Alternative energy advice from Ask Jeff Yago. Volume #23

Ask Jeff Yago
Solar & Energy-Related Issues

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

Sorry. Jeff no longer answers questions online

Remote cabin water heater


My cabin in Utah is almost complete. Solar equipment is on the way. (2) panels, (8) batteries, outback inverter, etc. Outside is done. Basically trim work and plumbing left on the interior. My question is what would you recommend for water heat. I am looking at tankless heaters. Do they pull a lot of electricity or should I go propane? Also, what is your opinion on composting toilets?


Brent Toft


Don’t even think of using electricity to heat water. We rarely do this with large systems, much less a system the size you described.

You have 3 choices depending on how much you use this cabin and access.

My first choice is an instant tank-less hot water heater as some brands like a Infinion does not require any electricity and uses just propane. The problem with any tank-less water heater is there piping will quickly freeze if the home is not heated while you are away and should be drained each time.

My second choice is a solar hot water heater, which you can buy with an optional DC pump powered pump which uses very little battery power but also can freeze when away for long periods if not properly designed and installed.

If you are not lazy, several companies still make a wood fueled water heater that is an old style insulated water tank with an internal flue pipe and a fire-box below. most hold less then 30 gallons, so they heat up fairly quickly when you build a fire. However, their fire-box is small and will not hold much wood so don’t expect to have hot water all day after building one small fire. There are also hot water heating coil options for many standard wood cook stoves that can heat a separate insulated water storage tank.

I own 2 composting toilets, one in a garage and one in a trailer. They are great if you do not have a large family. For one or two people, you may be able to go many months without emptying the recycled soil and you only need to add a little compost material each time it is used. They also make larger models with a separate holding composting tank located under the floor and separate from the seat part. These usually requier an electric motor and some even have electric heaters so keep it simple.

Good Luck,

Jeff Yago

Wood stove/radiant floor heat

Hi Jeff,

I saw your site for the first time tonight and thought you might be able to offer some advice.

I am ever so slowly modifying our existing home. We currently have a “woodchuck” which is a wood burner with forced air. The system is installed in our basement. Although it heats much better than our heat pump, I would prefer radiant type heat over forced air. Also, most of the radiant heat from the unit is lost to the dark corner of the basement.

What I would like to do is install a traditional wood stove on our main floor to use as our primary heat. Here is my big question- Is there a way to enjoy a traditional wood stove and use that stove to heat water for a subfloor radiant heat system or even wall mounted radiator for hard to reach bedrooms and bathrooms???

I have seen someone install an old beer keg at a 45 degree angle, suspened about 6 inches above a wood stove. They had brought their water supply into the keg and preheated their water before it got to their hot water heater. This significantly reduced their electric bill.

I guess I’m looking for something similar and code friendly of course….

Thanks for your time,

Polk County, NC


Although most heating of buildings and homes before the advent of central air conditioning systems was hot water or steam radiators. Now things are changing again and many up-scale homes are starting to utilize hydronic heating due to the higher energy savings and comfort. Our 3 story solar home has a built-in masonry fireplace in our ground level (partly below grade) family room. This fireplace has a Hydro-Heater hydronic firebox which is “hollow” on all 3 sides and the bottom which allows water to flow around these areas then this water flows up into a heat exchanger containing 90 feet of boiler tubing. This heated water is then pumped into a air heat exchanger located in the discharge side of my central air handling unit, which circulates this heated air to every room of our home including all 3 floors. When we have a roaring fire in this fireplace, every room of our home stays at the same temperature and there are no cold spots.

I have also designed many systems like this for others only we piped the heated water to baseboard hot water radiation located in each room, and used motorized zone valves to allow each room wall thermostat to separately control the temperature of each room. Although most of the wood-forced boilers you will find advertised these days usually are the self-contained type that is located outside and piped into the home, there are still several manufacturers that offer “hydronic inserts” that look like a log holder that you place inside a standard fireplace. Many wood stove manufacturers offer an optional hot water coil feature, but these are usually intended to only heat a domestic hot water tank and not the entire house.

Yes, you can heat a radiant floor, but the problem is most radiant floor heating systems keep the water temperature in the lower 100 to 120 degree range, and most hydronic wood stoves can easily produce hot water in the higher 160 to 180 degree range which is much better suited for a baseboard radiation system. This means a radiant floor system will require a storage tank with one small pump circulating tank water through the hydronic fireplace to heat the tank, and a second small pump to circulate heated tank water at a different flow rate through the radiant floor piping. Remember, boiler water or water passing through hot water radiators and radiant floor piping usually will include additives to reduce sludge and rust, and you cannot mix with your domestic hot water system (sinks and baths), so if you want to also heat your domestic hot water tank, you will need a separate coil in this storage tank for that piping.

You are on the right track, but remember, these are classified as a “boiler” and if you don’t include the proper pressure and temperature safety relief valves in your piping, these things can blow up and do some real damage. Also, manufactured hydronic stoves are made from “boiler grade” steel which is much stronger with no flaws or weak spots. This may be why there are not as many manufacturers these days and why I do not agree with your “beer keg” idea!

Good luck,

Jeff Yago

RV power to house

Hi Jeff,

I’ve been working on a solar trailer design similar to yours for a few months now. I really loved finding your article last month. I also plan to generate a surplus of power to help out at a group camp, event or disaster.

Is there a way I can plug the trailer in to supplement my home electrical supply to knock down my electric bill when the trailer is sitting unused at home?


Steve Sonntag MD
Lame Deer, MT


The short answer is yes, the long answer is this may be more trouble than its worth. Your state has had a net metering law since 1999, so it is legal for a homeowner in Montana to sell back to the utility. However, each state has allowed the local utility to set up specific requirements that must be met to ensure the safety of their service people and the quality of the power for the other customers.

Normally, in most states these requirements include filing a form with the local utility that describes the system, the installed hardware, indication that this equipment meets grid-interaction safety requirements (usually listed on nameplate), and the wiring into the electrical system was completed by a licensed electrician who also signs the form. Some states also add the requirement for an exterior dis-connect with a lever handle that can be locked-out by their service people. Again, these requirements vary from state to state, and you can contact your local utility for more information.

However, it does not matter that the source of the power that will be “back-fed” into the utility line is coming from a portable trailer, you will still need to meet most if not all of the states requirements just as if the solar system was mounted on the roof of your home. THey may omit the dis-conect at the meter since you or they could “un-plug” the trailer from the house, but I am betting this will be too complex a decision to make for the non-technical person you will most likely be dealing with and they will still insist on meeting all of their requirements.

Keep in mind that many inverters will meet the requirements for grid-interconnect and can easily be switched manually over to the “sell” mode. However, your trailer will most likely only have an “input” cable to allow charging the batteries from the house or a generator, so your trailer will need a second cable to connect its output to the house and this should NOT be a standard “male” plug with exposed pins since these exposed pins will be HOT at 120 or 240 VAC, depending on the model inverter you install.

If you want to stay “legal” but not go through all the hoops, why not just run a heavy extension chord from your solar trailer into your home and plug in a few appliances like a freezer or other load that closely matches the output of your trailer. This will remove this load from your utility bill, yet keep your trailer wiring from connecting into the other house wiring.

Hope this helps and good luck!

Jeff Yago

Propane generator


You have a great website!

My wife and I have won two Emmys for sound on the show “24” on Fox using sun power, hehe That’s a first I’m sure!

We have been off the grid for 13 years and just recently upgraded to a Xantrex 5500 watt inverter and a 25kw Guardian generator.

My question is can I take one leg of the 220v (120) to power my washer and propane dryer and one leg (120) to power my new inverter – charger?

Due to the writers strike in my biz I will have the time to tinker with the new gear.

Thanks again,

William Dotson


First, my wife and I are 24 fanatics and have all of the past seasons on DVD. We also live almost off-grid in a solar home, air conditioning required here all summer and we use grid power for that. Most everything else is on solar since 1994.

If you just upgraded to a SW5548, I am sure you think you have died and gone to heaven, although if you had waited for the new Xantrex XW6048, it has 240VAC output and you would not need to split generator output.

You have a problem related to your generator that you need to consider. Not to bad-mouth any generator brand, but most of the generators like the brand and model you selected are designed for true “stand-by” service while still connected to the utility grid. Most are shorter life 3600 RPM, and most have a very complex diagnostics control package and battery charger circuit which operate 24 hours per day. This constant drain of electrical power is of no concern when they are connected to the utility grid, but this is a really big deal when battery-powered and no grid. Also, most high speed 3600 RPM generators are only designed to operate a few hours per year, and at most for only a power outage lasting 1 to 3 days. However, when used in an off-grid application, most dealers will void the warranty because they will have a very short lifespan when operated every few days throughout the year. If you have a large solar system and this generator will only be called upon to run a few hours each month during bad weather and no sun, then you should be OK, otherwise, expect lots of service calls and an engine over-haul every year or two. A good match for your inverter would be more like a 12 or 15 kW Kohler or other lower speed 1800 RPM generator, which are designed for this type service.

Now to your question. Yes, you can connect one leg of the generator to the inverter and the other to your washer and dryer without a problem, but here is the best way to do this. Install a standard 120/240 VAC circuit breaker panel. The “main” breaker should be 100 amp, which is less than the 104 amp rating (at 240 VAC)for this model generator. In this panel install a 60 amp single pole breaker to feed the 120 VAC inverter input. Then install other breakers to supply your large loads that will only operate when the generator is running like your washer and dryer. I assume your well pump is 120 VAC, otherwise, unless you add a 120/240 VAC transformer, any 240 VAC well pump will only operate when the generator is operating.

Final note – look at the buss bars in the circuit breaker panel. Your generator will be connected to the “L1” and “L2” buss bars, and the neutral buss bars, all near the top of this panel. This means connecting anything to only “L1” and neutral, or “L2” and neutral will provide 120 VAC, and anything connected to both “L1” and “L2” will provide 240 VAC from the generator. However, if you look and the buss bar arrangement, they alternate left and right down the panel, so for you to achieve the desired load balance on the generator, you need to make sure the circuit breaker supplying the inverter is attached to a different buss bar from the circuit breakers that will be connected to the other loads. This means you will either have them opposite each other left and right, or will need to “skip” a space as you go down the panel. Hope that makes sense.

Good luck.

Jeff Yago

Inverter and battery charger question

Hi Jeff,

Thanks for being such a great resource. I’ve had fun reading your archives. I have an inverter question and a battery charger question.

1) I’ve heard inverters are most efficient when operating near their max wattage, so I’m wondering if it’s better to run small stuff from a small inverter. I have a 350w inverter for lights and computer stuff, but I plan to buy a 1500w inverter that can run our well pump when the power is out (which is pretty often). Can I hook them both up to the same battery bank so I can plug in selectively to the one that is most efficient for the job, or should I just run everything off the 1500w inverter.

2) My battery bank will have more solar power eventually, but for now when it needs a quick boost I’ll need to charge it up with the 10amp car-battery charger. Will this hurt the charge controller, inverter and DC circuits attached? Or can I just slap the car charger on the battery bank as it sits.

Thanks a bunch,

Steve Sonntag MD


Not sure why you want to charge the batteries with a 10-amp car battery charger as this will take forever. The the battery charger built into most inverters is much faster and will do a better job of providing the proper charge without battery damage.

The answer related to using two inverters will depend on their quality and size. Yes, some people use dual inverters, with a small inverter taking care of a group of smaller loads that run more often, and a larger inverter for the larger loads with less run time. However, I have used some “cheap” small inverters that consumed more battery power just sitting there with no loads turned on, then some of the larger inverters that have a low energy “idle” feature. If you are planning to purchase a new inverter and can select one with a very low idle or standby energy usage, you may be better off to just use it for all loads and get rid of the smaller model.

If you are planning to purchase a larger inverter that is a modified sine-wave model, these do great on larger loads like well pumps, furnace fans, power tools, but have problems with some electronics, computer printers, and light dimmers. In this case, you can buy a small “pure sine-wave” inverter to handle your sensitive electronics, and use the modified sine-wave inverter for your well pump. Also remember that most existing well pumps are 240 VAC and most inverters are 120 VAC, so you may need a transformer or will need to replace your well pump with a 120 VAC model, and most likely if you do this you may discover the wire run to the well was sized for a 240 VAC pump and will be under-sized with double the voltage drop when using a 120VAC pump.

Yes, you can wire each inverter to the same battery bank, just make sure each one has its own dis-connect switch and circuit breaker or fuse, and make sure these are rated for DC service. AC fuses and AC circuit breakers cannot be used safely on DC circuits -trust me on that one. However, the SquareD “QO” line (not Homeline) circuit breakers are dual rated for up to 24 volts DC and can be used if that is all you can find.

Yes, you can attach a battery charger to a battery bank while a solar charge controller is also charging and connected. The solar charge controller “looks” at the battery voltage to decide when to put more charge into the battery bank. If the battery voltage is high during charging by another charger, it just decides the battery is full and shuts off. If you have other DC lights or DC appliances connected to the same battery bank, remember these can be damaged if you set your charger voltage higher than the voltage rating for these devices. This is a real concern during battery equalizing charging as this requires a much higher charge voltage than normal charging.

Hope this helps,

Jeff Yago

Solar panel safety concerns

I am in the process of using solar panels as my total source of energy but have been hearing that some of the products in the solar panels are cause for concern. Have you heard any concerns with any of the products used in the solar panels, such as cadmium telluride.?




What you are probably hearing about is the European Union issued a directive in 2006 that clarified their regulations on banned materials in products imported. From this long list it further identified 6 materials that it considered “the worst of the worst” which they were now applying even stronger limitations. One of the six totally banned materials was cadmium, and the normal restriction of 1000 parts per million on all other restricted materials was lowered to only 100 parts per million allowed for these. This applies to any single part of any product sold, so even if only one tiny part contains any of these materials, the entire product is banned.

Cadmium Telluride has been used for years in many electronic components and recently in some thin film solar cells due to its very high efficiency to convert sunlight into electrical energy. However, only a few solar module manufacturers use thin film technology, and only a few of the thin film materials use cadmium telluride in their manufacturing process.

Thin film solar modules made by First Solar Inc. was identified when this import ban was imposed, as having 470,000 parts per million of cadmium telluride in one of the layers of the thin film. I do not know if they have changed their product line since this ban or if they do not plan to market overseas. Although cadmium telluride is less of a danger to humans than the banned cadmium, it appears that any company still making modules that have even a tiny amount of cadmium telluride in the process will not be allowed to be sold anywhere in Europe due to the cadmium ban.

I am not aware of this banned material being used in solar modules other than thin film, and am not aware of any bio-hazard associated with any brands of single crystal and poly-crystal modules, but its always good to check before making a purchase. Also, some solar module manufacturers offer a recycling program to keep more toxic materials from going into landfills. I would be more conerned with the very toxic materials being used in new battery technology than in solar modules, due to the much shorter lifespan of batteries.

Good Luck,

Jeff Yago

Switching power supply from Inverter?

Hi Jeff!

Hoping you can help.

I need to run a switching power supply (MasTech 5020E: ) off an Inverter.

It seems to trip off/overload 800 & 1000W units; is bigger going to work?

Thanks in advance.

Jim Blanner


The specific power supply you have selected can provide up to 1000 watts of DC power output at full load. Even assuming a high conversion efficiency of 90%, this means it can draw up to 1,110 watts from the wall outlet (inverter) when dialed all the way up to full output load.

However, if it is still tripping out when powering a very small load, most likely it will not operate on a lower cost modified sinewave inverter due to its very high quality voltage control which is expecting a pure sinewave 120 volt AC input at exactly 60 cycles. If you do not need to operate it at its full power output, you still may be able to use an inverter in the 800 to 1000 watt range, as long as its a pure sinewave type. I have found many sensitive electronic devices will not work when powered from a modified sinewave inverter.

I have actually seen some of these sensitive electronic devices actually heat up and start smoking when connected to a modified sinewave inverter, and power supplies and battery chargers of any type not only do not work well on lower cost inverters, but also do not work well when powered from a generator.

Good Luck,

Jeff Yago

Alternative energy in new home construction

My wife and I are starting on our new home March 1, 2008 and are desiring to utilize as much in the way of Alternative/Renewable energy as is practically possible. My question is; where would you recommend non expert/informed parties start in efforts to educate and inform for such a purpose? We are old-time Mother Earth News subscribers and are taking advantage of our local library but are hoping to find a source(s) that give pro/cons of particular approaches, systems etc… . Any and all help is greatly appreciated!

Oscar Ratmaker


Years ago there were very few solar and energy saving devices sold for the homeowner and home builder, and your selection was based on what was available, and you usually had to modify other wiring to allow inter-connection. Today there are many more energy saving and solar products to choose from, and some can be in conflict with each other if you are not aware of the many options. For example, some home automation systems are installed to save energy, but some of these systems do not work well with alternative energy power systems. Some of the newer backup generators are designed for constant connection to a standard utility grid and are almost impossible to inter-connect with many solar inverters and their automatic generator start controls for battery re-charging. The selection of your home’s appliances can sometimes save more in energy than what you can achieve with a solar system trying to power lower efficiency appliances. If you really are interested in a home design that is state-of-the-art energy efficient, all of the building systems and their design will be critical. This includes, appliance selection, lighting selection, HVAC system type and efficiency, well pump selection, well expansion tank selection, alternative energy system selection, gray water recycling, window selection, wall and ceiling insulation, roof color and type, home orientation on lot, shading from nearby trees or hills, size of piping and number of elbows, room and window orientation to solar path, window shading and over-hangs, heat recovery air ventilation, geo-thermal, and many many more things to consider.

If you want to do this right, first select an architect to work with you, and make sure they have experience in low energy type residential design. Ask for references and examples of recent projects. Next, you need to involve a solar energy consultant if you are planning to include any type of active, passive, or photovoltaic solar system. I suggest that the solar consultant work for you and not the architect, but this person needs to work with the architect, make suggestions on any architecture details or space allocation that may be required to incorporate an alternative system, and be involved with the selection of all lighting and appliances. I have worked with hundreds of architects and have found that many think they know more than they really do regarding solar systems, and will usually try to obtain free design advice from a local solar dealer with a promise that the architect will specify their brand of solar hardware. If the solar consultant is hired by or working for the architect, then it is much harder for the solar consultant to know what the homeowner wants and how best to achieve these energy goals.

If you try to go it alone, you will find that many of the Internet based solar retailers are there to sell products, not offer design advice, and many will have no idea what you need. A really good solar dealer will ask for a design fee up front to provide this initial design assistance to you and your architect, but this fee is usually credited towards the cost of a system if you purchase one later from them. This is because it takes many hours of design effort to select the best solar products and appliances for your specific project, and if there is no guarantee that you will actually make a purchase from them, most really good dealers will not provide this service for free. Remember, you get what you pay for and a really good solar dealer will select the products that are best for your specific needs, not what he happens to have in stock.

I assure you that you will save far more in installed system costs later than you will ever spend for initial design assistance. I receive many calls from homeowners who tried to order a solar system on their own, only to find out the individual components they ordered will not connect to the other products they purchased, were the wrong voltage, or had the wrong cable connectors. There are many solar “dealers” across the US and in most major cities, but only a few have achieved the highest rating of NABCEP certified. This certification not only requires extensive knowledge of all types of solar energy systems and their design, but also the dealer must install a certain number of systems each year that have been inspected and approved by local building inspectors. They must also take additional classes each re-certification cycle to maintain this solar installer certification. This is a national certification and there may only be a few NABCEP certified solar installers in your state so check their web site –>

Good Luck!

Jeff Yago

Flashlight review question

Thanks for the information from the flashlight review. I had a min mag old bulb but had a battery go bad and corroded inside so I threw it away. I like the looks of the Garrity and Dorsy led but can’t tell if either has the capability of going from spot to flood light by twisting the head.

Interested in the small 3 AAA models.

Thanks for any information forwarded.

Joe Lucey


Most LED style flashlights do not have the same distant beam “focusing” you may expect as compared with incandescent or halogen type flashlights. However, the models you are asking about will provide some bean size adjustment, just don’t expect a super bright center spot of light.

Good Luck,

Jeff Yago

Turning heat into electricity

Hi Jeff,

I’m planning a hydronic system using a wood gasification boiler. I found a very efficient boiler ( ) that suit me but the problem is it requires a fan that draws 1/3HP all the time and I want to find a way to turn some of the heat into enough electricity to run the fan. I’m off the grid don’t have enough renewable energy to power the fan all the time.

I’ve heard about thermoelectric heater/coolers (as seen in some cheap refrigerators) and understand that they can run the other way, turning a heat difference into electricity ( ).

How about installing a “heat pipe” into the boiler’s gasification chamber to draw out some of the heat to a metal plate outside the boiler, where the thermoelectric device could be mounted? The delta T might be well over 1000-1500 degrees which could make generating a few hundred watts feasible, at least in theory. Have you ever made such a system or have any advice?

Thank you,

Scott Onstott


First, the 1/3 HP fan on the boiler sounds really large unless the boiler combustion air path is very restrictive. My entire 3-story 3,400 sq. ft. home only has a single 1/3 HP fan to distribute both heating and cooling air flow to all room registers. See if this was just a motor size they “guessed” at to be safe, or if the boiler actually requires that much fan power. In other words, just having a 1/3 HP fan motor does not mean the fan load requires the full motor horsepower. Also determine how many hours this fan will need to operate each day.

I am very familiar with the thermo-electric systems you are asking about, and I can tell you this is not the way to go. The hardware you would need to power even a much smaller fan motor would be very expensive due to the very limited power output you get. Also, it is not always a good idea sticking other piping into a very hot flue unless the system was specifically designed for doing this.

I would find out more about the fan motor provided with the boiler and its actual power draw (not just nameplate rating). Also ask if this is a high efficiency fan motor. When I was building my solar home, as soon as they delivered my central air handling unit, I removed it from the shipping box and ripped out the fan motor that came with it and replaced it with a super high-efficiency fan motor with a 94% efficiency rating. The longer hours the fan needs to run, the more important this will be.

Finally, if you are wanting to be off grid, the best solution is a small solar power system and batteries to power this fan. If you do not want or need any other AC power, then forget the inverter and replace the fan with a DC motor-driven fan. However, DC motors require motor brush replacement about every 2 years.

Hope this helps,

Jeff Yago

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