Birken Forest Monastery is a retreat center in the mountains of British Columbia. It’s located at an elevation of 4,000 feet at Latitude 51, and experiences about 9,000 heating degree days (Fahrenheit) per year. The buildings are about 15 years old.
We are off the grid. The nearest electricity line is 4 miles away, and it would cost about $200,000 to bring grid power in. (Then, of course, we would still have to pay for the electricity.) So off-grid it is, and will remain.
Years of off-grid experience
I have lived here for 14 years and have gained much off-grid experience and knowledge by the sometimes harsh teaching methods of Mother Reality. I should mention that I have been a Buddhist monk for the last 28 years. It doesn’t matter much, except that my training is to find simple and sufficient ways of life. How we do things, I believe, is appropriate to a comfortable American lifestyle as well, so I hope you can apply any of these strategies to your own houses, whether off-grid or on.
I won’t go into too much detail about the evolutionary process, but it is important to note that our first set of photovoltaic (PV) panels, rated at 1.8 kW, cost about $10 per watt installed. At that price, the PV system still made sense compared to our 12-kW Kubota liquid-cooled 1,800 rpm diesel generator. (By the way, the Kubota generator about as fuel-efficient as possible for any kind of generator.) We charged a bank of batteries with it, which optimized the engine efficiency even more.
How efficient was the generator, you wonder? About 32%. The energy you capture from a gallon of diesel is about one-third of its potential. Diesel fluctuates in cost; it’s at least $4 per gallon in Canada… sometimes $5. That translates to 50 cents per kWh of electricity, plus the life-cycle cost of the generator — so add maybe 20 cents. So the brutal reality of high-cost electricity (70 cents per kWh) turns you into an inventor/economist/minimalist, overnight.
PV costs are dropping fast
Fast forward in time, through an 80 kWh wet lead-acid battery bank for 7 years, to an 80 kWh maintenance-free AGM lead-acid battery bank for 6 years, to the present: we now have a recently installed 40 kWh AGM maintenance-free Surrette battery bank. Notice that this bank is half the size of the previous two. The cost of our latest battery bank: $8,000; life expectancy, 8 years.
The reason for the smaller battery bank: the PV array went from 1.8 kW to 3.4 kW in 2009, and then in November 2014 to 11.4 kW!
That’s a startling jump in solar power. Why? The economics are these: The additional 8 kW array was installed by an electrical engineer and two journeymen electricians for $3 per watt. There were no subsidies, no tax rebates, no special deals. The only things that weren’t new were the previously installed inverters.
A new age in off-grid living has arrived. Old formulas must be revisited.
Monitoring is essential
I carefully monitor all systems with sophisticated devices such as the Pentametric battery monitor, an hour counter on the diesel generator, a TED 5000 whole-house monitor, and daily notes and observations. December is the worst month, averaging 47 hours of bright sunshine (about 1.5 hours per day).
Now that we have a much bigger PV array, what will happen to our diesel use? In December 2013, when we had a 3.4-kW PV array, the diesel run-time was 60 hours. In December 2014, with our new 11.4-kW PV array, generator run-time was only 10 hours. Hmmm.
We are short about 50 kWh from being 100% off-grid solar. The generator run-times occurred on seven occasions, with each occasion requiring no more than 10 kWh. Conclusion? An additional battery bank rated at 20 kWh would zero out the generator year ’round! Now that may not mean much to you on-grid types, but any off-gridder will know that that is traditionally impossible amongst us forest-dwelling folk.
Think again, my fellow hobbits, think again!
Lowering electrical demand
Now the question: “Is it worth it?” In order to answer that, I have to expand the view to include the rest of the set-up.
Here is a snapshot of the main house. It measures 10,000 square feet. (Yes, you heard that right.) It has 12 bedrooms. It can accommodate 15 people and another 8 can use the facilities (sleeping in 8 separate “tiny houses”). The total population of 24 uses 5 washrooms, showers, cooking, 4 computers, all LED lighting, a 300-foot-deep drilled well, refrigerators, freezers, etc.
Now our average population is 12 to 15 people, but hundreds of people stream through year ’round. Our average electrical demand is only 12 kwh per day!
Yes, there is a deep back story to how we do it. I mean, we are talking about ¾ kWh per day per person, with all modern conveniences, including four-slice toasters, microwaves, dual-flush toilets, 4 showers, pressure pumps, a well pump, two refrigerators, and a freezer. (The refrigerators and freezer together use 1.2 kWh per day. They are in a large “cool room.”)
So without carefully controlling our electrical demand with super-efficient appliances, our 100% off-grid solar community would not be possible.
Not much sun during the winter
Our climate is not good for solar in the winter. Virtually anywhere in the U.S. is at least as good as we are, or better. Certainly the eastern U.S. has similar solar resources. But here’s the thing: for nine months of the year, we will produce about 7 times what we need for our electrical demand! Yikes, what a nice problem to have. (We deserve this problem, we created it!)
So, how much domestic hot water do we use? (You may have guessed that I know exactly how much.) I have installed a water meter on the 95% efficient 200,000 BTU/h propane on-demand water heater that supplies the whole house: 80,000 BTU/day, or 23.5 kWh if we think in terms of an electric plain-Jane water heater tank. Easy: we have up to 50 kWh on many days leftover. Now we could chop that down to 9 kWh by using a heat-pump water heater, but do we need to scrimp? It is an edgy question.
We plan to get an electric vehicle soon to mop up some of that excess electric production, but both together could be supplied rather easily for nine months per year.
So back to economics. How much propane savings? About $1,000 year.
How much gasoline savings? $2,000.
How much diesel and generator life wear? Maybe $800. Total savings, about $3,700 per year.
The payback period for the off-grid set-up (PV and battery payback) is (drum roll) 10 years. That includes the rather short life of the batteries (8 years) and the rather long life (30 years) of the solar panels.
Superinsulation helps reduce our energy needs
I’ll conclude with a brief description of the enormous house. It is superinsulated, with R-80 ceilings. The walls range from R-60 down to R-20 (on the south wall.) The big innovation is our R-25 polyiso-and-birch-plywood insulating shutters for all our windows. The building has 1,350 square feet of argon-filled low-e dual-pane windows. When it became apparent that the building is over-glazed, we permanently installed insulated R-30 exterior shutters over about 500 square feet of glazing, leaving about 850 square feet of windows exposed. These windows have been fitted with hinged R-25 shutters that open inward. Most are hinged at the top, although some are side hinged.
More than any other feature, these gasket-sealed insulating shutters contribute more to heat retention than any wonder machine or triple-glazed German miracle windows, for far less money… 80% less. (I’d be happy to go into detail if requested). During the 12- to 16-hour night, we basically don’t have any heat loss through our windows. In the daytime, with panels open, there is solar gain. It’s a win-win situation! For eight months of the year, we leave the panels open.
The space heating is supplied by two indoor high-efficiency wood stoves. We burn 5 cords of fir per year, locally collected. (British Columbia is the Saudi Arabia of firewood.) We don’t need any electric fans for air circulation.
Although there is in-floor radiant heat distribution throughout, we do not use it, ever. (Another learning experience). So for space heating, we need about 75 MBTU per year in a 9,000 heating degree day zone. Not bad. It’s not a Passivhaus (that would require 50 MBTU for a house this size), but it doesn’t require a heat-recovery ventilator! We have exhaust-only ventilation using 5 bathroom fans and 2 kitchen fans. Natural air purification also occurs through 70 large houseplants — a method recommended by NASA for air purification (not kidding).
By the way, the kitchen is completely isolated from the main building by a glass door during cooking, so no air contamination spreads throughout the house. (This design detail just might catch on; this type of kitchen isolation was standard in large 19th-century houses.)
All in all, good air, good light, good vibe, good economics. And thank you, Green Building Advisor, for so many good thoughts on building. I have benefited immensely.
A concluding note: Our total energy use from all sources is 35,000 kWh per year. The Passivhaus allowance for a house this size would be 110,000 kWh per year. So we use 70% less energy (total kWh) per year than the Passivhaus allowance. Something to reflect on.
Ajahn Sona was born in Canada. His background as a layperson was in classical guitar performance. He was ordained as a Theravada Buddhist monk at the Bhavana Society in West Virginia. In 1994, he founded the first Birken Forest Monastery near Pemberton, British Columbia. In 2001, Ajahn Sona established Birken in its final location just south of Kamloops, British Columbia. Ajahn Sona posts comments on the GBA web site under the pen name “Ven Sonata.”