Alternative energy advice from Ask Jeff Yago. Volume #24

Ask Jeff Yago
Solar & Energy-Related Issues

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

Sorry. Jeff no longer answers questions online

Pumping water in Brazil

I live in a semi rural area in Belo Horizonte, Brazil (lots of direct sun) and am interested in pumping my water from the closed reservoir to the holding tanks above by solar power.

The head is 105 feet at a distance of 350 feet through a two inch PVC pipe.

I see Northern Industrial Tools has these High Wattage Solar Panels – 15 Watt With these panels as a start, what else do I need?

Thank you for your help.

John D Martin


I realize you do not have easy access to many specility suppliers, but unless you plan to buy a trailer truck load of these 15 watt modules, you need to re-think this project. Although you did not indicate the amount of pump flow you required, which determines the pump size and in turn the pump’s power requirements, you did indicate a fairly high pump head and large pipe size which tells me you will need a pump that will require far more power than you can achieve with these small modules.

First, determine the size pump you need and voltage. As a starting point, I am making a wild guess that you will need at least 150 to 200 watts of solar modules wired for a 24 volt pump, which would be better to use two modules at 75 watts each, or 4 modules at 50 watts each to reduce the wire and mounting issues of using many smaller modules.

There are many solar pump suppliers that can provide you with a complete packaged system with pump, controls, modules, and mounting if you can provide them with more details on the pumping requirements you have. Since you are pumping up to a storage tank, you may want to use a smaller flow high head pressure pump and smaller pipe and let it run all day than a larger pump that quickly fills the storage tank and shuts off, since this would require a smaller solar array and have a lower cost. Contact Dankoff Pumps

Good Luck!

Jeff Yago

Hybrid System

Hi Jeff

I read your article on a Battery Powered Weekend Retreat.

We have some land in Western NC and was thinking of a Hybrid Solar-LP Gas Generator system to power a single wide home. Our property also faces the north with tall pine trees so not the best for Sun.

Would it be possible to build the same type system for a single wide home? Would I be able to use the AC Refrig Energy star and TV’s?

I was thinking the Solar could keep it charged while we are gone and the Generator would come on every couple of hours to top off the Batteries.

Would one of the Kohler 7KW generator work?


John Godwin


Size and type home has less to do with hybrid system sizing than your estimated power needs. However, most systems will need a large battery bank which can have a total weight of almost one ton (2000 pounds) so your single wide will not be able to support this and you will need a separate storage shed or garage to install this equipment. If you install a quality inverter that is sized properly you can use almost any type appliance, but don’t forget that most well pumps are 240 VAC and most inverters are 120 VAC so you will either need two inverters or a step-up transformer if you have a well pump.

Good luck!

Jeff Yago

EPA wood stoves

Dog bless the EPA. They have made my new wood stove so clean-burning that it just doesn’t act right. It seems to me that I’m using more wooe than needed. If I fill it with wood and close the air control, it burns at the same high rate as with the control open.

I can’t find any information online about this. Is there some way to defeat the low-emission features and enable me to “bank” my fire for the night?

Todd SeCoy


I know what you mean. A generator manufacturer we have represented for many years made a really great residential size home backup generator with a 1800 RPM cast iron engine. This low RPM unit would last forever, but in the mid 90’s, new EPA regulations were implemented that this low speed engine could not meet so they stopped making them altogether and now you must buy a larger model with a 3600 RPM engine that meets the new EPA regulations but does not live long due to the higher RPM and light weight engine. Also, the larger model uses more fuel than the smaller unit that was killed off.

During one winter under Jimmy Carter, he mandated that all Federal buildings had to set their thermostats down to 68 degrees due to the energy crisis. I was involved in facility engineering at that time and almost all large office buildings could easily stay above 73 degrees in the winter just from the heat of people and lights without using any heating. In order to meet this presidential dictate, we had to run the air conditioners in many of these buildings to “lower” the space temperature since most high rise buildings no longer have windows you could open and these large internal heat gains could only be reduced using the air conditioners! Just another mindless regulation made by people who do not realize all the un-intended results of their decisions.

As to wood stoves, it depends on the type you have. All new EPA approved wood stoves have either a catalytic insert near the flue outlet or require baffles to pass the intake combustion air around the fire box to pre-heat the air first. It sounds like you have the baffle type as the combustion air intake is usually a “grille” or series of vent holes under the stove bottom, not the old style “damper” you could open and close off. I do not know how your stove is designed, but your air control may be more cosmetic than functional, and most of the combustion air may be entering at the bottom or rear through a much larger opening.

A final note, many newer stoves do not require the large flues that older stoves needed to get a good draft, and if your flue is too large, it may be causing the stove to “suck” air around any draft closure you are trying to damper the fire. I would put this back on the sales outlet where you purchased the stove for their input.

Good luck,

Jeff Yago

Solar-run water purification


I was wondering what batteries you believe would work best for a solar run water purification unit. Are there ion batteries available? They must be sealed and ranging from 160 to 200 amp.

Thank you

Devera Denker


Sorry, but not enough information to make an informed guess.

Sealed could mean AGM batteries which are better for “float” service where batteries are kept at full charge and only occasionally need to be discharged. Sealed gel batteries are better for daily cycling and cold temperatures.

You did not indicate voltage and amp load of purifier, and if the battery will be charged each day and if it will be deeply discharged each night. Will it provide power for several days with no sun and deeply discharge, or is the load small in comparison to battery capacity.

Batteries are usually sized based on their voltage and amp-hour rating. Saying 160 to 200 amp would normally mean the load is this big, but most water purification units that use ultra-violet light are usually a small power load so I assume you actually mean 160 to 200 amp-hour. I also assume this is a 12 volt DC system but you did not say and this would change the number of batteries in series or parallel.

Not sure what you mean by ion batteries unless you are talking about the small lithium-ion batteries. These do not like to by cycled very deeply and will only last about 2 years.

Hope this helps,

Jeff Yago

Off the grid

Dear Jeff,

Having recently bought some land in Missouri that is located out the the sticks and very much at the end of the power grid. I have pretty well deduced that I will need some back up power.

Recently I have discovered the website and a number of your articles. As one who is not totally familiar with alternative power IE wind, solar everything I read seems only to confuse me more.

With interest I have read about l-16 industrial batteries for a battery bank in some articles. In an article about adding a solar cell to a truck camper a RV/marine battery is recommended. Since RV/marine batteries are easy to find and will take to repeated charging wouldn’t they be logical choice for a battery bank vice the harder to find L-16?

I have noticed too that with wind power most often suggested is a dc wind generator that requires upwards of 6 or 7 kts of wind to operate. In searching around I have found a source for a AC wind generator that begins operation in the sub 7knot range. AC generators have to best of my knowledge a big advantage over DC generators and that is in size of the cable between the transmission line from the tower to the battery bank. An ac generator can use a standard ac power cord and suffers no loss in current between the tower and batteries.

I have to admit that my understanding of the way a ac generator works is taken from the following website: On the opening page there is a photo of a customer using 9 ac wind generators on his farm in Wisconsin. Although wind power as such is confusing to me I believe that this ac system must be quite good or the farmer who had added to it and bought these generators would not be doing so if they weren’t efficient.

Perhaps you can give some insight into battery banks and DC versus AC generators in a future story. Also the battery bank issue of l-16 versus marine batteries is very confusing to a novice seeking information like myself.

Any information you can provide along these lines would be greatly appreciated.

Thank You

Keith McElroy


Lots of questions! Actually you are talking about “L-16” batteries, not “I-16”. When I suggest using an RV/Marine battery, you will find that it is for a small 12-volt DC system that does not have a large load that would fully discharge it each day. These batteries are much heavier duty than a typical car battery, and most have re-combiner caps and do not need to add water. However, they will NOT hold up to a daily deep charge/discharge cycling like a solar powered home or cabin. For these larger loads and system sizes, the lowest cost battery designed for a heavy charge/discharge cycling each day is a 6-volt golf cart battery ( T-105 size). These are less than $100, and can be found at most big box stores during the summer months. They are about the same size as a car battery, but because they are 6-volt, the plates are very thick and very heavy.

For a 12-volt system you will need two 6-volt batteries wired in series, and for larger systems you will need 4, 8, or 12. When you start getting above 8 batteries of any size, its better to switch to a larger amp-hr battery and stay less than 16, as this can cause problems with un-even charging and dis-charging when you have multiple strings of parallel batteries.

I think you are caught up in the AC or DC debate as a marketing ploy. There is no engineering difference in the amount of wind it takes to turn a wind turbine based on AC or DC output voltage. Wind energy is a “cubic” function of the area of the blades, and below around 7 MPH I think you will find most small-scale generators will not provide any real power, although the blades might turn. There are now both AC and DC wind turbines and each has its advantages, but only in wiring and additional equipment that will be required.

A 24 or 48 volt DC output wind turbine is very easy to add to an existing solar-power system, and some models have built-in charge controllers and can be hooked directly to the batteries. Yes, this will require a larger wire size since the voltage is lower, but the ease of wiring is its real advantage. Also, unless you are talking about some huge wind machine on a 150-foot tower, the difference in wire costs would most likely be less than 50 cents per foot for the larger wire caused by using a lower voltage DC model. An AC wind turbine can use a smaller wire size since the voltage is higher, and these are usually designed for grid-connect systems without batteries. There are a few other issues, but you cannot say an AC unit works better than a DC unit having the same size and blade design, and the reverse is also true.

Good luck!

Jeff Yago

On demand water heater used for hydronic heating

Hello Jeff.

I really appreciated your article in Backwoods Home Magazine on Hydronic Wood Stoves, as well as many others.

I have been interested in the practicality of setting up a propane on-demand water heater in a small off-grid cabin to provide both domestic hot water, as well as hydronic space heating. I have birds that do not do well with wood stoves or with un-vented propane, but need a somewhat constant minimum temperature of 60 degrees F. I was thinking to be able to dump hot water into a water tank (say, an old water heater with insulating jacket removed) in the space, which would act as a thermal mass slow radiator. My only quantry is how to pressurize the system to return water to the on-demand water heater. Do you have any thoughts on this, or criticisms in general of this setup?

Thank you for your consideration.



Please read this very carefully – it is possible to do what you want to do, but there are many design issues that most do-it-yourself type installations do not resolve and usually end up destroying the instant hot water heater. First, any heated hot water also used for space heating most first heat a pressurized storage tank. This does not need to be large, but it must use a second pump to circulated the heated water through any radiation or in floor heating loops.

Second, if you route the same “drinking” water through the heating system and do not use a heat exchanger to keep them separate, then your pumps will need to be stainless steel, the tank will need to be glass lined (use an electric hot water tank), and all piping in the heating circuit will need to be copper or brass, and no lead solder used anywhere.

Almost all instant in-line heaters will have a disclaimer that voids the warranty if you re-circulate hot water that was already heated back around and through the heater again. This is because their heating coils and flow rates are based on cold ground water entering the heater. If you re-circulate hot water, the heater will over-heat and damage some of the parts. Also, the built-in thermostat will not know what to do if it “sees” hot water entering the heater.

The storage tank and related valves and pumps allows the water in the heating loop to keep re-circulating at the desired flow rate back to the tank, and the separate pump only cycles flow through the heater at a different flow rate when the tank temperature drops. Even then you will most likely need to operate the domestic hot water temperature much hotter than desired, and install an automatic tempering mixing valve to limit the water temperature of the water going to the bathroom and kitchen faucets.

I have designed and installed a few of these systems, but found its much less complicated and will take up less space if you have an instant gas-fired domestic hot water heater for sink and shower hot water, and a separate packaged gas or wood fired hydronic hot water boiler. These are very small and very efficient.

Finally, remember that many of these components have tiny orifices that will freeze and break if this home will not be heated during cold winters.

Good luck,

Jeff Yago

Diesel alternator


I have several question about diesel alternator. First of all I want build micro hydro system using diesel alternator. That means I just take the alternator and using water to rotate the turbine and the alternator will produce the power. Do you think this system is possible to do?

Before this I use the car alternator, and the problem is before alternator connected to the battery I get about 3000 RPM, but when I connect the alternator to the battery and field current occur, the RPM dropped to 500 RPM. So the alternator can’t produce the current. So I want try using diesel alternator.

Since we know diesel alternator power output in AC, so no field current needed. If I get around 3000 RPM, whether diesel alternator produce the power? Or it same with car alternator.



First we need to clarify that all alternators have an AC output, regardless of being installed on trucks or cars, that is why they are called alternators. Until the early 1970’s all cars and trucks had DC generators, and since the DC output required brushes that would constantly need service, they were finally phased out with alternators which have no brushes to replace. There are different types of alternator designs, but all have a bridge rectifier mounted on the rear which converts the AC output to DC for battery charging. Some inverters “self-generate” their own field current and some more expensive models have permanent magnets which can really generate the amps.

Your main problem will be RPM. Almost all alternators need to operate in the 600 RPM or higher range and their pulley sizes are determined and sized to provide this RPM in relation to the engine speed. It will be difficult to build a hydro system that turns this fast unless you use some form of indirect belt drive to change the RPM. There are many web sites that provide details on how to convert an alternator into alternative energy use although most are related to wind energy. Since you have the same type design issues, check out these links:

Good Luck,

Jeff Yago

Grants for solar

Where might I find information about free grants to install solar panels or an inexpensive way to finance the installation of the solar panels?
Misty Brice
I receive many emails like this and you will not like my answer. Solar is expensive, and some countries like Germany provide very heavy “buy downs” to make it affordable there. Some states like California and New Jersey have their own version of solar rebates, and some utilities that are having problems meeting higher demands are even offering some form of solar rebates.
Unfortunately, although most of these started with very good intentions, after a few years they become so plugged up with added forms, additional inspections, insurance requirements, and more overhead that most installers just raise their prices to a level that totally offsets any price reduction benefit.
I believe the market will adjust supply with demand and establish a fair pricing level for all, but again, this is hard to do when some areas of the international market is not playing by the same rules.
There is some form of “Energy Office” in every state and they would be able to help you if there are grants available where you live. I suggest staying away from those out there promising to “Lease” or some other form of time payments, as most of these are tax related arrangements that heavily favor them, not you.
For example, in these third party arrangements, the “leasor” could lease a solar system that is installed on your house, you pay them a big cash down payment and so much a month, then they default at the bank where they borrowed the money to buy the solar system, then the bank sends somebody to your house and rips it off your roof, and sometimes they are not too concerned about plugging any holes they leave behind.
If you can’t afford solar then perhaps you should not buy at this time. As an alternative, many solar systems are “modular” and if you start with the right basic hardware, you can add the more expensive solar modules a few at a time as you have the funds.
Good luck,
Jeff Yago

Wind power

I was wondering what power would be needed or how big of a wind/solar set up would be neeeded to power 2, 12.5 hp motors running at about 6kw each?

You have provided almost no information for me to help you other than to say a really really big one!

Normally, a standard electric motor nameplate is its maximum HP rating, and most motors are selected using the next largest size for a given load. This would mean a 12-1/2 HP motor may have been chosen for a 10 HP load or even smaller. However, due to motor and drive efficiency losses, we usually use 0.9 KW per Horsepower, not the 0.7457 kW from tables. If you say each motor is a 6 kW load, did you measure it? Also, any motor this large is 3 phase, so you will be talking about a very large wind turbine system to meet this load with a commercial 3 phase output. Finally, you did not say if the motors operate only when the wind is blowing or 24 hours per day. My advice – buy a generator!

Good Luck,

Jeff Yago

Passive Solar/ Photovoltaic System Home Design Question

We have a piece of raw land located in the upstate of South Carolina (zone 7, upper 90's for a month or two to a light dusting of snow maybe twice a year) with a sloping southern exposure but no existing shade trees. We want a passive (and active) solar home designed specifically for the site, and situated properly to take advantage of a fabulous West to East summer breeze.

1. Is there a tool that will ACCURATELY measure June and December sunlight angles so that we optimize the orientation of the house on the site? (The site is 400 miles from our current home, but we can visit it during these months to take readings.)

2. (Pardon this nutty question)Is there a tool that we can place on site that can passively record mean prevailing wind information as the seasons change? (We think the great summer breeze could turn into an ugly wind in the winter, but we are not there enough then to be sure.)

3. Can you suggest a definitive PV and passive solar design "bible" that we can reference to begin our design process with our architect (my dad!) so we can get the overhangs, window placement, and standing seam metal roof pitch JUUUUST right?

We have about three years to gather the sunlight and wind information and complete our design while my husband finishes up his service in the Marine Corps.

I TRIED to keep it short, ;) Thanks!

Laura Cobham
Liberty, South Carolina


Not sure why you want all this site data, as it is not normally required to design an alternative energy system. There are many low-cost solar calculators and several free on-line sites that can provide this information. If we know the site latitude, time of day, and month, you can easily find all three sun angles for ANY place in the world without the need to measure anything.

The same sources can provide weather data and solar data to help estimate available energy, although these are 10 year averages and will not be exact for a specific month.

There are also wind charts for each state that show prevailing wind directions and speeds by month, but wind tends to be much more site specific and height above ground is the real measurement you need, not ground level.

Yes, there are many meters available to record all this is you really want to, but they are expensive and all you will end up with is a record of the years you made the recordings, not future data as the weather does vary from year to year.

In the non commercial and smaller solar and wind applications, window and solar array orientation are far less critical, as all you are doing is changing the time of day the peak will occur. For example, a window or solar array facing 15 degrees west of due south will “see” the sun maybe 20 to 30 minutes later in the morning, but will still have direct sun 20 to 30 minutes later in the evening. If I am designing a solar home in an area with very overcast or foggy mornings but sunny afternoons and evenings I face them more south-west or even due west. I have had to install solar arrays facing due east at some locations where a large cliff or mountain totally blocked the afternoon sun. We typically locate bedroom windows on the north side (cooler), and bathrooms on the east (early morning sun). Large glass windows facing due south can really overheat a room if there is not lots of thermal mass, and all your furnishings will fade. We use very large roof overhangs to block summer sun.

There are several good solar books listed in the book store section of this magazine.

Good luck,

Jeff Yago

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