New Trends in Reliability Assessment

As energy markets evolve in terms of rules, competition and diversity of supply so the framework of conducting studies for long-term reliability should also evolve.

IEEE recently hosted a two-day meeting of the Loss Of Load Expectation (LOLE) Best Practices Working Group to discuss industry trends in the study of long-term reliability. The meeting featured each reliability region in North America and provided a forum for discussing new trends in assessment practices.

Historically, long-term reliability studies have been conducted on large control area or multi-control area (regional) basis. These studies typically accounted only for supply, load growth, weather and in some cases where critical, hydro-conditions. As we enter the 21st-century, energy supply has migrated, in most regions, to a competitive marketplace.

In addition to the element of competition, the supply of energy itself is changing from fossil-fuel based to more reliance on intermittent resources as well as demand response products. As such modeling of these resources has become more complex. In addition to the changes in supply, the industry is also recognizing that increased granularity in-terms of modeling of the network is also critical.

The role of network modeling in reliability studies has become paramount. Why? Because reliability is always Job-1 and competitive markets tend to extract maximum value from existing network resources. As network resources become more constrained the study of the impact of supply on the network over the long-term becomes more critical.

This is where ECCO International comes into the picture. ECCO has long been an industry leader in the areas of energy market design and network modeling for competitive markets. Our models account for the complexities of the market while accounting for network “realities.” As such, ECCO has incorporated in its long-term market simulation software, ProMaxLT™, which is deployed for reliability studies a detailed transmission model.

ProMaxLT™ uses exactly the same transmission models as used by an ISO/RTO for clearing its nodal market to model the effect of transmission constraints on the network. ECCO proposes that this model can be used to calibrate and assess the accuracy of the zonal constraints and proxy transmission constraints being proposed for any LOLE study. ECCO has been using this formulation for nodal market simulation, price forecasting and reliability studies for over 7-years very successfully. Our unique experience as energy market designers in implementing energy markets around the world over the last 15-years has given us a competitive advantage in building a software platform that exactly mimics the Day-Ahead market clearing engines of ISOs/RTOs. This configuration is critically important for LMP market analysis and price forecasting purposes. For short-term operational studies, the full AC model is used by ProMaxLT™ with no approximations or simplifications. A power flow solution is solved for each trading interval to provide a network model to compute sensitivities of the flows on heavily loaded lines to changes in generation output for use in the LP/MIP formulation and to compute the loss sensitivity factors for use in calculating the loss component of the LMP (if the AC power flow based models are used for the market clearing).

For such nodal market simulation and price forecasting studies, ProMaxLT™ can perform a full hourly Day-Ahead MIP-based Unit Commitment using forecast load profiles, bidding profiles, renewable schedules, forecast maintenance schedules, etc. ProMaxLT™ has the capability to use forecast economic bids for energy and ancillary services, or alternatively can perform a classic LP-based economic dispatch using unit heat rates and forecast fuel prices. In both cases a full or reduced AC or DC network model can be deployed. The power flow model can be iterated with the MIP engine exactly the same way with the market clearing methodology various ISOs/RTOs deploy to clear the spot market. This approach models startup costs and inter-temporal constraints. Note that constant proxy costs can be used for all generation resources for the purposes of typical reliability studies. However, if a financial tradeoff between reliability and associated costs is to be evaluated, then a realistic representation of all costs associated with generators is required.

However the selection of MIP-based capability with explicit transmission modeling is not recommended for LOLE studies using Monte Carlo simulations. In case explicit transmission constraints are required by a region to be included in such studies, we recommend to use a full unreduced DC network model, which explicitly includes contingency constraints. A fast iterative solution between LP dispatch and DC power flow is then performed to enforce the security constraints in solution using the well known shift factors or Power Transfer Distribution Factors (PTDFs).

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