PV Power Systems for Disaster Situations

by the CADDET Japanese National Team

INTRODUCTION

Two Japanese filling stations capable of refuelling emergency vehicles in disaster situations opened for business in 1996. Each of these disaster-ready filling stations has a photovoltaic (PV) power generation system with a battery bank and can refuel ambulances, fire engines and other emergency vehicles when earthquakes or other natural disasters stop the power supply. This article describes one of these filling stations, situated in Sakai City.

DISASTERS

It must be assumed that devastating disasters, such as a large earthquake or a severe typhoon, will cut electric power supply from public grids and make it difficult to carry out disaster relief activities. When the Great Hanshin-Awaji Earthquake occurred in January 1995, for example, the stoppage of power supply hindered the communication of  information indispensable for appropriate relief operations. The lack of power also prevented ambulances, fire engines, police cars and other emergency vehicles from refuelling at filling stations. To cope with such situations, disaster prevention bases called 'Life Spots' were quickly developed in Japan. Life Spots have their own independent power sources and are completely self-sufficient in disaster situations so that they can sustain disaster relief operations for some time without power supply from public grids.

As a part of these efforts, two new power-independent filling stations capable of refuelling emergency vehicles have opened for business: one in Osaka City and the other in Sakai City. These Life Spot filling stations were constructed under the guidance of the Agency of Natural Resources and Energy and the Kinki Regional Bureau of International Trade and Industry.

SAKAI CITY'S LIFE SPOT

The Sun Plaza Akasaka-dai service station of Cosmo Oil Co is built on a 2,645 m2 site with a frontage of 44.5m and a depth of 59.1m. Its fuel tanks can store 90kl of fuel in all: 60 kl of gasoline; 15kl of gas oil (diesel fuel); and 15kl of kerosene. This filling station is situated near the Senhoku New Town, a large-scale residential development area with 140,000 households.

Picture

A disaster-ready station with a PV power generation system in Sakai

A fire station and police station are located in the core of the New Town, so the position of the filling station was considered well-placed to support disaster relief operations. Hence, this petrol station was selected as a Life Spot service station and equipped with a PV
power generation system of 10.77 kWp, which enables the service station to maintain fuel supplies to emergency vehicles, medical facilities, disaster refuges and other public facilities in a disaster. A 4.5 m3 potable water tank for emergency use was also installed at the filling station.

THE PV SYSTEM

The main components of the PV power generation system installed in this disaster-ready filling station are a 10.77 kW PV array; a lead-acid battery bank (100 Ah,
288 V); and a power conditioner comprising a grid-connection control unit and a
10 kW inverter.

The installed capacity of the PV array was determined by a predicted load of 24.74 kWh/day based on the assumption that the filling station feeds 8,000 l/day of fuels to emergency vehicles through four dispensers with a flow rate of 40 l/min in an emergency (see Table 1). This load setting required a solar array capacity of 11.1 kWp, a mean solar radiation of 3.92 kWh/m2/day (at an azimuth of 45o to the west from the south and a tilt angle of 20o ) and an overall correction factor of 0.57 correcting losses due to temperature rises; contamination of PV modules; losses in wiring; inverter efficiency; and charging efficiency. Based on this required array capacity and the capacity of available inverters (ie 10 kW), the installed capacity of the PV system was set at 10 kWp.

Item

Load/unit (W)

Number of units

Operating hours

Operating day

Total (kWh/day)

Mercury lamp

400

2

6

1

4.8

Fuel dispenser

750

4

0.84

1

2.52

Room lighting

40

4

10

1

1.60

Lavatory lighting

40

2

6

1

0.48

TV

160

1

24

1

3.84

Computer sales system

572

1

18

1

10.30

Fuel level meter

50

1

24

1

1.2

Total

 

 

 

 

24.74

Table 1: Load on the PV System

The array, mounted on the canopy of the filling station, consists of 126 panels of Sharp's single crystal silicon solar cell modules, NT51A85. Each module is 1,200 mm long, 530 mm wide and weighs 8.5 kg, with a power generating capacity of 85.5 Wp and a conversion efficiency of 13.4% under standard test conditions (AM 1.5, 1.0 kW/m2 solar intensity and 25 oC module temperature). Seven sets of 18 modules, connected in series, are arranged in parallel, giving a total capacity of 10.77 kW. The battery bank consists of forty-eight 100 Ah, 6 V sealed lead-acid modules connected in series (288 V in total) and can supply electricity required in the filling station for one completely sunless day.

Direct current (dc) power generated by the PV power generation system is converted to alternating current (ac) power by the inverter and is either used to operate the station or is stored in the battery bank. When the energy generated by the PV system exceeds the power use in the station and the battery is also fully charged, the surplus power is sold to an electric utility company. Electrical power is automatically supplied from the utility company at night and on rainy days. The control unit operates the whole PV system fully automatically, by constantly monitoring the output of the PV array, thereby making manual manipulation of the system unnecessary during ordinary grid-connected operation.

IMPACT OF THE SYSTEM

The southern district of Sakai City, where the Senhoku New Town and its Life Spot station are located, is a densely populated residential area. Hence, it is anticipated that the amounts of petroleum products demanded by emergency vehicles, medical facilities, disaster refuges and other public facilities would increase considerably in a natural disaster. It is also highly probable that a devastating disaster such as a large earthquake would destroy the ring road surrounding the New Town and other trunk roads, cutting the area off from supplies and outside help.

When a disaster cuts the power supply from a public grid, this disaster-ready filling station can continue in its basic function of supplying fuels to ambulances, fire
engines, police cars and other emergency vehicles and can contribute to disaster relief operations in the area

Table 2: Estimated Output of the PV System

Month

Solar flux (kWh/m2/day)

Daily output
(kWh/day)

Output
Days in month

Monthly output
(kWh/month)

1

2.75

22.21

31

688.51

2

3.25

26.25

28

735.00

3

4.01

32.39

31

1,004.09

4

4.52

36.51

30

1,095.30

5

4.92

39.74

31

1,231.94

6

4.39

35.46

30

1,063.80

7

4.76

38.44

31

1,191.64

8

5.05

40.79

31

1,264,49

9

4.03

32.55

30

976.50

10

3.59

28.99

31

898.69

11

3.05

24.63

30

738.90

12

2.66

21.48

31

665.88

Average

3.92

31.62

 

 

Total

 

 

365

11,554.74

OTHER APPLICATIONS

PV power generation systems have been introduced as emergency power sources in many places in Japan. In Saitama Prefecture adjacent to Tokyo, for example, PV systems, each of 30 kWp, started generating power in April this year in 17 prefectural senior high schools designated as disaster prevention bases. The power generated by these PV systems is expected to amount to 30,000 kWh annually. In ordinary times, this power is consumed in the schools and partly sold to an electric utility company. In the event of a disaster, the power will be used solely for disaster relief operations. The number of such PV installations in Japan will continue to grow in the future.

For more information contact the CADDET Japanese National Team in Tokyo.

The CADDET Renewable Energy Newsletter is a quarterly magazine published by the CADDET Centre for Renewable Energy at ETSU, UK.

The articles published in the Newsletter reflect the opinions of the authors. They do not necessarily reflect the official view of CADDET.

Enquiries concerning the Newsletter should be addressed to
Pauline Toole, Editor, CADDET Centre for Renewable Energy, ETSU, Harwell, Oxfordshire OX11 0RA, United Kingdom. Tel: +44 1235 432968, Fax: +44 1235 433595.