The Energy Supply System
uninterruptable Power Supply (UPS) - Tom Grassie
SHIRATI HOSPITAL, founded in 1934, serves a large collection of villages scattered along the shores of Lake Victoria in Northeastern Tanzania. Like many villages in remote regions of the country, Shirati often has long - and completely unpredictable - periods with no electricity. Evening thunderstorms commonly trip the network and leave the hospital without power overnight. Not until the following morning can the main standby generator be started up, and it is often several days before mains power is restored. Although the hospital's diesel generator, can meet the hospital's electricity requirement for approximately 2 days, a reliable supply of diesel is not always guaranteed.
There are inevitably a large number of emergency procedures in a big rural hospital like Shirati, with a catchment population of 200,000, and many of these happen at night. Operating theatre staff are frequently caught out by sudden power cuts, and must complete the operation at hand with the help of car batteries, by the light of torches, or, distressingly often, by the light of mobile phones. This situation clearly puts their patients at a much higher risk than is acceptable.
It is not surprising that, in an area where 80% of the population lives below the UN poverty line, funding for Shirati Hospital comes largely through charitable donations. Over the past years these have provided medicine and medical supplies; equipment such as ultrasound machines, an incubator, and an autoclave; and, more recently, modern hospital beds for the wards and large operating room lights for the operating theatre. Crucial to the operation of much of this equipment, and to many of the hospital's daily services and procedures, however, is an uninterruptable power supply (UPS), to ensure there is sufficient power, particularly at critical times such as during emergency operations, to run equipment - and the light to see by.
In June 2008, we, two renewable- energy engineers from Napier University in Scotland, visited Shirati. We conducted an electrical survey of the Hospital with a view to specifying and designing an appropriate system which would utilize locally available, renewable sources of energy (for example, the sun) to supply uninterruptable power to Shirati Hospital's operating theatre and associated lab and prep room. Key remit of such a system is that it should:
- require the minimum of maintenance
- be able to provide uninterruptable power for a minimum of 3 days and
- have a long life expectancy.
Vital to the future sustainability of such a system is that it be developed and put in place in collaboration with our locally-based Tanzanian colleagues.
Shirati is located at 33.9833 longitude and -1.1333 latitude. Because it is so close to the Equator, it enjoys plenty of sunshine: approximately 2.5 times that of Central Scotland. As can be seen in the graph below, average daily sunshine in Tanzania is almost constant, whereas in Scotland there is approximately 6 times as much useful sun in summer as in the winter months. This makes Shirati Hospital, with its greater availability of sun year-round, an excellent candidate for a solar system to supply its energy needs.
Bearing this in mind, and with our hospital energy audit to hand, we concluded that the best solution for the hospital was to have a large bank of deep cycle rechargeable batteries charged by an array of solar electric panels (PV panels). Incorporating inverters into the system means that both the generator, when on line, and the national grid, when connected, will be able to add charge to the batteries. With this "Triple Charging" system (PV, grid and generator) it will be possible to guarantee a UPS for a period of 4 days without using either mains power or the generator. Modern deep cycle batteries require minimum maintenance and can last longer than 10 years. The PV panels have a life expectancy in excess of 25 years.The costs of the main system components are detailed below.