One of the more intriguing elements of the BASF energy-efficient home featured in last month's column (See “Seal the Deal,” July 1, page 99) was the photovoltaic system and the device that runs it. Upon further investigation, I discovered that this device, a GridPoint Connect, is akin to having a battery of Enron energy traders in your basement, although this trader is not at all crooked.

To be sure, with a retail price of about $10,000 (around $7,000 for a builder buying in volume), it is an expensive feature, particularly when joined with a solar PV array. By itself (not including the “free electricity” provided by a PV array), the intelligent energy management appliance can shave 30 percent off a homeowner's utility bill. When the appliance is connected to a PV array, it can reduce energy bills to nearly nothing.

“It's like an energy trader in a box,” says Peter Corsell, co-founder and CEO of the Washington D.C.–based GridPoint. “It can arbitrage the [power] grid.”

How it does this is nothing short of remarkable. The appliance is essentially an inverter, converting DC power into 110-volt AC power. It first converts and conditions the DC power produced by a PV solar array, wind turbine, or conventional generator then decides whether to route the power to be used immediately, stored in the batteries, or pumped back onto the power grid—spinning the electric meter backwards and reducing the monthly bill.

If the utility offers time-based rate schedules, as all must by early 2007 per the energy bill passed by Congress in 2005, the system will decide automatically whether it would be cheaper to run the home off the batteries while pumping power back onto the grid at times of higher rates or to run the home off the grid while charging the batteries. Some utilities actually offer higher paybacks for power that is pumped onto the grid at times of peak usage, so the GridPoint appliance can actually sell power at a higher rate than what the homeowner pays for using it.

The Connect appliance, the size of a small refrigerator, can be controlled through a real-time Web portal called GridPoint Central. Here, homeowners can schedule appliance usage, monitor energy usage, and even determine how much carbon they have kept out of the atmosphere. Installation is a snap, according to Chris Vanarsdale, who owns GBO Construction in Washington, D.C., and used the GridPoint system in a rehab of a 100-year-old row house. “The GridPoint has a battery backup, and it monitors everything. It's very simple, you basically just hook it up to the PV array, the utility's meter, and a communication line, either telephone or Ethernet,” he explains.

There are drawbacks to the GridPoint system and its attendant PV array. At $7,000-plus to the builder and another $30,000-plus for a 3.6 kilowatt-hour PV array, the payback period to the homeowner would have to be measured in decades, not years.

However, the GridPoint system is eligible for a $2,000 federal tax credit that can be taken by the builder or passed on to the homeowner, and there are federal and state rebate programs for renewable energy systems including photovoltaics that vary from state to state. The batteries in the GridPoint appliance—which are of the deep-discharge, valve-regulated lead acid type used as backup in most cell phone transmission towers—need to be replaced every five or six years at a cost of around $800. Finally, the inverter is guaranteed for only five years (they usually last around seven), and the replacement cost is between $2,500 and $3,000.

Still, the energy savings are considerable, and to a certain type of environmentally conscious home buyer, the prospect of living in a home that actually reduces carbon emissions is priceless. Corsell says the company is currently in negotiations with both Lennar Corp. and Shea Homes. He says he is also talking to Toll Brothers and KB Home.

Although the GridPoint technology might not be practical for most production homes, it's a valuable option to environmentally conscious home buyers willing to roll the added cost into the mortgage in exchange for the peace of mind that comes with low utility bills and clean living.