There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Data Mining Practical Machine Learning Tools and Techniques

The paper reviews different approaches, technologies, and strategies to manage large-scale schemes of variable renewable electricity such as solar and wind power. We consider both supply and demand side measures. In addition to presenting energy system flexibility measures, their importance to renewable electricity is discussed. The flexibility measures available range from traditional ones such as grid extension or pumped hydro storage to more advanced strategies such as demand side management and demand side linked approaches, e.g. the use of electric vehicles for storing excess electricity, but also providing grid support services. Advanced batteries may offer new solutions in the future, though the high costs associated with batteries may restrict their use to smaller scale applications. Different “P2Y”-type of strategies, where P stands for surplus renewable power and Y for the energy form or energy service to which this excess in converted to, e.g. thermal energy, hydrogen, gas or mobility are receiving much attention as potential flexibility solutions, making use of the energy system as a whole. To “functionalize” or to assess the value of the various energy system flexibility measures, these need often be put into an electricity/energy market or utility service context. Summarizing, the outlook for managing large amounts of RE power in terms of options available seems to be promising.

https://research.aalto.fi/files/6557604/lund_et_al_review.pdf

Review of energy system flexibility measures to enable high levels of variable renewable electricity

This paper reviews water electrolysis technologies for hydrogen production and also surveys the state of the art of water electrolysis integration with renewable energies. First, attention is paid to the thermodynamic and electrochemical processes to better understand how electrolysis cells work and how they can be combined to build big electrolysis modules. The electrolysis process and the characteristics, advantages, drawbacks, and challenges of the three main existing electrolysis technologies, namely alkaline, polymer electrolyte membrane, and solid oxide electrolyte, are then discussed. Current manufacturers and the main features of commercially available electrolyzers are extensively reviewed. Finally, the possible configurations allowing the integration of water electrolysis units with renewable energy sources in both autonomous and grid-connected systems are presented and some relevant demonstration projects are commented.

Hydrogen Production From Water Electrolysis: Current Status and Future Trends

Overvoltages in low voltage (LV) feeders with high penetration of photovoltaics (PV) are usually prevented by limiting the feeder's PV capacity to very conservative values, even if the critical periods rarely occur. This paper discusses the use of droop-based active power curtailment techniques for overvoltage prevention in radial LV feeders as a means for increasing the installed PV capacity and energy yield. Two schemes are proposed and tested in a typical 240-V/75-kVA Canadian suburban distribution feeder with 12 houses with roof-top PV systems. In the first scheme, all PV inverters have the same droop coefficients. In the second, the droop coefficients are different so as to share the total active power curtailed among all PV inverters/houses. Simulation results demonstrate the effectiveness of the proposed schemes and that the option of sharing the power curtailment among all customers comes at the cost of an overall higher amount of power curtailed.

Coordinated Active Power Curtailment of Grid Connected PV Inverters for Overvoltage Prevention

This paper addresses the problem of voltage rise mitigation in distribution networks with distributed generation. A distributed automatic control approach is proposed to alleviate the voltage rise caused by active power injection. The objective of the proposed approach is not to control bus voltage but to guarantee that generator injections alone do not cause significant voltage rise: a solution in which distribution network operators (DNOs) are kept to their traditional task of voltage regulation for load demand. The approach is discussed in the perspective of effectiveness and adequacy. Its consequences to DNO control effort are evaluated. Illustration is provided for a single feeder with stochastic generation and transformer on-load tap-changing voltage regulation.

Distributed Reactive Power Generation Control for Voltage Rise Mitigation in Distribution Networks

This paper surveys major technical challenges for power system operations in support of large-scale wind energy integration. The fundamental difficulties of integrating wind power arise from its high inter-temporal variation and limited predictability. The impact of wind power integration is manifested in, but not limited to, scheduling, frequency regulations, and system stabilization requirements. Possible alternatives are suggested for a more reliable and cost-effective power system operation. New computationally efficient methods for improving system performances by using prediction and operational interdependencies over different time horizons remain critical open research problems.

Wind Integration in Power Systems: Operational Challenges and Possible Solutions

The influence of the operational environment on the efficiency of water utilities

https://mpra.ub.uni-muenchen.de/32894/1/MPRA_paper_32894.pdf

A meta-regression analysis of benchmarking studies on water utilities market structure

This paper updates the literature on water utility benchmarking studies carried out worldwide, focusing on scale and scope economies. Using meta-regression analysis, the study investigates which variables from published studies influence these economies. Our analysis led to several conclusions. The results indicate that there is a higher probability of finding diseconomies of scale and scope in large utilities; however, only the results for scale economies are significant. Diseconomies of scale and scope are more likely to be found in publicly-owned utilities than when the ownership is mostly private; as would be expected, multi-utilities are more likely to have scale and scope economies.

/pdf/a-meta-regression-analysis-of-benchmarking-studies-on-water-2xlin7e0pb.pdf

Pedro Carvalho

Papers

Distributed Reactive Power Generation Control for Voltage Rise Mitigation in Distribution Networks

Wind Integration in Power Systems: Operational Challenges and Possible Solutions

The influence of the operational environment on the efficiency of water utilities

A meta-regression analysis of benchmarking studies on water utilities market structure

A Meta-Regression Analysis of Benchmarking Studies on Water Utilities Market Structure