South Africa's midday solar glut is driving curtailment instructions to over 1,000 per month in 2026 — and private wheeling PPAs have zero regulated compensation for oversupply curtailment. Here's the contractual framework every C&I buyer must demand before signing in Q4 2026.

The Midday Solar Glut Is No Longer a Distant Risk — It's a Contract Problem You Must Solve Today

South Africa's renewable energy boom has created an uncomfortable paradox: the country now generates so much solar power at midday that the grid operator is routinely switching generators off — and if your commercial wheeling PPA doesn't contain the right contractual protections, you could be the one paying for energy that was never delivered. For C&I property owners and energy buyers finalising off-site wheeling agreements in Q4 2026, curtailment risk is no longer an abstract modelling assumption. It is an active operational reality with a direct line to your energy bill.

This guide explains what is happening, why the regulatory framework leaves you exposed, and exactly what contractual language you need before you sign anything.

The Structural Oversupply Problem: By the Numbers

"We had a particularly bad time during winter 2026, where we've seen curtailment of up to 3GW in a particular day," said Gav Hurford, acting GM of the National Transmission Company South Africa (NTCSA) system operator. That figure is not a one-off event — it reflects a structural shift in how South Africa's grid behaves.

Curtailed volume in the first half of 2026 was roughly ten times all of 2025. Curtailment instructions rose from roughly 100 a month to more than 1,000 a month during 2026. At the national level, "We're losing potential revenue of close to R49-billion per annum [through curtailment]," Electricity and Energy Minister Kgosientsho Ramokgopa warned at Windaba 2026 in October.

The problem is regional, and is worst where the best sun and wind sit farthest from demand, made worse by must-run coal and a midday solar glut. The NTCSA schedules most new transmission lines for 2028 to 2034. They need environmental approval, land, and long lead times that cannot be rushed — which is what makes the problem lasting, and why a 2026 curtailment figure tells every counterparty to expect similar exposure for years.

The IRP 2025 first determination has already acknowledged the structural problem directly: existing renewables are already being curtailed because the grid cannot absorb midday solar output, so more volume would deepen the waste.

The Regulatory Gap: Two Classes of Producer, Wildly Different Protections

This is where the risk becomes personal for C&I buyers. South Africa now operates a two-tier curtailment compensation system — and private wheeling buyers sit firmly in the unprotected tier.

Private renewable energy producers that wheel power — selling it directly to data centres and other large users and delivering it over the grid — have no regulated compensation if the grid operator switches them off because of oversupply.

A NERSA-approved congestion curtailment mechanism does exist, but its scope is tightly limited. That decision gave private producers some cover, but only for curtailment caused by grid congestion. Under the mechanism NTCSA proposed and NERSA approved, "the off-taker's account will be credited with the curtailed energy as if the IPP had supplied it." The approval runs from 1 April 2025 to 31 March 2028, and the mechanism may only be used to connect additional generation capacity in the Eastern Cape and Western Cape.

Critically, a regulatory mechanism approved for 2025–2028 covers congestion-related curtailment but explicitly excludes oversupply curtailment, leaving compensation to bilateral contracts between IPPs and off-takers. In plain language: the midday solar glut — the most common and growing form of curtailment — is entirely unregulated from a compensation standpoint.

Sapvia's technical and policy manager confirmed that IPPs operating under private PPAs "do not have a contractual mechanism for deemed energy payments" when it comes to oversupply curtailment. For oversupply, compensation depends entirely on the buyer or the bilateral power purchase agreement.

Bottom line for buyers: If your PPA is silent on oversupply curtailment — and most standard IPP offtake agreements are — you carry the full delivery shortfall risk with zero regulated remedy.

What "No Compensation" Actually Means for Your PPA

The financial consequences cascade in three directions:

1. PPA Delivery Certainty

Your wheeling PPA is priced on an assumed annual energy yield. Financial models for these plants assume a specific annual energy yield, and high curtailment rates destroy those return projections. If your IPP is curtailed during peak solar hours and your contract contains no deemed-energy or curtailment make-good clause, every MWh lost is simply not delivered. You revert to Eskom at full tariff rates — Eskom tariffs rose 12.7% in April 2026 alone — eroding the price certainty that was the primary reason for signing a long-term PPA in the first place.

2. Behind-the-Meter BESS Sizing

Battery storage at your premises cannot recover energy that was never produced at the generator. Industry voices note that if oversupply curtailment reaches wheeling deals, data centres and commercial off-takers would see reduced renewable energy credits, and behind-the-meter batteries are floated as a partial mitigation, though they cannot recover power lost at the generator. What BESS can do is protect your on-site demand profile: batteries can be programmed to absorb excess solar power during midday curtailment events and inject that power back during the evening peak. Size your behind-the-meter BESS not just for load-shedding backup, but as a midday arbitrage buffer — capturing cheap, available wheeled energy during non-curtailment periods and discharging during grid peak. This changes the optimal sizing calculation materially.

3. Wheeling Revenue Assumptions

Underpricing curtailment risk is a key concern: grid curtailment — Eskom or NTCSA instructing a plant to reduce output due to grid constraints — is not fully accounted for in many project models. Grid connection constraints and wheeling tariff uncertainty remain the two largest near-term barriers to accelerating the 2026–2031 deployment pipeline. For energy traders and aggregators acting between generator and your meter, curtailment-hit revenue assumptions will translate directly into renegotiation pressure on your contracted price or volume — unless the original PPA allocates that risk unambiguously.

The Regulatory Landscape You're Operating In: Q4 2026

NERSA published its regulatory rules on network charges for third-party wheeling of energy, which included methodologies for developing transmission and distribution use-of-system charges, in April 2026. Participants must be licensed and registered with NERSA, and power purchase agreements, connection and use-of-system agreements must be appropriately concluded.

NERSA's revised Trading Rules (Version 03) for the bilateral market are in active consultation. Provisions for virtual wheeling are introduced, allowing contestable consumers with connections exceeding 100 kVA to benefit from flexible energy allocation across multiple sites, subject to the implementation of non-bypassable charges and SAWEM go-live. However, transition risk is real but manageable. Full private market participation may only materialise several years into the 2030s, despite the April 2026 Market Code launch.

Meanwhile, South Africa has an oversupply of renewable energy projects under development with limited grid access — meaning that a project registered with NERSA is far from guaranteed a viable transmission slot. South Africa's wheeling sector is racing toward 5,700 MW of financial closes in 2026 — nearly double last year. Every new megawatt connected during peak solar hours deepens the midday oversupply curve.

Five Contract Clauses Every C&I Wheeling Buyer Must Demand

The good news: curtailment risk is contractually manageable. Here is what to require before signing:

1. Deemed-Energy Clause for Oversupply Curtailment

Demand that the PPA treats curtailed energy — including oversupply curtailment ordered by NTCSA — as "deemed delivered" for billing purposes. This mirrors the protection that Section 34 state-procured projects receive under their government offtake agreements. If your developer refuses to accept this risk at all, negotiate a capped deemed-energy provision covering a defined annual curtailment threshold (e.g., up to 4% of contracted annual energy).

2. Explicit Force-Majeure Carve-Out for Grid-Operator Instructions

Standard IPP offtake agreements often classify grid-operator curtailment instructions as a force-majeure event, relieving the generator of delivery obligation with no compensation. "The risks and costs associated with lost production due to curtailment are addressed in contracts between private generators and their energy off-takers," NTCSA has stated — placing the burden squarely on your bilateral agreement. Insist that oversupply curtailment is explicitly excluded from the force-majeure definition, or that a separate curtailment compensation waterfall applies.

3. Curtailment Reporting and Audit Rights

You cannot manage what you cannot measure. Require monthly curtailment reports disaggregating: (a) congestion curtailment (NERSA-compensated), (b) oversupply curtailment (uncompensated), and (c) planned maintenance curtailment. Attach audit rights allowing your energy advisor to verify NTCSA dispatch logs against the generator's metered output.

4. Generator-Side BESS Co-location Obligation or Option

Procurement design needs to address curtailment directly as renewable energy penetration increases, potentially requiring future projects to co-locate with energy storage. Build this into your PPA now rather than waiting for regulation to mandate it. Include either a right of first offer if the developer adds on-site BESS within the PPA term, or a curtailment-triggered BESS deployment milestone linked to contracted delivery performance.

5. Delivery Performance Ratchet and Step-Down Pricing

If the generator delivers less than a defined annual energy floor (after excluding agreed deemed-energy curtailment), the PPA tariff should step down or the buyer should have a termination right. This aligns developer incentives toward grid-friendly project siting — prioritising corridors with confirmed transmission headroom over the congested Cape nodes.

The BESS Sizing Recalculation Every C&I Buyer Must Run Now

Legacy BESS sizing models in South Africa were built around one primary use case: load-shedding backup. South Africa's 476-day load-shedding-free streak — backed by Eskom's Energy Availability Factor hitting a six-year high of 67.79% — is unwinding years of suppressed commercial demand. That changes the BESS value proposition entirely.

In a midday-glut environment, your on-site BESS must now serve three stacked functions: (1) absorbing wheeled solar energy during low-curtailment midday windows for discharge during Eskom peak periods; (2) providing backup against any residual load-shedding risk; and (3) acting as a demand-charge management tool against Eskom's TOU peak tariff windows. Running these three use cases through a combined dispatch model — rather than sizing for backup alone — will typically increase optimal BESS capacity by 30–60% versus legacy models, with the additional capacity justified by arbitrage revenue from the midday price differential.

Site Selection and Corridor Risk: Where You Sit on the Grid Matters

The approved congestion curtailment allowance is 4%, not the 10% originally sought. It unlocks about 1,100 MW of hosting capacity in the Western Cape and 400 MW in the Eastern Cape, taking those provinces to 7,205 MW by 2028. Projects connecting into already-saturated corridors face the highest oversupply curtailment exposure.

Confirm that your proposed wheeling corridor has confirmed capacity before committing to an off-site PPA. Ask your developer to provide a written NTCSA grid capacity confirmation — not just a NERSA registration number — before financial commitment. A 19.3 GW NERSA queue does not equal 19.3 GW of deliverable wheeled energy.

The Bottom Line for Q4 2026 Decision-Makers

South Africa's private wheeling market is mature, legally recognised, and commercially compelling — SOLA's Naos-1 project combines a 435 MWp solar PV plant with 660 MWh of contracted battery storage, and will supply large industrial off-takers through long-term PPAs using wheeling, demonstrating that the right structure works at scale. The economics remain strong: long-dated PPAs with fixed escalation clauses offer genuine insulation against Eskom tariff volatility.

But the midday solar glut has introduced a delivery-certainty gap that standard PPA templates have not caught up with. South Africa is paying R1.5-billion for solar curtailment, and NERSA says no rule covers how that money is recovered or who carries the cost. Until regulation fills that gap, the cost lands in your PPA — unless you contractually ring-fence it first.

Do not sign a wheeling PPA in Q4 2026 without a deemed-energy clause for oversupply curtailment, explicit force-majeure carve-outs, curtailment audit rights, and a BESS sizing model that reflects the new midday dispatch reality. The developers who resist these terms are the ones whose financial models haven't priced the risk — which means you would be the one absorbing it.