Imperial College London

Philip Sandwell

Faculty of Natural SciencesDepartment of Physics

Academic Visitor







Blackett LaboratorySouth Kensington Campus





Publication Type

15 results found

Sandwell P, Winchester B, Beath H, Nelson Jet al., 2023, CLOVER: A modelling framework for sustainablecommunity-scale energy systems, The Journal of Open Source Software, Vol: 8, Pages: 1-5, ISSN: 2475-9066

Sustainable Development Goal 7 aims to provide sustainable, affordable, reliable and modernenergy access to all by 2030 (United Nations, 2015). In order for this goal to be achieved,sustainable energy interventions in developing countries must be supported with design toolswhich can evaluate the technical performance of energy systems as well as their economic andclimate impacts.CLOVER (Continuous Lifetime Optimisation of Variable Electricity Resources) is a softwaretool for simulating and optimising community-scale energy systems, typically minigrids, tosupport energy access in developing countries (Winchester et al., 2022). CLOVER can be usedto model electricity demand and supply at an hourly resolution, for example allowing users toinvestigate how an electricity system might perform at a given location. CLOVER can alsoidentify an optimally-sized energy system to meet the needs of the community under specifiedconstraints. For example, a user could define an optimum system as one which provides adesired level of reliability at the lowest cost of electricity. CLOVER can provide an insightinto the technical performance, costs, and climate change impact of a system, and allow theuser to evaluate many different scenarios to decide on the best way to provide sustainable,affordable and reliable electricity to a community.CLOVER can be used on both personal computers and high-performance computing facilities.Its design separates its general framework (code, contained in a source src directory) fromuser inputs (data, contained in a directory entitled locations) which are specific to theirinvestigations. The user inputs these data via a combination of .csv and .yaml files. CLOVER’sstraightforward command-line interface provides simple operation for both experienced Pythonusers and those with little prior exposure to coding. An installable package, clover-energy, isavailable for users to download without needing to become familiar with GitHub’s interface.Informat

Journal article

Matthey-Junod A, Sandwell P, Makohliso S, Schönenberger Ket al., 2022, Leaving no aspect of sustainability behind: A framework for designing sustainable energy interventions applied to refugee camps, Energy Research and Social Science, Vol: 90, Pages: 1-20, ISSN: 2214-6296

The issues of forced displacement and energy for sustainable development are convergent: an estimated 90% of displaced people globally have no access to electricity, while 85% of refugees are hosted in developing countries. However, few tools to plan and design sustainable energy access interventions have been transposed to displacement settings. This paper presents a novel framework for the holistic planning of energy projects which considers both sustainability aspects and the specificities of displacement settings. The framework is the result of a review of literature which aimed to define a “sustainable energy intervention” in displacement contexts and an assessment of relevant planning tools against this definition. The framework includes the use of an energy delivery model toolkit, an inclusive design approach, an assessment of the desired impacts, energy system modelling, business model design, and an assessment of economic viability. We apply the framework in the design of a solar mini grid of Holl Holl refugee camp in Djibouti, in which a sustainable intervention and business model are proposed that could be compatible with the local conditions. We highlight issues that arise from the humanitarian sector status quo and propose that this framework could help to enhance sustainable energy practices in the humanitarian and development sectors.

Journal article

Sandwell P, Candelise C, Solomon B, Few S, Ghosh A, Wu B, Blanchard R, Barton J, Panocko J, Milanovic Jet al., 2022, The role of mini-grids for electricity access and climate change mitigation in India, The role of mini-grids for electricity access and climate change mitigation in India


Few S, Barton J, Sandwell P, Mori R, Kulkarni P, Thomson M, Nelson J, Candelise Cet al., 2022, Electricity demand in populations gaining access: Impact of rurality and climatic conditions, and implications for microgrid design, Energy for Sustainable Development, Vol: 66, Pages: 151-164, ISSN: 0973-0826

Almost 800 million people currently lack access to reliable electricity, for many of whom solar microgrid systems are expected to be the most cost-effective solution. Quantifying current and future electricity demand is crucial for cost-effective design of reliable microgrids. However, electricity usage is connected to a wide range of social and economic factors alongside climatic conditions, making estimation of demand challenging. This paper presents a framework facilitating each stage of solar microgrid design from demand estimation through to cost-optimal sizing of the microgrid and its economic and environmental characterisation. Household demand is simulated based upon (1) climatic conditions, (2) appliance ratings and usage patterns, and (3) rates of growth in appliance ownership based upon the Multi-Tier Framework for measuring household electricity access. Microgrid demands are simulated based on the combination of these with (4) nondomestic demand based upon locally available data. The framework is demonstrated across four rates of domestic demand growth and two climatic conditions (‘tropical savanna’ and ‘humid subtropical’), alongside nondomestic demand based upon two operational microgrids (one rural and one peri-urban). When growth rates are high, newly introduced appliances tend to dominate, with differing impacts on the demand profile depending on power and usage times. Cooling represents a modest contribution to demand in the tropical savanna climate. However, in the hotter and more seasonally varying humid subtropical climate, cooling becomes the dominant driver of demand, increasing seasonality and proportion of demand at night. Nondomestic demand in the rural microgrid is primarily agricultural, and exhibits more seasonality and better alignment with daylight hours than demand in the peri-urban setting, which is more service-based. Across cases, increased seasonality and proportion of demand at night lead to poorer alignme

Journal article

Thomas PJM, Sandwell P, Williamson SJ, Harper PWet al., 2021, A PESTLE analysis of solar home systems in refugee camps in Rwanda, Renewable and Sustainable Energy Reviews, Vol: 143, Pages: 1-12, ISSN: 1364-0321

There is a paucity of data on energy access in refugee camps and limited analysis regarding the viability of modern energy technologies such as solar home systems in these contexts. This paper addresses these by presenting an overview of the household and small enterprise electricity access situation in Kigeme, Nyabiheke and Gihembe camps in Rwanda and through the application of a Political, Economic, Social, Technological, Legal and Environmental (PESTLE) analysis to assess the barriers influencing solar home system provision. Most households and small enterprises currently have limited or no access to electricity and there is significant unmet demand for energy services such as mobile phone charging, lighting, and entertainment in the camps. The analysis suggests that solar home systems can meet these energy needs and identifies important factors in ensuring projects are successful. Projects should be informed by the needs and priorities of end-users and should be aligned with national policies, such as achieving Tier 2 energy access, to garner political support. Where possible, local market systems should be nurtured to normalise paying for energy products and to avoid free distribution. This can support private sector engagement and result in longer system lifetimes through improved maintenance. Energy literacy programmes can also improve awareness of solar home systems and their benefits compared to traditional sources of energy. These findings can inform practitioners on the supporting policy/financial frameworks, design requirements and implementation measures needed to maximise the benefits of future solar home system projects and help achieve electrification targets.

Journal article

Baranda Alonso J, Sandwell P, Nelson J, 2021, The potential for solar-diesel hybrid mini-grids in refugee camps: A case study of Nyabiheke camp, Rwanda, Sustainable Energy Technologies and Assessments, Vol: 44, Pages: 1-18, ISSN: 2213-1388

Electricity access in refugee camps is often limited to critical operations for humanitarian agencies and typically powered by diesel generators. We study the economic and environmental benefits that optimised fully renewable and diesel-hybrid mini-grid designs can provide in humanitarian settings by displacing diesel use. Considering the case study of Nyabiheke camp in Rwanda we found that these benefits are substantial, with total cost and emissions reductions of up to 32% and 83% respectively, and cost payback times ranging from 0.9 to 6.2 years. Despite their different cost structures, we find that all levels of hybridisation provide cost and emission savings compared to the incumbent diesel system, with hybrid systems being able to offset emissions more cost-effectively than fully renewable systems. We highlight how modelling tools can facilitate the introduction and progressive expansion of systems, improving asset utilisation and reducing lifetime costs compared to one-off installations, and can inform operational considerations on the ground. These benefits are enhanced when connecting productive users for whom demand matches the solar generation profile. Multiple energy needs and objectives can be met simultaneously but financial resources, environmental considerations and operational timeframes will influence the most appropriate system design for humanitarian actors on a case-by-case basis.

Journal article

Chambon CL, Karia T, Sandwell P, Hallett JPet al., 2020, Techno-economic assessment of biomass gasification-based mini-grids for productive energy applications: The case of rural India, Renewable Energy, Vol: 154, Pages: 432-444, ISSN: 0960-1481

As the costs of solar PV continuously decrease and pollution legislation imposes less burning of agricultural residues, decentralized renewable energy is increasingly affordable for providing electricity to one billion people lacking access to a power grid. This paper presents a techno-economic feasibility case study of biomass gasification in off-grid and grid-connected mini-grids for community-scale energy application in rural Uttar Pradesh, India. Energy demand data was collected through surveys in a village with irrigation and agro-processing loads and off-grid households and used to construct a seasonal load profile based on statistical methods. This was used to simulate single-source and hybrid mini-grids based on solar PV, biomass gasification and diesel generation using HOMER Pro. Hybrid PV-biomass or PV-diesel systems were found to offer the highest reliability for off-grid power at the lowest cost. Single-source PV was cheaper than biomass gasification, though the cost of electricity is highly sensitive to biomass supply and gasifier maintenance. Both renewable options were around half the cost of diesel generation. The findings held across grid-connected systems with weak, moderate and strong reliability of grid supply. This suggests that biomass gasification-based mini-grids are not cost-competitive with PV unless the two generation sources are combined in a hybrid system, though they require operational testing prior to implementation.

Journal article

Baranda Alonso J, Sandwell P, 2020, Sustainable mini-grid systems in refugee camps: A case study of Rwanda, Sustainable mini-grid systems in refugee camps: A case study of Rwanda,, Publisher: The Grantham Institute, 12

This briefing note considers how clean energy solutions can be used by humanitarian organisations to both reduce the cost and environmental footprint of their operations, and promote the resilience and independence of displaced communities. Using Rwanda as a case study, the authors provide recommendations for how the private sector and policymakers can encourage greener humanitarian operations.


Sandwell P, Ekins-Daukes N, Nelson J, 2017, What are the greatest opportunities for PV to contribute to rural development?, SNEC 11th International Photovoltaic Power Generation Conference and Exhibition (SNEC), Publisher: Elsevier Science BV, Pages: 139-146, ISSN: 1876-6102

Minigrid systems powered by solar photovoltaics and battery storage are being deployed around the world to provide basic energy access and facilitate economic development. We use a minigrid simulation and optimisation tool that we have developed to assess various minigrid options in meeting the growing electricity demand of a community in rural Uttar Pradesh, India, in terms of the reliability of the service they provide, the cost of electricity, and total greenhouse gas emissions. We assess the breakeven distance at which off-grid minigrids are favourable in comparison to extending an unreliable grid network with a minigrid backup system, both with and without a carbon price. We suggest that policy recommendations that would encourage the use of minigrids for sustainable rural development, for example allowing subsidies to be available for system expansions and minimum service reliability requirements.

Conference paper

Sandwell P, Chambon C, Saraogi A, Chabenat A, Mazur M, Ekins-Daukes N, Nelson Jet al., 2016, Analysis of energy access and impact of modern energy sources in unelectrified villages in Uttar Pradesh, Energy for Sustainable Development, Vol: 35, Pages: 67-79, ISSN: 0973-0826

Bringingaccesstomodernenergysourcestothepoorestinsocietyisakeygoalofmanypolicymakers,businessesandcharities,butinorder tobea success projects and schemesmust be foundedonaccuratedata. We undertooka survey of energy demand and usage patterns in households in unelectrified villages in Uttar Pradesh, India toassess access to and utilisation of energy sources for lighting and cooking. The times of usage were recordedand analysed and the effect on usage patterns of transitioning from traditional to modern energy sourcesis assessed. We quantify the cost and greenhouse gas emissions of current energy use in order to provide abenchmark of potential mitigation through the use of renewable energy technologies: a typical householdwith kerosene lamps only for lighting spends INR 3243 (US$50.67) and emits 381 kgCO2eqper year; householdswithmoderncookingenergyspend17%morethroughincreasedusage,butemit28%lessgreenhousegasescom-pared to those with traditional stoves only. Cell phone ownership was found to be 50% amongst adults. We usedemographic and utilisation data to construct an hourly demand profile of basic electricity demand extrapolatedto each month of the year, and present an example of aspirational demand assess the impact of desirable appli-ances. A Monte Carlo simulation is used to highlight the daily and seasonal variation in total energy and powerdemand. A hybrid system, with solar power and battery storage meeting daytime demand and higher-capacitydiesel- or biomass-powered generation meeting the remainder during evening peaks and winter months,would satisfy demand most effectively.

Journal article

Ekins-Daukes NJ, Sandwell P, Nelson J, Johnson AD, Duggan G, Herniak Eet al., 2016, What does CPV need to achieve in order to succeed?, 12th International Conference on Concentrator Photovoltaic Systems (CPV), Publisher: American Institute of Physics, ISSN: 0094-243X

The recent and dramatic reduction in flat-plate crystalline silicon (c-Si) technology has changed the competitive land-scape for concentrator PV (CPV) systems. Three system cost targets are considered, €1/Wp corresponding to the system cost of c-Si today, €0.75/Wp corresponding to the likely c-Si cost in 2020 and €0.5/Wp corresponding to a likely lower limit for c-Si in the long term. To compete successfully with c-Si, system efficiency needs to be raised from the present 30% to 40%, suggesting cell efficiencies of 50% and module efficiency of 44%. The module should be manufactured at an area cost below €275/m2 which implies a packaged cell cost of €3/cm2 and module + tracking cost €190/m2.

Conference paper

Sandwell P, Duggan G, Nelson J, Ekins-Daukes Net al., 2016, The environmental impact of lightweight HCPV modules: efficient design and effective deployment, Progress in Photovoltaics, Vol: 24, Pages: 1458-1472, ISSN: 1099-159X

We present a life cycle analysis of a lightweight design of high concentration photovoltaic module. The materials and processes used in construction are considered to assess the total environmental impact of the module construction in terms of the cumulative energy demand and embodied greenhouse gas emissions, which were found to be 355.3MJ and 27.9 kgCO2eq respectively. We consider six potential deployment locations and the system energy payback times are calculated to be 0.22–0.33 years whilst the greenhouse gas payback times are 0.29–0.88 years. The emission intensities over the life- times of the systems are found to be 6.5–9.8 g CO2eq/kWh, lower than those of other HCPV, PV and CSP technologies in similar locations.

Journal article

Gambhir A, Sandwell P, Nelson J, 2016, The future costs of OPV - A bottom-up model of material and manufacturing costs with uncertainty analysis, Solar Energy Materials and Solar Cells, Vol: 156, Pages: 49-58, ISSN: 0927-0248

Organic photovoltaic (OPV) technology has the potential to provide cheap solar electricity, given advances in low-cost production and module efficiency and lifetime. However, several uncertainties remain in terms of the future costs of OPV modules, which depend on future material and manufacturing costs, as well as key performance characteristics. This assessment takes an engineering-based approach to assessing the potential future cost of each component of OPV modules, as well as the future scale of OPV production plants and associated scale economies, using stochastic analysis to account for uncertainty. The analysis suggests that OPV module costs could fall within a (interquartile) range of US$0.23–0.34/Wp, with a median cost estimate of US$0.28/Wp in the near-term, with future costs most sensitive to manufacturing scale, cell efficiency and module fill factor. This compares to a projected range of module costs for more established PV technologies (crystalline silicon, cadmium telluride and copper indium gallium selenide) of US$0.35–0.6/Wp by 2020. In levelised cost of electricity terms, OPV could compete with the established technologies in both roof- and ground-mounted systems if it can achieve a 10-year lifetime.

Journal article

Sandwell P, Chan NLA, Foster S, Nagpal D, Emmott CJM, Candelise C, Buckle SJ, Ekins-Daukes N, Gambhir A, Nelson Jet al., 2016, Off-grid solar photovoltaic systems for rural electrification and emissions mitigation in India, Solar Energy Materials and Solar Cells, Vol: 156, Pages: 147-156, ISSN: 0927-0248

Over one billion people lack access to electricity and many of them in rural areas far from existing infrastructure. Off-grid systems can provide an alternative to extending the grid network and using renewable energy, for example solar photovoltaics (PV) and battery storage, can mitigate greenhouse gas emissions from electricity that would otherwise come from fossil fuel sources. This paper presents a model capable of comparing several mature and emerging PV technologies for rural electrification with diesel generation and grid extension for locations in India in terms of both the levelised cost and lifecycle emissions intensity of electricity. The levelised cost of used electricity, ranging from $0.46–1.20/kWh, and greenhouse gas emissions are highly dependent on the PV technology chosen, with battery storage contributing significantly to both metrics. The conditions under which PV and storage becomes more favourable than grid extension are calculated and hybrid systems of PV, storage and diesel generation are evaluated. Analysis of expected price evolutions suggest that the most cost-effective hybrid systems will be dominated by PV generation around 2018.

Journal article

Emmott CJM, Moia D, Sandwell P, Ekins-Daukes N, Hosel M, Lukoschek L, Amarasinghe C, Krebs FC, Nelson Jet al., 2016, In-situ, long-term operational stability of organic photovoltaics for off-grid applications in Africa, Solar Energy Materials and Solar Cells, Vol: 149, Pages: 284-293, ISSN: 0927-0248

Journal article

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