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Ask Jeff Yago
Solar & Energy-Related Issues

By Jeffrey Yago, P.E., CEM
Jeff Yago


Alternative energy

Hi Jeff.

My husband and I live pretty far out in the country with 4 kids. We are striving to be self reliant. We have a barn with 2 horses, a 3 feeder calves, chickens, rabbits, 2 goats.... We want to get off of electric power. We utilize a creek for the animals, burn wood, use candles and lanterns alot, do laundry during non-peak hours, and use 40 watt light bulbs, but our electric bill runs $100.00 - $170.00 per month! We have had the electric company come out and check for "leaks" and found none. I just think we're being ripped off.

What type of system would you suggest we look into? We are on a hill in a valley, but get pretty good sun exposure. We get some wind, mostly during storms and winter weather. We have a creek, but it is about 1200 feet away from the house.

Thank you for your time.

Alyce Shane

Alyce:

Sounds like you all are heading in the right direction but I have a few suggestions. First, there is no way a few 40 watt bulbs, using candles and wood heat, and an occasional laundry would run your electric bill up to $170 per month. I do not think you are being ripped off, but it is possible your meter is not calibrated.

First, I would ask to have the meter tested or replaced. Second, I am convinced you do not realize that something is using lots of power. For example, you did not mention a refrigerator or freezer. Any refrigerator or freezer over 6 or 7 years old will be a real energy hog. This can represent one-third of your bill if you do not have other major appliances. New models are much better insulated and I suggest trading up.

Next, you mentioned washing, but you did not indicate a water heater, well pump, or dryer. With 4 kids I bet you wash clothes about every 3 days and running a washer, clothes dryer, well pump to fill washer, and a clothes iron combined is where another one-third of your bill is going. If you want off the grid, I suggest getting a tankless instant propane hot water heater. They are very small, super efficient, and will save you money. They also make water heaters that are wood fired. I also suggest getting a Staber washer. These are great for off grid as they use very little electricty and about half the water of a normal washer so this is also less water heating and water pumping.

Finally, I would not recommend using candles and lanterns for lighting all the time with 4 kids around. I also would not use 40 watt incondescent bulbs. Throw out all your light bulbs and replace with 13 and 20 watt compact fluorescent lamps. These will give you about 75 watts of light for less than half of the electricity your current bulbs are using, not to mention you won't go blind trying to read!

Once you have made all these changes your electric usage should drop to about 300 killowatt-hours per month, or probably half of your current usage. Check your bill each month for the killowatt usage, not the dollar amount which includes all kinds of taxes, fees, and changing rates which is not a good indicator of usage. After you have dropped below 300 killowatt-hours, you are in a better position to meet this smaller load with a solar power system. Check the back issues as I have had lots of articles that tell how to do this.

Good luck,

Jeff Yago


Snow melting

Dear Jeff,

My husband and I recently purchased an off-the-grid cabin in the mountains outside Missoula, Montana. Since we have no well, I'm interested in learning how to build something that will allow us to melt enough snow in the winter for our minimal water needs (drinking water for us and dogs, water for cooking, dishes, washing our faces etc.).

We live at 5200 ft and are blanketed in 2-3 ft of snow from Nov.-Apr. We have a catchment system that uses the gutters on our house to funnel snow melted from the rooftop into a 55 gallon cistern on our porch. This works nicely in the spring and fall when temperatures are above freezing or during periodic warm spells in winter. However, during the coldest parts of winter when no melting occurs, we must haul our water from town.

Our cabin is a 2-story structure with the second story being an open loft-like area. This upstairs remains quite warm due to the rising heat from our wood stove, and thus seems a natural place to implement some sort of snow melting system. Has backwoods home addressed this topic in detail (your online search doesn't suggest so, but I'm not sure how comprehensive it is), and if so, can you provide me with the volume number? If not, can you provide me with some assistance in this arena? Thanks!

Lisa Eidson

Lisa:

There are very limited methods to melt snow to make water without getting into more cost than its worth for your limited requirements. I would strongly suggest a deep well that can use a DC pump and small solar array to power, and keep all piping fairly deep underground from the well into the house. If you are away for an extended period and danger of freezing without the fire, you can add a drain valve at a low point to drain out all above ground water.

If a deep well is not possible at your elevation, you could bury a large surplus tank next to the house and increase your spring summer and fall rainwater collection system. A 4000 gallon tank would be about 6 feet in diameter and 20 feet long. At 50 gallons per day usage, this would last almost 3 winter months. A past article describes how to make a water purification system that will make stored water potable (safe to drink), and uses a solar powered pressure pump down in the bottom of the tank that provides water up into the house.

Any surface water available like a creek or stream? This purification system will also make this water 99.999% clean and free of bacteria if this can be piped into a below ground holding tank. We have had several back issues that address solar powered water pumping systems.

Good luck,

Jeff Yago


Summer cooling

Does the info from [this link which describes how to bury PVC pipe in your yard and move air through it to cool your house in summer] really work. I live in south Alabama. Thanks for any response. Dave Rowland

Dave:

My reply will probably make the people promoting this concept very upset but lets review a few theromdynamic facts. The web site points out how an underground cave is a very cool year round temperature in the low 50's which is true. All you need to do is drill a duct from your house down into the cave and you get all the free cooling you will ever need and the world energy crisis is over! What, no cave under your house, then just bury some pipe from the local hardware store that ends in your basement and free energy for life!

First, if you do have a huge cave under your house and you did pipe a little cool air up to your tiny house then the heat gain from your small cooling load into this huge cave would have little effect on the temperature of the large cave. However, what if you could take the top off the cave and expose it to the outside, it would not stay cool for long on a hot day. In other words, it's the insulation of the ground that keeps the below ground cave cool. Once you start removing the heat from large amounts of hot outside air, it starts to warm up. If you go to back issues of Popular Mechanics Magazines for late 50's and early 60's, you can actually find several articles on these "earth tubes" buried in the back yard that cooled the air as it was drawn into the house from the hot and humid outside air entering the other end of the tubes. In addition, unless these underground tubes are the size of heating ducts with a very short length, you will need far more fan energy than you think. Ever try to [blow] some air through a 50 foot garden hose?

After a few days of constant cooling of hot air by an underground pipe, the earth around the pipe starts to warm up the ground and after a point the surface temperature of the underground pipe aproaches the outside air temperature just like what would happen if you exposed this ground layer to the outside by removing the top covering of earth. In addition, when this was tried in areas with high humidity, very nasty things started to grow on the interior of the moist tubes and mold spores were being blown into the home.

If you can limit the amount of heat being absorbed by the ground by using a "temperature amplifier" or heat pump, you can gain some "free" cooling without raising the ground temperture too high, but this is still a design issue. For example, there have been may successful ground source heat pump systems that have used an outdoor swimming pool, nearby pond, drilled wells, or buried coils of plastic pipe as a way to exchange the hot or cold interior air with these heat "sinks". However, anytime these designs under-sized these exterior heat sinks in relation to the heating or cooling load of the home, they also had problems with increasing the ground temperature around the coils. Another advantage of a ground source heat pump that you do not get with only an earth tube, is the heating up of a large area of underground heat sink during summer cooling mode is partially off-set by the re-cooling of this same ground during the winter when the heat pump switches to heating mode (absorbing heat from the ground or water).

My advice, if you do just happen to live over top of a large cave and your house is small, then go for it - but be sure to have a bat screen over the end of the ducts!!

Jeff Yago

P.S. Yago's first law of thermodynamics - "If someone promises you an un-believable endless source of free energy for life at no cost, keep your hand on your wallet"


Solar power

Jeff:

My daughter is in the U.S. Peace Corps, stationed in a very small village in east Kenya.....no electricity. She is in the process of learning Swahili and will be teaching hard of hearing children Sign Language in Swahili. I want to make living a little easier by sending a solar system to charge her AAA, AA and D Nickle-Cadmium batteries and her I-Pod (the I-Pod internal battery is 0.4 volts). I would appreciate your advice on what I will need to make an uncomplicated solar system to charge the above batteries. Naturally, weight is also a factor.

I look forward to your reply. Many thanks.

D. Donald Smith

Don:

Your daughter should be comended for doing this needed work. One of the back issues has an article I wrote titled "Keep those Gadgets Working During the Next Power Outage" which addresses what you are asking. You may want to order that back issue. I have attached a photo from this article that shows a 5 watt solar module you can buy from Radio Shack and several adapters that allow using this module to charge all kinds of gadgets. Several modules this size are available that are bonded to a stainless steel plate and are very rugged. A module this size will measure about 5" wide by 12" long. They also now have a small battery charger that charges seveal AA and AAA size batteries at the same time and the cover is a solar module, but I think you will find this too small for her needs. You need at least a 5 to 10 watt module, and it will take a 10 watt module or larger to power a small laptop computer.

Good Luck,

Jeff Yago


Solar collectors

I have two commercially manufactured solar collectors that measure 1x8x12 ft. These are air collectors not liquid. I have southern exposure to the south and east without any obstructions. I want to mount these collectors to be free standing units, unattached from a stucture and wish to move my collected (heated ) air to my home.

What would my options be and which is/are my most logical,energy effient method of doing this. I have chosen to stay away from the liquid system as I live in Michigans Upper Peninsula and we have too much freezing temps to contend with. This morning it was -14 degrees and its not yet Christmas.

Thanks for you efforts and Merry Christmas.

John

John:

I am not sure you will like my answer but here goes. I was involved in a project in the early 1980's to heat a large commercial office building with free standing solar air collectors on the roof. This rack mounted array on a flat roof was unlike most residential installations that have their air collectors mounted directly to the roof surface to reduce heat loss with their rear air ducts going directly into the attic space.

This commercial project required multiple short runs of exposed ductwork connecting the individual rows of solar air collectors down through roof penetrations. This project suffered endless problems for years with air leaks, rainwater leaking into the roof penetrations, and problems with duct insulation failures. It also required large energy using fans.

Although better mastics are now available, air systems suffer two major dis-advantages over a water loop solar heating system that you cannot get around. Air is a much poorer "conveyor" of heat than water, so you need to move a larger amount than a water system to transfer the same number of BTU's. Instead of using a small copper or PVC pipe in a water system, you are dealing with much larger air ducts, which have a larger surface area, have more heat loss, are harder to insulate, and are harder to seal at any wall or roof penetrations. Another often over-looked area is transport efficency. It takes much more horsepower to move the same amount of "heat" when the media is air instead of water. A typical solar hot water system may only require operating a 1/20 HP circulating pump, while a solar air collector system may require a 1/3 HP or larger fan to move much more air through a long duct run.

Bottom line - you will want the minimum length of exposed duct run from your solar air collectors into the area being heated, and that most likely means directly on a south facing roof with back mounted air ducts entering directly into the attic space. Also make sure your system has a back-draft or automatic damper, as you will get reverse air flow at night even with the fan turned off due to black-body radiation at night.

Jeff Yago


Tower for solar panels

Jeff,

My house is too shaded for solar panels. I would like to build a tower to put 9 panels about 30 feet high. Any suggestions on construction?

Grace Ury

Grace,

Forget the tower! I just returned from a porject in Florida and while there observed a solar powered street light in a strong afternoon wind gust. This street light had 2 solar modules mounted on the 30 foot high pole which was 12" diameter heavy steel bolted to a large concrete base. This was supporting only 2 solar modules and I thought it was going to bend the pole in half! The solar modules were also twisting side to side over 45 degrees and swaying several feet in each direction. Now imagine what it would be like with the same pole supporting your 9 solar modules.

If you cannot find a ground or roof level place to install a solar array that is un-shaded, you can achieve almost the same reductions in your monthly electric bills by replacing all light bulbs with compact fluorescent lamps, installing a clock thermostat, and replacing an older refrigerator, freezer, or air conditioner with new high efficency models. I know this is not as exciting as a solar system, but you will not believe how much it can save you, and at one-tenth the cost of the solar system you were considering!

Jeff Yago


Whole house power

Hi Jeff,

Could I power everything in a conventional house (including computer and printer, stove and oven, refrigerator and freezer, washer/dryer, and hot water heater) using a diesel generator, battery bank, and solar array? l'll be moving into a house that's off the grid and would like to avoid using propane if possible. (In my on-grid house, I currently use 130-160 Kwh per month to power all those things except the water heater, which is gas, plus an aquarium.) Thanks for your advice.

Ingrid

Ingrid:

Yes, you can power anything from a solar/generator system. The question is - are you willing to spend a large sum of money doing it? A diesel generator is an excellent power source for an off grid home, except most off grid applications have a propane stove and propane heater to supplement a wood stove and that means you now have to deal with two fuel tanks and keep both serviced. However, most diesel generators are much heavier constructed than a standard propane/gas generator and operate at a lower RPM which greatly extends life. Even with a diesel generator you will probably still want to have a propane fueled kitchen stove and hot water heater.

Although possible, I do not recommend trying to power a standard electric stove/oven, electric hot water heater, electric space heaters, or air conditioning system from a generator due to the large size required, and absolutely not from a solar electric system. The size of the solar array to supply this much power and its installed cost would probably exceed the cost of the home you are planning to build. You may also want to check your figures as your 130 kWh per month figure sounds low for all the electric loads you listed. An electric bill for that low of usage would run about $9.00 per month at the current rates for my area.

Jeff Yago


Cabin power

Hi Jeff!

I am new to all of this "off-the-grid" stuff, but I have finally managed to amass enough money to build my summer home in Montana. I would like to build the whole thing myself and let nature supply all my power and water. It's going to be small (about 500 sq. ft.) and the only one's there will be me and my two dogs from June until August. The rest of the year it will be vacant (the roads are impassable in winter). I don't need anything fancy, just enough power to run a small fridge, a hot plate, a light, and a radio.

Running hot and cold water is a definite plus. Can you recommend a good book to lead the way? Perhaps there is a group there that I could contact for leads...? I am so overwhelmed with information on the internet that my head is spinning!

Thanks in advance,

Brecken

Brecken:

As you have found out, sometimes the internet provides so much information you know less than when you started! My book, Achieving Energy Independence is a good place to start as it was written for people just getting into solar and needing some basic system selection guidence.

Although expensive, a small Front Load SunFrost or top load SunDanzer 12 or 24 volt D.C. refrigerator or freezer would give you all the refrigeration you need and either requires less than two 75 watt solar modules to power. If you install 12 volt DC compact fluorescent lights and a DC radio, you would not need an expensive AC inverter, which would greatly reduce your electrical standby losses and costs. You probably could get by with four 6 volt golf cart batteries and four to six 75 watt solar modules for the loads you have listed, and could add an inverter, TV, and micro-wave oven later by adding more solar modules. My book has several examples and wiring diagrams for systems this size.

SInce there is danger of freezing when you are not home and I assume you will use a wood stove to heat, there are several small instant hot water heaters available that do not require a storage tank and are propane powered. There are also optional hot water coils that fit into wood stoves that can provide all the hot water you need, but would require building a fire in the summer. They make several good 12 and 24 volt DC deep well pumps that require very little power to operate.

If your water is available from a surface spring and not a deep well, you might be able to use a 12 volt DC pressure pump sold for RV's which would provide pressurized water without the need for a pressure tank and pump pressure controls. Make sure all plumbing slopes down to a low point valve that allows easy system draining each time you leave to prevent freezing standing water in your piping system.

For lighting I suggest stopping a boating or RV parts center as they have all kinds of low voltage lighting and appliances that operate from a battery.

Gook luck and send some photos when finished. You should also check BHM's back issues which include several articles on small off grid solar power systems like you are planning.

Jeff Yago


Battery bank location

Jeff:

Can I keep the battery bank farther away from the generator rather than closer? (70 feet) Or should I keep them closer and run heavy guage wire from the generator to the inverter. (70 feet) Whew I hope you can follow that.

Chris

Chris:

I assume your generator is AC and you are charging your batteries with either an AC powered battery charger or the charging output from an inverter. With that said, your largest cables will be between the batteries and the DC to AC inverter, as this will be low voltage DC, which can have as much as 175 amp draw at 24 volts for a typical 4 kW inverter, which would require #4/0 size cable. ( 4000/24 = 167 )

The output from a typical 6 to 8 kW sized 120/240 volt AC generator will be in the 50 amp range, which is usually #6 or larger wire. ( 6000/120 = 50 )

You will almost never want to have the battery to inverter (largest load) cable to be longer than 10 to 15 feet due to the very high voltage drop at high current draw. However, the #6 wire to the generator is still fairly small and low cost, and could easily be increased to a larger wire size to allow much longer distance between the generator and the AC load distribution panel, without a high voltage drop. 70 feet is not excessive for a 120/240 volt AC line to reach the generator.

Voltage drop and amp draw determine the wire size and distance between electrical components in any circuit. Keep your batteries near the inverter and battery charger.

Jeff


System design

Hello Jeff,

I hope you don't mind me writing directly for help on designing a system for my new off the grid home. I have not installed a system before and want to make sure I am sizing it correctly. I am building a 3500 square foot home (I know, size doesn't matter if your only using one light bulb) and plan on running the major appliances on (water heater, oven clothes dryer, space heaters) propane and purchasing a Sun Frost R19 refrigerator.

The system that was recommended to me, to supply a weeks worth of power, is 16 Trojan L16HC batteries tied into Outback Pp Vfx3648/D W/Com Pak & 240vac . I am planning on wiring 2 banks of the Trojans into the Inverters using your diagram below. The power consumption for the week should only be lighting, refrigerator and possibly a microwave at night. I am using an ultra-violet system to purify the water system. The washer and dryer will be run off the generator most of the time but can I run them off this system? The oven would be propane and the heating system is propane heaters complimented by fireplaces in the great room and master bedroom.

My well in a 240 volt, 1.5hp motor that I only plan on running with the generator to refill the 1700 gallon water tank. I want to configure the system to kick the generator off when the batteries are too low automatically. Is there a generator you recommend? I want to be able to switch the power to my house from generator, batteries or both should the need arise.

The house is a 3 bedroom and 2 ceiling fans in the great room. Taking all this in mind the lights and ceiling fans would be the primary drain on the system. My kids may have their computers plugged in too.

As I read the home magazine there are numerous configuration settings for the inverter whether they be Master/Slave or parallel I also read about refrigerator compressors burning out. Should I go with the SunFrost or purchase a different unit? I am also concerned to make sure the wiring is correct when supplying power to the house. My intention is to have the generator, batteries and inverters in my pole barn. A separate room for the generator, the batteries and inverters in their own room. The inverters would be plugged into a main breaker which is wired to the AC main panel in the house some 60 feet away. I do have a portable generator I use as a backup which has a surge capacity of 13000kw. Normally 7500kw.

I looked for a wiring diagram for the 3648 Outback pak and batteries but did not see a configuration for a 48v system. Is there something you can recommend? I wanna make sure I fuse the batteries correctly. Is there someone I can hire to diagram the configuration to ensure I set it up correctly?

Thank you for your attention,

Don Clifford

Dear Don:

Its not possible to provide a detailed review of your plans or wiring diagram over the internet, but I will be glad to provide some general tips that I noticed after a quick review.

1. Your system appears to be designed for 48 volt D.C. operation, but you have selected a SunFrost refrigerator. Unless they have recently changed their product line, I think SunFrost units are only made in 12 and 24 volt models.

2. I am not sure what you mean by wiring two battery banks and suggest you refer to the Outback Inverter installation recommendations. If each inverter is wired to a separate battery bank, you will get un-balanced dis-charge as one inverter will usually have a different loading.

3. I like Kohler low speed propane gererators, but I think they have stopped making these in the small Kw ratings. The 3600 RPM generators you see at builder supply and warehouse outlets are intended to only operate a few hours or days each year during an occasional power outage. Also, lower cost generators have power control circuits that adjust the peak to peak 169 volts(120 volt arerage) down as the generator is loaded up. This will not affect the operation of lights and small appliances, but all battery chargers require the full peak to peak part of the sinewave or they will produce very little charging. Check out the lower speed 1800 RPM propane generators and make sure they will produce full output. Most generators in this 8 to 12 kW range that are designed for weekly operation will cost in the $5000 range.

4. The inverters MUST be located no more than 10 to 15 feet from the batteries, not in a separate building. These inverters can draw almost 200 amps of current and that is the same as a welder output. Long cables at low voltage will have a very high voltage drop at this amp draw and will reduce the performance of the inverters.

Hope this helps,

Jeff Yago



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