Jimmy Ehnberg

Hydrokinetic turbine effects on fish swimming behaviour.

Hydrokinetic turbines, targeting the kinetic energy of fast-flowing currents, are under development with some turbines already deployed at ocean sites around the world. It remains virtually unknown as to how these technologies affect fish, and rotor collisions have been postulated as a major concern. In this study the effects of a vertical axis hydrokinetic rotor with rotational speeds up to 70 rpm were tested on the swimming patterns of naturally occurring fish in a subtropical tidal channel. Fish movements were recorded with and without the rotor in place. Results showed that no fish collided with the rotor and only a few specimens passed through rotor blades. Overall, fish reduced their movements through the area when the rotor was present. This deterrent effect on fish increased with current speed. Fish that passed the rotor avoided the near-field, about 0.3 m from the rotor for benthic reef fish. Large predatory fish were particularly cautious of the rotor and never moved closer than 1.7 m in current speeds above 0.6 ms-1. The effects of the rotor differed among taxa and feeding guilds and it is suggested that fish boldness and body shape influenced responses. In conclusion, the tested hydrokinetic turbine rotor proved non-hazardous to fish during the investigated conditions. However, the results indicate that arrays comprising multiple turbines may restrict fish movements, particularly for large species, with possible effects on habitat connectivity if migration routes are exploited. Arrays of the investigated turbine type and comparable systems should therefore be designed with gaps of several metres width to allow large fish to pass through. In combination with further research the insights from this study can be used for guiding the design of hydrokinetic turbine arrays where needed, so preventing ecological impacts.

A Probabilistic Model for Hydrokinetic Turbine Collision Risks: Exploring Impacts on Fish

A variety of hydrokinetic turbines are currently under development for power generation in rivers, tidal straits and ocean currents. Because some of these turbines are large, with rapidly moving rotor blades, the risk of collision with aquatic animals has been brought to attention. The behavior and fate of animals that approach such large hydrokinetic turbines have not yet been monitored at any detail. In this paper, we conduct a synthesis of the current knowledge and understanding of hydrokinetic turbine collision risks. The outcome is a generic fault tree based probabilistic model suitable for estimating population-level ecological risks. New video-based data on fish behavior in strong currents are provided and models describing fish avoidance behaviors are presented. The findings indicate low risk for small-sized fish. However, at large turbines (≥5 m), bigger fish seem to have high probability of collision, mostly because rotor detection and avoidance is difficult in low visibility. Risks can therefore be substantial for vulnerable populations of large-sized fish, which thrive in strong currents. The suggested collision risk model can be applied to different turbine designs and at a variety of locations as basis for case-specific risk assessments. The structure of the model facilitates successive model validation, refinement and application to other organism groups such as marine mammals.

Generation reliability for small isolated power systems entirely based on renewable sources

This paper investigates generation reliability for power systems entirely based on renewable energy sources. Stochastic models for solar and wind power are used together with simpler models of small scale hydro power and storage. The load model is deterministic and based on industrial activities with a maximum load of 28 kW. 38 different cases with different supply configurations are simulated using Monte-Carlo simulation. It can be concluded that a system with only wind power has a higher availability than a system with only solar power. However solar power is more regular which allows for a more efficient use of storage. To obtain a high availability large storage capability is needed or a combination of sources.

Assessment of load profiles in minigrids: A case in Tanzania

Over 500 million people lack access to modern energy sources in sub-Saharan Africa as of today. Many of these people live in remote rural areas. Improving access to modern energy sources is considered an important goal towards reaching the Millennium goals. Minigrids are seen as an important technology to increase electricity access in non-electrified rural areas. There is currently a lack of measured load data from minigrids in developing countries. This paper investigates the differences between daily load profiles created from measurements and from appliance data collected through interviews. The paper reports differing results from the two methodologies. Specifically the interview data largely underestimate the base load from household. However, the study also concludes that measurements require special equipment and knowledge that can obstruct the access to data. Interview based load profiles can furthermore be used in previous non-electrified areas to indicate electricity usage before minigrids are constructed.