Comparing Instanton Contributions with Exact Results in N=2 Supersymmetric Scale Invariant Theories

We discuss the general issues and ambiguities involved in matching the exact results for the low energy effective action of scale invariant N=2 supersymmetric QCD to those obtained by instanton methods. We resolve the reported disagreements and verify agreement between an infinite series of coefficients in the low energy effective actions calculated in the two approaches. In particular, we show that the exact low-energy effective couplings for SU(N) for all N with 2N fundamental hypermultiplets agree at a special vacuum on the Coulomb branch where a large unbroken discrete global symmetry makes the matching of parameters relatively straightforward.Comment: 26 pages, 1 figure; report-no. correcte

The M theory lift of two O6 planes and four D6 branes

We solve for the effective actions on the Coulomb branches of a class of N=2 supersymmetric theories by finding the complex structure of an M5 brane in an appropriate background hyperkahler geometry corresponding to the lift of two O6^- orientifolds and four D6 branes to M theory. The resulting Seiberg-Witten curves are of finite genus, unlike other solutions proposed in the literature. The simplest theories in this class are the scale invariant Sp(k) theory with one antisymmetric and four fundamental hypermultiplets and the SU(k) theory with two antisymmetric and four fundamental hypermultiplets. Infinite classes of related theories are obtained by adding extra SU(k) factors with bifundamental matter and by turning on masses to flow down to various asymptotically free theories. The N=4 supersymmetric SU(k) theory can be embedded in these asymptotically free theories, allowing a derivation of a subgroup of its S duality group as an exact equivalence of quantum field theories.Comment: 45 pages, 3 figures. Reference adde

Performance Prediction of Grid-Connected Photovoltaic Systems Using Remote Sensing

Photovoltaic Power Systems Programme (IEA - PVPS Task 2), report IEA-PVPS T2-07:2008This document reports, in the first part, on the possibility to use solar irradiation calculated from satellite images for performance predictions. In the second part, different system performance evaluation models are described. The use of calculated irradiations as an input to a simple parametric model is compared with measurements from systems existing in the Task 2 Performance Database. Conclusions are drawn on the related achievable accuracy

Nemiah Valley photovoltaic-diesel mini-grid: System performance and fuel saving based on one year of monitored data

Abstract-Canada's first battery-free photovoltaic (PV)-diesel mini-grid was installed in the Nemiah Valley of British Columbia, Canada in the fall of 2007. Since loads in this community are relatively small (peak load of ≈75 kW), photovoltaic penetration on the mini-grid is much higher than what has been achieved in any large-scale centralized grid: the 27.36 kW of PV represent 36% of peak load, and supply roughly 11% of the electricity used in the community on a yearly basis. The goal of this research was both to assess the performance of this PV-diesel mini-grid over a one year period, as well as to highlight some of the lessons learned and inform the design and operation of other such systems. In particular, this case study examined fuel savings that were achieved through a number of modifications to a pre-existing mini-grid, including the addition of photovoltaics, the removal of a dump load, the reconfiguration of the commercial load feeder and the use of a smaller genset during weeknights and weekends. The fuel savings achieved amount to about 26,000 L per year, or a reduction of ≈25% over business-as-usual. With respect to photovoltaic systems performance, the main issue encountered was the occurrence of conditions under which PV output would, if not curtailed, exceed system load. It was estimated that the PV system would deliver about 10% more energy on a yearly basis if all of its output could be absorbed (as in the case of connection to a large, centralized grid). Given that this effect will worsen as PV penetration levels are pushed beyond this system's, a number of avenues for mitigating this loss are discussed

Spatial insolation models for photovoltaic energy in Canada

Spatial models of global insolation and photovoltaic electricity generation potential for Canada were developed. The main objective was to provide Canadians with an easily accessible, reliable tool for rapidly estimating the monthly and yearly electricity production potential of grid-connected photovoltaic systems anywhere in the country, and for assessing the dependence of production on location, time of year and array orientation. Monthly mean daily insolation data from 144 meteorological stations across Canada were used, along with data from an additional eight stations in Alaska to improve the models in that region. Several photovoltaic array orientations were considered, including South-facing arrays with latitude and vertical tilts and a sun-tracking orientation. Partial thin plate smoothing splines as implemented in ANUSPLIN were used to generate the spatial insolation models. The models were based on geographic position and a transform of monthly mean precipitation, the latter variable being a surrogate for cloudiness which affects surface insolation. Photovoltaic electricity generation (in kW h per kilowatt of photovoltaic installed power capacity) was estimated for each month and for the entire year from the insolation models by assuming international standard values for the performance ratio of photovoltaic systems. The yearly average root mean square predictive error (RTGCV) on the mean daily global insolation ranges between 0.75 (vertical tilt) and 1.43 MJ/m2 (sun-tracking orientation) (or about 4.7-9.0 kW h/kW in terms of PV potential), or from 5.6% to 6.9% of the mean. Ultimately insolation and photovoltaic potential were mapped over the country at a 300 arc seconds (∼10 km) resolution. The maps are available on a Natural Resources Canada Website. This is an important new tool to help Canadians gain an overall perspective of Canada's photovoltaic potential, and allow estimation of potential photovoltaic system electricity production at any chosen location