Alternative energy advice from Ask Jeff Yago. Volume #3

Ask Jeff Yago
Solar & Energy-Related Issues

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

Sorry. Jeff no longer answers questions online

Two part question


1) I have a large footprint house. The foundation size is 2000 sqr. ft.

Also I have something that few people do not, a rubber roof – pitch black.

In the early spring, even while the outside temperature is only 40-50 degrees, my roof gets hot enough to burn skin on. Is there someway to harness the power of the sun via heating water to convert to electrical power? Can heat be extracted from the water to generate electricity?

2) I have a stream that runs about 1500ft from my house. Something usually runs through it during 3 out of 4 seasons. I’d like to tap into it for power. I estimate that it flows as little as a gallon second on the low size and as much as 25 gallons a second on fuller times. It probably has a drop of about 15ft every 100 feet run. I’d like to harness the power of this stream. Any ideas? What kind of power can I expect?

Thank you for any ideas you may have!



First, you do not say where you live so I do not know if you have cold or mild winters. Having a black roof get hot in the sun is good if it is in the dead of a cold winter, but not that good if it is the summer! First, although it is technically possible, it is not practicle to use luke warm water to generate electricity. You can, however, use the hot water to provide space heating or domestic hot water heating. You might search the net for some mid-70’s articles on Harry Thomason, as this will give you some ideas.

He was a D.C. patent attorney who had a roof like yours and he installed corrigated metal roofing on his steep south facing roof, added a homemade wooden frame to support a layer of glass just above the corrigated metal, then used a header pipe at the top to distribute a water flow down the painted black corrigated metal. A drain trough at the bottom collected the heated water and he piped this under the house to a tank surrounded by rocks in an insulated box.

He then passed forced air across the rocks to heat the air, or sometimes directly heated the floor slab with the heated water. He was trying to charge so much a square foot for anyone who used his idea, but since everything was do-it-yourself and site built (not a kit or pre-manufactured) I do not think he collected much, if any money. He was however, one of the first to do this and he got lots of publicity during that time period.

As for the water power, most of the hydro projects I have been involved with had either much more water flow, or more fall. If you own enough property that you could run a pipe up the stream bed for 200 or more feet, the resulting 30 foot head would work, but you will need more than a few gallons of flow. It sounds like the flow is low and the periods there is no water flow is also a problem.

Gook Luck!

Jeff Yago

Battery bank storage

I made a battery bank storage container out of a non-working chest freezer which are not hard to find. They are sealed, insulated, and most have a drain plug for easy cleaning. You do have to install proper venting.



This is a good idea if you live in a very cold climate, but several items need to be resolved. Yes, the drain plug is a must for cleaning, but any acid environment can really corrode aluminum. Some codes do not allow aluminum or steel conduit in a battery room, so most battery room conduit is PVC.

If the interior of the freezer has exposed aluminum, you may want to paint with a coating that will not burn and will take acid spills.

I would definitely remove any lock or latch, as a freezer will be “air tight”. I would not want to risk a small hydrogen explosion sealed inside creating shrapnel out of the freezer walls! Yes, you will need a PVC vent pipe to the outside (These outside vents have been known to seal up from freezing rain which is why I would remove the latch). I would make it a minimum of 2″ size, and it needs to be located near the top of the freezer (hydrogen gas will rise). Be sure this pipe slopes UP to the outside, and terminate with a lid that keeps the rain out and screen to keep out insects.

Many years ago I helped design explosion proof electrical equipment. We placed the air tight metal electrical boxes inside a large metal room that was filled with natural gas to test for proper design. Gas and dust were remotely injected into the electrical box and caused to explode. If any fire escaped from the box, it caused the gas filling the large room to also explode. A large hole in the roof of this room was sealed with a large paper seal. The paper kept the gas inside but allowed the explosion to easily blow through the paper seal and no harm was done to the room(except for the ear shattering boom!)

A final note to anybody making their own battery box out of anything. I prefer putting a large battery bank in their own battery room having a concrete floor, drywall or masonry walls and ceiling construction, and vapor proof lights, light switch, and vent fan. I have one PVC pipe from the outside ending at floor level where fresh make up air can enter the room. I place a small (pancake) exhaust fan and outside louver near the ceiling. Batteries generate the most hydrogen as they near their final full charge level. I control this fan based on high battery voltage, as it does not need to operate when the batteries are providing power or during initial charging.

I have built or used many different types of battery “boxes” and found that placing lead acid batteries in a small and tight enclosure greatly increases problems with battery terminal corrosion and acid mist covering all interior surfaces. I rarely need to clean batteries located in a larger battery room.

Jeff Yago

Wet cell

How does a wet cell battery store electricity?

Ted Rodrgiuez, Jr.


To answer you in more detail than just saying “its magic” requires discussing the chemical balance equation for the process and reviewing the various types of wet cells. Since this is more than can be addressed by email, I am putting together an article for a future issue that will explain everything you wanted to know about batteries, and maybe more than you wanted to know!

If you cannot wait, check out the back issues of the magazine which include several articles that address battery charging and battery safety.

Jeff Yago

Will this combo work ok?

A 12 volt 7amp hr sealed wet cell lead acid battery to be charged 14.1v with an eleven watt solar module operating a RAB (stealth-power consumption 1 watt) motion detector which will turn on a 12 v relay to switch on 120 v to garage door opener two times daily in East Central Illinois.

James Greuel


I have only one question – Why would you want to do this?

The fact that you are wanting the solar system to power the controls that in turn operate a 120 volt AC garage door opener means that there is 120 volt AC available. Since this garage door opener cannot operate when there is a power outage, I see no reason to power the controls by a solar charged battery system when the power is out and the motorized door will not open.

I also question why you would want any large animal or stranger passing by to be able to open your garage door by just walking past the motion sensor.

If you already have the solar panel and battery, why not use it to power something more useful, like a 12 volt DC fluorescent light on a remote shed that is too far to run a power line?

Jeff Yago

Hydronic heating cost vs forced air

Hi Jeff,

I live in Washington state. I was trying to find out operating cost of radiant floor heat vs forced air using propane or natual gas as a source of fuel.

I am also wondering when using hydronic heat is it better in your opinion to use one heat scource or two, as in a boiler and hot water tank or just a boiler and share domestic water with floor water.

The third question would be should I circulate anti-freeze in the floor heat system so it can be turned off in winter for snow birds.

I appreciate any input

Thanks Jon


Regardless of fuel source (propane or natural gas), a radiant floor heating system will use far less energy than a forced air system. I have projects with an hour run time meter on the client’s air handling unit and it operates about 40 to 50% of the time during the winter, depending on location. Most central air handling unit fans are 1/3 HP, but some are 1/2 HP. This is a 300 to 450 watt load operating half of the winter hours. Most small under slab heating systems use only a 1/20 HP pump as a circulator, with 1/12 HP (45 to 75 watt load) for the largest mult-zone homes. Also, since the slab acts as a heat sink, the pump cycles off for longer periods.

I would not recommend connecting the domestic hot water in with the radiant floor heating system, although it can be done with a buffer tank, heat exchanger, and added controls. The problem is your domestic hot water is potable (you can drink it!), and the water in most radiant floor systems is re-circulated and may include additives to reduce sediment. Fresh hot water also includes dissolved oxygen, which comes out of the water during heating and can cause pump cavitation (no flow). This is why hydronic heating systems have lots of air vents at the high points. Also, most radiant heating systems require 140 to 180 degree loop temperature, while this would be too hot for showers and sinks (and against code due to scalding danger.)

Some hydronic systems can have additives to reduce chance of freezing, but this is based on piping material and piping manufacturer’s recommendations. Bottom line – Use an instant on propane tankless hot water heater for your domestic hot water, and a small high efficency hot water boiler for the heating loop. This also allows turning off the heating system for the summer months, while allowing the domestic water heater to stay on. If you are off grid, don’t forget to make sure there are no motorized zone valves or boiler controls that use lots of standby electricity. Some brands of boilers and zone valves have a constant 24 hour/day electric load to hold their setpoints or valve positions.

Hope this helps,

Jeff Yago

Solar home insurance


I’m having a very difficult time finding homeowners insurance for my off-grid property. At the moment I’m looking for a “builders risk policy” since I’m still in construction, but eventually I’ll want a full-blown homeowners policy for the building as well as standard liability on the property. Any inputs or suggestions would be greatly appreciated.

My current company, American Family, won’t touch “off-grid” with a 10 pole.

State Farm gave me a quote a few months ago, but upon asking for an updated quote recently, they completely denied the possibility.

Farmer’s Insurance gave me a quote so high it was probably illegal -AND- they required a “qualifying vehicle” to be insured as well (at a rate at least double my current policy).

The first place I thought might have an answer was Backwoods Home. Would you happen to know if others are having trouble getting homeowners insurance due to living off-grid? Would you also happen to know of any insurance companies willing to cover a home that is off-grid?

Thank you very much for any and all information you can provide. I will be checking with numerous insurance companies, but would value your advice as well.



Home insurance has been a problem for some off grid homeowners due to several wrong ideas about what “off grid” actually means, so be careful how you discuss it. Many “old-school” insurance carriers have had very bad past experience with some early homeowners trying to obtain fire insurance on “wood shack” construction, miles up some impassable dirt road, with exposed un-vented batteries in the living space, a generator with several large leaking fuel drums nearby, and an exposed mix of bare DC and AC wiring that would never meet even a basic electric code inspection. This is what they are thinking about as soon as you say “off grid”.

In addition, insurance carriers know that many off grid homes are being built in a very remote wooded area that is far from any fire department, and served only by a small well pump that could not be used to fight a fire. Many banks also would not provide construction loans for these off grid homes in the past for the same reasons.

Most of the off grid builders today are building extremely well designed and constructed homes that meet all building codes and are inspected. If you are building in a state or county that has not gone through this process with anybody before you, you may have a problem with getting insurance and a loan. However, today there are banks actually advertising that they provide solar related loans, once they have had some experience, and more solar homes are being built in their areas. The same is true for the insurance firms.

I suggest that you show the inspection and permit forms indicating the construction and wiring meets current code as you shop for your insurance. Photos are also helpful.

I had one of the first electric vehicles in Virginia over 20 year ago. You should hear the trouble I had getting a license plate and insurance. It also failed a state safety inspection because “it did not have a working muffler!!” Remember, it takes much longer and is much harder to do anything if you are the first, and that is especially true when dealing with banks and insurance companies!

Hang in there and shop around, and don’t make a big deal about the off grid power. You will find a carrier if you keep trying.

Jeff Yago

Alternate power for refrigerator

I live in Boynton Beach, Florida and I’m currently engaged in building a battery back-up system for the upcoming hurricane season. I wish to power a GE side by side frost proof refrigerator on an intermittent basis for a period of 5 days or about 144 hours.

The sticker on the refrigerator reads as follows: 11.2 amps at 120 volts. What I don’t know is if this is the constant draw or peak power consumed during a start-up and/or defrost cycle. What I can’t find out for sure is the average power consumed which I think is substantially less. This fact will make all the difference in the actual run time for the batteries.

The battery pack is as follows:

There will be (4) 6 volt Trojan batteries each rated at(20Hr.AH) 225 amp/hrs. There will be 2 wired in series to make 12 volts and the other two wired in series for another 12 volts. The two pairs are them paralleled to give 12 volts.

The Refrigerator:

My calculations: 120v x 11.2amps =’s 1344watts

If the inverter is 90% efficient it will draw from the batteries 10/9 or 1493 watts. At 12 volts, using your formula, this is 124 amps. (225+225)/124 =’s is about 3.6 hours! If this is the truth, it’s time to buy a generator. I may be all wrong on these assumptions what I need is some expert advice to clarify the situation.

At any rate, I certainly appreciate your help and thank you for your response.



Calculating refrigerator energy consumption is always a major “guess” for the solar installer since there are so many variables. Yes, there will be a high startup load each time it cycles, but this is more of a problem for sizing the inverter than estimating battery life. The constant current draw when actually operating, and how often it cycles on/off is the real question. You can measure the current draw during operation easy enough, but that still does not tell you how long it stays on per cycle, and how many cycles it has per day. Also, the run time is greatly affected by room temperature, space humidity, and the amount of food being cooled.

Most of us just plug the refrigerator in question into a small recording kWh meter and leave it at the home for a week. This will give a good indication of what it consumes over time, but for a maximum number, this test needs to be done when it is warmer and there is more humidity in the air (how often the high energy using de-frost cycle comes on).

Battery backup for any typical residential refrigerator should be only considered for a 24 hour outage. The batteries you are planning to use will provide about 1 kW of useful stored energy (225 x 6 x 80%).

Suggestions –

For any backup power longer than 2 days, buy a generator unless your loads are very small.


Buy a solar-rated top load freezer. Most solar suppliers offer these freezers that are designed for minimum kWh usage. I still think you will need to at least double your battery bank even for these low energy models, or add a small solar array to offset the daily energy usage of the refrigerator.

Hope this helps,

Jeff Yago.

Converting to alternative energy

I am not currently a Backwoods Home subscriber. I came across a letter from Backwoods Home I had received a long time ago as I was going through a pile of papers that needed to be filed. As soon as I can afford it, I plan on ordering.

I have a home that is roughly 4750 Sq. Ft. I am wanting to convert it from all electric to all alternative energy because in the long run alternative energy is more cost effective and efficient. I live in East Texas and am looking for information from an unbiased source on what kind of alternative energy is the best for me. How do I determine this? Also, about how much money am I looking to spend to convert my home to solar power, wind power, hydro, and/or generator, respectively? I have heard of a type of solar power “shingle” that eliminates the need for the ugly, out of place photo voltiac panels. Do you know anything about this, what it is called? I want my home and my property to be esthetically pleasing, and the most cost efficient. I don’t want my children or grandchildren to have to pay an electric company for electricity when they inherit my place.


Dear Nancy:

Although sizing a solar system is based on total electrical load not square foot size, your home is very large compared to most single family residences and I must assume you have a very large electric bill. There are several books available from the Backwoods Home Bookstore, and I suggest you first read several on this subject to give you a better understanding on what may work for your situation.

The solar shingles you asked about are still very expensive compared to other above roof modules, and I have several concerns including inter-connect wiring access and module replacement if there is a failure. There is a non-glass solar module for direct application to metal roofing but this requires a like new metal roof that can take special adheasives. Unless you are in a county that offers a tax rebate or area that has very hign electric rates, don’t expect your solar system to have a very good payback. Many systems installed today in areas with little or no financial incentives are installed as part of either a backup power system, or to power homes or equipment located in areas not served by the electric grid. The few clients that want to purchase a solar system to “save our precious resources” are not as alturistic when they see what it will cost them!

Good luck!

Jeff Yago

Passive solar

I am in need of information on passive solar systems in New York. I live in a hilly section of New York State, we have snow for about half the year, yet we do have brilliantly sunny days. Is a passive solar system feasible for us? I am hoping to go PS for my workshop/studio.

Lois Ann Zendarski
Franklinville, NY

Dear Lois:

Assuming you have a good southern solar exposure with no shading from nearby trees or buildings, yes passive solar works well in the northern states. In fact, many of the early passive solar homes were built in the New England area. The biggest concern is heat loss for any large glass windows intended for solar heat gain and these must either have a very good thermal rating, or have some type of insulated “shutter” or covering during the night.

Your real concern for a studio application is too much sunlight. Most studios use north facing glass to provide indirect day-lighting. Large south facing windows let in lots of paint and finish damaging sunlight when the winter sun has a very low path across the sky. The winter sun coming in our passive solar greenhouse can be blinding! A Trombe Wall is a south facing glass area in front of a masonry or heavy mass wall which heat the wall but does allow any direct sun into the studio space behind this wall unless there are openings. This may be better suited for your application.

Good Luck!

Jeff Yago

What about Alaska?

I have been reading your series Solar Power 101 and found it very informative. However, I wonder if any of it is applicable in Alaska? I currently live in Anchorage, but own about 13 acres 3 hours south of here in a little community called Funny River.

Right now I have a 10X12 cabin, but eventually hope to build a house there and live in it full time. I figure the house would be about 1600 square feet and be built to be as efficient as possible. I am used to conserving, especially since my cabin has no electricity, phone or running water, but since I would be living there full time, I would like to have electric lights and a few other conveniences.

I do not want to hook up to the grid. I also do not want to deal with a generator full time, although having one as a back up is fine. Is it feasible that most of my energy needs could be met using solar power? How do I know what would be needed, as far as output? Also, a few years ago, BHM had a few articles about a type of solar panel that was similar to metal roofing. What do you know about those?

What are the advantages/disadvantages to using that type of panel as opposed to the more traditional type of solar panel? I am hoping to build this house in about 5 years and am in the research stage. I would appreciate any information you can give me, including information about where to find reliable information (besides BHM)!

[Name withheld]

Solar in your very northern latitude is not easy. Short days and long periods of darkness do not make it easy, as any reasonable sized battery bank will only store a few days of backup power when the sun is not available. When you do have direct sunlight, a solar module works just fine, and the colder, the more efficient! I would not plan on much more than a few compact fluorescent lights and a radio however. Batteries also do not do well when the temperature drops, but I assume you have a possible battery area that will stay above freezing. The modules you are asking about require a factory trained installer, as they are bonded to a metal roof using a very special adhesive. The metal roof also must have the correct finish and size. I am not sure how well the bonding will hold up with the extreme freeze-thaw issues you will have.

I had an article in the Jan/Feb 2002 Issue #73 that described how to make a small solar powered lighting system that may help you get started. Many of my clients in areas with limited solar use a small solar array to keep some charge on the batteries when they are not home (no loads), and run a generator a few hours every 3 days to put a full charge on the batteries when they are home. With high efficiency lighting and limited electric loads, you can get by with minimum generator run time and coast several days without the generator.

Keep warm!

Jeff Yago

Read More Ask Jeff Yago

Read Articles By Jeff Yago

Read Energy Articles

Sorry. Jeff no longer answers questions online

Comments regarding this column may be addressed to Comments may appear online in “Feedback” or in the “Letters” section of Backwoods Home Magazine. Although every email is read, busy schedules generally do not permit a personal response to each one.

Comments are closed.