CPV Environmental Impact

 

Today I read the paper “An Assessment of the Environmental Impacts of Concentrator Photovoltaics and Modeling of Concentrator Photovoltaic Deployment Using the SWITCH Model” June 2011 by Dr. Daniel Kammen of the Renewable and Appropriate Energy Laboratory at UC Berkeley and his Ph.D. students James Nelson, Ana Mileva, and Josiah Johnston.  [cf. www.rael.berkeley.edu]  It’s not too long (25 pages) and is packed with information.  I recommend it.  The review/summary here contains my comments.

The paper discusses, in the context of other forms of energy generation, the comparative environmental impact of CPV.  The short answer, if you don’t want to read any more, is that CPV has comparatively minimal environmental impact, and in particular is slightly worse than PV due to the former’s tracking system (see below) and a tiny bit better than CSP due to the latter’s cooling and water use.  Of course, oil, coal, and even natural gas are bad environmentally for a variety of reasons, and thankfully the paper doesn’t harangue about this too much.

The report considers three Life Cycle Assessment (LCA) phases: (1) fabrication and deployment of the energy generation facility, (2) energy production and maintenance, and (3) recycling and disposal at end of life of the facility.  Discussed in this context are the environmental issues of energy, emissions, water use, and land use.  Also considered in this report is the Energy Pay-Back Time (EPBT) which is the time (in years) that it takes to generate the net energy (roughly the energy generated minus energy used) in Phase 2 to be equal to the energy used in Phases 1 and 3, i.e. in creation and disposal of the generation facility.  Heretofore, this number has been estimated in the 3-15 year range; however, this report estimates it as less than 1 year for both PV and CPV. Caution:  one review of this paper that I read has challenged the logic and data used by the authors in their calculations of EPBT.  The authors point out that EPBT calculations are also sensitive to the geographic location of the generation facility, and hence have significant variance.

Green House Gas (GHG) emissions for Phase 1 are considered.  They are highest for large tracking systems such as CSP and CPV that use a lot of GHG-intensive steel in their structures. Such steel is heavy and incurs greater shipping costs in Phase 1.  Not only can the designs be improved to reduce the amount of steel used, but such steel could be manufactured where a large portion of the steel production energy came from solar or at least renewable energy sources.

Water use during Phase 1 is difficult to estimate due to lack of data on recycling, CPV use is estimated at 2 times that of PV.  Water use during operations, Phase 2, is significant since the large sites tend to be in water constrained regions.  In any case, for PV and CPV, water is only used for washing as opposed to CSP where it is used for wet cooling.  If dry cooling, i.e., air cooling, is used in a CSP plant, then water use is reduced 90% and is relegated to washing and steam production.

When mining, transportation, and disposal of non-renewable fuels are taken into consideration, the land use per GWh of renewable and non-renewable generations turns out to be comparable.  Hydroelectric and Wind are several times higher, and rooftop PV systems, where the land is already used by the building, are several times less. CPV has an advantage in land use over PV and CSP.  In addition, most large CPV and CSP systems are pole mounted, allowing potential reuse of most of the land under the arrays for plants and small animals.  Such use, it is noted by the authors, is not currently common; although CPV vendors seem to be leading here. Environmental impact studies should (by law) address impact on flora and fauna in the region; however, such studies can get around this by stating the impact is minimal in the large.

The authors also model CPV deployment in the southwest area covered by the Western Electricity Coordinating Council (WECC) by starting with around 1000 existing installations of various types and varying the mix of 10,000 additional renewable and conventional installations.  Their model runs thousands of wind and sun conditions on an hourly basis to meet the forecasted needs and to minimize the cost of generation, storage, and transmission.  The model uses NREL’s System Analysis Model (SAM) to get various costs of operation and maintenance.  At this point the paper is somewhat unclear as to just how the mix of the additional 10,000 generation types is determined.  It appears that CPV sites are preferentially added and CSP sites are not considered by this modeling.  That said, the conclusions are:

  • It would be economical to install between 12 and 43 GW of CPV by 2030 in the United States Desert Southwest
  • Including CPV allows for deeper CO2 reductions in the electric power system
  • CPV displaces natural gas generation on the margin
  • Strong carbon policy (e.g. charging $40/ton for CO2 generation) increases the deployment of CPV

Analyzing several of the graphs in this paper, it also appears that with the authors’ investment assumptions, the WECC area will need to increase its use of natural gas to cover peak usage.

In summary, I wish there were more studies like this.  Indeed, the authors’ model could be run many times over with differing investment assumptions to generate additional fascinating information.

-gayn

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