Ask Jeff Yago
Solar & Energy-Related Issues
By Jeffrey Yago, P.E., CEM
Is there a rule of thumb or a reliable formula that can give a good estimate of how long it will take to charge a 12V battery? I will definitely charge from a 1000 watt Honda or Yamaha generator and would like to know how long this process will take. Also, how long from a typical solar panel, say a 65 watt.
You can use the simplest figures for example, I just need the proper method.
We struggle with this question all the time, especially when using a generator to provide the charging power. First, with a generator, you want to charge fast to reduce fuel usage. However, generators usually do not like battery chargers unless the generator is very large. Most battery charger designs "chop" off the "peaks" of the sinewave output for use in charging. However, most generators reduce their peak to peak voltage (usually around 169 volts) as the loads increase. When you measure 120 volts AC with a voltmeter, this is the "average" voltage of a sinewave output. Your small 1000 watt generator may have an output of 8 to 9 amps (1000/120 or 1000/115), but the battery charger may not be able to use all this power due to the drop in peak to peak voltage as it approaches full load. If your Honda generator has an "i" on the end of the model number for "inverter", then it includes an electronic circuit on the generator output to maintain the exact 60 cycle waveform regardless of loading.
Now to charging. If you have 8 amps available at 120 volts AC from the 1000 watt generator, then you could use a 12 volt charger with a capacity of about 80 amps at 12 volts DC output. (120 / 12 * 0.80 eff) which allows for some efficiency losses in the charger. This is the maximum amp output you can expect for this charger, but actual amp output may be less due to differences in chargers.
However, regardless of how much amp output you have available from a charger (solar, generator, wall outlet), the rate of charge should be based on actual battery size and type. For larger sizes of vented liquid type lead acid batteries, many battery manufacturers suggest the initial charge rate should be based on the battery's amp-hour capacity divided by 10. Knowing the battery's amp-hour capacity is the most important information we need and you have not provided this. You said you had a "12 volt battery". this could be anything from a 12 volt diesel truck starter battery having over 400 amp-hours, to 8 "D" cell flashlight batteries wired in series for 12 volts. Obviously, each have a very different charging rate.
Trace Engineering (now Xantrex) inverters with built-in chargers recommends a charge rate of 20% of the battery's capacity (amphour rating / 5) when using a generator which reduces generator run time, but you need a heavy duty battery to take this high a charge rate.
Finally, all batteries must have this charge rate reduced as they approach full charge or you will either over-heat the battery, boil off all the liquid, or warp the battery plates, so all quality battery chargers automatically start to reduce their initial high charging amp rates as the battery starts to reach full charge. To make it even more confusing, from zero to about 80% fully charged, this battery charging process can be fairly fast and is over 90% efficient. However, after you pass this level of battery charge state, the charging efficiency drops off almost half, so the last 20% of charge may take 2 or 3 times as long as it took to charge the initial 80%, so this can really extend the generator run time. For this reason, many combination system owners will use the generator for 2 hours in the early morning to do the first heavy charge of a deeply discharged battery bank, then turn off the generator and allow the solar charger to handle the remaining final charge for the rest of a sunny day.
Any battery will also have a different amp-hour capacity and require a different charging rate depending on the temperature of the battery, which is why all really good battery chargers have a temperature sensor to provide this feedback and automatically adjust its charge rate.
So you see, how long it takes to charge any battery depends on the charger capacity and efficency, the generator's capacity and voltage waveform, the temperature, and the amp-hour capacity and present voltage of the battery when you start the charging process.
If you want my very simplified method to answer your question of how long it takes to charge your battery, use a battery hydrometer tester to check charge level and just start charging until its full and your watch will tell you how long it took with your specific charger and generator - no calculations required!
Corn Stove/steam generator
I've been researching corn stoves, particularly the outdoor ones designed to heat the whole house. They seem to be designed like the reverse of an air conditioning compressor, creating heat in a boiler and pumping hot water through a closed-loop system to a plenum located in the house and using a fan to blow across the plenum - thereby transferring the heat into the house. Is that right?
However it occured to me that such a system is about half the way towards a steam-turbine generator. Has anyone built a generator using a corn stove?
These outdoor stoves are designed to heat water in a coil around the firebox and pipe this hot water through insulated pipes (usually underground) into a home. The hot water can be piped through hot water tubing embeded in a concrete/tile floor, piped through baseboard fin-tube radiation or stand-up hot water radiators, or through a hot water heating coil added to a forced air furnace ductwork. It does not matter if the outdoor stoves are designed to burn corn, coal, wood, wood chips, fuel oil, gas, or trash, they all work like I have described. However, they all have a few things in common related to the hot water loop.
For safety against boiler steam explosions and the pressure limitations of most common household piping, all of these hydronic stoves usually include an expansion tank, a circulating pump, a temperature relief valve, an automatic fill valve, and a pressure relief valve (usually set for 15 PSI). The purpose of all this plumbing is to make sure the system does not get so hot that the water turns to steam, which is what you need to run a turbine. Steam is usually produced when the pump fails and the water not flowing starts to boil inside the hot water coils inside the stove. The temperature and pressure relief valves start dumping this very hot or high pressure water to drain and the auto-fill valve starts letting in well or city water to replace what was dumped and things cool down.
The point I am trying to make is these are hot water boilers, not steam boilers, and they would be extremely unsafe if you tried to operate them as a steam boiler to make steam to drive a steam turbine. In the world of steam, we usually talk about low pressure, medium pressure, and high pressure systems. Most commercial and institutional buildings that still have steam heating systems operate their boilers around 5 to 8 PSI which is typical for any low pressure steam heating system. Usually when you get up around 25 to 30 PSI we call this medium pressure steam, and would be typical for a hospital steam sterilizer or commercial steam kettles where you need the higher temperature of the higher pressure steam. Any steam boiler and related piping operating at this pressure would need to be built from special boiler plate steel and use boiler tubing for their construction, and all welding would be required to be by boiler certified welders using special welding equipment. The hot water boilers you are talking about are not usually made to these standards.
Back in the mid 70's I purchased a surplus steam engine-driven generator designed for powering military ship's electrical systems when the main engines are not operating. This thing weighed 6 tons and only turned at 400 RPM, so all its steam piston and flywheel were very big. It required 25 to 30 PSI to operate, and this is most likely the lowest pressure you can get by with to run any kind of generator with steam. This means you will need a steam boiler, not a hot water boiler, and it needs to be designed to make steam, not hot water.
On a final note (which is already more info than you probably wanted!) High pressure steam is usually 100 to 125 PSI and above, and this is typical for the steam distribution piping between buildings which are heated from a central steam plant like found on a university campus. The really big steam turbines that drive large generators may operate at hundreds of PSI. Unlike the movies where the bad guy is sneeking and shooting inside a boiler plant with all that "steam" shooting out of piping and valves, real high pressure steam is a gas, and as a gas it is colorless! Because you cannot see a real high pressure steam leak, many "old timers" I have worked with will carry an old broom and hold it out in front of them as they walk around a boiler room. A real steam leak will cut that broom in half and you would never see the steam!! It will also cut off arms and legs which is why I recommend the average person should forget about steam systems unless you are using equipment designed for this level of safety and know what you are doing!
Hope this helps,
I have a small remote cabin that I have been running on battery/solar for many years now. I am in the process of upgrading/rebuilding my system. I am building an insulated battery storage box and was wondering if it is alright or safe to also put my inverter in this box to help protect it from the cold Northern Michigan weather. Is there a risk of spark from the inverter igniting any trapped gas within the storage box? The box of course will be vented with 2 inch pipe.
Any help would be greatly appreciated.
I would NEVER place the inverter or solar charge controller inside a vented, but enclosed, battery box. Yes, most inverters and many charge controllers have mechanical relays that will give off a spark as the contacts open or close which can ignite any hydrogen-rich gas inside the box.
However, I have cleaned many batteries located inside battery boxes and in larger battery rooms and I can say in every case, the batteries inside the battery boxes always had extensive corrosion on all the terminals even if only a few months old. I have had to replace large 2/0 cables almost totally corroded off that were only a few years old, while the batteries in larger open battery rooms stayed clean and had no corrosion.
Batteries being charged give off gasses and "bubble" as they are charged, and any enclosed battery box quickly builds up an acid "mist" on all interior surfaces from this charging effect. This can get so extensive that it will actually "leak" an electrical charge across the top of the batteries between battery posts and will increase the standby charge loss. If this acid mist will eat through a solid copper terminal, it will destroy small electrical wiring and electronic parts inside any inverter or charge controller.
If you need a battery box to protect batteries from the weather, you could mount the electronics on an outside wall of the battery box which will keep the battery cables short, and add a separate exterior wall around the electronics. Be sure this space is vented during warmer weather as this equipment will have a reduced life if it is required to operate in a hot ambient condition.
Radiant floor heat
I've been a Backwoods Home subscriber for years and years. I just purchased a home built in 1883 with beautiful hardwood floors. The house has a new forced air furnace. I would like to install radiant floor heat from the basement below the floor. When I research the energy savings, they always compare with a slab foundation. Would I still have a significant savings on my gas bill if the pipes were just installed from below?
Thanks so much!
I am not sure if you are comparing "apples and apples". Something has to make the heat which is not a radiant floor. If your new forced air furnace is electric and the source of heat for a radiant floor heating system is a gas hot water boiler, then you could compare the utility cost to make 100,000 BTU with a gas boiler at its efficiency and fuel cost against the same for an electric or heat pump forced air furnace. However, most people like a radiant floor for the nice comfort you feel and not having to operate a large central fan.
Many designers use radiant floor heating for slab floors as the heavy mass helps hold the heat and release it slowly, and distribute it evenly without drafts and blowing air. Its hard to get a cold concrete floor to ever feel warm just by heating the air in a room.
You can a install radiant heat system under a wood floor by using special "pan" type reflectors that mount between the floor joist and hold the radiant tubing centered. This reflects the pipe's heat up to the underside of the wood floor. However, there is always the chance this higher heat and its drying effect will warp a wood floor. If your furnace is new and you have a beautiful old wood floor, I would leave well enough alone and concentrate on adding floor, wall, and attic insulation which is usually non-existent in a house that old. Since you have a basement you could insulate the floor above if it is not heated and yes, insulate any ducts passing through un-heated spaces.
Generator/ battery charging
My Honda 3000is generator just died again. I needed a generator in a hurry but the Honda dealer was backordered so I ran down to Sears and got one of those 3600 rpm screaming gas gulpers figuring, well, at least the 5600 watts of power would have no problem pounding my 1600 amp-hour battery bank in no time. Wrong! After researching on the web the answer is pretty clear.
Those generators don't run clean enough power to make use of the charger in my (old Trace) sine-wave inverter. On the other hand the Honda, which is gasoline powered did the job extremely well considering its low power, and it was sooo quiet and would throttle down and just sip fuel as the amp draw went down. The question is, do the low-end diesels handle a 20-30 AC amp charging load efficiently and are they quiet as well? I'm hesitant to get another Honda because I charge batteries frequently and had that generator break down 4 times now in the past 5 years.
Sounds like you did not read my article on buying a back-up generator in the July 2003, Issue #82!
Honda makes a really good quality generator line and yes they are quiet. "The 3000i" model you were using has an inverter circuit indicated by the "i" after the wattage, and this really holds the voltage and cycles to specs even under a heavy load. This is important as a cheaper generator lowers its voltage output as you add load, as you have found out. Remember that its not the engine that drives the generator section, its the generator and any related built-in voltage regulator that impact your battery charging.
If you measured the voltage output from a low cost generator using one of those $15 multi-test meters, you might read a voltage between 110 and 120 volts which appears good. However, if you use a $200 volt meter that can measure true "RMS" AC voltage, you should actually read a peak voltage of around 169 volts. Since any AC voltage crosses the zero voltage point 60 times each second with a sinewave shaped voltage curve, the standard 120 volts is the "average" voltage which actually varies from zero to 169 peak volts 60 times each second.
Any generator (regardless of gas, steam, diesel, or water power) that has a cheap generator section, with minimum wire winding and little or no voltage regulation, will start lowering this peak to peak voltage as the current load increases. This would show up as a dimming of a light connected to the generator as other loads are added. Although this will not hurt the lights, it plays havock with any battery charger, which are designed to use the "peak" parts of the AC sine wave. This means unlike the light which just dims slightly, the battery charger will quit charging altogether. Since this drop in voltage happens when the generator starts to load up, any generator used for battery charging also needs to have lots of extra capacity.
My advice is to read the specs on any generator you are considering to make sure it includes a really good quality voltage regulator, and thet the specs indicate the generator can handle battery charger loads. I think you will also find anything under 6500 watts output is a little lightweight for any serious battery charging like an Outback or Xantrex inverter, and this may also be a reason your generators are not living very long.
Off Grid Systems
Hello there Jeff! I am a frustrated puppy. I am trying to cost out a non-solar off grid system that I can use in a remote cabin. Do you know of any system packages combining deep cycle batteries and propane generators? I want to retire in a small cabin and use a laptop, TV with built-in VCR, and have two 60 watt li-hy bulbs running all the time. I will use a wood stove for heat and a small propane fridge. I also want the option open to run a well pump, but may truck water in instead. I would like to have a hot shower, but do not know how the system would keep water hot and how water could be stored without freezing or how the water would get from an outside tank into my cabin.
Obviously I know very little about all this stuff. Can you recommend a list of people or organizations that can put a system together for me? Is there somewhere I can go to see a system that is set up? I want a very quiet system. I live near Seattle, WA and it is too cloudy for solar (I think). There is a lot of info on solar for off-grid, but little I can find to tell me what to do for a prime system off grid using propane generator only. So far the costs seem way too high for me when you get into the higher powered propane generators as they suck up too much fuel. The gas generators seem too noisy and inconvenient for refilling all the time. Can you answer my prayer and tell me what the best thing is for me to do? The only solar systems I have found as a package are more than $22,000 and I can't afford that. I could afford up to about $10,000 with low operating costs (<$1,000 per year).
Looks like you are not a regular subscriber to Backwoods Home Magazine, as I have already answered almost every question you have asked in several recent issues!
The most recent June '06 (#99) and August '06 (#100) were part 1 & 2 of a long article called Walden Pond - the Solar version and discussed how to design and build a battery-based power system (with and without solar) for a remote off grid cabin.
My article in Issue #91 dated Jan '05 described how to build a solar powered water system, and if you go back to Issue #71 dated Sept '01, you will find my lengthy article about water pumping, water storage tanks, and surface water purifying for off grid homes when a well is too deep to pump or drill.
Please note you stated "I will have two 60 watt light bulbs running all the time". Nobody who is serious about living off the grid or using a generator-charged battery would use standard 60 watt light bulbs. Two 60 watt light bulbs running all the time would consume over 86,400 watt-hours of electricity EVERY month!! You really need to read more of the back issues of this magazine before heading down this path as we have discussed almost everything you need to do, to not do, and to watch out for.
As to installers who can help, there is a national listing of installers who can provide all kinds of solar systems, off grid and battery power systems, and all have passed very strict training requirements and testing. This national certification board is called "North American Board of Certified Energy Practitioners" and you can find this listing at the following link: http://www.nabcep.org
As to your budget, I think it will take more than you indicated you were willing to pay to do what you want to do. Also, be careful about buying one of those cheaper generators you find in builder supply stores, as these are designed for operating a few hours during a power outage once or twice a year, not on a daily or weekly basis.
If all else fails, subscribe to this magazine and order the anthologies that contain all of the back issues!!
Off-grid mortgage lending
I am a broker in the lending business in Colorado but as many of us know, “off-grid, solar and straw bale” are not in the vocabulary of most investors. I have the opportunity to work with clients who are looking for funding for their “green” home projects but I often have to turn them away due to the lack of investors willing to fund such projects. Could you please relay any information about companies who are willing to work with these clients.
Actually things are getting better, although it depends a lot on where you live and if there have been a few projects funded already by the lender to "break the ice".
I tell my clients the best way to handle the lender is to not make a big deal about any alternative energy features you are planning to include. After all, telling a banker that the home they are getting ready to fund will include some kind of "expermental power system", the first thing that will pass through their mind is hazardous wiring and a house fire! I do not tell them to hide information or mislead anyone, just don't talk like your home will be some kind of science fair project.
When a person goes for a typical real estate loan for a typical home, they do not usually tell the lender what kind of furnace or roof it will have, so why get into that level of detail in the first place unless you are asked.
I advise our clients they can say the home will have several "energy saving" features that will reduce the monthly utility expenses and leave it at that. If the lender wants more information be truthful about it, but point out all materials and equipment involved are still required to have the same UL labels and building inspections as the other more traditional materials and systems.
The solar industry now has NABCEP certified solar installers in each state who are required to pass very difficult exams as well complete a minimum number of installations and continuing education courses each year to keep their certification. Your loan officer expects you to hire a licensed contractor who in turn hires a licensed plumber, a licensed electrician, a licensed furnace installer to build you new home and install these traditional systems. The lender will also expect you to hire a licensed and certified installer for any "non-triditional" equipment or materials, and unless you are planning to install something yourself, there is no reason your lender needs to be concerned.
As long as you work with certified and experienced alternative energy installers and suppliers, you and your lender will not have any "surprises" later, and the next potential solar-home loan applicant that comes along will have an much easier process. Who knows, that next person may actually be you!
Pump on hot water heater
I have a Crown Aruba gas fired hot water heater and it turns on but does not generate hot water upstairs to the radiators. I have opened the radiators and there is no air. There is cold water and I let it run, but it never turned hot. What can I do next? I think I could fix it if I were led in the right position. Could you please help me.
Thanks for all your help.
You do not say how old this system is but this is a fairly good quality brand and model boiler. It is not possible to diagnose your specific problem without a lot more information, so I will give some general points about hydronic heating systems that may help and could also apply to other readers.
1. Most non-steam hydronic heating systems consist of a hot water boiler, a pump, no zone valve or several zone valves depending on layout, and terminal heating units. These can be radiant piping loops embedded in a concrete floor, stand-up radiators, baseboard radiation, or even fan-coil units.
2. The hot water boiler does not know anything about the system or what is piped to it. All it knows is when it is turned on, its controls fire the boiler until the water flow output has reached the setpoint temperature then the burner turns off. If the boiler fires and there is no flow (failed pump or blocked flow) the high limit control will sense the boiler inside getting too hot and will then shut off the gas. In other words, the thermostat control and the safety high limit sensor determine the output temperature of the water flow and turn the burner on and off to maintain this setpoint.
3. If you have a single zone system and no zone valves, when your wall thermostat calls for heat it turns on the circulating pump which in turn tells the burner to fire. Many systems have the pump operating all the time during the heating season by a manual summer/winter switch. In this case, you may have several wall thermostats with each operating a 24 volt AC zone valve. The pump is always pumping water around a loop with the temperature control cycling the burner on and off to maintain water loop setpoint (usually 160 to 180 degrees).
4. If you have zone valves activated by wall thermostats, when one calls for heat in a given zone or room, the hot water is diverted through that loop of piping just like switching tracks on a train. If your boiler is circulating hot water but it is not getting to a specific loop, you may have a failed thermostat or zone valve. Sometimes these can be manually over-ridden by a lever on the valve.
5. The number ONE reason hydronic heating systems stop circulating hot water is air bubbles trapped in the water loop which makes it back to the pump and causes cavitation. These hydronic pumps are very small capacity, usually only 1/20 HP, and they will not pump anything if air gets into their intake housing. You said you vented the air out, but if it is trapped in the pump, you have a lot more work to do! Most hydronic heating systems have more than one air vent, and they are always located at all high points in the piping loop or loops. They have a cap that looks like a filler cap on a car tire, and when you remove the cap and press down on the center stem, you will get air until it is all out. There is a float inside that will close this valve when all the air is out, but they tend to leak so most people keep the caps tight.
6. Finally, system pressure may be low or no pressure. All residential hydronic heating systems are "closed loop" design. This means the water (which may include anti-freeze or rust inhibitors) keeps flowing around and around the loop from the boiler out to the zones then back again, but never leaves the piping loop unless there is a leak. All closed systems include an expansion tank which is usually a metal tank about the size of a basketball which has a rubber air bladder inside. This bladder inside the tank is slightly compressed by the water loop pressure which is usually between 5 and 15 psi. When the water in the loop heats up, the bladder is compressed more inside the tank. When the boiler shuts off and the water in the loop starts to cool, the volume of water contracts and the bladder expands to make up this difference which keeps the loop pressure in this pressure range. If flow stops and the burner stays on, the water temperature and pressure will build up and will be vented out through a pressure relief valve (usually 30 PSI) or a temperature relief valve (usually 210 degrees) but your relief valve setpoints may be different so if defective, replace with the same rated valves your system was designed for.
7. If you have a leak, a "make-up" valve senses the water loop pressure has dropped below this 5 to 15 psi setpoint and allows some "city" or well water to enter the closed piping loop until the pressure is brought back up to minimum setpoint then this valve closes. If you have a slow leak over a long time, you can end up with all "raw" well or city water which introduces lots of dissolved air and chemicals that will drop out of solution when the water is heated. The air can stall the pump and the chemicals can form deposits on interior piping and boiler surfaces which reduces the heat transfer. This is why any domestic hot water tank slowly builds up a "pile" of sediment at the bottom that must be drained out each year using the drain valve at the tank bottom or the tank will suffer an early failure.
8. If this does not help, do what I do - call the repair man and bend over.
I'm upgrading my system and am wondering about prices for used equipment. Can you give me a range of what the following stuff is worth? It's all been kept in good condition and is about 10 years old...
-Trace DR1512 V3.0 inverter-charger Original price $845
-APT Powercenter (3T85) Original price $1200
-Trimetric Battery Moniter Original price $155
-Morningstar controller Original price$155
-BP90 solar panel Original price $572
Is 3/4's the original price fair? 1/2?
Thanks for your help....
Hard to say, but you may get more as a package deal. The 10 year old inverter is risky and you may have a hard time getting over $300. However, the solar module should have lots of life left and could sell close to what you paid for it. The APT power center is obsolete and no longer made, so doubt if you will get much for it. The Morningstar charge controller is a good product and should be worth at least half. I still think you should sell everything together as a packaged kit (less batteries).
Solar Well Information
I'm trying to get information for my solar well for feeding livestock. Someone stole my five Sharp Solar Panels Model NT-175U1 (175 is the panel volts) earlier this week. When I had the well dug earlier this year I thought that was more panels than needed to run this for my needs. Know I would like to get some experts opinions!
My well is 260' deep with the pump sitting at 200' and a static water level of 70'. I have a main water line 1" running out into my pasture 1250'. The solar pump is a 11SQF-2-SQ with a Grundfos IO1012-115v interface box for generator back-up.
I have off this main line 6 hydrants that I use on and off for watering trees and other livestock as needed. Normally, I never need more than one hydrant pumping at one time. Pumping rate for the well was 12 gpm at the well and 8(+) gpm at the hydrant in the well.
Do I need to replace all five panels especially since they would be replaced with the newer Sharp Solar Panels Model NT-180U1? Also, do you have any recommendation on how to secure the panels on the angle-iron pedestal frames? Finally, do you know any good dealers I can contact for replacement panels?
Thanks from Colorado…
Sorry to hear about your theft, but you are not the first. As solar modules have become larger, individual prices have also increased to where a single 150 to 160 watt module may be worth $1000!
I have never understood how some people think there is nothing wrong with stealing somebody else's property, as long as they are not caught. This is why I strongly believe in buckshot!
To address your sizing question, the Grundfos #11SQF-2-SQ solar pump is designed to operate on any voltage between 30 to 300 volts D.C, and the higher the voltage the better for really deep wells as this will allow using less current. I imagine the five modules you had were wired in series to produce 60 volts (5 X 12 ). For replacement, you could try 4 modules of same size and see if this gives you the flow you need, but of course this would be less flow than the five original modules produced.
You could also stay with five modules, but use a smaller wattage module to save money as long as you realize this also will reduce the pumping flow. Base your decision on how well the original system pumped, and if it was more than you require or about right.
As far as security, some installers have switched to vandal-proof screw heads and nuts like you find on public restroom hardware and security lighting. Be sure to record the serial numbers on the back of the modules. However, the ones stolen from you were probably not re-sold and ended up on the thief's fishing or hunting cabin.
Good luck and keep the shotgun handy,
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