MC4 Connectors SUCK for off-grid systems!!!

[garybeck]

Whatever panel arrangement you come up with you still need about 135amps to charge that 1350Ah 12V battery system. The 90 amps you think you can get is still not enough.

If you have a 16.2kwh system you need to be able to generate 3 times that amount in 4 to 5 hours because people will just use as much power as they can. So that requires about a 10kw worth of panels. Good luck building that with 50watt panels.

Im going to have to disagree with you on that. the battery bank is just for storage, and you can't have too much storage, the array is what is sized to the load. the array size is properly sized for the load. i've done a load estimate, is about 3500 watt-hours per day. when you account for battery efficiency, and modules being rated at standard test conditions, I need to create about 5000 watt hours per day. the 940 watt array will create almost year round in Haiti, with ~5 peak sun hours per day. the battery size is based on days of autonomy and maximum depth of discharge. with 4 days of autonomy and 80% maximum depth of discharge, a battery bank of 16.5 KWH is called for. so my 16.2 is just about right. anything smaller would be too small.

with all due respect, I disagree with your method of calculating. you don't size the array by the size of the batteries. everything is sized from the loads. there has to be at least 4 days of storage in the batteries, based on the average daily load. or it is too small. if your battery bank can be charged up in 4 to 5 hours, it is too small. they don't need 10KW of panels just because the battery is a certain size. the array size is based on the load and so is the battery. I put another system in a different area of haiti 2 years ago and it is operating flawlessly and part of that is because I put 5 days of storage in the battery bank and a maximum depth of discharge on 80%. but i would do the same in the US.

your point is well taken that they could just drain the battery anyway and it would be nice to have more solar. but if that were the case then I would want to add more batteries. but I worked with them extensively on the load calcluations and that is where it all starts. they will be using 3500 watt hours per day and that's what we're designing the system around. on rare occasions when they need more they will have a generator.

no offense, and I appreciate your input.

-gary

[SunEagle]

thanks for your advice. to answer the questions...

-no i can't get any specs on the panels that are there already. they are in a very remote location, and they are bolted down with security bolts.

-when i originally installed the system I put a charge controller there. it has been removed.

-i might be able to get specs on the 160 watt panels I'm adding, but you should try communicating with people in Haiti and asking them to go to the store and take a picture of the label on the back of a panel. the bottom line is I'm not going to know for sure exactly what I have until I get there.

-i am wary of putting a PWM controller on one sub array and MPPT on the other. I think they will fight each other. as you know the battery voltage is affected by the charge rate. if one subarray decides to taper the charge, it will affect the system voltage and the other controller will react. I'm worried they will be in constant battle. that is why i wanted to wire these two sub arrays in parallel and get a high amperage controller to handle it all.

and now i'm running out of time to figure this out!

Whatever panel arrangement you come up with you still need about 135amps to charge that 1350Ah 12V battery system. The 90 amps you think you can get is still not enough.

If you have a 16.2kwh system you need to be able to generate 3 times that amount in 4 to 5 hours because people will just use as much power as they can. So that requires about a 10kw worth of panels. Good luck building that with 50watt panels.

[garybeck]

Bite the bullet and buy a cheap 30 amp PWM controller for the 50 watt panels and series wire all four of the 160 watt panels into the Midnite Solar controller.. THAT is how to keep this as simple as possible.

But i take that all back if you have a Classic and it's charging now.
Do the panels have a Vmp spec printed on them ?
50W:___
150W: ___

thanks for your advice. to answer the questions...

-no i can't get any specs on the panels that are there already. they are in a very remote location, and they are bolted down with security bolts.

-when i originally installed the system I put a charge controller there. it has been removed.

-i might be able to get specs on the 160 watt panels I'm adding, but you should try communicating with people in Haiti and asking them to go to the store and take a picture of the label on the back of a panel. the bottom line is I'm not going to know for sure exactly what I have until I get there.

-i am wary of putting a PWM controller on one sub array and MPPT on the other. I think they will fight each other. as you know the battery voltage is affected by the charge rate. if one subarray decides to taper the charge, it will affect the system voltage and the other controller will react. I'm worried they will be in constant battle. that is why i wanted to wire these two sub arrays in parallel and get a high amperage controller to handle it all.

and now i'm running out of time to figure this out!

[littleharbor]

Bite the bullet and buy a cheap 30 amp PWM controller for the 50 watt panels and series wire all four of the 160 watt panels into the Midnite Solar controller.. THAT is how to keep this as simple as possible.

[Mike90250]

Unless it's already installed and you are adding to it, I don't believe the Midnight Classic 150 can charge a 12V bank from only 19V panels. I think it needs more overhead voltage. But i take that all back if you have a Classic and it's charging now.
Do the panels have a Vmp spec printed on them ?
50W:___
150W: ___

You might be better off using the 50w panels with their current controller, and wire the new 150's in series for 100V and let the Classic do it's MPPT magic downconversion

Also, with all the parallel panels, you really should use Combiner Boxes with fuses or breakers in them. Breakers will make troubleshooting easier.
ATC fuses and fuse holders often fail with the continuous power a solar system puts through them, their spring contacts are OK in a car, but not for long period high amp applications.

Before you wire all the parallel batteries up, study the smartguage article on parallel batteries, and wire them the best you can.

http://www.smartgauge.co.uk/batt_con.html

[garybeck]

MPPT controller, series wired panels. Combiner boxes, or Parallel branch connectors.

ok i should explain more.

there is already there an array of (6) 50-watt 12V panels (with no charge controller).
im adding a 2nd array of about 600 more watts. I don't want to install 12 more 50 watt panels. I can get 150 watt panels at a decent price there.

i think this is a rare situation where it makes sense to wire all the panels in parallel. there will be two sub-arrays, but they are both 12V and the arrays themselves are in parallel, meeting at the input of the single charge controller (90-amp midnite solar).

i don't think it would be a good idea to have these 50 watt panels and 150 watt panels in series. and I don't want two charge controllers. I have to keep this thing as simple as possible.

schematic.jpg

[littleharbor]

MPPT controller, series wired panels. Combiner boxes, or Parallel branch connectors.

[garybeck]

That would be foolish, there is no reason to parallel panels.

what do you mean there is no reason to parallel panels? i'm working on a 12V system that has a 12V inverter and 12V battery and 12V panels. unless i wire each module directly to the charge controller, I don't see a way around makng parallel connections.

[Sunking]

I am also having that problem and was thinking can I splice the cables and solder them the are 210w 47v panels and I'm a long way from the shop but have a soldering iron any help greatly appreciated

That would be foolish, there is no reason to parallel panels. You can solder providing you meet two NEC conditions.

1. Solder cannot be used to make the electrical connection.

2. Solder cannot be used to make the mechanical connection

[bcroe]

For anything exposed to water, I use a couple methods. One is to install weatherproof connectors. Those could be automotive
grade or MC4s. Note that MC4s left unconnected too long can be corroded and may fail later or not even mate. Don't leave
panels sitting around with loose leads; plug them together.

My other method is to coat the splice with liquid tape, then immediately install some snug heat shrink over it. When the liquid
tape squeezes out both ends of the heat shrink, its fairly waterproof.

MC4 splitters might plug together, but remember the current capacity of them is limited. Maybe not so good for a low voltage
high current setup. The object here is to get a durable design together in an expedient manner. The warrantees may fall where
they may, they haven't been very useful in my life. Bruce Roe

[Wy_White_Wolf]

I am also having that problem and was thinking can I splice the cables and solder them the are 210w 47v panels and I'm a long way from the shop but have a soldering iron any help greatly appreciated

Doing so will void the warrantee on the panels.

WWW

[Szabie]

I am also having that problem and was thinking can I splice the cables and solder them the are 210w 47v panels and I'm a long way from the shop but have a soldering iron any help greatly appreciated

[garybeck]

One of many adapters
http://www.aliexpress.com/product-fm...olesalers.html

thanks. that is exactly what I needed. too bad I didn't know they exist before I left. that's what I get for quitting my job at Real Goods 15 years ago. I'm still stuck in the solar stone age. Next time I'll get those.

[billvon]

I just got back. Everything went OK but I have to rant a little bit about MC4 connectors. THEY SUCK! I can see they would be nice if I had to string a bunch of panels together in series. But don't you think if a panel is 55 watts and 12 Volts that there's a good chance that the user would want to wire them in parallel?

Yes! Splitters, my good man, splitters.

[Naptown]

One of many adapters

http://www.aliexpress.com/product-fm-img/521472866-Free-shipping-by-Post-1-pair-of-MC4-Parallel-connector-Adapter-1M2F-2M1F-TUV-certification-wholesalers.html