Demands for electricity and hot water continue to rise worldwide, with many people in low-income countries, especially in rural areas, lacking access to these basic services. Decentralised minigrids, capable of powering small off-grid communities, are increasingly used in low-income countries as a means of providing power to the 13% of people globally without access to electricity. Hybrid solar photovoltaic-thermal (PV-T) collectors combine both photovoltaic (PV) cell and solar-thermal absorbers and, therefore, output both electricity and heat from a single collector with efficiency benefits over standalone PV panels and solar-thermal collectors. Despite this, no models have yet been developed capable of assessing the performance of PV-T collectors generalisable across a range of off-grid settings. We present an integrated model for simulating and optimising combined systems comprising PV panels and PV-T collectors, accurate to within +/- 5% rms error, connected to wider electrical and hot water systems, and employ this to evaluate their potential to meet both electrical and hot-water demands of rural communities. We provide a tool for simulating the lifetime output from
combined PV and PV-T systems, assessing their economic and environmental impact, and for optimising the systems to meet the needs of specific communities. We carry out simulations for a case study of a combined PV and PV-T system in Uttar Pradesh, India, and find that the system is able to meet 59.3% and 33.5% of hot water demand for upper and lower bounds for installed capacity. We carry out optimisations for static high demand and growing low-demand scenarios and find that that 35 kWpel and 5 hot-water tanks and 75 kWpel and 15 hot-water tanks are needed to meet these demand scenarios respectively.