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Sizing a PV system with contracted demand: a practical guide for Brazil's Group A consumers

In Group A, the customer pays for demand and consumption separately — and solar does not reduce demand. How to size industrial and commercial projects without promising what solar cannot deliver.

Sizing for Group A (high-voltage consumers) is a different league from sizing a home. Here the customer pays a two-part tariff: one part for contracted demand (kW) and another for consumption (kWh). The installer's most expensive mistake is promising to "zero the bill" — solar offsets consumption but does not reduce demand. Understanding this difference is what makes your proposal technically honest and sellable.

Demand vs consumption: what solar really reduces

Demand is the power (kW) the customer reserves from the utility and pays for every month, used or not. Consumption is the energy (kWh) actually used. Distributed generation offsets only the energy portion (TE + TUSD). However good the system, the bill never reaches zero, because the demand charge remains. Make this explicit in Group A proposals — it is the point that causes most frustration after the sale.

Tariff modality: Blue or Green

Before sizing, confirm the modality on the bill:

  • Green (usually A4, up to 25 kV): a single demand, but energy priced differently at peak and off-peak. Very common in retail and small industry.
  • Blue: separate contracted demands for peak and off-peak. Typical of large consumers.

The tariff period matters: energy exported at peak is worth more than off-peak. Since the sun generates mostly off-peak, compensation happens in that period — analyse how much of the customer's consumption happens in each.

Step-by-step sizing in Group A

1) Separate peak and off-peak consumption (kWh) and demand (kW) on the bill. 2) Set the compensation target on energy only, not on demand. 3) Calculate kWp as in any project (consumption to offset ÷ PSH ÷ PR). 4) Consider reviewing the contracted demand with the utility: many industries have poorly adjusted demand and pay penalties for exceeding it or for idle capacity — fixing this can be worth as much as the plant itself. 5) Check whether the connection point can take the mini-generation and whether a protection study is needed.

Group A: what solar offsets

Bill componentDoes solar offset it?
Energy consumption – off-peak (kWh)Yes
Energy consumption – peak (kWh)Yes (with a period adjustment factor)
Contracted demand (kW)No
Demand overrunNo
Availability chargeNot applicable (Group B only)
Estimate the system size Get a first estimate of kWp, modules and generation for the energy portion of the bill.
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Frequently asked questions

Does solar reduce contracted demand in Group A?

No. Distributed generation offsets only the energy (kWh). Contracted demand (kW) is still billed in full, regardless of generation.

What is the difference between the Blue and Green tariffs?

In the Green modality there is a single demand and energy priced at peak and off-peak. In the Blue modality, peak and off-peak demands are contracted separately.

Is it worth reviewing contracted demand together with the solar project?

Almost always. Poorly adjusted demand causes overrun penalties or payment for idle capacity. Optimising demand can bring savings comparable to the plant itself.

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