Earlier quoted context omitted.
Panel temps go up and down depending on time, date, location, and weather. On cool, sunny spring days you can see panels produce more than they are rated. You can’t simply apply a fixed worst-case derate for all time to all panels regardless of installation details. Further, the derates are not additive, they are multiplicative. (A a 20% panel which has degraded in lab efficiency by 10% operating at 90% thermal effic…
A device that's 15% efficient is inherently more wasteful than a device that's 100% efficient, right? Therefore we're wasting something . That thing isn't input fuel, it's the materials used to build the device, and manage its lifecycle. That doesn't mean it's free - it just means we're considering different inputs. Total efficiency here is the sum of all inputs over outputs. For solar panels that's land use, that's…
You are confusing operating/marginal efficiency with lifetime efficiency. Think about a power plant as a series of payments. You have one big up front payment to build the thing and a series of smaller payments to buy fuel and run it.
For solar, those smaller payments are zero. There is still the fixed upfront payment and that is why you would prefer 40% efficient panels to 20% efficient panels everything else being equal.
The marginal cost of rooftop solar is zero. Nothing is wasted. Really! No fuel is bought, the roof underneath is cooler and lasts longer, there are systemic benefits, etc. There is virtually no maintenance. No land is used (Solar land use is complicated but most places you can put solar wouldn’t support a nuclear plant). Light which would have bounced back into space or turned into infrared is instead made into usable, high grade energy. Land/build area that would otherwise do nothing is made useful. It is literally close to economic and physical magic. It is true that panels break, inverters die, upgrading is compelling, etc. However, most components are silicon, glass, copper, and aluminum. These are some of the most recyclable materials on earth. There are plenty of analyses of lifecycle energy and material costs and it is generally pretty favorable (1-2 year operating recovery time). The panels are warrantied in many cases for 25 years so idk where your 20 year then scrap lifespan comes from. Inverters tend to be the weaker link.
Finally batteries have marginal round trip efficiency because what you put in doesn’t come back out 1-1 so I am not sure I follow your point.