I used to have a system similar to what you are suggesting. Only 960watt solar and 24 volt batteries. I can recomend Morningstar.
Running since 2009 until I recently switched to a grid tied inverter. Never given any trouble. You will need to check if they have model suitable for 3.5kW solar.
When PV panels are new, and conditions are “just right,” each of your panels will indeed put out 500 (or very close to 500) Watts. As they age, their output dops off steadily till it reaches approximately 80% of the rating on the label. Degradation rates vary, but typically fall in the range of 0.3 to 0.5% per year.
So what are those “just right” conditions? Here’s a brief explanation:
PV panels produce their rated output at Standard Test Conditions which is:
Solar irradiance of 1,000 W/m2
Cell temperature is held constant at 25°C (77°F).
Air mass coefficient is 1.5.
However, STC are ideal conditions that don’t really occur in the real-world.
(e.g. when you put solar panels on a roof). To more precisely account for real-world conditions, the NOCT and later NMOT test conditions were introduced.
Temperature affects PV panels as well. As they heat up, their output voltage drops.
More info here:
So it’s quite likely your array isn’t putting out 3.5kW.
On another note…
You’d be much better served if you configured your system for 24 Volt operation
vice 12 Volt. At 24 Volts, the current will be half that of a 12 Volt system.
Mr Ohm tells us that losses in a conductor increase with the square of the current.
e.g. if the current is doubled, the losses increase by a factor of four.
That means larger conductors for a 12 Volt system vice what’s needed for a 24 Volt setup. Translation: That cabling will cost more. Possibly much more.
When PV panels are new, and conditions are “just right,” each of your panels will indeed put out 500 (or very close to 500) Watts. As they age, their output dops off steadily till it reaches approximately 80% of the rating on the label. Degradation rates vary, but typically fall in the range of 0.3 to 0.5% per year.Blockquote
I think that you’re unduly pessimistic. The 80% output at 25 years is the guaranteed performance; in real life the degradation is likely to be much less.
For instance these are 12 year old nominal 285W panels, peak output of 292W.
And these are also 12 year old nominal 280W panels, peak output 312W. (There’s partial shading and some of the panels are 220W which explains the output difference.)
Yes, high temperatures reduce output, but if you’ve got enough solar energy to raise the panel temperatures significantly you’re going to be well supplied with energy anyway.
Appropriate degradation rates of solar panels are estimated at 0.5% per year considering a well-maintained PV system featuring ideal conditions. However, solar panel degradation rates can reach up in some extreme cases, going as high as 1.4% or 1.54% per year.
That said, the reverse is also true in certain instances.
e.g. Top quality manufacturers like SunPower, have been able to reduce degradation rates to as low as 0.25%
Not necessarily. If it’s a hot day, yet cloudy, the insolation is not going to be there
like it would be in a cloud-free situation. Granted, that doesn’t happen most of the time, but it does happen.
