1 Western Wind & Solar Integration Study Phase 2: Cycling Impacts on Thermal Generators Dick Piwko, Gary Jordan March 16, 2011

2 Cycling Costs: what are we missing now? Additional cost of cycling, when incremental costs are not included in commitment and dispatch : Incremental Variable Cost Cycling Variable Operating Cost, VOC (per MAPS) Addition VOC for Cycling (outside of MAPS) Total Variable Operating Cost, VOC MAPS Solution “Cycling”? Means lots of things, but in broad terms we are concerned about 2 chunks: 1.Start/stop - decommit 2.Ramp – up/down, turnback, dispatch

3 Cycling Costs: new optimum Incremental Variable Cost Cycling Additional cost of cycling, when incremental costs are included in commitment and dispatch : VOC (per MAPS) Addition VOC for Cycling (outside of MAPS) Total VOC Solution considering Total VOC

4 Cycling Costs: looking for benefits Incremental Variable Cost Cycling Quantifying the VOC benefit of reducing the additional cost of cycling: Solution considering Total VOC VOC (per MAPS) Addition VOC for Cycling (outside of MAPS) Total VOC Reduced cycling cost with mitigations implemented

5 Cycling Costs & Production Cost Simulations What is presently in the MAPS model: Start up cost (not a function of any frequency, past or subsequent dispatch) Non-fuel variable cost (O&M, a fraction of MWhr) Minimum down time Heat rate vs P (static multi-segment curve) Minimum and maximum dispatch Emissions vs MWhr (as a function of static heat rate) What is presently not in the MAPS model: Non-fuel O&M cost as a function of (a) depth of cycle; (b) ramp rate; (c) duration of cycle Heat rate (and emissions) impacts due to rate-of-change of power during ramps Minimum down time as a function of previous history Variable minimum downtime/start up – and cost, heat rate / fuel penalty, emissions penalty associated with shorter/longer downtime Lots more Plexos has similar characteristics.

6 Mitigation Options: From Solution to Value Power plant technical experts define specific modifications What is the modification (boiler features, pumps, controls, fans, coal mills, etc.) How does it modify operation of the power plant (faster ramp, lower turndown, etc.) What is the cost (capital cost, variable cost) What is impact on emissions GE team translates these modifications into data and/or procedures for evaluating operational impacts/costs with production simulation tools (MAPS & Plexos) Variable cost parameters for items included in MAPS & Plexos Post-processing of annual operation profiles to assess costs that are not specifically modeled in MAPS or Plexos Iterative MAPS & Plexos simulations to refine unit operation profile with new operating cost characteristics Bottom Line: Calculate system-wide production cost impacts with mitigation in place; Establishes the value of the solution.

7 Mitigation Options: From Need to Solution (and its value) Postulate an attractive solution (eg., turndown to 20% load) If achieved, what is its value to overall operating cost of the power grid? Can the required physical modifications can be done to the plant within that value? Initially focus on a few units Then generalize to groups or types of generating units