Existing Solar Setup

[antonycurley]

Hi guys n gals?

Im a total newbie at all this solar stuff to be fair but have got half an idea about most things. This post is just about making the existing solar setup run better for a while - I have another system in planning which i will go into in another thread.

I have a small house in France, NO mains electricity at all. We don't need masses of power running toasters and kettles etc.

Currently there are some LED lights, a 12v USB charging point for a phone, a Shoreline 12v Fridge and an inverter for when i want to use the 240v cooker.

The previous owner has the panels set up something like this -

6 x 80w Baird panels, wired in pairs each going to their OWN Sinsola PWM (junk) charge controllers, he has then linked each charge controller and the last one outputs to the batteries! (does this means that we are getting the same output as one pair of panels??)

Panel data:
PMP - 80W
VOC - 21.8V
IMP - 4.55A


Then its off to the batteries which are 4 x 110ah 12v leisure batteries wired in parallel which can't be charged by those panels in that configuration??

I have removed one of the batteries and suspect i might have to remove another.....

So here is my proposal to get this system running a bit better -

5 x panels running in series which would give me -

PMP - 400W
VOC - 109V
IMP - 4.55A

If I'm correct?

These would be running into a MorningStar Tristar TS45 then out to the batteries which i would probably cut down to 2 in parallel to give me 12v - 220ah....

This is just a temporary solution to making good the existing system so that it works the best it can. I know about getting better panels, controllers, batteries etc and I'm in the process of sourcing everything for that so will post a different thread about that system.

Look forward to hearing some advice.

Antony

[MichaelK!]

Hello Antony. I can see at least three serious problems with the design that is resulting in the failure of your system. First, you are wiring panels in series while using a PMW controller, Second, you are wiring 4 low capacity 12V batteries in parallel, and three, you total power is inadequate for your application. Let's break the problems down one by one.

6 x 80w Baird panels, wired in pairs each going to their OWN Sinsola PWM (junk) charge controllers, he has then linked each charge controller and the last one outputs to the batteries! (does this means that we are getting the same output as one pair of panels??)

Panel data:
PMP - 80W
VOC - 21.8V
IMP - 4.55A

Your panels have a on-load voltage of about 17.5VDC. VOC means open circuit, or not connected to anything. You want to look at the Vmp, which is the voltage they will produce when connected to the load. It sounds like your panels are wired in a 2S3P configuration. That means you are feeding (4.55A X 3 arrays of two panels) = 13.65A at (17.5Vmp X 2 panels in series) = 35VDC into a PMW controller. Your batteries can only utilize 12-13VDC, so the rest of the power is totally wasted. You can only wire your panels in series if you have a MPPT controller like Morningstar's TS-MPPT-45 controller.

Then its off to the batteries which are 4 x 110ah 12v leisure batteries wired in parallel which can't be charged by those panels in that configuration?

Wiring batteries in parallel is NEVER a good idea. That's why they are trashed. Resistance inequalities result in unequal charging that results in one battery being chronicly overcharged and others chronicly undercharged. You need to replace these leisure batteries with off-grid batteries like two 6V L-16's, which will give you the same capacity, but in a single 12V string.

5 x panels running in series which would give me -

PMP - 400W
VOC - 109V
IMP - 4.55A

If I'm correct?

Absolutely NOT. This would be a perfectly good design if you had a MPPT controller, but you have a PWM controller. You would want to run them in a 1S5P configuration. That would give you ~23 amps of power at ~12-13VDC

Now, the power levels. Conventional thinking is to charge batteries at 1/8 to 1/12 of their capacity. In your case, (110AH X 4 batteries X 12VDC) =5280 watthours of power. Dividing 5280/12= 440 watts, 5280/8 = 660 watts. So, on paper, you want to charge at a minimum of 440 watts, but not much more than 660. However, panels almost never produce their rated output, so it's standard to derate panel output by 20%. So, the wattage you need is between 440watts/0.8 = 550watts to 660watts/0.8 = 825watts. You see, once factoring in derating, the wattage you actually need is about double of what you thought it was.

OK, to do this properly you need to replace almost everything. Buy 6V off-grid batteries and get rid of the leisure batteries. Buy Morningstar's MPPT controller instead of the TS-45 PWM one. Invest in larger 250-300 grid-tie style panels instead of those little Baird ones. Then you will have a reliable system that will not fail you.

[Mike90250]

welcome.
MPPT controllers generally work best being fed a PV voltage 2x battery nominal charging voltage. [ 12v battery charges at 15v, 30PV is a good start] As you increase PV voltage, MPPT efficiency decreases a % or 3. This gets dissipated as heat. Sometimes you evaluate the trade off between voltage/wire loss and expense of wire.

with the MS-TS-MPPT you are looking at, notice that the 60A model has a very handy Web HTTP interface

[antonycurley]

Thanks for the input so far guys. Im not entirely sure how they are wired now. They are probably in 2S3P as you say but each into their own controller which can't be great. Its difficult as I'm not actually in France at the moment to look!

I will run them at 1S5P into a PWM with the 2 batteries in parallel and see how it goes.

There is no point in me buying anything for this system as it will be getting torn down in 18 months to be replaced by 4 x Panasonic 285w HIT panels, a MPPT controller and 6volt batteries - I'm just trying to make this one perform a little better than it does at the minute.

Antony

[SunEagle]

Thanks for the input so far guys. Im not entirely sure how they are wired now. They are probably in 2S3P as you say but each into their own controller which can't be great. Its difficult as I'm not actually in France at the moment to look!

I will run them at 1S5P into a PWM with the 2 batteries in parallel and see how it goes.

There is no point in me buying anything for this system as it will be getting torn down in 18 months to be replaced by 4 x Panasonic 285w HIT panels, a MPPT controller and 6volt batteries - I'm just trying to make this one perform a little better than it does at the minute.

Antony

Depending on which PWM controller you have I doubt you will be able to wire all 5 panels in series because at 109V you will probably exceed the maximum DC input voltage.

If you plan on using your PWM CC you might have to wired them in parallel which will get you the highest input amps and output charging amps. You will still lose about 33% of your panel wattage because a PWM CC does not convert 100% of the wattage to charging amps.

Also with more that 2 panels (or strings) wired in parallel you will be required to install over current protection (fuse or breakers) for each panel or string. With 5 panels that will require 5 overcurrent devices.

To correct my early statement above, a Morningstar TS45 has a max DCV input of 125V. That might allow you to wire those 21.8Voc panels in series but be careful due to cold temperatures that may increase the Voc to exceed the 125v limit.

[antonycurley]

Depending on which PWM controller you have I doubt you will be able to wire all 5 panels in series because at 109V you will probably exceed the maximum DC input voltage.

If you plan on using your PWM CC you might have to wired them in parallel which will get you the highest input amps and output charging amps. You will still lose about 33% of your panel wattage because a PWM CC does not convert 100% of the wattage to charging amps.

Also with more that 2 panels (or strings) wired in parallel you will be required to install over current protection (fuse or breakers) for each panel or string. With 5 panels that will require 5 overcurrent devices.

To correct my early statement above, a Morningstar TS45 has a max DCV input of 125V. That might allow you to wire those 21.8Voc panels in series but be careful due to cold temperatures that may increase the Voc to exceed the 125v limit.

So I'm as well just purchasing the Controller that I'm going to use in my final system and using that by the sounds of it.....

Probably something like a Tristar MPPT, Outback Flexmax or Midnite Solar - least that way i cloud wire them all in series without adding any breakers or anything?

Antony

[SunEagle]

So I'm as well just purchasing the Controller that I'm going to use in my final system and using that by the sounds of it.....

Probably something like a Tristar MPPT, Outback Flexmax or Midnite Solar - least that way i cloud wire them all in series without adding any breakers or anything?

Antony

I believe that you will get more out of your panel wattage using an MPPT then even that Morningstar TS45.

I made the mistake of going with a 30A PWM CC for a 400watt off grid system and then realized I was wasting over 100 of that wattage due to the inefficient way a PWM works.

Try to remember that the following is true for PWM CC's. They will lose a % of the panel wattage due to a high Vmp of the panels yet low DC voltage of the battery being charged.

PWM is amps in = amps out (usually results in at least a 33% panel wattage loss)
MPPT is watts in = watts out (converts ~ 100% of the panel wattage into charging amps)

[AzRoute66]

Hi guys n gals? [...] 6 x 80w Baird panels, wired in pairs each going to their OWN Sinsola PWM (junk) charge controllers, he has then linked each charge controller and the last one outputs to the batteries! [...] Then its off to the batteries which are 4 x 110ah 12v leisure batteries wired in parallel which can't be charged by those panels in that configuration?? [...] I have removed one of the batteries and suspect i might have to remove another..... [...] So here is my proposal to get this system running a bit better - 5 x panels running in series [...]

When I first read that I didn't see any panels in series, and still don't. I suspect that the six panels are wired in parallel pairs, then the outputs of the three pairs to their own PWM controller (as opposed to being combined and run into one controller). I have no problems with that and the panels need no overcurrent protection - however each of those three wires coming out of the three PWM controllers are in parallel and might need individual overcurrent protection.

I have no problem with upgrading the controller and putting them in series either, but you will be removing 1/6th of the production if you are limited to 5 panels for voltage reasons. Probably get that back in efficiency, so it is probably a wash. I'd leave it alone if the panels are all in parallel - certainly wouldn't buy an 'interim' controller.

Since the four batteries are in parallel, you should remove any battery that is detrimental to energy storage for whatever reason, shorted cell, sulphated, etc. Other than that, I don't see anything you should be doing prior to full system replacement in 18 months.

[antonycurley]

I know the system is limited. What I'm looking to do is get the best out of that existing system for the time been.

I understand that if i wired the 6 in parallel i would get ROUGHLY -

6 x 80w - 480w
VOC - 21.8v
IMP - 27.3

Minus whatever for running through a PWM.

But.....what am i getting at the moment with it running in 3 parallel pairs into 3 controllers that are linked together....? This doesn't look like an efficient way to connect them to me, especially when the controllers are junk.