Warehouse solar savings
A Johannesburg warehouse using 30 000 kWh a month could cover 70% of its grid electricity with a 151 kWp rooftop system, avoiding about R764 000 a year in per-kWh charges (excluding VAT) at City Power's published 2026/27 rate. Here is exactly how My Solar Plan arrives at that, and what it leaves out.
Hypothetical warehouse, real engine and a published tariff. The building and its consumption are illustrative inputs, not a customer. The tariff is a verified entry from Red Energy's tariff catalogue, and every result is the output of My Solar Plan's own sizing and savings code.
The inputs
| Input | Value | Where it comes from |
|---|---|---|
| Roof | 80 m × 40 m, 5° pitch — room for 952 panels (595.0 kWp) | Hypothetical building, packed by the layout engine |
| Average consumption | 30 000 kWh per month | Customer input (illustrative) |
| Share used in daytime | 70% | Customer input; 70% is also My Solar Plan's default |
| Electricity rate | R3.0317 per kWh, excluding VAT: R3.3979 in the high-demand season (June to August) and R2.9096 in the low-demand season (September to May), weighted 3:9 by months | City Power Johannesburg 2026/27 “Three Part Tariff: LPU, Low voltage”: the energy charge plus City Power's per-kWh network surcharge, from Red Energy's verified tariff catalogue. City Power's 2% account surcharge is not included |
| Solar resource | 1 674 kWh per kWp per year | PVGIS for each roof face's pitch and direction, with a 7% system-loss allowance |
The result
- 150.6 kWprecommended system (about 241 panels)
- 252 000 kWhsolar production per year
- 70%of annual grid consumption replaced
- R764 000indicative saving on per-kWh charges per year, excl. VAT
Why the system is smaller than the roof
The roof could carry 595.0 kWp, but My Solar Plan recommends 150.6 kWp. The engine sizes solar to the electricity the site uses while the sun is up: 30 000 kWh a month is about 690 kWh of daytime use on an average day, and 150.6 kWp produces that much on an average day. Anything larger would generate electricity the warehouse cannot use at the time, and My Solar Plan gives that surplus no value.
How the saving is worked out
- Daytime use per day = monthly kWh × daytime share ÷ the average days in a month.
- Recommended size = daytime use ÷ the daily production of one kWp, capped at what fits on the roof.
- Grid electricity replaced = solar used directly by the daytime load (plus, with a battery, surplus solar stored for the evening). Nothing is counted as exported.
- Indicative saving = electricity replaced × the blended rate: 252 000 kWh × R3.0317 ≈ R764 000.
The other 30% — night-time and other non-solar use — stays on the grid. A battery can move some of it onto solar; see the system sizing example.
What this figure does not include
- Demand, capacity and fixed charges. No saving is claimed on maximum-demand or notified-demand (NMD) charges, capacity charges, fixed, basic or service charges, reactive-energy charges, or connection, metering and administration charges, or on City Power's 2% account surcharge. Only per-kWh charges are valued.
- Days the site is closed. The model works on one average day, repeated across the year. It does not yet reduce the saving for weekends or public holidays when a warehouse is shut. Solar produced on those days only has value if it is used or stored, so for a site that closes at weekends this figure overstates the saving.
- Tariff increases, panel degradation, finance and tax. The saving uses the 2026/27 rate without escalation and does not model degradation, financing or tax treatment.
- System price and payback. A price comes from Red Energy's priced equipment configuration after a site inspection. Until then My Solar Plan shows no payback period, rather than guess one. Simple payback is the system price divided by the annual saving.
- VAT. Tariff rates and the saving are shown excluding VAT, as the tariff is published.
On a time-of-use tariff
Many larger commercial sites are on time-of-use tariffs such as Eskom Megaflex or Miniflex. There, Red Energy values solar used directly at the Standard rate, up to the daytime load, and models a battery shifting energy into the Peak periods (net of what charging it costs) instead of using one blended rate. Peak, Standard and Off-Peak rates differ between the high-demand season (June to August) and the rest of the year. See the commercial solar buyer's guide for which tariffs My Solar Plan covers.
Frequently asked questions
How much can a warehouse save with solar in South Africa?
It depends mostly on how much electricity the warehouse uses while the sun is up and on its tariff. In Red Energy's engine, a Johannesburg warehouse using 30 000 kWh a month, 70% of it in daytime, on City Power's 2026/27 large-power-user low-voltage tariff could avoid about R764 000 a year of per-kWh charges (excluding VAT) with a 151 kWp system. That figure is indicative: it assumes the same average daytime use every day of the year, so a warehouse closed at weekends would save less, and it is not guaranteed.
Does solar reduce demand charges?
My Solar Plan does not claim any saving on maximum-demand or notified-demand (NMD) charges, capacity charges, fixed, basic or service charges, reactive-energy charges, or connection, metering and administration charges. It values only per-kWh charges for grid electricity that solar actually replaces: the energy charge, plus a per-kWh surcharge only where Red Energy has established that it varies with consumption. Whether solar lowers a site's maximum demand depends on when that demand occurs, which the model does not assess.
Does My Solar Plan count solar exported to the grid?
No. My Solar Plan gives no value to solar electricity the site cannot use or store at the time it is produced, because no export-credit model is applied today. That is why the recommendation is sized to the daytime load.
Build an indicative plan for your own site
My Solar Plan runs the same engine on your property: start with the address, confirm the roof, describe how the business uses electricity, then save the plan privately and refine it with Red Energy.
Start with my propertyLast reviewed 2026-10-13.