Load Shedding & Church Services

My client was a church looking to avoid their services being interrupted by load shedding. The church has services once each week and the service lasts about 3 hours (from 9:15 to around 12:15). Load shedding is a big nuisance to the whole country and there are several ways of dealing with the issue to ensure that activities can go on as planned. The question, of course, is “Which method is best for my circumstances?”

I monitored the energy consumption during during a few of their services and found their maximum power usage to be around 2.8 kW. This is shown in the chart from my energy monitor below.?Converting this power value to an energy value over a 3-hour service, gives us 8.4 kWh. In other words, in the worst case, the church requires a back-up of 8.4 kWh of energy.

I looked at 5 options for comparison.

Option 1: A 3.5 kVA generator

Although I am a proponent for the energy transition to renewable energy technology, I also understand that this change will not happen overnight and for time-being some conventional methods still make sense. A 3.5 kVA generator would provide all energy requirements at a fuel cost of around R80 per week. The cost of the generator would be around R 6 500.

Option 2: A silent generator

Since it is a church, a silent generator of the same power output (3.5 kVA) would be a reasonable option. A typical silent generator sounds more like a vacuum cleaner, significantly quieter than a standard generator. The silent generator would cost around R 14 000, plus R80 for fuel each week.

Option 3: Battery Back-up

This system would included batteries, the charger, and an inverter. To maximize the life the system, batteries should not discharge more than 50% per cycle. To supply 8.4 kWh of energy with the batteries discharging no more than 50%, around 1440 Ah of battery back-up would be required. This system, together with the additional required components, would cost R 60 000.

Option 4: Solar Panels and Batteries

If we combine the battery back-up system with a solar PV system, we can reduce the total size of the battery bank. However, solar energy is not constant. I used the solar resource data for the church’s location to check how much solar energy would typically be available during the church services. With the energy from the sun, we could reduce the size of the battery bank to 960 Ah, also discharging no more than 50% per cycle. Total cost of this system:?R 66 000.

Option 5: Solar panels and generator.

If we combine the generator system with a solar PV system, using the energy from the sun as with option 4, we could reduce the generator size. Again, using the solar resource data for the location, with the energy from the sun, a PV system would reduce the required generator size to 2.2 kVA. Total cost of this system: R 51 000.

The client decided to go for the silent generator. This works, since load shedding is their only issue.