Alternative energy advice from Ask Jeff Yago. Volume #35

Ask Jeff Yago
Solar & Energy-Related Issues

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

Sorry. Jeff no longer answers questions online

Solar battery room

Dear Jeff,

I have been reading your articles on solar power and have decided to build a small battery room in the basement, as opposed to the battery box. However I am not certain about something and would like your advice. I will put the batteries on a treated plywood on upright 2×4’s floor in this 4′ x 7′ floor area room x 8′ ceiling height.

I am planning to run a vent from the wood furnace into the room to keep it at optimal temperature for battery performance. However I am not certain about how much venting to the outside is needed and won’t the vent to the outside also cause all the heat in the room to be lost?

Is there a one way valve of some kind that will allow fumes out but no cold air in? The furnace vent will provide fresh air as I am not going to have a cold air return from this room back to the furnace because of the battery fumes getting into the house air. Currently there are 8 batteries but there may be more batteries added in the future.

Your insight and advice in this matter will be greatly appreciated and hopefully will help other readers as well.


John Mc Andrews.


We do not get into detail design advice for a specific application on this web site for obvious reasons, but I will pass along the following general guidelines for building a battery room. Under no condition would I duct supply air into a battery room from a furnace, wood stove, air conditioner, or anything else that moves air. Any room, no matter how well it is sealed, is not air tight, and if you duct or blow air into any room it will find its way out, and not always out the path you intended.

I have seen a sealed battery room with a small exterior pipe to vent battery gases to the outside actually “suck” air back into the room located in the basement due to wind pressure acting on the home’s exterior wall surfaces, and this backward air flow forced hydrogen gas back into the basement. You want to always EXHAUST air at the highest point in a battery room and let the makeup air come from a louver located near the floor, under the door crack, or anywhere else it can find a path, but the room should be under a negative pressure (air being forced OUT of the room to the outside) in reference with the rest of the house and basement so any hydrogen gas will be exhausted to the outside and not forced back into other rooms or up through the ceiling to the floors above.

We usually use a battery-powered in-line exhaust fan installed inside a 3″ PVC pipe. These are made for battery gases and the brushless fan they use will not spark and cause a gas explosion. I would expect almost any basement under a house to not get too cold or too hot and would not expect any heating will be required. However, if you want to heat a battery room the only safe method that I am aware of is a very expensive explosion-proof electric radiant heater, or baseboard radiation around the walls that is heated by a hot water heating boiler or domestic hot water tank.

We always build a battery shelf made from pressure treated 2 x 4’s on edge with 1/2 x 4 spacers between each to allow for good draining and air flow. We place these on 8″ concrete blocks spaced every 3 or 4 feet to provide good air flow and to keep the battery bottoms from touching the much colder concrete slab floor. A floor drain is also helpful as it can get a little wet when you wash down the batteries with water and baking soda. Finally, we always add a good ABC type fire extinguisher, a vapor-proof glass “jelly jar” type light fixture, and a locking door having a warning sign.

Good Luck and don’t light a match when you are in your battery room if you can’t see!

Jeff Yago

Inverter outputs

Can two or more inverter outputs be connected in parallel?

Robert Jefferson


Your question sure was short and to the point!

The answer is yes, you can most of the time, but there are a few electrical issues to deal with. Most high-end battery-based sinewave inverters made today have “stacking” communication links between each inverter. Since most residential-size inverters used with a battery based solar system are under 4 kW and only available in 120 volt AC, if you want 120/240 VAC you use the link which will synchronize the sinewaves of each separate inverter to provide true 120 and 240 volt AC power.

If you want to supply a load larger than 4 kW at 120 VAC, these same inverters can use the same communication “link” and their outputs are paralleled. To keep standby inverter losses low, only one inverter starts, then as the load increases the second inverter (or 3rd, or 4th) come online as needed to meet the load. You can also program multiple inverters to do both, with several staged for each leg of the 240 volt output. I would not mix and match inverters, and some lower cost inverters may “see” the output waveform of the other inverter connected to the same load panel and think the voltage or cycles are out of allowed range.

If you are doing a grid-tie system with no batteries, you can usually put as many inverters as you want in parallel with all their outputs supplying the same loads panel, but again, I would make them all the same brand as sometimes you still have some out-of-range problems that you have to adjust programming and this is easier if they are all the same size and model. Make sure each inverter has its own circuit breaker on the input and output for system service, and try and equal all wire lengths for separate array and grid connection circuits that are in parallel.

Good Luck!

Jeff Yago

How can I become a CEM?

Dear Jeff

How can I become a CEM?

I am particularly interested in the broad area of Sustainable Energy & Refrigerants for Heating, Cooling and Refrigeration. On the Energy side I want to explore the application of Solar Systems to power residential and commercial HVACR appliances. I have been working in the HVACR industry for over 6 years and would like to acquire the specific knowledge and necessary certification in Sustainable Energy to broaden my skillset and marketability in this exciting and developing industry. If you don’t mind I would greatly appreciate your guidance on how to do this and I have the following questions for you:

1. What are the certification requirements to become a Sales Engineer/Marketer of Solar Systems?

2. Where can I access accredited training courses?

3. On completion of the required training & certification which are some of the companies that I could target for business opportunities preferably in Sales, Technical Training, Management Consulting and even starting a Small Business in sales, installations and servicing Solar Systems.

4. On the commercial Refrigeration side I have a solar concept that I would like to explore and am looking for an organization that has the facilitiy, resources and might be interested in working on developing and testing the prototypes that could be taken to a few Commercial clients that would be interested in this type of innovation.

Thanks and looking forward to hear from you.

Best Regards



There are two areas of interest, and both will really pick up after the new solar energy credits take effect after Dec 31, 2008.

If you are interested in Solar hot water heating it sounds like you already have a good background in this field which is more plumbing related. Skills would include all types of plumbing and piping related products for domestic hot water.

Some community trade schools offer adult classes in plumbing and electrical fields, and this may be a good place to start.

If you are interested in solar electric, then I suggest getting in with a local electrician and learning more about wiring by helping out and start studying for the state electricians license.

Regardless of which path you choose, the best certification you can earn in the solar field is to be a NABCEP certified installer, and they offer an entry level certification. This requires both testing and field experience, which you can only get by working under someone who can provide work experience.

Review the NABCEP site for more information –

Good Luck!

Jeff Yago

Generating electricity by burning wood

Hello Jeff,

I am interested in generating electricity by burning wood. I haven't seen much about this subject on the website. Why would burning wood be a good choice or a bad choice for generating electricity?

Any information that you could pass along would be much appreciated.



The reason you have not much about this subject is it is not very practical today. This does not mean it does not work, but 99% of these systems require a wood-fired steam boiler which could explode if not designed and operated properly, it takes constant fire management to maintain proper steam pressure, it takes a good supply of water that is properly tested and treated to reduce chemical buildup inside water tubes, it takes a daily “blow-down” of the mud drum which will fill up with sediment, it takes daily removal of ash, and it takes regular lubrication and adjustment of all the moving parts.

If you check, you will find that almost all of this equipment is refurbished equipment somebody found or saved from the 1930’s and 40’s. Many states require any steam boiler, regardless of use, to be inspected every year by the states safety inspector, and many require that you maintain liability insurance for its use. Many states require steam boilers above a specific size to be operated by a full time boiler operator, and many states require this operator to be a licensed steam plant operator.

In other words, turning firewood into steam is not as simple as you think and is not very cost effective unless you already have the equipment and have lots of time to operate and maintain all the working parts. Most of these systems today are part of a steam show or other event. At one time I had a 20 kW steam driven generator that was new WW2 surplus and it was almost 10 feet tall and weighed 4 tons. It was too big, too heavy, and too much trouble to keep operational so I finally scrapped the whole thing.

Here is a test for you. Put a very large pan on your stove full of water right out of your tap. Now boil it until all of the water has been boiled off, then see how much scale and chemical deposits remain on the sides and bottom of your pan. Now do this 24 hours per day and how long do you think it will take to totally coat the pan with deposits you can’t remove and that reduce heating efficency. Now imagine this was boiler tubing inside a steam boiler to convert water to steam to drive a steam boiler.

Good Luck and be safe!

Jeff Yago

Battery hookup

I hope this is a easy question.

I have a motorhome that has 3 deep cycle 12 volt batteries.

I want to keep them charged with solar as much as possible.

Will connecting 2 or more 45 watt separate systems charge them better than just one?

As they are all the same watt I am not sure adding 2 or more same watt systems will charge any more than 1.

Help Please.

Thank you

Att: Help Please:

I assume you mean connecting each battery to its own solar module and charger verses connecting one solar charging system to all three batteries. For good battery voltage balance, its better if you connect one solar charger to all batteries wired in parallel. I don’t know how you could do this separately unless each battery can be disconnected from the others, since normally they all are wired to the same 12 volt positive and negative mains. Assuming you could separate them from each other, as soon as you connected a battery that was at a higher charge than the others, current will flow from one to the other until they are equal in voltage.

Keep it simple,

Jeff Yago

Submarine batteries

Greetings from Antigua,

I have been offered 12 X 2 volt 300Ah new exide batteries that were destined for a submarine.

Can they used as the basis of a solar storage system?

The house has a total daily wattage use in the region of 51800 watts .


Ken Stuart


Normally these would be an excellent battery choice for a large off-grid solar power system. However, I am wondering how you were “offered” these because usually un-used batteries purchased by the government after a specific date are sold as surplus if not put into service. If this is the case, they could be in excellent condition, or they could be damaged and will no longer take a charge after being left un-charged for several years in some storage facility.

See if you can find out history before you take possession.

Good luck,

Jeff Yago

Heating System/Smokehouse

Our farm entails 90 acres of woodland and I know there's a new technology where you install a "smokehouse" on your property and you can burn almost anything to produce heat for your home as long as your current heating system uses a hot-water radiator system which ours does.

Can you please point me to a website/s where I can learn more about this product/system and its cost to install?

Thank you.

Bruce R. Petrie


I did an entire article on this subject last year. Refer to back issue for May/June 2007 Issue #105. This issue also included several ads for this equipment. You must not be a regular subscriber – see what you have been missing!

Jeff Yago

Solar-powered refrigerators

Hi Jeff,

In this article you said you like MPPT solar charge controllers and then endorse the Morningstar Sunsaver Model #SS-10L and 20L, a PWM controller? Is the (4x) more expensive MPPT controller worth it?

Thanks for any info.


Like everthing else, it depends on the application. If I am designing a small system under 20 amps, which would be about 200 watts of solar at 12 VDC, then to keep costs down I will usually go with the Morningstar line. These are very rugged and have lots of features you need with many smaller systems like programmed on/off control for an exterior light and low-battery cut-off of the load to prevent battery damage.

On larger systems where you are spending several thousands of dollars for the solar array, the extra annual output you would get with a MPPT charge controller is worth the extra cost. These larger charge controllers have larger wire terminals on display meters which the smaller PWM charge controllers do not. There are actually several newer brands of charge controllers now available which are also very good.

Good Luck and FYI, don’t wire your PWM to your MPPT or you will be SOL and should go ASAP with short ETA to hospitol for EKG and MRI,

Jeff Yago

Hi Jeff,

Thank you for the distinction. I currently have a small system (50w panel, 12V) I am learning from and could grow slightly bigger. It is only powering 12v devices off the charge controller with a 51amp/hr battery.

I am currently using the Morningstar SS-10 and I could benefit from the low-battery-cut-off and programmed on/off control. I would also like an amp/volt display that some seem to incorporate now. Any recommendations?

Thanks again for any info and any further TLAs.


Since you are already using the Morningstar line, they have a next size up model with a display window that will do what you want. However, until you increase your array size I would not spend the money.

Good Luck,

Jeff Yago

Or should I say watt


Recently I contacted the electric utility company servicing my home inquiring about negative metering. Prior to contacting them I had discussed the possibility of erecting a windmill on my property and selling surplus energy back to my supplier with an electrician friend. He told me the rate stunk but it could be done.

The person I talked to at NIPSCO was an absolute zero. She sent me some paperwork saying that for the privilege of giving them free electricity it would only cost me about $8.00 per month. WHAT?

So I called the number on my state’s, (IND), energy website and got a recorded message saying the person I’d reached doesn’t work there anymore. WWHAT?

Finally, I did something I’ve never done in my life. I wrote my congressman. Actually his website told me to fax his office in South Bend, IN. So, I faxed Mr. Donnally my concerns about negative metering and guess what? I received specific instructions from his office on how to file an application for welfare benefits! I was asking about watts, not welfare! WWWHAT?

Jeff, can you tell me where I can get valid useful information on negative metering for my state? Thanks.



Welcome to the new world order! Its now just like Alice in Wonderland isn’t it.

OK, I will provide you some sanity and real information.

Your state of Indiana has a net metering law that is almost just like many other states. Your local utility is REQUIRED to purchase any power you can generate up to 10 kW, and your local utility is NOT allowed to charge you any fees or other charges for this privilege.

This link will take you to your state’s utility commission’s web site where this is explained in simple terms, along with a real person’s name and phone number you can contact who understands how this works and can help you fill out the forms. Many utilities just do not have the staff or time to deal with these “smaller” projects and will play dumb in hopes you just go away.

Keep in mind that before the net metering laws were passed to allow you to do this, most of these systems were just hooked up anyway and since all it would do is turn the meter backwards, as long as you do not sell back more than you use you would just end up with a smaller monthly bill. Of course this can be un-safe if you do not use the proper equipment, but the point was, if the utility did not make this easier to do legally and at no cost, everyone would just go ahead and do it anyway!

Let us know how this turns out,

Jeff Yago

Water pump – AC or DC to supply main pressure to an off-the-grid house

Hi Jeff,

Must say I enjoy your website and value the information given.

I am trying to build an energy efficient house – too far away to get a grid connection. I am trying to find out what pump to buy for my system. Our appliances run on 240V – 50 hz

I have a 24V battery system with a whisper H100, 10 solar panels and 6 X 4V batteries and an inverter. I collect rain water (ok – in New Zealand) and it drains to a couple of tanks that are about 40 ft below the house level and 240 ft distant.

Our plumber has insisted to go with a mains pressure system so that we have good showers (no bath due to not sufficient rain for these) and so I have purchased the correct shower heads. Given that I cannot change this part of the system what sort of pump do I go with?

1. A DC pump with a reservoir so that once the pump is on it pumps up to a certain pressure – turns off and then only comes on again once a minimum pressure is detected? (Would I observe surging in the shower if this was the case?)

2. A DC pump with no reservoir that would come on every time a tap was turned on – in this household it would be 80 to 100 times a day?

3. If a DC pump is recommended could you indicate a model or give some indication as to what I should ask for? How should this be connected to the system? Direct to the batteries?

4. An AC pump + reservoir?

5. An AC pump with no reservoir?

Thanks for your time.


Louise Coats


A standard well pump will kill your small solar power system and really small battery bank. Check out what I designed for another off grid family with limited solar due to mountains blocking most of the southern sky.

You should use a small 24 VDC solar Jack pump down in the lower cistern, which draws very little power since it pumps very slowly and is only filling a storage tank inside your house. This holding tank has a second 24 VDC pump but this one is a pressure pump and will pressurize your homes piping system just like a standard pumping system on the grid. Note that we have a sand filter on the line entering the holding tank, and an ultra-violet light filter and carbon filter on the pressurized line leaving the holding tank. This allowed drinking the water as it was tested as being free of all bacteria and other bad things even though the water source was a nearby river.

Good Luck,

Jeff Yago

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