emissions. These results can be seen in the following Figs. 4–6, where the assessed error is presented. For the error’s percentage assessment in calculation of carbon emissions, the following relation was used:

NLIF ¼

EVAL ECO 2 CALC ECO 2

!  1 $100%

(7)

CALC where NLIF is the network losses impact in CO2 calculation ECO 2 corresponds to the CO2 calculation by the common used calculators EVAL to the CO emission evaluation by the methodology and ECO 2 2 presented in this work. The aforementioned two cases for the emission factor were 1 is the carbon intensity that includes the examined, where EFCO 2 2 is the carbon intensity that is based only in the electricity grid, EFCO 2

18,00 16,00

% Impact 14,00 12,00 10,00 8,00

(4)

6,00

and 4,00

( NLiTOTAL ¼

NL1TOTAL ¼ NL2TOTAL ¼

ELE gEPþEIMP EEXP ELE nEPþEIMP EEXP

(5)

where EsTOTAL are the total energy savings including the network losses reduction, or the total energy consumption including the network losses. In order to include the position in the grid where the building is connected, a factor fNL is proposed to be included in the losses calculation in the above equations, corresponding to the connection of the building. The values of fNL should vary between (0,1], where the value 1 corresponds to connection to the low voltage network (all the losses are included). Since data about the network

2,00 0,00 EU 27

Estonia

Latvia

Poland

Romania

Slovenia

EF1-NL1total

0,00

0,00

0,00

0,00

0,00

0,00

EF1-NL2total

0,00

0,00

0,00

0,00

0,00

0,00

EF1-Ele/gEP

0,00

0,00

0,00

0,00

0,00

0,00

EF2-NL1total

6,64

12,80

11,85

9,99

10,34

6,45

EF2-NL2total

7,01

14,66

12,18

11,00

11,11

6,90

EF2-Ele/gEP

6,67

10,81

17,04

9,28

9,84

6,31

Fig. 4. Losses’ impact in carbon reduction evaluated for buildings connected in low voltage networks, by country.

C.S. Psomopoulos et al. / Energy 35 (2010) 485–490

14,00

% Impact 12,00

10,00

8,00

6,00

4,00

2,00

0,00 EU 27

Estonia

Latvia

Poland

Romania

Slovenia

EF1-NL1total

1,10

1,21

1,20

1,16

1,17

1,10

EF1-NL2total

1,11

1,25

1,20

1,18

1,18

1,11

EF1-Ele/gEP

1,11

1,18

1,29

1,15

1,16

1,10

EF2-NL1total

4,98

9,60

8,89

7,49

7,76

4,84

EF2-NL2total

5,26

10,99

9,14

8,25

8,33

5,18

EF2-Ele/gEP

5,00

8,11

12,78

6,96

7,38

4,73

Fig. 5. Losses’ impact in carbon reduction evaluated for buildings connected in medium voltage networks including the transformer losses (fNL ¼ 0,75), by country.

multiplant generation. The buildings’ connections to the grids, which were assumed for the evaluation of the network losses impact, were buildings connected to the low voltage network, buildings connected to the medium voltage distribution network and buildings connected to the medium voltage network, for which the distribution transformers’ losses were included in the network losses. These results are presented in Figs. 5 and 6. The network is an important parameter affecting the electricity needs to cover the demand. The electricity generation plants must produce adequate power to cover the demand and the network losses, which are increased if the length is high or the installed equipment is old or moderately maintained. In many cases such as

489

the ones presented here, the network losses are very increased, reaching sometimes the 15%. The inclusion or not of this amount of electricity that is consumed, can have significant impact in the calculation of CO2 emissions. [1,5,6,14–18,24–28,35]. The commonly used calculators are based on the ‘systemaverage’ factor calculated by estimating the total carbon emissions from the system during a year, and dividing that figure by the total quantity of electricity transmitted (or delivered, if end-use intensities are being considered). [1,6,24–26,35,44,45]. The ‘system-average’ presents thus a simplification: it doesn’t consider the fact that when there is a change in the electricity consumption not all power stations are equally affected. By default, this renders the calculation less accurate, but in the typical calculators under discussion, this has a minimum effect since the time interval under consideration is usually the year, and the system average changes almost yearly in many countries [1,14–18,24–28]. The CO2 calculators do not always consider the network losses affecting further the accuracy of the emission calculations. As it is presented here, the exclusion of electricity network losses can affect significantly the results of the CO2 calculations. If the emission factor is calculated only based in multiplant generation, without considering the electricity losses in the network, then the calculation error can become high depending on the networks position where the building is connected. The closer to the generation the building is connected, the lower the error is in the CO2 emissions calculation. This can be easily concluded considering the fact that the closer to the generation the building is or the higher the connection voltage is, the lower the network losses are. This error can be minimised, if in the electricity savings (or production) calculation the respective network losses are added [6,9,10,13– 18,25–29,31–33,38–42]. The inclusion of the network losses in the emission’s factor calculation, provides more accurate results, while the network position to which the building is connected does not actually affect the results, since the evaluation of the error has shown that the latter remains very low.

4. Conclusions The calculations presented, evaluated the network losses as a parameter affecting CO2 emissions’ calculation results, for two basic and most commonly used calculators, in the case of public buildings. The electricity grid was considered up to the distribution’s point in which the building is connected, meaning the low voltage distribution network (230/400 V in EU) or the medium voltage distribution network (15 kV or 20/24 kV most frequently in EU). The results showed that only when the electricity grid is considered in the calculation of the emission factor, the type of connection of the building (meaning low or medium voltage) does not actually affect the losses.

9,00

% Impact 8,00 7,00 6,00 5,00 4,00 3,00 2,00

References

1,00 0,00 EU 27

Estonia

Latvia

Poland

Romania

Slovenia

EF1-NL1total

1,07

1,14

1,13

1,11

1,11

1,07

EF1-NL2total

1,07

1,16

1,13

1,12

1,12

1,07

EF1-Ele/gEP

1,07

1,11

1,19

1,10

1,10

1,07

EF2-NL1total

3,32

6,40

5,93

5,00

5,17

3,22

EF2-NL2total

3,51

7,33

6,09

5,50

5,56

3,45

EF2-Ele/gE P

3,33

5,40

8,52

4,64

4,92

3,16

Fig. 6. Losses’ impact in carbon reduction evaluated for buildings connected in medium voltage networks not including the transformer losses (fNL ¼ 0,5), by country.

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