Solar and battery backup for a rural clinic through load-shedding

Siyakhula clinic sees about 120 patients a day. Its vaccine fridge, two oxygen concentrators, lights and borehole pump all stop when the grid goes off. During Stage 6 the clinic lost power for up to three blocks a day, one of them four and a half hours long. Last winter the cold chain broke twice and R18,000 of vaccines had to be thrown away.

Right now an 8 kVA diesel generator covers the gaps. It burns about 2.2 litres an hour at half load, diesel costs around R27 a litre, and the nurse in charge has to start it by hand, often in the dark.

The NGO has a donor grant of R250,000 for a solar and battery system. The brief from the operations manager is clear: - Critical loads (vaccine fridge, oxygen, lights, borehole pump, laptops and router) must ride through every Stage 6 day with no generator. - The battery must also carry the vaccine fridge and night lighting through one unplanned outage of 24 hours, which happens about twice a year when cables are stolen. - Non-critical loads such as the autoclave and kettle may run on grid only. - The installation must meet SANS 10142-1 and the municipality's rules for small embedded generation.

You will build the critical load list, model the load-shedding stages hour by hour, size the battery, inverter and PV, simulate a full year with PVGIS hourly data, and draw the single-line diagram with the changeover arrangement. Students do not need any hardware: the whole design is done in Python or a spreadsheet, PVGIS and a drawing tool.

Done looks like a design report the NGO can give to installers for quotes. It should show that the fridge never loses power in the simulated year, how often the battery falls below 20%, the cost against the grant, and the diesel the clinic will stop burning.