An Off-Grid Education: Page 2 of 3

Intermediate

Inside this Article

The Bowkers' garden and home.
Using local materials can reduce a home’s embodied energy. Wood flooring was locally sourced, and even the plywood for sheathing and subflooring came from mills only a couple of hours away.
The wood heater is fueled only until late morning, when the sun-tempered house then starts gaining heat from the winter sun through the southern windows.
A Danby refrigerator (no freezer) joins a host of energy-efficient appliances.
Though traditional country style, the home’s design takes advantage of some passive solar heating.
The PV array grew incrementally. Here, Jerry gardens beneath the pole mount prior to the most recent addition of modules.
A propane wall heater provides backup heating when solar gain is minimal and the wood heater is not in operation.
A SunDanzer DC freezer in the utility room provides efficient food storage.
A Whirlpool Duet horizontal-axis washer and propane-fired dryer make efficient work of laundry with less load on the batteries.
A Bosch propane on-demand water heater serves the home.
The OutBack VFX3524 inverter and balance-of-system components.
The eight Deka L-16s provide 740 Ah at 24 VDC.
System designer Kurt Nelson (left) with Sally and Jerry under the array.

System Evolution

Although only a mile from the closest utility line, it would have cost about $12,000 to bring in utility electricity that is largely (60%) coal-fueled. Both Jerry and Sally felt using solar electricity was far more environmentally responsible, but neither of them was really interested in the technical aspects of designing or installing a system. In 2007, Kurt designed a 440 W PV system—four 110 W modules and four 370 Ah flooded batteries—to provide energy for constructing the studio. A 10- by 10-foot gambrel-roof utility shed housed the balance-of-system equipment and batteries, with the PV modules mounted on the lower portion of its roof. This small system provided their first practical experience of using solar electricity and, along with a generator, some of the electricity needed for the home’s construction.

In 2009, when construction of the house began, a pole-mounted array was installed, with six new 110 W modules added to the original four. The battery bank grew to eight 370 Ah L-16s. In 2014, two 310 W modules were added (and two 110 W modules removed, see “Adding PV” sidebar). Most recently in 2016, two more 310 W PV modules were added—the winters are increasingly cloudy and generator use had been growing. This brought the total array capacity to 2.12 kW.

Located near the south shore of Lake Superior, the late fall and early winter months are often cloudy and windy. A nearby off-grid household is both solar- and wind-powered—the two renewable energy sources mesh well, providing consistent energy. However, the Bowkers had already invested as much money as they felt they could on an electrical system.

The array was sited in a south-sloping meadow that is also Jerry’s garden. There was discussion about how many of the surrounding trees needed to be thinned, especially some spruce and firs at the southern end of the meadow. However, Jerry and Sally refused to cut them, though they knew that keeping them would affect the array’s production to some extent. Trees are very important to the couple, and marginally reduced array output is a trade-off they are comfortable with.

The studio has its own electrical distribution panel, and the utility room in the house has another electric panel, plus the inverter, and other PV balance-of-system components, where the system metering can be easily viewed. The batteries are located in the insulated crawl space under the house, where they are buffered from temperature extremes. The batteries are vented to the outdoors via a schedule 40 PVC with a Zephyr power vent driven and controlled by the OutBack MX-60 charge controller. Wheeled stools make it easy to get around that space and check on battery water, connections, and cleanliness. The generator is located in a woodshed, about 50 feet from the house, which keeps the noise at a distance, but line losses from the wire run acceptable.

Comments (6)

Bill Loesch_2's picture

Sally & Jerry,
Congrats on the successful adaptation of your RE system to your lifestyle (and vise versa). Would you care to share your philosophy with the microwave and using a separate freezer and fridge? Thanks, Bill

RMichael Curran's picture

Very nice house and RE system.

I'm wondering how their MX60 charge controller is holding up, what with 2100 watts of PV for a 24V battery system. Normally (I thought, anyway) for a 24V system the MX60 can't use more than about 1500 watts of PV (24V x 60A = 1440W). I'm asking because I have an MX60 and am currently considering adding PV but was going to go the added CC route, since I'm already near my MX60's max power input for my 24V system.

Thanks, great article.

Fred Golden's picture

If I where to upgrade my solar today, I would not spend $500 on a MPPT controller. The 40 amp Schneider controller at SunElec.com (a long time advertiser here) is only about $125. 250-300 watt panels can be bought for less than $200 now. So I would spend more on panels, not the controller. Another slightly risky thought would be to have two panels with just a on-off switch. 10 extra amps going into the battery anytime the sun shines. It might slightly overcharge your battery if you don't have afternoon loads, the main controller has shut off. But if the battery is not getting full every day, or you have a constant 5 amp average load, you will not have a problem, (with late afternoon overcharging) as long as you shut off the extra panel in summer or while on vacation.

Yes I have a SB 50 MPPT controller in my motorhome 415 watt solar system. That system cost $3000 in the 90's, and could be replaced for about $800 today.

Todd Cory_2's picture
Todd Cory_2 (not verified)

the (now discontinued) mx60 can be set for 70 amps, which means it will process around 72 amps before "de-optimizing" the mppt tracking at this limit. 72 amps X 52 volts = 3.7 kW. mine has processed this amount of power for over 10 years with no problems (on a 24 volt system, this would be 72 X 26 = 1.8 kW).

RMichael Curran's picture

Not to beat a dead horse but the system in the article is 24volts with 2100 watts of PV. Although the MX60 WILL run up to 70A output, seems like frequent operation at the MX60's max rating would shorten its life. Thus my original question.

I guess perhaps the short answer is, if there had been any problems this article would have read differently.

Todd Cory_2's picture
Todd Cory_2 (not verified)

the mx60 will off track the mppt to protect itself. in addition it will shut down if "too hot" (fan failure). outback would not have designed a charge controller designed to fail when operated within the allowable software parameters. these things are very robust!

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