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Working Toward a Sustainable Home

For the last twenty-five years, my wife Michelle and I have been consciously working on reducing our impact on the planet. We are both vegetarians. We live simply, with solar thermal and solar-electric systems. I am self-employed, designing and installing renewable energy systems in our local area. Over the last three years, I've been reading more and more about our dwindling global oil supplies and specifically "peak oil." My research has convinced me that we must do more.

Todd Cory

©2005 Todd Cory

Peak Oil

What is peak oil? Peak oil is when the extraction of oil from the earth reaches its highest point and then begins to decline. Unfortunately, peak oil is coinciding with escalating demand. Combine our decreasing oil supply with an increasing level of consumption, and it is easy to see the rapidly approaching "perfect storm."

Twenty-five years ago, we started to read about the serious need to prepare for this situation. To date, world "preparation" has gone in the opposite direction. Our global population has increased by more than 2.3 billion to 6.5 billion people! Here in the United States, wasteful, oversized homes have become the standard, and we have seen the widespread proliferation of low-efficiency vehicles.

Look around you and try to find one thing that was not made possible by hydrocarbon energy. Even in the food we eat, every calorie has been produced with around 10 calories of fossil fuel. This very sobering issue is beyond the scope of this article. You can research peak oil and educate yourself: to start, see HP81 for an excellent article on the topic by Randy Udall.

What to Do?

With an increased awareness of peak oil, my wife and I decided to see what we could do in our personal lives to retrofit our existing home to reduce its impact. For the last

A 960 W array of twelve, Shell 80 W panels overshadows the power shed, which houses the inverter, controller, and batteries.

With its fantastic fuel economy, the Corys' hybrid-electric Toyota Prius helps them achieve their energy conservation goals.

A 960 W array of twelve, Shell 80 W panels overshadows the power shed, which houses the inverter, controller, and batteries.

eight years, we have enjoyed net zero electricity use with our grid-tied, 1.4 KW solar-electric system. But we still consumed fossil fuel energy (kerosene) for winter space heating.

I was curious to find out what it would take to heat our 1,600-square-foot (150 m2) home with solar electricity. This is not as crazy as it may sound. For eight months of the year, we have abundant, renewable sunshine. A net-metered photovoltaic (PV) system with an annual billing cycle could "store" that energy over the summer for use during the winter. How much additional solar-electric input would we need to replace our kerosene consumption to a point where our home would use no outside energy?

Step One—Reduce Waste

The first step is always reducing waste. While we had done this with the home's electrical system, we had not done much to the house's thermal system. Because this is a retrofit, it is harder than if the house had been built with energy efficiency in mind from the start.

We blew R-60 cellulose insulation into the attic and put 2 inches (5 cm) of rigid foam on the outside of the north wall, with new siding on top. We weather-stripped and sealed air leaks. We installed pleated, R-4 insulating blinds on all the windows.

We also changed the way we heat the house, only heating the spaces when we are in them. We close doors to unused areas and program the heater's setback timers to change the temperature at different times of the day. This provides comfortable temperatures when spaces are used and reduces heat loss when they are unoccupied. The changes resulted in a dramatic 55 percent annual reduction of kerosene use, from 265 to 120 gallons (1,000 to 450 l)!

Step Two—System Changes

The proper way to get to zero energy would be to first determine the amount of additional energy we need, and then design a system to accommodate those needs. Because our space for added PVs was limited, I decided to install what was possible, and see how close that brought us to our desired goal.

PV System Tech Specs


System type: Battery-based, grid-tie PV Location: Mount Shasta, California Solar resource: 4.5 average daily peak sun hours Estimated average production: 410 KWH per month Utility electricity offset: 100 percent


Modules: Twelve Solarex MSX-60, 60 W STC, 17.5 Vmp, 12 VDC nominal; twelve Shell SQ80, 80 W STC, 17.5 Vmp, 12 VDC nominal; eight Sharp 185, 185 W STC, 36.2 Vmp, 24 VDC nominal

Array: Six sets of four 12 VDC nominal module series strings, 70 Vmp; and four sets of two 24 VDC nominal module series strings, 72.4 Vmp; 3,160 W STC total, 48 VDC nominal

Array combiner boxes: Three OutBack PSPV

Array disconnects: Two OutBack OBDC 40 A breakers

Array installation: Three Array Technologies, dual-axis active trackers

Energy Storage

Batteries: Eight Trojan L-16H, 6 VDC nominal, 420 AH at 20-hour rate, flooded lead-acid

Battery bank: 48 VDC nominal, 420 AH total

Battery/inverter disconnect: OutBack PS2DC with 175 A breaker

Balance of System

Charge controller: OutBack MX60, 60 A, MPPT, 48 VDC nominal input voltage, 48 VDC nominal output voltage

Inverter: OutBack GVFX3648, 3,600 W, 48 VDC nominal input, 120 VAC output

Performance metering: Xantrex Link-10 (only provides relevant data when the grid is down)

In July 2004, I retired our ten-year-old, grid-tied, Trace SW4024 inverter and replaced it with an OutBack GVFX3648 inverter. (We are using a battery-based inverter system because our utility often goes down during severe winter snowstorms.) The battery-based OutBack inverter has a higher conversion efficiency when feeding solar energy to the grid. It also has the intelligence to shut itself off when it's not needed, instead of constantly floating the batteries. The original Trace SW series inverters always floated the battery bank using energy from the grid. This amounted to a huge phantom load on my system, averaging about 250 KWH a year!

In October 2004, I added a third tracked rack of panels, increasing our grid-tied solar-electric system from 1.4 KW to 3.2 KW (STC). In Spring 2005, we began "banking" our surplus solar-electric generation (spinning our meter backwards). This winter, we will use that "stored energy" in electric heaters to offset the fossil fuel heating.

The 3.2 KW PV system will generate around 5 megawatt-hours (MWH) a year. We have historically used about 2.5 MWH a year (about 210 KWH a month) to operate the house's nonheating, electrical loads. This leaves around 2.5 MWH for resistance electric space heating. A ground-source heat pump would produce a higher KW-to-Btu energy return than resistance heaters. Our calculations demonstrate that the house should now be close to net zero energy on an annual basis.

The Numbers

Last year we used 120 gallons (450 l) of kerosene. Our Monitor brand kerosene heater delivers 19,500 Btu per hour using 0.16 gallons (0.6 l) of fuel. So 120 gallons allows the heater to run for 750 hours, delivering 14,625 KBtu.

The 2.5 MWH of available electrical storage used as resistance electrical heat is equal to 8,532 KBtu (2,500 KWH x 3,413 Btu per KWH = 8,532,500 Btu). This leaves us with an energy deficit (14,625 - 8,532) of 6,093 KBtu per year.

So, our banked solar-electric energy will take care of about 58 percent of our heating needs, or an equivalent of about 70 gallons (265 l) of kerosene. This will reduce our annual consumption to about 50 gallons (190 l).

Two solar thermal collectors mounted on the garage roof provide the Corys with most of their domestic hot water. A small PV panel (between the collectors) powers the pump.

Two solar thermal collectors mounted on the garage roof provide the Corys with most of their domestic hot water. A small PV panel (between the collectors) powers the pump.

The PV power shed houses an OutBack inverter, charge controller, AC and DC disconnect panels, and the battery bank.

Estimated Costs

Because this system has evolved over the last twenty years, it is difficult to determine the exact costs. Most dealers estimate the cost of installed PV at around US$10,000 per rated kilowatt, so a rough cost for our system would be about US$30,000.

Conventional thinking would laugh at spending US$30,000 on a system that would mitigate only US$500 a year of "brown" (nonrenewable) energy costs. However, let's remember that brown energy is subsidized and does not include environmental, social, and military expenses. We still pay those costs, but they are hidden—in our taxes, our budget cuts, our declining standard of living, and our decreasing international popularity.

Step Three—Solar Thermal Heating

In the spring, summer, and fall, we have a surplus of hot water available from our solar thermal system. This summer, I installed a commercially manufactured hydronic heater to dump this waste heat into the house. This is a length of coiled, copper fin tube that you run hot water through. A fan forces air through the fins and exchanges water heat to air heat. When the solar thermal system heats the water in our storage tank above 130°F (54°C), the fan and pump turn on if the thermostat calls for heat. This system shuts off at 110°F (43°C), leaving the rest of the hot water for domestic use.

Empirical testing has shown that when the sun is shining, this unit typically runs for about four hours a day, delivering 5,000 Btu per hour. This equals about 20,000 Btu per day, or an equivalent of 0.16 gallons of kerosene a day. This surplus, solar thermal heat is used for approximately three months a year, which amounts to about 14 gallons (53 l) of mitigated kerosene.

Calculated Conclusions

Our calculated, annual net energy load will still require close to 36 gallons (136 l) of kerosene (50 - 14 = 36). These 36 gallons of kerosene burned in our Monitor brand heater would equal about 4,387 KBtu.

Our house is not "zero energy," but it's getting close. The kerosene we still end up using would require almost 1.3 MWH of additional annual electrical generation, or about 700 more watts added to the current 3.2 KW array. So for our home's typical energy requirements, 3.9 KW of solar-electric capacity would make us "zero energy." Of course, these are calculated numbers; seeing how this performs in the "real world" this year will be interesting.

Solar Hot Water System Tech Specs


System type: Antifreeze, PV-direct pumping

Climate: Extreme to hard freezes throughout the winter

Production: Estimated at 1,200 KBtu per month average

Number of people in household: Two

Percentage of hot water produced annually:

Approximately 80 percent

Collectors: Two, used, 4 x 10 ft., black chrome

Heat transfer fluid: Ethylene glycol

Collector installation: Roof mount, SSW orientation, 35-degree tilt

Storage: Existing 80-gallon electric hot water tank

Heat exchanger: Used, flat plate

Circulation pumps: Glycol loop; Hartel, 24 VDC, brushless, high-speed pump, model #MD10HEH. Potable loop; Hartel, 24 VDC, low-speed pump, model #MD10DCL

Pump controllers: Glycol loop runs array direct. Potable loop runs array direct via a used Independent Energy C-30 differential controller

Performance metering: Two, GC brand thermometers and a pressure gauge

Kerosene Usage

Original After After PV After Solar

Use Conservation Heating Thermal

Original After After PV After Solar

Use Conservation Heating Thermal

BP Solar, 630 Solarex Ct., Frederick, MD 21703 • 800-521-7652 or 410-981-0240 • Fax: 410-981-0278 • [email protected] • PVs

Shell Solar Industries, 4650 Adohr Ln., Camarillo, CA 93011 • 805-482-6800 • Fax: 805-388-6395 • [email protected] • • PVs

Sharp Electronics, Solar Systems Division, 5901 Bolsa Ave., Huntington Beach, CA 92647 • 800-S0LAR06 or 714-903-4600 • Fax: 714-903-4858 • [email protected] • PVs

Array Technologies Inc, 3312 Stanford NE, Albuquerque, NM 87107 • 505-881-7567 • Fax: 505-881-7572 • [email protected] • Wattsun PV trackers

OutBack Power Systems, 19009 62nd Ave. NE, Arlington, WA 98223 • 360-435-6030 • Fax: 360-435-6019 • [email protected] • Inverter & charge controller

Short-term thinking says "green" energy is more expensive. But what you are buying is not typical brown energy, subsidized by future generations. You are purchasing a renewable energy generation appliance that may still be capturing usable energy 100 years from now, when oil costs may have climbed from US$50 a barrel to US$500 a barrel!

Peak Oil Revisited

For about the last hundred years, we have been surrounded by the luxuries provided through cheap energy. With the arrival of global peak oil, this is about to change. As fossil fuel production declines, so goes the easy, comfortable, and unsustainable life on which it was founded. We cannot drill our way out of this.

Some credible estimates show petroleum production peaking—with demand exceeding supply—sometime around 2007. Global peak oil is a brick wall we are traveling towards, full speed. While I have worked at covering our home's electric and heating needs, I have not addressed our other energy consumptions. These include transportation and the food we eat. This year we purchased a Toyota Prius and have expanded our garden to provide a greater percentage of homegrown food. A greenhouse is also on the project list.

Peak oil represents a profound impetus for our planet to awaken to the necessity of living sustainably. Gandhi said it best: "You must be the change you wish to see in the world."


Todd Cory, Mt. Shasta Energy Services, PO Box 689, Mt. Shasta, CA 96067 • 530-926-1079 • [email protected]

Trojan Battery Co., 12380 Clark St., Santa Fe Springs, CA 90670 • 800-423-6569 or 562-946-8381 • Fax: 562-906-4033 • [email protected] • Batteries

Beacon/Morris, 260 North Elm St., Westfield, MA 01085 • 413-562-5423 • Fax: 413-572-3764 • [email protected] • Kickspace hydronic heaters

"When Will the Joy Ride End?" by Randy Udall with Steve Andrews in HP81

Peak oil Web sites: .

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Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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