A: Definitely for insulation and draft sealing, these often pay for themselves in the first winter. Adding window insert, particularly on drafty sash windows, will pay for themselves within 10 years. Solar panels will probably pay for themselves in 5-8 years. However, large academic studies show that house prices increase by between 4-7% by adding heat pumps and by similar amounts for adding solar panels. Both of these house-price increases would exceed the installation cost (after the subsidies) so adding heat pumps and solar panels is actually a good way to prepare your house for sale.