Assuming there is no congestion in your system model, the generator which has its marginal cost (assuming you are using marginal cost in your LMP determination), equal to LMP (at that market clearing), is the marginal generator. By creating simple supply curve can also help you identify which generator is the marginal generator.

If you have one binding constraint in the market results (meaning one transmission line is binding), then, you will have two marginal generators. The algorithm that you are using should be able to determine those generators. 

I can only say this without knowing what you are actually doing and trying to achieve.

Feel free to write to me if you have further questions: [email protected]

salaam,

as we discussed, one way is by equating the marginal cost of generator to the LMP of the bus to which the generator is connected. 

also take a look on the book, Power System Economics, by Stoft

Assuming there is no congestion in your system model, the generator which has its marginal cost (assuming you are using marginal cost in your LMP determination), equal to LMP (at that market clearing), is the marginal generator. By creating simple supply curve can also help you identify which generator is the marginal generator.

If you have one binding constraint in the market results (meaning one transmission line is binding), then, you will have two marginal generators. The algorithm that you are using should be able to determine those generators. 

I can only say this without knowing what you are actually doing and trying to achieve.

Feel free to write to me if you have further questions: [email protected]

maybe i can help you but need more explanation what you want exactly!

In simple words, the generator whose offer price is equal to the LMP at its bus,  is the marginal generator. Usually, marginal generators will be selected partially, i.e., MW amount will be in between minimum and maximum limit bus not equal to limits.  

In other cases in which there are multiple congestions in the system, it is very difficult to identify the marginal generators because you cannot relate the final LMP with the cost of the marginal units. Whoever runs the market (clearing the market) knows exactly which units are the marginal units. But, if you are a market participant, you have NO WAY of knowing which units are the marginal units. One US university got funded and spent lots of money to solve that very problem you are mentioning. Even with that, the results are just approximate. The main reason lies in the mathematical formulation of the LMP-type market clearing.

Hope this helps.

It is a simple question, but there is no simple answer. If there is not any network or security constraints, the generator whose marginal cost (or its offer in oligopoly market) equals to the LMP is the marginal generator. However, only market operator can detect which generator is  marginal, if the market is not completely competitive. There are many ways to guess the marginal generator from a market player's viewpoint, but it generally works only in small-scale systems.

We could have a whole debate on what it actually means by 'market is competitive or not competitive'!!!

cheers...

very difficult to identify the marginal generators because you cannot relate the final LMP with the cost of the marginal units. Whoever runs the market (clearing the market) knows exactly which units are the marginal units. But, if you are a market participant, you have NO WAY of knowing which units are the marginal units. One US university got funded and spent lots of money to solve that very problem you are mentioning. Even with that, the results are just approximate. The main reason lies in the mathematical formulation of the LMP-type market clearing.

Hope this helps.

Hashem,

I appreciate your reply. But, I found that you just copied part of my previous reply. I don't know if it is intentional or just reinforcing what I just said.

Feel free to ask more questions if you have. I'll be more than happy to answer. In fact, I would like to clarify a lot of difficult questions here because sometimes, we cannot really explain WHY we got the optimal solutions that we tried to solve. Solutions from optimization problems are sometimes difficult to explain in real-world physical terms particularly when that optimization problem formulation is pretty complex!!!

Regards,

Jeremy

Dear Jeremy,

I used "competitive market" phrase to indicate that the market players offered equal to their marginal cost. If the market model allows them to increase their offers, an oligopoly market can be simulated. In an oligopoly environment, market players have two approaches to increase the LMPs more than the marginal costs. First, the Tacit collusion that is the increase of the price by almost all the Gencos without any contract or agreement between them. Second, the Explicit collusion that is based on an agreement between two or more players to benefit from the weakness of the market structure or the network to increase their profit.

Detecting the collusions is not an easy task for an ISO at all, but the ISO knows which players are marginal. However, the problem from a player's viewpoint is totally different. Because, although it can estimate the marginal cost of other players, it cannot find how much the offers of other players are more than their marginal cost. 

More details are presented in following articles:

M. Shafie-khah, M. Parsa Moghaddam, and M.K. Sheikh-El-Eslami, "Ex-Ante Evaluation and Optimal Mitigation of Market Power in Electricity Markets including Renewable Energy Resources", IET Generation, Transmission & Distribution, vol. 10, no. 8, pp. 1842-1852, 2016.

M. Shafie-khah, M. Parsa Moghaddam, and M.K. Sheikh-El-Eslami, “Development of a Virtual Power Market Model to Investigate Strategic and Collusive Behavior of Market Players,” Energy Policy, vol. 61 pp. 717-728, 2013.

It is a simple question, but there is no simple answer. If there is not any network or security constraints, the generator whose marginal cost (or its offer in oligopoly market) equals to the LMP is the marginal generator. However, only market operator can detect which generator is  marginal, if the market is not completely competitive. There are many ways to guess the marginal generator from a market player's viewpoint, but it generally works only in small-scale systems.