Development of NREL Performance Acceptance Test … · • The capacity of parabolic trough projects under construction ... code development, which typically may take several years

Development of NREL Performance Acceptance Test Guidelines for Large Commercial

Parabolic Trough Solar Fields

MENASOL 2011

CSP Today 4-5 May Morocco

Dr. David Kearney, K&A, USA Mark Mehos, NREL, USA

1 MENASOL 2011

Morocco K&A/NREL

Objectives

•  Performance acceptance tests are required for the turnover of all major power plant equipment but as yet no formal codes exist for the solar field

•  To fill this gap, NREL initiated development of performance

acceptance test Guidelines for the solar system, starting with parabolic troughs using oil HTF

•  Solar system acceptance testing is unique due to: –  variable nature of the energy source, and –  necessity for a performance model to compare

results to measurements

MENASOL 2011 Morocco

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Scope


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•  Thermal power or energy delivery of the solar system to the heat exchanger train (for steam production)

•  Solar system is comprised of solar field & HTF system •  Power block and BOP are not included in the Guidelines

•  Thermal equilibrium (steady state) conditions are a critical test requirement •  Uncertainty level in result equally critical

A sense of scale

•  The capacity of parabolic trough projects under construction generally range from 50 to 250 MWe turbine net capacity

•  A 250 MWe, with thermal storage, can have a total mirror aperture area of ≈1.8 million m2 covering a land area of about 540 hectares (1335 acres)

•  This scale presents several challenges that will influence the level of uncertainty and transient errors in the test results


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Commercial Project Issues

•  Testing parties can differ by virtue of different project structures, but the applicable codes remain unchanged. One example of parties would be EPC contractor accepting solar field from technology provider

•  Top-level test procedures are set between the testing parties at contract signing

•  Subsequently, but well before testing, detailed test procedures are laid down in a Test Plan. Examples include exactly where and how the measurements are made, the duration and number of tests, and pass/fail criteria.


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Considerable CSP industry input has gone into development of these Guidelines

•  The process adopted by NREL was designed to include input from a wide spectrum of CSP stakeholders

•  Advisory Committee was formed to periodically review and critique direction and progress. This 12-person group included EPCs, Technology Providers, Developers, Utilities, Independent Engineers, and Utilities.

•  In parallel, U.S. ASME independently initiated a process to develop a Performance Test Code (PTC 52) for all CSP technologies, also restricted to thermal, not electrical, output. The NREL Guidelines will provide a jump-start to the ASME code development, which typically may take several years to complete


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•  Short Duration Steady State Thermal Power Test –  Objective is to measure the thermal power and efficiency under

clear sky conditions. –  Multiple short-duration tests run sequentially over mid-day

time period, e.g., 0900 - 1500 –  Satisfactory test runs (e.g., runs where steady-state conditions

exist) are extracted based on examination of the data. –  Pattern can be repeated over multiple days based on agreement

between parties

•  Governing Equations Thermal Power: Thermal Efficiency:


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Recommended Tests First

•  Multi-Day Continuous Energy Test

–  Objective is to collect continuous daily thermal energy output (integrated power output) for comparison against model projections

–  Continuous 10-day test suggested (though this period to be set by agreement between parties).

–  Both clear sky and partly cloudy conditions are acceptable –  Additional information on system response to startup, shutdown,

and transient weather event to be collected over test period.


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Second

Attainment of Thermal Equilibrium

•  Thermal equilibrium is a crucial test condition for acceptable results

•  Analyses* have been carried out to evaluate the effects of gradients in the solar resource during a test period

•  Important considerations are the transient effects on test results of a gradient in radiation input to the solar field and the transit time through the collector field header piping

* from Mike Wagner, NREL


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Solar Field Test Schematic


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Attainment of Thermal Equilibrium (cont)

•  Thermal equilibrium is a crucial test condition for acceptable results

•  Analyses have been carried out to evaluate the effects of gradients in the solar resource during a test period

•  Important considerations are the transient effects on test results of a gradient in radiation input to the solar field and the transit time through the collector field header piping

•  Analyses for actual DNI data show that the disparity in results due to these effects are real, but small, and generally acceptable


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Other test issues

•  Characterization of representative reflectivity of the mirrors for the model calculation

•  Contribution of HTF properties to uncertainty •  Solar field with high solar multiple


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•  The methodology to evaluate test uncertainty is founded in ASME PTC 19.1 “Test Uncertainty”

•  Sources of uncertainty are systematic (bias) and random (precision) errors, the former dominating the test results

•  Major contributors are the measurements of HTF specific heat

and Direct Normal Radiation •  Example uncertainty calculations give:

≈ 4% for the solar field power output and ≈ 5% for the solar field thermal efficiency


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Measurement Uncertainty

Future Work

•  Expansion of guidelines to tower and linear Fresnel systems •  Investigation of better methods for measuring average

reflectivity of large solar fields •  Reduction of uncertainty contributions due to known issues,

such as HTF properties


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Thank you


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Summary Performance acceptance tests of large solar trough fields (and other CSP technologies) require careful attention to the unique effects of a varying energy source and the characteristics of the solar system This work represents an important step forward in providing a usable set of Guidelines for parabolic trough systems, while also identifying important issues that require further work to reduce test uncertainties

Documents

Development of NREL Performance Acceptance Test … · • The capacity of parabolic trough projects under construction ... code development, which typically may take several years