Sara Walker

Standing column wells—Modeling the potential for applications in geothermal heating and cooling

Standing column wells (SCWs) have the potential to deliver much higher rates of heat transfer to geothermal heating and cooling systems in buildings via heat pumps than can conventional vertical borehole heat exchange arrays. The development of a numerical model for clusters of standing column wells is described in this article. The model is three-dimensional, dynamic, and solves the governing equations using a finite-volume discretization scheme with a fully implicit algorithm. The slower-acting field equations are solved using a wider time interval than that used for the faster-acting well equations, and the two sets of equations are coupled through the field equation source terms. A groundwater bleed feature is incorporated. The model has been verified thermally and hydraulically using existing field data. Two test cases have been applied to reveal the advantages of using SCWs in U.K. conditions, competing with the conventional closed-loop system of vertical borehole heat exchangers. Results of the applications suggest that SCWs can deliver substantially higher rates of heat transfer than conventional closed loop borehole heat exchanger arrays, especially when groundwater bleed is operational. With appropriate earth conditions in the United Kingdom, SCWs can deliver space heating and direct cooling, for example, chilled beam or chilled ceiling, successfully to offer a substantial saving on carbon emissions. Another important practical consequence of this is that far less geotechnical drilling is needed when using standing column wells than is the case with closed-loop arrays.

A modelling tool to investigate the effect of electric vehicle charging on low voltage networks

The market for electric vehicles (EV) is currently limited, but this is expected to grow rapidly with the increased advances in technology, particularly battery technology. Due to their high energy capacity and potential mass deployment, EVs will have significant impact on power networks. This paper presents a novel, user-friendly modelling tool which uses universally accepted, mathematically robust software to allow analysis of the effects of typical loads, microgeneration and EV charging on the distribution network, mainly the low voltage (LV) feeders, 11/0.4 kV substation and also part of the 11 kV section. Network asset ratings, voltage limits and thermal overloads are determined over a 24 hour period. The model allows the user to input any number of houses, schools, shops, microgeneration and EV charging posts which may be connected at each 400 V node. The EV charging post is modelled using pre-set connection times, battery capacity and battery state of charge (SOC). The effects of different EV battery charging scenarios on the LV network are investigated and presented in this paper. Comparison of different charging regimes demonstrates the effectiveness of the modelling tool and gives guidance for the design of EV charging infrastructure as more drivers choose EVs for their travelling needs.

The UK Electricity System and Its Resilience

Purpose Security of supply is a relatively outdated concept for the twenty-first-century electricity systems in a low-carbon future. Resilience is proposed as an alternative, and application of the term to the UK electricity system is discussed.

Urban Electricity Systems: A UK Case Study

The electricity sector worldwide is facing considerable pressure arising out of climate change issues, depletion of fossil fuels and geo-political issues around the location of remaining fossil fuel reserves. Electricity systems are also facing technical issues of bi-directional power flows, increasing long-distance power flows and a growing contribution from fluctuating generation sources. There is a concern that these systems are vulnerable. Investigation of vulnerability has focussed on shocks to the system associated with weather risks, equipment failure, supply (fuel) failure and price shocks, and analysis has been primarily based on financial measures such as the value of lost load. As the UK electricity system makes the transition to a low carbon future, it is unclear what this new future will look like. Transition pathways research using a multi-level perspective has identified a general picture of the drivers in future systems architecture. In such futures, vulnerability becomes multi-dimensional, and security becomes a more complex issue than that of supply of fossil fuels. These issues are not specific to the UK. Electricity systems across the globe face the same issues of multi-dimensional vulnerability and complexity of security. Research into the transition to a low carbon electricity system has, to date, been primarily focussed on the national scale in the UK. The aim of this work is a critical analysis into the use of the resilience concept for electricity systems, applied in particular to the distribution network in a case study urban area in the north east of England. The case study shall examine the low carbon scenarios for the UK, what this means in particular for domestic buildings for the case study area, and the nature of the stress on the electricity distribution system which may result from the expected growth in electrical load.

Environmental and thermal benefits of linking Brayton, absorption chiller, and organic Rankine cycles with low-enthalpy geothermal source at an arid-zone area of Libya

A combined system which consists of Brayton, LiBr/H2O absorption chiller, and HFC 245fa organic Rankine cycles has been developed and linked to a high potential low-temperature geothermal source of energy. Situated in an arid-zone area at Waddan City Libya, the geothermal source could provide sufficient energy for the City and surrounding villages and satisfy their full electrical demand of 100 MW in an uninterrupted and stable way. The system could also supply district heating and hot water. The simulated results show that the output power and thermal efficiency of the combined cycles were improved by 5 per cent and 1.5 per cent, respectively, compared to a standalone gas turbine and it also reduced carbon emissions by 55.7 per cent (291 g/kWh instead of 649 g/kWh). Incorporating district heating to the electrical energy raised the energy utilization factor to 55.1 per cent.