Selling Solar Surplus as a Company: How Exported Energy Is Paid and What It Is Worth in Colombia

A solar plant produces according to the sun, not the company's schedule. Whenever output at a given instant exceeds consumption at that same instant, the difference flows through the meter into the network operator's grid. That energy is surplus, and the bidirectional meter required by Resolución CREG 174 de 2021 records it separately from imported energy.

Even a well-sized plant generates surplus: consumption drops on Sundays, public holidays and production stoppages while the plant keeps generating. What changes between companies is the share. In a Monday-to-Saturday operation with steady daytime demand, surplus can be a small fraction of output; in an office closed at weekends, considerably more.

For a small-scale self-generator (up to 1 MW of installed capacity, Resolución UPME 281 de 2015 (UPME scale threshold)) using renewable sources, Resolución CREG 174 de 2021 recognises surplus as an energy credit. In practice it works as a swap: each kWh delivered to the grid offsets one kWh imported in the same billing period.

The swap has a cost. For each kWh offset, the retailer charges the retail component if the plant is up to 100 kW. Above 100 kW and up to 1 MW, it charges the sum of the transmission, distribution, retail, losses and constraints components. That is why an offset kWh is worth less than a self-consumed one, and the gap is wider for plants above 100 kW.

If in the period the plant delivers more energy to the grid than the company imported, the energy credit runs out and the rest is valued hour by hour, under article 25 of Resolución CREG 174 de 2021, at the spot price of energy. XM calculates and publishes that price for each hour, and it is usually well below the tariff the company pays as a customer.

This rule is what caps the sensible size of an AGPE plant. Oversizing to "sell energy" pushes the extra kWh into the lowest-value bucket of all, and that rarely pays back the extra panels.

Above 1 MW the company is a large-scale self-generator and has no energy credit. To deliver surplus, Decreto 1073 de 2015 (Energy Sector Decree), as worded by Decreto 1403 de 2024, requires it to be represented in the wholesale market by a retailer or a generator. Resolución CREG 024 de 2015 (large-scale self-generation rules) governs the rest of the activity.

The value of each exported kWh comes from the contract with that representative: a fixed price, one indexed to the spot market or a mix, with the representative's fee deducted. Since there is no regulated formula, an installer's proposal for an AGGE must state which representative and which surplus price were used to calculate the return. If it does not, the financial model is incomplete.

An AGGE must also sign a backup contract with the network operator, whose charge reduces the project's benefit, and it does not get the reactive-energy exemption that Decreto 929 de 2023 grants to renewable AGPEs.

The alternative is to export nothing. With zero-export control, the inverter curtails output so it never exceeds instantaneous consumption. Decreto 1403 de 2024 provides that in that case no connection authorisation is required, there is no small- versus large-scale distinction and no capacity limit; the RETIE (technical electrical regulation) and the network operator's connection procedure still apply, without a simplified connection study.

The cost is the curtailed energy. It makes sense when daytime demand is high and steady every day, when a large plant wants to avoid the AGGE category, or when a faster procedure is worth more than a surplus that would be small anyway.

The practical rule is to size against consumption during sunlight hours. Each self-consumed kWh saves the full tariff; each offset kWh saves the tariff minus the swap charges; each kWh above imports is worth the spot price. As the plant grows, a larger share of its output falls into the lower-value buckets.

Doing that calculation properly requires the company's hourly load curve, which the network operator or retailer can supply from the meter, not just the monthly consumption on the bill.