new system I need to up efficency

[jim k.]

I've just built a new system here in the coast range in Oregon, sumertime isn't a problem but now with the fall and winter with fog, clouds and rain today with overcast I'm getting 4.2 amps to my charge controller. This is what I've got.

On a wooden frame work at a 45 degree angle facing directly south there are 7 grape solar 235 watt by 7.8 amp panels, going thru two runs of #6 copper75 feet to a disconnect then to a morningstar tristar 60 charge controller to two rolls s 530 batteries, I don't have any intention of having anything but a backup power system, no grid tie, would adding more panels or a different charge controller or maybe moving everthing right at the panel location be the answer, I'm a farmer with a wife who is starting to look sideways whenI talk about buying more stuff.

[Vic]

Hi jim k,

In this exact situation,  if you had twice the number of PVs,  you would expect to have almost exactly twice the power that you noted,   assuming that there no shadows on the current array that you have.

Assuming that the present array has no shadowingf except early and late in the day,   moving or reorienting the array that you have may make some small differences.  Perhaps changing the tilt angle of the array could make a small difference,  but Nov,  Dec,  Jan and Feb are usually poor production months,  due to low sun elevation/short days,  cloudy,  stormy days and so on.

You will need to monitor the State Of Charge of the batteries,  and have an additional charger available  if there are too many dark days in a row.  Hope that you have and are using a Hydrometer to measure the SOC.

http://www.nrel.gov/rredc/pvwatts/grid.html
It is often surprising just how little PV arrays produce when there is significant overcast.  Our eyes,  and brain tend to mislead us on just how much solar energy is available with cloudy skies.

If you cannot cast a significant shadow,  usually,  there is not much solar power available.  This is a poor description,  but you get the idea.

The US Government site NREL,  has some great resources for estimating monthly production for almost any location in the US:
http://www.nrel.gov/rredc/pvwatts/

There is an additional page for a bit more comprehensive estimator, PV watts II:
http://www.nrel.gov/rredc/pvwatts/grid.html

Others will have additional/differing comments.  Have fun with the new system,  Vic

[jim k.]

vic, I noticed you did not mention my charge controller, would a mppt contoller maybe up things a little on these cloudy days. thanks jim

[Vic]

Hi Jim,

YES,  I needed to look at the Data Sheet on the Grape PVs.  Are these PVs GS-P-235-PDX??

They are probably similar if not exactly that model.  60 cells per panel.  Well,  the DS for those note 8.09 Imp,  so mabe not what you have ...  hmmmmm

PWM CCs are best if the PV module string voltage does not exceed the battery V by too much.  Looks like your system is 12 V.  The ideal string voltage would be about 17.7 volts Vmp or so.

What is the exact model number of the PV modules that you are using?
Vic

[jim k.]

does this sound right, gsp-235-f-ab1

[Vic]

OK,  Thanks Jim,

OK,  as you were saying,  the TS-60 CC  will waste quite a lot of power due to the  highish string voltage.

You must be running all seven PVs in parallel.  No problems,  hope that each  PV module has a fuse or circuit breaker in the Combiner Box.

For a 12 volt system,  you have too much available current in full sun -- around 110 amps in Bulk,  and early Absorb.  So with a single MPPT CC,  like the Classic or Classic Lite,  at peak sun, will clip and waste the power that exceeds its maximum rated current.  This would only be an issue if the batteries needed fairly heavy charge currents around solar noon,  or if the loads on the system were heavy enough to demand this amount of current.

Some council against running a CC an input that exceeds its max output capability.   And if the temerpature of its surroundings is HOT,  it would result is additional clipping and power waste potential.

On a 12 volt system the maximum available charge current to the batteries is 96 Amps with reasonable ambient temps.

Here is a comparison chart of a number of Charge Controllers:
http://www.midnitesolar.com/pdfs/comparisonChart.pdf

The Classic 150 has the largest output current of any mainstream CC,  into 12 V batts.  There is a Classic Lite which has almost a $100 lower street price,  by substuting LEDs and DIP switches in place of the MNGP's four line LCD display/controls.  The Classic  is really very hard to beat,  and it just keeps getting better.   More Later,  Vic

[mtdoc]

Vic has hit on the issue I believe.  You will get much better output from a MPPT controller with those panels.

If they are 235 watt panels with a Imp of 7.8 amps then that means the Vmp is about 30 Volts.  Using a PWM controller with these on a 12 volt system will not be making even close to full use of their potential.  And their voltage is too low to use with a 24 volt system.

With an MPPT controller you will see much better power output - cloudy or sunny!

[jim k.]

thanks guys, I am starting to get educated now, prior to finding this forum I checked out a lot of sites but everything was always kind of general in discussion.

[Westbranch]

JIM, you did not discuss loads yet, there might be a need to up the system voltage to 24 based on what the backup system needs to run, IE FRIDGE, FURNACE... these are big loads for a 12v system...

[jim k.]

my loads are really quite lite, I've done things like a tankless propane wt ht and propane kitchen range, in times of emergency I would need to power a medium size chest freezer, lights and tv and such plus this computer, yesterday for a test I ran my grain mill grinding flour with good results, my inverter is about twice the size of my draw if that makes any difference, I don't know, it was sold by a usa company but made in china.

[Westbranch]

have you used your Kill a Watt meter on the freezer yet? If it is older it will have a high start-up load.

[jim k.]

freezer is two years old.  I've also got the backup generators but my goal is not to run them

[Westbranch]

Jim, did you design the system yourself or did you have a contractor do it?
Do you have a transfer switch for the 'backup' loads? 
Kind of sounds like there is a bit of experimentation going on.

[jim k.]

as you can guess I did it myself, and I guess there was never any intention of doing anything but being able to charge the batteries and use the excess power during the day for what ever, one idea was to have timers on things like the freezer to only let them use power say between 12 noon and 6pm

[Westbranch]

If you had a Classic there are options for the controller to do that switching for you when for example, absorb is reached.