To face the grand challenge of transforming the energy system to include at least 42 % photovoltaic energy in 2050 (as forecasted in a scenario by IRENA), our proposed project, SITA, aims to explore innovative concepts for tandem solar cells based on two technologies with strong competence base in Europe: Silicon Heterojunction (SHJ) and high bandgap Cu(In,Ga)(Se,S)2 (CIGS). A novel tandem concept with a 2-terminal (2T) approach requiring no additional cables or electronics will be developed, enabled by recent and further development in wide gap CIGS devices leading to high efficiency (>18%). SITA will demonstrate the durability of the new modules under realistic outdoor conditions delivering the next generation of stable inorganic tandem solar modules with superior device efficiency (>30%). SITA’s technology will build on and increase the efficiency of SHJ modules by a factor of 1.5 with marginal increase in the use of the costliest raw materials. This in turn leads to a considerable reduction in area related system costs of up to 25 % per installed power and a corresponding reduction in the levelized cost of electricity (LCOE). Tandem-junction efficiencies have recently approached or even surpassed the single-junction Shockley-Queisser limit for prototype devices. SITA will address the remaining limitations in terms of stability, scaling and manufacturing costs, as well as environmental impact.