Alternative energy advice from Ask Jeff Yago. Volume #19

Ask Jeff Yago
Solar & Energy-Related Issues

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

Sorry. Jeff no longer answers questions online

Low RPM genrator

Dear Jeff

I am looking for a low rpm (70 – 200 rpms) AC 1120volt 2kw to 5kw (preferably no cog) generator I can put on a vertical wind turbine.

I am searching the internet for providers and came upon your web site.

Might you have a word of advice or direction?

Thanks much.



You are asking the impossible. The only generators I know of that operate even close to this low speed are major power plant generators in the 1 to 2 mega-watt range, and the slowest of these are 400 RPM.

The problem is producing the 60 cycle per second reversing current that is required for all 120 VAC power applications. You cannot generate this 60 cycle/sec with a multi-coil generator that turns this slow. Also, an AC generator must rotate at a constant speed or the 60 cycles per second will speed up and slow down.

If you would try to power a motor driven appliance with this system, as soon as the cycles dropped down to around 30 cycles per second, the motor would stall and most likely burn up. A light bulb would get dim and then bright as the wind slowed down your generator then speeded it up. You would have no way to maintain a constant voltage and frequency which all appliances require.

Most wind driven generators are either DC generators or DC alternators. This DC power is then used to directly charge a DC battery bank, or is transformed into 120 Volt AC @ 60 cycle using an inverter that is designed to take a DC voltage and current input that are constantly changing with wind speed.

Most homemade wind generators use truck alternators and a belt drive system to speed up or slow down the RPM as required. A major problem with homemade units is a way to slow or stop them in very high winds or they will self destruct.

Hope this helps,

Jeff yago

Solar water well problem


I have a solar water well in my pasture for the cattle, which was really great last year when we had the drought. this well was on the property when we bought it and now it has quit working, we’ve cleaned the panels and the wire but it still is not pumping, any suggestions?

Thank you

Susan Jones


We have designed and installed many of these systems for local farmers and the biggest call-backs we receive is due to cattle destroying the float switch in their drinking tank or the wires to this float switch. This would be the first thing to check as most solar water pumping systems have some type of control to turn them off when the tank they are filling gets full. Also, some drilled well pumps have a float switch near the pump elevation is they are slow re-fill, to protect the pump by shutting it off if the well water gets too low.

Since a solar panel is fairly durable, these float switches are usually the problem with these systems. Most solar pumps have a controller mounted nearby to boost the current from the solar panels to avoid stalling out the pump at low sun conditions. If you can access this controller, it will have clearly marked terminals for the float switches and if there are wires to these terminals, then you have these switches connected and this is where you can either remove these wires (one at a time) or “short” out across the terminals where a float switch was connected to simulate the float switch being “open” or “closed”. This will tell you which float switch is bad or the wires are broken or shorted out. Of course I am assuming this is a low voltage DC system and you take proper safety measures.

While at the controller, most have a small LED light that indicates if the solar panel is providing power. If not, check with a volt-meter on both the wires coming from the solar panel to this controller, and the wires leaving the controller to the pump, to make sure the controller has not failed.

If all this checks out, the final check is the pump. Many small DC solar pumps will fail in about 6 years (although our deep-well DC solar water pump has been working for 14 years so far without a problem). Most of the better brands have replacement kits you can order parts to re-build yourself if the pump has failed.

I am assuming your system does not have a battery and just operates the pump during the day when the sun is up. If you do have a battery, these rarely last over 3 years in outdoor applications due to major temperature swings and may need to be replaced. However, very few solar pumping systems use a battery.

Hope this helps, let us know how it goes…..

Jeff Yago

48 volt battery bank and a 12 volt charger

Hi Jeff,

Great read and your knowledge seems to be tempered with a fair degree of wisdom.

Now for the unwise question. What would happen if I connected a 12 volt charger to one battery in the middle of my 48 volt battery bank? Would the input equalize over the whole bank or would I be damaging the charger and/or the batteries.

Currently the batteries are connected to an UPS.


Kindest regards

Brendan Kehoe


First, it would depend if the individual batteries are 6-volt or 12-volt that make up the 48-volt battery bank.

Assuming they are 12-volt and you connected a 12-volt charger to just one battery, the current would flow just through the one battery as this is the only complete circuit. The balance of the battery bank does not complete a circuit that would “circle back” around to the charger unless you connected the positive and negative leads together and that would be a very very bad thing – melted cables and possible battery explosion!

However, I don’t know why you would want to charge just one battery. Lets assume you charged this single battery to a state of charge higher than the other batteries in the battery bank. As soon as you connected the battery bank to a load, this would immediately “draw-down” the higher charged battery because all the cells will try to reach the same voltage level.

This is what happens when you equalize a battery bank. Any already fully charged cells will “boil” off gasses until the lower charged cells reach the same level of charge. I see no reason to do this unless your 48-volt battery bank is not being charged and you only have a 12-volt battery charged and are trying to charge each battery separately.

Its not good to have any battery in a string that is charged much higher than the others.

Hope this helps,

Jeff Yago

Solar water heating for campervans, motorhomes and RVs

Dear Jeff,

I’m hoping to develop a low tech, low cost solar water heater for use in a camper van. As such, it needs to be capable of supplying sufficient hot water for showering and dish washing for a family of four.

Assuming two daily wash-ups, and each family member showering perhaps every other day (we are roughing it in the great outdoors after all), daily water usage should be fairly small. I’ve seen the commercially available ‘Solar Shower’ bags, and have read about water-filled truck inner tubes and the like, but I’d like to develop something a little more sophisticated, if only to impress my (slightly more smelly) campsite neighbours!

Initially, I planned to make an open thermosiphon type system, utilising an insulated ground level collector, incorporating a secondhand refrigerator matrix, with a suitably sized storage tank sited on the van roof. This would be fine assuming we’re pitched up for a day or two- more often than not, we’re on the move for much of the day, and pitch camp in the evening- so any system would need to be permanently installed in/on the van and capable of making use of the sunshine on the move during the day.

Due consideration would have to be given to reducing the effect of cooling air passing over the collector while driving, but would a closed, pumped glycol based system, with a heat exchanger and on-board storage tank be feasible?

What precautions would I have to take regarding temperature and pressure build up, and how would one calculate the various capacities involved?

As you may have guessed, this idea hasn’t even reached the drawing board yet, but I’d be keen to hear your views, even if it’s to dismiss it out of hand!

Thanks for your time.



You may want to check out the next issue of Backwoods Home Magazine (#108) as I show how to mount solar electric modules on a trailer which can tilt up.

Back in the 1920’s and 1930’s Florida did not have any piped natural gas or propane, and those homes with electricity back then usually only had one or two 15 amp fuses for lights and the radio. The did not wire homes for large electric hot water heaters. Therefore, almost every family home in Florida during this period had commercially made solar hot water heaters. The located the solar panel at the lowest part of the roof just up from the roof eve, then they cut a hole in the roof at the peak and stood up a hot water storage tank. They piled insulation around this tank which stuck up above the roof eve then fabricated a fake chimney around it to hid it. They did this so the tank would be much higher up than the solar hot water panels which allowed thermo-syphening and did not require a pump. Back in the late 1970’s we removed one of these old solar hot water heaters from an older Florida home that was still operational and replaced with a new system.

If you also want to use a thermo-syphen system, you must have the solar module as low as possible and the storage tank as high as possible. If you operate in colder locations you will need some type of anti-freeze. However, commercial solar hot water heaters are required to use a double-wall heat exchanger due to the danger of the heat exchanger getting a leak inside the storage tank and letting anti-freeze leak into water you could be drinking. Ethylene-glycol (automobile anti-freeze) is very poisionous, but propolene-glycol (red food coloring) is not poisionous and this is what they sell in RV stores for winterizing an RV. The problem with any system that uses anti-freeze is this reduces the heat transfer efficiency of the water mixture, so there is a down-side if you must prevent freezing.

If you can utilize a small DC powered pump, you will not need any anti-freeze. You have a small insulated non-pressurized holding tank just below the elevation of the solar panels. When the sun starts heating the panel, the pump is turned on and moves water up into the solar panels flowing from the bottom to top. When the sun goes down the pump shuts off and all the water drains back into this small holding tank, which is NOT the hot water storage tank. Your hot water storage tank will need a heat exchanger for this heated water to pass through as it moves back down from the top of the solar panels through the heat exchanger then into the small drain-back tank.

They also make special controllers that you connect a temperature sensor on the solar panel and the other in the hot water storage tank and it will turn on the pump anytime the solar panel is hotter than the water in the tank.

Since the solar panels are empty when the pump shuts off, there is nothing to freeze.

There are lots more to the design of these systems, but this should get you started.

Good luck,

Jeff Yago

Utility disconnect


I am installing a 1kw solar grid tied system with an Outback VFX 3524 inverter.

The local utility requires a system disconnect next to their meter. The local utility has determined the placement of the disconnect device outside the home but they will not indicate what size or model of DG disconnect should be used for this installation. My electrician is also uncertain of what is required here.

Can you recommend a suitable outdoor rated disconnect for this installation? Is the size of this disconnect determined by the the output of the solar (1kw max) or the 3.5 kw inverter?




First, make sure your VFX Inverter was ordered for “sell-back” grid inter-connect (Model #GVFX3524) as the basic VFX models do not have this optional feature and will not work in grid-tie mode.

Second, a 1 Kw solar array will have very little capacity to sell anything back to the utility grid after charging a battery bank, so this may not be worth the trouble until you enlarge the solar array.

Finally you have hit a raw nerve with all of us in the solar industry as these outside dis-connects are next to worthless and serve no purpose. All solar inverters labeled as meeting all requirements for grid inter-connection will shut down the micro-second the grid goes down and will not put out any power. This is because by design the inverter is constantly measuring the voltage, current, and sine wave form coming from the grid in order to match it for power sell back. If it can’t find the grid it cannot function and shuts off. This means the only purpose for this switch is if the Power Company “thinks” their linemen will shut this switch off if they are working on the lines in the area as a safety precaution.

However, I have not met any linemen that had any idea there was a solar power system anywhere near where they were working on a line, and they do not have record books they carry around that can cross reference the location where they are working with any solar homes around them. Also, many people blow up their portable generators each winter when the connect them into their dryer outlets to back feed their home during a power outage. This works great unless the forgot to turn off the main house circuit breaker and then as soon as the power comes back on their generator is toast. Because some people actually do this and back feed into the utility line during an outage, this 120/240 VAC power goes up to the house side of the utility pole transformer and comes out on the utility line side as 480 volt or higher which can kill a lineman not expecting a downed line to be energized. This is why linemen are taught to place grounding clamps on both sides of the line they are working on just in case the load side is being back-fed from something unknown.

Now back to your problem. Since this is a requirement of your local utility and not the National Electric Code, the type of dis-connect is determined by them. For example, some utilities allow just a rain-proof circuit breaker that is labeled as the “Solar Disconnect”. Some utilities require a dis-connect with a lever handle that can accept a padlock, and some really nasty utility companies require a very high cost lock-out switch with a window in the door that you can see when the switch contacts are open. Since the most power you can sell back with a 1 kW solar array is 8 amps @ 120 volts (1000 watts / 120 volts) plus 10% added efficiency losses, and since circuit breakers are usually sized for 125% of the load, a 10 amp circuit breaker or dis-connect switch is close enough for your application.

Keep in mind your inverter is 120 volts AC and your utility power is 120 / 240 volt split phase, so you will only be selling power back on one leg of their 240 volt line. Square D makes a nice outdoor un-fused dis-connect with an external handle that can be locked. Most utilities are allowing this switch, but the smallest it comes in is 3-pole with a 30 amp rating so its fairly large for your application. See if they will allow an air conditioner type 10 amp 120 VAC outdoor dis-connect. It does not have a lock type handle, but they will never use it anyway!

Good luck,

Jeff Yago

GTIs and Inverters


Is it code compliant to have an Inverter on a trailer and tie into the grid, as long as the GTI is located attached to the home/Grid service?

I have a mobile solar system & battery backup that I would like to tie into my home grid while parked in my driveway.




I have enough trouble trying to figure out how a local code official will rule on what I plan to install, let alone systems by others! Also, we do not want to get into specific code issues in this forum due to the many unknowns about a specific installation. However, I can provide some general information.

Since you could remove the wheels on your trailer and attach it onto your home, nothing changes from this arrangement if it stays portable, except the grounding. I am not aware of any specific codes that would keep you from using a portable system, and most likely this would be viewed the same as using a portable generator to power your home during a power outage.

The National Electric Code (NEC) article #445 deals with generators in general, but you should review Article 250.20 “System Grounding”. It includes how a remote generator is wired and grounded to the main system, and also addresses what is called a “Separately Derived System”. Without getting too technical, the grounding and neutral “bonding” connections are different, depending on if you will be using a transfer switch that switches the “neutral” conductor along with the “live” conductors, or if the neutral is not switched. In other words, its how the transfer switch is wired and the number of poles being switched that determine how a portable power system is wired into the house panel, and not if its on wheels or not.

Your safest path may be to purchase a transfer switch from a generator dealer that has the capacity you need and wire this the same as if your portable system was a portable generator. The next issue of Backwoods Home magazine (#108) will have an article I wrote about my portable solar power trailer. Please note that I use a 4-foot copper clad 1/2″ steel ground rod and bare copper ground wire that is attached to the grounding buss bar in the trailers circuit breaker panel. I drive this into the ground when I am using the trailer to power off grid tools and lights. This also helps to make sure the GFI breakers operate properly since the trailers electrical system would normally be insulated from earth ground due to the rubber tires. Its not the same as the 8-foot long ground rod required by the NEC for homes, but then its better than nothing and they don’t have to pull theirs up each time I move! I also will pour water aroung the area I plan to drive the temporary ground rod if the ground is very dry.

Stay safe,

Jeff Yago

Double duty for a Honda/Yamaha inverter generator


I have a remote cabin that I am currently running off of a Honda EU3000is generator. I am planning on adding a battery bank, inverter and solar panels at a later date as funds allow. In order to save money now, I was thinking that I could buy the battery bank and hook up the battery bank to the inverter on the EU3000. Why not use the EU3000 inverter for double duty? I could get 110V pure sine wave power off of the bank or the generator.

There would still be the issue on charging the battery bank (you would need to purchase an appropriate charger for the bank) – could you charge the batteries from the EU3000 and run the EU3000 to provide 110V power simultaneously. I would then add the proper pure sine wave inverter to handle the solar panels, charging the bank from the EU3000 and to provide 110V power.

Too complicated? Not any monetary savings? Crazy idea? How would you go about engineering the system so you didn’t hurt anyone or damage/destroy any electrical equipment?


Paul Chan


This is a standard layout for a generator based off-grid homes without solar. I would match this with a Xantrex 4024 or an Outback 3624 inverter if you plan to expand later, but these are a little large for your 3 kW generator, and you will need to adjust the battery charger setpoints or they will overload the generator. In addition, these inverters can be programmed to “assist” a generator which means during battery charging and also supplying other 120 volt loads from the generator, if the generator demand goes above setpoint, the inverter will first back off the charging to reduce the load.

If the load still is increasing (like starting a well pump for a few minutes) the inverter will take some battery power back and “assist” the generator to avoid over-loading. You can even program either of these inverters to start the generator when the battery charge level drops below a minimum setpoint.

For this type system, its best to operate your LARGEST loads while the generator is running and also charging the batteries, instead of first charging the batteries then stopping the generator and powering the same loads from the inverter. Since there is a loss of efficiency during the charing process and again during the inverter process, large loads are better operating only when the generator is running and supplying the power directly.

Since the solar array will have its own solar charge controller, this will be totally separate charging system, although it will be charging the same batteries so you can add the solar later. You can also add solar modules a few at a time since they are expensive, but get the charge controller that will be large enough from the start so you don’t have to keep upsizing.

Good Luck,

Jeff Yago

Bike energy?

Hi Jeff,

I was wondering why someone hasn’t come up with having an excercise bicycle set up in their house hooked up to generate electricity for the house.

Has that ever been tried before? Bike in the home for 2 hrs a day and live off the grid?



Like all good ideas, others have thought of it before us. Over the years there has been several different manufacturers of this product. Some are like a bike stand so you can use your own bike, and others are like exercise bikes with just one wheel.

The most recent entry is the “Human Power Trainer” at

Good exercising!

Jeff Yago

Solar collector on a trailer

Hey Jeff.

I heard about a 30 amp solar collector that was built on a trailer. I thought by Independent Energy Systems. But I can’t find them and was wondering if you had any info. on portable solar collectors.




Not sure what you mean by a “30 amp solar collector”. This is not usually how we reference their capacity. If you are talking about a “30 watt” solar collector (we call them solar “modules” if the generate electricity, and solar “panels” if the make hot water), but a 30 watt solar module would be about 10″ X 36″ in size so it would not need a trailer. If you are talking about a 30 kW solar array, this would definitely require a semi-tractor trailer to move around as it would be over 90 feet long.

If your interest is trailer mounted solar power systems in general, check the next issue of Backwoods Home Magazine (#108) as I will have a 2-part article on how to build your own using a 6 ft X 12 ft enclosed utility trailer.


Jeff Yago

Starting out the right way

Hello Jeff,

I was hoping you can point me in a right direction :

Question#1 – I live in eastern Canada and am looking for material/reference /books or guidance from you on starting out with solar (ie) Solar panels – generator-battery and banks – hooking up ..consumption would be for approx 6 months a year including a small fridge, tv, radio and possibly 4 cf lights. (wood stove would most likely be my heat/cooking source since my place will only be approx 12×24 on beam posts )

Question #2 with question #1 in mind, I would like to adopt a system to add to the panels /batteries in the future for a permanent residence .

Thanks for you time Jeff .keep in mind when you read this, I have 0 experience in this field, so all the help I can get would greatly be appreciated.


Dan Miles


The best advice I can give you is to go back and read the many articles I have published in Backwoods Home Magazine over the years on this exact same subject.

Check out –

  • Water – A safe supply when you are off the grid – Sept 2001 Issue #71
  • A solar Primer – Nov 2001 Issue #72
  • Battery Powered Weekend Retreat – Sept 2003 Issue #83
  • Solar Power 101 – Batteries – May 2004 Issue #87
  • Solar Power 101 – Batteries cont. – July 2004 Issue #88
  • Solar Power 101 – Inverters – Sept 2004 Issue #89
  • Solar Power 202 – Solar Arrays – Nov 2004 Issue #90
  • Build your own solar powered water pump – Jan 2005 Issue #91
  • Build a solar powered Outdoor light – Mar 2005 Issue #92
  • The care and feeding of Solar Batteries – Sept 2005 Issue #95
  • Walden Pond – The solar version – May 2006 Issue #99
  • Walden Pond – the solar version, part 2 – July 2006 Issue #100
  • Solar powered Refrigerators – Nov 2006 Issue #102

You can read many of these on the web site, but I suggest ordering the back issues on CD. They are low cost and include all of the graphics.

Good luck,

Jeff Yago

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