Off grid solar setup

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Off grid solar setup

Postby homesteader » Sun Jan 15, 2017 5:45 pm

Hello everyone, I've been doing some research into an off grid solar setup and would appreciate any suggestions on what I've ended up with. I'm just aiming to do a bit of power tool work with this setup on the weekends, along with maybe running a fridge when I'm not there.

MPP SOLAR 4048ms. Which is a 48v MPPT solar charger and inverter (4KW) in one.
4x250W panels. Just some generic cheap stuff off ebay, 12v or 24v.
4x12v AGM 100+AH batteries.

So am I right in thinking this will at least "Work" for what I want, and is there anything else I should add to make it better. I feel like this setup would give me a little room to grow in regards to solar panels and batteries down the line but maybe I am wrong on this. Thanks!
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Re: Off grid solar setup

Postby Gordon-Loomberah » Mon Jan 16, 2017 11:04 am

Welcome to the Energy Matters Forums Homesteader :)

12V or 24V is a bit irrelevant when talking about solar panels these days, number of cells/maximum power voltage is a better way to talk about them. Just make sure you have high enough Vmp to charge your batteries, but be sure that Voc is below the max allowed input for the MPP Solar 4048ms

With those batteries, you may not be able to add too many more PV panels, as the charging rate may be too high- depending on the specs.

It will work, but is not really ideal for expansion.
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Re: Off grid solar setup

Postby homesteader » Mon Jan 16, 2017 10:25 pm

Hi Gordon, thanks for the welcome.

The 4048ms seems to have a 150v max input, which should be ok I think for 4x12v panels in series. Max voltage for the panels I've seen is around ~22v , times that by 4 and it is only 88v. So I feel fairly confident it will be ok. Is there an advantage in running at a higher voltage with a charge controller that says it is 48v? I saw on another site that people were even running at ~72v nominal with this thing which would be getting close to its 150v maximum with no load.

In regards to charging rate am I correct in that it is a pretty manual thing you need to match the panels to batteries? I know some MPPT chargers allow you to set a max amperage as a safety feature but it seems the MPPT chargers pretty much dump as much amperage as they are getting into the batteries during the bulk phase. Since lead acid batteries are pretty fickle things it seems that is one thing you should be careful about. I can't wait until better battery technology is here (and priced good) as I feel like this lead acid stuff has just about run its course.

I ended up getting 4x120AH batteries which I think should be enough to give me 2KWH of regular usage without killing the batteries too quickly. I hope to gain enough experience with this setup to then do a much bigger setup for my yet to be built house. I am quite excited to be joining the solar power community, it is something I have wanted to do for such a long time.

Thankfully my new land has no grid connection at the moment so I won't have to worry about the electric companies doing what the water companies did with forcing you to pay fees even if you don't use their service. For the last block I had to pay the water company about $400/year just because they ran a pipe by the block that I didn't even use. The laws allow them to slug everyone and I feel like electric companies are going to do this soon to us as more people go to solar and other renewable energy sources.
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Re: Off grid solar setup

Postby lantern » Tue Jan 17, 2017 7:50 am

Tons of info here.

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Re: Off grid solar setup

Postby Gordon-Loomberah » Tue Jan 17, 2017 10:56 am

homesteader wrote: Is there an advantage in running at a higher voltage with a charge controller that says it is 48v?


The higher the input voltage you run, the lower the cable losses, but the voltage conversion will be slightly less efficient at higher input voltages, so it is a trade-off. However, for long runs it is better to go with higher voltage, which can result in $avings due to not needing quite as large a diameter cable.

In regards to charging rate am I correct in that it is a pretty manual thing you need to match the panels to batteries?


You can set a maximum charging rate in good quality charge controllers, doesn't matter if it is bulk or absorb stage. The battery manual should specify max charging rate. Limiting your panel rating to the max the batteries can take is one way of doing it, but you might struggle to get charged in cloudy periods of weather.
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Re: Off grid solar setup

Postby homesteader » Tue Jan 17, 2017 8:47 pm

The 4048ms seems to support 80A on the MPPT side of things, which at 48v x 80A = 3840W, they say it supports 4000W on the solar side.

Wouldn't putting in a higher voltage allow you to get more than they say is the limit? I assume the limit is simply to do with the wiring inside the unit, and if they allow upto 150V then you are looking over 10000W the unit can support? Or am I missing something here.

Why would they call this unit 48V if you can run it much higher? And if you run the solar side at 60V or 72V nominal do the batteries have to match that too?
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Re: Off grid solar setup

Postby davidg » Tue Jan 17, 2017 9:58 pm

homesteader wrote:The 4048ms seems to support 80A on the MPPT side of things, which at 48v x 80A = 3840W, they say it supports 4000W on the solar side.

That would be roughly correct, it might support overdriving a bit some products do, others don't. For instance a MIDnite Classic 150 for a nominal 48V battery pack will support 5.25kW's for sure.

homesteader wrote:Wouldn't putting in a higher voltage allow you to get more than they say is the limit? I assume the limit is simply to do with the wiring inside the unit, and if they allow upto 150V then you are looking over 10000W the unit can support? Or am I missing something here.

Yes missing something. 80A is related to the OUTPUT, if you put 10kW's into it, it will either decide it can't cope "very likely", and let the smoke out or assuming it could, then it would simply clip and only allow a maximum of 80A for the OUTPUT.

homesteader wrote:Why would they call this unit 48V if you can run it much higher? And if you run the solar side at 60V or 72V nominal do the batteries have to match that too?

Because it's related to battery pack connected to it. Which I should point out that while 48V is regularly used it is common for a charge unit to output more than that based on what the batteries require to charge properly, which is ALWAYS more than 48V. If the array that is connected is not running at a sufficiently higher enough voltage then the battery pack will never charge up properly.

Maybe MPP Solar have improved their product/s because not that long ago ,there were issues with the programming and control of their products. When you consider the cost of batteries and you expect them to well looked after by a charging system I would always go for a known to be high quality MPPT charge controller that really works with NO hiccups for a DC coupled system, it'll save you thousands in batteries and longevity, etc.
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Re: Off grid solar setup

Postby jaahn » Wed Jan 18, 2017 9:25 pm

homesteader wrote:The 4048ms seems to support 80A on the MPPT side of things, which at 48v x 80A = 3840W, they say it supports 4000W on the solar side.
Wouldn't putting in a higher voltage allow you to get more than they say is the limit? I assume the limit is simply to do with the wiring inside the unit, and if they allow upto 150V then you are looking over 10000W the unit can support? Or am I missing something here.
Why would they call this unit 48V if you can run it much higher? And if you run the solar side at 60V or 72V nominal do the batteries have to match that too?

Hi Homesteader :)
The others have talked about this but I will add my 2cents as you do seem to have a few misconceptions.

The 48v that these units refer to is the NOMINAL working voltage. THE COMMON NOMINAL VOLTAGES are 12v with 1 LA battery or two in series is 24V, 3 is 36V, 4 in series is 48Volts. However the actual voltage of a 12V battery gets up to 14 or 15 when fully charged depending on the settings and type and down to 11V perhaps under high load. The others are x2, x3, x4 this voltage so the 48V systems can get up around 60Volts or down to 44V.

So the panels must put out a voltage higher than the maximum required to make the current run into the batteries. Does not matter what the controller does, if the panels voltage is lower than the batteries there will be NO CHARGING.

A MPPT regulator will take higher voltages from the panels and convert that internally to a suitable charging voltage that suits the battery. A PWM regulator will waste that higher voltage. However the panel voltages must no be higher than the allowed maximum specified for the regulator or it will 'burn out'.

The maximum current specified for the regulator, if it is MPPT is the output current to the batteries. which will be greater than the panel current, so It is not so straight forward, so just read the specs on the max wattage allowed, for a simple answer. do not try and second guess the specs. The current is the limiting factor for rating due to the heat caused.
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Re: Off grid solar setup

Postby BruceM » Sat Jan 21, 2017 10:20 pm

http://www.mppsolar.com/manual/PIP-HS,M ... manual.pdf

I've got 10 X 190w X 48V (nom) panels connected to it with 100Ahr of LiFepo4 batteries.
Equ to 400Ahr @ 12V.
I'd love another 4 panels plus another similar sized bank of batteries!!!
Panels are 5 strings of 2.
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Re: Off grid solar setup

Postby davidg » Sun Jan 22, 2017 12:07 am

BruceM wrote:Panels are 5 strings of 2.

I hope all your strings are fused properly .................. with 5 strings there is a need for correct fusing, JIC
Off-grid Systems specialist- You could store Sun to use later- I Do!
SELECTRONIC SPMC-482 7.5kW, 8.2kW's of Arrays

with AC-Coupled Grid-Connect Inverters,
1100Ah 48V Bank

Auto Backup Genset
PVOutput Stats

Sparkys light up your life :)
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