Why Your Prepaid Electricity Meter Doesn't Work With Your Inverter And What To Do About It

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In South Africa, prepaid electricity meters have become somewhat of a tenuous refuge from utility monopoly price gouging. In Johannesburg, you can expect to hand over around R1000 (about US$55 at the time of writing) for a post-paid electricity connection before even using a single unit of power, a number that has steadily increased over the years. Given this fixed cost alone could purchase the equivalent of around 400 kWh of usage on the same connection, many people, especially solar users, have switched to prepaid meter connections. Prepaid connections, typically have no or much lower fixed monthly connection costs, at the expense of higher per-unit pricing, which is of course, ideal for solar users. 

An issue that tends to crop up fairly frequently with solar users that have existing or switch to prepaid meters is intermittent or non-functioning of the Customer Interface Unit (CIU). The CIU is the mobile /battery backed unit typically installed indoors that contains a display and keypad, and connects to the meter in the meter box either via wireless or power-line communication (PLC), with the latter being seen more frequently. For PLC, the CIU connects to a regular power socket and uses the physical electrical connection to communicate with the meter in the meter box.

This all works well and fine, until an inverter is introduced between the plug point and the meter - something that is almost certain to occur if a solar/inverter system is installed at a home. The main issue is that the high frequencies and noise transients introduced by the inverter into the electrical system , which appliances are generally indifferent to, can disrupt the (also) high frequency signals the CIU is using to connect to the meter. Thus the CIU often reports it is unable to connect with the meter, or only works sporadically or partially, and the home owner is unable to load any prepaid credit onto the meter. For some reason, this usually occurs late at night, when the power is usually off already.

The solution is to connect the CIU to a plug point that is connected directly and as close to the utility supply as possible.

There are a couple of ways of achieving this:

  1. If you already have one or more plug circuits that are not connected to the essential loads circuit (the loads that stay powered when the utility power goes off), try connecting the meter to one of the plug sockets on those circuits.
  2. If all your plug sockets are on the essentials circuit, try temporarily switching your essential-loads change-over switch to your utility source instead of your inverter. Your inverter should have been installed with a change-over switch for the essential loads at minimum, which usually includes the lights and plugs of the home. If this hasn't been installed, you should fire your installer and find someone competent that can install this for you. Changing this switch to the utility source temporarily will connect the plug circuits directly to the utility source allowing the CIU to connect with the meter.
  3. In some cases, it may also be necessary to disconnect the inverter from the utility side connection. Hybrid inverters are able to feed solar/battery power back to the utility side, so temporarily disabling this connection may be necessary for the CIU to communicate with the meter. You should have a double-pole switch (breaker) in the distribution boards that allows you to disconnect the utility power to the inverter. Temporarily pulling this switch down before attempting to connect the CIU may solve the problem.
  4. Try unplug and re-plug the CIU immediately after you change any chang-over/breaker settings as some CIUs only attempt to connect to the meter periodically after first power on.
  5. Some CIU's, if they haven't been able to connect to the meter for a while, need to go through a "re-pairing" procedure (e.g. Hexing), involving entering specific number sequences on the CIU. These procedures can often be found quite easily by searching online for e.g. "Hexing prepaid meter pairing". For the Hexing meters for example, after connecting the CIU unit to a plug socket that is now connected directly to the utility, one would enter the numbers 18075773902 and then hit enter. The CIU should report "Success". Then you need to enter your 11-digit meter number to connect to followed by Enter. If successfully, you should see "Success" again.
  6. A more permanent solution is to have a dedicated electrical socket installed for the CIU, usually right by the main distribution board, where it can be wired to be as close to the incoming utility connection as possible. One can then typically leave the CIU permanently connected to that socket so that you can monitor the prepaid status as normal.








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