Iain Staffell

Fuel cells for micro-combined heat and power generation

Micro-combined heat and power (CHP) holds great potential for lowering energy cost and CO2 emissions in the residential housing sector. Of the various micro-CHP technologies, fuel cells, and in particular solid oxide fuel cells, show great promise due to their high electrical efficiency and resulting low heat-to-power ratio that is better suited to residential applications. However, fuel cells are still under development and the capital cost of units available today remains high. This paper looks at the technological aspects and operating modes of fuel cells relevant to micro-CHP as well as examining the state of commercial development, life cycle issues and the techno-economics of fuel cells for micro-CHP at the residential scale.

A review of domestic heat pumps

Heat pumps are a promising technology for heating (and cooling) domestic buildings that provide exceptionally high efficiencies compared with fossil fuel combustion. There are in the region of a billion heat pumps in use world-wide, but despite their maturity they are a relatively new technology to many regions. This article gives an overview of the state-of-the-art technologies and the practical issues faced when installing and operating them. It focuses on the performance obtained in real-world operation, surveying the published efficiency figures for hundreds of air source and ground source heat pumps (ASHP and GSHP), and presenting a method to relate these to results from recent UK and German field trials. It also covers commercial aspects of the technologies, the typical savings in primary energy usage, carbon dioxide emissions abatement that can be realised, and wider implications of their uptake.

Divide and Conquer?

We use a k-means clustering algorithm to partition national electricity demand data for Great Britain and apply a novel profiling method to obtain a set of representative demand profiles for each year over the period 1994-2005. We then use a simulated dispatch model to assess the accuracy of these daily profiles against the complete dataset on a year-to-year basis. We find that the use of data partitioning does not compromise the accuracy of the simulations for most of the main variables considered, even when simulating significant intermittent wind generation. This technique yields 50-fold gains in terms of computational speed, allowing complex Monte Carlo simulations and sensitivity analyses to be performed with modest computing resource.

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Summary As wind and solar power provide a growing share of Europe’s electricity1, understanding and accommodating their variability on multiple timescales remains a critical problem. On weekly timescales, variability is related to long-lasting weather conditions, called weather regimes2–5, which can cause lulls with a loss of wind power across neighbouring countries6. Here we show that weather regimes provide a meteorological explanation for multi-day fluctuations in Europe’s wind power and can help guide new deployment pathways which minimise this variability. Mean generation during different regimes currently ranges from 22 GW to 44 GW and is expected to triple by 2030 with current planning strategies. However, balancing future wind capacity across regions with contrasting inter-regime behaviour – specifically deploying in the Balkans instead of the North Sea – would almost eliminate these output variations, maintain mean generation, and increase fleet-wide minimum output. Solar photovoltaics could balance low-wind regimes locally, but only by expanding current capacity tenfold. New deployment strategies based on an understanding of continent-scale wind patterns and pan-European collaboration could enable a high share of wind energy whilst minimising the negative impacts of output variability.

-Means Clustering of Demand Data Allows Rapid and Accurate Simulations of the British Electricity System

The merit order stack is used to tackle a wide variety of problems involving electricity dispatch. The simplification it relies on is to neglect dynamic issues such as the cost of starting stations. This leads the merit order stack to give a poor representation of the hourly pattern of prices and under-estimate the optimal level of investment in both peaking and inflexible baseload generators, and thus their run-times by up to 30%. We describe a simple method for incorporating start-up costs using a single equation derived from the load curve and station costs. The technique is demonstrated on the British electricity system in 2010 to test its performance against actual outturn, and in a 2020 scenario with increased wind capacity where it is compared to a dynamic unit-commitment scheduler. Our modification yields a better representation of electricity prices and reduces the errors in capacity investment by a factor of two.

Balancing Europe/'s wind-power output through spatial deployment informed by weather regimes

Many studies have quantified the cost of Carbon Capture and Storage (CCS) power plants, but relatively few discuss or appreciate the unique value this technology provides to the electricity system. CCS is routinely identified as a key factor in least-cost transitions to a low-carbon electricity system in 2050, one with significant value by providing dispatchable and low-carbon electricity. This paper investigates production, demand and stability characteristics of the current and future electricity system. We analyse the Carbon Intensity (CI) of electricity systems composed of unabated thermal (coal and gas), abated (CCS), and wind power plants for different levels of wind availability with a view to quantifying the value to the system of different generation mixes. As a thought experiment we consider the supply side of a UK-sized electricity system and compare the effect of combining wind and CCS capacity with unabated thermal power plants. The resulting capacity mix, system cost and CI are used to highlight the importance of differentiating between intermittent and firm low-carbon power generators. We observe that, in the absence of energy storage or demand side management, the deployment of intermittent renewable capacity cannot significantly displace unabated thermal power, and consequently can achieve only moderate reductions in overall CI. A system deploying sufficient wind capacity to meet peak demand can reduce CI from 0.78 tCO2/MWh, a level according to unabated fossil power generation, to 0.38 tCO2/MWh. The deployment of CCS power plants displaces unabated thermal plants, and whilst it is more costly than unabated thermal plus wind, this system can achieve an overall CI of 0.1 tCO2/MWh. The need to evaluate CCS using a systemic perspective in order to appreciate its unique value is a core conclusion of this study.

Is There Still Merit in the Merit Order Stack? The Impact of Dynamic Constraints on Optimal Plant Mix

Abstract A new approach is required to determine a technologys value to the power systems of the 21st century. Conventional cost-based metrics are incapable of accounting for the indirect system costs associated with intermittent electricity generation, in addition to environmental and security constraints. In this work, we formalise a new concept for power generation and storage technology valuation which explicitly accounts for system conditions, integration challenges, and the level of technology penetration. The centrepiece of the system value (SV) concept is a whole electricity systems model on a national scale, which simultaneously determines the ideal power system design and unit-wise operational strategy. It brings typical Process Systems Engineering thinking into the analysis of power systems. The model formulation is a mixed-integer linear optimisation and can be understood as hybrid between a generation expansion and a unit commitment model. We present an analysis of the future UK electricity system and investigate the SV of carbon capture and storage equipped power plants (CCS), onshore wind power plants, and grid-level energy storage capacity. We show how the availability of different low-carbon technologies impact the optimal capacity mix and generation patterns. We find that the SV in the year 2035 of grid-level energy storage is an order of magnitude greater than that of CCS and wind power plants. However, CCS and wind capacity provide a more consistent value to the system as their level of deployment increases. Ultimately, the incremental system value of a power technology is a function of the prevalent system design and constraints.

Quantifying the value of CCS for the future electricity system

Abstract The mitigation of climate change requires a near total decarbonisation of the power generation sector by 2050. Decisions on the amount of generating capacity, the types of technologies, and their operation are crucial to achieving emission targets. As power plants operate in an interconnected system, their evaluation should be based on their contribution to overall system performance as opposed to their individual costs when operating in isolation. In this contribution, we present a methodological approach for deriving the Levelised Value of Electricity (LVOE) as a new metric determining the value of a technology to the electricity system. The methodology is based on a mixed-integer linear program (MILP) which simultaneously optimises the electricity system design and operation. It considers both security of supply and environmental aspects and presents the technology value as a function of the prevalent system conditions. An illustrative study on the LVOE of Carbon Capture and Storage (CCS) power plants reveals how the economic deployment of CCS could reduce total system cost in the future UK energy system.

A systems approach to quantifying the value of power generation and energy storage technologies in future electricity networks

The UKs first fleet of hydrogen fuel cell vehicles – the Microcab H4 series – has been demonstrated at the University of Birmingham for 21 months. The five prototypes have been used interchangeably as four-seat urban taxis and light goods vehicles around campus, accumulating over 4,000 km on the campus road network and being filled with 68 kg of hydrogen. The performance and efficiency of these vehicles have been monitored in-situ throughout the trial, using custom-built data loggers for the fuel cell and other powertrain components. This paper presents the key findings relating to the powertrain performance and efficiency. While the peak tank-to-wheel efficiency was 27%, the Microcabs were found on average to be 18% efficient at converting hydrogen into tractive power. The causes of this loss in efficiency are analysed and discussed, and show that improving the control and interaction of the individual components would result in substantially improved vehicle performance.

Levelised Value of Electricity - A Systemic Approach to Technology Valuation

This paper looks back through the 1960s to the invention of carbon fibres and the theories of Strong Solids. In particular it focuses on the fracture mechanics paradox of strong composites containing weak interfaces. From Griffith theory, it is clear that three parameters must be considered in producing a high strength composite:- minimising defects; maximising the elastic modulus; and raising the fracture energy along the crack path. The interface then introduces two further factors:- elastic modulus mismatch causing crack stopping; and debonding along a brittle interface due to low interface fracture energy. Consequently, an understanding of the fracture energy of a composite interface is needed. Using an interface model based on atomic interaction forces, it is shown that a single layer of contaminant atoms between the matrix and the reinforcement can reduce the interface fracture energy by an order of magnitude, giving a large delamination effect. The paper also looks to a future in which cars will be made largely from composite materials. Radical improvements in automobile design are necessary because the number of cars worldwide is predicted to double. This paper predicts gains in fuel economy by suggesting a new theory of automobile fuel consumption using an adaptation of Coulomb’s friction law. It is demonstrated both by experiment and by theoretical argument that the energy dissipated in standard vehicle tests depends only on weight. Consequently, moving from metal to fibre construction can give a factor 2 improved fuel economy performance, roughly the same as moving from a petrol combustion drive to hydrogen fuel cell propulsion. Using both options together can give a factor 4 improvement, as demonstrated by testing a composite car using the ECE15 protocol.