Entry · Models
DESSEM
Which model estimates the operating cost every half hour?
Acronyms: CMO, Marginal Operating Cost; ONS, National Electric System Operator; CCEE, Electric Energy Trading Chamber; PLD, Settlement Price for Differences (spot price).
In one sentence
Model that estimates the CMO on a half-hourly basis for each bus of the system, according to the ONS.
Real example
R$ 63.31/MWhNature of the data: Calculated
Sep 19, 2026, 00:00 to Sep 25, 2026, 23:30 · Southeast/Center-West
Source: ONS, CMO Semi-Horário (DESSEM). Reference up to Sep 25, 2026. Captured on Sep 30, 2026.
Average, over the half hours of the operating week, of the CMO that DESSEM estimates for the Southeast/Center-West, side by side with the PLD of the same week in the panel.
In the same cut (Southeast/Center-West, same operating week), the average PLD was R$ 124.09/MWh, above the average DESSEM CMO. The PLD starts from the CMO, but it is not the CMO: it is calculated by the CCEE by hour and submarket and applies the regulatory limits.
Calculated: Deterministic transformation made by Scrutiniums, with a published formula.
Why it matters
How it is measured
Computer model, not a quantity. The ONS publishes the CMO it estimates every half hour, by bus; the CMO of the subsystem is the average of the CMOs of the buses weighted by the loads. In the example, the observatory uses the CMO of the subsystem and averages it over the half hours of the operating week.
Not to be confused with
Both estimate the CMO published by the ONS: DECOMP by operating week, subsystem and load level; DESSEM by half hour and by bus.
What cannot be concluded
- The source describes DESSEM only through the CMO it estimates; the technical documentation of the model was not read.
- The half-hourly CMO is not the PLD: the PLD applies regulatory limits and is calculated by the CCEE on an hourly basis.
Related entries
In the learning paths
See in the panel
Official source
ONSOpen data portal, dataset “CMO Semi-Horário” (description and data dictionary)
Literal excerpt from the document
Portuguese only“Este CMO é estimado pelo modelo DESSEM para cada barra do sistema em base semi-horária. O CMO do subsistema é obtido pelo média dos CMOs nas barras de cada subsistema, ponderados pelas respectivas cargas [...]”
In other words: every day the CCEE calculates the prices for each hour of the following day, in each submarket, with three computer models, starting from the marginal operating cost and respecting a minimum limit and two maximum limits.
Literal excerpt from the document
Portuguese only“O Preço de Liquidação das Diferenças (PLD) é calculado pela Câmara de Comercialização de Energia Elétrica (CCEE) diariamente para cada hora do dia seguinte, considerando a aplicação dos limites máximos (horário e estrutural) e mínimo vigentes para cada período de apuração e para cada submercado. Este cálculo é realizado por modelos computacionais (Newave, Decomp e Dessem) e tem como base o Custo Marginal de Operação (CMO).”
Documents accessed and text checked on Sep 28, 2026.