The Miniflex tariff is Eskom's Time-of-Use (ToU) structure for large commercial and industrial customers — typically those consuming more than 100 MVA or on dedicated Transmission-connected supply. If you're on Miniflex and you haven't analysed your invoice in detail, there's a very high probability you're missing significant optimisation opportunities.
This guide walks through each component of the Miniflex invoice and explains what it means for solar PV and BESS system sizing.
The Four Main Invoice Components
1. Network Access Charge (NAC)
A fixed monthly charge based on your contracted Notified Maximum Demand (NMD), regardless of how much electricity you consume. This charge is not reducible through solar generation — it's a connection fee. However, if you can demonstrate a sustained reduction in your actual peak demand over time, you may be able to renegotiate your NMD with Eskom, which would reduce this charge.
2. Network Demand Charge
Charged per kVA of your highest measured demand during the billing month, within each tariff period (Peak, Standard, Off-Peak). This is where BESS systems can have a dramatic impact — by discharging during peak demand events to suppress the measured kVA, you directly reduce this charge.
Example: A cold storage facility with a 1.2MVA peak demand during a single 30-minute peak period in the month will be billed at the full 1.2MVA rate for the entire month's demand charge. A 500kWh BESS discharging during that window could reduce the measured peak to 800kVA — saving potentially R80,000–R120,000 per month on demand charges alone.
3. Energy Charge (kWh)
The most visible line item — what you pay per unit of electricity consumed, split by ToU period:
| Period | Hours (Weekdays) | Approx. Rate (2025) | Solar Offset Potential |
|---|---|---|---|
| Peak | 07:00–10:00, 18:00–20:00 | R6.20–R8.80/kWh | Morning peak: high. Evening peak: BESS only. |
| Standard | 06:00–07:00, 10:00–18:00, 20:00–22:00 | R2.40–R3.20/kWh | High (core solar generation hours) |
| Off-Peak | 22:00–06:00 | R0.90–R1.20/kWh | Low (BESS charging window) |
For solar system sizing, the Standard period represents the highest opportunity — it aligns with peak solar irradiance hours and carries a significant tariff. Off-Peak hours are the optimal window for BESS charging.
4. Reactive Energy Charge (kVArh)
If your power factor drops below 0.95 lagging, Eskom charges you for reactive power consumption. This is primarily addressed through power factor correction capacitors rather than solar, but it's worth auditing alongside any energy project.
What This Means for System Sizing
Most solar sizing exercises that focus solely on kWh consumption miss a significant portion of the financial case. A comprehensive Miniflex savings analysis should model:
- Energy displacement — kWh offset by solar generation during Standard and Peak hours
- Peak demand reduction — BESS discharge during Peak demand windows to reduce Network Demand Charges
- Arbitrage — BESS charged during Off-Peak hours and discharged during Peak hours to capture the tariff differential (currently R5–R7/kWh)
- NMD optimisation — sustained demand reduction to enable NMD renegotiation
Rule of thumb: For a Miniflex customer with significant peak demand charges, the BESS component of a solar+storage system often delivers more rand value than the solar PV component. Size both correctly or you'll significantly understate the business case.
Getting Your 12-Month Load Profile
To size a system accurately for a Miniflex customer, SOCO ENERGY requires 12 months of interval meter data (typically available in 30-minute intervals from your metering service provider). This data enables:
- Accurate ToU energy profiling by period
- Identification of demand spikes and their frequency
- BESS dispatch strategy modelling
- Solar generation yield modelling against actual consumption patterns
If you're on Miniflex, request your interval data from your metering service provider (often Actom, Elster, or direct from Eskom) before your first consultation with us. It will materially improve the accuracy — and the value — of your proposal.