Benedict Winchester

Agrivoltaic systems offer the potential to boost land productivity, reduce water consumption and improve access to energy: an energy-food-water nexus solution. Agrivoltaic systems are promising for regions with relatively low land productivity and both energy- and water-access challenges, such as sub-Saharan Africa. However, there is a lack of research exploring the use of agrivoltaics in such contexts. This study addresses that gap. It uses both energy-system and crop modelling to explore optimal agrivoltaic system design and deployment for a medium-sized farm, located in Zimbabwe, where electricity is expensive and unreliable. We compare conventional, ground-mounted PV mini-grid systems with three agrivoltaic system configurations. We model fixed-tilt, single-axis tracking and vertical bifacial configurations installed above wheat and maize. We calculate the optimal required system sizes at 100% and 95% reliability levels. We find that the cheapest agrivoltaic system (on a unit cost basis) is single-axis tracking, with a unit cost only 11% higher than the ground-mounted PV at an equivalent 95% reliability level. Under our base-case scenario, high electricity costs from the grid mean that the farm is operating with a deficit (when considering crop revenues). However, with agrivoltaic systems, the deficit is significantly reduced and at 95% reliability, the farm becomes profitable with crop revenue exceeding upkeep costs. Of the agrivoltaic systems, all were profitable though this varied depending on the ratio between module spacing and height (P-by-H ratio). We found greater system profitability at higher P-by-H ratios, with the largest improvement when switching from a P-by-H ratio of 2 to 3. All agrivoltaic system types can achieve land-equivalent ratios (LERs) greater than 1, depending on the P-by-H ratio, indicating improved efficiency. Our calculation of the price-performance ratio (PPR) found that all system types were economical.

Around 700 million people around the world do not have any electricity, and there are many more that only have access to electricity some of the time. Many of these people live in places that are hard to reach, and solar (photovoltaic) panels are a good way for them to get electricity. However, installing new solar panels can be expensive. Knowing how much electricity people need, and how much they might need in the future, is important to make sure that the right number of solar panels are installed, and in the right places, so that nobody goes without electricity. In this article, we discuss how openly available computer programs can help us to work out the best way for these communities to receive electricity.

Despite recent improvements to electricity access in lower-income countries, reliability remains low for many. Local renewable electricity infrastructure supplementing the national grid offers a promising route to improved reliability for rural communities. However, improvements in the reliability of national grids create risks for investors including the possibility of “stranded” renewable assets. We use energy-system modelling to explore ways in which solar photovoltaic (PV)-based mini-grids could be interconnected with national grids. We explore the impact of reduced electricity demand to quantify the investment risks of losing customers. Our results indicate that national grid–connected mini-grids can reduce the unit electricity costs for communities whilst also increasing reliability and reducing the carbon intensity of electricity in line with Sustainable Development Goal (SDG) 7. Reductions in demand have a minimal impact at lower levels but at moderate levels are likely to undermine economic viability. Finally, we discuss policy interventions to facilitate and protect investing in national grid-connected mini-grids.

Approximately 80% of the global population without access to electricity live in sub-Saharan Africa (SSA) with rural areas disproportionately affected. Solar-powered mini-grids are being used to increase rural electrification. However, their deployment is hindered by high costs, low electricity demand, and limited incomes in rural households. Agriculture constitutes 70% of rural incomes in SSA and faces threats due to a reliance on rainfall coupled with low irrigation levels in the context of climate change. Irrigation loads have been suggested as a strategy to enhance the economic viability of solar mini-grids by boosting electricity demand: reducing the levelised cost of used electricity (LCUE) whilst improving farmer yields and incomes. This study investigates a case study in Tanzania, selected based on the amount of population without access to electricity, the potential for irrigation, and the prevalence of photovoltaic solutions in the least-cost pathways for rural electrification. The seasonality and timing of irrigation demand, as well as crop mixes, are varied to optimise for the lowest LCUE using the open-source modelling framework continuous lifetime optimisation of variable electricity resources. Evapo-transpiration and energy-system modelling are used to estimate energy demand. We find that adding irrigation loads has the potential to increase the LCUE and lower asset utilisation (load factor) when compared to residential loads but that, by selecting crops with longer growth periods, optimising irrigation timing, and implementing multiple planting seasons, the LCUE can be up to 7% less than residential-only systems with an increase seen in asset utilisation. LCUE values of 0.54–1.30 $/kWh were found: higher costs were associated with shorter crop-growth periods, single planting seasons, and poorly timed irrigation loads whilst lower costs were observed with bimodal cropping and solar-coordinated irrigation times. The research highlights that, when incorporating irrigation loads into rural-electrification strategies, specific factors should be considered to enhance their viability within mini-grids in SSA. We recommend to both policymakers and mini-grid developers to promote multiple planting seasons (bimodal cropping) and encourage optimal crop mixes where relevant alongside irrigation schemes and rural electrification projects as well as adopting the use of flexible tariffs for irrigation loads.

Photovoltaics (PVs) are a critical technology for curbing growing levels of anthropogenic greenhouse gas emissions, and meeting increases in future demand for low-carbon electricity. In order to fulfill ambitions for net-zero carbon dioxide equivalent (CO₂eq) emissions worldwide, the global cumulative capacity of solar PVs must increase by an order of magnitude from 0.9 TW_p in 2021 to 8.5 TW_p by 2050 according to the International Renewable Energy Agency, which is considered to be a highly conservative estimate. In 2020, the Henry Royce Institute brought together the UK PV community to discuss the critical technological and infrastructure challenges that need to be overcome to address the vast challenges in accelerating PV deployment. Herein, we examine the key developments in the global community, especially the progress made in the field since this earlier roadmap, bringing together experts primarily from the UK across the breadth of the PVs community. The focus is both on the challenges in improving the efficiency, stability and levelized cost of electricity of current technologies for utility-scale PVs, as well as the fundamental questions in novel technologies that can have a significant impact on emerging markets, such as indoor PVs, space PVs, and agrivoltaics. We discuss challenges in advanced metrology and computational tools, as well as the growing synergies between PVs and solar fuels, and offer a perspective on the environmental sustainability of the PV industry. Through this roadmap, we emphasize promising pathways forward in both the short- and long-term, and for communities working on technologies across a range of maturity levels to learn from each other.

The Royal Society and UK Department for International Development supported a consortium of three universities across sub-Saharan Africa and Imperial College London with the aim of developing new knowledge on direct-steam-generation concentrated solar power (CSP) plants and supporting relevant capacity building across the Universities of Lagos, Mauritius and Pretoria. Key research findings from the programme include an improved flow-classification scheme for two-phase, liquid–liquid flows; testing of advanced surfaces with much-improved steady-state heat transfer performance—the commercial nanoFLUX surface showed up to 200% higher heat-transfer coefficients (HTCs) in pool boiling compared with other surfaces with R-134a/R-245fa; first-of-a-kind measurements of transient flow boiling HTCs, which were up to 30% lower in step perturbations than quasi-steady-state expectations in horizontal pipes with R-245fa; error estimation and corrections for laser-induced fluorescence (LIF) measurements, leading to the development of an adapted planar LIF technique with uncertainty <10% for local, instantaneous film thickness measurements in annular flows, and the application of such diagnostic methods to pool, falling-film and flow boiling in pipes; and predictions of an ~80% increase in the net present value of a case-study CSP plant when integrated with solid storage media.

We compare the performance of photovoltaic (PV), flat-plate and evacuated-tube solar-thermal (ST), and hybrid photovoltaic-thermal (PV-T) collectors to meet the energy demands of multi-effect distillation (MED) desalination plants across four locations. We consider three scales: 1700 m³day⁻¹, 120 m³day⁻¹ and 3 m³day⁻¹. We find a strong dependence of the capacity and configuration of the solar collectors on both the cost of sourcing electricity from the grid and the specific collector employed. We find specific costs as low as 7.8, 3.4 and 3.7 USDm⁻³ for the three plant capacities. We find that solar-driven systems optimised for the lowest specific cost result in CO₂eq emissions equal to, or higher than, those from grid-driven reverse osmosis (RO) and in line with PV-RO. This highlights the need to consider the environmental footprint of these systems to ensure that desalination is in line with the United Nations’ Sustainable Development Goal 6.

Off-grid photovoltaic systems have been proposed as a panacea for economies with poor electricity access, offering a lower-cost “leapfrog” over grid infrastructure used in higher-income economies. Previous research examining pathways to electricity access may understate the role of off-grid photovoltaics as it has not considered reliability and carbon pricing impacts. We perform high-resolution geospatial analysis on universal household electricity access in Sub-Saharan Africa that includes these aspects via least-cost pathways at different electricity demand levels. Under our “Tier 3" demand reference scenario, 24% of our study’s 470 million people obtaining electricity access by 2030 do so via off-grid photovoltaics. Including a unit cost for unmet demand of 0.50 US dollars ($)/kWh, to penalise poor system reliability increases this share to 41%. Applying a carbon price (around $80/tonne CO₂-eq) increases it to 38%. Our results indicate considerable diversity in the level of policy intervention needed between countries and suggest several regions where lower levels of policy intervention may be effective.

We compare the performance across different locations of systems employing photovoltaic (PV) panels, flat-plate and evacuated-tube solar-thermal (ST), and hybrid photovoltaic-thermal (PV-T) collectors to fulfil the energy demands (both thermal and electrical) of multi-effect distillation (MED) desalination plants. We consider large- (1700 m³/day), medium- (120 m³/day) and small-scale (3 m³/day) MED plants. We find a strong dependence of both the capacity and configuration of the solar collectors used on both the cost of sourcing electricity from the grid and the specific collector employed. We find mean grid-electricity fractions range from 47%, for the lowest grid-cost location, to 2.5% for the highest grid-cost location. We find that systems using PV-T and ST collectors meet between 49% and 62% of the hot-water demand at these locations, respectively. We find lifetime costs for the smallest-, medium- and largest-scale plants' energy-generation systems as low as 0.209, 3.35 and 50.8 million USD, respectively, corresponding to specific costs of 6.37, 2.55 and 2.74 USD/m³. We find that systems using solar collectors, when optimised for the lowest specific cost, result in associated CO₂eq emissions equal to, or higher than, those associated with grid-driven reverse osmosis. These results highlight the need to consider the environmental footprint of these systems, not only their cost, to ensure that desalination is in-line with the United Nations' Sustainable Development Goal 6 (SDG6).

The rising energy prices in Europe and the urgent need to address global warming have sparked a significant increase in the installation of domestic photovoltaic systems to harness solar energy. However, since solar energy is available only during daytime hours and its availability varies daily, effectively shifting energy use becomes crucial. Whilst batteries can assist in storing excess energy, their high prices hinder their widespread adoption. In this study, we explore the importance of load to maximise return on investment. We propose an incremental approach to fitting load profiles into the production envelope, allowing for practical implementation. We compare different meter resolutions: 1 second, 5 minutes, 15 minutes, and 1 hour. Our analysis reveals that making real-time decisions (per second) leads to significant energy savings of 16\% compared to hourly decisions. Furthermore, we explore three types of device management strategies: ON/OFF management independent of PV production, ON/OFF management based on the current PV production, ON/OFF management based on both current and forecasted PV production, utilising an optimal fit algorithm. Through our study, we demonstrate that our implementation of the third approach outperforms a standard management approach, resulting in more than 17% cost savings. This study provides insights into the optimisation of load-shifting strategies in domestic photovoltaic installations, highlighting the importance of load control and the potential benefits in maximising the utilisation of solar energy while minimising energy costs and environmental impact.