Adding more panels

[jimbo]

After this bad weather (Winter in Victoria, Australia Lat 37.5 degrees) I have decided to add some more panels and try and get the most out of the Classic.  We get cold, wet winters (-3 at night and 8 degrees during day) and dry hot summers (10 degrees at night and 40+ in the day) so production varies widely throughout the year.

I currently have 14x170W Schott panels, Vmpp=35.5, Impp=4.78, Voc=44v.  These will soon be wired in series with 2 strings of 7 (Voc=90v but more like 63v under load). They are pointing directly North at 25 degrees (roof pitch) and now in the middle of winter the maximum i have seen is 64amps (briefly today) and 1880W (5 degrees Celcius outside and blowing a gale, wind chill -1). 

According to the manual with a 24v bank the midnite can handle 2700W/94amps. I was looking at adding some panels on my shed to gain a little more in winter, pointing them around 30 degrees west and tilting them 35-40 degrees.

1)When adding panels of a different brand/type and using an mppt reg what is the most important thing i should be looking for in the specs?

I really want to improve my winter power production But with 2300W of panels already I don't have much headroom although i never see that 2300W. 

My main worry is feeding too much into the classic and going over spec and doing some irreversible damage.  By facing the next string 20-30 degrees away from North i'm hoping to add power away from it's usual peak and increase charge later in the day.

Is there any way of adding a lot more panels and having the system limit the input so not to damage the controller?

Battery bank is 1660 amp, 24v Raylites.

Thanks

James


Sorry for all the questions but i have just switched from 2 x PWM controllers after spending quite a few months getting everything spot on but decided to move forward with mppt

[Vic]

Hi Jimbo,

The Classic has a reliable current limit which can be set manually,  and it should not allow maximum current or the current you have set  to be exceeded for more than a very short period of time.

You may find  some work that has been done by Gordon Loomberah interesting,   with his "Virtual Tracker" with PVs facing different directions on a single CC:

http://forums.energymatters.com.au/solar-wind-gear/topic5064.html

FWIW,  Vic

[jimbo]

Thanks for that. Already speaking to Gordon.

My problem is that on days like today where i'm averaging 300w in (just after midday) i would love more North facing panels (another 1kw would be great) but if the sun comes out....

[vtmaps]

When adding panels of a different brand/type and using an mppt reg what is the most important thing i should be looking for in the specs? 

It all depends on the configuration.  Each string should have the same Vmp.  Each panel in a string should have the same Imp.  Each panel in a string should have the same orientation. 

If your new panels have the same Imp as the old panels, you may want to add one new panel to each of your existing strings (assuming you have enough Voc headroom).

I really want to improve my winter power production But with 2300W of panels already I don't have much headroom although i never see that 2300W. 
<snip>
i have just switched from 2 x PWM controllers after spending quite a few months getting everything spot on but decided to move forward with mppt

Perhaps you should use your old PWM controllers with some of the (old or new) panels.  PWMs become more efficient as the battery voltage rises, so perhaps a few panels aimed at the late afternoon sun, through a PWM would help with the final stages of charging.

--vtMaps

[jimbo]

So has anyone successfully added say around 3kw (or more) of panels (24v bank) and then turned down the max output current to maybe 85 amps to give the controller a little bit of headroom and run a bit cooler.