How to confirm my panels/micro-inverter are actually injecting power in my grid?

lobito · December 2013

Hello,

Electricity in my country is getting more and more expensive, so I bought in ebay one of those consuption-measurement devices (eco-eye mini2), in order to have an ideia of the instantaneous electrical consuption.
With this device I realised there was a fixed overhead of at least 300w maybe due to the equipment that is always connected (freezers, alarm clocks, TV's on stand-by, etc.).

So I thought: "If I get a couple of photovoltaic panels and an inverter, maybe I can reduce this overhead during the day. I don't want to sell power to the power company, so I want it to produce less than 300w".

I started studying what would be the most cost-effective solution and also bought online two Photovoltaic panels and a enecsys micro inverter.

The High level equipment specifications are:

Panel 1:
Seller stated as 12V/100W solar panel.
opencircuit voltage at a sunny day: 20.4V

Panel2:
Seller stated as 12V/120W solar panel.
opencircuit voltage at a sunny day: 21V

Micro-inverter:

Model: Enecsys SMI-240-72
Max input voltage: 54V
Min MPP voltage: 30V
Max MPP voltage: 42V
Minimum DC Voltage: 27V
Nominal Input Power: 240W
Recommended PV Power (STC): 260W
Maximum DC Voltage: 48V
Peak Effi ciency: 94.0%1

I have everything monted on the roof, faced south, with good solar exposition. The panels are connected in series and the open-circuit voltage of both is 41.4V. In theory, the panels should provide at least the required 27V for the inverter to "start working" and should provide around 220W. Worst case scenario, considering an inverter efficiency of only 90% (less than the spec), this should inject in the grid around 200W.
When I connected the panels into the micro-inverter the voltage droped to 1.4V (I used two Y cables momentarily just to measure the voltage drop when connected to the micro-inverter). I don't know if this value is normal.

In the AC side I connected the AC cable to a home power plug, and I was expecting to see some instantaneous consuption decrease (with the eco-eye), but nothing. Connected it and disconnected it several times in order to notice some difference but also without success... So, I'm not sure if this setup is working

So, finally, my questions:

- In theory, according to the specs above, I believe my setup is OK. Anyone sees anything that I may have missed?
- Is it normal to have such a low voltage at the DC entrance of the inverter? (I know there is a voltage drop from open-circuit to closed-circuit, but having just 1.4V seems too low).
- Is there any way to know if the whole set-up is working? How do people know if their grid-tie inverters are really giving the expected power?
- Enecsys have a kind of "management system" (communication gateway) that communicates with the micro-inverters via XBee in order to get its status. I don't have this system (and doesn't make sense to buy it just for one inverter). Does anyone know f it would it be possible to implement some communication scan with arduino/raspberry-PI in order to get updates (or would the enecsys communication be encripted)?

Thanks,
Lobito

Blackcherry04 · December 2013

Re: How to confirm my panels/micro-inverter are actually injecting power in my grid?

In the AC side I connected the AC cable to a home power plug

I am not sure what this is ?? 120 V or 240V ?? It requires 240V Reference voltage to even wake the Inverter up. Then again I don't know where your country is or it's voltage, here it's not so legal.
.
SMI-S240W-72

Peak Inverter Efficiency: 94%
CEC Weighted Efficiency: 92%
Recommended PV Input (STC): 260W
Maximum DC Input Voltage:50V
Maximum DC Input Current: 8.9A
AC Nominal Voltage: 240 V
AC Frequency: 60Hertz
Continous AC Power Output: 240Watts
Nominal AC Voltage: 240Volts
.

lobito · December 2013

Re: How to confirm my panels/micro-inverter are actually injecting power in my grid?

Blackcherry04 wrote: »

I am not sure what this is ?? 120 V or 240V ?? It requires 240V Reference voltage to even wake the Inverter up. Then again I don't know where your country is or it's voltage, here it's not so legal.
.

Thanks for your reply.
The grid here is 220V AC and the inverter is of course adequade for this voltage.
Not sure why it should it be relevant for this problem... I guess as long as the inverter is according to the grid voltage, shouldn't the general way of working be the same, no matter if its 110V-AC/220V-AC?

Thanks,
Lobito

Cariboocoot · December 2013

Re: How to confirm my panels/micro-inverter are actually injecting power in my grid?

lobito wrote: »

Thanks for your reply.
The grid here is 220V AC and the inverter is of course adequade for this voltage.
Not sure why it should it be relevant for this problem... I guess as long as the inverter is according to the grid voltage, shouldn't the general way of working be the same, no matter if its 110V-AC/220V-AC?

Thanks,
Lobito

No; if you were to connect a 240 VAC GT inverter to a 120 VAC line it will see it as "no grid" and not run.

What you need is a clamp-on Ammeter to measure current (if any) flowing from the inverter to the household wiring. The drop of panel Voltage from Voc to 1.4V indicates a problem, probably insufficient insolation to cause the panels to produce sufficient current and Voltage under load (Imp * Vmp to get rated power).

I would start by checking each panel's short circuit current and see if you get about 5-6 Amps. You should be able to do that with a standard DMM on DC Amps connected between the two leads of one panel at a time. If there is no power from the panels there is no chance the GTI will work.

Blackcherry04 · December 2013

Re: How to confirm my panels/micro-inverter are actually injecting power in my grid?

It's hard to tell you, because I don't know exactly what you have. Here they require 240 split phase ( two 120 V hot wires ). They are very frequency sensitive as you can see. If your at 110/220 V and 60 Hz, split phase, if thats the one you have. If you have 50 hz then thats a different story and different Inverter.

AC Input / 240V / 211V - 264V
Nominal Output Frequency / Range 60Hz / 59.3 - 60.5

Country Specific Configuration

The Enecsys Micro-inverter is configured with Country Specific Grid Connection requirements prior to despatch from our factory. These Country Specific Requirements are;
•Nominal operational grid voltage.
•Nominal grid frequency.
•Over/Under voltage trip limits.
•Over/Under frequency trip limits.
•Grid connect/disconnect times.

Watt · December 2013

Re: How to confirm my panels/micro-inverter are actually injecting power in my grid?

" When I connected the panels into the micro-inverter the voltage droped to 1.4V (I used two Y cables momentarily just to measure the voltage drop when connected to the micro-inverter). I don't know if this value is normal. "

Do you possibly have a bad connection at one of the panels causing the voltage to drop so far?

As mentioned, a clamp around current meter would let you know what sorta current is flowing on the dc side and with voltage, you can calculate wattage or load. May not have enough to power the inverter at this point.

BC04 commented on the frequency, what country are you in that may help these guys help you.

Good luck.

Cariboocoot · December 2013

Re: How to confirm my panels/micro-inverter are actually injecting power in my grid?

The OP appears to be in Portugal, and their power standard is 230 VAC 50 Hz.

For a GTI to work it must have enough power on the input to function and have the output connected to an AC power grid which has the correct frequency and Voltage range.

As Blackcherry has pointed out the Enecsys SMI-240-72 does not meet these criteria.

bill von novak · December 2013

Re: How to confirm my panels/micro-inverter are actually injecting power in my grid?

lobito wrote: »

When I connected the panels into the micro-inverter the voltage droped to 1.4V (I used two Y cables momentarily just to measure the voltage drop when connected to the micro-inverter). I don't know if this value is normal.

No, it's not normal. If you are measuring it correctly, either you connected the panel backwards or the inverter is dead.

Watt · December 2013

Re: How to confirm my panels/micro-inverter are actually injecting power in my grid?

" The OP appears to be in Portugal, and their power standard is 230 VAC 50 Hz.

For a GTI to work it must have enough power on the input to function and have the output connected to an AC power grid which has the correct frequency and Voltage range.

As Blackcherry has pointed out the Enecsys SMI-240-72 does not meet these criteria. "

Musta done the Ip check cuz I didn't see that listed. Yes, BC04 made a fine catch there if the OP is in fact in Portugal and does not have another problem.

If the OP does in fact have the Enecsys SMI-240-72 and not the Enecsys SMI-240w-72 at this link http://reseller.segen.co.uk/reseller/docs/Enecsys%20Data%20Sheet%20200%20240%20280%20-%2072%20Cell.pdf

It could be that the UK or W was left out, just making sure, that's all.

It shows the Enecsys SMI-240-72 at this link http://www.thesolarelectricitycompany.com/index.php?page=installers&pagename=Enecsys+Micro-Inverters , however, an additional click indicates ( As BC04 indicated ) a more specific model number.

By the way, when I went to EBAY and that is EBAY.US and did a search for Enecsys SMI-240-72 I did not get a listing. But when I went to EBAY.co.uk I did get a few options and one was a 72 cell version 240. I wonder what EBAY the OP bought from and which specific version he has.

lobito · December 2013

Re: How to confirm my panels/micro-inverter are actually injecting power in my grid?

Watt wrote: »

" The OP appears to be in Portugal, and their power standard is 230 VAC 50 Hz.

For a GTI to work it must have enough power on the input to function and have the output connected to an AC power grid which has the correct frequency and Voltage range.

As Blackcherry has pointed out the Enecsys SMI-240-72 does not meet these criteria. "

Musta done the Ip check cuz I didn't see that listed. Yes, BC04 made a fine catch there if the OP is in fact in Portugal and does not have another problem.

If the OP does in fact have the Enecsys SMI-240-72 and not the Enecsys SMI-240w-72 at this link http://reseller.segen.co.uk/reseller/docs/Enecsys%20Data%20Sheet%20200%20240%20280%20-%2072%20Cell.pdf

It could be that the UK or W was left out, just making sure, that's all.

It shows the Enecsys SMI-240-72 at this link http://www.thesolarelectricitycompany.com/index.php?page=installers&pagename=Enecsys+Micro-Inverters , however, an additional click indicates ( As BC04 indicated ) a more specific model number.

By the way, when I went to EBAY and that is EBAY.US and did a search for Enecsys SMI-240-72 I did not get a listing. But when I went to EBAY.co.uk I did get a few options and one was a 72 cell version 240. I wonder what EBAY the OP bought from and which specific version he has.

Hello,

Thank you for your replies.

Yes, indeed I'm in Portugal and the voltage is 220AC/50Hz. The Inverter is appropriate for this conditions.
I'm not sure about the difference between SMI-240-72 and SMI-240W-72 but I can tell you mine is SMI-240-72 (checked from the inverter label).

So, now that the basic troubleshooting is done, what else can I try?

Thanks,
Lobito

Cariboocoot · December 2013

Re: How to confirm my panels/micro-inverter are actually injecting power in my grid?

lobito wrote: »

So, now that the basic troubleshooting is done, what else can I try?

Thanks,
Lobito

Is the basic troubleshooting done? As I said earlier you want to check the panels to see if they produce current under full sun. Having only 1.4 Volts coming from them when connected to the inverter indicates a problem somewhere on the solar side. Without that being cleared up the inverter is never going to try and start no matter what model it is.

Watt · December 2013

Re: How to confirm my panels/micro-inverter are actually injecting power in my grid?

lobito wrote: »

Hello,

Thank you for your replies.

Yes, indeed I'm in Portugal and the voltage is 220AC/50Hz. The Inverter is appropriate for this conditions.
I'm not sure about the difference between SMI-240-72 and SMI-240W-72 but I can tell you mine is SMI-240-72 (checked from the inverter label).

So, now that the basic troubleshooting is done, what else can I try?

Thanks,
Lobito

Sorry for the long post Lobito, just trying to point out that your inverter could actually be right. So much post fluff up there, want to make sure you saw the part about the potential loose connection and the troubleshooting Cariboocoot suggests.

lobito · December 2013

Re: How to confirm my panels/micro-inverter are actually injecting power in my grid?

Hello,

Tests done today, sunny day:

a) Panel1: 100W panel
Panel1: Test open-circuit voltage: 20.4V
Panel1: Cover it with a blanket and connect amperimeter. Uncover it and check the value. Cover again and disconnect amperimeter: 3.22A

b) Panel2: 120W panel
Panel2: Test open-circuit voltage: 21V
Panel2: Cover it with a blanket and connect amperimeter. Uncover it and check the value. Cover again and disconnect amperimeter: 4.83A

c)
Check polarities of the cables, specially the MC3 <--> MC4 adapters
In fact, the polarities were wrong. I changed it over with a pair of MC4 Y cables and now the voltage at the entrance of the inverter is 41.4V with the panels in series (not anymore the 1.4V as before). But anyway, shouldn't be there some voltage drop when connecting to the inverter?

Now, testing if this setup is really giving me some electrical power: With the eco-eye I'm seeing my house's instantaneous consuption: between 520W and 550W. Disconnecting and connecting back again the micro-inverter don't have visible effect. Even if the pannels aren't giving all of its power (max 220W) I believe I should see at least some change in the instantaneous consuption, right?

So, with this testing, should I assume there is a problem with the inverter?

Thanks,
Joaoabs

Blackcherry04 · December 2013

Re: How to confirm my panels/micro-inverter are actually injecting power in my grid?

lobito wrote: »

So, with this testing, should I assume there is a problem with the inverter?

Thanks,
Joaoabs

Considering that you had reverse polarity going into it, could be.

Cariboocoot · December 2013

Re: How to confirm my panels/micro-inverter are actually injecting power in my grid?

The Isc readings are also too low: if you multiply 3.22 * 18 you get 57.96 which is way below 100 Watts, so either the insolation is poor or there's panel damage. Likewise with the 4.83 * 17.5 yielding 84 Watts on the 120.

Yes there should be a drop from Voc when the panels are connected to the inverter. The inverter may indeed be damaged, but the first problem is that the panels are putting out what is about 1/2 power which may indicate they are damaged as well (shorted bypass diodes for example).

BB. · December 2013

Re: How to confirm my panels/micro-inverter are actually injecting power in my grid?

Remember too that GT inverters are suppose to have a ~5 minute timeout... So, when you reconnect DC or AC power, it will take ~5 minutes for the GT inverter to turn on its AC output again.

I believe the Kill-a-Watt type meters will read power from a "plug in" GT inverter. It cannot tell the direction of the power (i.e., loads and GT inverter will read the same). If you have only a GT inverter on the watt*hour meter, and you see power output, you should be able to assume that the GT inverter is outputting power to the grid.

Otherwise, if you can get a Current Meter clamped onto one of the AC mains from the GT inverter (to circuit breaker--assuming a dedicated GT inverter 240 VAC branch circuit) and monitor current. It should be near zero when no light/GT inverter shut down--And will show current when all is running correctly (again, the simple AC clamp meter cannot determine the direction of current/power flow--So a "bad" GT inverter could consume current instead of generating power and you could not tell the difference with a Clamp meter--Why I suggest measuring current at night/panel covered to confirm that you are near zero amps when the GT inverter is shut down).

-Bill

lobito · December 2013

Re: How to confirm my panels/micro-inverter are actually injecting power in my grid?

Cariboocoot wrote: »

The Isc readings are also too low: if you multiply 3.22 * 18 you get 57.96 which is way below 100 Watts, so either the insolation is poor or there's panel damage. Likewise with the 4.83 * 17.5 yielding 84 Watts on the 120.

Yes there should be a drop from Voc when the panels are connected to the inverter. The inverter may indeed be damaged, but the first problem is that the panels are putting out what is about 1/2 power which may indicate they are damaged as well (shorted bypass diodes for example).

Considering that the panels are in a latitude 38.750ºN, and with an inclination of 36º, faced to south and the measures were taken about 13:30 local time, I'll have to agree that the readings seem low, even though that the sun cannot go much lower than today (we are within the shortest 8 days of the year, where the sun is low on the horizon). Even doing the calculations with the open circut voltages (3.22 * 20.4 = 65.69 and 4.83 * 21 = 101) seems a bit low for a day like this https://www.dropbox.com/s/e630kkuporu6nqu/2013-12-21%2013.46.15.jpg.

Now, if there is panel damage like shorted bypass diodes, would it be something that could be fixed?
Could it be that the panels came without these diodes? And would these diodes be really needed? I thoght it were just for protection in case the panels were wrongly connected (as it was the case).

Thanks,
Lobito

BB. · December 2013

Re: How to confirm my panels/micro-inverter are actually injecting power in my grid?

By pass diodes are to protect "shaded cells" from over voltage in a large series string of panels. Solar cells go high resistance" in shade and the by-pass diodes allow the current to go around dark cells.

Solar panels that are connected backwards to higher sources of current (other paralleled panels, directly to battery, etc.) will be toasted.

It is possible that you have a bad by-pass diode. And on some panels, you can open the junction box and replace a bad by-pass diode.

-Bill

niel · December 2013

Re: How to confirm my panels/micro-inverter are actually injecting power in my grid?

if it was only just a case of the pvs wired back to back, i'm of the opinion it should not have affected the inverter. voltage is just too low for it to turn on. not sure of pv damages either as what you did was equal to like putting 2 batteries back to back with slightly different voltages on them. only the difference voltage would appear, but the weaker of the 2 would pass current in the opposite direction. the current from either pv passing in reverse to the other should not be enough to damage either pv. something else may have been faulty even before your error of wiring the pvs back to back. the pvs do need to be individually tested again for their output. may have been just not enough insolation that day, but do it at solar noon +/- 1 hour or so on a very sunny day.

AceNZ · December 2013

Re: How to confirm my panels/micro-inverter are actually injecting power in my grid?

Another thing to check: where is your eco-eye monitor's sensor connected? It should be along a feed coming from the grid, not one that's going to one of your loads.

You might also be able to use the eco-eye to measure current coming from the inverters, by placing the sensor on the AC output.

Are micro-inverters considered grid-safe in the event of a grid failure? I don't know about other locations, but New Zealand requires a physical isolation switch whenever a PV power source is connected to the grid -- and not having one risks hefty fines.

How to confirm my panels/micro-inverter are actually injecting power in my grid?

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