Monday, July 8, 2013

World Renewable Energy Congress

Next week, I’ll attend the World Renewable Energy Congress in Perth, where I’ll present a paper entitled “Life-Cycle Assessment for BRRIMS Solar Power”.  I’ll take this opportunity to mention key findings of the paper and also provide a brief progress report on my research.

The abstract for the paper is as follows:

This paper presents a life-cycle analysis for a new concept in solar thermal power generation.  BRRIMS denotes Brayton-cycle, Re-heated, Recuperated, Integrated, Modular and Storage-equipped.  This concept envisages collection temperatures of around 250°C, thermal storage in pebble beds, thermal-electric conversion in a piston-cylinder engine and air as the heat transfer fluid and working gas of the engine.  The analysis applies to the manufacturing phase of the overall power plant and separately to the pebble bed thermal storage component.  Three sustainability metrics are included – life-cycle greenhouse gas emissions, cumulative energy demand and energy payback time.  On these metrics, the BRRIMS concept has broadly similar results to a conventional parabolic trough plant with molten salt thermal storage.

The last sentence says it all – for the manufacturing phase, my findings are that the BRRIMS concept will have similar life-cycle metrics to conventional parabolic trough solar plants.  My life-cycle investigation didn’t extend to the construction, operation, decommissioning and disposal phases, but my expectation is that life-cycle contributions are not large for these phases with the BRRIMS concept.  That was generally the case in a detailed study of a parabolic trough plant by Burkhardt et al. [1].

In the paper, I also used Barnhart & Benson’s concept of “Energy Stored On Invested” (ESOI, [2]) to investigate thermal storage in pebble beds.  ESOI for a storage device measures the (equivalent) electrical energy stored in whole of life relative to the energy embodied during manufacture.  On this metric, solar thermal concepts have a good rating.  Their ESOI score is much better than for chemical storage in batteries, but not as good as geologic storage such as pumped hydro and compressed air energy storage. 

Here are the ESOI scores (my calculations for the solar thermal concepts, other data from [2]):

Concept
Technology
ESOI
Geologic storage
CAES
240
PHS
210
Solar thermal
BRRIMS
61
Trough, molten salt
47
Batteries
Li-ion
10
NaS
6
PbA
2
Flow batteries
VRB
3
ZnBr
3

In other work, I continue to establish the technological case for investment in solar thermal concepts such as BRRIMS.  These concepts are easy enough to understand (see e.g. explanations at www.sunoba.com.au), but many engineering questions need to be resolved prior to any decision to design and build power plants. 

Much of this work has to remain confidential for the moment.  I’ll post details here when I am able to do so.

References

[1]  J.J. Burkhardt III, G.A. Heath and C.S. Turchi, “Life cycle assessment of a parabolic trough concentrating solar power plant and the impacts of key design alternatives”, Environ. Sci. Technol. 45 (2011), 24572464.

[2]  C.J. Barnhart and S.M. Benson, “On the importance of reducing the energetic and material demands of electrical energy storage”, Energy Environ. Sci., 6 (2013), 1083-1092.

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