A building integrated photovoltaic (PV) and fuel cell (FC) system is proposed for assessment of the energy self-sufficiency rate in a city in Japan. The electricity consumed in the building is mainly supplied by solar panels, while the gap between the energy demand and supply is solved by the FC that is powered by the H2 produced by water electrolysis with surplus power of PV. A desktop case study of using the proposed system in Tsu city which is located in central part of Japan, has been conducted. The results found that the self-sufficiency rates of PV system to electricity demand of households (RPV) during the daytime in April and July are higher than those in January and October. The results also reveal that the self-sufficiency rate of FC system to the electricity demand (RFC) is 15% - 38% for the day when the mean amount of horizontal solar radiation is obtained in January, April, July and October. In addition, it is found the optimum tilt angle of solar panel installed on the roof of the buildings should be 0 degree, i.e., placed horizontally.
Fossil fuel reserves are limited and intensive burning of hydro-carbon based fuel sources are impacting on global climate. There is continuous encouragement to increase the penetration of environmental friendly energy sources for fulfilling growing energy demand and also to minimize the use of hydro-carbon based power plants. Renewable energy sources such as wind, solar photovoltaic (PV), solar thermal, geothermal, bio-energy are drawing attention as alternative environment friendly energy sources. However, the energy density of these renewable energy sources is low. Most of them are dependent on nature and have intermittent characteristics. Therefore, it is very important to develop proper strategies and technologies to integrate these renewable energy sources into the power system network in order to fulfill the energy demand.
Integrating renewable energy sources into the existing energy system network is an effective approach in the development of the so-called smart cities. Introducing renewable energy systems into the built environment (i.e. building) is a typical such approach. However, in the built environment, it is challenging to integrate intelligently renewable energy sources and distributed generators as the existing building infrastructures are not designed to accept them into the power system infrastructure. The development of a smart city or a smart building requires harmonizing the renewable energy system with existing heat and power system infrastructure, and with new monitoring and control system [
Integrating renewable energy on the building has been investigated recently well. Many researches on building integrated that wind turbine has been conducted recently [
Integrating/installing solar panels on the roof and/or side wall of the buildings is a typical way to make the building energy self-sufficient. Such kind of building integrated that PV systems (BIPV) have been studied by many researchers [
Due to solar energy’s intermittent nature, the BIPV system normally requires a sort of energy storage system or grid-connected mechanism. The typical energy storage system in associated with normal PV systems such as battery bank and hydrogen produced by water electrolysis produced by the power of PV system are well known and these combination systems have been studied numerically as well as experimentally [
In this paper, a desktop case study has been conducted on a proposed BIPV system. The proposed BIPV system consists of solar panels and fuel cell (FC). The H2 required by the FC are provided from the water electrolyzer with surplus power of PV. The FC would therefore be able to solve (partly) the gap between the electricity demand (by the building) and supply capacity of the PV panel due to the intermittent power generation of the PV system. As the PV panels were assumed to be installed on the roof of the building, the solar panel setting procedure is also investigated in this paper in order to clarify the maximum power could be generated from the BIPV. Compared the electricity demand data of household in Japan [
The building model used in the case study is 10 m width, 40 m length and 40 m height (=10 stories) [
The power generated by PV system is calculated by using the following equation [
where EPV is hourly electric power of PV system (kWh), H is amount of solar radiation (kWh/m2), K is power generation loss factor (−), P is system capacity of PV (kW), 1 is solar radiation under standard state (AM1.5, solar radiation: 1 kWh/m2, module temperature: 25 degree Celsius) (kW/m2).
In this study, the high performance PV P250a Plus produced by Panasonic whose module conversion efficiency and maximum power per module are 19.5% and 250 W [
where Kp is power conversion efficiency of power conditioner (−), Km is correction factor decided by module temperature (−), Ki is power generation loss by interconnecting and dirty of module surface (−). In this study, Kp and Ki are set at 0.945 and 0.95, respectively. Kp is assumed by referring to the performance of commercial power conditioning device VBPC259B3 manufactured by Panasonic [
where Tm is PV module temperature (degree Celsius), Ts is temperature under standard test condition (=25 degree Celsius), C is temperature correction factor which is 0.35 [
where Ta is ambient air temperature (degree Celsius), Um is wind velocity over module of PV (m/s).
The meteorological data, such as solar radiation, the ambient air temperature, and wind velocity of some cities in Japan are from the data base METPV-11 during the period from 1999 to 2009 [
It is important to consider the impact of shadow on power generation performance when PV system is installed. The longest shadow length which is obtained at AM 9:00 on the winter solstice is calculated by the following equation [
Year | Month | Day | Hour | Min | Sec | Amount of horizontal solar radiation (kW/m2) | Air temperature (degree Celsius) |
---|---|---|---|---|---|---|---|
2013 | 8 | 1 | 9 | 0 | 0 | 0.1179 | 30.7 |
2013 | 8 | 1 | 9 | 0 | 10 | 0.1158 | 30.8 |
2013 | 8 | 1 | 9 | 0 | 20 | 0.1115 | 30.7 |
2013 | 8 | 1 | 9 | 0 | 30 | 0.1130 | 30.8 |
2013 | 8 | 1 | 9 | 0 | 40 | 0.1150 | 31.0 |
2013 | 8 | 1 | 9 | 0 | 50 | 0.1120 | 30.9 |
2013 | 8 | 1 | 9 | 1 | 0 | 0.1107 | 30.8 |
2013 | 8 | 1 | 9 | 1 | 10 | 0.1123 | 30.8 |
2013 | 8 | 1 | 9 | 1 | 20 | 0.1166 | 31.0 |
2013 | 8 | 1 | 9 | 1 | 30 | 0.1179 | 30.9 |
2013 | 8 | 1 | 9 | 1 | 40 | 0.1183 | 30.8 |
2013 | 8 | 1 | 9 | 1 | 50 | 0.1194 | 30.8 |
2013 | 8 | 1 | 9 | 2 | 0 | 0.1229 | 30.8 |
2013 | 8 | 1 | 9 | 2 | 10 | 0.1249 | 30.6 |
2013 | 8 | 1 | 9 | 2 | 20 | 0.1267 | 30.5 |
2013 | 8 | 1 | 9 | 2 | 30 | 0.1270 | 30.3 |
2013 | 8 | 1 | 9 | 2 | 40 | 0.1262 | 30.1 |
2013 | 8 | 1 | 9 | 2 | 50 | 0.1258 | 30.1 |
2013 | 8 | 1 | 9 | 3 | 0 | 0.1298 | 30.4 |
where L is the longest shadow length of solar panel to north direction (mm), α is solar altitude (degree), β is solar azimuth angle from north and south direction (degree), h is height of solar panel (mm).
In other words, the solar panels need to keep L distance apart in N-S direction to avoid the shadowing each other. The number of solar panels, which can be installed on the roof of building without shadowing other panels, was estimated with various tilt angles.
In this case study, it is assumed that the surplus power generated by PV system over the electricity demand of households [
whereVH2 is amount of H2 produced (Nm3), Es is surplus power generated by PV system (kWh), Pe is power consumption (kWh/Nm3), ηe is electrolysis efficiency (−).
It is assumed that the H2 produced by the electolyzer would be used to generate power through a polymer electrolyte fuel cell (PEFC) system. H2 is converted into electricity by FC following the below equation:
where ηf is power generation efficiency of latest PEFC stationary system based on lower heating value (=0.39) [
In this study, 4 monthly values of the self-sufficiency rate of the proposed combination system consisting of PV and FC was investigated, which are representative of four seasons for Tsu city in Japan. The self-sufficiency rate is defined as the power supplied (from the combined PV and FC system to electricity demand of the building), in this study. The hourly time change in the self-sufficiency rate in the day when the daily mean amount of horizontal solar radiation per month was obtained was estimated.
At first, the optimum tilt angle for installment of solar panel on the roof is investigated using the hourly meteorological data base [
To clarify the optimum at of solar panel installed on the roof of the building model universally in Japan, this study investigates the daily power energy of PV system averaged per month for five cities in Japan such as Tsu (north latitude: 34 degrees; east longitude: 136 degrees), Fukushima (north latitude: 37 degrees; east longitude: 140 degrees), Tokyo (north latitude: 35 degrees; east longitude: 139 degrees), Sapporo (north latitude: 43 degrees; east longitude: 141 degrees) and Naha (north latitude: 26 degrees; east longitude: 127 degrees) using the hourly meteorological data METPV-11 including air temperature, solar intensity and wind speedat 1 hour interval [
Figures 2-5 show the relationship between daily power energy of PV system averaged per month and at of solar panel installed on the roof of the building model. In these figures, January, April, July and October are selected as the months which are representative of four seasons in Japan, respectively. In addition,
at (degree) | 0 | 10 | 20 | 30 | 40 | 50 | 60 | 70 | 80 | 90 |
---|---|---|---|---|---|---|---|---|---|---|
L (mm) | 0 | 312 | 615 | 898 | 1155 | 1376 | 1555 | 1688 | 1770 | 1796 |
Ns (−) | 300 | 200 | 175 | 150 | 125 | 125 | 125 | 125 | 125 | 125 |
Ns/N (−) | 1.00 | 0.67 | 0.58 | 0.50 | 0.42 | 0.42 | 0.42 | 0.42 | 0.42 | 0.42 |
Figures 7-10 show hourly power generated from proposed BIPV system and energy demand of 40 households assumed living in the building model in Tsu city in Japan. Hourly power generated by PV system was estimated for the standard day in the month with the mean amount of horizontal solar radiation of the month using the meteorological data base of PV300 [
From Figures 7-10, it is obvious that the generation of PV system increases in the morning up to the noon and decreases after noon to the evening due to solar trajectory, while the electricity demand keeps almost constant during the day and increases from the evening until the midnight. Due to the mismatch between the power generation and electricity demand, RPV is over 100% during the daytime and is 0% during the night-time. Moreover, RPV during the daytime in April and July are higher than those in January and October. Since the amount of horizontal solar radiation in spring and summer are higher than those in autumn and winter in Japan, the RPV are higher in April and July than those in January and October.
It was assumed that the surplus electricity generated was used for water electrolysis to produce H2 which is fed into the FC system. The self-sufficiency rate of the FC system (RFC) is defined as the ratio of the power generated by FC system to the electricity demand which is not covered by PV system. The average daily RFC in representative months is calculated and it is given in
From
As we know that the electricity demand/consumption depends on the number of households in the building,
EFC(kWh) | ED (kWh) | RFC (%) | |
---|---|---|---|
January | 24 | 186 | 13 |
April | 56 | 149 | 35 |
July | 49 | 130 | 38 |
October | 29 | 138 | 21 |
January (%) | April (%) | July (%) | October (%) | |
---|---|---|---|---|
3 days ago | 15 | 13 | 41 | 38 |
2 days ago | 0 | 35 | 18 | 37 |
1 day ago | 10 | 18 | 12 | 41 |
Mean solar radiation day | 13 | 35 | 38 | 21 |
1 day after | 9 | 31 | 19 | 0 |
2 days after | 15 | 47 | 0 | 33 |
3 days after | 15 | 49 | 14 | 40 |
January (%) | April (%) | July (%) | October (%) | |
---|---|---|---|---|
3 days ago | 38 | 28 | 66 | 61 |
2 days ago | 0 | 64 | 34 | 59 |
1 day ago | 29 | 38 | 29 | 65 |
Mean solar radiation day | 33 | 65 | 59 | 35 |
1 day after | 28 | 56 | 39 | 1 |
2 days after | 36 | 80 | 6 | 53 |
3 days after | 38 | 83 | 30 | 63 |
January (%) | April (%) | July (%) | October (%) | |
---|---|---|---|---|
3 days ago | 46 | 40 | 100 | 93 |
2 days ago | 1 | 85 | 55 | 90 |
1 day ago | 36 | 52 | 39 | 99 |
Mean solar radiation day | 40 | 86 | 98 | 56 |
1 day after | 33 | 82 | 49 | 2 |
2 days after | 46 | 114 | 9 | 81 |
3 days after | 46 | 118 | 42 | 97 |
same amount of solar panels installed), respectively.
According to
In addition, the proposed systems in different buildings with different energy demands may be connected in future, so the surplus electricity generated from PV and/or H2 can be transferred between buildings. Moreover, H2 as an energy storage medium has longer term storage efficiency than secondary battery.
This study has investigated the proper solar panel setting procedure to be installed on the roof of the building. This study proposed a combined PV and FC utilizing H2 produced with surplus power of PV for Japanese buildings. The PV’s installation angles and performance of the system have been studied with meteorological data of several cities in Japan. The (energy) self-sufficiency rates of the combination system of PV and FC are also studied with meteorological data for Tsu city in Japan. As a result, the following conclusions have been drawn:
1) The optimum installation angel for solar panel on the roof of the building is 0 degree irrespective of city or season due to the limitation of the roof area of building.
2) Due to the mismatch between the power supply and electricity demand, RPV is over 100% during the daytime while it is 0% during the night-time. RPV during the daytime in April and July is higher than that in January and October since the amount of horizontal solar radiations in spring and summer are higher than those in autumn and winter in Japan.
3) It is revealed that RFC is in the range of 15% - 38% for the day for a big building (i.e., with 40 households).
4) For the smaller buildings with 20 or 12 households, the RFC over 100% could be possible in April and high RFC near 100% is possible in July and October in the case of 12 households (=3 stories).
Nishimura, A., Kitagawa, S., Hirota, M. and Hu, E. (2017) Assessment on Energy Self-Sufficiency Rate for Building Integrated Photovoltaics and Fuel Cell System in Japan. Smart Grid and Renewable Energy, 8, 195-211. https://doi.org/10.4236/sgre.2017.86013