Solax Power inverters questions

Re: Solax Power inverters questions

UL is "Underwriters Laboratory"... It is the original organization started by insurance companies to come up with uniform safety standards for various "stuff" (electrical equipment, fire extinguishers, fire resistant wall/building materials, etc.).

They are now known as as NRTLs (nationally recognized testings laboratories). There are many... ETL, CSA, TUV, etc. (many countries have at least one "NRTL").

To a degree, these standards/testing organizations became part of the methods governments limited imports/spread money around (originally, you could not import to Japan electrical equipment unless you had their NTRL do the "testing").

In some ways, these NRTL "Listings" have become a way of judging quality. Although a Listing does not test/approve quality--In general, companies would not spend $50,000+ USD (plus yearly fees+factory inspections) if they were just trying to make "quick money".

The specification referenced above is used by many utilities to ensure that the GT inverters are "safe" when connected to their Grids. I.e., if the power fails, the GT inverter would not try to feed power back to the grid and kill a lineman or start a fire in a home next door.

-Bill

Re: Solax Power inverters questions

The concern is sort of a carry over from the older Inverter and backup generator days...

Some of the older GT capable inverters would "synchronize" with the 50/60 Hz AC voltage wave form and feed back power to the utility--Just like if you had a motor+generator set (you can take a motor+generator and get the RPM+Phase exactly right, connect to the Grid, and then feed power to the grid and your local loads).

Because these were (are) voltage sources--They supply current to the loads/grid up to the capability of the inverter (or generator). If the AC utility power/grid failed, they could still feed energy back out to the loads/grid. And supply the neighbors with backup power, electrocute linemen working on a fallen power line etc.

So--"They" created a standard to make sure that these inverters could never feed energy back out to a "dead/failed" utility line. The inverters would "monitor" the frequency and voltage for 5 minutes--If they were within specifications, the GT inverter would "turn on" and feed power out. If the voltage or frequency fell out of range, they would turn off and wait for 5 minutes of "good utility power" before reconnecting.

Note I said that the older GT inverters and motor+generator sets were voltage sources... They actually would synchronize with the utility power and actually feed power if there was no utility power (grid failed).

Most modern GT inverters (at least less than 10 kWatt, I have no idea about >>10 kWatt GT inverter systems) are current sources--They output current by "following" the exact utility voltage/wave form--So, if the power fails, the GT inverter would see near zero volts, and output no current (as well as see that the AC wave form is no longer in specifications, and shut down within a few cycles anyway).

So--A GT inverter mfg. would hire UL/CSA/TUV/etc. or other NRTL to "List" their device as meeting the safety requirements (and the factory would be inspected by the NRTL around once per year to ensure that the factory was still using "legal" material and producing the same "Listed" product).

The end result--A GT inverter will never feed power to the grid (and local loads) unless there is "good utility power" available. And a GT inverter cannot do "backup" or "emergency" power (as always, there are exceptions--But this statement is "correct" as far as the power utility is concerned).

-Bill

Re: Solax Power inverters questions

#1 missconception and disappointment with GT Solar--THE GT SYSTEM SHUTS DOWN IF THE AC MAINS FAIL. THERE IS NO BACKUP POWER CAPABILITIES.

-Bill

PS: As always there are exceptions (battery backed hybrid GT capable systems, SMA makes a smaller system that can supply ~1kWatt maximum to a local AC plug if the AC Mains fail and the sun is shining--But, in general, a pure GT Inverter + Solar Panel system shuts down when AC mains fail).

-BB

Re: Solax Power inverters questions

Regarding panels/array configuration... You have to first understand the input requirements for the GT Inverters.

Nominally, the "average/typical" GT inverter will use a Vmp-array in the range of ~200 to 400 VDC (standard test conditions--STC).

So, if you have, for example, panels with Vmp-stc of 30 volts, then you can put:

200 volts / 30 volts = 6.67 = 7 panels minimum
400 volts / 30 volts = 13.3 = 13 volts maximum

And when you parallel strings, you will need to match Vmp-string to another string within 10% or better... If you have 10 panels in one string (300 VDC), then the other string Vmp-stc-array must be somewhere within 270-330 volts or closer.

In general, mixing/matching panels is not always possible... Sometimes the mixing/matching of Vmp and Imp is just not possible.

-Bill

Re: Solax Power inverters questions

Generally, for smaller GT inverters, there are two (or sometimes more) connection pairs... One for each Panel String.

In general, if you have one or two strings, you simply wire them in parallel--Either at the array or in the GT inverter.

If you have three or more parallel strings, then each string usually needs a fuse or circuit breaker per string (i.e., ~10-20 amp + series protection fuse--check the panel specification for exact value). When you have three or more strings, a shorted panel can be fed current from the other 2 or more parallel strings. The per string fuse/breaker is to prevent the shorted panel/wiring from catching fire by being feed current from the other parallel connected panels/strings.

For smaller GT inverters, you may usually need 1-3 or so strings of panels. Depends on the GT inverter input power requirements and the size of your panels. Say you can get Vmp~30 volt panels and they range from 180 to 250 Watts:

i.e., 10 panels * 180 Watts panels = 1,800 Watt string
or, 13 panels * 250 Watt panels = 3,250 Watt string

It all depends (the first couple of times you go through the array configuration process--It is confusing).

-Bill