Even municipal electricity distributors in South Africa considered to be progressive and forward-thinking, such as the City of Cape Town, have ridiculous, self-serving rules regarding domestic solar PV systems that feed electricity back into the grid. Other municipal and Eskom electricity distributors are no different.
NRS 098 2-1, the outdated Eskom and municipal electricity standard used as the rulebook for small-scale embedded generation (SSEG), limits the size of grid-tied, rooftop solar PV systems in residential installations.
For example, a solar PV system on a house with a 60A single-phase supply is limited to 3.68kW. Similarly, other limits apply to residential installations with 40A, 80A or 10A single or three-phase supplies.
Apparently, the 3.68kW limit was calculated on the basis that if every single house connected to a final distribution transformer had a 60A single-phase supply, and all were to install identically sized grid-tied solar PV systems, then 3.68kW would be the size per solar PV system above which voltage rise may become a problem.
Obviously, this was and still is a completely absurd and unrealistic assumption for such a calculation in the first place.
Furthermore, the NRS standard was written at a time when smaller inverters for rooftop solar PV systems did not necessarily provide voltage regulation.
These days, however, even small inverters have voltage control facilities, thus obviating any need for concerns about voltage rise.
Therefore, there is absolutely no technical need for such unrealistic restrictions on the size of domestic grid-tied, rooftop, solar PV installations on single or three-phase supplies, and grid-tied solar PV sizes three times higher could be comfortably accommodated with the right approach.
However, the benefits of compensation for electricity generated back into the grid from rooftop solar PV installations are specifically excluded. They are not available to domestic customers with prepayment electricity meters.
The reality is that the prepayment meters currently provided by Eskom and municipal electricity distributors in South Africa are largely outdated and anything but smart.
Eskom and municipal prepayment meters have problems accommodating even the existing inclined block tariffs off properly, let alone handle time-of-use tariffs or feed-in tariffs for grid-tied solar PV systems.