| 1. |
- Hobe, Alex, et al.
(author)
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Estimating fluid flow rates through fracture networks using combinatorial optimization
- 2018
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In: Advances in Water Resources. - : Elsevier BV. - 0309-1708 .- 1872-9657. ; 122, s. 85-97
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Journal article (peer-reviewed)abstract
- To enable fast uncertainty quantification of fluid flow in a discrete fracture network (DFN), we present two approaches to quickly compute fluid flow in DFNs using combinatorial optimization algorithms. Specifically, the presented Hanan Shortest Path Maxflow (HSPM) and Intersection Shortest Path Maxflow (ISPM) methods translate DFN geometries and properties to a graph on which a max flow algorithm computes a combinatorial flow, from which an overall fluid flow rate is estimated using a shortest path decomposition of this flow. The two approaches are assessed by comparing their predictions with results from explicit numerical simulations of simple test cases as well as stochastic DFN realizations covering a range of fracture densities. Both methods have a high accuracy and very low computational cost, which can facilitate much-needed in-depth analyses of the propagation of uncertainty in fracture and fracture-network properties to fluid flow rates.
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| 2. |
- Lundberg, Liv, 1987
(author)
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Auctions for all? Reviewing the German wind power auctions in 2017
- 2019
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In: Energy Policy. - : Elsevier BV. - 0301-4215. ; 128, s. 449-458
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Journal article (peer-reviewed)abstract
- In 2017, Germany introduced auctions to determine the support level for onshore wind power. To protect small-scale actors, citizens’ energy cooperatives were allowed longer realization periods and did not need to have an approval pursuant to the Federal Immission Control Act to submit a bid. Winning cooperatives were given the highest accepted bid, while other participants were paid-as-bid. The aim of this paper is to examine how this auction design affected actor diversity and the risk of winning projects not being realized. Unexpectedly, the outcome of the auctions was that over 90% of the winners were cooperatives, and the average project size of their bids was twice the size of other winning bids. There was also a significant decrease in the highest accepted bid, from 5.78€ct/kWh in the first auction, to 3.82€ct/kWh in the third auction. However, the pricing rule combined with uncertain technology costs and strong competition, may have encouraged overly aggressive bidding. This, as well as cooperatives being exempt from having an approval pursuant to the Federal Immission Control Act, could increase the risk of winning projects not being realized. A conclusion is that special rules for small-scale actors, should be used with caution, especially if they give significant competitive advantages and may affect realization rates.
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