A construction block (10) is described, comprising an input wall (16) and an output wall (22) spaced apart from the input wall (16), a void (32) being formed between the input wall (16) and the output wall (22), wherein the input wall (16) has a plurality of projections (18) formed integrally therewith, the projections (18) extending toward but stopping short of the output wall (22) and serving to disrupt convection currents forming in the void (32), at least one of the projections (18) comprising a solar concentrator which has a photovoltaic device (28) mounted thereon.