• Energy Research

Abstract With the rollout of proposed smart grid tariff structures in the Republic of Ireland the modelled role of an energy storage device in reducing the energy and economic loads of a public school building is presented. The school building has a 33kWp photovoltaic system, the performance of which is compared to other PV systems in the Irish environment. Concurrently, a Zinc Bromine flow battery has been operated under various charge and discharge rate cycles and the overall energy performance of this system has been virtually matched to the output of the PV. The scenarios trialled include ‘business as usual’ modelling the economic impact of smart grid tariffs versus a flat rate tariff as currently operation with PV in situ; a ‘peak shifting’ scenario where the battery operation is linked solely to the smart grid tariff rates and ignores PV resource and a ‘PV optimisation’ scenario where the PV output is considered ‘free’ energy and as such has priority in storage. The three scenarios show that the greatest economic impact comes from the ‘PV optimisation’ scenario, which is mainly related to PV generation at low economic value times.

It is a common sense expectation that the efficiency of wind turbines should decline with age, similarly to what happens with most technical systems. Due to the complexity of this kind of machine and the environmental conditions to which it is subjected, it is far from obvious how to reliably estimate the impact of aging. In this work, the aging of five Vestas V52 wind turbines is analyzed. The test cases belong to two different sites: one is at the Dundalk Institute of Technology in Ireland, and four are sited in an industrial wind farm in a mountainous area in Italy. Innovative data analysis techniques are employed: the general idea consists of considering appropriate operation curves depending on the working control region of the wind turbines. When the wind turbine operates at fixed pitch and variable rotational speed, the generator speed-power curve is studied; for higher wind speed, when the rotational speed has saturated and the blade pitch is variable, the blade pitch-power curve is considered. The operation curves of interest are studied through the binning method and through a support vector regression with a Gaussian kernel. The wind turbine test cases are analyzed vertically (each in its own history) and horizontally, by comparing the behavior at the two sites for the given wind turbine age. The main result of this study is that an evident effect of aging is the worsening of generator efficiency: progressively, less power is extracted for the given generator rotational speed. Nevertheless, this effect is observed to be lower for the wind turbines in Italy (order of −1.5% at 12 years of age with respect to seven years of age) with respect to the Dundalk wind turbine, which shows a sharp decline at 12 years of age (−8.8%). One wind turbine sited in Italy underwent a generator replacement in 2018: through the use of the same kind of data analysis methods, it was possible to observe that an average performance recovery of the order of 2% occurs after the component replacement. It also arises that for all the test cases, a slight aging effect is visible for higher wind speed, which can likely be interpreted as due to declining gearbox efficiency. In general, it is confirmed that the aging of wind turbines is strongly dependent on the history of each machine, and it is likely confirmed that the technology development mitigates the effect of aging.

Abstract As wind energy continues to expand, new markets for distributed wind applications are expected, including behind-the-meter deployment at industrial consumer sites in peri-urban areas. The presence of buildings in these areas can give rise to complex wind regimes. This study compares the measured annual energy output of an operating Vestas V52 wind turbine, in a peri-urban environment, with predictions from four microscale wind flow models. The models upscale and downscale onsite LiDAR wind measurements at six heights from 10 m to 200 m. The models consist of a linear shelter model and three RANS CFD approaches, implemented in two widely used micro-siting tools, namely WAsP and WindSim. Variations from 1.4% to 64% between model predicted and measured electrical energy output are observed. For low-rise buildings with heights up to 20% of the turbine hub height, the models are most accurate using wind measurements at ~ 3 times the height of the buildings. In the case of a tall narrow building, ~ 80% of the hub height, best model predictions are from twice the height of the building. Wind shear measurements suggest that obstacles down to 20% of the hub height, up to distances of 100 obstacles heights away, are significant.

Abstract Dundalk Institute of Technology (DkIT) is a third-level college in the east of Ireland with approximately 5000 registered students. The college is an autoproducer with an 850-kW wind turbine in operation on campus. In this study, DkIT’s half-hourly electricity usage over the 2017/18 academic year was measured and the benefit of the wind turbine was assessed in terms of energy, cost and carbon savings. In the period studied, the college imported electricity at fixed time-of-use (TOU) rates, although an alternative billing approach that was analysed is half-hourly pricing (HHP) based on the system marginal price (SMP). Furthermore, after a sizing study, the operation of a large Li-ion battery to be used for time-shifting was modelled. Over the study year, the wind turbine was found to reduce the college’s required import of electricity substantially, while also creating some export. This decreased the net electricity cost and net carbon emissions considerably. Irrespective of this, switching to HHP would also have provided further substantial economic savings. Conversely, the modelled time-shifting using the battery generated far too little revenue to cover the associated costs, although reserving the battery for use in the Irish grid-response markets appears to be an economically viable option.

Cascade air-to-water heat pumps have better overall efficiency than single-stage air-to-water heat pumps when operating at low ambient temperatures for high temperature water supply. While many studies in the literature investigated the specific features of equipment performance of cascade heat pumps, there is little information about retrofit applications of these heat pumps in residential buildings using experimentally validated dynamic building simulations. In this study, the techno-economic assessment of a variable capacity cascade air-to-water heat pump retrofitted into residential buildings is conducted by means of experimentally validated TRNSYS simulations. The cascade heat pump coupled with thermal energy storage operating in different scenarios is further studied. Laboratory and field trial results were obtained to develop and validate a cascade heat pump model integrated with a dynamic building simulation model. Regarding the heat pump system without storage, the predicted annual COPs were almost below 2.5 at ambient temperatures of from −11.2 °C to 29.5 °C, even the heat pump adopted weather compensation control. Simulation results also indicated that the cascade heat pump could not defeat gas boilers and high-efficiency oil boilers (90%) in terms of operating costs, but there were CO2 reductions (from 14% to 57%). As for the heat pump coupled with storage, simulation results showed that at ambient temperatures of between −5.6 °C and 23.8 °C, the continuous coupling between the heat pump and the storage revealed the lowest annual performance (actual COP of 1.41), while the direct heating obtained the highest efficiency (actual COP of 2.12) followed by the load-shifting (actual COP of 1.88).

The worsening with age of technical systems performance is a matter of fact which is particularly timely to analyze for horizontal-axis wind turbines because they constitute a mature technology. On these grounds, the present study deals with the assessment of wind turbine performance decline with age. The selected test case is a Vestas V52 wind turbine, installed in 2005 at the Dundalk Institute of Technology campus in Ireland. Operation data from 2008 to 2019 have been used for this study. The general idea is analyzing the appropriate operation curves for each working region of the wind turbine: in Region 2 (wind speed between 5 and 9 m/s), the generator speed–power curve is studied, because the wind turbine operates at fixed pitch. In Region 2 12 (wind speed between 9 and 13 m/s), the generator speed is rated and the pitch control is relevant: therefore, the pitch angle–power curve is analyzed. Using a support vector regression for the operation curves of interest, it is observed that in Region 2, a progressive degradation occurs as regards the power extracted for given generator speed, and after ten years (from 2008 to 2018), the average production has diminished of the order of 8%. In Region 2 12, the performance decline with age is less regular and, after ten years of operation, the performance has diminished averagely of the 1.3%. The gearbox of the test case wind turbine was substituted with a brand new one at the end of 2018, and it results that the performance in Region 2 12 has considerably improved after the gearbox replacement (+3% in 2019 with respect to 2018, +1.7% with respect to 2008), while in Region 2, an improvement is observed (+1.9% in 2019 with respect to 2018) which does not compensate the ten-year period decline (−6.5% in 2019 with respect to 2008). Therefore, the lesson is that for the test case wind turbine, the generator aging impacts remarkably on the power production in Region 2, while in Region 2 12, the impact of the gearbox aging dominates over the generator aging; for this reason, wind turbine refurbishment or component replacement should be carefully considered on the grounds of the wind intensity distribution onsite.

This research case study assesses the impacts of peri-urban features such as buildings on the performance of an operating 850 kW Vestas V52 wind turbine that has a 60 m hub height and 52 m rotor diameter located at the outskirts of Dundalk town in Ireland. Multi-annual 10-minute SCADA data is analysed to assess the directional electrical energy rose (EER) of the wind turbine. This is compared to predictions from WAsP-IBZ that uses an obstacle model to assess buildings and to WAsP-CFD treating buildings as surface roughness elements in the terrain. Onsite LiDAR measurements are used to initialise the WAsP programme in both cases. Measured directional wind shear profiles are also assessed to give further insights into discrepancies between the predicted and actual energy performance of the wind turbine. "The authors wish to acknowledge the support of the INTERREG VA SPIRE2 project. This research was supported by the European Union's INTERREG VA Programme (Grant No. INT-VA/049), managed by the Special EU Programmes Body (SEUPB). The views and opinions expressed in this document do not necessarily reflect those of the European Commission or the Special EU Programmes Body (SEUPB)."