An exported solar unit earns less than the unit you buy because the two are priced on different sides of the municipal mechanism: consumption is billed at the full retail rate with every component loaded into the kilowatt-hour, while export is credited at a separate, pre-agreed export rate, normally set at avoided-cost level, and that credit is usually applied against energy charges only. The fixed side of the account — service charge, meter fee, levies — stays payable in cash, and any embedded generation administration fee and bi-directional meter charge sit on top of that. Trace one kilowatt-hour from the inverter to the bill and the shortfall is not a rounding error. It is the reason an export-led case rarely survives contact with a municipal account.
Two counters, one cable
There is a kiosk on the boundary wall and inside it the meter has two registers. Stand there at about two on a clear afternoon. The import register is sitting still. The export register is stepping through its digits while the inverter pushes the surplus off the roof, past you, out into the street.
Same cable. Same electrons. Two separate numbers.
Most people arrive at this expecting net metering — one meter that subtracts what you send out from what you draw in and bills the difference. That is not usually what a bi-directional municipal meter does. It measures both directions and reports both, and the municipality applies its own rate to each direction afterwards on the bill. Nothing cancels at the point of measurement. On a day where you import ten units and export ten units, you are billed retail on the ten you took and credited the export rate on the ten you gave.
And if your meter is still a plain prepaid unit with no export register, none of this exists for you yet. There is nowhere for an exported unit to be recorded, so it earns nothing. The whole mechanism only starts once a bi-directional meter is in place.
Where the unit goes, and what it gets paid
That exported unit now carries a price tag it did not choose. It is the export rate: a figure the municipality publishes in its embedded generation or SSEG tariff schedule, normally derived from what the municipality avoids spending by not having to buy or generate that unit itself.
Your imported unit carries something else entirely. The retail rate is not one number. It is an energy charge, plus network and service recovery folded into the volumetric rate, plus whatever levies and environmental charges are bundled in. The unit you buy is hauling the whole municipal cost stack. The unit you sell is paid the thin slice at the bottom of it.
That spread exists before anything else is added. It is the first cut.
The credit lands on the energy line, not the whole bill
Then the credit arrives, and in a lot of schemes it is set against energy charges only. It does not touch the fixed side: the service charge, the meter fee, the levies. Those come out in cash whether you exported four hundred units or none at all.
Which produces the situation that confuses people most. A month where your export register outran your import register, and you still owe money. The kilowatt-hours cancelled. The fixed charges did not. And because the export rate is lower per unit, the credit may not even have covered the volumetric side in full.
The fees that only exist because you export
- A bi-directional meter charge, monthly, for the meter itself. Your old meter did not have it.
- An embedded generation service or administration fee, where the municipality levies one on registered generators.
- Once-off: the application, possibly a limiter or relay device, the certificate of compliance and the commissioning paperwork under SANS 10142-1, and the NRS 097-2-1 settings your inverter has to hold.
These are standing costs. They do not fall when you export less. So the more of your account is fixed, the more units you must push out just to stand still — and at an export rate below retail, standing still takes more units than you sent.
When the unit cannot leave at all
Two hard limits sit under the whole arrangement.
The first is anti-islanding. When the grid goes down, the inverter must stop exporting. That is not a municipal preference, it is NRS 097-2-1 — no islanding, because the person up the street working on the same transformer cannot have your roof energising the lines. So during load shedding, export is zero and credit is zero. If your hybrid inverter is configured to export out of the battery, you are cycling stored energy into a credit at the export rate, which is a poor trade before you even count the round-trip losses inside the battery.
The second is the cap. Registration approves an export limit, usually expressed as a proportion of the connection size, the inverter rating, or the approved generation capacity. Push past it and the limiter throttles you or the meter flags it. The "oversize the array and sell the surplus" plan has a ceiling written into it before the first panel goes up.
The year-end cliff
This is the part that catches people who plan in calendar years. Municipal financial years run to 30 June. What happens to a positive credit balance at that boundary differs between schemes: some carry it forward, some zero it, some pay out a small cash amount.
The practical version: if your surplus piles up through a sunny summer and you do not draw it down before the year-end adjustment, you may be looking at a number that no longer exists. Do not build a case on accumulated credit. Anything you cannot use inside the municipal year should be treated as worth nothing.
What it changes about how you design
If an exported unit is worth less than a consumed one, and the fees are fixed, the design question is not "how much can I export". It is "how much can I consume myself before the meter ever sees it".
A unit that runs the geyser at eleven in the morning avoids the full retail rate — energy, network, levies, all of it. A unit that goes out the gate earns the export rate and then has to carry its share of meter and admin fees on the way back. Same panel, same sunshine, two very different values.
So the geyser element, the pool pump, the borehole, the tumble dryer, the EV charger if there is one — anything with a timer and a heavy draw wants to be in the middle of the day. Battery for the evening block. Export as the leftover, not the product.
I will say plainly that this is not an argument against registering. A scheme where the credit can offset fixed charges, or where the export rate sits close to retail, changes the arithmetic completely — and those schemes do exist. It depends on your municipality, your tariff category and how the credit is applied. What does not change is the need to know which side of the bill your credit touches before you size anything.
What to ask before you sign
Work through these with the municipality and the installer, in writing where you can:
- Does my tariff category permit export at all? Some do not, and the rest is moot.
- Is there a separate export rate, and is the credit applied to energy charges only or to the whole account?
- What happens to a positive credit balance on 30 June?
- What monthly charges apply to an embedded generation customer, and is the bi-directional meter charge billed separately?
- How is the export limit expressed — inverter rating, connection size, or a percentage?
- Does the meter need replacing, and who pays for that?
- What is the inverter set to do when the grid is down, specifically with regard to the battery?
The test worth running on your own bill
Take your last full municipal account and add up every fixed line: service charge, meter fee, levies, admin. Ignore the energy line for a moment. That total is what you pay before a single unit moves in either direction.
Now ask how many exported units, at the export rate, it would take to cover it — and then how many kilowatt-hours your roof can realistically push out past your own daytime loads. In most homes the second number comes out well short of the first. That gap is the honest answer, and it is the thing the glossy proposal never puts on the front page.
