Orientation of PV Modules

[WindFarmer]

Good day MidNite Solar Forum.

I am working in North Sudan on a mission with Medecins Sans Frontieres/Doctors Without Borders (MSF).

I was lucky enough to bring a few Kids with me to install in a few PV systems for remote hospital near the Ethiopian border.

On a mission a few years ago to Western Ethiopia near the South Sudan border I noticed a PV set up for a solar fridge that vaccines were stored in that had the orientation of the modules East/West on one string to take advantage of the morning/noon/evening sun, I’m guessing because it was located very close to the Equator and seemed to work well though I did not check any electrical measurements but I did notice the vaccine fridge always stayed at the required 2c-8c.

My question is how would the MidNite Solar Kid work in this configuration, half facing East half facing West on 1 string with a 25 or less degree tilt? We have four 80W BP modules that we are using for this part of the project.

Thanks for the help in advance.

[tecnodave]

Wind farmer,

All the panels in series with different orientation to the sun will comprise the output of power as the total string power will be limited to the maximum current from the most shaded panel.

A much better solution would be to split the strings in two and have one array facing approx 10:00 a.m sun and the other array facing 2:00 p.m. sun. These two strings would be connected in parallel. With only two strings of panels , the general consensus is no combiner is required.

Connected in this fashion the semi- shaded array will not limit the output of the more directed array.

If you go to 3 strings or more then the general consensus is to use a combiner which places a circuit breaker in series with each string of panels in case of a module failure or short in one of the strings.
The two good strings of panels would have enough power to force reverse current through the faulty string thereby possibly creating a fire hazard.

td

[Westbranch]

WF, how many panels do yo have and what size/composition is the battery?

[tecnodave]

WindFarmer,

I didn't look at the type of panels close enough!    Some of those BP 80 watt panels are thin film panels with a very high voc   The thin film panels are usually frameless. You do not see individual cells in this type of panel!
If this is what you have DO NOT USE SERIES CONNECTION!  The voltage will go way too high for the Kid.    This will cause non warranty damage to the Kid.  Read the labels on the panels and list here the v.o.c.    v.m.p.   i.s.c   and  I.m.p.  Values listed on the label and one of us tecno junkies will give the best advice on connections

I destroyed a BZ500 watt controller with First Solar CdTe thin film panels rated at 92 volts v.o.c.  One freezing morning the controller blew out before sunrise!

I don't think it's going to snow in the Sudan but what I am saying......leave plenty of margin....

Stay tuned.   td



Edited.  Additional data:      I think this is what you have:

   BP Thin film panel with following specs.    I didn't get a model number

V.o.c.  45.2   V.m.p.  32.8   I.s.c. 3.01   I.m.p.   2.48
  Black face. With silver band on outer edge...frameless     Glass front and back

If this is what you have you can use 2 in series in with 2 arrays in different directions, you can use 3 in series but this will stress the kid more because of the higher voltage....90-110 volts....4 in series will go over voltage and do damage

Back to option one.  2 arrays, each with 2 panels in series would be the best option


Disclaimer:   I'm an Alaskan!  what do I know about deserts?  lol

td

[WindFarmer]

 tecnodave

Thanks for the info. The BP modules are not thin film.

Here is a link I found for the specifications.


http://www.shop.solar-wind.co.uk/acatalog/BP_Solar_Panel_BP380J.PDF

Thanks for the help

[WindFarmer]

Westbranch

"We have four 80W BP modules that we are using for this part of the project." see post to  tecnodave for link of spec.

As far as batteries....Two Victron Energy 12V 220Ah Gel Deep Cycle Battery for 24V (or 12V in parallel) to run lighting.

Have a question concerning load sizing as well but I will hold off till this question is answered.

Thanks for the help.

[tecnodave]

WindFarmer,

Good deal, those are not the ones that I have has experience with, these are much better.
I think the thin films were discontinued due to low efficiency. The bp80 I had were almost as big as my 165 & 170 watt poly panels.

What you have are 36 cell polycrystalline, an excellent choice for your application.

If you are planning 24 volt them you will need two in series to get the required voltage, however if you are going 12 volt then there are more options series or parallel will work.

Please tell us a bit more about what you expect from your system, how far in wire run from the solar panels to the controller / batteries.  Plan on the controller being as close to the battery set as possible, charging will be better.

David

[mike90045]

These are 2, small pv panels, and have limited charging capacity.   A single LED light, recharging a phone or 3, or a couple hours of  laptop is about all these can manage to handle.   
but for getting a light in a remote area, or running a small RV water pressure pump for a couple minutes it beats dragging a generator

[tecnodave]

Mike,


I must disagree with that statement......he has 320 watts of panels and 400 or so a.h. of battery...and a first class controller!
No it will not run a first world house!    It will run many small electronic devices, lighting, and small refrigerator......keep in mind.....he is in Sudan!     It's a bit different there.  Doctors without borders runs a first class operation on a shoestring!     


Ok rant over,


David

[Westbranch]

Please let us know more about the loads.... unless that medical fridge is a power sipper, which I doubt, you will probably need about 1000W of panels.  battery determination to come once we know the specs on the fridge...

One major problem is the startup surge and the time between cycles...

[WindFarmer]

 Good discussion and allot to think about…….I was not in on the design  and most of the gear was already on site when I arrived and I cannot tell you how difficult it has been to source DC rated over current protection in Khartoum. I am definitely going to have to consolidate the system which brings me to my next question.

A large amount of 12V DC LED light bulbs where purchased to be installed in the hospital wards. Could I wire the battery bank and configure the Kid for 24V and run the load at 12V or am I restricted to match the battery to the load?

Honestly this is the first time I have used the Kid. I have one of the first Classics installed at my Homestead in Nebraska and truly love it not to mention most of my customers I fitted with the same gear and I have also been using the Brat for the ranchers for their remote fence chargers with the same success rate.

Again thank you for your help and for the kind words about MSF.

[tecnodave]

Wind farmer,

The load needs to match the battery bank unless you have a DC-DC converter.  That is going to be really hard to find there, stick with 12 volts for the lighting.

If you do get a DC-DC converter do not connect it to the load output of the Kid. The Kid output will be damaged by the input capacitors of the DC-DC converter but if that converter were hooked directly to the batteries it would work fine.

My system is 24 volts but I found LED bulbs meant for RV's that are rated 9-30 volts, but not all LED fixtures are wide range, read the documentation for the fixtures that you have, all LED lamps must use a voltage regulator/current limiter of some sorts. If you don't have docs send me the specs for what you have, I do a lot of research of super energy efficiency.

I am an California Certified Energy Auditor.      CEA #42   Been a interest a long time!

I do use two DC-DC converters on my system. I have a Samlex America SDC-30 buck converter and a Samlex IDC-360-24B fully isolated converter and both work very well.the latter one is very expensive but is totally isolated for noise free radio silence.

Dave


Edited to correct iPad's spelling attempts!

[tecnodave]

@westbranch

Wind farmer did not mention a fridge on this setup, he saw one on another mission

For your information those vaccine fridges are digital inverter compressors made by danfoss.....they will maintain required temp with only a 80 watt 36 cell panel and no battery in the desert! I have experience with them, awesome insulation and a very elegant design funded by the United Nations

I now have all digital inverter compressor refrigeration after I saw what they are capable of

I bought a very early production Grape Solar GS-5 ser # 28  and am super happy with it

Dave

[tecnodave]

@WindFarmer,

I am getting personal messages from you but they only contain my quote, your message is not included.........it's ok post a question here......I have a lot of respect for what your group does and will help any way I can

BTW, MidNite buys their din rail breakers from Circuit Breakers International , in South Africa, they are DC rated.....

Yeah I know just how hard it is to get things when you are not downtown!

I do not know a hill of beans about international shipping but will help in obtaining equipment for you

dave

[mike90045]

my bad, I thought I read 2, 80w panels.    Always good to have more power !