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Ask Jeff Yago
Solar & Energy-Related Issues

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

Converting to solar

I have been trying off and on for a year or two to get answers about making my house solar powered or at least partly solar powered. Every time I have emailed or called someone I never get an answer about how to do it. I don't want to go messing around with my electrical system myself and mess it up or get shocked. I also work quite a bit and my time is limited.

I live in St. Louis county in Missouri. Can you give me any advice or maybe there is something better for me to do than solar?

Sincerely,

Tim Randolph.

Tim:

In the past 10 years I have had numerous articles in this magazine about home energy, how-to solar projects, solar-powered cabins, solar powerd pumps, energy saving appliances, and emergency solar power systems. I suggest you start reading these back issues and get a good understanding of the basics before contacting these dealers and suppliers who are blowing you off.

We get hundreds of calls each week and many are people who know what they want and how it works. We barely have time to deal with all these contacts let alone time to talk to somebody who does not have a clue what we are asking and have to keep explaining to them every single term we are using. This is what you are running into. The first questions any of these dealers are going to ask you is - are you wanting an off-grid or on-grid system, will it have storage, will it do sell back, will the array be roof mounted, ground mounted, or pole mounted, liquid or gel cell, and similiar questions to help them find out what type equipment you will need. If you cannot answer the questions I just asked, you will need to do some reading!

Good Luck,

Jeff Yago


60 watt solar system

Hi Jeff:

Thanks for being available to answer questions:

I purchased a 60 watt solar system from Costco to keep my travel trailer batteries charged. The batteries are two 115 amp. The system appears to work for lights but when I use any electrical appliance it shuts down. My question for you is: Could the inverter that came with the system be a block to full delivery of the needed amps from the batteries.

Also, since the two 12 volt batteries are connected in series does this make the system a 24 volt? Is a possible solution then to disconnect the two batteries from each other and charge one at a time. Maybe I need a larger inverter?

I would appreciate your comments and recommendations.

George

George,

No reflection on Costco, but most of these "retail" solar products are too light weight to provide any real backup power. I put these in the same category as those car emergency kits that include a toy hammer that could never break glass, a toy cutter that could never cut a seat belt, and a cheap flashlight.

The batteries are most likely wired in parallel for 12 volt operation, and they better be that way since all of the DC lights and appliances in travel trailers are usually 12 volts. The solar array size determines how fast the battery gets re-charged, not what loads the inverter can supply. Most likely the problem is your inverter is a "toy" and cannot handle any electrical load other than a few lights. For example, if you tried to power your microwave oven, it draws about 10 to 12 amps at 120 VAC. In order for any inverter to supply a 12 amp load @ 120 VAC output, it will require over 120 amps going into the inverter from the battery at 12 volts DC.

Your wire from the batteries to the inverter would need to be a #2 or larger cable, and I would have used a #2/0 cable to reduce the voltage drop if this wire is over 3 feet long. Also, as you see, your two batteries at 115 amp-hrs at 100% full means you have a total of 115 amp-hrs of capacity to get to them both to 50% discharged, which is as low as you should go to avoid battery damamge over time. This means operating your micro-wave oven, or equal size load for a total of 1 hour will drain your battery bank.

You need larger batteries, larger battery cables, a better quality inverter to handle any laods larger than a few lights, and about 3 more solar modules to keep the batteries charged.

Good luck!

Jeff Yago


Solar Inverter basics

Hi Jeff:

I am building a couple of solar systems and have been very frustrated getting detailed design info on inverters. A Ph.D. in Physics looks like a strike against me, but I did design microwave power transistors for a while and have some limited circuit background. Also used circuit analysis programs for thermal problems using equivalent circuits.

I just find the typical explanations pretty useless.

A super brief response would be helpful.

Wesley H. Weisenberger, Ph.D.

Wesley:

I am not sure what you are asking, if you are "building several solar systems" why not just buy an inverter, as there are many to choose from and today they are much less expensive. For example, you did not indicate a system size, but a very high quality inverter like the Outback FX3648 provides pure sinewave 120 VAC with a 48 VDC battery bank, and costs around $2,000 plus the added switchgear you will need (circuit breakers, fuses, wiring).

If you are asking for design information to actually "design" and build your own inverter I can give you some basic information, but my background is not electronic circuit theory. The first inverters were "square wave" units that just took a 12 vot DC input and used a transistor switching circuit to "reverse" the current using a 60 cycle per second timing circuit. This was much like the power supplies in original tube car radios.

This "square wave" was then passed through a transformer to raise the voltage to 120 volts and then used large filter capacitors to smooth out this current. As you know, you cannot pass straight DC current through any transformer, which is why it had to be "switched" first. This square wave output worked good for 120 VAC lights and power tools, but would not work with electronic equipment like TVs, stereos, microwave ovens, light dimmers.

The next step was to add additional "steps" in the switching circuits to produce more of a "stair step" switching wave form, with the voltage rising up in two or more "steps" before reversing to do the same on the back side of the simulated sinewave AC output. These "modified sinewave" inverter designs are still being sold as they are about half the cost of a true sinewave inverter and will power almost anything including most electronics and computers, but they still have problems with micro-wave ovens and some computer printers.

Most of today's "pure sinewave" inverters increased the number of "stairsteps" even more to generate an almost perfect 60 cycle smooth sinewave 120 VAC output using very small "steps" of voltage increases and reverses. Almost all use a bank of "FET" power devices mounted on a large heat sink, coupled to a heavy transformer and capacitor bank to smooth out the waveform. The higher quality models also have added micro-processor circuits to provide all kinds of digital display and safety alarms.

Inverters with output capacities above 2500 watts are only available in 24 and 48 volt models, and inverters above 4,000 watt range are usually sold only in 48 VDC input models to keep down high battery current flows and the higher costs for the electronic components to handle these high currents. For example, a 20 amp 120 VAC load on an inverter will have a 200 amp draw from a 12 volt battery bank, which is near the limit for most battery cables and DC components. However, at 48 volts this would only be a 100 amp load on the batteries and internal components.

Good Luck,

Jeff Yago


Old mill generators

I just purchased an old mill here in SC and along with it are 2 very large hydro power generators that have been stored for several years .One is a 1000 KW Westinghouse and the other is a 1200 KW General Electric.

I am trying to find a market to sell these to be used instead of just scrapping them

If you have any ideas please send me some contact info.

Thanks,

Mike Teal

Mike:

If I had just purchased an old mill with generators this large I would be looking into putting them back into service. With electric rates getting ready to climb through the roof in the next 2 years, these would provide all of your power needs plus selling lots of excess power back to the utilities. I would not scrap these as there are many old mills across the country that have been placed back in service by private owners and I am sure they are looking for replacement equipment and parts. As long as these have been protected from the weather they should be in good condition since they are just a rotating coil of wire.

Here is a friend of mine that is involved in this field who may be able to help you---> http://www.oldmillpower.com

Good luck,

Jeff Yago


Existing well convert to solar/wind

Mr. Yago,

I have purchased some property that has an exist ing well on it. It is powered by 230v 1hp webtrol submersible pump. I would like to convert it to solar/ wind for off grid applications when we lose the grid power out there. Being out in the sticks this happens a lot. Do you have any suggestions for transfer switch/ batteries/ controller/ inverter/ panels? Or can it even be accomplished using my existing pump?

Sincerely,

Larry Wiley

Larry:

This is a large motor load and would require a very expensive inverter and associated batteries, switchgear, and solar array to supply this large load. Since you would not want to spend about $15,000.00 for the basic battery-inverter system plus another $10,000.00 for a solar array just to power this single pump, most people would install the solar system to power ALL of their critical electric loads including the well pump which makes it more cost effective.

A far easier and less costly way to do this is install a SECOND well pump which would be located "above" the elevation of you existing well pump, and would have its own smaller pvc pipe up and out of the well. Since this would be a 12 or 24 volt DC deep well pump depending on depth, you could drive your truck over and power it using jumper cables during a power outage and just pump out into a large tub or barrels. If you want this to also supply the house piping system, you will need a check valve in each line from each pump before they are tied together into one line feeding the house. This will keep one pump from trying to pump back down into the well through the other pump which will be off.

Both pumps have to "see" a pressure switch at the expansion tank for proper control so we always install two switches side by side. The AC pump switch is set for 50 to 60 psi, and the DC pump switch is set for 30 to 40 psi. Since the AC pump is larger and will have much more pressure, it will always be the pump that satisfies the higher setting switch. However, when the AC power fails and the pressure keeps dropping below the low limit for the AC pump. the lower setting switch will activate the DC pump if it is connected to a source of emergency power.

If the depth of water is less than 50 feet, you may want to install a hand pump like you see in old westerns. They are still available but are only for shallow water depths.

Here is a recent article that may help: Build your own solar-powered water pumping station

Good Luck!

Jeff Yago


Solar refrigerator

I read your article from Issue #102 entitled "Solar-Powered Refrigerators" because my family and I were considering purchasing one for our backwoods cabin. It was very helpful and I have recommended it to my family as a good source of information but I was curious to know if you still had the SunDanzer and Sun Frost solar refrigerators and if so, how they are holding up with time.

Thank you,

Alex Walowicz

Alex:

We have owned both an RF-16 and RF-19 size SunFrost refrigerator/freezer since 1994 and two SunDanzer top load freezers since 2001. Since we have had the SunFrost units longer, we have had more repairs. Although SunFrost may still be the most energy efficient refrigerator made and are clearly designed for very long life, they have in my opinion, several problems that only recently have seen any improvement.

First, the door latch is plastic with slotted screw holes and both sides are attached with screws. If these get out of alignment, and they will, when you close the door they break off. Although they are cheap and easy to replace yourself, you better have several on hand. Second, the seals around the doors are made of a thin plastic strip that has been "crimped" into a "V" shape with peel and stick adhesive on one side. These also are low cost and easy to replace yourself, but they need to be replaced about every 2 years. The thermostat for the freezer compartment will fail, and this was clearly anticipated as the design includes a spare sensor built in when manufactured. When this sensor fails, and it will, you have to abandon the mechanical capillary-tube temperature sensor that controls the compressor and install a new electronic sensor that you connect to the extra sensor wires. The earlier models also had very-easy-to-break adjustable door shelves that would always fall off and break when over-loaded, but a recent design change has made these much better.

Finally, to achieve the very high energy efficiency, no SunFrost models have automatic defrost of circulating fans, so expect to learn how to defrost a freezer and refrigerator like your parents had to do. This sounds like a minor problem, but if you live in a humid area like we do, you can build up several inches of ice in the freezer in only a few months, and the back of the refrigerator section can build up an inch of ice over the entire surface in about the same time. Once this happens, the refrigerator section will no longer keep foods below 40 degrees as all the heat removal is going into keeping the ice from melting and your food will soon spoil. Since the refrigerator/freezer models have separate compressor and temperature controls for each compartment, it is possible during de-frosting to only turn off one compartment at a time. To avoid damaging the plastic interiors while chipping off the ice buildup, we just move everything into the section that is still operating, turn off the other section, and prop open the door. In about an hour you will hear the ice start to fall, which can usually be removed as one or two large sheets all at once. Then a quick wipe down, then reverse the process and do the other compartment.

The SunDanzer has a type of "lung" or bladder somewhere in the inner workings that expands and contracts when you open and close the top door. They claim this reduces the unit "sucking" in warm humid air after you re-close the lid due to the lower interior air pressure from the cold. This actually works as we have gone as long as 2 or more years without defrosting. To appreciate what is going on, if you close the door of a SunFrost refrigerator/freezer, you can clearly hear room air being drawn into the interior as it makes a hissing sound as it passes the door seals. SunDanzer does not make combination refrigerator/freezer units, while the SunFrost can be a 2 door unit having both sections. I thought I would have problems with a top load freezer getting access to foods near the bottom, but all SunDanzer models include a system of top racks mounted in a track system that lets you move the upper half of frozen foods sideways to expose what is stored below.

If you need a super-efficient 12 or 24 volt DC refrigerator that includes a freezer section, and you can handle the nuisance repairs described above, then I still recommend the SunFrost models. They are very expensive, but with regular maintenance they will last and last. If you can get by with just a freezer or just a refrigerator that must be super efficient and run on 12 or 24 volt DC, or can afford to buy one of each, then I would recommend the SunDanzer. I think they are just as energy efficient and require much less maintenance, but again they are top loading.

On a final note, all models from both manufacturers are either 12 or 24 volt DC unless something has changed recently, and since most off-grid solar homes are starting to use 48 volt battery banks to reduce wire sizes you will need a DC to DC converter to use any of these on these higher voltage battery systems.

Good luck,

Jeff Yago


Add a secondary generator

Jeff,

My question is about this article: http://www.backwoodshome.com/articles2/yago93.html

The article is great for getting started with solar/battery systems. I never knew it was so simple.

My question is, how would one add a secondary generator for days when the batteries are dead at night? Basically, I want something that will combine the power of the solar, with the power supplied by the alternator in my car. That way each power source can charge the batteries.

Thanks!

Anthony Hildoer

Anthony

Any boating supply store will have "dual" battery chargers, "dual" charge controllers, and "dual" voltage regulators. There are other solar suppliers you can check out, but for small 12 volt systems you can usually find these items at a local boating supply store. Almost all recreational boats have two identical batteries and a switch to allow changing from one to the other. This makes sure if you run down one battery while listening to radios or running lights while anchored out in the water, you will still have a fully charged battery to start the engine. The dual battery voltage regulators will charge the first battery then the second battery without connecting them to each other. That was the equipment used in the article.

On the other hand, if you wanted to also charge this battery from a separate energy source like a solar panel or small gas generator, just be sure to use the proper charge controller for each source which will allow charge to flow into the battery even if it is also being charged by other chargers at the same time. The charging current from the other charging sources will not "back up" into each other. As long as each charging source has its own charge controller, nothing will cause a problem with the other devices. However, if one of the charging sources has a much larger charge capacity or is set for a higher charging voltage than the others, it will take over all of the charging as the other charge controllers will "see" this higher voltage and assume the battery is fully charged and then stop their charging.

Good luck,

Jeff Yago


Air conditioning for a pickup camper

Hi Jeff.

I would like to put Air conditioning in my pickup truck camper shell to keep my dogs cool in the summer. It would only be in use when I was traveling down the road, not while the truck was turned off. Here was what I was thinking - could you offer an opinion on whether it would work or how to to do it, if it is even possible.

[I want to] put an RV air conditioning unit on the top of my camper shell and run that off an inverter connected to my pickups battery.

I do have a 2500/5000 watt inverter but I wonder if the air conditioning unit would suck so much energy that the alternator could not keep the truck battery charged up going down the road.. My truck has two batteries up front

Mike

Hello, MIke.

The problem is not battery size, it's your alternator capacity. There is no way an RV air conditioner can run off one or two truck batteries for more than a few minutes without draining them. For example, the smallest, newest, and most efficient truck camper AC unit draws 8 amps at 120 VAC. Assuming a 90% system efficiency, this would be a 1,100 watt "run" load on your inverter, and require an inverter that can handle at least 2 kW "start" load since any compressor load is a dead short on the power source for the first few seconds it is trying to rotate.

You said you had a 2,500 watt inverter which should be able to handle a small RV air conditioner, but that is not your main problem. Your inverter will have a constant draw of 88 amps at 12 volts DC while an 8 amp load air conditioner is running, and could draw up to 150 amps for a few seconds every time the compressor kicks in. This means your truck alternator and all related cables need to be large enough to handle these larger current flows and still have enough excess power to operate your lights and other electrical loads in the truck. Each time you stop at a light, there will not be enough amps coming from your alternator even if it is a larger 150 to 170 amp heavy duty model.

This is why the air conditioning unit in an RV is always wired into the exterior shore power or generator panel, and not powered from the batteries. Any 120 VAC electrical load on an inverter will draw 11 times the AC amps from a 12 volt DC battery.

I suggest letting the dogs ride in the back seat!

Jeff Yago


Generator puzzle

I have a Yamaha 1000 watt generator. If I plug in my battery charger or even if I use the generators battery charger mode, my deep cycle battery does not charge as full or as fast as it does if I use my household 110 outlet.

Why is this ? Both are 110 Volt sources.

Jim Mowatt

Jim:

Actually they both are NOT 110 volts as you suggested. AC power is alternating current with the voltage going from a maximum negative value to a maximum positive value, which makes this reversing of polarity 60 times each second. If you could see this voltage it would form a perfect sinewave curve with half above a zero voltage and half below. When you connect a voltmeter it will read 110 to 120 volts depending on your utility supplier, but the meter is reading the "average" voltage since the meter cannot move fast enough to display what the actual voltage is for that fraction of a second. If you use a special root-mean-square (RMS) type voltmeter, it will actually read 169 volts, which is the voltage between the highest and lowest peak of the sinewave curve.

Now comes the rub. When you start plugging more appliances or lights into a wall outlet, this 169 peak volts remains solid and does not "lug down". However, all lower cost and smaller generators will start lowering this 169 peak volts as you add more loads to the generator. This is how these generators handle heavy loads and avoid damage.

Unfortunately, almost all battery chargers are designed to utilize ONLY the top peak and bottom peak area of this voltage sinewave, which means any drop below the 169 RMS voltage will cause the charger to not function at all. There are battery chargers and inverters designed to operate from generator power without any problem, but if your charger does not specifically say so then it will not. There are also high end generators that do not have this voltage drop problem. For example, the Honda generators that have an "i" after the model number means the generator includes a built-in inverter circuit to maintain a perfect sinewave output and should power any battery charger or anything else as long as it does not exceed its load capacity.

Finally, regardless of the battery charger you have, I would not expect any 1000 watt generator to have enough capacity to charge a bank of deep cycle batteries. You will need to replace either, or both, the generator and charger, depending on their design.

Good luck,

Jeff Yago


Low E Argon windows

Dear Jeff

I live in alaska and am going to replace the windows in my home with Low E Argon gas filled glass. I am getting different advice as to which side of the glass should be on the outside.

Bob Yerger

Bob:

I am tempted to give you a smart answer like they tell the guys installing sod on new lawns - put the green side up!. You put the outside side of any window facing the outside! Unless you are just buying glass panels, all window frames are made with interior trim for looks and exterior trim to keep out rain and drafts, and this determines which side faces out.

You will find that Low-Emissivity glass (Low E) means there is a coating on the glass or by lowering the iron content in the glass itself that helps reduce thermal heat transfer by increasing the "U" factor of the window. If this is done by a coating, it is usually applied to the interior glass and since it "reflects" thermal heat it makes no difference from which direction this heat is coming. In other words, it will reduce thermal heat passing through the glass from the outside to inside without reducing solar radiation passing through the glass, and it will reduce thermal heat on the inside from passing through to the outside which would be a heat loss.

I think you will find the Argon-gas filled space between the two layers of glass provides far more heat loss reduction and going with a larger "gap" will improve the energy performance over a "thinner" window assembly. Just for the record, they also make 3-layer thermal windows for very cold locations but remember that each layer you add will reduce the solar heat gain.

Hope this helps,

Jeff Yago



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