What happens if say 2 panels go down in 5 years time. Assuming the manufacturer is still around and honours the warranty, what if they no longer make the same panel? Can you substititue with different panels with different specs?
The other thing I was thinking about, If a single panel fails does this cause the whole array to stop functioning?
Different brands of panels run with different volts or amps.
However, an array with two strings could have one string replaced with new panels and the other old-but-functional panels used as spares for the other array. One day there could be quite a market in "used" solar panels of commonly-installed makes.
Or convert one string to two strings and use a dual-input inverter, or add a smaller inverter for the new string of replacement panels.
In fairness, the inverter is far more likely to malfunction than the panels.
I reckon that about half of all inverters will have failed by the time the system has reached half of its lifespan (13 years) and probably almost every inverter will be replaced/repaired at least once during the 25-year FiT timeframe. A few will be lucky and boast at how their inverter lasted the whole 25 years. Others will grumble becuase they were unlucky and had to replace the inverter two or three times.
As for the panels: I'd guess that less than half of the arrays out there will need any panels replacing during the lifespan of the system as the panels will probably degrade slowly rather than fail catastrophically. Of course, the panels may declinine in output as they age, due to occasional single-cell or failures or subsections of a panel - mostly suffering from a damaged connection due to weathering (hot/cold/wet/wind-stress etc).
But even if I lose a section of a panel, it'll not be a major influence on the whole system due to bypass diodes.
My panels are 6 rows of 10 cells, with every two rows being served by a bypass diode.
I have 15 panels.
That's 900 cells in 45 groups of 20 cells.
If I lose one group of 20 cells, it is about a 2.2% drop in output. From 3.6kW to 3.52kW.
Many manufacturers guarantee their panels to perform to 90% after ten years and 80% after 25 years. While we can't measure it exactly, we could certainly tell if the panels had degraded at twice that rate, but even if they did degrade twice as fast as expected, the FiT returns from the system would still be attractive.
At 21p and a cost of a £8500, 3.6kW system, total earnings (FiT, export tariff and bill savings, assuming 3% inflation and 3% energy price rises)
(20% loss of performance) 80% of performance after 25 years: £18300
(30% loss of performance) 70% of performance after 25 years: £17700
(40% loss of performance) 60% performance after 25 years: £17000
Chances are, that as time passes, the cost will continue to come down.
Look at today's biscuit-sized MP3 players compared to the book-sized, tape-playing "Walkman" of the 1980's. The cost and performance of a MP3 is dramatically superior to the Walkman. Solar technology will probably dramatically improve too, over the rest of our lifetimes
