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Hacking Your Way Off The Utility Grid

by Brian McConnell
12/03/2004

It is pretty obvious that sooner or later we need to do something about our petroleum addiction. Regardless of how you feel about climate change, saving cuddly animals, and such, the economics of the energy industry are pretty stark. There is a finite supply of fossil fuels. Demand for energy is increasing and will increase rapidly as developing countries modernize. We can ignore this, or we can do something about it. Fortunately, alternate energy sources are now a practical reality.

Last year, I began work to retrofit my home in San Francisco to generate most of its own energy (both heating and electric). My design goal was to reduce my home's energy footprint by 80 to 90%. I approached this project in three stages. In stage 1, I installed a grid-intertied solar electric system that generates most of the house's electric power. In stage 2, I supplemented the solar electric system with solar water heating that reduced the electric energy consumed by my backyard hot tub. In stage 3, I installed solar forced air heaters that reduce the need for natural gas central air heating.

I got involved in this project for a number of reasons. First, I am an engineer and tinkerer. Since I already have all of the electronic gadgets I want or need, I was looking for something new to play around with. The idea of turning my home into a personal power production facility was interesting to me. I also wanted to lock in my cost of power, as a hedge against future energy crises and the long-term trend toward increasing energy prices. Lastly, the idea of doing something to protect the environment was appealing, although it was not my primary motivation for doing this.

Phase One: Net Metered Solar Electricity

In phase one, I spec'd out a net metered solar electric system to be mounted on my roof. My house was built in 1939. It is a three bedroom, 1500 sq. foot home with approximately 1000 sq. feet of roof area. I wanted to generate as much power as I could, while leaving several hundred square feet of space for a roof deck to be installed in later stages of this project.

The system I decided on is a 2,500 Watt (peak output) system consisting of 18 BP (British Petroleum) solar panels coupled to a 2500 Watt Sunny Boy inverter (which converts the DC power from the panels to 120 volt AC power). The system is net metered and is connected to the PG&E electric grid. When the system is generating surplus power, which it typically does during mid-day (even in the winter), the meter runs backward. PG&E bills me for my electric use on a 12 month cycle, so usage is averaged out over a one year period.

Bay View
Solar Electric--Bay View

Street View
Solar Electric--Street View

The goal in net metered solar electric is to size the system so that it generates up to 100% of the power the house consumes on average, throughout the course of a year. PG&E does not pay for surplus power, so the game is to get as close to net zero consumption as possible.

My strategy was to start with a system that generates 65 to 75% of the home's average electricity consumption, and then eliminate the remaining 25 to 35% through the conservation measures in phase two and phase three of this project.

The rooftop solar electric system was installed by Occidental Power, a solar electric contractor based in San Francisco. Solar electric systems require the help of licensed contractors because the system is connected to the public electric grid and, therefore, must conform to numerous electrical and fire safety codes.

The system cost approximately $25,000 prior to the California rebate, and $16,000 after the state rebate (for a net cost of about $6,500 per kilowatt). At first glance, this seems expensive, but the system has a 30 year life span. The initial cost of the system was rolled into my mortgage when I refinanced my house, and when amortized, costs about $80/month, about the same as my electric bill. However, instead of sending money to PG&E, I am paying down an asset attached to my house (installing the array increased the value of my home proportionally). This monthly payment is also tax exempt (it's part of my mortgage), and so the real, post-tax cost of the array is more like $50 per month, less than my monthly electric bill.

From January through November of 2004, my system has generated 4,400 kilowatt hours of electricity. During this period, my home has drawn 2,200 kilowatt hours from the public grid (for total consumption of 6,600 kilowatt hours). My system is currently generating roughly 65 to 70% of the electricity my house consumes. The system reduces the cost of my electricity even more because it lowers my home's average consumption enough to get me into the lowest pricing tier ($0.13/kWh versus $0.19 to $0.25/kWh). So what electricity I do pull from the grid is now billed at the cheapest rate.

This is an important point, especially if you draw 500 kilowatt-hours per month or more (as most modern homes do). If your utility company uses a tiered rate structure, it is likely that the majority of your power is billed at high above-baseline rates that can be two to three times the baseline rate. The power generated by the PV system will offset the most expensive grid-supplied electricity first. So even if your system generates only a modest share of the home's power, say 35 to 50%, it can reduce your electric bill by substantially more than this.

The bottom line: in phase one, I reduced my home's electrical energy footprint by 65 to 70% in kilowatt-hours and by 80 to 85% in dollar terms (because of being knocked down into the lowest $/kWh pricing tier). The system is currently generating about $1200/year of electricity. Not bad, and since the array will last 30 years or more, it will more than pay for itself, even if the cost of energy remains flat (though it is more likely to increase as competition for finite fossil energy supplies increases).

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