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Hallo all

Thank you for excepting me to your forum. I am from Kuruman and live of the power grid.

Currently running a 12 kva generator for workshop and home. Run time approximately 5 ours a day up to full days depends on the amount of heavy welding needs to be done.

On order now for my house is a 5 kva/4kw axpert mppt inverter

8x 6 volt Troyan t105 re batteries and 12 x 275 watt Canadian solar panels with all the bells and whistles needed for installation.

I do have a 2.2 kw single face lister engine/ generator for house back up with the solar if needed.

My budget does not allow any thing else at this stage so I will adapt my cosumption around the available solar instead off visa versa.

My biggest concern is that the only way to get full sun for the panels is more than 100 meters from my house. 

Thick 3 phase cable is in place.

I had to connect all 3 phases together to get power to db box in the house so that everything get power. What will the voltage drop effect be on that distance.

 

 

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1 hour ago, Bere said:

Thick 3 phase cable is in place.

Thick as your thumb? your arm? your leg? Sorry - its late on Sunday after a tough weekend.

To offer an opinion we would need better info - when you say 3 phase is it a 3core or a 4core cable? is there a separate earth? Do you know what size the cores are (4mm/6mm/10mm/16mm/bigger)? is it an armoured cable or some other type?

 

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11 hours ago, Bere said:

... the panels is more than 100 meters from my house ...

A point to ponder is to send 220v AC down the 100m cable than DC.

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We did the math in a previous thread. Sending around 3kw worth of power at 100V (approximately, it makes the math easy)  is 30 amps.

Off the top of my head, 25mm^2 has a resistance of 0.9Ω per km. You have to use the total distance (there and back), so for you it is 0.2km, or around 0.2Ω total. 30 amps over that is a 6V drop, or 6%. (Not counting the 6*30 = 180W of heat you'd be dissipating).

Maximum acceptable drop is 3%. So the cables needs about 2 times the capacity, so you're looking at 200m of 35mm^2 cable to even get at a remotely workable number. You don't want to know how much that is going to cost... you can buy a good inverter for the equivalent cost.

Two ways to go about this. The first is to forget about the Axpert and get a Infinisolar with high voltage DC inputs, so you can use thinner cable. The second is to use a grid-tied inverter and pass the power over the existing 230VAC wiring.

Tying all your panels in series will run them around 400V and a much more manageable 8 ampere or so, which again just using the square rule says now you can get away with 10mm^2, about a 1% drop (4V or so out of 400V), and a 30W heat dissipation.

Or buy a 3KW Fronius and with some software hackery, make the Axpert on the other end charge the batteries from AC during the day (so it essentially charges with the power generated by the Fronius).

Or skip the hackery and .... you know... get another inverter that already works well in such a setup :-)

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Hi @Bere

There is 2 ways that you could go about this;

Option 1: Install panels/inverter/batteries at the remote location if suitable structure is available for the inverter and batteries, then use the 35mm cable (L + N + earth + spare) to transmit AC to the house (your AC volt drop will be negligible over the 35mm cable).

Option 2: Install only the panels at the remote location, and transmit the DC power over the 35mm x4 cable to the inverter/batteries located at the house. I prefer this option as you may need to interface with your inverter regularly in an Off-Grid situation, and you will need to be quite fit if it is 100m away!

If you go for option 2 I would recommend the following;

  1. I believe that your panels have an Open Circuit voltage of your panels [Voc = 38.3], that being the case I recommend that you use a 3s4p arrangement [4 parallel strings of 3 panels in series]. That will give an open circuit voltage of 115V which is well within the 145V maximum voltage for your inverter.
  2. At a Imp [max power current] of 9amps you can expect a maximum current of 4x9 = 36 amps. The 35mm cable has an impedance of about 0.6ohms/km, so using just 2 core [red+ / blk-] your cable resistance would be about 0.12ohms giving a volt drop of 4.32or about 4%.
  3. You could either accept this 4% drop, or double up on the 35mm cable [Red,Wht+ || Blk,Blu-], which will put you below 3% voltage drop.
  4. Personally I would use a single pair and accept the 4% drop, and then use the other pair to carry generator power and locate the generator at the panels (generator noise drives me nuts!). Just dont ever tell anyone that I suggested using a common cable for AC and DC.
  5. Use the armouring for earth back to a common earth point near the house, and please put surge arrestors on the house side of the cable (DC arrestors for the PV supply and AC arrestors for the Gen supply if used) as the 100m long lightning enticer could cause you ongoing problems.
  6. Remember that surge protection is only effective with a good quality earth.

As soon as the budget allows add 2x HA02 battery balancers (4 batteries per HA-02), after that add the Victron BMV-702 and ICC control software (search this site for detailed info). The Axpert battery management is pretty dodgy, and these items will go a long way towards maximizing battery life.

Good Luck with the install. 

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22 minutes ago, pilotfish said:

your cable resistance would be about 0.12ohms giving a volt drop of 4.32or about 4%.

4.32 * 36 ~= 150W of dissipated heat. Spread over a distance of 100 meters so probably not a big concern. I'd prefer an electrician to check this number. I also seem to recall that the amount of current you are allowed to put through a cable varies depending on whether it is in the open air or not, and when you have two cables together and there is more heat to get rid off, you also have to derate it somewhat. I agree with you though that the 35mm^2 is probably sufficient to do the job, even if just barely.

I still think the better option is to use a higher string voltage. See if you can swap the inverter for a higher-end model that allows >300V on the MPPT. It's probably going to be more efficient for direct daytime use too (which I assume is going to be the bulk of the use). A cursory google check does however suggest you're going to spend upwards of 10k to make such a swap (and the next one up, the Infini super, has not received particularly favourable reviews on this very forum).

You could also try a high voltage external MPPT, but that's also going to add at least 15k to things.

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3 minutes ago, plonkster said:

I also seem to recall that the amount of current you are allowd to put through a cable varies depending on whether it is in the open air or not, and when you have two cables together and there is more heat to get rid off, you also have to derate it somewhat. I agree with you though that the 35mm^2 is probably sufficient to do the job, even if just barely.

The current rating of a 35mm x4 armoured cable is:

  • In ground                    143amps
  • Enclosed Duct           116amps
  • Free Air                       135amps

So you should be OK.

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I agree with Plonkster. Going higher panel volts with another inverter make.

Or, as I said, go AC.

Re. the 100m x 2 walk in rain and at night (for that is when it happens), I would have remote access to said inverter installed at the panels.

And because I am a Blue fan, the remote access is really only for PVO and Emon benefit, for I would seldom need to go there. :D (Could not resist.)

 

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1 hour ago, The Terrible Triplett said:

because I am a Blue fan

There isn't really a blue solution here, other than placing the inverter in that building 100 meters away, which you can also do with the Taiwanese model. The remote console you get with our CCGX firmware really does kick some *ss, that is true, but in the interest of fairness, if you want to put the inverter and batteries at the house for easy access, we really don't have a better solution.

We have a nice 250V MPPT, yes, but what you really want to do is go double that.

The one solution I know would work absolutely beautifully in this case would be to have a Fronius GTI on that end and a Multiplus with batteries on this end, because these two are well integrated. You transfer the power using 230VAC, but because of the integration the Fronius essentially does the job the MPPT would do otherwise. But this really works best when you have grid power. A grid tied inverter in an off-grid setup... not really very stable.

This is a rather interesting use case. The kind of inverter you really want here is either a 5KVA InfiniSolar (they cost like 50k) or a 5KVA Quattro (which costs about the same, but you need to add on 10k for a good MPPT). If you need 5KVA and you want to go cheaper, your options are 1) Infini Super, which did not get a glowing review, or 2) Axpert.

Perhaps ask @Chris Hobson how regularly you need to visit anyway. Perhaps we're making too much of this 100 meters. Just put all your power stuff at the other building, noisy generator included.

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14 hours ago, viper_za said:

Haven't even touched my inverter since the last firmware update I did and that was 2 years ago and no it's not blue :P

Been going since 2012 boet, so that make it 6 years and counting with not one days drama ever. :P

 

13 hours ago, plonkster said:

There you go. Put the inverter and batteries with the panels :-)

Ditto. Send the 220v down the 100m cable for in ALL my years of poking around solar systems, nowhere does anyone who are truly are off-grid, go for such a long distance with DC unless the volts are very high. Reminds me of KISS.

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2 hours ago, The Terrible Triplett said:

Been going since 2012 boet, so that make it 6 years and counting with not one days drama ever. :P

I've had a lot of firmware updates (of course, I test the stuff). One thing that truly irritated me is that I had to open the inverter and move dip switches every time (this is only on the Multi compact models, and only when you run with the Lithium batteries and a BMS, more details below). I found out that there is a way to change the dip switch settings inside your MK2 dongle. Since I've done that... problem solved, no more opening the inverter.

But... good news, although this is still pre-release. There is a feature coming where you'll be able to configure all those things you need the mk2 for remotely, using only VRM and a CCGX/Venus-GX/Raspberry Pi. You'll be able to do remote firmware updates in other words, and soon also remote veconfigure.

As I said... the remote console stuff really does kick Voltronic rear-ends.

So about the dip switch stuff. This is actually a cool feature of the Multi. When the BMS indicates that there is a low cell, the inverter goes into ultra-low power consumption mode. It turns off just about everything including the comms channels. Problem with that, of course, is there is nothing around to turn things back on again. So in the vebus cable (which is mostly rs485) there are some signal connectors you can use to implement a remote switch-on, and this is what the BMS does: When the battery recharges a bit, or if the grid power returns, it can use this signal wire to turn the inverter back on. This feature is enabled in the inverter using a dip switch. And when you're updating firmware, you have to unplug the BMS, which causes the inverter to switch off. So you either need to flip a dip switch in the inverter to disable this feature, or you flip the dip switch in the dongle to keep the signal up.

Our Taiwanese brother, of course, has none of these fancy features. 99% of the time it doesn't matter of course, that 1% of the time you'll have to walk 100 meters. Or fly in with a chopper. Depends where it is of course :-)

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22 hours ago, plonkster said:

 

Perhaps ask @Chris Hobson how regularly you need to visit anyway. Perhaps we're making too much of this 100 meters. Just put all your power stuff at the other building, noisy generator included.

Sorry I have been fighting with a pump inverter but we now have 3000l/hr going into the reservoir so I am smiling. 

Now to the question at hand  I would put everthing 100m away and feed the 220V to the dwelling. Chances are the panels will go up at the workshop where Bere spends a large part of the day anyway.

I would make use of ICC and use Emoncms to remotely (100m away) keep tabs on the inverter. Once set up one does not fiddle with the inverter. I have not changed settings since Xmas  (when I got some Pylontechs) and prior to that I had not fiddled with settings since 2015.

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On 3/18/2018 at 9:06 PM, Bere said:

My biggest concern is that the only way to get full sun for the panels is more than 100 meters from my house. 

Nowhere does @Bere say that he has a suitable structure to house the inverter/batteries at the remote location, only that this is where full sun is available.

On 3/20/2018 at 10:28 AM, pilotfish said:

Option 1: Install panels/inverter/batteries at the remote location if suitable structure is available

So are you all advocating that he slap up a building to house this equipment when he has already mentioned his restricted budget, rather than accept a MAX 4% DC loss, which he could reduce to MAX 2% by doubling up on the 35mm cores?

If we ever get to have a lunch then you lot can split the bill, because you seem to be impervious to cash constraints:wacko:

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Either solution is fine, but I'm sure you agree that your own option 1 is the better one.

Using a higher voltage would be preferable if you cannot house the inverter and batteries where the panels are, but I did say above that the price of doing that is prohibitive.

Your option 2 is acceptable... but doesn't it just feel a little like buying the Porsche Cayman because you cannot afford the Turbo? :-P

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Thanks for the replies. Yes panels will go up ontop off workshop. Batteries and inverter with back up generator will also be at workshop. 

I had test my voltage from workshop to home with the generator power and directly at the generator. Only 0.2 volts difference. I am willing to gamble with that.

This weekend I will buy the second bank Troyan batteries from Solarnoob.

 

 

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26 minutes ago, Bere said:

This weekend I will buy the second bank Troyan batteries from Solarnoob.

I don't want to interfere too much but is SolarNoob's bank compatible with your first bank in terms of age and usage? I don't want to do SolarNoob out of a sale (his bank is at good price)  but I also don't want you to buy them and later discover that you perhaps should not have bought them. :unsure:

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1 hour ago, Bere said:

Thanks for the concern Chris.

I am willing take that chance on his word. 

Perhaps I should explain. I have no doubts SolarNoob's word is good. He knows the batteries are partially used and is selling them as such. If you have a new string of Trojans and you combine them with SolarNoobs batteries then your new batteries are going to work harder than the second (older) string you added. Fairly soon you will have 2 sets of batteries that chemically are the same "age".

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10 hours ago, plonkster said:

You'll be able to do remote firmware updates in other words,

Already tested that. Just wish my Phoenix could have the same. Not that I need to upgrade it ...

10 hours ago, plonkster said:

... soon also remote veconfigure.

Now that would make me smile. Broadly if I can set the BMV's relay's SOC settings remotely ... 

Have tried Victron's free web site with my data lately, I am impressed. Even send some bugs, suggestions and observations through, all where responded on within hours.

 

7 hours ago, pilotfish said:

MAX 2% by doubling up on the 35mm cores?

Question: Out of interest, if one must buy it new, what would the cable costs be in the end?

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On 3/22/2018 at 12:04 AM, The Terrible Triplett said:

Question: Out of interest, if one must buy it new, what would the cable costs be in the end?

Thinking to the last time I had to buy, it's around R60/meter to R80/meter. 200 meters of that is around 12k-16k.

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6 hours ago, Chris Hobson said:

I have just bought 70m of 4 core  25mm2 armored cable. R170/m.

Yup, the R60-R80 per meter is for 35mm^2 single conductors, which is why you'd need 200 meter of it (there and back). At R170/meter for 100 meters you're also at around 17k, so we're within the ballpark.

That was sort of my point. In this case he already has the cable, so that changes things... but if you still had to put in the cable, the difference in cost could potentially buy a nicer inverter or a high voltage MPPT. Or at least that is what I initially thought before I looked at some prices. At that point I realised your only option would be to upgrade to the Infini Super (the one that got the poor review), if you wanted to spend no more than 10k-15k extra. The decent 5kva infinis cost almost as much as a Multiplus.

Now if you could get by with a 3kva inverter, then the extra cost more or less pays for a blue upgrade. But not at 5kva.

I think you could potentially get a high voltage MPPT for that kind of money though, but you'd still have to buy 200 meters of thinner and cheaper cable, so it is going to cost more. I think that spending the extra money would have been the right thing to do in that case. But since we've now figured it out, that's all academic.

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