Wind and Solar GHG Emissions Vary Substantially, but are Lower than Coal or Gas in all Cases

by Tim Storer

            Renewable energy sources, such as wind power generation, are often touted as preferable alternatives to fossil fuels because they produce electricity in an “emissions-free” manner. In actuality, some emissions are created during the production, distribution, and disposal of these technologies, making them not a truly “emissions-free” means of energy production. In order to determine the real relative advantages of various energy sources (in respect to carbon emissions), the full life cycle must be considered. Daniel Nugent and Benjamin Sovacool conducted a literature review of 153 lifecycle studies examining total carbon emissions associated with energy from wind and solar plants and determined estimates of industry averages. Of the 41 studies deemed “best,” an average of 34.1 g CO2/kWh was seen for wind energy and 49.9 g CO2/kWh for solar. Among these cases, substantial variability was observed, with wind emissions varying between 0.4–364.8 g CO2/kWh and solar emitting 1–218 g CO2/kWh. Continue reading

Of the many Energy Storage Systems, Integrated Hydrogen-Oxygen Storage Stands Out

by Tim Storer

Wind power comes with the disadvantage of intermittent gaps in energy production and instances of excess supply. This variability puts strain on the electric grid and is the primary barrier to large-scale wind power integration. In order to combat this issue, various forms of energy storage have been considered to bridge the gap between supply and demand of wind power. Gao et al. 2014 conduct a brief literature review on all existing energy storage systems (ESS) for wind power. Each method comes with drawbacks associated with scale, cost, or safety, but hydrogen-oxygen storage was seen here as the best future option. By improving storage technologies, wind energy will become more viable in the market and help to reduce the share of energy coming from fossil fuels that contribute to climate change. In addition to the literature review, this study examined a possible hydrogen-oxygen ESS in Jiangsu Province, China and saw that such an operation could be profitable in the current market.

While there are some operational forms of ESS, there is a variety of issues preventing ESS –and subsequently, wind power– from becoming widespread energy sources. For example, battery power is too costly and difficult to build at a large scale, systems that involve pumping water upward for energy storage have geographical limitations, and magnetic energy storage has low storage time. In the case of hydrogen generation from electrolysis, the costs are simply too high to be competitive in the energy market with capital costs of 1000-2500$/kW (when they need to be near 400 $/kW).

Hydrogen-oxygen combined storage consists of electrolyzers that break water down into hydrogen and oxygen. The hydrogen and oxygen are combusted to form super-heated steam that powers turbines. The system is closed, and uses water as a recycled fuel. Gao and colleagues examined three variants of hydrogen-oxygen ESS: simple integrated ESS, integrated ESS with a feed water heater, and an integrated ESS with both a feed water heater and a steam reheater. In simple terms, these systems each contain an additional measure to capture heat from the steam turbines and use that heat elsewhere in the process, thus improving efficiency. All of these integrated systems contain a complex web of mechanisms that can be adjusted alongside price fluctuations in the power market to minimize costs. The former two had roughly equivalent efficiencies of 49%, but the latter system had efficiency of up to 54.6%, thus demonstrating the benefits of feed water heaters and steam reheaters.

While the 54.6% efficiency of the fully integrated system is marginally below that of some other ESS technologies, hydrogen-oxygen systems come with certain advantages. They can be implemented on a large scale, are fully eco-friendly, not limited by geographical and material restraints, and can be adjusted rapidly based on demand changes. The system was analyzed under two extreme scenarios: an “intermittent operation mode” simulating an extremely variable wind supply, and “continuous operation mode” simulating a perfectly steady supply. Because of how effectively the system dealt with times of low wind, it was actually more profitable under the intermittent scenario with annual income of $13 million per year. Real wind conditions lie somewhere between these extremes, and efficiencies of approximately 50% and prices of 0.03–0.05$/kWh were estimated.

Dan Gao, Dongfang Jiang, Pei Liu, Zheng Li, Sangao Hu, Hong Xu, 2014. An integrated energy storage system based on hydrogen storage: Process configuration and case studies with wind power. Energy, Vol. 66: 332–341.

http://www.sciencedirect.com/science/article/pii/S0360544214001170

 

 

Norway’s Path to Zero Emissions: Large Scale Hydrogen Production from Off-Grid Renewable Sources

by Tim Storer

Norway currently generates over 95% of its power from hydroelectric dams, making it one of the most climate friendly energy systems on the planet. In efforts to bring Norway carbon neutral by 2050, the government aims to eliminate emissions from the transportation sector. Konrad Meier of the Stuttgart University of Applied Sciences examines the possibility of using a hypothetical 100 megawatt offshore wind farm to generate hydrogen fuel via electrolysis. Because water hydrolysis uses only electricity and water, it offers an emissions-free means to generate hydrogen as long as the electricity is generated from a renewable source, such as wind power. This could achieve Norwegian political goals of carbon neutrality by providing the hydrogen necessary to transform their transportation sector. Unlike other proposed wind-to-hydrogen technologies, Meier examines an off-grid operation, rather than producing hydrogen at the fuel refill site. The analysis was conducted under three scenarios, and the hydrogen from this proposed operation is profitable in the energy market under only the “best case” scenario.

This is a clever use of wind power for several reasons. First, if this operation were integrated into the power grid, wind variability would become an issue. Keeping the production off-grid avoids costs of transmission infrastructure and variable supply. Second, the variability also makes exporting excess power to the E.U. infeasible. The remaining 5% of domestic power is more likely to come from untapped hydroelectric resources, so wind has no use in Norway either. Using wind power for hydrogen synthesis circumvents these issues that have previously prevented wind production from being a viable energy source in Norway.

To examine costs, Meier used a location proximal to an operational German wind farm, Alpha-ventus, and incorporated its data. He uses 2010 data as his “worst case” scenario, which is a very conservative baseline considering how much lower the power output had been in previous years and how the proposed system would not be subject to transmission losses. The “best case” scenario was calculated simply by the predicted estimates. Given the likely increases in electrolysis efficiency in upcoming years, this scenario also yields conservative estimates of overall output costs. Meier discusses four types of electrolysis, but focuses on proton exchange membrane electrolysis cell (PEMEC) and solid oxide electrolysis cell (SOEC) that require water as the only input material. Unfortunately, research on the efficiency of PEMEC and SOEC is unable to offer precise estimates, and herein lies a major source of ambiguity in the study.

Because there is currently no market for hydrogen transportation fuel, this study is limited by the assumption of a future in which infrastructure has been implemented to support a hydrogen market. Unfortunately, given how variable the results are (dependent on optimistic/pessimistic assumptions), it is unclear whether such an investment is worthwhile at all. However, in as much as the best and worst case scenarios were estimated in a very conservative way, it is possible that such an operation could be an economic way to transform the transportation sector. Further research is needed on the efficiency of the PEMEC and SOEC processes to indicate whether the proposed wind farm is an economically viable solution to attaining a carbon neutral transportation sector.

Konrad Meier, 2014. Hydrogen production with sea water electrolysis using Norwegian offshore wind energy potentials. International Journal of Energy and Environmental Engineering Vol. 5: 1–12. http://link.springer.com/article/10.1007/s40095-014-0104-6/fulltext.html#CR1

 

 

A Convenient Partnership Between Carbon Capture and Wind Energy

by Tim Storer

Carbon Capture Storage (CCS) technologies help to reduce emissions from fossil fuel energy operations, such as coal fired power plants. While these technologies have the benefit of reducing greenhouse gas emissions and making the operations more climate friendly, they are costly for extraction companies. Wind power has the benefit of low emissions, but is dependent on weather and fails to provide a stable energy supply. This paper identifies a way to reduce the cost of CCS, which involves partnering with wind powered energy. Bandyopadhyay and Patiño-Escheverri (2014) find that this partnership can make CCS vastly cheaper for the producers and the partnership would also create additional incentives for developing renewable energy sources in the form of wind power. Through the partnership, power providers will have the flexibility to direct power to multiple uses depending on price fluctuations, thus minimizing profit loss from incorporating CCS. Continue reading