arXiv subjects

Roland Schmehl

Publications and source records attributed to Roland Schmehl.

5 recordsLinked to original sources

arXiv2021

Combined Airborne Wind and Photovoltaic Energy System for Martian Habitats

Generating renewable energy on Mars is technologically challenging. Firstly, because compared to Earth, key energy resources such as solar and wind are weak as a result of very low atmospheric pressure and low solar irradiation. Secondly, because of the harsh environmental conditions, the required high degree of automation and the exceptional effort and costs to transport material to the planet. Like on Earth, it is crucial to combine complementary resources for an effective renewable energy solution. In this work, we present the result of a design synthesis exercise, a 10 kW microgrid solution, based on a pumping kite power system and photovoltaic solar modules to power the construction as well as the subsequent use of a Mars habitat. To buffer unavoidable energy fluctuations and balance seasonal and diurnal resource variations, the two energy systems are combined with a compressed gas storage system and lithium-sulfur batteries. The airborne wind energy solution was selected because of its low weight-to-wing-surface-area ratio, compact packing volume and high capacity factor which enables it to endure strong dust storms in an airborne parking mode. The surface area of the membrane wing is 50 m2 and the mass of the entire system, including the kite control unit and ground station, is 290 kg. The performance of the microgrid is assessed by computational simulation using available resource data for a chosen deployment location on Mars. The projected costs of the system are 8.95 million Euro, excluding transportation to Mars.

astro-ph.IM↗

arXiv2020

Enhancing Control System Resilience for Airborne Wind Energy Systems Through Upset Condition Avoidance

Airborne wind energy (AWE) systems are tethered flying devices that harvest wind resources at higher altitudes which are not accessible to conventional wind turbines. In order to become a viable alternative to other renewable energy technologies, AWE systems are required to fly reliably for long periods of time without manual intervention while being exposed to varying wind conditions. In the present work a methodology is presented, which augments an existing baseline controller with a prediction and prevention methodology to improve the resilience of the controller against these external disturbances. In the first part of the framework, upset conditions are systematically generated in which the given controller is no longer able to achieve its objectives. In the second part, the generated knowledge is used to synthesize a model that predicts upsets beforehand. Eventually, this allows to trigger an avoidance maneuver which keeps the AWE system operational, however, leads to a lower power production. The methodology is applied to the specific case of tether rupture prediction and prevention. Simulation results are used to demonstrate that the presented methodology leads indeed to a predictable economic benefit over systems without the proposed baseline controller augmentation.

eess.SY↗

arXiv2019

Airborne Wind Energy Resource Analysis

We compare the available wind resources for conventional wind turbines and for airborne wind energy systems. Accessing higher altitudes and dynamically adjusting the harvesting operation to the wind resource substantially increases the potential energy yield. The study is based on the ERA5 reanalysis data which covers a period of 7 years with hourly estimates at a surface resolution of 31 x 31 km and a vertical resolution of 137 barometric altitude levels. We present detailed wind statistics for a location in the English Channel and then expand the analysis to a surface grid of Western and Central Europe with a resolution of 110 x 110 km. Over the land mass and coastal areas of Europe we find that compared to a fixed harvesting altitude at the approximate hub height of wind turbines, the energy yield which is available for 95% of the time increases by a factor of two.

physics.ao-ph↗

arXiv2018

Quasi-Steady Model of a Pumping Kite Power System

The traction force of a kite can be used to drive a cyclic motion for extracting wind energy from the atmosphere. This paper presents a novel quasi-steady modelling framework for predicting the power generated over a full pumping cycle. The cycle is divided into traction, retraction and transition phases, each described by an individual set of analytic equations. The effect of gravity on the airborne system components is included in the framework. A trade-off is made between modelling accuracy and computation speed such that the model is specifically useful for system optimisation and scaling in economic feasibility studies. Simulation results are compared to experimental measurements of a 20 kW kite power system operated up to a tether length of 720 m. Simulation and experiment agree reasonably well, both for moderate and for strong wind conditions, indicating that the effect of gravity has to be taken into account for a predictive performance simulation.

eess.SY↗

arXiv2015

Dynamic Model of a Pumping Kite Power System

Converting the traction power of kites into electricity can be a low cost solution for wind energy. Reliable control of both trajectory and tether reeling is crucial. The present study proposes a modelling framework describing the dynamic behaviour of the interconnected system components, suitable for design and optimization of the control systems. The wing, bridle, airborne control unit and tether are represented as a particle system using spring-damper elements to describe their mechanical properties. Two kite models are proposed: a point mass model and a four point model. Reeling of the tether is modelled by varying the lengths of constituent tether elements. Dynamic behaviour of the ground station is included. The framework is validated by combining it with the automatic control system used for the operation of a kite power system demonstrator. The simulation results show that the point mass model can be adjusted to match the measured behaviour during a pumping cycle. The four point model can better predict the influence of gravity and inertia on the steering response and remains stable also at low tether forces. Compared to simple one point models, the proposed framework is more accurate and robust while allowing real-time simulations of the complete system.

eess.SY↗