Innovation: SDG&E device lowers cost of going solar

Peter Key | Sep 10, 2015

 

San Diego Gas & Electric Co. has invented a device that makes installing rooftop solar-power generation systems quicker and cheaper for many of its residential customers, especially those with older electrical systems.

The subsidiary of San Diego-based Sempra Energy began making the device, which is called a renewable meter adapter, available July 30 and had installed more than 200 as of the last week of August.

"We're really, really excited about it. It's been really well-accepted so far, we've learned a ton, and I think that moving into 2016 it's going to be really changing the marketplace in San Diego," said SDG&E Customer Generation Manager Ken Parks.

The adapter, or RMA, costs $1,300, but SDG&E said the device allows residential customers to have rooftop solar installed without upgrades to their electrical service panels that typically cost more than $2,500 and often require construction and landscaping work. 

"We can install this device in less than an hour with one employee," Parks said.

The RMA works with service panels of 200 amps or less. Parks said the "less" part is important because installing a rooftop solar system typically requires a 200-amp service panel, which many homes served by SDG&E don't have. 

That means the RMA will make rooftop solar systems affordable for customers who previously would have found them prohibitively expensive because the customers now won't have to get their service panels replaced to have the systems installed.

The RMA can handle solar systems up to 11.5 kilowatts. Parks said solar systems in San Diego average 5 to 6 kilowatts.

The device also has a 60-amp circuit breaker for over-current protection. If it is tripped, the customer can use a plunger to reset it without calling SDG&E, Parks said.

The RMA and a fused disconnect are installed between the meter and the service panel. The disconnect means the installer doesn't have to get into the customer's breaker system.

Energy generated by a rooftop solar system goes to the RMA, which uses it to service the customer's load. If the amount of energy being generated by the system exceeds the customer's load, the RMA puts the excess through the meter and back to the grid.

"The electric meter is bidirectional," Parks said.

SDG&E applied for a patent on the RMA in 2013 and got it certified by Underwriters Laboratories in March of this year.

Rob Weber, the CEO of AgileSwitch LLC, a Philadelphia maker of insulated-gate bipolar transistor drivers used in solar inverters, wind turbines and electric vehicles, said that from looking at SDG&E's information on the RMA, and the patent application for it, the device could have a major impact on the rooftop solar market.

"This would be a significant boost to residential solar because getting the power back on to the grid [from rooftop solar systems] is a major hurdle and monitoring it . is a big challenge," he said.

"Everything [SDG&E] has identified in terms of cost and construction issues, they've maybe not eliminated, but minimized."

Parks, who invented the RMA with Michael Colburn, a research and development manager at SDG&E, said the company plans to look at marketing the device to other utilities, but will need permission from the California Public Utility Commission to do so. Right now, he said, SDG&E is focused on getting the device to its customers.

Parks said he didn't know how long an RMA would last in the field, but since it has no moving parts, he guessed it would last as long the solar systems it's attached to, which is typically 20 to 25 years.

"If something goes wrong with the device, [SDG&E] will go out and maintain it or replace it at no cost so I guess you could say this is truly a lifetime warranty," he said. 

The RMA is the second big product SDG&E has developed to make installing rooftop solar systems easier for its customers. 

The first was a web-based distribution interconnection information system the utility's customers can use to apply to get their rooftop solar systems connected to the grid. The website has lowered SDG&E's interconnection times to four to five days, which the utility thinks is the fastest in California. It also has helped SDG&E connect to more than 62,000 rooftop solar systems with a generation capacity of 415 megawatts.

http://www.energycentral.com/news/en/37318006