Solar Utility

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Bill Layman

©1998 Bill Layman

Northern Saskatchewan is a rugged landscape of rock and trees located in the Precambrian Shield of Canada. It is scattered with clear, cold, deep lakes that are filled with trout, pike, and walleye, and people are few and far between. A lease on one of these lakes can easily find you thirty miles away from your nearest neighbor with moose and wolves as your only visitors. Winters are long, with the mercury dropping to -40° C (-40° F) on many days. "Freeze up" of the lakes comes early in November and "break up" not until the end of May. My partner, Lynda Holland, and I had long wanted a remote seasonal home on one of these lakes.

And Then We Found Our Own Place in the Woods

When we acquired our lease on Bob Lake in northern Saskatchewan ten years ago, my knowledge of electricity was limited to a vague remembrance of something in high school about volts x amps = watts. Our lease is located thirty miles from the nearest grid power and is accessible only by chartered airplane (floats in the summer and skis in the winter).

When it comes to power, the prevailing mindset of others with leases up here was an old adage I often heard repeated: "If it ain't diesel, it ain't jack squat." In plain English: a diesel power plant was the only way to go. But we just couldn't see ourselves sitting in our home watching the northern lights and listening to music on the radio with the racket of a generator in the background! Besides, it seemed a crime to be using total daily loads of less than 700 watt-hours on a power plant which could easily service an urban home or two. When asked what to do if (or when) the power plant should break down, the answer was simple—you have a standby unit ready to go at all times. No kidding!

The other downside of a remote power plant up here is the cost of flying the fuel to the site. Flying 100 gallons of fuel thirty miles from the nearest community (La Ronge) costs about $200. Amazingly enough, multiple diesel power plants are still the most common power source for tourist camps throughout the North. We wanted to consider renewable energy sources for our electrical power. Not located near any flowing water and with limited wind, we knew solar would be the logical choice. Needless to say, there weren't a lot of people in the area to turn to for design help. In fact, most looked at me like I was an idiot when I said I was considering a solar power system.

Now, Where to Start?

Not knowing what else to do, I started to acquire catalogues, design guides, and library books. In fact, anything that had the word "solar" in it ended up scattered around our house in La Ronge. Months of reading later, with my head filled to overflowing, I started to design our system. Of most help to me were the catalogues of Soltek, Solar Energy Ltd., Northern Alternate Power Systems, Sunelco, and Real Goods Trading Co. These catalogues have a wealth of basic renewable energy information and numerous design configuration schematics. They are well worth the price and a good starting point for anyone designing a renewable energy system. I have spoken or written to each of these companies and found them to be more than willing to answer my questions. Also of great assistance was Ron LaPlace of Photron Canada (now Sun Direct Energy, Inc.). Somehow, I missed Home Power magazine and only discovered it when my system was complete!

Below: The power center/pantry.

Above: The power shed with nine Kyocera J43 panels.

Lately, more and more people are looking at solar as a viable option for remote homes in northern Saskatchewan. In fact, a new RE dealer/installer, Sask Solar Systems, recently opened in La Ronge. I guess there is light at the end of the solar tunnel!

Design Considerations for a Frozen North

I soon learned that stand-alone photovoltaic systems at a 55° latitude are not cost effective. An average 45 watt solar panel produces only about 80 watt-hours on a good day in the dead of winter up here. PV systems with a backup generator and charger are the more cost effective choice.

Our location also has another unique weather factor that makes such "photo-genset" combinations the best all around choice. During the freeze up of the hundreds of lakes up here, a tremendous amount of moisture is put into the atmosphere. This moisture means low overcast skies for about six weeks from early October until about mid-November. As I write this article at Bob Lake, we have had only three days of partial sun in the last three weeks!

Batteries

At a temperature of -20° C (-4° F), battery capacity drops to less than 50%. With winter lows hovering at -40° C (-40° F) on many days, our battery needed to be located inside our home if we were to get any reasonable amount of power out of it. Locating the

Above: The author with power!

battery in the house presented a problem. Regular charging of flooded lead acid batteries can produce small amounts of very explosive hydrogen gas. The necessary periodic equalization charging of these batteries produces large amounts of gassing. We were not keen on having hydrogen gas in our home. This concern was later addressed by our choice of an absorbed glass mat battery. This battery does not need periodic equalization charging and is very unlikely to vent hydrogen gas under normal charging conditions.

Our home at Bob Lake is unmaintained for weeks at a time, so any battery we picked had to be able to tolerate a very irregular maintenance schedule. Conventional flooded lead acid batteries would not be suitable. Four to five days of stand-alone battery capacity needed to be designed into our system. Why not just start up the power plant every other day to recharge the battery in a northern system? Because it is a real pain in the "you know what" to heat the power plant shed from -40° C (-40° F) for a minimum of three hours before you can even pull the starter cord! In the end, we chose GNB's Absolyte battery—more about that later.

Inverters

We had always planned to build a small guest cabin where we could house friends and "eco-tourists." The site for this cabin was about 300 feet from our main home. Adding an inverter to our system would allow the use of 117 volt power tools for construction of this cabin. The maximum load that this second cabin would use when completed was anticipated to be about 250 watt-hours per day. Transmitting low voltage DC power to the cabin was far too expensive a proposition—4/0 wire at $7.50 per foot would have been required! At 117 volts, however, the current could easily be transmitted through the supply of 10 gauge 3 conductor Teck wire I had on hand. Given the need for a battery charger in our system, it soon became obvious that an inverter with a built in transfer switch and charger was the best way to go.

Power Plant

The Canadian division of GNB Batteries, Inc. recommends a maximum C/5 charge rate for their batteries. Trace recommends a rate of C/5 for non-sealed batteries and as high as C/3 for sealed batteries. Northern Alternate Power Systems recommends a maximum charge rate of C/10. We decided to split the difference and use a C/7 rate. Our GNB Absolyte battery has a 20 hour 630 amp-hour capacity. This results in an acceptable maximum charge rate of 90 amps (630 divided by 7 equals 90 amps).

Transformer based battery chargers, which are found in inverter/charger combinations, need 164 peak volts to operate at full capacity. So the 120 amp charger in the Trace SB2012 inverter we chose dictated the size of power plant we needed. Power plants which can put out about 6,000 watts will generally deliver the necessary 164 peak volts. Since we only needed a maximum 90 amp charge rate, a somewhat smaller power plant would work for us. The used 5,000 watt gas fueled Yamaha unit we found easily handles a 90 amp charge rate.

Charge Controllers

As ambient temperature drops, a battery requires a higher charge voltage to allow for full recharging. Typically, this increase in required charge voltage is 3 millivolts (0.003 volt) per cell per degree Fahrenheit drop from 77° F (25° C). Wow! Our battery was to be left at lows of -40° F (-40° C), a drop of 117° F! To recharge our battery properly, we needed to increase our charge voltage by 117 times 0.003 equals 0.0351 volts per cell (2.106 volts for a nominal 12 volt battery). Obviously any charge controller for a northern system should be temperature compensated.

The high rates of charge required at low temperatures often take a battery beyond gassing voltage. To deal with this potential problem, we split our solar array into a six panel and a three panel subarray. We often leave our home unheated for an extended period of time when ambient temperatures are low. Before leaving, we make sure that our battery is fully charged with the

Table 1: Daily Energy Use (Main Cabin Only)

generator and charger while the battery is still warm. We then turn off the six panel subarray and leave the three panel subarray on. Even at the elevated temperature compensation charging rates, it is incapable of getting the battery charge above 15 volts, so there is no significant gassing.

Battery Energy Use

Our primary electrical energy uses are lighting, two computers, radio, radio telephone, TV and VCR, and a water pressure system. Used less often are a myriad of household gadgets—microwave, toaster, waffle iron, soldering iron, and vacuum cleaner. I also have a variety of 117 volt construction power tools—miter saw, jig saw, table saw, belt sander, circular saw, drill, etc. These tools were used to build our guest cabin, a power plant shed, and a utility shed, all powered by the sun!

Our electrical usage varies from season to season. Summer daylight hours are long and we rarely need to use any lighting. We also find little interest in inside activities when the fish are biting! However, in the fall and winter, we spend a lot more time inside. This time of year, our energy use skyrockets—just when we have the worst chance of generating any solar power! The best advice for anyone designing for northern Canada is to prepare for the worst case season. The figures in Table 1 detail our average fall and winter daily energy use, for our main cabin.

Table 1: Daily Energy Use (Main Cabin Only)

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