1. Texas Nodal © 2005 - 2006 Electric Reliability Council of Texas, Inc. All rights reserved. 1 Ancillary Services – Day-Ahead & Real Time Markets Mini Market Examples Formulas

2. Texas Nodal © 2005 - 2006 Electric Reliability Council of Texas, Inc. All rights reserved. 2 Ancillary Services A service necessary to support the transmission of energy to Loads while maintaining reliable operation of the Transmission Service Provider’s transmission system using Good Utility Practice Types – Regulation (Up and Down), Responsive Reserve, Non-Spin

3. Texas Nodal © 2005 - 2006 Electric Reliability Council of Texas, Inc. All rights reserved. 3 Ancillary Service Timeline Ancillary Service Trades reported before 10:00 will be included in the Day Ahead Market Day-Ahead Ancillary Service awards communicated by 13:30 in Day Ahead Ancillary Service Trades reported after 10:00 and before 14:30 will be incorporated into the DRUC DRUC from 14:30 through 16:00 Real Time Ancillary Service or SASM awards completed in the Adjustment Period

4. Texas Nodal © 2005 - 2006 Electric Reliability Council of Texas, Inc. All rights reserved. 4 Ancillary Service Day Ahead Market

5. Texas Nodal © 2005 - 2006 Electric Reliability Council of Texas, Inc. All rights reserved. 5 DAM – Ancillary Service Payments PCASAMT = (-1) * MCPCAS * PCAS Used to pay QSEs for bids that have been accepted in the DAM Using AS in place of RU (Regulation Up), RD (Regulation Down), RR (Responsive Reserve), NS (Non-Spin) All Day-Ahead Market settlements are hourly

6. Texas Nodal © 2005 - 2006 Electric Reliability Council of Texas, Inc. All rights reserved. 6 DAM Ancillary Service Charge DAASAMT = DAASPR * DAASQ Used to charge to QSEs who have load, their AS obligation not provided by them Using AS in place of RU (Regulation Up), RD (Regulation Down), RR (Responsive Reserve), NS (Non-Spin) All Day-Ahead Market settlements are hourly

7. Texas Nodal © 2005 - 2006 Electric Reliability Council of Texas, Inc. All rights reserved. 7 DAM Ancillary Service Charge (cont) DAASPR = (-1) * PCASAMTTOT / DAASQTOT Allocating all AS charges for a particular AS (PCASAMTTOT) over all of the AS provided for a particular AS (DAASQTOT) These bill determinants are ERCOT wide totals

8. Texas Nodal © 2005 - 2006 Electric Reliability Council of Texas, Inc. All rights reserved. 8 DAM Ancillary Service Charge (cont) PCASAMTTOT = ∑ PCASAMT q DAASQTOT = ∑ DAASQ q Sigma sums up the bill determinant by QSE Used to sum up all of the volumes and all of the payments to AS suppliers

9. Texas Nodal © 2005 - 2006 Electric Reliability Council of Texas, Inc. All rights reserved. 9 DAM Ancillary Service Charge (cont) DAASQ = DAASONET – ASSQ Used to calculate the AS quantity not provided by the QSE

10. Texas Nodal © 2005 - 2006 Electric Reliability Council of Texas, Inc. All rights reserved. 10 DAM Ancillary Service Charge (cont) DAASONET = DAASO + DAASCS – DAASCP Used to figure out the amount of AS obligations, net of trading activity DAASO is calculated based on previous LRS times total AS necessary This is calculated hourly

11. Texas Nodal © 2005 - 2006 Electric Reliability Council of Texas, Inc. All rights reserved. 11 Real Time Ancillary Service Market Mini Market Formulas

12. Texas Nodal © 2005 - 2006 Electric Reliability Council of Texas, Inc. All rights reserved. 12 Real Time Market Ancillary Services

13. Texas Nodal © 2005 - 2006 Electric Reliability Council of Texas, Inc. All rights reserved. 13 RT Payment for Ancillary Services Sold in Supplemental Market RTPCASAMT = (-1) * MCPCAS * RTPCAS Used to pay QSEs for bids that have been accepted in the RTM Using AS in place of RU (Regulation Up), RD (Regulation Down), RR (Responsive Reserve), NS (Non-Spin) All Real Time Market AS settlements are hourly

14. Texas Nodal © 2005 - 2006 Electric Reliability Council of Texas, Inc. All rights reserved. 14 RT – Charges for Ancillary Services Replaced Due to Failure to Provide ASFQAMT = MAX ( MCPCAS * ASFQ ) Used to charge QSEs for failure to provide AS obligations

15. Texas Nodal © 2005 - 2006 Electric Reliability Council of Texas, Inc. All rights reserved. 15 RT – Adjustments to Cost Allocation for AS Procurement - Formulas RTASAMT = ASCOST – DAASAMT ASCOST = ASPR * ASQ ASPR = ASCOSTTOT / ASQTOT ASCOSTTOT = (-1) * (∑RTPCASAMTTOT + PCASAMTTOT + ASFQAMTTOT) RTPCASAMTTOT = ∑ RTPCASAMT PCASAMTTOT = ∑ PCASAMT ASFQAMTTOT = ∑ ASFQAMT ASQTOT = ∑ ASQ ASQ = ASONET - ∑ ASSQ ASONET = (∑(∑ASSQ + ∑(PCAS + RTPCAS) - ∑ASRP - ASFQ)) * HLRS + ASCS – ASCP + ∑ASRP

16. Texas Nodal © 2005 - 2006 Electric Reliability Council of Texas, Inc. All rights reserved. 16 RT – Adjustments to Cost Allocation for AS Procurement RTASAMT = ASCOST – DAASAMT Used to charge to QSEs who have load, their AS obligation not provided by them

17. Texas Nodal © 2005 - 2006 Electric Reliability Council of Texas, Inc. All rights reserved. 17 RT – Adjustments to Cost Allocation for AS Procurement (cont) ASCOST = ASPR * ASQ Calculates the total AS cost in the RTM allocated to a QSE who does not supply all of their obligations

18. Texas Nodal © 2005 - 2006 Electric Reliability Council of Texas, Inc. All rights reserved. 18 RT – Adjustments to Cost Allocation for AS Procurement (cont) ASPR = ASCOSTTOT / ASQTOT Allocating all AS charges for a particular AS (ASCOSTTOT) over all of the AS provided for a particular AS (ASQTOT) These bill determinants are ERCOT wide totals

19. Texas Nodal © 2005 - 2006 Electric Reliability Council of Texas, Inc. All rights reserved. 19 RT – Adjustments to Cost Allocation for AS Procurement (cont) ASCOSTTOT = (-1) * (∑ RTPCASAMTTOT + PCASAMTTOT + ASFQAMTTOT) Sigma is used to sum up the Supplemental markets. Should there be more than one. Used to calculate the total dollars to be allocated

20. Texas Nodal © 2005 - 2006 Electric Reliability Council of Texas, Inc. All rights reserved. 20 RT – Adjustments to Cost Allocation for AS Procurement (cont) RTPCASAMTTOT = ∑ RTPCASAMT q ASFQAMTTOT = ∑ ASFQAMT q ASQTOT = ∑ ASQ q Sigma sums up the bill determinant by QSE Used to sum up all of the volumes and all of the payments to AS suppliers

21. Texas Nodal © 2005 - 2006 Electric Reliability Council of Texas, Inc. All rights reserved. 21 RT – Adjustments to Cost Allocation for AS Procurement (cont) ASQ = ASONET - ∑ ASSQ m Used to calculate the AS quantity not provided by the QSE

22. Texas Nodal © 2005 - 2006 Electric Reliability Council of Texas, Inc. All rights reserved. 22 RT – Adjustments to Cost Allocation for AS Procurement (cont) ASONET = (∑ (∑ ASSQ + ∑ (PCAS + RTPCAS) - ∑ ASRP - ASFQ )) * HLRS + ASCS – ASCP + ∑ ASRP Up to HLRS used to figure out the amount of AS obligations, remainder is trading activity and ERCOT replacement Sigmas used to sum by market Sigma used to sum by QSE

23. Texas Nodal © 2005 - 2006 Electric Reliability Council of Texas, Inc. All rights reserved. 23 DAM & RTM Ancillary Services Questions