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• 2050 low-carbon economy pledge and Spanish photovoltaic investment plan. • Photovoltaic spatial allocations minimising unpredictable variability. • Impact of wind energy investments on the optimal photovoltaic spatial allocation. • Allocation of photovoltaic and wind investments minimising supply–demand mismatch. • Assessment of the current photovoltaic investments in Spain. After a period of stagnation that lasted until approximately 2018, Spain has established an ambitious investment program in photovoltaics, derived from the pledge to switch to a carbon-free energy system by 2050, the sustained cost decreases of the technology, and the excellent irradiance values over its territory. This paper implements an additional criterion for the spatial allocation of these investments based on minimising the energy variability generated because of weather intermittency. The analysis is based on hourly data for the years 2005–2020 (inclusive), in various locations homogeneously spread throughout Spain. Subtracting the deterministic daily and annual irradiance cycles to estimate the variability of the random component is discussed. Failing to do that yields significantly higher and distorted values for solar energy variability, resulting in low investment proportions when combined with other energies, like wind. The first results show that a straightforward, equally-weighted allocation of investments is suboptimal. It is also shown that investing in low-irradiance locations contributes to reducing overall variability. Secondly, the study analyses overall power variability minimisation conditional on a given wind investment weight. It is found that the impact is significant spatially, and that proportions of wind energy above 10% increase aggregated variability across all levels of aggregated power generated. Nevertheless, investment proportions in wind energy below 10% reduce the overall combined variability significantly due to the negative correlation between wind and solar irradiation. The third point addressed is the minimisation of the mismatches between renewable energy supply and aggregate electricity demand. The optimal proportion for solar and wind investments becomes close to 50% in this case. However, this proportion tilts towards solar investments if variability minimisation is also considered. Finally, the current spatial distribution of photovoltaic investments in Spain is analysed, and it is shown that there is room for improvement. It is also found that the current ratio between wind and photovoltaic energy may not be optimal, and that it would be advisable to increase proportionally more photovoltaic energy. [ABSTRACT FROM AUTHOR]