GHG emissions and energy performance of offshore wind power

This paper presents specific life cycle GHG emissions from wind power generation from six different 5 MW offshore wind turbine conceptual designs. In addition, the energy performance, expressed by the energy indicators Energy Payback Ratio (EPR) Energy Payback Time (EPT), is calculated for each of the concepts.There are currently few LCA studies in existence which analyse offshore wind turbines with rated power as great as 5 MW. The results, therefore, give valuable additional environmental information concerning large offshore wind power. The resulting GHG emissions vary between 18 and 31.4 g CO₂-equivalents per kWh while the energy performance, assessed as EPR and EPT, varies between 7.5 and 12.9, and 1.6 and 2.7 years, respectively. The relatively large ranges in GHG emissions and energy performance are chiefly the result of the differing steel masses required for the analysed platforms. One major conclusion from this study is that specific platform/foundation steel masses are important for the overall GHG emissions relating to offshore wind power. Other parameters of importance when comparing the environmental performance of offshore wind concepts are the lifetime of the turbines, wind conditions, distance to shore, and installation and decommissioning activities.Even though the GHG emissions from wind power vary to a relatively large degree, wind power can fully compete with other low GHG emission electricity technologies, such as nuclear, photovoltaic and hydro power.     

Life cycle assessment of the offshore wind farm alpha ventus

Due to better wind conditions at sea, offshore wind farms have the advantage of higher electricity production compared to onshore and inland wind farms. In contrast, a greater material input, leading to increased energy consumptions and emissions during the production phase, is required to build offshore wind farms. These contrary effects are investigated for the first German offshore wind farm alpha ventus in the North Sea. In a life cycle assessment its environmental influence is compared to that of Germany’s electricity mix.In comparison to the mix, alpha ventus had better indicators in nearly every investigated impact category. One kilowatt-hour electricity, generated by the wind farm, was burdened with 0.137 kWh Primary Energy-Equivalent and 32 g CO₂-Equivalent, which represented only a small proportion of the accordant values for the mix. Furthermore, the offshore foundations as well as the submarine cable were the main energy intensive components. The energetic and greenhouse gas payback period was less than one year.Therefore, offshore wind power, even in deep water, is compatible with the switch to sustainable electricity production relying on renewable energies. Additional research, taking backup power plants as well as increasingly required energy storage systems into account, will allow further calculation.     

Cofiring versus biomass-fired power plants: GHG (Greenhouse Gases) emissions savings comparison by means of LCA (Life Cycle Assessment) methodology

One way of producing nearly CO₂ free electricity is by using biomass as a combustible. In many cases, removal of CO₂ in biomass grown is almost the same as the emissions for the bioelectricity production at the power plant. For this reason, bioelectricity is generally considered CO₂ neutral. For large-scale biomass electricity generation two alternatives can be considered: biomass-only fired power plants, or cofiring in an existing coal power plant. Among other factors, two important aspects should be analyzed in order to choose between the two options. Firstly, which is the most appealing alternative if their Greenhouse Gases (GHG) Emissions savings are taken into account. Secondly, which biomass resource is the best, if the highest impact reduction is sought. In order to quantify all the GHG emissions related to each system, a Life Cycle Assessment (LCA) methodology has been performed and all the processes involved in each alternative have been assessed in a cradle-to-grave manner. Sensitivity analyses of the most dominant parameters affecting GHG emissions, and comparisons between the obtained results, have also been carried out.     

Greenhouse gas emissions reduction by use of wind and solar energies for hydrogen and electricity production: Economic factors

This study addresses economic aspects of introducing renewable technologies in place of fossil fuel ones to mitigate greenhouse gas emissions. Unlike for traditional fossil fuel technologies, greenhouse gas emissions from renewable technologies are associated mainly with plant construction and the magnitudes are significantly lower. The prospects are shown to be good for producing the environmentally clean fuel hydrogen via water electrolysis driven by renewable energy sources. Nonetheless, the cost of wind- and solar-based electricity is still higher than that of electricity generated in a natural gas power plant. With present costs of wind and solar electricity, it is shown that, when electricity from renewable sources replaces electricity from natural gas, the cost of greenhouse gas emissions abatement is about four times less than if hydrogen from renewable sources replaces hydrogen produced from natural gas. When renewable-based hydrogen is used in a fuel cell vehicle instead of gasoline in a IC engine vehicle, the cost of greenhouse gas emissions reduction approaches the same value as for renewable-based electricity only if the fuel cell vehicle efficiency exceeds significantly (i.e., by about two times) that of an internal combustion vehicle. It is also shown that when 6000 wind turbines (Kenetech KVS-33) with a capacity of 350 kW and a capacity factor of 24% replace a 500-MW gas-fired power plant with an efficiency of 40%, annual greenhouse gas emissions are reduced by 2.3 megatons. The incremental additional annual cost is about $280 million (US). The results provide a useful approach to an optimal strategy for greenhouse gas emissions mitigation.     

Greenhouse gas balances of transportation biofuels,electricity and heat generation in Finland—Dealing with the uncertainties

One way to reduce greenhouse gas emissions from the transportation sector is to replace fossil fuels by biofuels. However, production of biofuels also generates greenhouse gas emissions. Energy and greenhouse gas balances of transportation biofuels suitable for large-scale production in Finland have been assessed in this paper. In addition, the use of raw materials in electricity and/or heat production has been considered. The overall auxiliary energy input per energy content of fuel in biofuel production was 3–5-fold compared to that of fossil fuels. The results indicated that greenhouse gas emissions from the production and use of barley-based ethanol or biodiesel from turnip rape are very probably higher compared to fossil fuels. Second generation biofuels produced using forestry residues or reed canary grass as raw materials seem to be more favourable in reducing greenhouse gas emissions. However, the use of raw materials in electricity and/or heat production is even more favourable. Significant uncertainties are involved in the results mainly due to the uncertainty of N₂O emissions from fertilisation and emissions from the production of the electricity consumed or replaced.     

An offshore wind resource assessment study for New England

This paper gives a summary of ongoing work on the assessment of the wind energy resource off the coast of southern New England in the United States. This project was carried out to determine the potential for the near-term development of offshore wind energy projects in that region. The work summarized here consists of four aspects: (1) a review of existing offshore wind data, (2) the measurement of new data at an offshore site, (3) correlation and prediction of long-term data at a new offshore site by reference to a longer-term island site and (4) assessment of the overall coastal resource through the use of the MesoMap software.     

Greenhouse gases (GHG) emissions reduction in a power system predominantly based on lignite

In this paper the GHG mitigation potential of a power system with prevailing use of lignite is assessed through the example of the Macedonian power system. The analysis is conducted using the WASP model in order to develop three different scenarios (business as usual - BAU and two mitigation scenarios) for the power system expansion over the period 2008-2025. In the first mitigation scenario two gas power plants with combined cycle are planned to replace some of the lignite-based capacities. The second mitigation scenario, besides the gas power plants, assumes electricity consumption reduction related to the large industrial consumers and an increased share of new renewable energy sources. Detailed calculations of the GHG emissions are made for all scenarios. The comparison of emissions in 2025 and in 2008 shows that the increase of 78% in the case of predominantly lignite BAU scenario is reduced to 41% by the first mitigation scenario, and to 14% by the second mitigation scenario. The mitigation costs appeared to be less then 10 $/t CO₂-eq for the first mitigation scenario, and even negative for the second one.     

A framework for data integration of offshore wind farms

Operation and maintenance play an important role in maximizing the yield and minimizing the downtime of wind turbines, especially offshore wind farms where access can be difficult due to harsh weather conditions for long periods. It contributes up to 25–30% to the cost of energy generation. Improved operation and maintenance (O&M) practices are likely to reduce the cost of wind energy and increase safety. In order to optimize the O&M, the importance of data exchange and knowledge sharing within the offshore wind industry must be realized. With more data available, it is possible to make better decisions, and thereby improve the recovery rates and reduce the operational costs. This article describes the development of a framework for data integration to optimize the remote operations of offshore wind farms.     

Development of a viability assessment model for hydrogen production from dedicated offshore wind farms

Dedicated offshore wind farms for hydrogen production are a promising option to unlock the full potential of offshore wind energy, attain decarbonisation and energy security targets in electricity and other sectors, and cope with grid expansion constraints. Current knowledge on these systems is limited, particularly the economic aspects. Therefore, a new, integrated and analytical model for viability assessment of hydrogen production from dedicated offshore wind farms is developed in this paper. This includes the formulae for calculating wind power output, electrolysis plant size, and hydrogen production from time-varying wind speed. All the costs are projected to a specified time using both Discounted Payback (DPB) and Net Present Value (NPV) to consider the value of capital over time. A case study considers a hypothetical wind farm of 101.3 MW situated in a potential offshore wind development pipeline off the East Coast of Ireland. All the costs of the wind farm and the electrolysis plant are for 2030, based on reference costs in the literature. Proton exchange membrane electrolysers and underground storage of hydrogen are used. The analysis shows that the DPB and NPV flows for several scenarios of storage are in good agreement and that the viability model performs well. The offshore wind farm – hydrogen production system is found to be profitable in 2030 at a hydrogen price of €5/kg and underground storage capacities ranging from 2 days to 45 days of hydrogen production. The model is helpful for rapid assessment or optimisation of both economics and feasibility of dedicated offshore wind farm – hydrogen production systems.     

Assessing offshore wind resources: An accessible methodology

This paper describes a method for assessing the electric production and value of wind resources, specifically for the offshore environment. Three steps constitute our method. First, we map the available area, delimiting bathymetric areas based on turbine tower technology, then assess competing uses of the ocean to establish exclusion zones. From exclusion zones, bathymetry, and turbine tower water depth limitations, the water sheet area available for wind turbines is calculated. The second step is calculation of power production starting from available area, which determines the location and count of turbines. Then existing wind data are extrapolated to turbine height and, along with the turbine power output curve, they are used to establish the expected electric power production on an hourly basis. The third step calculates market value based on the hourly electric market at the nearest electric grid node.To illustrate these methods, we assess the offshore wind resource of the US state of Delaware. We find year-round average output of over 5200 MW, or about four times the average electrical consumption of the state. On local wholesale electricity markets, this would produce just over $2 billion/year in revenue.Because the methods described here do not rely on constructing meteorological towers nor on proprietary software, they are more accessible to a local government, state college, or other organization. For example, these methods can be carried out as an initial assessment of resources, or by a government or public entity as a check on claims by private applicants.     

Minimizing maintenance cost for offshore wind turbines following multi-level opportunistic preventive strategy

Cost of energy generated from offshore wind is impacted by maintenance cost to a great extent. Cost of maintenance depends primarily on the strategy for performing maintenance. In this paper a maintenance cost model for offshore wind turbine components following multilevel opportunistic preventive maintenance strategy is formulated. In this strategy, opportunity for performing preventive actions on components is taken while a failed component is replaced. Two kinds of preventive actions are considered, preventive replacement and preventive maintenance. In the former, components that undergo that action become as good as new (i.e., the replaced components, are not just as good as new, but are actually new), but in the latter, ages of components are reduced to some degree depending on the level of maintenance action. Total cost associated with maintenance depends on the setting of age groups that determine which component should be preventively maintained and to what degree. Through optimum selection of the number of age groups, cost of maintenance can be minimized. A model is formulated where total maintenance cost is expressed as a function of number of age groups for components. A numerical study is used to illustrate the model. The results show that total cost of maintenance is significantly impacted by number of age groups and age thresholds set for components.     

Life-cycle cost analysis of floating offshore wind farms

The purpose of this article is to put forward a methodology in order to evaluate the Cost Breakdown Structure (CBS) of a Floating Offshore Wind Farm (FOWF). In this paper CBS is evaluated linked to Life-Cycle Cost System (LCS) and taking into account each of the phases of the FOWF life cycle. In this sense, six phases will be defined: definition, design, manufacturing, installation, exploitation and dismantling. Each and every one of these costs can be subdivided into different sub-costs in order to obtain the key variables that run the life-cycle cost. In addition, three different floating platforms will be considered: semisubmersible, Tensioned Leg Platform (TLP) and spar. Several types of results will be analysed according to each type of floating platform considered: the percentage of the costs, the value of the cost of each phase of the life-cycle and the value of the total cost in each point of the coast. The results obtained allow us to become conscious of what the most important costs are and minimize them, which is one of the most important contributions nowadays. It will be useful to improve the competitiveness of floating wind farms in the future.     

A comparison of environmental benefits of transport and electricity applications of carbohydrate derived ethanol and hydrogen

It may soon become possible to produce hydrogen from hydrolysed carbohydrates instead of ethanol via fermentation and distillation, employing aqueous phase reforming. The environmental merits of these two different energy products and their uses are compared on a life cycle basis, based on expanded systems in the context of a coal-intensive energy economy. Eight industrial options are defined: ethanol for peak power generation with or without heat integration, hydrogen for peak power generation with and without heat integration, ethanol for use in a flexi-fuel vehicle and a fuel cell vehicle, and hydrogen use in an internal combustion engine vehicle and a fuel cell vehicle. Aqueous phase reforming to produce hydrogen is shown to generally out-perform the corresponding fermentation–distillation ethanol options. Peak power generated from ethanol would be a preferred short-term option, with peak power from hydrogen in the medium term ceding to the environmentally preferred option of hydrogen fuel cell vehicles in the long-term.     

Consequential environmental system analysis of expected offshore wind electricity production in Germany

Taking advantage of offshore wind power appears to be of special significance for the climate protection plans announced by the German Federal Government. For this reason, a comprehensive system analysis of the possible CO₂ reduction including the consideration of all relevant processes has to be performed. This goal can be achieved by linking a life-cycle assessment model of offshore wind utilisation with a stochastic model of the German electricity market. Such an extended life-cycle assessment shows that the CO₂ emissions from the construction and operation of wind farms are low compared with the substitution effects of fossil fuels. Additionally, in the German electricity system, offshore wind energy is the main substitute for medium-load power plants. CO₂ emissions from the modified operation and the expansion of conventional power plants reduce the CO₂ savings, but the substitution effect outweighs these emissions by one order of magnitude. The assumptions of the model, shown here to be above all CO₂ certificate prices, have a considerable influence on the figures shown due to a significant effect on the future energy mix.     

Greenhouse gas emissions and energy balances of jatropha biodiesel as an alternative fuel in Tanzania

This paper evaluates GHG emissions and energy balances (i.e. net energy value (NEV), net renewable energy value (NREV) and net energy ratio (NER)) of jatropha biodiesel as an alternative fuel in Tanzania by using life cycle assessment (LCA) approach. The functional unit (FU) was defined as 1 tonne (t) of combusted jatropha biodiesel. The findings of the study prove wrong the notion that biofuels are carbon neutral, thus can mitigate climate change. A net GHG equivalent emission of about 848 kg t⁻¹ was observed. The processes which account significantly to GHG emissions are the end use of biodiesel (about 82%) followed by farming of jatropha for about 13%. Sensitivity analysis indicates that replacing diesel with biodiesel in irrigation of jatropha farms decreases the net GHG emissions by 7.7% while avoiding irrigation may reduce net GHG emissions by 12%. About 22.0 GJ of energy is consumed to produce 1 t of biodiesel. Biodiesel conversion found to be a major energy consuming process (about 64.7%) followed by jatropha farming for about 30.4% of total energy. The NEV is 19.2 GJ t⁻¹, indicating significant energy gain of jatropha biodiesel. The NREV is 23.1 GJ t⁻¹ while NER is 2.3; the two values indicate that large amount of fossil energy is used to produce biodiesel. The results of the study are meant to inform stakeholders and policy makers in the bioenergy sector.     

Does the production of Belgian bioethanol fit with European requirements on GHG emissions? Case of wheat

This paper undertakes an environmental evaluation of bioethanol production, using wheat cultivated in Belgium. Cultivation steps are modelled using Belgian specific data. Wheat transformation in ethanol relies on industrial data. GHG emissions of the whole life cycle are calculated and compared with the default values given by the European Renewable Energy Directive. Belgian wheat bioethanol achieves a 5% higher GHG reduction than the one mentioned in the European directive but impact repartition is different with a higher importance of cultivation step in our case. Belgian wheat bioethanol complies with the current sustainability criteria but is also able to conform to further ones. Sensitivity analyses are performed on the importance of N fertilizers and associated emissions known as main important parameters. These analyses reveal non negligible variations and then a range of available GHG reduction when using wheat bioethanol.     

A decision support system for strategic maintenance planning in offshore wind farms

This paper presents a Decision Support System (DSS) for maintenance cost optimisation at an Offshore Wind Farm (OWF). The DSS is designed for use by multiple stakeholders in the OWF sector with the overall goal of informing maintenance strategy and hence reducing overall lifecycle maintenance costs at the OWF. Two optimisation models underpin the DSS. The first is a deterministic model that is intended for use by stakeholders with access to accurate failure rate data. The second is a stochastic model that is intended for use by stakeholders who have less certainty about failure rates. Solutions of both models are presented using a UK OWF that is in construction as an example. Conclusions as to the value of failure rate data are drawn by comparing the results of the two models. Sensitivity analysis is undertaken with respect to the turbine failure rate frequency and number of turbines at the site, with near linear trends observed for both factors. Finally, overall conclusions are drawn in the context of maintenance planning in the OWF sector.     

Life cycle energy consumption and GHG emissions of hydrogen production from underground coal gasification in comparison with surface coal gasification

Developing underground coal gasification (UCG)-based hydrogen production (UCG-H₂) is expected to alleviate hydrogen supply and demand contradiction, but its energy consumption and environmental impact need to be clarified. In this paper, comparative study of energy consumption and greenhouse gas (GHG) emissions between UCG-H₂ and typical surface coal gasification (SCG)-based hydrogen production (SCG-H₂) is carried out using life cycle assessment method. Result shows energy consumption of UCG-H₂ is only 61.2% of that of SCG-H₂, which is 1,327,261 and 2,170,263 MJ respectively, reflecting its obvious energy saving advantage. 80% capture rate can achieve an appropriate balance between energy consumption and emissions. Under this capture rate, emissions of UCG-H₂ and SCG-H₂ are roughly equivalent, which are 207,582 and 197,419 kg CO₂-eq respectively. Scenario analysis indicates energy consumption in hydrogen industry can reduce by 38.8% when hydrogen production is substituted by UCG with CCS to fully meet demand of 21 Mt in 2030.     

Good or bad bioethanol from a greenhouse gas perspective – What determines this?

The purpose of this study is to describe how the greenhouse gas (GHG) benefits of ethanol from agricultural crops depend on local conditions and calculation methods. The focus is mainly on the fuels used in the ethanol process and biogenic GHG from the soils cultivated. To ensure that “good” ethanol is produced, with reference to GHG benefits, the following demands must be met: (i) ethanol plants should use biomass and not fossil fuels, (ii) cultivation of annual feedstock crops should be avoided on land rich in carbon (above and below ground), such as peat soils used as permanent grassland, etc., (iii) by-products should be utilised efficiently in order to maximise their energy and GHG benefits and (iv) nitrous oxide emissions should be kept to a minimum by means of efficient fertilisation strategies, and the commercial nitrogen fertiliser utilised should be produced in plants which have nitrous oxide gas cleaning. Several of the current ethanol production systems worldwide fullfill the majority of these demands, whereas some production systems do not. Thus, the findings in this paper helps identifying current “good” systems, how today’s “fairly good” systems could be improved, and which inherent “bad” systems that we should avoid.     

Assessing the lifecycle greenhouse gas emissions from solar PV and wind energy: A critical meta-survey

This paper critically screens 153 lifecycle studies covering a broad range of wind and solar photovoltaic (PV) electricity generation technologies to identify 41 of the most relevant, recent, rigorous, original, and complete assessments so that the dynamics of their greenhouse gas (GHG) emissions profiles can be determined. When viewed in a holistic manner, including initial materials extraction, manufacturing, use and disposal/decommissioning, these 41 studies show that both wind and solar systems are directly tied to and responsible for GHG emissions. They are thus not actually emissions free technologies. Moreover, by spotlighting the lifecycle stages and physical characteristics of these technologies that are most responsible for emissions, improvements can be made to lower their carbon footprint. As such, through in-depth examination of the results of these studies and the variations therein, this article uncovers best practices in wind and solar design and deployment that can better inform climate change mitigation efforts in the electricity sector.