G. Lavidas
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Due to the complexity of the ocean environment and wave energy converter (WEC) system, it has been an effort-demanding work to assess either the power performance or fatigue loads of WECs. This work attempts to apply a data-driven approach to increase the efficiency of the collective prediction of the power and fatigue load of a point-absorber type WEC. Nonlinear time-domain modeling is first established to estimate the power and fatigue loads, which is considered the reference data in this work. To demonstrate the performance of the applied data-driven approach, two prevalent power take-off (PTO) mechanisms are implemented to represent different characteristics of WECs. A data-driven approach, active learning Kriging (AK), is adapted to predict power and fatigue loads collectively, and a new learning function is defined to select the enriched wave cases for the active learning process. Results show that the applied active learning approach can accurately and simultaneously predict power and fatigue loads in both PTO mechanisms. Compared to pure numerical simulation, the proposed method only requires 15 simulations of sea state, and the computational effort is reduced by more than 20 times. The maximum prediction error is less than 2%. The data-driven approach could be a powerful tool for WEC system optimization, considering both power performance and fatigue loads.
Wave-to-Wire (W2W) modeling simulates the whole operation process of wave energy converters (WECs), which plays a pivotal role in the systematic design and optimization of WECs. Existing W2W models are predominantly constructed based on time-domain (TD) analysis to coherently incorporate relevant nonlinearities. However, TD models require a high computational cost, which hinders the design iterations of WECs. As a newly emerging alternative approach, spectral-domain (SD) modeling has demonstrated the applicability of describing the W2W process while efficiently covering nonlinear effects through statistical linearization. This study aims to develop an SD W2W modeling approach for WECs coupled with a gearbox and rotary generator. The application of the proposed model is exemplified in two case studies: (1) a point absorber with a rack-pinion system and a rotary generator; (2) a flap-type WEC with a revolving gearbox and a rotary generator. The simulation results obtained by the SD W2W model are compared against a higher-fidelity nonlinear TD W2W model to verify its accuracy across a variety of sea states. A good agreement between the two modeling approaches is observed, in which the maximum relative error is below 7 % with regard to the estimation of important system outputs. Meanwhile, the computational efficiency of the SD W2W model is thousands of times higher than the TD modeling approach.
Recent studies have demonstrated the merits of spectral-domain (SD) modeling in efficiently addressing nonlinear dynamic behvavior of stand-alone wave energy converters (WECs). However, the potential of the SD modeling approach deserves further exploitation by examining its applicability in simulating the entire wave-to-wire (W2W) process of WEC arrays. This article proposed and verified a SD W2W model of WEC arrays. The WEC arrays are considered as five same-sized heaving cylindrical point absorbers, and they are all equipped with linear Permanent Magnet (PM) generators. The established SD W2W model is verified by being compared with results of a nonlinear time-domain-based W2W model across a variety of operation conditions. The computational efficiency of the two simulation approaches in modeling WEC arrays is also identified and compared. The results suggest that the SD W2W model is associated with a relative error of less than 11 % to the nonlinear time-domain reference, with regard to the estimates of significant statistical performance indicators, such as WEC velocity, absorbed and electrical power of individual power, and total electrical power production of the WEC arrays. At the same time, the SD W2W model presents a high computational efficiency, being around 2000 times faster than the time-domain W2W model of WEC arrays.
Wave power for e-fuels and e-chemicals production
Technical feasibility, economic viability, and regional opportunities
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Different numerical modeling methods have been developed and applied to evaluate a variety of performance indicators of wave energy converters (WECs), including the power performance, structural loads, levelized cost of energy, etc. Based on the modeling fidelity, the commonly used numerical modeling approaches can be classified as linear modeling, weakly nonlinear modeling and fully nonlinear modeling approaches. Each method differs in accuracy and computational efficiency, making them suitable for different stages of WEC design. However, the selection of modeling approach could significantly impact evaluation outcomes. For instance, simplified linear models may underestimate structural loads or overestimate energy production in some operational conditions, potentially leading to less cost-effective designs. Given the widespread utilization of these models, it is essential to understand the uncertainties brought by them in performance evaluations. This work is dedicated to benchmarking different linear-potential-flow-based numerical models for evaluating the systematic performance of WECs. Three representative numerical modeling approaches are considered in this work, including linear frequency-domain modeling, statistically linearized spectral-domain modeling and Cummins equation-based nonlinear time-domain modeling. A generic point absorber WEC is considered as the research reference in this work, and different sea sites are taken into account. The numerical models are utilized to predict critical performance indicators, including power performance, the annual energy production, the capacity factor, the levelized cost of energy and the PTO fatigue loads. By comparing the results, this work identifies the uncertainties associated with different modeling approaches in evaluating WEC performance.
Marine renewables in Energy Systems
Impacts of climate data, generators, energy policies, opportunities, and untapped potential for 100% decarbonised systems
In this paper, a SD model is derived to simulate the wave-to-wire process of a point absorber WEC. A mechanical PTO system coupled with a rotary permanent-magnet generator is considered for the WEC. Representative nonlinear effects of the wave-to-wire process are incorporated, including viscous drag force, nonlinear PTO force, and the current limit of the generator. A nonlinear time-domain (TD) wave-to-wire model is established correspondingly to serve as the accuracy reference because it is inherently associated with higher modelling fidelity. The dynamic response and the power performance of the proposed SD model are verified against those of the nonlinear TD wave-to-wire model. Additionally, the computational efficiency of the proposed SD model and the TD model is identified and compared. ...
In this paper, a SD model is derived to simulate the wave-to-wire process of a point absorber WEC. A mechanical PTO system coupled with a rotary permanent-magnet generator is considered for the WEC. Representative nonlinear effects of the wave-to-wire process are incorporated, including viscous drag force, nonlinear PTO force, and the current limit of the generator. A nonlinear time-domain (TD) wave-to-wire model is established correspondingly to serve as the accuracy reference because it is inherently associated with higher modelling fidelity. The dynamic response and the power performance of the proposed SD model are verified against those of the nonlinear TD wave-to-wire model. Additionally, the computational efficiency of the proposed SD model and the TD model is identified and compared.
This study presents a first long term (30 years) assessment to quantify the effects of both, the wave spectrum representation, and occurrences of multi-modal sea states, on power production estimations from a point-absorber Wave Energy Converter (WEC). Analysis in 3 different offshore locations (Portugal, Ireland and The Netherlands) is included to ensure robustness of results. In general, traditional methods based on the use of the JONSWAP spectrum, with an adequate gamma shape value, can lead to mean overestimation in yearly power production >12% when compared to reference hindcast spectral data. This can be partially reduced when capping is applied to power production, but still can be close to 10%. An alternative method is proposed to modulate the JONSWAP spectrum at each time step which helps to reduce differences, but leads to slight yearly underestimations (−2.5 to −5% in average). Although in all analyzed sites the occurrences of multi-modal spectra is >30%, contribution to errors due to misrepresentation of these sea states are estimated to be of about 2.5%. These findings provide valuable insights on the uncertainties introduced in power production estimations, related to wave conditions characterization, that can have important economic impact when planning for large scale deployments.
To evaluate the feasibility of establishing an energy hub on Kerguelen Islands, a scenario was developed using the EnergyPLAN modelling software. The scenario involves producing e-fuels and e-chemicals, which will be essential for sectors like marine and aviation transportation and chemicals as the world transitions to a defossilised economy. This analysis assumes that the islands could supply fuel for East Asia, particularly Japan, South Korea, and Taiwan. By 2050, the 7 GW wave power system could meet 3% of the demand for e-fuels and e-chemicals in these countries, producing 3.5 TWhth,LHV of e-kerosene, 2.6 TWhth,LHV of e-diesel, 19 TWhth,LHV of e-methanol, 2.5 TWhth,LHV of e-LNG, and 4.9 TWhth,LHV of e-ammonia. The cost projections for 2050 suggest that e-fuels and e-chemicals produced from Kerguelen Islands could be highly competitive, with projected costs of 95.0 €/MWh for e-kerosene and e-diesel, 78.7 €/MWh for e-methanol, 64.5 €/MWh for e-LNG, and 68.4 €/MWh for e-ammonia.
In addition to wave power, the system would incorporate 2 GWhcap of battery storage and 50 GWh of underground rock cavern hydrogen storage, further enhancing the energy hub's capacity and flexibility. These costs, assumed for 2050, are projected to be competitive compared to leading global sites, such as the Atacama Desert, which has excellent solar PV resources. For comparison, the Atacama Desert’s e-fuels production cost is estimated to range from 70-75 €/MWh, e-methanol is between 49-57 €/MWh and e-ammonia at 53 €/MWh.
However, the costs mentioned above do not include shipping costs. Shipping costs for ammonia for 10,000 km to East Asia could add up to 8 €/MWh, while shipping costs for methanol could add up to 4 €/MWh. For the Kerguelen Islands an attractive business model could be established to diversify the global e-fuels and e-chemicals production that may largely shift towards solar energy. This creates a promising opportunity for investment in a gigawatt-scale energy hub for e-fuels and e-chemicals on Kerguelen Islands, including the necessary infrastructure for shipping and workforce to maintain such a system. ...
To evaluate the feasibility of establishing an energy hub on Kerguelen Islands, a scenario was developed using the EnergyPLAN modelling software. The scenario involves producing e-fuels and e-chemicals, which will be essential for sectors like marine and aviation transportation and chemicals as the world transitions to a defossilised economy. This analysis assumes that the islands could supply fuel for East Asia, particularly Japan, South Korea, and Taiwan. By 2050, the 7 GW wave power system could meet 3% of the demand for e-fuels and e-chemicals in these countries, producing 3.5 TWhth,LHV of e-kerosene, 2.6 TWhth,LHV of e-diesel, 19 TWhth,LHV of e-methanol, 2.5 TWhth,LHV of e-LNG, and 4.9 TWhth,LHV of e-ammonia. The cost projections for 2050 suggest that e-fuels and e-chemicals produced from Kerguelen Islands could be highly competitive, with projected costs of 95.0 €/MWh for e-kerosene and e-diesel, 78.7 €/MWh for e-methanol, 64.5 €/MWh for e-LNG, and 68.4 €/MWh for e-ammonia.
In addition to wave power, the system would incorporate 2 GWhcap of battery storage and 50 GWh of underground rock cavern hydrogen storage, further enhancing the energy hub's capacity and flexibility. These costs, assumed for 2050, are projected to be competitive compared to leading global sites, such as the Atacama Desert, which has excellent solar PV resources. For comparison, the Atacama Desert’s e-fuels production cost is estimated to range from 70-75 €/MWh, e-methanol is between 49-57 €/MWh and e-ammonia at 53 €/MWh.
However, the costs mentioned above do not include shipping costs. Shipping costs for ammonia for 10,000 km to East Asia could add up to 8 €/MWh, while shipping costs for methanol could add up to 4 €/MWh. For the Kerguelen Islands an attractive business model could be established to diversify the global e-fuels and e-chemicals production that may largely shift towards solar energy. This creates a promising opportunity for investment in a gigawatt-scale energy hub for e-fuels and e-chemicals on Kerguelen Islands, including the necessary infrastructure for shipping and workforce to maintain such a system.
Additional features in HAMS-MREL
A new open-source BIEM solver for offshore energy applications