One of the constraints of solar power is that it is not always available: it is dependent on daylight hours and clear skies. In order to fill these gaps, a storage solution or a backup infrastructure of fossil fuel power plants is required — a factor that is often ignored when scientists investigate the sustainability of PV systems.
Morgan Stanley expects off-grid solar PV to be commercially viable in some European countries and across most of the USA by 2020
Lead-acid batteries easily double the energy and CO2 payback times of a solar PV system
If solar panels and batteries are produced in China, the CO2-emissions are double those of conventional grid electricity
6.6 kWh Energy management and lithium-ion storage solution in one. Bosch Power Tec.
The total storage capacity to be manufactured over the complete lifetime of a solar PV system is 6 times lower for lithium-ion than for lead-acid
Off-grid solar systems with lithium-ion battery storage can have GHG emissions below 30 gCO2e/kWh if they are produced in countries with clean electricity grids, and installed in countries with high solar insolation and carbon-intensive grids.