advertisement

Print

Hacking Your Way Off The Utility Grid
Pages: 1, 2

Phase Two: Solar Water Heating

After phase one was completed, I surveyed my home's electrical usage to determine where I could use conservation measures to eliminate the remaining electrical energy footprint (about 150 to 200 kilowatt-hours per month after the solar system was installed). I have a hot tub in my back yard which has a 5 kilowatt electric heater. Although the hot tub is well insulated, it consumes several kilowatt hours of electricity to maintain its temperature. As it turned out, the hot tub's electric energy consumption was almost the same as the remaining difference in my household consumption. If I could reduce the hot tub's electric consumption by 60 to 80%, I could close the gap and achieve net zero electrical consumption, or close to it.

To do this, I bought a small solar water heater. This is a low tech device, essentially an insulated glass box with a black plate backed by copper tubing. When directly lit, the heat absorber heats to over 200 degrees (hot enough to boil water). You circulate water through the collector in a loop, and store the heated water in an insulated basin (i.e. the hot tub). The solar heater in my backyard is 3x8', captures about 1500 Watts of heat energy when lit, and receives 3 to 4 hours of direct sunlight per day. On average, it captures several kilowatt hours of heat energy per day. This energy is used to heat the water, so the hot tub's electric heater kicks in much less frequently.

Solar Water
Solar Water Heater

Phase Three: Solar Air Heating System

My home is located in Twin Peaks, one of the windier spots in San Francisco. This city is famous for its weird weather patterns. The weather is often quite cool here, especially during the day, and even in the summer.

I have forced air natural gas heating and wanted to complement this system with solar heat. This used to be a very expensive proposition, but newer technologies drop the prices of solar heating dramatically and require no major structural modifications to existing homes.

For my house, I opted for forced air solar heaters made by Clear Dome Solar. These are surprisingly low tech devices and are similar in design to solar water heaters. The heater is simply an insulated box containing a sheet of black polycarbonate plastic. Air ducts draw air across the polycarbonate surface, which heats up to 150 to 200 degrees when lit up, enough to heat the air by 20 to 40 degrees.

Solar Air Heater
Solar Air Heater

I installed three heaters on my roof, each positioned to heat a different zone of the house. Apart from generating free heat, solar air heaters are great for zoned heating systems, since each one is essentially a miniature, self-powered furnace. I hired a ductwork contractor to run ducts from each heater to different parts of the house.

The solar air heaters, unlike a conventional furnace, run continuously throughout the day. A typical furnace injects a large amount of hot air into a room to quickly increase the ambient air temperature. Solar heaters, by contrast, run constantly, and inject a relatively small flow of warm air (usually 80 to 120 degrees) throughout the course of the day. The net effect is the same, with one big difference--a properly designed solar air heating system uses the house itself as a giant heatsink. So by the end of the day, every object in the house is heated up to 70 to 75 degrees. When the sun goes down, the house re-radiates heat back into the interior space, keeping temperatures up for several hours after sunset.

Solar heating is not a replacement for conventional heat, but it can reduce the need for central air heating, especially during the day and early evening. One of the greatest benefits of solar heating is that you can often heat outside air rather than recirculate stale, indoor air. My system is rigged with dampers, so I can select between recirculated and outside air. As long as the temperature difference between outside air and the desired indoor temperature is less than 30 degrees, the solar heaters can heat fresh outdoor air on a sunny day.

Miscellaneous Improvements and Conservation Measures

In addition to installing power production systems, I have also built conservation measures into my home's electrical system, primarily by installing motion sensor light switches and by replacing some incandescent lightbulbs with flourescent bulbs. Lighting is a good way to waste electricity. For example, a single 100 watt bulb that is habitually left on for eight hours at night will burn 24 kilowatt hours of electricity per month (about $6/month if you're in a high rate tier).

Upgrading your home's lighting system is an easy and cheap do-it-yourself project. I recommend installing Leviton motion sensor light switches in high traffic locations such as hallways, stairways, garages, and storage rooms (don't put them in living areas). Florescent light bulbs also work well in high traffic areas, storage rooms, and bathrooms. They look much better than when they were first introduced and do a good job of mimicking incandescent lights. They also last forever. They can't be dimmed, however, so I don't recommend them for living areas where you want adjustable lighting.

Get rid of your old refrigerator! If your refrigerator is more tha five years old, it is probably burning more power than you realize. Older models can cost several hundred dollars per year to operate. The payback time on a new energy efficient refrigerator can be less than two years.

The Results So Far

It has been about a year since I completed the first phase of this project. The results so far have met my expectations, and with a few more months of tinkering, I should be close to my goal of a 80+% reduction in my home's energy footprint.

Phase One: Solar Electric System

The solar electric system has been operating for about a year and will have produced about 5,000 kilowatt-hours of electricity during its first year of operation. Since this mostly offsets above-baseline usage, the system will have generated $1,000 to $1,200 worth of electricity, or about $80 to $100 per month in direct savings. The system is generating about 70% of the electricity my home consumes. Overall, I have no complaints about the system. It has performed very well, and I recommend net metered solar. It's a great investment, adds value to your home, and saves money.

Phase Two: Solar Water Heater

The solar water heater has been operating for about three months and is producing part of the energy required to heat the spa. I originally set the water heater up as a thermosiphon. With a thermosiphon, there is no circulating pump; as water is heated in the collector, it rises. This causes water to flow through the collector, albeit slowly. I determined that the thermosiphon was not quite efficient enough because of heat loss from the tubing connecting the water heater to the spa. I am installing a small circulating pump that will pump water through the heater. This should substantially reduce heat loss and eliminate most of the hot tub's electrical consumption once I get everything fine-tuned.

Another bonus feature...when the Big One arrives, while the rest of the populace is festering in squalid tent cities, we'll be relaxing in a toasty self-powered hot tub (assuming my house hasn't rolled down the hill along with it).

Phase Three: Forced Air Heaters

The forced air heating system has been a bit tricky to troubleshoot, mainly because the fans installed by the ductwork contractor were not matched correctly for the size and length of the duct runs. The contractor also made a mess of the DC electrical wiring, so two of the three thermostats did not work correctly. (NOTE: some ductwork contractors are not exactly the brightest bulbs in the universe; do not assume they understand what needs to be done).

The heaters performed well in the standalone tests I have run and produce heat as advertised. However, because the fans are mismatched, they do not have enough power to force air efficiently when connected to the ducts. I need to replace a couple of the fans to get the efficiency I need.

I will know more about the system's impact on the overall natural gas consumption in a few months. I am expecting to reduce my furnace usage by 50% or more, as the system is slightly oversized for my house.

If you are considering installing forced air heating, my main advice is to choose an HVAC contractor carefully. A lot of them are not very smart, and you can also get hit with high labor charges for something that is very low tech and does not require much thought. If you are comfortable with carpentry, you may want to consider doing this yourself.

The Bottom Line

This project has worked out about as I expected it, except for the snags with the forced air heater installation, which should be worked out in a few weeks.

The total cost for all three projects worked out to about $22,000, all of which was rolled into my refinanced mortgage, which works out to approximately $140/month in debt service (30 year fixed rate, 6.5%). After the mortgage interest deduction is factored in, the after-tax cost of the system works out to about $90/month.

The systems produce direct savings in the form of direct electrical production, reduced electrical consumption (the solar water heater offsets electrical heat usage), and reduced gas heat usage.

  • Net metered solar electric : 5000kWh/year @ $0.22/kWh avg rate = $1100/year, $92/month
  • Solar water heater : 1800kWh/year (projected) @ $0.15/kWh avg (relects elimination of baseline tier usage) = $270/year, $22.50/month
  • Solar air heaters : ~50% of natural gas usage versus baseline average of $50.00/month = $300/year, $25.00/month
  • Net savings: $1670/year, $140/month

So when all of the savings and tax breaks are added up, the solar systems produce net revenue of about $50/month or $600/year, which isn't too bad. In addition to the direct return on investment, the systems provide several additional direct and indirect benefits, including:

  • Increase in home value: each $1 in utility bill reduction is estimated to increase home value by $20. Therefore, the energy production systems increase the value of my home by about $34,000, yielding an immediate 50% return on investment.
  • Stable, long-term energy costs: because it produces most of its power, my home is largely protected against increases in energy costs. As energy costs increase, the math becomes even more favorable toward renewable energy systems.
  • Protection against property incursions: local zoning rules often prohibit neighboring property owners from building anything that will cast a shadow on rooftop solar installations. This is a helpful protection in urban environments, as it prevents someone from building a "McMansion" next door to your home, which helps to protect your home's appearance and value.

Overall, I am quite happy with the way these projects have panned out. It is a nice feeling to see the electric meter running backwards during the day, even during the winter. With some additional tinkering, I should be able to meet my goal of reducing my home's energy footprint by at least 80%.

Why should you follow suit? Leave the financial incentives aside. Since you're reading this article on O'Reilly's website, there's a pretty good chance you like playing around with electronic gadgets. Most tech people I know spend an inordinate amount of money on the latest PDAs, computers, iPods, etc. If you're willing to spend several thousand dollars per year on electronic devices, subscriptions to wireless internet service, and such, you can probably invest some of this money in upgrading your home. It's always good to learn new things, and this is fun stuff to play around with.

Brian McConnell is an inventor, author, and serial telecom entrepreneur. He has founded three telecom startups since moving to California. The most recent, Open Communication Systems, designs cutting-edge telecom applications based on open standards telephony technology.

Return to the O'Reilly Network.