East/West Facing Panels

ChrisOlson

We recently put in 1 kW additional installed capacity made up of four 250W Helios panels (30.8 Vmp). I wired the east facing panels series, the west facing panels series, and parallel'd them into the combiner. Then feed our new XW-MPPT60 solar controller with it.

Our house roof is 22.5° slope (5/12 pitch), facing east and west.

Comparing the energy production of this array to our south-facing array (3.5 kW) on a Classic 150, and tilted at optimum angle for this time of year, there is no difference in kWh output/kW installed capacity - 5.6 kWh/kW is what I have been getting from both arrays for the month of March.

I have seen the XW-MPPT60 getting 1,014 watts out of the east/west array at solar noon with the bank absorbing at 62.0.

I had asked about doing this in an earlier thread once. But now I have actually done it and got hard numbers on how it performs. And I'm going to say it works fine. I don't think you'd want to try it with east facing panels in series with west facing, as it would probably confuse the controller.

But now that I've seen that it works we're going to extend the rails and throw another kW up there in April because one of the things we're putting in this year is a 2-ton Trane central AC unit. We decided we're not going thru another summer of torture in the heat like we did last year - and our XW will run the AC unit with no problem if we can throw enough solar at it
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Chris

icarus

Re: East/West Facing Panels

For the sake of argument you could run multiple controllers. For example 1 for the south faxing array,and 1 each for the east ns west faxing arrays. Not a particularly cheap alternive, but in the grand scheme of things, the increased production might make it worth the cost?

Tony

ChrisOlson

Re: East/West Facing Panels

Tony, my gut feeling is that it wouldn't make any difference.

Basically, from sunup to 10:00 in the morning the east/west facing array tends to produce slightly more watts/kW installed capacity than the south facing array does, simply because the sun is coming up due east now and those east-facing panels come up to full power pretty fast after sunup.

For two hours on either side of solar noon the south facing array pulls ahead and produces more watts/kW, but it's not much. Afternoon is like morning in reverse and the west facing panels stay at full power for a long time.

So I don't think putting a controller on each "bank" would improve anything. The panels seem to perform good under a 5 Vmp swing with no problem. And, for example, when the east ones are at full power they get hot which reduces their Vmp some. And at the same time the west ones don't have optimum sun angle so they're running cooler. With the less than optimum sun angle they seem to put out normal amps for that sun angle at the lower than rated Vmp that the east ones are running at.

At the end of the day, the total energy production from either array (south facing vs east/west) has been the same per kW installed capacity with close to one month of data collected on it. So my conclusion is that there's two options:
- buy another controller for $480 and probably not see any improvement
- buy four more panels for $1,400 and see a 100% increase in energy production

It's a no-brainer. The controller won't pay for itself. The extra panels will.
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Chris

gww1

Re: East/West Facing Panels

For referance,

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

I say one cc is a better arangement.

Now to hijack the thread a bit, What would be the startup surge and running watts of a two ton trane a/c unit? I think I have a reem or something but reading the lable I wasn't sure what it ment.

I wondered what kind of solar/inverter I would need to supliment its running for a portion of the day-light with out having to add to the battery bank.

Cheers
gww

ChrisOlson

Re: East/West Facing Panels

It's interesting that the graph that fellow shows is about how it works here - the east facing panels come up to full power really fast in the morning. But I get more of a peak than he's getting because my panels are 22.5 degrees tilt instead of 60 degrees, like he did. I don't think he's making maximum use of his east/west panels with 60 degree tilt - he's just trying to get a flat power curve. I wanted to see if putting panels in the arrangement I have works as well as south facing. At this time of the year it does, and I am convinced as summer progresses it will work better.

The Trane XR13 2-ton pulls 8.7 amps @ 240V for the compressor and 1.3 amps @ 120V for the fan. Locked rotor amps is 47 for the compressor. So you will need 12 kW surge capacity to start one with pressure on the head.
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Chris

gww1

Re: East/West Facing Panels

Chris
Thank you
gww

icarus

Re: East/West Facing Panels

I am not arguing that one "should" use multiple controllers, but merely that one could. You are right, with the price of the PV as cheap as it is, adding more PV makes better financial sense. It like the argument I have always made against multiple axis trackers. For the price and headache of a tracker, a few more watts of PV is usually more cost effective, especially now that PV is under $1/watt.

Tony

gww1

Re: East/West Facing Panels

One thing that would make it hard for me to change and there fore I have "two" charge controllers, is I have done built the majority of my solar ground mount facing south and it would not be cheep to build two more facing different directions.

How many sentances did I put in to one sentance?

It is hard to learn fast enough, you don't want to keep changing stuff cause you learned more and never get anything installed. If I ever move and do it again I hope you guys have did it long enough (and tell me about it) so that I know what to do next time.

cheers
gww

ChrisOlson

Re: East/West Facing Panels

I don't know if the east/west thing is good for everybody. I did it because I ran out of rooftops facing to the south. I can't use a ground mount here. The panels end up being a snow fence and the one time I tried it several years ago the array got buried under a 12 foot deep snow drift. I went to dig it out with the skid steer loader and the weight of the snow on it busted 3 panels.

These new ones I put in, I think, will work good 9 months out of the year. And the main reason I'm putting them east/west is for extra power to run our new AC unit in the summer. We got lots of wind power for winter, so I don't need them then anyway.
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Chris

gww1

Re: East/West Facing Panels

Chris
I'm not off grid and I don't have the snow but If my inverters would do it and I had the extra power during the day I would sure like to run some ac. I am wanting to up my bought panels to about 6000 watts but I want to stick with the 16 sams club batteries. I would need to come up with a trasfer switch for the ac to take if off grid and put it back on based on time of day and sunlight. I am going to have the hot water opertunity load which may be enough to eat my extra power If I even have any. I figure the sub panel from the inverter will have to be loaded pretty light due to not enough batts so I am going to try and do whatever opertunity loading I can during the day. I mostly built a solar rack big enough for at least 5600 watts and I find I am probly going to fill it.

I might be crazy and nothing will work like I think it does.
Cheers
gww