It's not just the unit itself, but everything the sun shining on nearby heating the air which is getting blown through the coils. The temperature increase effec

It's not just the unit itself, but everything the sun shining on nearby heating the air which is getting blown through the coils. The temperature increase effect is also superlinear; the efficiency goes down as the temperature increases so 250W extra heating might cause an extra 120W of loss (that number is made up, but the amount is greater than zero).