Electrical grid tied PV systems

[David Morrow]

1. I have not seen IEEE 1547-2003 as this question pertains to it. They say that small PV systems are tied into the grid, if the wave sign of a PV inverter is a square wave how does that marry to the wave of electricity flowing on the existing grid? Does this current just get gobbled up so to speak or is this considered dirty current and goes no where past the net meter?

Homework Equations

I have no equation.

The Attempt at a Solution

The solution would require an electrical engineer familiar with IEEE 1547-2003.

 

[berkeman]

1. I have not seen IEEE 1547-2003 as this question pertains to it. They say that small PV systems are tied into the grid, if the wave sign of a PV inverter is a square wave how does that marry to the wave of electricity flowing on the existing grid? Does this current just get gobbled up so to speak or is this considered dirty current and goes no where past the net meter?

Homework Equations

I have no equation.

The Attempt at a Solution

The solution would require an electrical engineer familiar with IEEE 1547-2003.

Why would you think that the power utility would allow a square-wave output inverter to be tied to the grid?

 

[David Morrow]

All the dot coms in pv say that these systems are grid tied.

 

[berkeman]

All the dot coms in pv say that these systems are grid tied.

And they claim to be connecting square wave output inverters to the grid? Can you provide some links?

(It might be true, but it's hard for me to believe. For example, the FCC in the US dictates how much noise you can put on the powerline, and I would think that a square-wave output inverter would exceed those levels...)

 

[David Morrow]

The IEEE wants $80.00 for a copy of IEEE 1547-2003 which it appears is the bible for hooking up small and large pv systems to the grid.

 

[David Morrow]

I agree with your assessment but am doing a research paper and need definitive proof.

 

[David Morrow]

no one states implicitly that these systems (small PV) are tied to the grid except anyone selling these systems. As far as DOE they skirt the issue very well after 200 hours of research and what was a very limited knowledge of electricity, it comes down to IEEE 1547-2003 of which my PhD professor was unable to get a free copy.

 

[berkeman]

The IEEE wants $80.00 for a copy of IEEE 1547-2003 which it appears is the bible for hooking up small and large pv systems to the grid.

Perhaps your local university libraries might have a copy that you can look at?

Also, I did a Google search on connecting photovoltaic systems to the grid, and got lots of good hits:

http://www.google.com/search?source...302&q=connecting+photovoltaic+systems+to+grid

The references at the end of the Wikipedia article on Solar Inverters looks like it might have something that would discuss the allowed noise content of the output of the inverter that is tied to the grid:

http://en.wikipedia.org/wiki/Solar_inverter

.

 

[berkeman]

no one states implicitly that these systems (small PV) are tied to the grid except anyone selling these systems.

The Wikipedia articles seem to state that pretty clearly, don't they? You would not have anti-islanding requirements if they did not connect to the grid...

 

[David Morrow]

Thanks for your valuable time.

 

[The Electrician]

UL1741 has much to say about connecting inverters to the grid. I can send you a copy; if you want it, PM me with a valid email address.

 

[David Morrow]

Thank you my name is David Morrow my email is << personal e-mail address deleted by berkeman >> I do so much appreciate this. It is for my Capstone project.

 

[David Morrow]

At this point I could really use a copy of IEEE1547-2003 and any changes to it that may have occurred, at least a copy of IEEE 1547-2003 would be great if anyone has one, my school e-mail is << personal e-mail address deleted by berkeman >> . Thanks to everyone this site has been extremely helpful.

 

[David Morrow]

OK, I have done my due diligence on PV inverters and have come to the conclusion that inverters made after 2001 seem to have everything that makes the grid happy so they can be tied to the grid, if it is a 10kw inverter and it is producing max output, and your nearest neighbor is 100 yards away how much of the energy actually gets to them assuming you are using 0 load from the inverter?

 

[berkeman]

UL1741 has much to say about connecting inverters to the grid. I can send you a copy; if you want it, PM me with a valid email address.

UL 1741 is a copyrighted publication, and is available for purchase here:

http://ulstandardsinfonet.ul.com/scopes/1741.html

Offering to send an electronic copy for free is illegal.

 

[berkeman]

At this point I could really use a copy of IEEE1547-2003 and any changes to it that may have occurred, at least a copy of IEEE 1547-2003 would be great if anyone has one, my school e-mail is << personal e-mail address deleted by berkeman >> . Thanks to everyone this site has been extremely helpful.

Trying to obtain copyrighted materials for free is illegal. Please do not do this again here on the PF.

 

[David Morrow]

Sorry, will not happen again.

 

[David Morrow]

OK, the inverter for a 10 Kw pv system is rated at 10 Kw max output. There is no load being used at this residence by this grid tied system, it is noon and the inverter is putting out max power, the nearest neighbor is 100 yards away is there any way of calculating how much of this current they could utilize? Or would the resistance at the transformer and wire along this 100 yard stretch negate any usable current?

 

[The Electrician]

Assuming both houses are connected to the same pole transformer, and the grid is providing voltage, it would be possible to calculate if one knew the resistance of the wires from each house to the pole transformer, the reflected impedance of the grid at the transformer, and the impedance of the loads at the neighbor's house. I would expect that a negligible amount of the power from the inverter would supply the neighbor because the reflected impedance of the grid at the transformer would be very low and would absorb most of the inverter's output power.

 

[David Morrow]

I would assume for this problems sake that each residence has their on step down transformer from the grids point of view and these would then at least the pv inverter side would be considered a step-up transformer in this case. Would I be able to state in my paper that this amount of usable current would be negligible because of the resistance at the transformer and length of wire the current must travel upon?

 

[The Electrician]

With separate pole transformers, the power delivered from the inverter to the neighbor would be even less than negligible--it probably would be unmeasurable.

A crude way to determine how much coupling there is between the neighbors would be to connect voltmeters at the service entrance (the fuse or circuit breaker box) of each house, then apply a large load at one house of several kilowatts. An easy way to apply a large load would be to turn on all the burners and the oven of the electric stove (if there is one). Note the decrease in voltage at the service entrance at the house with the stove turned on and at the same time make the same measurement at the neighbors house.

If the homes have separate pole transformers, the effect of a large load at one house upon the voltage at the other will be very much less than if the two homes are served by a single pole transformer. The effect of a large load at one home on the voltage at the other is essentially the same as the effect of delivering a large amount of power (from the inverter) at one home on the voltage at the other home. If supplying power to the grid from the inverter doesn't cause the voltage at the neighbor's home to rise, then there isn't delivery of power from the inverter to the neighbor.

If you were to connect a voltmeter to the grid at a typical home, you would see the voltage is varying a few volts all the time. This is because in a typical neighborhood, the people living there are turning things on and off all the time. Also, industrial equipment is being energized and de-energized. These things are happening city-wide, county-wide and nation-wide. The variation at the neighbor's home due to supplying or not supplying 10 kW of inverter power would undoubtedly be completely swamped by the voltage variation from the other causes I just mentioned. This is how you would be able to show that hardly any of the power from the inverter was arriving at the neighbor's home.

 

[David Morrow]

Thank you so much again, I think that does it for me on my quest. Hope you have a wonderful life as you have made my research paper a little better than I could have done on my own.