Net Metering: exports cancel imports first
Net Metering is like a monthly swap. Energy you send to the grid cancels energy you take from it. If you export more than you import, the extra is credited at Rs 3.00/kWh. Here is the same household worked through under Tariff 150A_NM.
The example household
Home
4-bed
family home, Mauritius
System
6 kWac
hybrid PV + battery
Month
June 2026
illustrative period
Tariff
150A_NM
residential prosumer
The monthly swap, step by step
Imported (I)
240 kWh
Exported (E)
430 kWh
Excess export
190 kWh
Net import: 240 − 430 = 0 kWh · Excess: 430 − 240 = 190 kWh
The detailed bill
Because exports exceeded imports, there is no running energy charge. CST applies on the energy offset, and the excess export earns a credit.
| Net imported energy charge0 kWh net import | Rs 0.00 |
| CST charge290 kWh offset × Rs 0.82 | Rs 237.80 |
| Power-base generation & network charge6 kW × Rs 163 — currently exempted | Rs 0.00 |
| Excess net export credit190 kWh × Rs 3.00 | − Rs 570.00 |
| Current month balance | − Rs 332.20 |
Amount payable
Rs 0
no bill this month
Credit to account
Rs 332
carried forward
vs 100% CEB
Rs 3,821
benchmark avoided
CST band for 501–1,000 kWh is Rs 0.82/kWh of energy offset. Monthly Energy Offset = consumption (530) − imported (240) = 290 kWh. Prosumers are currently exempt from the Rs 163/kW power-base charge.
How the 290 kWh CST charge is calculated
The CST (Corporate Social / system) charge is not applied on every kWh you use — it is applied only on the energy you actually offset with the grid. That offset volume drives the Rs 237.80 figure shown above.
| Total home consumption (C) | 530 kWh |
| Less: energy imported from grid (I) | − 240 kWh |
| = Energy offset by your own solar | 290 kWh |
Of the 530 kWh you used, 240 kWh was drawn from CEB and the remaining 290 kWh came from your solar/battery — that self-supplied portion is what carries the CST charge.
Offset units
290 kWh
self-supplied energy
CST band rate
Rs 0.82
501–1,000 kWh band
CST charge
Rs 237.80
290 × 0.82
290 kWh × Rs 0.82/kWh = Rs 237.80
Baseline CEB cost vs your real monthly cost
The figures above are only the CEB line. To compare fairly with simply buying everything from CEB, we must add the system repayment (system cost spread over 60 months) to get the true all-in monthly cost.
| Baseline cost — 100% from CEB530 kWh @ domestic tariff (no solar) | Rs 3,821 |
| Net Metering CEB resultthis example — a credit | − Rs 332 |
| Asset repaymentRs 420,000 ÷ 60 months | + Rs 7,000 |
| Actual total monthly cost (incl. repayment) | Rs 6,668 |
During the 60-month repayment, the all-in figure can sit above the CEB baseline because you are buying the asset. From month 61 the Rs 7,000 repayment falls away, leaving only the small CEB result — at which point the saving versus CEB becomes substantial. System cost is illustrative; your quote determines the real numbers.
Paying off the system over 60 months
A solar system is an upfront investment. Spreading an illustrative system cost of Rs 420,000 evenly across 60 months lets us see the true all-in monthly position while the equipment is being paid off.
Rs 7,000
Rs 420,000 ÷ 60 months
+Rs 332
credit to your account
| CEB bill under this option | − Rs 332 |
| System finance (over 60 months) | + Rs 7,000 |
| All-in monthly cost | Rs 6,668 |
Versus 100% CEB (Rs 3,821/month): all-in you pay Rs 6,668 — about Rs 2,847/month more during the 60-month payoff. After month 60, the finance line falls away and the saving grows.
After month 60: the system is fully paid. The finance line disappears, so the monthly saving versus CEB increases for the remaining life of the system. Net Metering produces a small credit here rather than a bill, which offsets part of the system finance. System cost is illustrative — your actual quote determines the figures.
Net Metering is usually the strongest on-grid result — here it even produces a credit. But it is still not a guaranteed monthly reduction product: CST applies when relevant, excess export is credited at Rs 3.00/kWh, and future months depend on whether you import more than you export, the weather, your load profile and any prevailing tariff notices.