Hi Forumites... I'm starting out on this journey and already have sooo many questions.. I've been lurking in the shadows, reading many posts and I want to know the following.

I'm on a smallholding outside Centurion.

I've been looking at the InfiniSolar Plus 3K  or maybe the Goodwe GW5048 Em 5KW or Infini Solar 5kW Dual MPPT Hybrid Inverter

1. Why would one want to have an inverter that can be connected in Parallel?  Would it not be better to have one 10Kw hybrid than 2x 5Kw

2. Almost in the same area; Why does some Hybrid Inverters have Dual MPPT?

3. There seems to be a few Voltage variables that Solar panels have; Voc(open Circuit) and then Operating Voltage (12/18/48)  Which one is most important when pairing a PV to the Inverter ?

4. Some PV max voltage can harm the Inverter if it is more than the inverter can handle. How does this work (in which circumstances can this max voltage be "activated"?

5. It seems that very cold conditions also have an impact on the voltage , why is this ? ... Maybe in general if someone can just summarise the voltages, as my head is spinning from trying to make head and tails reading Wikipedia and other websites that explains PV panel voltages

6. The InfiniSolar Inverters are sometimes branded as Mercer and sometimes Voltronic and sometimes ?? this seems confusing.. is there a Branding one should avoid (e.g. InifiniSolar 3K PLUS Single Phase Hybrid Single MPPT Inverter Charger bi directional with grid 48V DC(SOL-I-IS-3M)  .../// Mecer Infinisolar 3KVA . Plus Hybrid Inverter Single Phase)

7. From some posts it seems that Mono PV is better than Poly , but then someone mention something about operating temperatures ,, which is best for South Africa?

8. I get my mains power directly from Eskom , I have 3phase power. In the main Box I have 3 meters, One is a grey box with a blinking light, the other 2 are the old type with the spinning wheel. I'm hoping that I can put all the loads that will be paired with my solar setup on one phase and install a hybrid Inverter and hope to push back power into the grid, making the wheel spin in reverse  during the day and forward during the night when I use Eskom power... As I'm not on Jhburg Power or Tshwane Power, will I have to register and apply for this from Eskom or do I just sneak this in and hope they never notice?

There are many more questions, but for the moment these are the few I find most pressing.

Hope the Forum will shed some light (solar) on these 🙂

 

 

Pardon me addressing just a few questions.

2 hours ago, PlanB said:

6. The InfiniSolar Inverters are sometimes branded as Mercer and sometimes Voltronic and sometimes ?? this seems confusing.. is there a Branding one should avoid (e.g. InifiniSolar 3K PLUS Single Phase Hybrid Single MPPT Inverter Charger bi directional with grid 48V DC(SOL-I-IS-3M)  .../// Mecer Infinisolar 3KVA . Plus Hybrid Inverter Single Phase)

Yes, the branding is confusing. Voltronic Power are the manufacturers, but they don't want to hand hold the customers. So they leave all that to the resellers, who get their own brand name on the box. I haven't seen an actual Voltronic branding, but I could be wrong. The problem is that the resellers can also change the model name, sometimes slightly, sometimes a lot, sometimes with overlaps (one model name could refer to two different actual models, for example).

The best you can do is to carefully read the specifications of the model(s) you are considering buying, so that you are getting what you expect, and can meaningfully compare them.

[ Edit: it's Mecer, not Mercer, no "r". Mercer made computers back in the day, I'm told. ]

2 hours ago, PlanB said:

2. Almost in the same area; Why does some Hybrid Inverters have Dual MPPT?

It's to cater for the situation where you have dissimilar panel orientation and/or shading. The classic case is where you have no north facing roof, so you split the panels east and west. These will have very different insolation at different times of the day, so the MPPTs can optimise each better than if the strings were paralleled.

Similarly with shading. If you have one string that is prone to shading, and one that is not, or is subject to different shading, the independent MPPTs can get the most from the two strings.

2 hours ago, PlanB said:

5. It seems that very cold conditions also have an impact on the voltage , why is this ?

All panels have a negative voltage-temperature coefficient, something like -0.4%/°C. That means you get higher voltage at lower temperatures. Less than half a percent doesn't sound like much, but a cold morning can be 25°C or more colder than the 25°C that the panel has its voltages specified at, so that's some 0.4 x 25 = 10% difference. In deciding how many panels you can connect in a series string, that 10% can put the open circuit voltage over the edge, possibly damaging the inverter's solar charge controller.

I note that as the temperature goes up, the current goes up, but the voltage goes down faster, so you end up with less power when the panels heat up. It's just a fact about silicon, though monocrystalline and pollycrystalline panels have slightly different coefficients, and they can vary slightly from manufacturer to manufacturer.

Edited April 5, 20197 yr by Coulomb
As noted.

Go for the GoodWe, less confusion and a very good product. 

2 hours ago, Coulomb said:

[ Edit: it's Mecer, not Mercer, no "r". Mercer made computers back in the day, I'm told. ]

https://mecer.co.za/ sells computer hardware in SA.

They where one of the first to import the Axperts into SA due to UPS shortages during the first few rounds of Eskom failures.

It took off from there. 🙂 

2 hours ago, Coulomb said:

[ Edit: it's Mecer, not Mercer, no "r". Mercer made computers back in the day, I'm told. ]

I think Mercer was a typo. Mecer is a computer brand owned by Mustek, some of the first 80286 models we got in this part of the world were Mecer units (again, giving away my age). They've sold everything from UPSes to monitors, modems, mice and mousepads under that brand, and finally they also sold a couple of inverter/chargers under the same brand.

8 minutes ago, plonkster said:

I think Mercer was a typo.

Ok, but it seems to be a very common one.

Also, @Chris Hobson said he thought there was a Mercer computer in the 1980s.

Edited April 5, 20197 yr by Coulomb
Oops, forgot link.

17 minutes ago, Coulomb said:

 said he thought there was a Mercer computer in the 1980s.

Yeah that might be a typo too, even a remembered typo 🙂 I remember them, friend of mine had one around 1993. It is a very common misspelling though.

16 hours ago, PlanB said:

Hi Forumites... I'm starting out on this journey and already have sooo many questions.. I've been lurking in the shadows, reading many posts and I want to know the following.

I'm on a smallholding outside Centurion.

I've been looking at the InfiniSolar Plus 3K  or maybe the Goodwe GW5048 Em 5KW or Infini Solar 5kW Dual MPPT Hybrid Inverter

1. Why would one want to have an inverter that can be connected in Parallel?  Would it not be better to have one 10Kw hybrid than 2x 5Kw

2. Almost in the same area; Why does some Hybrid Inverters have Dual MPPT?

3. There seems to be a few Voltage variables that Solar panels have; Voc(open Circuit) and then Operating Voltage (12/18/48)  Which one is most important when pairing a PV to the Inverter ?

4. Some PV max voltage can harm the Inverter if it is more than the inverter can handle. How does this work (in which circumstances can this max voltage be "activated"?

5. It seems that very cold conditions also have an impact on the voltage , why is this ? ... Maybe in general if someone can just summarise the voltages, as my head is spinning from trying to make head and tails reading Wikipedia and other websites that explains PV panel voltages

6. The InfiniSolar Inverters are sometimes branded as Mercer and sometimes Voltronic and sometimes ?? this seems confusing.. is there a Branding one should avoid (e.g. InifiniSolar 3K PLUS Single Phase Hybrid Single MPPT Inverter Charger bi directional with grid 48V DC(SOL-I-IS-3M)  .../// Mecer Infinisolar 3KVA . Plus Hybrid Inverter Single Phase)

7. From some posts it seems that Mono PV is better than Poly , but then someone mention something about operating temperatures ,, which is best for South Africa?

8. I get my mains power directly from Eskom , I have 3phase power. In the main Box I have 3 meters, One is a grey box with a blinking light, the other 2 are the old type with the spinning wheel. I'm hoping that I can put all the loads that will be paired with my solar setup on one phase and install a hybrid Inverter and hope to push back power into the grid, making the wheel spin in reverse  during the day and forward during the night when I use Eskom power... As I'm not on Jhburg Power or Tshwane Power, will I have to register and apply for this from Eskom or do I just sneak this in and hope they never notice?

There are many more questions, but for the moment these are the few I find most pressing.

Hope the Forum will shed some light (solar) on these 🙂

 

 

Welcome Great post! I promoted it. J

17 hours ago, PlanB said:

1. Why would one want to have an inverter that can be connected in Parallel?  Would it not be better to have one 10Kw hybrid than 2x 5Kw

Mainly for expansion; you buy the 5 kW model now, and buy another 5 kW later when you can afford it.

But there is also the idle power drain; you can switch off one inverter at night (possibly automatically), and save the idle power load, if you don't need it. Our patched firmware (for Axpert off-grid models, not the hybrids you are considering) even has a facility called Dynamic Load Control, which allows you to turn on and off some of your paralleled inverters with a command over the RS232 port.

1 hour ago, Energy said:

3. There seems to be a few Voltage variables that Solar panels have; Voc(open Circuit) and then Operating Voltage (12/18/48)  Which one is most important when pairing a PV to the Inverter ?

Really, it's Voc, since that determines the maximum number of panels in a string. But Vmppt tells you if that number of panels will be efficiently handled by the inverter. For example, many Axpert models have a maximum PV voltage of 145 V, but the MPPT range is stated as 60-115 V. So if you squeak under the absolute maximum voltage, but your string's highest power voltage exceeds 115 V, then you know that you won't be getting the most out of your panels, as the MPPT is only at its most efficient up to 115 V. (Turns out the real figure for Axperts is 130 V).

I don't know what you're referring to with the "operating voltage"; perhaps you mean the nominal panel voltage (the vast majority are "24 V", but some smaller panels are "12 V"). These are for directly connecting panels to batteries, usually via a PWM controller. Ignore those specifications; they mean little in the context of a home energy system.

17 hours ago, PlanB said:

4. Some PV max voltage can harm the Inverter if it is more than the inverter can handle. How does this work (in which circumstances can this max voltage be "activated"?

There is electronics that is always connected to the PV input. On some models, like the Axperts, there is no relay to disconnect this voltage. So there will be MOSFETs, electrolytic capacitors, and other devices that have absolute maximum voltage ratings. Operating above these limits means you're operating beyond the design limits. In the case of MOSFETs, even a few percent above the design limit can mean catastrophic failure, like a bang and a bad smell, not working after that. For electrolytic capacitors, the limit is more rubbery, usually causing the life of the capacitor to be reduced. However, they can also go out with a bang, and a different bad smell.

The panel voltage will be highest on clear cold mornings. So you work out your likely coldest temperature, and what panel voltage you will likely see at that temperature (usually around 10% more than the string's Voc), and make sure that this is under the maximum permitted panel voltage for your inverter.

17 hours ago, PlanB said:

8. ... I'm hoping ..., making the wheel spin in reverse

I don't know specifically about South Africa, but in most areas, this is never allowed. It's equivalent of paying the full retail price for your exported power. They'll only want to pay you (if they pay you anything at all) for the wholesale cost of generated power, which is roughly a third of the retail price. I get the impression that in many parts of SA, you aren't even allowed to export power at all, and if it's detected, the meter might cut your power.

Thanks Coulomb (and others) for clearing this up for me.

I've got another question.

Last week as a precursor to getting my house on solar, I started by converting my Gate motor and Electrical fence to solar.

Both these 2 devices works from a standard 12 V 7Ah sealed battery. I obtained a 30amp Charge controller, a 95Ah deep cycle battery and a 135W solar panel.

I didn't need an Inverter, I connected the 12V load from the controller directly to each of the Centurion D5 Evo gate motor and Merlin M28S Energiser.

I thought this would be overkill, but I was wrong.. with the lovely rain we had on Thursday and over the weekend I woke up Sunday morning with no security Fence off) and no gate operation.

It's wasn't to much of a problem, I restored Mains power to the 2 devices and all was fine. I hope to get a bigger panel this week, Maybe a +250W , as long as it's Voc is within the limits of the small Charge Controller.

My Question though is: IS there a Charge controller on the market that has 2 x Charge inputs 1 from the PV and one from 220v Mains, so that I can Trickle charge the battery at night if the solar panel was not able to get it to 100% during the day?

Thanks again

Edited April 8, 20197 yr by PlanB

1 hour ago, PlanB said:

IS there a Charge controller on the market that has 2 x Charge inputs 1 from the PV and one from 220v Mains,

Short answer: No.

I'm trying to calculate the Voc of these panels if I know that my property has had temperatures of -5'C for the last 2 winters.

Is it correct that for every 1'C below the Normal operating temperature the can be a 0.33% increase in voltage.

therefore -5'C is 25 'C lower than NOCT  and would therefore have a possible increase of the Voc of (25 x 0.33 = 8.25)

 Does this mean that hypothetically the Max voltage of this panel (72 cell)on a very cold morning could be 38.6 + 8.25  = 46.85V?

(see attached Picture)

On 2019/04/08 at 10:04 AM, The Terrible Triplett said:

Short answer: No.

Hey, don't be too quick. I believe Ctek might make one. But I might be mistaken. They definitely have a model that takes power from a PV panel as well as from your alternator, for 4x4/camping type people. You could theoretically use one of those and feed it with a mains transformer... but they are not cheap. You might be better off just using two separate chargers.

Just now, plonkster said:

... but they are not cheap. You might be better off just using two separate chargers.

Therein the No answer. 🙂 

Ok ok ... I  did not know CTEK might have PV and AC on same device, but price always is a killer to good ideas.

Quote

I'm trying to calculate the Voc of these panels if I know that my property has had temperatures of -5'C for the last 2 winters.

Rather use the attached to plot your panel voltages and check your overall solution.

VE-MPPT-Calc-3_0.xlsm

2 hours ago, Ingo said:

Rather use the attached to plot your panel voltages and check your overall solution.

Difficult maybe to convert to  Goodwe GW5048 Em 5KW or Infini Solar 5kW Dual MPPT Hybrid Inverter requirements.

That calc caters for Victron MPPT's to a T, or is that a TTT? 🙂 

😆 But you can still plot your panel voltages over the temperature ranges.

Generally when it is -5 degrees, there is no sun. Once you get some sun on the panels they will start to heat up, so I don't think it is too much of an issue. Just don't put the total voltage too close to what the MPPT can handle.

5 hours ago, DeepBass9 said:

Generally when it is -5 degrees, there is no sun. Once you get some sun on the panels they will start to heat up...

Sure, generally. But the sun could burst out from behind thick cloud, and the panels could give a burst of power, enough to blow up the solar controller. It only takes once.

Hmm, maybe in Australia that can happen, but I don't think in Pretoria. 

On 2019/04/05 at 1:29 PM, The Terrible Triplett said:

Go for the GoodWe, less confusion and a very good product. 

Are you converting? Nice touch

22 hours ago, plonkster said:

Hey, don't be too quick. I believe Ctek might make one. But I might be mistaken. They definitely have a model that takes power from a PV panel as well as from your alternator, for 4x4/camping type people. You could theoretically use one of those and feed it with a mains transformer... but they are not cheap. You might be better off just using two separate chargers.

Those are pretty neat chargers!