Alternative energy advice from Ask Jeff Yago. Volume #15

Ask Jeff Yago
Solar & Energy-Related Issues

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

Sorry. Jeff no longer answers questions online

Water tank information

Dear Jeff:

I live in a small single wide mobile home, currently heated by Propane gas. I would like to change to alternative power inexpensively. A friend of mine has suggested an idea using hosepipe on the roof in an “S” shape with a water reservoir under the mobile home. We are looking for inexpensive ideas for the water reservoir. Water beds was a suggestion but maybe there is something else??

Any ideas would be very welcome.

Linda Slasberg


You have not provided enough information for me to help. For example, yes, if you live in Florida or other areas with lots of sun and very warm non-freezing winters, you can heat domestic water really hot by nothing more that leaving a black water hose un-coiled on a roof (and many people do). Since you plan to have a storage tank below the roof, you will need a small circulating pump to move water from the tank through this hose on the roof then back down into the tank.

In Florida back in the 1930’s before gas and electric water heaters were available, many people put a water tank at the highest point inside their attic, and mounted a wood box (containing rows of pipe covered with a glass front) down near the roof eve. Because this very basic solar water heating panel was located below the elevation of the attic tank, the heated water in the solar panel would “rise” and flow up and into the storage tank with the cooler water from the tank flowing back down and into the lower end of the solar panel piping to be re-heated. This process is called “thermo-siphoning” and does not require any pumps or electronic temperature controls.

If you locate your tank in the crawl space, not only will you need a circulating pump, but you will also need some form of temperature control to turn off the pump once the tank has been heated or you will pump hot water from the tank up through the roof piping at night and lower the temperature of the water in the tank. A factory-built solar system uses a differential temperature controller which has a sensor in the solar panel and a second sensor in the storage tank, and starts the pump only when the solar array is hotter than the water in the tank.

I also am not sure what you mean by using a water bed as a low cost hot water tank. Your water system is under city or well pressure, which will be over 40 psi. This would most likely damage a plastic water bed which is not designed to stay under high head pressure. Why not use a standard water tank. Many people will trash a gas water heater after the gas burner fails, but the insulated tank may still be in good condition.

Sorry I could not be more helpful, but I do not have enough information to provide more.

Good luck,

Jeff Yago

Hydro-power question

Hi Jeff,

We have a home with separate guest house/ art studio powered by year round Hydro-electric plant built in the 1980’s. The intake is on a US Forest Service creek that requires permitting only every 20 years. The SolWest fair in Oregon is very near to our house but we have never met anyone that was familiar with this Pelton Wheel Hydro-Electric plant using USFS diversion. We would like to compare notes with you or anyone with advice for us.

Thank you,

Debbie and Joe Letosky

Debbie and Joe:

I am not sure what you mean by “compare notes” as you did not indicate if you were having a problem with this turbine or with the permitting process.

It is my understanding that the USFS permitting process has been very “loose” over the years due to the many existing permits and waivers that were granted in very old deeds which still may be in effect. I also believe there has been a lack of standardized permit requirements that differ from state to state and most data still stored in paper files. In other words, if you are operating under some kind of pre-existing approval or waiver, leave well enough alone.

Your “Pelton Wheel” design is considered a high pressure-low flow type water turbine, so this tells me you must have a high drop in elevation and do not need a high flow rate to generate your power needs. This is good, as most people must rely on much lower head pressures (low elevation drop) and make up for it with a much higher flow rate through larger piping. If this is not the case, you may want to consider one of the other wheel designs that do not require a high head pressure, but need more flow.

Hope this helps,

Jeff Yago

Water powered electric power generation


I would like to generate electrical power for my home located next to a significant rushing stream. Is there an existing product or is it possible to fabricate something.



Ten years ago I would say get out the pipes and build your own, but today there a many good quality and low cost hydro-power kits you can buy. These are very reasonably priced and easy to install if you have basic pvc plumbing skills and a good stream elevation drop nearby. Contact any of the solar dealers advertising in this magazine as they also carry these products.

Good luck!

Jeff Yago

Picking a Standby Generator

Hi Jeff,

With the start of the 2007 hurricane season, I am in the market for a good LP standby generator system to power my whole house in south Florida. My home is fully electric, 2100 sq. ft. under air and the A/C compressor unit outside is quite large. It stands about chest high. First, how do find out how large (tonnage) my A/C unit is? Second, I’m looking at 15Kw Generac systems but I’m not sure if this is the optimum size for a full main transfer. Lastly, what’s the best way to determine the size needed for this application?




You have two choices. You can install a smaller generator to handle all “critical” loads like all lighting, kitchen appliances, audio/video, and well pump if you have one. Most people install a generator on the 6 to 8 kW size range for these loads. If you really need to also power your air conditioner, I am guessing you will need a minimum of 15 kW for a home this size, plus, this size generator will have a much higher fuel usage per hour than if you can get by without the air conditioner.

You may want to add one of the small transfer switch boxes that lets you select which loads are operating during any specific time. Lowes and Home Depot have these for around $300.00 that have around 8 separate switched circuits and a pre-wired cable that is easy to retrofit into your existing breaker panel. This can really keep from over-loading a smaller generator since you could turn off the electric hot water heater during the time you are running the air conditioner or other large load, then switch as needed. Many generators are being sold for emergency backup that are designed to only operate for one or two power outages per year, lasting only a few days. If you think your area may experience longer outages, check the manufacturers data and look for a model that is designed for longer run time. The extra cost for a heavier engine will be well worth the slight increase in cost.

Finally, most gas and propane generators have a fuel consumption that is not exactly linear. What this means is any given generator requires a “base” amount of fuel per hour regardless of how small the load is, and only starts to really increase when it gets fully loaded. This means a large generator operating very lightly loaded may require more fuel than a smaller generator that must operate at half or more loading to supply the same power. Do not go too far over-sized when selecting your generator. On the other hand, generators do not like a motor starting (like a refrigerator or AC compressor)while it is already powering other similar loads since the startup loading from any motor-driven compressor or well pump can be 2 or more times the actual nameplate load rating.

Good Luck,

Jeff Yago


Hi Jeff;

I currently have a oil burner hot water radiation system. I want to use wood. What would be my best option, remove the current system or buy a add on.

Thanks, Dan


Depends on age of your system and if you want oil boiler to still be available as a backup to the other. Most oil-fired hot water boilers can last up to 30 years if the water quality is good. However, the burner assembly will not always last this long and will be replaced every 15 years or so. If the water quality is not good and the system has not been maintained, the piping and boiler sections could be corroded from inside out and only a very thin wall left even though the piping looks good from the outside. I have see this older piping crumble when you try to replace a failed fitting due to internal corrosion.

Assuming the oil-fired boiler and piping is still good, you can add an outside wood boiler (see my article on wood fired boilers in the May/June issue #105) and keep the oil-fired boiler still piped in the system for those days you do not feel like going outside and firing up a big wood-fired boiler.

If your boiler is on its last legs and needs to be replaced, there are some wood-fired boilers that can be located where your old boiler was, that can operate on either wood or oil. These are larger than your old oil fired boiler, so be sure you have the space. If you go wood only, be prepared to have lots of split wood on had that must be kept dry through the winter. You will also need a pickup truck, wood splitter, leather gloves, steel-toed boots, chain saw, chain sharpener, trees, beer, and a very strong back!

Good luck,

Jeff Yago

How to start getting energy independent

Hi Jeff,

We have been reading your archives, much of which sounds wonderful, but more like a dream to us. We live in rural Arizona, on about 5 acres. We have power needs for 2 well pumps, and 3 residence structures (mobile homes) as well as two other buildings. How do we get started with alternative energy (solar is our top choice as we have plenty of sun!) methods? Can you get us pointed in the right direction? The amount of energy required to run our pumps, air conditioners, water heaters, etc., is high, especially in our extremely hot summers. The bills are becoming a financial hardship. We are trying to live on one income, and homeschool our kids, so we would need to be able to do most if not all of the work ourselves.

Any help and all information, sites, references, or whatever you can do for us would be a blessing. Thanks.

Cindy Barnett


Let me be very blunt. Solar power systems are very expensive, and if paying your high cost electric bills is a problem now, I think you will find that spending anywhere from $25,000 to $50,000 to save $50 to 75 per month on your electric bill may not be the direction you all need to go at this time. We design and install solar power systems all over the United States, and 50% are for clients who are located in areas not served by power lines, and the other 50% are for people who just want to have solar regardless of how much it saves on their monthly bills. Of course some clients are also interested in solar as part of a backup power system if they live in an area with lots of power outages, but we never sell any solar system based on the utility bill savings. Being in Virginia, we pay around 7 to 8 cents per kWh for electricity which is still fairly low. However, if you live in a state with much higher electric rates, you will have higher monthly savings, but it will still take up to 20 years to recover your initial investment.

Based on what you have said, here is what I suggest. You said you have to run air conditioners, well pumps, and water heaters, and you have 3 mobile homes. Mobile homes have minimum insulation due to the thinner walls and roofs. Anything you can do to improve this would help including painting the roofs a light reflecting color, or installing a separate roof structure over them to provide sun and wind screening. Arizona has a dry climate and “swamp coolers” work really well in your state (I wish they worked here!) and can provide cooling at much less cost than operating a standard air conditioner. They are also fairly cheap as they are just a metal enclosure, fan, and water filter pads which use the evaporation of the water to produce the cooling. You should consider this and yes I have seen them installed on trailers.

You said you have 2 wells so I assume several families share or garden watering is required. Check back to Issue #71 – Sept. 2001 where I describe a solar-powered water system for a home, or Issue #91 – Jan 2005 where I describe a solar-powered irrigation well. You would first install a small DC powered pump in at least one of the wells, and it would pump all day the sun is shining and fill a large plastic tank. This tank would have its own pressure pump which would then supply one or more homes from this tank with normal household water pressure. The two articles will explain this better and a pole mounted solar array just to power the pump would be a low cost way for you all to get into the solar without spending big bucks.

I would install solar hot water heaters on all homes as these are not that expensive and would have a really good savings and pay-back where you live. Lastly, look around for easy ways to reduce your electric usage. You will be surprised how much you can save by replacing all standard light bulbs with compact fluorescent, install flow restrictors on showers, and turn off any lights and appliances when not needed. I have written many other energy saving guidelines in prior issues, and you may want to consider buying one of the anthologies containing these back issues.

Good luck,

Jeff Yago

Deep cycle batteries

Hi Jeff,

Thank you for your time…

We have 12 x 2V 1100 Amp hour batteries that are 7 years old, …..we have recently had to replace two of them….is it ok to combine these new batteries with the old set….they are the same brand and capacity….




You have left out some important information that will impact my suggestions. Based on the size of the batteries you are asking about, I assume they are being used in a solar or wind powered home power system, and most likely off-grid. Second, you did not indicate what kind of batteries these are. Both Trojan and Decca make a 2-volt wet cell in this amp-hr range, but they are industrial rated and should have lasted much longer than 7 years unless you are off-grid with limited solar and they never get to be fully recharged and equalized before many deep discharge cycling. Having limited generator or solar array capacity for charging and never fully re-charging a battery bank before it is heavily discharged is the number one cause of early battery failure.

I do not recommend placing new batteries in with a string of older batteries as they will quickly “assume” the same charge levels as the others. I would change them all out at the same time with new batteries of the same size and type. If cost is an issue, use smaller and less expensive batteries to replace them all until you can afford to replace them with the original size cells. Of course you would have less system capacity, but this still might be better overall than what you are getting out of the present batteries. I have many systems out there using six-volt L-16 size batteries that easily make it 6 years and these only cost around $200 each. At 370 amp-hr each, you would need 12 to equal the battery capacity you have now (3 sets of 4 in series = 1,110 amp-hr @ 24 volts) which would cost around $2,400.

Final note – Before spending thousands of dollars to replace all of these high dollar 2-volt cells, I would find out why you lost almost 20% of a very heavy duty battery bank that should have lasted years longer.

Good luck,

Jeff Yago

Off-Grid Refrigerator

Heya Jeff–

I have a summer house completely off the grid in the woods in Vermont, and we keep our food spoilables in the well a half mile from the cabin. I’d like to find some way to use the same principles and elements–water, stone, air circulation, evaporation–to create a food cooler nearer by. But I haven’t found any good schematics or instructions online.

We have access to stone (or cement), water, shade……can you help?


Laura Buss


Sounds like you need an old uncle or grand-father to talk to.

It was not that long ago when folks in your neck of the woods used a “cellar house” ( also called a “spring house” or “root cellar”) to keep things cold all summer. These were small brick or stone foundations dug into the side of a hill. Most were only 8 to 12 feet square, with one side at ground level and three sides covered by the hill. They either had a wooden and shingle roof directly on top of the masonry walls, or second floor was built above to provide storage area and added shading and insulation from the hot sun. You MUST have a small stream of water running across the floor from the rear wall and out under the front door. They would select an area to build this cellar house where there was already a small spring or drip seeping out of the hillside, or look for a likely location and drive a small galvanized pipe (pre-drilled with lots os small holes along its length) horizontally into the hillside near the floor elevation of the future cellar house. Small rocks or stones cover the dirt floor to absorb the wetness and keep you from walking in mud if the dirt was left bare. You do not need a large stream of water, just enough to keep the floor damp which will evaporate on hot days and keep it much cooler inside than outside. Of course with todays building materials you could add lots of insulation in the walls and ceilings that was not available to the early farmers and ranchers.

Here is a link on construction –

Good luck,

Jeff Yago

72 volts needed


Hopefully you can help me…

I need to wire six 12 volt batteries to obtain 72 volts with greatest reserve capacity and amp hour rating.

Is there a particular series/parallel set up you recommend.

The object is to run a 72 volt electric motor from six [6] 12 volt AGM deep cycle batteries to achieve highest amp draw possible from batteries and for longest running time.




A battery’s amp-hour capacity changes only based on state of charge, not how it is wired in series or parallel. For example, if you take two 12 volt batteries with a 100 amp-hour rating each and wire them in series, you get a 24 volt battery at 100 amp-hour capacity which equals 2.4 kWh of stored power ( 24 volts x 100 amps). If we take the same two batteries and wire them in parallel, you get a 12 volt battery with a 200 amp-hr capacity which equals 2.4 kWh (12 volts x 200 amps). The amps and volts change depending on wiring arrangement, but the actual battery capacity (kWh) which does the work does not change except when we add or remove charge. The same is true for mixed series-parallel layouts.

For your question, there is no other way to get 72 volts with six 12-volt batteries but to connect them in series (6 x 12 = 72 volt). If you want more run time, switch to twelve 6-volt golf cart batteries wired in series which will last much longer in a constant charge/discharge cycling application than standard 12-volt batteries. You did not indicate the motor type, but most DC motors are series wound and they will adjust their speed based on voltage without harm. If you wire your batteries to provide 36 volts, the motor will operate at about half its nameplate RPM, which is how we control the speed of DC traction drive motors.

The AGM battery you plan to use is safer since it does not normally vent gasses when charged or have any liquid acid to spill, but they are more expensive and will not last any longer. They also require special charging procedures or you can soon dry them out and they cannot be re-filled.

Good luck,

Jeff Yago

Wind power

Hi Jeff,

Pure rookie trying to get information on what you suggest for self reliant wind power supply companies or better yet build your own kits. Hate utility companies and want to start generating enough wind power to supply my own needs. I have a very small house and live in the country, but I don’t know where to start looking for reliable dependable advice and suggestions for plans or supply companies. Hope you can help me.

Jim Knauss


You did not say where you lived but I have two suggestions for solar and wind equipment suppliers and both sometimes advertise in this magazine. I have worked with them both for many years and found them to work well with the smaller type buyer and have the experience to help you select what you need:

Northwest – Backwoods Solar Electric Systems, Idaho – (p) 208-263-4290

Central – Kansas Wind Power, Kansas – (p) 785-364-4407

Good luck!

Jeff Yago

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