Everything Old is New Again

As Energy Exemplar enters the closing stages of a project with the Australian Energy Market Operator (AEMO) to deliver PLEXOS as an upgrade to the market system in the Australian NEM known as “MT PASA”, we come to realise the quintessential case of “Sooner or later, everything old is new again.”

The story of MT PASA and of how the outage optimization phase of PLEXOS got its name “PASA” goes back to 1997 when the Australian electricity market was a still a toddler. Glenn Drayton was working in New Zealand for an operations research consulting firm called Core Management Systems (CMS) and had just finished his Ph.D. thesis, focussed on electricity market design. Out of that work came the electricity market simulation software, WEMSIM (which would eventually become PLEXOS).

The key enabling technology inside WEMSIM was AMMO (ActiveX Mathematical Modelling Objects). This API connected Microsoft’s VBA to CPLEX, which meant that commercial grade mathematical programming could be easily integrated into any VBA-aware program like Excel. In hindsight, AMMO is the best idea Glenn claims to have come up with because today it underpins the PLEXOS engine.

CMS consultants like Dr E. Grant Read (inventor of dual dynamic programming and Glenn’s Ph.D. supervisor) and Brendan Ring (who studied at University of Canterbury with Glenn and today is one of the world’s leading experts in electricity market design) were involved in the design of the Australian NEM. A US firm called ESCA built the market software systems including the market clearing engine SPD (Scheduling, Pricing and Despatch), affectionately known as “spud” and later renamed to NEMDE.

ESCA was under pressure to deliver the market systems but were short on time, especially with implementing “MT PASA” (“Medium Term Projected Assessment of System Adequacy”). This report looked ahead two years and computed available reserve generation capacity announced maintenance schedules, transmission availability and the forecast peak loads. Its key outputs were the expected reserve levels at the peak of each day in each region in the NEM.

While Glenn was upgrading WEMSIM to optimize the placement of outages, CMS volunteered to supply the MT PASA software until such time as ESCA could write the “official” version. The stars aligned and Glenn began writing MT PASA for the NEM.

Glenn realised that consulting companies are not good places to write software. Consulting and software cultures are very different and writing software whilst consulting is a recipe for a poor product, a philosophy that Energy Exemplar maintain to this day by not consulting.

So, it was because of MT PASA that the maintenance optimization phase of PLEXOS got the name PASA, and the “temporary” MT PASA Glenn originally wrote for the NEM lasted several years before ESCA finally got around to replacing it.

Today, we have come full circle. The original, simple, MT PASA has done its dash. It has not kept pace with the introduction of intermittent generation. AEMO recognise that a full Monte Carlo simulation which considers renewable intermittency as well as generator forced outages is paramount for meaningful mid-term indicators of shortage or surplus.

And so, as PLEXOS becomes set to replace MT PASA by November 2017, we find that sooner or later, everything old is new again.

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