A critical evaluation of deterministic methods in size optimisation of reliable and cost effective standalone Hybrid renewable energy systems

Reliability of a hybrid renewable energy system (HRES) strongly depends on various uncertainties affecting the amount of power produced by the system. In the design of systems subject to uncertainties, both deterministic and nondeterministic design approaches can be adopted. In a deterministic design approach, the designer considers the presence of uncertainties and incorporates them indirectly into the design by applying safety factors. It is assumed that, by employing suitable safety factors and considering worst-case-scenarios, reliable systems can be designed. In fact, the multi-objective optimisation problem with two objectives of reliability and cost is reduced to a single-objective optimisation problem with the objective of cost only. In this paper the competence of deterministic design methods in size optimisation of reliable standalone wind-PV-battery, wind-PV-diesel and wind-PV-battery-diesel configurations is examined. For each configuration, first, using different values of safety factors, the optimal size of the system components which minimises the system cost is found deterministically. Then, for each case, using a Monte Carlo simulation, the effect of safety factors on the reliability and the cost are investigated. In performing reliability analysis, several reliability measures, namely, unmet load, blackout durations (total, maximum and average) and mean time between failures are considered. It is shown that the traditional methods of considering the effect of uncertainties in deterministic designs such as design for an autonomy period and employing safety factors have either little or unpredictable impact on the actual reliability of the designed wind-PV-battery configuration. In the case of wind-PV-diesel and wind-PV-battery-diesel configurations it is shown that, while using a high-enough margin of safety in sizing diesel generator leads to reliable systems, the optimum value for this margin of safety leading to a cost-effective system cannot be quantified without employing probabilistic methods of analysis. It is also shown that deterministic cost analysis yields inaccurate results for all of the investigated configurations

Multi-objective optimization of a novel reversible High-Temperature Heat Pump-Organic Rankine Cycle (HTHP-ORC) for industrial low-grade waste heat recovery

Nowadays, a high amount of industrial thermal energy is still lost due to the lack of competitive solutions for energy revalorization. Facing this challenge, this paper presents a novel technology, based on a reversible High-Temperature Heat Pump (HTHP) and Organic Rankine Cycle (ORC). The proposed system recovers low-grade waste heat to generate electricity or useful heat in accordance with consumer demand. Compressor and expander semi-empirical models have been considered for the reversible system computational simulation, being HFC-245fa the working fluid selected. The built-in volume ratio and Internal Heat Exchanger (IHX) effectiveness have been optimized to reach the maximum energy efficiency in each operating condition. Although HFC-245fa exhibits energy performance attributes, its high Global Warming Potential (GWP) is an issue for climate change mitigation. Hence, multi-objective optimisation of the environmentally friendly working fluids Butane, Pentane, HFO-1336mzz(Z), R-514A, HCFO-1233zd(E) and HCFO-1224yd(Z) has been carried out. The results show that the system proposed, working with HFC-245fa, achieves a Coefficient of Performance (COP) of 2.44 for condensing temperature of 140 °C, operating in HTHP mode, whereas the ORC mode provides a net electrical efficiency of 8.7% at condensing temperature of 40 °C. Besides, HCFO-1233zd(E) and HCFO-1224yd(Z) are both appropriate alternatives for the HFC-245fa replacement. These working fluids provide a COP improvement of 9.7% and 5.8% and electrical net efficiency improvement of 2.1% and 0.8%, respectively, compared to HFC-245fa. This paper provides a reference study for further designs and developments of reversible HTHP-ORC systems used for industrial low-grade waste heat recovery

Lightweight, affordable, low power solar groundwater piston pump for rural remote regions.

Solar photovoltaic powered groundwater pumping systems (SPWPS) are popular way of fetching water from boreholes in semi-arid areas in rural remote regions of most developing countries, where commercial water and electricity supply is out of reach. As the climate changes and the water table drops in such marginal regions, borehole depth is ever increasing into hundreds of metres below the ground surface. In a SPWPS, the required energy to fulfil water demand at a certain head is termed as the required hydraulic energy which is maintained by the pump unit of SPWPS. However, this acts ultimately as a load on the PV generator. The pump unit typically requires more power in order to maintain this hydraulic energy. For high head systems, groundwater piston pumps perform better than centrifugal pumps. A detailed literature review established that the current piston pumps have design limitations that act as load on the pump driver, which uses extra external and internal mechanical components. These include long piston drive rods, connecting rod, meshing gears, crossheads and crossways. This study put forth a new concept design of a groundwater piston pump optimised for power consumption using a scotch-yoke mechanism that excludes unnecessary components in the pump in order to conserve power usage. A mathematical model was built to support the claim of low power consumption by the new pump design. The widely-used computer aided design and finite element analysis (CAD/FEA) technique was used to ensure the structural viability of the concept design for high head application, which is based on material selection process. The study also compares the concept pump power consumption among existing photovoltaic (PV) operated pumps including piston rod and non-piston rod pumps. The developed mathematical model for power consumption finds significant power savings when compared with benchmarked low-power long-piston rod pumps. For example, with a 200 m head and 10.2 lpm flow demand, the proposed pump uses up to 22.4% and 7% less power than a pump that uses either a steel or glass fibre reinforced composite (GFRC - e.g. polyester) rod, respectively. Hydraulic efficiency calculations show an increase of up to 76.7% compared to 59.5% and 71.4% using steel and GFRC piston rods, respectively. Additionally, significant energy savings of 1505.7 Wh/day and 383.7 Wh/day are also found for daily pump operation compared to commercial steel and GFRC piston rods pumps, which consequently reduces the associated costs of PV panels. Design safety factors of the conceived pump for high head loads such as 200 m are evaluated using structural FEA. Material selection process based on performance indices is also carried out using the Cambridge Engineering Selector (CES Selector) program. The design of the proposed pump components was also optimised for mass, based on the fatigue life constraint of selected materials using a FE parametric approach coupled with material variation. The optimisation model developed in this study reduces the mass with optimum fatigue safety factors contrary to yield strength criteria, incorporating performance factors such as material cost and energy consumption. Stainless steel 'BioDur 108' was found overall to be the best contender, with optimised dimensions saving up to 29.39% of mass and material cost, along with 29.25% reduction in power consumption. In conclusion, the developed design for a groundwater piston pump in this study is optimised for low power consumption, along with structural suitability for SPWPS with high head requirements in rural remote areas. The pump design's structural adequacy is checked by FEA, material selection and design optimisation. The pump is also suitable for other locations depending on its structural ability to withstand loads with suitable materials

Tapered-amplified AR-coated laser diodes for Potassium and Rubidium atomic-physics experiments

We present a system of room-temperature extended-cavity grating-diode lasers (ECDL) for production of light in the range 760-790nm. The extension of the tuning range towards the blue is permitted by the weak feedback in the cavity: the diodes are anti-reflection coated, and the grating has just 10% reflectance. The light is then amplified using semiconductor tapered amplifiers to give more than 400mW of power. The outputs are shown to be suitable for atomic physics experiments with potassium (767nm), rubidium (780nm) or both, of particular relevance to doubly-degenerate boson-fermion mixtures

An Optimised Investment Model of the Economics of Integrated Returns from CCS Deployment in the UK/UKCS

Publisher PD

Integrated simulation for (sustainable) building design : state-of-the-art illustration

Many buildings are still constructed or remodelled without consideration of energy conserving strategies or other sustainability aspects. To provide substantial improvements in energy consumption and comfort levels, there is a need to treat buildings as complete optimised entities not as the sum of a number of separately optimised components