Exploitation of the far-offshore wind energy resource by fleets of energy ships – Part 2: Updated ship design and cost of energy estimate

Abstract

Abstract. This paper deals with a new concept for the conversion of far-offshore wind energy into sustainable fuel. It relies on autonomous sailing energy ships and manned support tankers. Energy ships are wind-propelled ships that generate electricity using water turbines attached underneath their hull. Since energy ships are not grid-connected, they include onboard power-to-X plants for storage of the produced energy. In the present work, the energy vector X is methanol. In the first part of this study (Babarit et al., 2020), an energy ship design has been proposed and its energy performance has been assessed. In this second part, the aim is to estimate the energy and economic performance of such system. In collaboration with ocean engineering, marine renewable energy and wind-assisted propulsion’s experts, the energy ship design of the first part has been revised and updated. Based on this new design, a complete FARWIND energy system is proposed, and its costs (CAPEX and OPEX) are estimated. Results of the models show (i) that this FARWIND system could produce approximately 70,000 tonnes of methanol per annum (approximately 400 GWh per annum of chemical energy) at a cost in the range 1.2 to 3.6 €/kg, (ii) that this cost may be comparable to that of methanol produced by offshore wind farms in the long term, and (iii) that FARWIND-produced methanol (and offshore wind farms-produced methanol) could compete with gasoline on the EU transportation fuel market in the long term.

Experimental proof-of-concept of an energy ship propelled by a Flettner rotor

“…This was not the case at prototype scale because (i) the motor which was selected to spin the rotor was significantly oversized (which led to its electrical consumption being an order of magnitude greater than the mechanical power required to spin the rotor) and (ii) because the power consumption of the sensors and control systems is very high at small scale in comparison to the generated power. However, in [18], it was shown that a full-scale energy ship propelled by four 35 m tall Flettner rotors can produce a positive net power of approximately 1300 kW when sailing beam wind in a true wind speed of 10 m/s. As that prediction was obtained using the numerical model which we showed in this paper that it is able to predict the ship's performance and behaviour, it can be concluded that positive net power production can be achieved at full-scale with energy ships powered by Flettner rotors.…”

Comparison of optimal power production and operation of unmoored floating offshore wind turbines and energy ships

“…Wind propulsion technologies are maturing thanks to a growing interest in them as a method of decarbonizing the shipping sector, with a number of full-scale Flettner rotor equipped ships in operation (Pearson, 2014;Rojon and Dieperink, 2014). Studies by Babarit et al (2021bBabarit et al ( , 2020b have examined an ES design known as FARWIND which employs Flettner rotors. These studies demonstrate the expected power performance and economic case for the FARWIND ES concept.…”

“…Experimental work has further shown that ESs can produce similar amounts of electricity to conventional wind turbines (Babarit et al, 2021a). Power performance models presented herein are adapted from the work of Babarit et al (2021b). In general, ESs must move at significant speeds in order to create the relative flow past the hydro turbines; wave and slamming loads in more extreme sea states may therefore limit the practical sailing conditions possible and requires further investigation (Jacobi et al, 2014).…”

“…The ES model presented is based directly on that of Babarit et al (2021b). Forces on the ES from the Flettner rotors, water turbines, and hull are considered.…”

“…The hull resistance (F d2 ) is also directed opposite the motion of the ship. Resistance coefficients (C d2 (F r)) are shown in Figure 5 and are taken to be the sum of the residuary (wave) resistance and frictional resistance coefficients from (Babarit et al, 2021b).…”