Small system in the office/home

[HeinTheTerrible]

Hi guys

 

Here's a small system I did for my dad's office/house. Running everything except the kitchen and garage.

 

2 x Microcare 20amp MPPT's

4 x 250watt 24v monocrystalline panels

4 x Deltec 150aH batteries in a 24v config

1 x CB solar 3kva inverter

1 x "switch over" switch (select between eishkom and free power  )

DC 1000v 20amp  fuses on the panels, 100 amp fuse between battery bank and inverter and 50amp fuse between MPPT's and battery bank.

 

The system works like a charm. Got a electrician to install a 2nd DB board with a "switch over" switch in case something happens, the old man can just flick a switch and still have power.

 

Panels on a DIY mount

 

DB board (the old panel looks bad, I know)

 

Inverter

 

Battery bank

[Chris Hobson]

Hi Hein nice setup.

Why did you not use the CB Solar's built in SCC instead of buying two Microcare SCCs?

Read up about battery cabling for more than two strings in a battery bank. One cannot really see in the photos but find out what is the best way (probably busbars and even length of cabling for each string) and then check that yours is indeed wired up in that way. Since you only have 2 strings there are other ways to skin a cat.

[Guest]

Hey, there is only one Terrible on this Forum!!!

Nice setup ... but is 1000w array enough? Or is the load well below 1000w?

Batteries I presume are maintenance free, used for backup only?

EDIT: Sorry only 3 Terrible's ... Me Myself and I.

[Chris Hobson]

Die tweede ou van die drieling! Die derde ou is net skoon "missing".

[HeinTheTerrible]

Thanks Chris

 

The inverter is the model without a charge controller. The system was assembled in stages, 1 x MPPT, 2 x panels, 2 x batteries. 4 weeks later the other halve was added. I wanted to go with a 40amp Microcare but the price was a bitter pill to swallow for my dad so with the advice of the local Microcare distributor, we opted for two 20amp units. 

 

The batteries are wired up in two pairs. 2 banks in series and then paralleled together to give 24v. Its wired in the same

The battery cable (16mm copper) and charge controller cable (8mm KBE solar) are all the same length (I'm a bit OCD).

*fixed cable size*

[Chris Hobson]

5 minutes ago, HeinTheTerrible said:

(I'm a bit OCD).

Then it will be right.

[Chris Hobson]

The image for the wiring has just appeared. I do not like the way that it is wired up. The electrical path for the top set of batteries is shorter than the bottom.

[HeinTheTerrible]

20 minutes ago, The Terrible Triplett said:

Hey, there is only one Terrible on this Forum!!!

Nice setup ... but is 1000w array enough? Or is the load well below 1000w?

Batteries I presume are maintenance free, used for backup only?

EDIT: Sorry only 3 Terrible's ... Me Myself and I.

 

The average load is only about 300w. Couple of laptops, NAS, CCTV and 2 tv's is all it drives 98% of the time. 

These are Deltec deep cycle sealed lead acid batteries. I have a Noco Genius G3500 battery maintenance/charger that Ill use to "desulfate" the batteries every year. That should in theory give me atleast 20 to 25 years out of the battery bank.

[___]

That looks like the LED model of the Microcare MPPT with the Voc limit of 50V. So you probably have all the panels in parallel then, as a 24V panel (or 72 cell really) makes over 40V open circuit. At first I wanted to agree with Chris here, to use the one in the inverter, but that is also limited to 75V so you still cannot get two in series (even if you had an MPPT in there).

I like that you used two controllers. It gives you a bit of redundancy. The 40A LCD model does have an open-circuit voltage of 150V though, that's what you pay for.

If it was me, I'd use two Victron BlueSolar 100/30 controllers. It would set you back an extra 2k (which is the cost of the MC units, so 50% extra) but then you can run two strings of two in series, open circuit voltage around 90V.

For the size of the system though, the MC unit is a good compromise I think.

[HeinTheTerrible]

1 minute ago, Chris Hobson said:

The image for the wiring has just appeared. I do not like the way that is wired up. The electrical path for the top set of batteries is shorter than the bottom.

I forgot to finish my sentence above the image, sorry about that.

 

Its wired in almost the same way as in the picture. The "24v" output goes to the side of the bank with equal lengths running to all the components.

[Guest]

4 minutes ago, HeinTheTerrible said:

The average load is only about 300w. Couple of laptops, NAS, CCTV and 2 tv's is all it drives 98% of the time.

Then I say well DONE!!! Load and system is matched. Respect.

But, them Deltec's, not so sure about them. I know of no maintenance free lead acid batts that goes beyond a few hundred cycles to 50% DOD.

If I am wrong, pray tell me the model number of the batts?

EDIT: and 24v for the system ... I like! You obviously did a lot of homework.

[superdiy]

4 minutes ago, Chris Hobson said:

The image for the wiring has just appeared. I do not like the way that it is wired up. The electrical path for the top set of batteries is shorter than the bottom.

 

1 minute ago, HeinTheTerrible said:

I forgot to finish my sentence above the image, sorry about that.

 

Its wired in almost the same way as in the picture. The "24v" output goes to the side of the bank with equal lengths running to all the components.

The thing is not about equal wire lengths everywhere.  The key thing is total length of cable in each parallel string must be equal and of the same type / thickness up until the point where the strings are connected to each other, e.g. on busbars or to the inverter or the cable going to the inverter.

[HeinTheTerrible]

3 minutes ago, plonkster said:

That looks like the LED model of the Microcare MPPT with the Voc limit of 50V. So you probably have all the panels in parallel then, as a 24V panel (or 72 cell really) makes over 40V open circuit. At first I wanted to agree with Chris here, to use the one in the inverter, but that is also limited to 75V so you still cannot get two in series (even if you had an MPPT in there).

I like that you used two controllers. It gives you a bit of redundancy. The 40A LCD model does have an open-circuit voltage of 150V though, that's what you pay for.

If it was me, I'd use two Victron BlueSolar 100/30 controllers. It would set you back an extra 2k (which is the cost of the MC units, so 50% extra) but then you can run two strings of two in series, open circuit voltage around 90V.

For the size of the system though, the MC unit is a good compromise I think.

Yip, Microcare 20amp LED's. 2 panels in parallel on each controller yes. 

The inverter is the model without a charge controller so I had to use the Microcare units. I opted for Microcare because they are based in P.E so support and service is close by. I'm sure there are cheaper/better components but I opted to use the guys based in my town so whenever something goes south, I wont have to ship stuff away and wait,

[superdiy]

31 minutes ago, HeinTheTerrible said:

 charge controller cable (6mm KBE solar)

Is that the cable between the panels and charge controller(s)?  If all the panels are connected in parallel as Plonkster has mentioned, the 6mm² cable is a bit on the thin side.

[HeinTheTerrible]

4 minutes ago, The Terrible Triplett said:

Then I say well DONE!!! Load and system is matched. Respect.

But, them Deltec's, not so sure about them. I know of no maintenance free lead acid batts that goes beyond a few hundred cycles to 50% DOD.

If I am wrong, pray tell me the model number of the batts?

EDIT: and 24v for the system ... I like! You obviously did a lot of homework.

Thank you sir!

 

A smaller system probably would've sufficed but I never like running systems near their limit.

I spoke to my local battery centre (they sell solar equipment too) and they recommend these batteries. Budget was tight and the lead crystal batteries was almost double the price for the same amp hour rating. The batteries we have installed are Deltec BK12-150's.

[HeinTheTerrible]

5 minutes ago, superdiy said:

Is that the cable between the panels and charge controller(s)?  If all the panels are connected in parallel as Plonkster has mentioned, the 6mm² cable is a bit on the thin side.

My bad, its 8mm cable. Not 6mm.

 

Only two panels run in parallel to one charge controller, not all 4 panels on one pair of cable so the cable is thick enough according to my local supplier. 

[Guest]

3 minutes ago, HeinTheTerrible said:

... my local battery centre (they sell solar equipment too) and they recommend these batteries.

HTT, do me a flavour, can you ask them for the cycles to 50% DOD? (Depth of Discharge)
And 20% DOD?

Not that anything is wrong, if there was you can do anything about it now, but just for the future and that we can help managing potential disappointment.

[HeinTheTerrible]

14 minutes ago, superdiy said:

 

The thing is not about equal wire lengths everywhere.  The key thing is total length of cable in each parallel string must be equal and of the same type / thickness up until the point where the strings are connected to each other, e.g. on busbars or to the inverter or the cable going to the inverter.

The lenght of cable between each battery is the same lenght (35cm if I recall correctly)  

[superdiy]

2 minutes ago, HeinTheTerrible said:

My bad, its 8mm cable. Not 6mm.

 

Only two panels run in parallel to one charge controller, not all 4 panels on one pair of cable so the cable is thick enough according to my local supplier. 

OK, that sound better. Do you have each PV string fused before they are connected in parallel and going into the charge controller?

[HeinTheTerrible]

2 minutes ago, The Terrible Triplett said:

HTT, do me a flavour, can you ask them for the cycles to 50% DOD? (Depth of Discharge)
And 20% DOD?

Not that anything is wrong, if there was you can do anything about it now, but just for the future and that we can help managing potential disappointment.

Ill ask him, I need to drop off a couple of dead batteries soon so Ill get the info for you.

[HeinTheTerrible]

1 minute ago, superdiy said:

OK, that sound better. Do you have each PV string fused before they are connected in parallel and going into the charge controller?

Yip! 1000v 20amp DC fuses.

[superdiy]

5 minutes ago, HeinTheTerrible said:

The lenght of cable between each battery is the same lenght (35cm if I recall correctly)  

I think you are still misunderstanding this. The total length of cable per string needs to be the same. If the total length of cable per string is equal, then you are good to go. 

 

[superdiy]

5 minutes ago, HeinTheTerrible said:

Yip! 1000v 20amp DC fuses.

20 A seems a bit on the high side.  According to your panels's datasheet, what is the short circuit current per panel?

[HeinTheTerrible]

1 minute ago, superdiy said:

I think you are still misunderstanding this. The total length of cable per string needs to be the same. If the total length of cable per string is equal, then you are good to go. 

 

Maybe I am  

I tested each battery after a week and the voltage was spot on over all 4 batteries so I'm 99% certain its all up to scratch  

[Chris Hobson]

11 minutes ago, superdiy said:

I think you are still misunderstanding this. The total length of cable per string needs to be the same. If the total length of cable per string is equal, then you are good to go. 

 

With this provisio you could wire it up like this (excuse the farmer modification to your image). This negates the need for busbars which I think is an over kill on only 2 strings.

batteries.pdf

So each string would have a short positive to inverter and one long negative to the inverter (these are common). Then one shortish link to connect two batteries in series (These two links need to be the same length) and two longer links (also the same length as each other) one on the positive side for one bank and one on the negative side for the other bank.