EVALUATION ON DISTRIBUTED ENERGY SYSTEM AT KITAKYUSHU SCIENCE AND RESEARCH PARK DURING 2003 Yingjun Ruan 1†, Weijun Gao2, and Toshiyuki Watanabe1 2
1 Faculty of Human-Environment Studies, Kyushu University Faculty of Environmental Engineering, the University of Kitakyushu
ABSTRACT A distributed energy system in Kitakyushu Science and Research Park (KSRP) has been introduced since April 2001. In this paper, the system’s running situation was analyzed by using the recorded data in 2003. Generating electricity, heat recovery efficiency and recovery heat utilization efficiency for gas engine and fuel cell were calculated. Moreover, energy saving and CO2 reduction were evaluated by comparing with the corresponding traditional central energy system. The results can be summarized as follows: 1) 49.8% of the total electricity demand was provided by the on-site generating electricity equipments, including fuel cell with 33.1%, gas engine with 13.9% and PV system with 2.8%. Fuel cell had stable and lower electricity generating efficiency. On the contrary, despite of being shorter running time, gas engine achieved higher electricity generating efficiency. 2) About only 27.4% thermal demand were provided by the recovery heat, among of which 54% came from fuel cell. Fuel cell had lower heat recovery efficiency with about 20% and this recovery heat almost was utilized by the heat exchanger or absorption chiller. Just the contrary, gas engine had higher heat recovery efficiency with 30%, but only about 51% recovery heat was utilized by recovery equipments. 3) The distributed energy system achieved 54.9% primary energy utilization efficiency, 5.1% higher than the conventional system. Therefore, this system reduced 9.3% primary energy input than the corresponding traditional central energy system. The total energy saving in 2003 amounted to 6839.25GJ, including 1448.06GJ (about 2.0%) from PV system and 5391.19GJ from CHP system (7.33%).
KEYWORDS Distributed energy system, Fuel cell, Gas engine, Evaluation, KSPR
INTRODUCTION Distributed energy source provides electricity and other energy to one or more buildings or facilities by an on-site energy source. Compared with the traditional central energy supply, distributed energy source can utilize a wide range of power generators including: photovoltaic (PV) systems, gas engine, fuel cell, wind turbines, diesel generator sets; hybrid systems and, electrical power storage and all kinds of thermal recovery technologies. Distributed energy source benefits both the utility and the end user. For the utility, it can help to avoid concerns about transmission and distribution upgrades. Benefits to the customer or end-user included power reliability, peak shaving, choice and potentially lower energy costs. For above variety of reasons, both developed and developing countries experience an increasing contribution of distributed generation to their electricity supply. Analysts expect this increase [1,2,3] . lead to the percentages of 20-40 percent of the total generated electricity volume by 2025 In Japan, the shortage of energy source and the CO2 reduction pressure from Kyoto Protocol cause government take all kinds of measure to save energy and develop distributed energy. Although at present distributed energy sources accounted for only about 1% of the primary energy supply, with the development of technologies for distributed energy and the implementation of policies to encourage †
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[4,5]
. In their installation, it is expected to play a greater role in energy supply over the coming decades Kitakyushu Science and Research Park (KSRP), a hybrid distributed energy system including fuel cell, gas engine and PV have been introduced since April 2001. This paper aims to grasp the running situation of this distributed system by using the recorded data in 2003. Generating electricity system and heat recovery system are analyzed respectively. Also an environmental and energy saving effect will be evaluated.
RESEARCHED SYSTEM Figure 1 is the schematic illustration of energy supply system researched. In this system, 153kW PV system, 200kW fuel cell and 160kW gas engine are installed to supply the electricity of the end-use and the insufficient electricity is provided by the utility electricity. The heat discarded from the fuel cell and gas engine is utilized to supply the thermal demand for heating, cooling and hot water. The insufficient loads are provided by gas boiler. Table 1 shows details and the nominal power generation and heat recovery efficiencies of the fuel cell and gas engine. The equipment capacity of the fuel cell is 200kW with a nominal electrical power production efficiency of 40% and a heat recovery efficiency of 20% for both circuits, one at a high temperature of 90℃ and another at 50℃. Fuel cell is running for 24 hours except for some special period, such as maintenance and repair of equipments or national holiday. Gas engine capacity is 160kW with a nominal generating electricity efficiency of 28.7% and a heat recovery efficiency of 47.7% for one circuit with high temperature of 90℃. It is designed to run during 8:00~22:00 generally. Utility electricity
PV system (153KW)
Substation City gas （13A）
Fuel cell (200KW)
Electricity
Electricity distribution center
Heat recovery （90℃）
Electricity
Heat exchanger
Gas boiler
Hot water （60℃）
Electricity Gas engine (160KW)
Heat exchanger Space heating （55～46.6℃） Absorption chiller And heater
Space cooling （7～17℃）
Figure 1: Schematic illustration of the distributed energy system Table 1: Detail of CHP system Item
Fuel cell
Equipment capacity (kW)
200
Gas engine 160
Generating electricity efficiency
40%(at full-out generating electricity capacity)
28.7% (at full-out generating electricity capacity)
Heat recovery efficiency
20.0% (at 90℃ high temperature water） 20.0% (at 50℃ low temperature water）
47.7%(at 90℃ high temperature water）
Operational mode*
Running for 24 hours
Running during 8:00~22:00
*NOTE: Fell cell is running for 24 hours expect for some special period, such as maintenance and repair of equipment. Gas engine was desigend to running during 8:00~22:00 generally.
INVESTIGATION METHODOLOGY During the research investigation, generating electricity data were recorded hourly using an electricity meter. In order to analyze the heat recovery utilization efficiency, the difference between the input and
output hot water temperatures and the hot water flow rates were measured for each system at hourly intervals. Consequently, generating electricity amount and the heat utilized by the systems could be quantified. For the purposes of comparison, a conventional energy-supply system is shown in figure 2. In the conventional system, a boiler is used to supply heating energy and a steam absorption chiller is used to supply cooling energy. The basic parameters of the equipments and the emission of CO2 are assumed [6] as in the table 2 .
Electricity/gas company
GAS
District heating and cooling plant
Power plant
GAS
NOTE:
User
Electricity load
G-Boiler
G-Boiler --- Gas boiler ABS-C--- Absorption chiller
ABS-C
Cooling load
H-H-EX
Heating load
HW-H-EX
Hot water load
H-H-EX --- Heat exchanger for heating HW-H-EX --- Heat exchanger for hot water
Figure 2: The conventional energy supply system Table 2: The basic parameters of the equipments Generator of the utility electricity Efficiency
CO2 discharge quantily
[6]
35%
Gas boiler
80%
Absorption chiller
118%
Electricity for the utility (kg-C/kWh)
0.104
Natural gas (kg-C/m3)
0.584
INVESTIGATION RESULT AND DISCUSSION Electricity supply system Electricity supply included four parts: fuel cell, gas engine, PV and utility electricity. Amount of electricity coming from various systems can be calculated according to the recorded data every hour. Figure 3 is the variation of daily total amount of electricity in 2003 and shows the total electricity consumption amounted to 5024.30MWh. And the total electricity consumption varied with time, the maximum occurred at August.4 with 19.459MWh/Day and the minimum was at December 12 with 6.651MWh/Day. The average was 13.77MWh/ day. Electricity consumption in the heating and cooling period was 1737.37MWh and 2390.99MWh respectively, accounting for 38.6% and 47.6% of the total electricity. Fuel cell contributed 33.1% of the electricity load with 1646.50MWh, followed by gas engine 13.9% with 696.75MWh and PV system 2.8% with 140.76MWh. On-site equipments including fuel cell, gas engine and PV system provided 2484.01MWh electricity for the consumer, accounting for 49.8%. The insufficient part came from the utility electricity and amounted to 540.29MWh, about 50.2%. Generating electricity efficiency is an important evaluation index for distributed energy systems. Frequency of electricity generating efficiency for fuel cell and gas engine are shown in figure 4. From the profiles, it can be concluded that fuel cell had longer generating electricity time with 8598 hours than gas engine with 4803 hours, about 55% of the whole year 8760 hours. Fuel cell had the stable electricity generating efficiency. There were 8592 hours with more than 25% of electricity generating efficiency, accounting for 99% of the total running time. However, compared with the designed value 40%, electricity generating efficiency of fuel cell is entire lower, only 676 hours is over 35% electricity
generating efficiency. Although gas engine had the shorter running time, it achieved the higher electricity generating efficiency. There were 3952 hours with more than 25% (the designed value is 28.7%) electricity generating efficiency, accounting for 83% of the total electricity generating time. Fuel cell
Gas engine
PV
Utility electricity
Amount of electricity (MWh)
20
16
12
8
4
0 1/1
2/1
3/1
4/1
5/1
6/1
7/1
8/1
9/1
10/1
12/1 Day
11/1
Figure 3: Variation of daily total amount of electricity 5000
(a,b]: a < Electricity generating efficiency
