INVESTIGATION OF THE CONFIGURATION OF HYBRID SOLAR ENERGY
SYSTEM FOR DISTINCT ENERGY DEMAND
Masashi Ohkura, Department of Indutrial Administration, Tokyo University of Science, +81-4-7124-1501, ohkura@rs.noda.tus.ac.jp
Shunsuke Mori, Department of Indutrial Administration, Tokyo University of Science, +81-4-7124-1501, mori@ia.noda.tus.ac.jp
Overview
Solar energy such as photovoltaic and solar heat is promising technology for reducing CO2 emission. A photovoltaic produces
electrical energy, which is flexible but difficult to conserve. Photovoltaic also requires high cost compared to solar heat
collector or electricity from utility. On the other hand, solar heat is low cost and easy to conserve but heat energy is not flexible.
Some study investigates the use of solar heat for room cooling[1]. However, nowadays, the almost utilization of solar heat is
limited to hot water supply or room heating. In this paper, We describe an energy saving potential and optimal configuration of
hybrid solar energy system for distinct energy demand. An photovoltaic and a solar heat collector constitute the hybrid solar
energy system. Some examinations of hybrid solar energy system are being performed[2]. However, the optimal configuration
of the system varies with consumer type and with energy conversion apparatuses which introduced to each consumer.
Therefore, determination of a plan of the introduction of solar energy and analysis of behaviour of the system is required. Solar
energy can not supply enough energy for each consumers due to variation of solar irradiation and limitation of available area
for solar collector. Therefore, electricity or heat energy from utility or other energy supply system is required. We also
describe optimal configuration of the system which includes CGS or distinct heating and cooling(DHC) for effective thermal
energy use. We formulated optimization model to investigate optimal system configuration. The optimization model deals
with urban area which includes several types of consumers, i.e., collective housing, hotel, hospital, office and shopping mall.
The model also deals with several types of energy, i.e., solar electricity, solar heat, electricity and natural gas supplied from
utility and electricity and heat produced by CGS and DHC. The simulation result shows us that photovoltaic requires large
available area of solar collector for reduction of CO2 emission. On the other hand, only solar heat collector is introduced to
shopping mall which requires high heat demand in the noon. The introduction of heat pump for hot water supply affects the
optimal configuration. The electricity demand is increased by introduction of heat pump for hot water. This is because energy
source of hot water changes from gas to electricity. Therefore, surface area ratio of photovoltaic increased by introducing heat
pump for hot water supply. We also investigate the optimal configuration of solar energy system for detached house. The
estimation shows us that photovoltaic is effective solution for reduction of energy demand since energy demand of each person
in each area is low compared to collective housing.
Methods
We build up the optimization model to decide optimal system configuration of solar energy system with several energy supply
system for distinct energy demand. This optimization model also gives us the flow of energy supply for energy demand
satisfaction. The model deals with four demands; electricity, hot water, room cooling and room heating. Each energy demand
is determined from total floor space of each consumer and consumer type. Electricity demand is satisfied with electricity
supplied from utility, photovoltaic, CGS and DHC. Heat generated by gas from utility, CGS, DHC and solar heat collector are
supplied for hot water demand. The demands for room cooling and room heating are satisfied with heat pump, gas heater and
gas boiler. Each apparatus and energy source has cost and unit of CO2 emission. In this model, we calculate energy source
and capacity of apparatuses to minimize sum of cost and CO2 emission. The CO2 weight is assumed to compare cost and CO2
emission. The CO2 emission is multiplied by CO2 weight. The value of CO2 weight varies between 0 to 1. And the total
energy and apparatus cost are multiplied by the value of (1 - CO2 weight). Therefore, when CO2 weight equals 1, the model
gives optimal configuration to minimize CO2 emission. If the CO2 weight equalled 0, the objective of the model becomes cost
minimization.
We also investigate the effect of the ratio of surface area of photovoltaic and solar heat collector on household energy demand.
In this investigation, temperature of water supplied from solar heat collector was calculated and we focused on the behaviour of
the system. Heat collective efficiency of a solar water heater was defined by temperature of hot water, solar irradiation and
ambient temperature. Temperature of ambient air and solar irradiation is provided by Japan Meteorological Agency[3]. In this
calculation, energy demands for household such as electricity, hot water, room cooling and room heating are calculated every 1
hour. Household energy demand and the efficiency of photovoltaic varies with season.
Results
We applied the optimization model to urban area which include 5 consumers. 5 consumers are defined as follows: 1.collective
housing, 2.hotel, 3.hospital, 4.office and 5.shopping mall. The floor space of total consumers is 148300m2. Sum total of
consumers roof area which is available area for photovoltaic and solar heat collector is 7300m2. Fig.1 shows the optimal
surface area of photovoltaic and solar heat collector of each consumer without CGS and DHC to minimize CO2 emission.
Photovoltaic requires 55% to 94% of available surface area. Introduction of heat pump for hot water supply increases required
surface area of photovoltaic due to the increase in electricity demand of each consumer. In this case, gas boiler for hot water
supply does not introduce. For consumer1(shopping mall), only solar heat collector is installed since high hot water demand
was generated in the daytime. On the other hand, for consumer5(office), photovoltaic takes over 95% since demand of hot
water is relatively small. Photovoltaic and solar heat collector introduce to every consumer for CO2 emission minimization
combined with CGS. However, when DHC is installed, introduced surface area of solar water heater reduces due to
competition of heat energy. Fig.2 shows the variation of electricity demand, utilized electricity supplied by photovoltaic and
temperature of hot water supplied from solar heat collector, which is calculated by meteorological data in Tokyo on 25th Jan,
2006. Demands for hot water and room heating concentrate in the evening and in the morning. Therefore utilization rate of
solar electricity decreases in the daytime. The using rate of solar electricity becomes lower in the middle season due to the
decrease in demand for room cooling and heating. Hot water supplied from solar heat collector was using effectively due to
heat storage. However, surplus capacity of solar water heater causes spilth of hotwater and the decrease of surface area for
photovoltaic. Energy saving potential of hybrid solar system for household becomes larger in middle season due to gain of
much solar irradiation and decrease in energy demand.
2
3
consumer
4
5
0.00
Fig.1
1
2
3
consumer
4
5
Optimal installation ratio of photovoltaic for
each consumer.
solar electricity
3.00
hot water temperature
50.0
2.50
40.0
10000
2.00
8000
1.50
6000
4000
1.00
2000
0.500
0.00
Fig.2
50.0
30.0 40.0
30.0
20.0 20.0
10.0
0
2
4
6
8 10 12 14 16 18 20 220.0
[h]16 18 20 22
0 2 4 6 8 10時刻
12 14
10.0
0.0
温水温度 [ C]
1
0.20
electricity for room heating
Temperature of hot water
supplied fromoSHC[oC]
Ratio of photovoltaic to total
Ratio of photovoltaic
surface areato[-]total
surface area [-]
1.00
1.00
0.80
0.80
0.60
0.60
0.40
0.20
0.40
0.00
electricity demand
Electricity demand and solar
electricity [kWh]
with HP for hot water
エネルギー需要削減率 [-]
without HP for hot water
Time [h]
The amount of electricity demand and utilized
solar electricity and temperature of hot water
supplied by solar heat collector.
Conclusions
In this paper, the author described an energy saving potential and optimal configuration of hybrid solar energy system for
distinct energy demand. Introduction of solar energy should take into consideration other energy supply system such as DHC.
Solar heat collector has higher energy conversion efficiency than photovoltaic. However, the use of heat collector is restricted
to hot water supply or room heating. This competition mainly occurs in thermal energy use. DHC was effective solution of
disbalance of heat energy of each consumers. However, DHC also requires large ground. Therefore, CGS with solar water
heater or photovoltaic may be effective for consumers with few available area of solar energy such as urban area. Photovoltaic
without energy storage is not used effectively for household energy demand due to the discordance of power generation and
electricity demand. Purchase of solar generated electricity to utility has incentive for facilitation introducing photovoltaic. For
reduction of CO2 emission from household, storage of heat generated by photovoltaic or solar water heater may be effective.
The other reward to reduction of CO2 emission by solar heat collector is needed for introducing alternative solar energy system.
References
[1] Masashi Ohkura and Akio Kodama, “Design Concept for a Solar Driven Desiccant Cooling Process Combined with a
Conventional Chiller”, Renewable Energy 2006 Proceedings, October 2006, pp.493-496.
[2] Li Meia, David Infieldb, Ursula Eickerc, Dennis Lovedaya, Volker Fux, “Cooling potential of ventilated PV fac¸ade and
solar air heaters combined with a desiccant cooling machine”, Renewable Energy 31 (2006) pp.1265–1278.
[3] http://www.data.jma.go.jp/obd/stats/etrn/index.php