Series or Parallel?

[ZoNiE]

I was hoping to find some slightly smaller 100W panels to do just that, have four, in two parallel strings, or two larger 200W-ish panels with higher Voltage, But the only ones that seem to be available locally are the positive grounded ones. This being a Trailer, well, that was a non-starter. The old 100W siemens panels are loooong gone.

I could conceivably put a fourth panel, either as a loose mount, or hinged with the single one where it would only deploy when I am camping, so those two would be "off" leaving the two others to work alone when the trailer is sitting in my driveway for weeks on end. I could still get the fourth matching panel from the guy...

Another thing is, at 520W, the array is "excessive" on the Kid calculator (1.3), so I decided not to do that.

Then, I had also considered a 65W panel from the same series, to add to the lone panel, as there is room to do that, but then I would have a lower voltage on one string. I'm a bit anal about matching things, and, that one panel currently would cost 2X what My 130's cost.

I have a good way to run the three to a junction box in an upper cabinet, and install the three 10A pushbutton Breakers I am using, and then a 30A PB breaker for the run to the Kid. (I have tons of these things already for free).


http://www.alliedelec.com/search/productdetail.aspx?SKU=70128888

[Free Energy Freak]

Another thing is, at 520W, the array is "excessive" on the Kid calculator (1.3), so I decided not to do that.

Mine is maxed out at 405 watts (3 x 135, series), currently. That is 1.0. But, I don't get anywhere near that. Mine is closer to 325 watts, usually?

With system losses, you won't be anywhere near that high. Instead, you will probably be right at 1.0.

[Westbranch]

you could add some voltage drop by using undersized wire...

[tecnodave]

Zone,

Those breakers are rated for DC but only 50 volts but breakers are worth the trouble when krap happens.

I think that you should not try to match up mismatched panels.....things get too complicated. Three panels should be fine, I used old Siemens 55 watt panels for years but prices are falling and I am getting new panels for 33 to 75 cents a watt.....some old stock that has outdated MC-3 connectors....some odd ball.....some off brand but I stick with 72 cell panels so all will have same voltage.

On the current limit on the kid......I have 1020 watts in at 70 volt strings and can produce 30 amps at 31.5 volts .....942 watts out......kid got a bit warm at 53 deg. C. so my current limit is set down to 25 amps (found in battery menu)  to protect my equipment.  The current limiter is very active and is able to protect the kid from too much power. I have just received a second kid and plan to team them up with even more panels.  Running at that high a power level is taxing on the equipment.....my goal is never to exceed 80%  max power and run at more like 66 % of maximum power.



My motorhome is rarely  driven......it's used as a mountain cabin.....solar panels mount on a rack made up from awning arms and mounts. It's 7 feet wide and a bit over 16 feet long, folds down flat on roof and tilts up to 35 degrees....has 6 Sharp 170 watt  72 cell polycrystalline panels for 24 volt system , plus 8 Siemens 55 watt 36 cell monocrystalline panels for 12 volt system .   Air conditioner was in the way and was removed...I need to park east or west as rack will tilt either way.....Sun must be off side of motorhome.....

td

[ZoNiE]

EF, and TD, I was thinking about that. Will I Really get 520W. No, probably not.

My TT will eventually be a starter mountain cabin.

Prolly should get that 4th panel.

BTW, my panels have MC3's. came with 12Ft extensions for 18' total each line. Nice.

Also Nice to know the Kid will protect itself.

The CB's are 28VDC rated, btw.

Thanks for all the real world info folks. Just what I need.

[Westbranch]

Thing about solar power is:  once you have some you want more.... and will use more...

[Highflyer]

ZoNie,

I have three 230's attached to a Kid in 12V for now.  It makes better power on cloudy days like today(240watts), and in full sun, it makes 415 watts (30 amps).  Yes I am waisting some power, but the Kid has no problem with the extra on sunny days.  I'll check the temp on the next full sun day I am out there.  I am running an 12V 65 CFM fan 24/7 to keep everything cool, so that is going to reduce the temps some. 

I like having the extra power on cloudy days, and autumn is just around the corner.

My next Kid is going 24V and six panels.  I'll report as things go.

[Free Energy Freak]

Thing about solar power is:  once you have some you want more.... and will use more...

It's worse than drugs I tell ya! Worse than drugs!! I need my fix!

[tecnodave]

Over paneling is not a bad thing......just watch the current and temps. I was getting 130 watts out of 1020 watts of panels in yesterday morning through heavy fog. When the fog broke at 1:30 I was way behind in getting full charge so set current limit up to 30 amps and turned diversion off and saw 800-900 for early afternoon..... Floating by 5:30.....could not have done that without the big array. Tracer booster controller has been removed to make room for kid number two. I might just push things a bit and add 1050 watts of Eoplly 72 cell panels and experiment with bully mode or follow me.

My portable home  is now fully powered by Kid's and the Classic powers a 40 foot high cube shipping container portable workshop

5 years ago I had some ancient Siemens 30 cell panels, a sun saver and a D-8 truck battery....now three MidNite controllers , 9 other brand cc's and about 70 panels, 4 battery stacks

My real nickname is tecnojunkie ....according to the other side! I don't really have a defense on that!

td

[ZoNiE]

Thing about solar power is:  once you have some you want more.... and will use more...

Yup.

It's worse than drugs I tell ya! Worse than drugs!! I need my fix!

And Yup.

[New KID On The Block]

Zonie,

In your case parallel would better for two reasons ......the charge controller will be more efficient at a 1.4 to 1 conversion ratio than it will be at 5 to 1 conversion........more work to do....more heat..less efficient and with your RV  you will be much more likely to have  of shading issues. Parallel configurations will be less affected as only the shaded panel will have a power loss where if you are all in series all panels in the string will be down to the same power as the shaded panel.

td

tecnodave, wow, that's something I hadn't read/heard before -- yes, I'm definitely a newbie so that's no big surprise. I have (4) 100w panels. I have them wired up in series. I thought MPPT worked better the higher the difference between the PV voltage and the battery bank voltage.

Maximum Power: 100W   Maximum System Voltage: 600V DC (UL)
Optimum Operating Voltage (Vmp): 18.9V   Open-Circuit Voltage (Voc): 22.5V
Optimum Operating Current (Imp): 5.29A   Short-Circuit Current (Isc): 5.75A

My battery bank consists of (2) 125Ah 12v batteries wired in series to form norminal 24v bank. I was actually thinking of adding two more 100w panels, for a total of (6) panels in series. 22.5v x 6 = 135v, so still under the KIDS limit of 150v. According to your posting above, this is a bad idea? I would prefer not to deal with parallel setup as I prefer not to deal with combiner boxes.

BTW, I haven't been able to get more than just over 300w from my (4) 100W panels.   
I used 10AWG wires from PV panels to the KID, less than 40 ft. Should be more than sufficient for 5.75A though, right?

[Vic]

Ho  NKOTB,

Personally,   think that running 113 Vmp string voltage on a 24 V bank is a bit much ...  Have not read all of your posts to try to guess just where you are located,  to better estimate just how cold your PV environment might be ...  But  with a 600 STC Watt array and the envisioned HIGH string voltage,  think that the KID will run HOT,  and probably reduce its output current to try to keep cool.

Have you tried the KID String Sizer (?):
http://www.midnitesolar.com/sizingTool_kid/index.php

That might help you determine the best string arrangement.

And,  as you probably know,  the STC power specs are for PV cells that are at 25 degrees C.  When PVs are exposed to the sun,  they become warm/hot.   This reduces the output voltage and therefore the output power.  Normally one would estimate that in full sun,  midday,  with the PVs oriented at right angles to the sun that one would produce about 75% of the  STC rating.  On hot days,  a bit less,  and a bit more on cold days.  So your 300 W output is right in there.

My opinions,  Have Fun,    Vic

[Free Energy Freak]

I thought MPPT worked better the higher the difference between the PV voltage and the battery bank voltage.

I run double the battery bank voltage, on my PV array. As TD previously stated, the more the controller has to downconvert, the more inefficient it will be.

BTW, I haven't been able to get more than just over 300w from my (4) 100W panels.   

75%, not bad.

[New KID On The Block]

Ho  NKOTB,

Personally,   think that running 113 Vmp string voltage on a 24 V bank is a bit much ...  Have not read all of your posts to try to guess just where you are located,  to better estimate just how cold your PV environment might be ...  But  with a 600 STC Watt array and the envisioned HIGH string voltage,  think that the KID will run HOT,  and probably reduce its output current to try to keep cool.

Have you tried the KID String Sizer (?):
http://www.midnitesolar.com/sizingTool_kid/index.php

That might help you determine the best string arrangement.

And,  as you probably know,  the STC power specs are for PV cells that are at 25 degrees C.  When PVs are exposed to the sun,  they become warm/hot.   This reduces the output voltage and therefore the output power.  Normally one would estimate that in full sun,  midday,  with the PVs oriented at right angles to the sun that one would produce about 75% of the  STC rating.  On hot days,  a bit less,  and a bit more on cold days.  So your 300 W output is right in there.

My opinions,  Have Fun,    Vic

Thanks for replying Vic.

I live in sunny Silicon Valley -- south part of greater San Francisco Bay Area.  My environment is not cold at all. I think you have a good point about both the KID and solar panels running hot. Hmm.. So if I want to add more solar panels to my rig, my realistic option would have to be series-parallel string of panels?

Well I'm glad to read that my ~300W of power production is about right. I took a photo of today's best reading: 306W. 
That's the best I've achieved so far.

Yes, I have used that KID String Sizer tool before but I'll go take a look at it again. Thanks. 

[New KID On The Block]

I thought MPPT worked better the higher the difference between the PV voltage and the battery bank voltage.

I run double the battery bank voltage, on my PV array. As TD previously stated, the more the controller has to downconvert, the more inefficient it will be.

BTW, I haven't been able to get more than just over 300w from my (4) 100W panels.   

75%, not bad.

Thanks for commenting FEF.

I'm starting to understand that down converting from high panel voltage to lower battery bank voltage will incur efficiency losses at the KID, but I'm also concerned about losses due to wiring (size and length) from PV panel to the KID. The way I'm thinking, I'll have less voltage drop on the cabling from the PV panels to my charge controller by having all 6 panels chained in series. All that voltage would only be putting out about 5.3A to the KID. Is the DC voltage down conversion at the KID losing that much more than my gain from the lower voltage drop of using higher voltage from panel to KID?