Panels and mppt

terosity · April 2017

Hi All,

Just after a little bit of help.

Im looking to install 12x Trina solar tsm-295 to a victron mppt

http://static.trinasolar.com//sites/default/files/EN_TSM_DD05A_05_II_plus_datasheet_A_201702_K4.pdf

My plan was to run 3 lots of 4 panels in a series-parallel to a combiner.

Im trying to work out what the volts and amps are. most sites suggest around 12v and 5 amps for panels, im guessing they are just working on an average.

So what im looking for is.

1. what are the volts and amps for each panel, so i can work out the array.
2. what size fuse will i need for the 3 individual arrays
3. what size fuse will i need for all 3 arrays combined.

Thanks,

Estragon · April 2017

Open circuit voltage on those panels is ~40v. Putting them in a series string of 4 would be 160v (or higher if panels get cold). Your controller may not handle that voltage? Need specs.

At ~9a each, three strings would be ~27a. 4 strings of three would be ~120v and 36a.

Max fuse/breaker size per string is 15a.

terosity · April 2017

thanks estragon for the reply.

i will be running 4 panels in a series parallel then combineing the 3

you say 15a fuse why is that when you are saying 27/36a

Thanks

Estragon · April 2017

The 15a is the max for each string. You could use a 12a I think - 9a x 125%. The 27 or 36a would be the combined current for the 3 or 4 strings from the combiner box to controller.

Are you sure your charge controller will handle 160+ volts. Some will, but many won't.

Are you going a long distance from array to controller?

terosity · April 2017

what do you mean by a string ? ill have to look at the controller.

what do you suggest?

Thanks

littleharbor2 · April 2017

I see Victron Energy has a 250 volt 100 amp MPPT charge controller so your 4 panels in series are within its limits. It's a pricey affair at around $1000.00 USD. It appears to have 3 sets of MC-4 inputs which is convenient.

A string is a group of series wired panels in this case. You can run the strings into a combiner box and out as a single higher amperage line, or with the MC-4 version controller, apparently it will combine them for you.

terosity · April 2017

just looked its 250v 85a

ruuning at 48v

Estragon · April 2017

The 250v should be fine. Even in very cold temps, voltage will be well under that.

Using higher voltage strings is useful when you need to go long distances and want to minimize wire losses and/or use smaller wire. The trade-off is (usually) higher cost controller and some loss of efficiency is downconverting voltage.

Photowhit · April 2017

terosity said:

what do you mean by a string ?

In general, panels hooked together in series is called a 'string'.
All the panels using a charge controller is called an 'array' though this is sometimes applied to all the panels serving a single system, in cases of more than 1 charge controller.

Each string, when more than 2 strings should have it's own breaker or fuse, typically in a 'combiner box'. Where the strings are combined into a single set of wires for the run to the charge controller. The panel or string series fuse rating is on your solar panels spec sheet under "Maximum Rating". and is suggested as 15 amp, you can use less, but should not use a higher rated fuse or breaker.

http://static.trinasolar.com//sites/default/files/EN_TSM_DD05A_05_II_plus_datasheet_A_201702_K4.pdf

It is also nice to have a disconnect for the Array near the charge controller. Usually a DC rated breaker is used.

Estragon · April 2017

I had a quick look at the spec sheet for the Victron 250/85 and had one maybe minor quibble.

It apparently has internal temperature compensation with no provision for external sensor mentioned. This probably wouldn't be much of a problem if the internal sensor isn't affected by heat generated by the FETs etc., the CC is located in the same temp environment as the batteries, and the temp doesn't vary much. Maybe it does have provision for an external sensor and it just isn't mentioned in the sales sheet - seems odd for a pricey CC.

If the internal sensor is materially different than the battery temp, charging voltage supplied by the CC may be inappropriate. If the sensor is reading hot, voltage will be too low and bank could be undercharged. If batteries get warm with later stage charging or equalization, voltage may be too high.

In any case, just something to be aware of.

terosity · April 2017

Hi,

Thanks for the reply,

The two will be located close to each other in a barn, so the temps should remain the same.

Im just looking at DC disconnect and combiner, ideally i want to shut the strings / array off before it goes into the combiner, what would you suggest the best method here is, the combiner will be probably custom built with 15a breakers for each string, 60a main breaker for the combined and surge protector.

so not really sure if i need a dc disconnect if im doing it this way ?

Thanks

Raj174 · April 2017

The combiner gives you the ability to shut off individual strings. This one is made by Midnite Solar. It provides a little room for expansion.
https://www.solar-electric.com/mnpv6.html

They also make one for three strings.
https://www.solar-electric.com/mnpv3.html

If you want an array disconnect switch built in to the combiner then check this one out.
https://www.solar-electric.com/mndico.html

This is the PV breaker that fits these boxes.
https://www.solar-electric.com/mnepv.html

Rick

Estragon · April 2017

With CC and bank in the same place, temp compensation may not be an issue. I would check the battery temp vs what the CC thinks for a bit, especially if the barn warms up with the sun. The mass of the bank will keep it cool for some time as ambient rises.

I use the midnight combiners with a common manual disconnect. They work fine for me. You might want to check with local authority for any disconnect requirements if you need permits though. Fire dept may want something more elaborate.

Panels and mppt

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