METHODS: Streamlined Supply-Side Interconnection

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The family and their array
The Akin family with their PV array
The Meter box, with adaptor
The ConnectDER is mounted between the service kWh meter and the meter base for a simple supply-side connection.
The PV array and balance of system equipment
The Akin's PV array showing inverter, etc.
The family and their array
The Meter box, with adaptor
The PV array and balance of system equipment

Unique challenges to this batteryless grid-tied system required creative planning and using an innovative product.

Supply-side connections interconnect a PV system to the grid without being hindered by common load-side limitations, such as mains panel busbar size and whether there’s space for another circuit breaker. Supply-side connections are often more complex than load-side connections, and may still require accessing the main distribution panel (MDP) to splice into the incoming service conductors. However, this new interconnection method only requires meter access, and does not require working within the MDP.

The Akin family was determined to meet some of their electrical needs with renewable solar energy, but needed to develop the system as their finances allowed. Complicating matters were a completely shaded rooftop, which meant locating the array on a ground- or pole-mount. They decided that implementing the array in two stages, as two ballasted ground-mount subarrays, was a workable solution.

To avoid trenching more than once across the lawn, additional conduit was installed in the trench and run to the site of the second subarray. An AC inverter/combiner panel that can accommodate two inverters was placed adjacent to the first inverter, which was mounted to the first array. The AC output conductors running to the house were sized to meet the eventual combined output of the two inverters.

Interconnection was also complicated by the MDP, which was fully recessed into one of the dining room walls. Although a load-side interconnection (backfeeding a dedicated circuit breaker in the MDP) was possible because of a projected maximum inverter output current of 30 amps (15 A × 2) and a 200 A MDP, it was not practical or cost-effective. There were also no existing subpanels in the house. Interconnecting at the MDP would have been more costly, since it would have required cutting (and then repairing) the wall.

An innovative “collar” device—the ConnectDER—provided a streamlined method for code-compliant supply-side interconnection (NEC 705.12A). The ConnectDER is installed in-line between the utility meter and the meter socket, with the inverter output circuit terminating at the collar’s wire-box. An integrated two-pole breaker provides both overcurrent protection and a disconnecting means, negating the need for a separate fused PV system disconnect enclosure. The integrated disconnect is accessed via a removable gasketed cover on the top or bottom of the collar, depending on the version. The local utility not only approved the use of the device, but also assisted with its distribution. The method avoided the need to penetrate the building, saving both labor and material costs, and avoided disturbing a busy family.

—with Phil Parrish

Comments (12)

doug stecklein's picture

I think this may have been answered in the article but I would just like to confirm. Does this supply side connection device negate the need for a disconnect box as well as the junction box with over current protection?

Whit Fulton's picture

The treatment varies by jurisdiction. Some AHJ's have been happy to sign off on the embedded breaker switch as an AC disconnect, whereas others still want to see a switch with an air-gap, although it's likely it need not be fused.

Jason Szumlanski's picture

I was just about to reply similarly. For jurisdictions and utilities that require a visible load break type disconnect, a disconnect switch will probably still be required. For jurisdictions that do not require it, the integrated circuit breaker should suffice for circuit protection and disconnecting means.

Whit Fulton's picture

Hi, this is Whit from ConnectDER. First of all, thanks to Khanti and Home Power for a great article. And thanks to everyone who's reached out so far asking about the product. We'll get back to you individually, but here are the short answers for the popular questions:

Price: The Simple ConnectDER is about $400 unless we've worked out a discount deal with your utility. It is ITC eligible.

Utility service territories where you can use it: Green Mountain Power (VT) and Orlando Utilities Commission (FL). Pretty limited for now, we know. But we're in the process of opening a bunch more. An article in the National Rural Electric Cooperative technical review will be out in June, which should help quite a bit with the Coop utilities' awareness.

How to get one: Green Mountain Power has an online order form (http://www.greenmountainpower.com/i...). We do fulfillment by mail to you. Drop us an email re Orlando. If you've got a utility you'd like to shop it to, see below.

Because of the limitations where you can use the ConnectDER, we haven't really promoted it to solar developers like yourselves yet. We need to work with each utility AND local inspectors individually to get their acceptance and support to use it. That takes time and a lot of discussion, but should get easier as more and more places adopt it.

If you've got a good relationship with your local utilities and/or inspectors and would like to talk about putting us together, please just drop us a line at info@connectDER.com. We'll get back to you as soon as we can, and we love getting your insight on how things work in your area.

Jason Szumlanski's picture

For those of us that are installing systems with over 40 amps of rated backfeed, many times a line side interconnection is not possible with meter/main combinations that do not have a second service disconnect or conductors that can be tapped. This is a great solution to that problem that does not require a complete service change. I'm looking forward to it being available in Southwest Florida where Florida Solar Design Group is based.

In fact, I can see this being a cost effective solution even when there are interconnection alternatives. The reduced equipment and labor could make this product viable in all installations that require anything over a single 2-space breaker and where breaker space is not available in the main distribution panel. The added complexity of scheduling a meter pull by the utility is easily overcome by the advantages.

Whit - we've already emailed privately, but I wanted to lend my public support to such a great idea.

Whit Fulton's picture

Thanks, Jason. Public endorsements of the idea are a big help in generating critical mass. Your feedback goes a long way. All the best to you and everyone out there on the front lines getting more PV up and running.

gosolar@cheqnet.net's picture

Thanks very much for the clarification Whit,... getting the nomenclature clear helps. Great product! Wonderful for MDP's don't have the capacity to add more source amperage.

C.

gosolar@cheqnet.net's picture

Pardon me for wondering, but it sounds like you are landing on the load side of the meter (in the meter base), no? If that is the case it is still a load side connection, albeit up stream of the MDP.

If this is really a supply side connection (on the utility side of the meter) how is the production getting accounted for? I do not see a second meter.

Khanti Munro_2's picture

Good question Chris (hey long time - hope all is well with you), and thanks for jumping in Whit - was going to email you link to the article, but I see you already found it! ;-).

Yes, the version of the xDER that we have been installing interconnects the Inverter Output Circuit to the load side of the net meter. We've been referring it to a "Supply Side" point of connection, per NEC 705.12 (A) - that here in the Northeast, the main breaker in the MDP (Main Distribution Panel) is considered the "Service Disconnecting Means," for which we are connecting on the supply side of. I can see how if the AHJ considered the meter to be the service disconnecting means, this interconnection could still be considered 'load side.' Also note that in-line between the inverter and the interconnection point is a solar-only production meter, as required by the utility.

Regarding the acronym comment - I agree, and certainly tried to keep it to a minimum in this article, as was pointed out.

Cheers,

Khanti

Whit Fulton's picture

I'll jump in for Khanti here -- the term-line side tap is often used two ways: As Khanti is using it here, it means into the line above the breaker panel (MDP) but below the metering point at the premises service entrance. As it's used in the utility industry, it means above the metering point (line-side vs load-side). The electrical circuit contacts for the version Khanti described are on the load-side of the service entrance meter and therefore are metered identically to a standard interconnection at the MDP.

Charles Gulyash's picture

Would you not publish articles containing abbreviations. Everybody uses different terminology for everything. When I get to an abbreviation I quit reading. It's not cool or really "in crowd".

Tony Olson's picture

Charles, I agree that using acronyms / abbreviations without defining them at first use can leave readers wondering what is being discussed. In this article, the only abbreviation I see undefined is PV in the first sentence. MDP was spelled out at its' first use in paragraph 1, as the main distribution panel. In my writing, I would have capitalized the letters to make a clearer connection for the reader i.e. "Main Distribution Panel (MDP)".

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