Hi

Can someone explain the difference between these wrt inverters with the same capacity - as both 5kw 48v units of the same brand. 

I'm half dumb so a lay response would be great-lol

Tx 

Can I assume that you mean you want the difference between a  High Frequency inverter versus a Low Frequency Inverter?

Because if you are specifying that both inverters are 5kW and 48V, then you are saying that they have exactly the same battery voltage, namely 48V.

Maybe give examples of the make and model.

If this doesn't fit, please ignore.

If you really meant low frequency vs high frequency, then compare it in layman's terms to an old-school muscle car with a big engine versus a small screaming turbocharged engine in a small sports car.

Low frequency inverters work with internal transformers, heavy metal cores and copper windings, which are generally more robust, and have more grunt to run motorised equipment. For your fridge compressor, washing machines, pumps, etc. this type of inverter can handle a higher start-up surge that is caused by the magnetic windings in an electro-motor.

High frequency inverters run with fancier electronics doing high-speed switching to achieve a 230V output. This means they can be made lighter and cheaper, but any surge is carried more directly by your electronics, so the stress and wear and tear could be greater.

Not saying one is better than the other; a brand like Goodwe would make inverters of both types, but don't recommend their hybrid inverters as a dedicated off-grid solution, and don't advise putting heavier types of loads on pure backup side.

Tx Bud, but my question refers rather to the HV or LV nature of the MPPT function on the inverter eg. 145v vs 450v

 

Hope this makes sense. 

21 hours ago, RyanBM said:

my question refers rather to the HV or LV nature of the MPPT function on the inverter eg. 145v vs 450v

This is a subject that I've been poking into just recently.

The biggest problem with the most affordable inverters (made by Voltronics), is that their higher voltage SCC models (which is almost all of them now) don't have the ability to perform ground fault testing. That means that there is a small but avoidable chance of fire if a ground fault developed. That means that these inverters can never be IEC-62109-2 compliant, so they will never make it to for example the Australian approved inverters list, so they are not legal for use in Australia. (Despite that, plenty of them seem to be installed.) I have no idea how insurance companies would react if a fire is caused by an illegal inverter. It's likely not good, though. Many of the other brands that use higher voltage MPPTs (e.g. SunSynk, Victron) do have the ground fault testing, do conform to IEC-62109-2, and are approved for use in countries with strong regulation, like Germany and Australia. So these other brands don't have this particular problem.

Besides the legality, there is the fact that the array wires are at lethal potential with respect to earth, even at night (if connected to the inverter and it's running). Disconnected from the inverter, the total array voltage is also lethal. High voltage DC rated isolators and breakers are more expensive and difficult to source. Finally, if your panels happen to leak when it rains, there is a tendency for this leakage current to push up the bus voltage, so inverters can trip off with fault code 08 (bus voltage too high). Search this and other forums for examples.

On the positive side for higher voltage PV systems, array wiring is definitely easier and cheaper with a single or relatively few strings of panels in series. Losses are slightly lower for high voltage systems, though you can compensate for this by using thicker PV wiring.

4 hours ago, Coulomb said:

That means that there is a small but avoidable chance of fire if a ground fault developed.

I think that risk is extremely low as there is almost no combustible material involved, unless you have a tached or wood shindle covered roof unterneed the panels. 

 Question: Do the "low voltage" inverters have that protection or do they not require it?

16 hours ago, Beat said:

Do the "low voltage" inverters have that protection or do they not require it?

They do not require it. They connect directly to the battery side, which is isolated from any AC.

Hi guys

 

On a related topic...

 

what would the array look like if i had say eg

6 x 450w panels

array for low voltage would be? 2s and 3p strings?

array for high voltage would be? 6s ?

 

and say i wanted to achieve 3kw from low per inverter, what would the array look like? 

thanks and little insight would be appreciated.

 

 

35 minutes ago, Dollos1 said:

Hi guys

 

On a related topic...

 

what would the array look like if i had say eg

6 x 450w panels

array for low voltage would be? 2s and 3p strings?

array for high voltage would be? 6s ?

 

and say i wanted to achieve 3kw from low per inverter, what would the array look like? 

thanks and little insight would be appreciated.

 

 

Hello,
There are advantages and disadvantages to both systems:
in solar panels, low voltage forces thicker cables to be used due to voltage drop. On the other hand, if the panels are not all oriented exactly in the same position, it is convenient to use more strings, that way you will have low tension. Whatever the system, you need to know what you want and in what environment you are going to install it, if the panels are oriented to the same side, if you want microinverters, if you want a single inverter, if you want to connect batteries...

@Coulomb

hi, some more insight would be helpful. thanks

16 hours ago, Dollos1 said:

6 x 450w panels

array for low voltage would be? 2s and 3p strings?

array for high voltage would be? 6s ?

You didn't give specs for the 450 V panels. Assuming that Voc is about 49 V and Vmp is around 40.5 V, then yes, you need 2S (2 panels in each string). 2S3P (three strings of 2 panels each) would be 2 x 3 x 450 = 2700 W nominal.

16 hours ago, Dollos1 said:

say i wanted to achieve 3kw from low per inverter, what would the array look like? 

You usually only get about 75-80% of nominal power from panels, even under ideal conditions. So to get 3 kW max, you'd want about 4 kW of panels. 4000/450 = 8.9, so 9 panels is close. But you need an even number, so you'd need to drop down to 8 panels (2S4P for 3.6 kW) or up to 10 panels (2S5P for 4.5 kW). Many low voltage PV 5 kVA models have a maximum nominal solar power of 4 kW, and it's usually best not to "overclock" my more than 20%, so that's 1.2 x 4 = 4.8 kW. So 10 450 W panels would be OK.

Many of these inverters were designed when panels were no more than 200 W, so adding a pair of panels only made a 400 W difference. With todays giant panels, adding two can make a difference of 1200 W. I believe that you can still get smaller panels, say 320 W, which might help achieve specific goals.

My own panels are a mixture of 195, 200, and 215 W nominal, and I have 8P on one inverter and 6p on another. All 2S. My inverters are older models with only 3000 W solar chargers.