Tel: (845) 626-2627   Home   Contact  
Sun Volt

Sun Volt Solar

earth, the final frontier

Clean Energy, Clean Environment

We are at a cross roads in human history, we can choose to continue on as we have been, or we can make a change to improve our future and quite possibly the future for several generations to come. We are here to promote energy independence, a better environment, a secure future and a higher return on investment for your hard earned dollar. It is what I believe in, it is why I am in the solar business.

System verification for Enphase Inverters

16 Dec 09 | Solar Electric, Technology

In New York State, there is something called the Standardized Interconnect Requirements (or SIR) that governs how utility companies handle grid connected renewable energy systems such as Photovoltaic and Wind energy systems.

Among the requirements, usually known as “Step 5,” a verification that the system meets UL 1741 is required. This means that after a power outage, the inverter stays off for five minutes before it begins exporting power to the grid. For most inverters, the verification procedure is simple, turn off the breaker feeding the inverter for a short period, then turn it back on. Watch the LED indicators on the inverter and time how long it takes to come on line and produce power. If it is 5 minutes or longer, the system passes.

enphase energy M210 inverters

enphase energy M210 inverters

The problem with the [e] Enphase inverters is there are many of them, they are located with the solar panels, and it would be difficult to watch the LED start flashing green especially if the inverters are under a PV panel bolted to the roof. Therefore, an alternative verification procedure must be effected. One suggestion by the utility company was to use a clamp on ammeter to measure the AC current in the branch circuit between the inverters and the panel. One small problem was that some “leakage current” had been detected in previous tests of this nature.

I sent an e-mail off the [e] Enphase Energy, Inc. They responded very quickly with the following suggested verification procedure:

  1. Turn off the breakers to the array.
  2. Turn on the breakers to the array and make a note of the time down to the second.
  3. Using a clamp on ammeter, verify that the array is not producing current until 5 minutes have passed. During the non-producing period, the ammeter will show a slight current draw of 0.056 Amps +/- 5% for each installed inverter. In this case, there are 10 inverters in each string, therefore the clamp on ammeter will show 0.56 Amps +/- 5%.
  4. After 5 minutes have passed, the ammeter will show the array producing power by indicating greater than the quiescent current noted in step 4.

The test should be run when the array is in full sunlight so the AC current meter will obviously indicate the array is exporting power to the grid since AC current meters do not indicate the direction of current flow.

The second method proscribed by Enphase involves using the utility meter. This can only be used in arrays that are large enough to get the meter spinning, and should only be performed in full sunlight.

  1. Observe service meter and note direction it is turning while consuming power.
  2. Turn off main service breaker and all other breakers feed the various household loads, simulating a power outage.
  3. Turn on main service breaker and breaker feeding the inverter(s) only and note the exact time.
  4. Observe service meter. A very slight movement forward direction indicates the inverters are consuming a small amount of power in their monitoring circuit.
  5. After five minutes have passed, the meter will begin to turn in the opposite direction, indicating the inverters are exporting power.
  6. Close the breakers to the rest of the household loads.

Finally, if the inverters are ground mounted and the LED indicators can be readily observed, this procedure can be followed if the first two do not satisfy the utility company.

  1. Turn off the breaker feeding the branch circuit, if it is not already off, then turn back on.
  2. Observe the inverter(s) status LED, is should begin to flash red when AC power is applied then flash green when the inverter(s) begin to produce power. Time the period of the flashing red LED with a stop watch, it should be 5 minutes or greater.

This can be done for each individual inverter, or for each inverter string as the (utility company) representative present desires.

According to the manufacture, the system complies with the requirements of UL1741, which states that if the inverter detects that the grid has gone out of specification or has completely shut off, then the inverter will “cease exportation” of power. The inverter is allowed to draw current but cannot produce power. Therefore the small amounts of current indicated on an AC ammeter is not leakage current, rather it is the inverter consuming a small amount of power prior to in beginning operation.

Update: From Scott at Enphase Energy:

I had a brief, follow-up comment about one portion of the article. During the 5-minute wait time specified by UL-1741, the Microinverter is not consuming power. It is circulating reactive current in the A/C-filter section of the device.

I just wanted to make sure that the statement of “the inverter consuming a small amount of power prior to in beginning operation” was not potentially misinterpreted as tare-loss, with an Enphase customer thinking that he was losing some of that hard-earned energy during the 5-minute period.

No, we wouldn’t want them to think that, especially after I preached about unshaded locations and voltage drop during the sales presentation.

I have noted that these inverters come on line in 5 minutes and 20 seconds or so after a power outage.

Tags: ,

16 Dec 09 | Solar Electric, Technology
«
»


Leave a Reply