LTS Semantics for Compensation-based Processes

Business processes design is an error-prone task often relying on long-running transactions with compensations. Unambiguous formal semantics and flexible verification tools should be used for early validation of processes. To this aim, we define a small-step semantics for the Sagas calculus according to the so-called coordinated interruption policy. We show that it can be tuned via small changes to deal with other compensation policies and discuss possible enhancements

Everything Under the Sun: A Guide to Siting Solar in the Lone Star State

Encouraging energy production using renewable resources is a widely recognized public policy that is promoted by both the federal and state governments in the U.S., and with recent technological advances, renewable-electricity generation is rapidly becoming economically viable. The Energy Information Administration (EIA) forecasts that electricity production from all renewable sources will increase 72% between 2013 and 2040, with the renewable share of total U.S. electricity generation growing from 13% to 18%.1 The future of solar power is especially bright with a projected growth rate of 6.8% per year between 2013 and 2040. If this projection holds true, solar power will far outpace the growth of other renewables. Combined with the Investment Tax Credit (ITC) introduced in 2006, rapid improvements in photovoltaic (PV) solar panel efficiency and dramatic reductions in PV costs are driving a veritable solar boom in the U.S. In fact, the Solar Energy Industries Association (SEIA) reports a 73% decrease in the cost of installing solar since the implementation of the ITC, and anticipates an additional 20,000 Megawatts (MW) of solar generation capacity will come online in the next two years, doubling current U.S. solar capacity. Likewise, the EIA projects that solar power will account for nearly half of the total 109,000MW of renewable-generation-capacity that is expected to be added to the U.S. electricity grid by 2040.The Kay Bailey Hutchison Center for Energy, Law, and Busines

Recovery within long running transactions

As computer systems continue to grow in complexity, the possibilities of failure increase. At the same time, the increase in computer system pervasiveness in day-to-day activities brought along increased expectations on their reliability. This has led to the need for effective and automatic error recovery techniques to resolve failures. Transactions enable the handling of failure propagation over concurrent systems due to dependencies, restoring the system to the point before the failure occurred. However, in various settings, especially when interacting with the real world, reversal is not possible. The notion of compensations has been long advocated as a way of addressing this issue, through the specification of activities which can be executed to undo partial transactions. Still, there is no accepted standard theory; the literature offers a plethora of distinct formalisms and approaches. In this survey, we review the compensations from a theoretical point of view by: (i) giving a historic account of the evolution of compensating transactions; (ii) delineating and describing a number of design options involved; (iii) presenting a number of formalisms found in the literature, exposing similarities and differences; (iv) comparing formal notions of compensation correctness; (v) giving insights regarding the application of compensations in practice; and (vi) discussing current and future research trends in the area.peer-reviewe

Analysis of two heat storage integrations for an Organic Rankine Cycle Parabolic trough solar power plant

Among the concentrated solar power technologies, those based on Organic Rankine Cycles have a very low market presence. However they have favorable characteristics for applications with low temperature and small/medium size (<10 MW), such as off-grid applications or distributed power generation. In this paper is analyzed a 5MW parabolic trough plant integrated with an Organic Rankine cycle power block and thermal storage. On this purpose, two different thermal storage integrations are analyzed. They are based on two different heat storage layouts: direct system using Hitec XL both as Heat Transfer Fluid and as storage medium; indirect system using Therminol VP-1 as Heat Transfer Fluid and Hitec XL as storage medium. Full system performance at rated and off-design conditions is presented operating with different organic working fluids. Its potential application and main challenges for its development are discussed in terms of performance and costs. Among the analyzed working fluids, the best results were obtained for the cycle working with Toluene with an efficiency at the power block of 31.5% and an estimated power block cost of 825 €/kW. The indirect storage layout was the most interesting from the point of view of Levelized Electricity Cost (16.19 c€/kW) and productivity (28.2 GW h/y for a 5 MWel plant) for 10 h of storage However, it results in a storage tanks volume 26% greater than the obtained for the equivalent direct storage layout. The results show the competitiveness and the potential of the proposed integrated small size parabolic trough designs for isolated applications as mines or for some distributed generation uses where grid capacity is limited