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

[joaoabs]

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:

Panel1:	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). Would it be possible to implement some communication with arduino/raspberry-PI in order to get updates?

Thanks in advance,
Joaoabs

[DanS26]

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:

Panel1:	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:

- 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). would it possible to implement some communication with arduino/raspberry-PI in order to get updates?
- In theory, according to the specs above, I believe my setup is OK. Anyone sees anything that I may have missed?

Thanks,
Joaoabs

Obtain an energy monitoring system such as the TED system. There are many systems out there to do this.

After you have the TED set up and are satisfied with the monitoring system, then join the other 13,000 solar systems on PVOutput.org.

[joaoabs]

Obtain an energy monitoring system such as the TED system. There are many systems out there to do this.

After you have the TED set up and are satisfied with the monitoring system, then join the other 13,000 solar systems on PVOutput.org.

Hello,

Thank you for your reply.
So, from you suggestion I can infer that you suspect that the eco-eye (that is actually an energy monitor, similar to TED) is not measuring well, right? If so, can I ask what lead you to that suspicion? (would it be known in the market for not being reliable or anything? - just asking...)
Meanwhile, I have ordered another type of eco-eye: The eco-eye PV, that is intended to measure the DC current of photovoltaic panels. Still on its way, and once connected to a raspberry-pi will be able to send info to PVOutput.org and Xively.com.

Any other idea, while I don't get the eco-eye PV?

Thanks,
Joaoabs

[inetdog]

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.

This is not normal, and is perfectly consistent with not measuring any power out of the micro.

There are three basic possibilities:
1. You connected the panels to the micro with the wrong polarity. Some two-wire cable sets, including some supplied with Harbor Freight products, are non-standard and reverse the polarity of the leads labelled plus and minus from one end to the other.
2. The microinverter is defective and is shorting out the panels.
3. There is something wrong with one or both of the panels which is preventing them from delivering current even though the open circuit voltage is normal.

To check #3 you need to measure the short circuit current of each panel separately. You need a DC ammeter than can measure up to 20 amps safely.
Connect the ammeter to the plus and minus leads of a panel while it is covered (no light) then uncover the panel. You should read something like 10 amps from each of them. Cover the panel again before disconnecting the meter.

Come back with the results. This is not a complete test of the panels, but it will rule out most problems.

[joaoabs]

This is not normal, and is perfectly consistent with not measuring any power out of the micro.

There are three basic possibilities:
1. You connected the panels to the micro with the wrong polarity. Some two-wire cable sets, including some supplied with Harbor Freight products, are non-standard and reverse the polarity of the leads labelled plus and minus from one end to the other.
2. The microinverter is defective and is shorting out the panels.
3. There is something wrong with one or both of the panels which is preventing them from delivering current even though the open circuit voltage is normal.

To check #3 you need to measure the short circuit current of each panel separately. You need a DC ammeter than can measure up to 20 amps safely.
Connect the ammeter to the plus and minus leads of a panel while it is covered (no light) then uncover the panel. You should read something like 10 amps from each of them. Cover the panel again before disconnecting the meter.

Come back with the results. This is not a complete test of the panels, but it will rule out most problems.

Hi,

Thanks for replying. Some comments:

1. I doubt it. Otherwise the total voltage wouldn't be the sum of each panel, right?
2. Yes, maybe. I got the inverter in second hand (used) on ebay. I hope this isn't it...
3. Yes, maybe. I'll climb to the roof and do that test. Would a normal blanket do the trick? Wouldn't I damage the panel by short-circuiting it?

Thanks,
Joaoabs

[Mike90250]

A micro inverter should only pull the PV voltage down to it's (inverters) rated input voltage. Dropping to 1.4v indicates a mis-wire or faulty inverter.

[inetdog]

Hi,

Thanks for replying. Some comments:

1. I doubt it. Otherwise the total voltage wouldn't be the sum of each panel, right?
2. Yes, maybe. I got the inverter in second hand (used) on ebay. I hope this isn't it...
3. Yes, maybe. I'll climb to the roof and do that test. Would a normal blanket do the trick? Wouldn't I damage the panel by short-circuiting it?

Thanks,
Joaoabs

1. I mean that you have connected the two panels together to the inverter with the wrong polarity.
2. I also hope not, but one alternative is a bad panel or two.
3. Yes, and since the output of a panel is current limited it will not do it any harm. Do not try that with a battery though!

4. If your micro-inverter is the kind which just plugs into an AC outlet, it is not approved or legal in most countries and it also not safe, so we will not be able to help you with that.

[joaoabs]

1. I mean that you have connected the two panels together to the inverter with the wrong polarity.
2. I also hope not, but one alternative is a bad panel or two.
3. Yes, and since the output of a panel is current limited it will not do it any harm. Do not try that with a battery though!

4. If your micro-inverter is the kind which just plugs into an AC outlet, it is not approved or legal in most countries and it also not safe, so we will not be able to help you with that.

Thank you for your replies.

I'll have to wait for the weekend in order to access the roof. Not easy, so I need help that is only available during weekends...
I'll test each panel individually and I'll also verify the cables the seller included (there were some hand-made MC3 <--> MC4 adapters, maybe the plug genders are wrong). Hope I haven't damaged the inverter meanwhile..

So, my testing cases:

a)
Panel1: Test open-circuit voltage
Panel1: Cover it with a blanket and connect amperimeter. Uncover it and check the value. Cover again and disconnect amperimeter.

b)
(do the same on panel 2)

c)
Check polarities of the cables, specially the MC3 <--> MC4 adapters

By the way, since its difficult for me to go up there, is there any other test you could suggest in advance?

Thanks!
Joaoabs

PS:
Regarding 4., no I don't think my setup is ilegal, the enecsys inverters are built in the UK, CE certified and accepted in my country. If it was one of those cheap chinese inverters, I'd totally agree with you, but as I said, is not the case.

[Naptown]

You are correct the inverter is legal.
Actually this is the same inverter manufacturer Sunpower uses fr their AC panels

[inetdog]

By the way, since its difficult for me to go up there, is there any other test you could suggest in advance?

Well, after you have checked all of the polarities and short circuit currents, it would be interesting to see what the voltage at the inverter is with only one of the panels connected and then with only the other connected.
One possibility is that the inverter will draw no current and so you will see full open circuit voltage with each panel as it is below the minimum voltage for the inverter.
Another is that the voltage will be different with one panel than with the other. That would indicate that perhaps one or more sections of the lower voltage panel are bad and you are getting a lower output voltage once the bypass diodes are conducting. (That is one of the things that the simple short circuit current test would not detect.)
Or you get 1.4 volts in all combinations, which does not bode well for the health of the inverter.

[bcroe]

300 Watt Overhead

I bought in ebay one of those consuption-measurement devices (eco-eye mini2),
in order to have an idea of the instantaneous electrical consumption. 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.). Joaoabs

Several years ago I also found that with everything off, furnace & fridge not running, there was
a 300W continuous load. With a Kill-O-Watt here, I tracked it down to about a hundred standby
devices on 60 circuits. Attacking them one by one, I managed to get it down to around 50W
without giving up any service. Details on my PHOTOBUCKET; you might achieve the same.
Bruce Roe

[SunEagle]

Several years ago I also found that with everything off, furnace & fridge not running, there was
a 300W continuous load. With a Kill-O-Watt here, I tracked it down to about a hundred standby
devices on 60 circuits. Attacking them one by one, I managed to get it down to around 50W
without giving up any service. Details on my PHOTOBUCKET; you might achieve the same.
Bruce Roe

I believe they are called vampire loads. Constantly sucking them electrons.

Most electronic devices that have "instant on" capabilities (like TV's) usually have a small electrical load constantly on to keep things "hot".

Also just about anything that uses a cord to convert AC into DC (laptop power cords, baby monitors, wireless telephones, security cameras, battery chargers, clock radios, etc.) are constantly using electricity. If you see a small green or red light on equipment then it is using electricity. They are very small loads but as Bruce states they add up.

[joaoabs]

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 the 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