The Operator s Perspective: Lessons from CSP Projects in MENA, Spain, South Africa, and the U.S.

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1 The Operator s Perspective: Lessons from CSP Projects in MENA, Spain, South Africa, and the U.S. Mark Mehos Group Manager, Thermal Systems R&D Program Manager, CSP NREL World Bank MENA KIP Workshop, Dubai CSP Markets, System Value & Financing February 26-28, 2018

2 Discussion Very brief introduction to CSP capital/o&m tower optimization tool. Operational impacts of hydrogen permeation in parabolic trough receiver tubes. 2

3 NREL CSP Optimization Tool (Anticipated Fall 18 Release) Tool will co-optimize: o Initial capital and longterm operating costs. o Economic dispatch including ramping and start/stop costs. o Economic dispatch including resource and price uncertainty. 3

4 Manipulating performance characteristics The model quantifies the tradeoff between revenue and operating costs. Parameters such as ramping cost can fundamentally change the nature of the operating profile, all other factors equivalent. Revenue from electricity sales may be similar under a range of operating approaches. Example: Impact of ramping penalty on CSP dispatch profile 4

5 Partnership with SolarReserve: Exploring prospective plant operations Two operating scenarios with similar revenue, different maintenance implications o Black SR o Orange NREL tool Change in expected net revenue after accounting for expected O&M costs 5

6 Discussion Very brief introduction to CSP capital/o&m tower optimization tool. Operational impacts of hydrogen permeation in parabolic trough receiver tubes. 6

7 CSP Today Global Tracker 6000 MWs of CSP Trough Systems Operational or Under Construction 7

8 U.S. CSP Parabolic Trough Plants with Demonstrated Reduction in Solar Field Performance California SEGS Plants ( ) Nevada Solar One (2007) 8

9 Hydrogen Buildup in Parabolic Trough Power Plants Plant Components with Heat Transfer Fluid (HTF) HTF degradation generates hydrogen gas Essentially no hydrogen generation within o C Maximum hydrogen generation within o C Circulation distributes hydrogen evenly to all components Hydrogen can collect in the receiver tubes, increasing solar field thermal losses Expansion tanks (293 o C) Solar Collector Field Steam generators Cold header (293 o C) Receiver Modules Hot header (393 o C) 9

10 Hydrogen Problem in Parabolic Trough Power Plants Consequences for Power Plant Performance NREL s System Advisor Model (SAM) estimates a 15% decrease in power plant thermal efficiency after 8 years of operation. Power plant has corresponding loss in electricity production and revenue. 100 Percent of New Plant Performance % loss Opera: ng Year Operating Year 10

11 Receiver Heat Loss Testing and Modeling Test stand measures receiver heat loss as function of absorber tube temperature and hydrogen partial pressure. H2 saturated receiver from Nevada Solar One The good news - NREL has established that the H2 transfer process is reversible by scrubbing H2 in the heat transfer fluid! 11

12 Hydrogen Tracking Model H2 Generation and Removal Full-Plant Hydrogen Tracking Model Tracks hydrogen generation and circulating in all power plant components Hot & cold south headers Power block Hot & cold north headers SCAs Full model representation of U.S. Nevada Solar One Parabolic Trough Plant Tracks H2 levels with and without centralized hydrogen removal system 12

13 Receiver Heat Loss (W/m) Hydrogen Removal Proposed Full-Scale NSO Installation Benefits to New and In-Service Receivers In-service receivers that are saturated with hydrogen will recover about 75% of their original performance in 10 months. Receivers that have their original performance (new or in-service < 4 years) will maintain their performance for the full 30-year operating lifetime of the power plant. 1, Absorber temp = 350 o C In-service receiver with hydrogen buildup Improvement Recovered receiver after 10 months New receiver Annulus Pressure (mbar) 13

14 NREL and CSP Services Thermal Survey Systems CSP Services - Qfly NREL and CSP Services have developed systems that can be used to survey the receivers in a solar field. A fairly quick initial testing can be done by hand with any IR camera. But the testing should be done when the collectors are tracking and the plant is operating at full temperature. 14

15 Argon Injection At 350 C (662 F) 15

16 Summary Over time, HTF hydrogen mitigation into new receiver tubes will reduce field performance by 15% of more. International labs and industry are well aware of this problem, and several encouraging solutions are forthcoming. Solutions include: o Early identification (thermal surveys) o H2 removal at centralized location (e.g. expansion vessel) o Inert gas injection into receiver annulus (e.g. Ar or Xe) 16

17 Thank you! For more information: Mark Mehos USA