Infinisolar 3kw+ - Best PV voltage?

[Wetkit]

Anybody care to speculate as to what the best PV voltage should be to aim for a new installation?

I'm currently running 2 x 9 string panels. Voltage around 268V to 250V. This is working fine, but I am looking to add some more PV.

Thing is I cannot afford another 9 panels right now, so been thinking of running 3 strings of 7.

Would 208V do it?

[Guest]

 What is the load that needs to be powered?

Too much solar, and you waste. Too little and you use too much Eskom.

As you can set the charge current on the inverter to match the batt ah rating, you wont break the batteries with too much panels on the roof.

[Mike]

you have a infini 3k plus yes?  you can go up to 18amps max 510vdc on the controller. prolly 2 strings of 12 x 255w pv

[Wetkit]

Ok, let me try it this way....

I have 3 locations on my roof for solar panels. Problem is they can go max to 9 panels each due to space and shading, meaning 9 panels in a string is my max!!!

So if I now remove 2 panels from each string, I then only need to buy another 3 panels to get 3 strings of 7.

The biggest advantage is this is that I should then have very good PV for the whole day, not just morning and afternoon.

When I have more money again, I can the expand the strings, 3 panels at a time till I am back to 9 in a string.

 

The load currently is Pool Pump(750w), Irrigation pump(1100w), Wellpoint(800w), Greywater sump pump(600w), Computer stuff(800w), then also all the lights in the house, TV, security system, and then fridge and freezer.

[MaurizioZA]

On 2016/02/23 at 8:48 AM, Wetkit said:

The load currently is Pool Pump(750w), Irrigation pump(1100w), Wellpoint(800w), Greywater sump pump(600w), Computer stuff(800w), then also all the lights in the house, TV, security system, and then fridge and freezer.

... 3250W only for pumps ... your peak must be well over 5000W.

Curiosity: what is your maximum load recorded in Grid-tie with backup mode? (but I do not allow feed-in to the grid since I am charged for what i feed-in)

I am asking because after having gone over the 6000W load mark (6798.0 W 227%) I am starting to wonder what's the max limit is before my unit trips.

Maybe when my circuit breaker (40A) trips?

I am considering adding more appliances (heat pump would be great) under a relay switch which would disconnect non priority devices in case of load shedding but I am not sure running in super-overload mode too often would be such a great idea.

Any advise?

 

[Mike]

On 2016/02/23 at 8:48 AM, Wetkit said:

Ok, let me try it this way....

I have 3 locations on my roof for solar panels. Problem is they can go max to 9 panels each due to space and shading, meaning 9 panels in a string is my max!!!

So if I now remove 2 panels from each string, I then only need to buy another 3 panels to get 3 strings of 7.

The biggest advantage is this is that I should then have very good PV for the whole day, not just morning and afternoon.

When I have more money again, I can the expand the strings, 3 panels at a time till I am back to 9 in a string.

 

The load currently is Pool Pump(750w), Irrigation pump(1100w), Wellpoint(800w), Greywater sump pump(600w), Computer stuff(800w), then also all the lights in the house, TV, security system, and then fridge and freezer.

be careful if this is on the infini, you cannot go over 18amps which is what your two strings will get close to.

[Wetkit]

MaurizioZA, not all the pumps run at the same time.

Pool pump run say from 10:00 to 14:00. Irrigation pump from 14:00 to 15:30. Wellpoint can only run when irrigation pump is off.

Also I am NOT allowed to feedback to the grid due to my stupid pre-paid meter, so that is switched off.

 

The graphs on my unit have never showed it to go over 3kw, so will have to check on my Home meter.

But I do get about 20 alarms a day

 

Mike, do you think the MPPT will draw more than it is designed for? My panel amp limit is 8 amp, so with I'm still ok with 2 strings. So rather up the voltage by adding more panels to the existing strings?

[superdiy]

3 hours ago, Mike said:

be careful if this is on the infini, you cannot go over 18amps which is what your two strings will get close to.

As with any electrical / electronic device the inverter should only draw as much as required - up to 18A, even if the panels can produce 200A. Current is drawn, not pushed, so it should be fine. The maximum pv input voltage must just not be exceeded, because then you will have component failure inside the inverter.

[superdiy]

9 hours ago, MaurizioZA said:

I am asking because after having gone over the 6000W load mark (6798.0 W 227%) I am starting to wonder what's the max limit is before my unit trips.

Out of curiosity, are these spikes or for longer periods at a time (minutes / hours)?

[MaurizioZA]

12 hours ago, superdiy said:

Out of curiosity, are these spikes or for longer periods at a time (minutes / hours)?

6798.0 W 227% was a temporary spike after a Sunday lunch when a few appliances were activated at the same time.

I think that to the usual load at that time of the day (server with 24HDs+TV&pvr+fridge+freezer+ coldroom+poolpump) a couple of extra appliances must have started at the same time (my guess would be dishwasher and maybe espresso machine as well) while I was distracted  

... weather was party cloudy to overcast (don't exactly remember.

In general my load level is ~30% but obviously for a few minutes dishwasher requirements are heavy.

It is not a problem when grid is available but it will be definitely be with load-shedding at night.

That is why I have been considering some load shedding device of the type as in

http://www.electrodev.co.za/shop/dls3/

but I have no idea how to place such large unit inside my already full db board

A miniature 30A solid state relay, placed inside the cb board somehow,  controlled by a phase outside hybrid inverter (when grid power is off non essential circuits under inverter would be switched off)  might be the cheap way out.

The ideal and more elegant solution would be a software controlled (by datastream from inverter) system of relays of the type described in

which checks spare capacity available prior to powering up non essential loads ... but that would also require empty cb board slots which I don't have

So, the miniature 30A solid state relay appears to be the only feasible solution.

I spent all day installing a 24 000btu aircon (cassette + extra ducting) which I have experimentally added to my hybrid inverter load: we'll see soon enough at which ax load the inverter will trip in bypass mode

Tomorrow I will add solar support to this aircon (unit can be fed directly with 360V DC from PV panels - has dedicated MC4 connectors which have priority over 220V supply):    as long as there is any PV output it will (or rather: should) keep on running and when PV output is zero will switch over to grid power. I am curious to find out howt the hybrid inverter will react  to external PV usage.

 

[MaurizioZA]

19 hours ago, MaurizioZA said:

Tomorrow I will add solar support to this aircon (unit can be fed directly with 360V DC from PV panels - has dedicated MC4 connectors which have priority over 220V supply):    as long as there is any PV output it will (or rather: should) keep on running and when PV output is zero will switch over to grid power. I am curious to find out howt the hybrid inverter will react  to external PV usage.

 

Update: I've been too busy to test solar support and I have left aircon running all day in standard 230V mode. After checking my day meter reading I realize that even through inverter I've been running it "for free"

Nice to know that this winter I will not have too freeze, as it is usually the case, while working at my desk (although most probably in winter months low sun inclination will degrade PV output ...no idea by what %).

[viper_za]

Can you give some more details about that AC unit, make model number maybe?

[MaurizioZA]

1 hour ago, viper_za said:

Can you give some more details about that AC unit, make model number maybe?

It's a Solark 24 000btu cassette inverter type unit directly powered by PV panels (up to ~360V DC).  Strictly speaking only the ODU (outdoor unit) is PV powered, the IDU (outdoor unit - ~200W) is powered by 230V AC. 

To make the story simple: front end of a conventional inverter type ODU converts 230C AC to DC. From there a controller regulates the speed of the heat pump making it run faster when more cold/heat is required or slower when less is needed. With this technique not only temperature is maintained constant (no up and downs as in conventional ac) but also there are no continuous start/stops with the result that an inverter type ac is much more energy efficient than one of  a conventional type.

The Solark solar air conditioner takes all a step further by bypassing the AC-to-DC front end and feeding DC voltage directly to the unit.

There are a few advantages of this approach (vs PV panels feeding a solar inverter powering AC to the ac front end) but for me, since I need it during the day, the most important is that there will be no load on my inverter (except from IDU) as long as a tiny bit of PV voltage is available (solar aircon will continue to run even at very low PV voltage although at  reduced cooling/heating rate).

All the above is theory since I have not completed the solar connection and up to now I have only operated the unit in 230V AC mode through my hybrid inverter.

I have chosen this particular cassette unit because it allows for additional diffusers: in addition to the main unit in my office I have one diffuser in my server room (for cooling in very warm days when temp alarm goes off) and one diffuser in another office (for warming in winter). I am able to open/close extra diffusers according to my needs.

Strictly speaking the unit is manufactured by AUX  (ODU: AL-24/4DR1(U); IDU: ALCA-H24/4DR1) but branded Solark (which contributes the solar support).

I am actually happily surprised with Solark support: my unit was damaged on import during police and customs inspections (insurance inspector defined damage as "malicious") and not only Solark promptly shipped replacement parts free of charge (I only paid for courier costs) but also guided me on how to repair the unit as I purchased it  back from the insurer as salvage . The fact that it works on 230V AC is already a great step forward.

 

I'll post some pics once it runs solar.

 

[MaurizioZA]

Following up on solar aircon installation: I wasted the whole Friday running in a circle

AC in grid mode: I tried to identify reason why my earth leakage under inverter felt the need to trip (when I fist installed it I had disconnected earth and decided to sort issue later). No matter what I tried inverter did not like aircon ODU to be connected to earth.

After wasting lot of time I decided to leave this issue for later and test the aircon solar mode.
That did not work out either: as soon as "-" MC4 connector was inserted the inverter returned error 05 (05 An Inverter overcurrent event is detected) although PV DC circuit breaker was still off.

[90000000000000] [2016-03-04 13:54:47]
     An Inverter overcurrent event is detected

As I inserted "+" connector and switched on PV DC circuit breaker the error changed to 12 (12 Leakage current exceeds the allowable range) and my earth leakage under inverter would trip.

[90000000000000] [2016-03-04 13:56:10]
     Leakage current exceeds the allowable range

Inverter automatically disconnect PV input.

Disappointing. My rushed conclusion is that "mppt management in my hybrid inverter is too clever and interprets the presence of an external PV load as fault and shuts down the mppt controller. This solar aircon will not work with this inverter, nothing I can do about it".
The next step would be to test the solar aircon with the  stupid mppt charger supplied with the aircon (testing with this should have been the wise course of action in the first place) but that I am unable to do this because I need 2 more sets of MC4 connectors which I don't have

I had promised pictures: ODU (note MC4 connectors)

cassette IDU

one of the extra diffusers (the one in my server room).

I then decided to tackle the earth leakage issue: strictly speaking regulations do not require aircon to be under earth leakage (but require isolator to be lockable).

Still ... I should identify source of leakage: after carefully checking cabling and IDU I have isolated the leakage to occur inside the outdoor unit.
Problem: that is now 3-4m above ground and to open it up and check it is going to be a mission

[intermission: as i am writing this post I am freezing my but off with the aircon on But it is so rewarding to know that at the moment it is being fully powered through the hybrid inverter and that as a result I am wasting less PV potential production!]

Still: the fact that just plugging the MC4 "-" terminal from aircon causes error in inverter (with AC isolator off) gives me a tiny hope that the incompatibility aircon/inverter might be related to that leakage.

The only solution is scaffolding (and with that I will also be able to get up to the chandelier in the double volume which hasn't been cleaned in almost 10 years and replace the burned globe which freaks out my wife so much). I can see this solar aircon has just been shifted to the long term projects which will only be tackled in 12-24 months.

Next step: test solar aircon with stupid mppt charger supplied with the aircon.