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grid tie solar electricity with optimizers and inverters what would reduce the dc input voltage
6

grid tie solar electricity with optimizers and inverters what would reduce the dc input voltage

grid tie solar electricity with optimizers and inverters what would reduce the dc input voltage

(OP)
The Grid tie solar system a house was design to be overdriven for maximum continuous solar power during daylight cycle. The utility is 120/240 VAC single phase system 200 amp service. It has a 76kw SE7600-US Solaredge inverter with 28 Solaredge P320 power optimizers mounted externally on the side of the house adjacent to the meter. Each optimizer has a 300 watt Q-peak G4 solar panel (module) connect in parallel to it mounted on the roof facing east with no obstructions. The optimizers are suppose to be connected in three strings 9-9-10. The three strings are connected in a j box on the roof and run in EMT with # 8 cu wire to the inverter about 25 feet away. The workmanship and code compliance of the installation is excellent. The system works is producing 5250 watts at 240 VAC 60 HZ output. The inverter had a monitor reading display of 240 VAC-247 VDC-5250 PAC was taken at the installer about 2 pm in September on a cloudless day in southern Nevada.

The inverter is presently turned off waiting for the utility to connect their meters used for solar power. I will be monitoring it closely once the inverter power is on. With the power off the optimizer produce a safe power of 1 volt DC each. With the invertor off- The input voltage to the inverter input terminals is 13.03 volts DC.


My concern is that the Dc voltage is low at 246 VDC- it is suppose to be a constant 360 VDC. Per vendor specification-This 360 DC volt will be maintained if the string optimizers are connected in series string length a minimum of 8 to a maximum of 25. The inverter nameplate voltage operating voltage range is 270 -500 VDC.

The Electrical contactor who installed the system claims that some lower voltages are normal for this systems and that the Dc voltage reading was read in error by his technician that installed the system-That appears reasonable to me based on his experience. He claims the voltage would be 288 VDC from the strings in parallel. the lowest string 9 string would clamp the voltage to it voltage output of 288 VDC and projected amperes of 29.1 based of full peak wattage of 86400 from solar panels . He also said the current would increase to compensate for the lower voltage to maintain normal solar power output-also reasonable. His logic is coorrect for solar panels strings without optimizers. I have read on the internet that this is also normal for other manufactures optimizers and inverter.

I called the hot line from the manufacture twice- one reprehensive claimed the some of the optimizers could be connected backward causing reverse polarity problem's and he said that if a string was less that 8 the optimizer that string would shut off. The other representative claimed that the system was overdriven to high causing the lower voltage and was not cause by reverse polarity. They both thought the contractor was mistaken.

I don't have practical experience with this type of solar system. The inverters maximum input current is 23 amps and has short circuit protection of 45 amps so the # 8 copper stranded feeder from the roof are protected. I don't know if the input is current limited or it is some value of a Time Current curve for a current limiting fuse or breaker.


Is this normal or is there a problem to be concerned with.

RE: grid tie solar electricity with optimizers and inverters what would reduce the dc input voltage

If you can wait a little for the meter to show up that will be the final say regardless of your confusion and the contradictory responses you're getting. If you see your entire array's expected output on a sunny day you're good to go. If there's a problem you'll see it immediately as a large percentage missing.

Keith Cress
kcress - http://www.flaminsystems.com

RE: grid tie solar electricity with optimizers and inverters what would reduce the dc input voltage

If the electrician read 347 VDC as 247 VDC that would explain everything.
The lighting, shadows, contrasts and the type of display would all be factors.
It may be easy or it may be difficult to misread the display.
Also, when in doubt, check the voltages with a second meter.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: grid tie solar electricity with optimizers and inverters what would reduce the dc input voltage

(OP)
reference Itsmoked and waross-I am thinking the same thing. I am waiting for the inverter to be powered up. There is a button on the inverter that can be pressed to read the display Vdc, Vac and Pac (power ac in kw's).I also will verify dc amps and dc voltage with multifunction dc clamp on meter so I can calculate the actual dc power at the input of the inverter. Hopefully the dc wattage is what it is suppose to be during the solar cycle. I determined that If the inverter is clipping at a power rating of 5250 watt ac instead of 7200 watts ac- the over all yearly kWR production would be slightly less when over driven. That would be acceptable. Thanks for your help

RE: grid tie solar electricity with optimizers and inverters what would reduce the dc input voltage

A solar panel has an 'inverse' temperature dependence. I.e. lower voltage at higher temperatures (diode equation). A sunny day in southern Nevada sounds like it could be quite hot. A 100 C temperature increase can reduce voltage 25-30 percent.
It depends on what reference temperature is used in the specs. If 0C is used, which is not uncommon, and the panels reach around 100C, which is easy on a calm hot day in southern Nevada, then the voltage could drop around 100 V.

But that only happens if the rated voltage was given at 0C. I do not think that anyone in his right mind would install such panels in S. Nevada. But they are quite common up here in northern Europe where -20C is common during the winter.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: grid tie solar electricity with optimizers and inverters what would reduce the dc input voltage

Your solar panel instrumentation should show what it's generating in terms of total power and energy. With 28 panels at 300W, you should be generating a peak power of 8.4 kW.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

RE: grid tie solar electricity with optimizers and inverters what would reduce the dc input voltage

Apparently, I have a SolarEdge controller as well, but I'm not sure what my model number is. These are some pictures of what a couple of the display screens show.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

RE: grid tie solar electricity with optimizers and inverters what would reduce the dc input voltage

(OP)
irstuff-looks like my inverter except yours is about a 3kw output maybe model SE3000A-US-there is a label on the right side with the model number and other data. nice system it looks like it is working fine.

you are right The peak power of the solar panels is 8.4 kw the dc side. the inverter chokes the wattage and allows out only the size of the inverter which is in my case 7600 watts ac. I am over driving the system to get continuous maximum wattage out but still comply with the utility inverter size restriction.

skogsgurra-wow 100 volt drop-will check the temp spec.

Thanks to both of you.



RE: grid tie solar electricity with optimizers and inverters what would reduce the dc input voltage

Huh, that seems a bit weird to me. You've basically spent about an extra $3k for that, which also means that you're dumping about 4.500 kWh/day down the drain.

My panels do run hot; they were 106F back in April, when I took those pictures.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

RE: grid tie solar electricity with optimizers and inverters what would reduce the dc input voltage

Quote (IR)

4.500 kWh/day down the drain.
Compare that to the extra energy gained when the solar input is less than maximum.
ie: Mornings and afternoons.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: grid tie solar electricity with optimizers and inverters what would reduce the dc input voltage

Have a look at this:

http://www.pvresources.com/img/solarcells/solarcel...

This is for a single cell in a solar panel. The difference between lowest temperature (-25C) and highest (+75C) is around 40%

You can do the measurements on a 1N4007 diode (using around 1 mA fwd) and get similar results when heating it.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: grid tie solar electricity with optimizers and inverters what would reduce the dc input voltage

"Compare that to the extra energy gained when the solar input is less than maximum. ie: Mornings and afternoons."

My point was that yes, you gain that energy by throwing away your midday energy. That's just not an efficient thing to do. SoCal Edison doesn't seem to have that sort of restriction, so at peak insolation, I'm outputting to the grid, and in the late afternoon, I pull that power back from the grid. The net effect is that my 18 panels almost covers my entire power consumption for the entire day. The delta is only about 200 Wh/day difference.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

RE: grid tie solar electricity with optimizers and inverters what would reduce the dc input voltage

(OP)
IRstuff- I agree-I did a comparison calc using solar power software- the yearly KWH results were almost the same using a larger inverter.

RE: grid tie solar electricity with optimizers and inverters what would reduce the dc input voltage

(OP)
Doesn't make sense. I think some how the solar power cycle lost is not that much during the entire year.

RE: grid tie solar electricity with optimizers and inverters what would reduce the dc input voltage

Whilst I've never looked at the numbers, I've been advised that another benefit in terms of oversizing the array(s) as compared to the inverter is that output is not as likely to diminish under less than optimal (i.e. partly overcast) conditions. As I understand it, this is also partly dependent on the specific stringing arrangement.

There is also the restriction on what the utility will allow you to connect, if you're not permitted to connect an inverter greater than a certain size then it doesn't matter if you'd be 'throwing away your midday energy', as you'd not be able to use it under those circumstances anyway, but you would gain more from the morning / evening.

EDMS Australia

RE: grid tie solar electricity with optimizers and inverters what would reduce the dc input voltage

Interesting point Freddy.

Spend more money up front and not optimize the panelage so dirty panels/cloudy days/eclipses/etc don't actually impact the ROI or bill planning. It works better if the govm't is picking up some of the tab with subsidies. Or the system is completely designed by a greedy company in a customer knowledge vacuum. Or, panels are down in the $1/Watt range.


I have a friend who had a system installed to run his 3,500sqft house and a LARGE hot tub. About a month after the installation they permanently pulled the plug on the hot tub. Now he's always trying to figure out what to do with the massive monthly overage the POCO will never pay him a nickle for. He's put in an electric water heater to feed his gas water heater to try to use more of the excess electrons to shave off gas costs.

Keith Cress
kcress - http://www.flaminsystems.com

RE: grid tie solar electricity with optimizers and inverters what would reduce the dc input voltage

itsmoked, I edited my post out twice with the consideration of subsidies before I finally posted, but there's no way that they're not relevant in certain locations.

Here in Australia the discussion went from one extreme to the other, with export prices high enough that it would make the homeowner shut everything off during the day in order to export to the network, to the complete opposite where its way more cost effective to self consume before export. All of that is without the subsidies paid at installation time based on number of panels.

I've seen rental agreements for housing with the electricity costs included, as any change of connection agreement (as would normally occur if a tenant pays their own electricity costs) would result in loss of the (much) higher feed-in tariff.

You're right, watthours are watthours, but when the value of them is time dependent, or the rate at which they are generated is constrained by unrelated reasons, then the most economic solution may not be what is expected.

EDMS Australia

RE: grid tie solar electricity with optimizers and inverters what would reduce the dc input voltage

I did a little RTFM.
"The SolarEdge power optimizer is a DC/DC converter which is connected by installers to each PV module or embedded by module manufacturers, replacing the traditional solar junction box. The SolarEdge power optimizers increase energy output from PV systems by constantly tracking the maximum power point (MPPT) of each module individually."
I hope that this feature compensates for temperature changes.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: grid tie solar electricity with optimizers and inverters what would reduce the dc input voltage

(OP)
Okay the power company came and put in their meters. The time is 4 PM it gets dark about 6:30 pm. I fired up the inverter and amazingly the DC voltage is at 370 VDC at 245 watts (370 VDC is the correct value per Mfg.). So everything is okay when the sun is setting. Tomorrow I will check a full solar cycle with periodic time intervals measurement and see if and when the time interval the voltage drops.

RE: grid tie solar electricity with optimizers and inverters what would reduce the dc input voltage

You are already at less than 4% power level, so it's not going to drop until you get much closer to sunset, or sunrise. As can be seen in the attached photo, 45 minutes after sunrise, with practically no power, the voltage is pretty decent already.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

RE: grid tie solar electricity with optimizers and inverters what would reduce the dc input voltage

Interesting approach- generates lower cost than having microinverters on every panel I guess?

RE: grid tie solar electricity with optimizers and inverters what would reduce the dc input voltage

Thanks for the first hand info and for the pictures, IR.
advidana; Is a reading, reporting error the cause of the first suspect DC voltage reading? (247 VDC)

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: grid tie solar electricity with optimizers and inverters what would reduce the dc input voltage

(OP)
First -I was with the electrician when he recorded the 247 VDC . Saw the same value he did. T told him shouldn't it be about 370 VDC. He said no it was common to read lower voltages. I was not experience with this entire set up so I decided to check around that's how this wound up in this forum.

Second-The reading this morning started out great at 7:20 am it was about 2600 watt ac holding at 370 VDC (Voltage fluctuated a couple of volts). it peak out from about 9 Am to 11:30 am at 5,900 watts still at 370 VDC at a temp of 79 degrees F. My solar panels are mounted on the roof that is facing due east with about a 15 degree incline. For this time of year having 5,900 is great


I guess the heat must have caused the voltage to drop. it was 105 degree that day. So SKOGSGURRA was correct the heat caused the DC voltage to drop. The tech said it was common cause he has been installing these all summer with temp of 110 f or more. So it must be common here to see low voltages.

RE: grid tie solar electricity with optimizers and inverters what would reduce the dc input voltage

If your SolarEdge isn't connected to your solar panel supplier/installer, you can potentially hook it up to the WiFi and get lots of useful info from it.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

RE: grid tie solar electricity with optimizers and inverters what would reduce the dc input voltage

(OP)
Thanks again IRstuff-It's part of the 20 year warrantee that the installer monitors my inverter. His site allow a lot of information to be displayed to me thought the internet. he uses some type of wireless monitor that is connected hard wire to my internet router. I have it installed as an app on my cell phone too.

RE: grid tie solar electricity with optimizers and inverters what would reduce the dc input voltage

(OP)
The installer commissioned my solar system tonight. He also mention that this particular Solaredge model SE-7600-Us will work with battery backup or off grid. This to know for future modifications. He said not all of Solaredge models will do this.

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