The electricity bill is the single most useful document in a solar sale. It tells you how much the customer uses, how much each unit costs them, what their connection allows, and the numbers you need for the DISCOM and PM Surya Ghar applications. Learn to read it in one minute.
The parts of a bill
Formats differ between DISCOMs, but every bill carries the same core information. The sample below is illustrative, not a real DISCOM format.
1. Consumer number and DISCOM
You need it for the net-metering application, the PM Surya Ghar portal registration and the DISCOM's feasibility process. Copy it exactly.
2. Tariff category and phase
Residential (domestic), commercial, industrial or agricultural. The category decides the tariff, the net-metering rules and whether subsidy applies (PM Surya Ghar CFA is for residential connections). Phase (single or three) affects inverter choice: DISCOMs usually limit single-phase inverters to around 5–6 kW, and systems above 10 kW must be three-phase under the CEA connectivity regulations (check the local DISCOM's limit).
3. Sanctioned (contract) load
The load in kW the DISCOM has approved for the connection. Many states allow rooftop solar only up to the sanctioned load, so a 3 kW connection may need a load-enhancement application before a 4 kWp system. Do not confuse it with connected load (the total of all appliances) or with maximum demand recorded by the meter.
4. Units
Units = current reading − previous reading (× multiplying factor on CT-operated meters). One unit is one kWh. This is the number that drives system size.
5. Energy charges and slabs
Most states charge residential energy in slabs. Under a telescopic tariff, each slab's rate applies only to the units inside it. Under a non-telescopic tariff, once you cross a threshold, every unit is charged at the higher rate; Kerala works like this above 250 units a month.
6. Fixed charges, surcharges and duty
- Fixed charge: per connection or per kW of load. Solar does not reduce it.
- Fuel/power purchase adjustment (FAC, FPPAS, FPPCA): per unit, changes month to month. In Gujarat it can add ₹2–3 a unit.
- Wheeling charge (Maharashtra) and electricity duty (a percentage or per unit). These fall when units fall.
7. Consumption history
Many bills print 6 or 12 months of history. Otherwise ask for the DISCOM app download.
Worked example: the value of a saved unit
Take the bill above: a Maharashtra residential customer using 350 units. Indicative FY27 rates (MSEDCL, as of October 2026; check the current tariff order):
| Slab (units) | Rate (₹/unit) | Units | Amount |
|---|---|---|---|
| 0–100 | 3.96 | 100 | ₹396 |
| 101–300 | 10.80 | 200 | ₹2,160 |
| 301–500 | 15.03 | 50 | ₹752 |
| Energy total | 350 | ₹3,308 |
Add wheeling at about ₹1.60 on all 350 units (₹560) and the fixed charge (₹130). Electricity duty of 16% on the total brings the bill to about ₹4,638, before any fuel adjustment.
Now the important question: what does one unit saved by solar save the customer? Solar cuts the most expensive units first, the ones in the top slab:
(15.03 + 1.60) × 1.16 = ₹19.29 per unit at the margin.
Once net use falls below 300 units, each further unit saves (10.80 + 1.60) × 1.16 = ₹14.38. The average tariff on the bill (₹4,638 ÷ 350 = ₹13.25) is lower than both, because it includes cheap first-slab units and the fixed charge that solar never removes.
Compare a Jaipur customer with the same 350 units (JVVNL indicative rates: ₹7.00 top slab, about ₹1.00 regulatory surcharge, ₹0.40 duty and ₹0.15 urban cess per unit). The marginal saving is about ₹8.55 per unit. Same system, same units, less than half the rupee saving. This does not change the kWp you design; it changes the payback you promise.
Seasonal and bi-monthly bills
- Seasonal swing: a Chennai home might use 250 units in January and 520 in May. Add all 12 months and divide by 12 for sizing.
- Bi-monthly bills: Tamil Nadu and Kerala bill domestic consumers every two months. Halve the units for a monthly figure, but remember that Tamil Nadu slabs are defined per two-month period (for example the free 100 or 200 units), so savings must be worked out bi-monthly.
- Missing months: if the customer has only six bills, ask for the DISCOM app history, or use bills from both summer and winter and scale with care.
Reading a net-metered bill
After solar, the bill shows import (units taken from the grid), export (units sent out), net units billed, and often banked or carried-forward units. Train customers to read these three numbers so they understand why the bill is not zero in July (module m08).
Key points
- From every bill, record consumer number, tariff category, phase, sanctioned load and units.
- Units drive kWp; tariffs drive savings. Keep the two calculations separate.
- Solar removes the top-slab units first, so the marginal saving per unit is higher than the average tariff.
- Fixed charges stay; per-unit surcharges and duty fall with units.
- Size on 12 months of data, and handle bi-monthly bills carefully.
Check yourself
- A meter reads 8,215 last month and 8,540 this month. How many units were consumed?
- Why is the marginal value of a saved unit often higher than the average tariff?
- A customer has a 2 kW sanctioned load and needs a 3.3 kWp system. What do you tell them?
Answers
- 8,540 − 8,215 = 325 units.
- Solar removes the most expensive top-slab units first, while the average includes cheaper slabs and fixed charges.
- Many DISCOMs cap rooftop capacity at the sanctioned load, so they may need to apply for a load enhancement first. Check the local rule and include the step and any fee in the plan.