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Solar carport tracks impact of plugging in

By Alan Yonan Jr.

LAST UPDATED: 2:26 p.m. HST, Aug 5, 2011

Here's a concept: Build a solar carport and use it to charge your electric car.

That's what Hawaiian Electric Co. had in mind when it teamed up with an industry research group to test an experimental solar-powered charging station for electric vehicles at the utility's Ward Avenue facility.

The charging station features a nine-panel photovoltaic array mounted on a carport complete with a battery storage system. The project will allow HECO and the Electric Power Research Institute to collect and analyze a range of data on the potential impact vehicle charging will have on electrical grids, or distribution systems, as the number of EVs on the country's roadways grows.

Utilities from around the country are concerned that without proper preparation, the additional demand for electricity from widespread EV charging could put stress on their grids.

HECO will also use the experimental carport to help answer questions from customers who want to know how EV charging might affect their electric bills, said Peter Rosegg, HECO spokesman.

The nine PV panels have a combined rating of 2 kilowatts powering a 220-volt charge station capable of topping off a Nissan Leaf battery in about four hours, Rosegg said. The station also has a 20-kilowatt lithium-ion battery that can be used to store energy collected during the daytime for EV charging at night. The battery produces enough energy to provide more than 80 percent of the charge needed for the 24-kilowatt Leaf.

The battery, however, added a significant cost to the solar carport, which carried a price tag of around $50,000 before tax credits. The test project, funded largely by EPRI, includes monitoring equipment to collect the data and transmit it to a computer through a wireless Internet connection, Rosegg said. The charging station was designed primarily as a research project and wasn't intended to be a prototype to be commercialized, he said.

RevoluSun, which designed and built the system, said homeowners who want equivalent charging power can install a system on an existing house or garage rooftop for about $15,000 to $16,000, excluding the backup battery system and wireless monitoring equipment. A 35 percent state tax credit and 30 percent federal tax credit would drop the effective cost of the system to $5,200 to $5,600.

The PV panels can be tied into a home's electrical system to provide solar-generated electricity for other household uses when a vehicle is not being charged, said Josh Powell, a RevoluSun partner.

EV owners who choose to charge their cars using the HECO grid are being encouraged by the utility to do so at night when electricity demand is lower. HECO offers its Oahu customers a discount of 6 cents per kilowatt-hour on electricity used for charging electric vehicles between 9 p.m. and 7 a.m. On the neighbor islands the EV rate ranges from 7 cents to 10 cents lower per kilowatt-hour.

EV owners who already have PV panels on their homes can still offset the cost of charging their cars at night when the electricity being used is coming from the HECO grid. Under the utility's net energy metering program, a customer can receive credit for unused solar energy that is fed back into the grid during daylight hours. That credit can then effectively be used to pay for the electricity being drawn from the grid at night.

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