Combustion Turbine Flexibility

Transcription

1 Combustion Turbine Flexibility Presentation to: NorthWestern Energy ETAC June 6, 2013

2 Why Does NWE Need Flexible Resources? Variations in load (within hour flexible capacity) Hour-to-hour ramp (10 minutes before to 10 minutes after the hour) to reflect schedule changes Forced outage response Variable Energy Resource (VER) following primarily wind

3 7000 MW +/- Regional Wind (36 hours) 300 MW +/-

4 Northwest Resource Flexibility Prior to 2003, NW IOUs (PacifiCorp, PGE, PSE, Avista, Idaho Power) enjoyed adequate resource flexibility from Mid C projects and/or utility-owned hydro resources BPA, BC Hydro, Mid C PUDs, Seattle, Tacoma operate hydro resources with significant flexibility second-to-second, daily, seasonal The wind revolution and expiry of Mid C contracts (starting in 2004 with Priest Rapids) changed the regional flexibility landscape PacifiCorp and PGE joined NWE as hydro flexibility have-nots

5 Role of Gas Resources to Meet Flexibility Needs PGE, PacifiCorp, NWE, and (to a lesser extent) PSE use gas-fired generation to follow load and resource deviations Maintaining load resource balance can be particularly difficult in spring and over winter peak may need to run gas out-of-merit for regulation margin Entities with surplus hydro flexibility (large publics, BC Hydro/Powerex) generally make more money from load factoring (LLH to HLH) than providing regulation service

6 Types of Open Cycle Gas Turbines Frame SCCTs - Primarily capacity (large/fast w/controls) GE 7EA, GE 7FA, Siemens 501G, etc MW Heat Rate = ,400 Btu/kWh rarely dispatch (under 2% of hours) Reciprocating Engines - Primarily flexibility (small/fast) 9-20 MW Wärtsilä, Caterpillar (Basin Creek) Heat Rate = Btu/kWh higher variable O&M limits dispatch Aero derivative SCCTs - Capacity and flexibility (fast) GE LM6000 (Highwood), GE LS100, P&W FT-8 (DGGS) MW Heat Rate = Btu/kWh infrequent dispatch (under 5% of hours)

7 Open Cycle Turbine Dispatch Purchase spot market natural gas Infrequent dispatch complicates gas pipeline and transmission strategy Firm transport way too expensive, but interruptible may be interrupted or reduced over winter peak Avista Rathdrum California storage and exchange via GTN Back-up fuel (DGGS) Smaller unit size and flat HR curve may make reciprocating engines a better fit for flexibility requirements than other SCCT technologies Infrequent CT dispatch increases start-up forced outage risk

8 Combined Cycle CT Basics CCCT utilizes two turbine generator sets, usually with separate shaft for each T-G: Gas-turbine generator (GE Frame 7, MHI, or Siemens) thermal energy from fuel combustion directly spins the turbine Steam-turbine generator uses heat energy from gas-turbine exhaust to create steam to spin a second turbine Add additional combustion capability after combustion turbine to increase steam-turbine output (duct-firing)

9 Duct-burner

10 CCCT Math Large gas turbines have a heat rate under 7000 Btu/kWh - describes the conversion of thermal energy into electrical energy. Natural gas generally priced in $/MMBtu Incremental cost of production = Heat Rate/1000 x (Gas Price + Variable Transportation) x (1+ End Use Gas Tax Rate) + Variable O&M Depending on location of unit, may need to factor incremental transmission and losses into the calculation

11 CCCT Incremental Cost Example Heat Rate = 7000 Btu/kWh Gas Price = $4/MMBtu Variable Gas Transportation = $.10/MMBtu WA Gas Tax Rate =.038 (allows me to make a point) Variable O&M = $3.5/MWH Incremental Cost = (7000 Btu/kwh) /1000 x ($4/MMBtu +$.10/MMBtu) x ( ) + $3.5/MWH = $33.3/MWH

12 But CCCT Dispatch Decisions Rarely Straight-forward NW CCCT fleet usually sets daily market-clearing price wind and hydro push CCCTs in/out of the money CCCTs often economic HLH but uneconomic LLH - $1.5/MWH in-the-money HLH, -13.0/MWH LLH on 6/1/13 Start-up requires multi-hour ramp-up/ramp-down quick start package can shorten the ramp-up Maintenance contracts charge for starts after some maximum (around 50/yr) - $3000-$5000/start Best CCCT heat rate at full load Heat rate increases 1% for every 5% of output reduction between 80% and 100% of rated capacity Heat rate increases 2.7% for every 5% of output reduction thereafter to maximum turn-down of 50%

13 CCCT Ramp (GE Product) Slowly load STG Quickly load GT - Start charge - High HR

14 GE Part Load Performance +2.7% HR Per -5% Base Rtg +1% HR Per -5% Base Rtg

15 CCCT Part-load Performance + LM6000 LM6000

16 But Wait, There s More Different schedule for gas day (9 AM 9 AM PPT/MPT 8 AM 8 AM) versus electric day (midnight to midnight) introduces additional uncertainty on CCCT economics Dispatching CCCT up/down to minimize electric imbalance charges could cause imposition of pipeline imbalance charges Location on transmission system could limit ability to dispatch on some hours Note the number of discontinuities and uncertainties inherent in CCCT dispatch decisions!

17 CCCT Duct-firing Standard GE Frame 7FA CCCT GT-STG package includes 22 MW of duct-firing could be as much as 60 MW for a 1x1 CCCT configuration Duct-firing looks like a quick-start SCCT with 9400 Btu/kWh HR Duct-burner start and ramp to full output takes about 10 minutes due to need to have plant operator configure equipment On the ragged-edge of fast enough to use for spinning reserve.

18 And Did I Mention Hedging? Once you sign the confirm to purchase forward gas, the unit price you paid has no bearing on dispatch decisions However, purchasing gas in the forward market at a price well above the ultimate market price will attract attention, and Not purchasing gas in the forward market at a price that turns out to be well below the ultimate market price will attract attention Depending on hydro conditions, load growth, coal/nuclear performance, etc, a CCCT could dispatch on as few as 30% of the hours in a year and as many as 80% of the hours in a year. Regardless of hedging strategy deployed, a CCCT operator needs good access to liquid natural gas and electric market hubs and/or suppliers to sell excess and cover deficits

19 Modeling Implications Hard to predict CT actual operation with a dispatch model (requires perfect knowledge) Many examples of out-of-merit dispatch aware of one entity that won t turn CCCT on unless in the money on a multi-week basis, then doesn t adjust output until market indicates unit uneconomic on a multi-week basis Hydro flexibility often used to keep CCCTs either just in or just out of the money some dispatch models handle hydro complexity better than others

20 Integrated Uncertainty NWE Standards of Conduct limit ability of NWE Transmission to coordinate flexibility needs of the BAA with NWE Supply DGGS provides much of NWE s BAA balancing needs, with Shell Trading available to buy/sell real-time to recenter DGGS NWE Supply currently receives no information on DGGS operation NWE Transmission called NWE Supply for Basin Creek support during DGGS outage as an emergency measure NWE would need to change current model for provision of balancing resources to fully utilize flexibility of Supply-controlled natural gas generation resources and to minimize NWE overall expense for natural gas

21 Final Points CCCT Operation? Why, yes, it is rocket science!