Probably the most efficient 4kW system available. 

16 x Sanyo 250Wp array controlled by a Fronius 3.6kWp transformerless  inverter. The system is predicted to generate 3416 kWh units per year!

The Sanyo panels are 18% efficient and now come with a 10 year workmanship guarantee and a 10 year / 90% and 25 year / 80% output guarantee. The Fronius inverter is 97.2 % efficient and comes with an upgradeable 5 year guarantee.

The Sanyo panels have black frames which with matching panels clips looks very good on this modern slate roof.