Solar Panel Cost. The average cost to install solar panels is from $10,626 to $26,460 (after tax credit) for a 6kW to 12kW system to power an entire house. The average solar panel payback period is 7 to 12 years, and solar energy saves $600 to $2,000 per year on electricity costs.. Most solar panels last for 50 years, have a 25-year warranty, and start generating a return on investment after 8