Climate change abatement requires the achievement of net zero carbon emissions by 2050. To achieve this there has to be a shift to global energy to electricity supplied by renewable energy technologies, the majority coming from photovoltaics with 8.5TWp total global installations by 2050. This is implementable if global installation grow at 5% p.a. from a base of 773.2 GWp total installations in 2020. Learning curve studies have shown that costs as low as $0.09/Wp for silicon modules is possible but with module efficiency only at 26.4%. There is a reasonable expectation that this level can be exceed in the next 30 years. Two technologies offer efficiencies beyond 30% namely tandem cells of III-V alloys on silicon and perovskite cells on silicon. Applying learning curve theory to present best production costs for these materials shows that cost of epitaxy is a limiting factor for III-V/silicon tandems while a module efficiency of 36% is required for perovskite/silicon tandems to be cost effective against the projected cost for silicon modules.