Generate Electricity While Heating Your Home



We occasionally publish “classic” articles that we feel are still relevant to readers. This article is from the Jan/Feb 2009 issue of the Green News

This Year’s Solar Homes Tour included something new: The Goldsmith family of Waverley Avenue graciously invited Newton residents to tour their newly installed “combined heat and power,” or CHP system. The Goldsmiths, owners of a large Victorian, were heating with oil but were stunned by price increases and concerned with the inefficiency and advancing age of their old boiler.

So last year they decided to install a new heating system. While investigating what kind of system might most efficiently service his large home, Max Goldsmith attended a Green Decade workshop entitled “Insulate Your Older Home” and discovered that it is now feasible to install a system that generates both electricity and heat that can be used for space heating and hot water.

CHP has been used in commercial and industrial applications for decades, but only recently has its “Micro CHP” version—pioneered in Europe and Japan—become available for individual residences in this country. Micro CHP systems burn natural gas to power an electric generator.

Generating local electricity this way saves 60 percent of the fuel power plants burn to do the same thing—partly because no electricity is lost in transmission lines, and partly because the “waste heat” that power plants generally blow off is instead used in your home to provide heat and hot water. Your home becomes much more efficient, cheaper to run, and your carbon footprint is substantially reduced.

The Goldsmiths’ System

Max Goldsmith led us into his basement and pointed out large areas of space recovered when he removed an old oil-fired boiler and two storage tanks. In its place were new, compact, high-efficiency hot-water boilers to heat the family residence and a first-floor rental unit. And in front of these was a small unit that contained the “Climate Energy Freewatt Generator” CHP system made by Honda.

Whenever heat or hot water is needed, the CHP unit starts up, burning gas to generate electricity, with the accompanying heat used to heat water that flows to the space-heating boilers and to the house’s hot-water tank. The CHP generator fully heats the home’s hot-water supply, and it provides enough space heat for much of the year. In quite cold weather the gas boiler provides additional heat. All the while, the system also generates electricity.

If the Goldsmiths need the generated electricity at that moment, it’s immediately consumed. Any unneeded electricity is fed back into the electric utility grid—thus lowering the Goldsmiths’ electric bill (the meter actually spins backwards; a practice called “net metering”) and also increasing the grid’s overall electricity supply.

As befits cutting-edge technology, the CHP system includes an internet connection and its own personalized Web site. Max can not only monitor, graph and keep records on the electricity he’s generating, he can also remotely monitor and reset his home thermostat. Imagine the possibilities for managing your home’s energy consumption the next time you go on vacation. In the meantime, the system is monitoring itself and reporting any faults or problems to the company that installed and services it; should any problems arise, they get nearly immediate notification, and the homeowner gets a rapid response.

The Goldsmiths’ new system was installed this summer, so as this article is written, Max has a limited amount of data so far. During the warm months the new system was only called upon when the Goldsmiths or their tenants needed hot water.

Nonetheless, the CHP system generated 488 kWh of electricity in the first two months and reduced fuel consumption for hot water by almost 9 million BTUs compared to the average BTUs consumed by the old oil-fired system in comparable months in 2005 to 2007. Max estimates his savings for these two months combined at $350.69. During the heating season he expects monthly savings to rise considerably.

October’s electric bill from NSTAR [for mid-September to mid-October usage] showed that usage went from 1150 KWh in October 2007 to 518 KWh in 2008. Most of the savings, 449 kWh, came from the use of the CHP system, with about 200 kWh saved from the use of compact fluorescent lamps (CFLs). At full capacity, the 1.2 kWh Freewatt unit will generate about 800 kWh per month of electricity.

Max’s October gas bill also showed savings—the new system generating electricity as well as heat and hot water used 41 percent less fossil fuel than did the old oil-fired boiler that generated only heat and hot water. Though these data remain quite preliminary, they are encouraging.

The CHP system adds about $6,000 to $7,000 to the cost of a new heating system. Based on what he has read about other people’s experiences with CHP, Max expects his fuel savings and reduced purchases of electricity from the grid to pay back the cost of CHP in seven to eight years. If fuel costs continue to rise as they have in recent years, the payback period could be shorter.

Various incentives and rebates are also available to help with the additional cost. NSTAR covered $1,000 of the CHP cost and $1600 for each high-efficiency boiler. Federal tax deductions will help further. And a program run by Mass Save [http://www. masssave. com/about/heat_loan.php] provides no-interest loans of up to $10,000 for installing qualified energy-efficient systems.

Stay tuned for future reports on the longer-term experiences of the Goldsmiths and others with micro CHP systems.

–by Stephen T. Barry