Need some ideas on solar energy battery bank

Hello, Jeff.

I am planning to go completely solar energy. I have 800 watts of solar panels and also bought a Xantrex 4024 inverter. I am presently using 6v golf cart batteries for 24v bank with sixteen batteries. They recommend using 4/0 AWG cables for both the inverter and battery bank jumper cable; Can I use two 1/0 cables parallel for battery jumper cables instead of 4/0 AWG ?The reason I want to do this is because I have the 1/0 AWG cables available and copper is very expensive. However, I would use the 4/0 AWG on the inverter itself. My goal is to get more panels to run the house.

Thank you for the help on this matter.

Marcelino.

Marcelino:

We do not like to get into specific equipment sizing issues on these web questions due to limited time and not knowing all of the specific conditions that can affect a recommendation. For example, when sizing wire, a specific wire has a specific code specified amp rating. However, the type of insulation on the wire, if it is in open air or under-ground, if it is alone in a conduit or with multiple cables in the same conduit, and ambient temperature will all raise or lower the table amp ratings of any wire being considered. With this being said, here is a “general” wire guideline as long as you keep in mind the above issues that can affect this.

It is NOT a good idea to parallel smaller cables to increase total load capacity although some people do it. There are both code reasons and practical reasons and there is not enough time to explain here, but I do not do it. About the only time I see this allowed is in 3-phase high voltage primary feeds which have proper fusing at both ends.

A Xantrex 4024 inverter has a manufacturer’s suggested fuse or breaker size of 250 amps using a #4/0 copper cable at 10 feet of length. The smaller #2/0 cable is intended for circuits having a 175 amp fuse or breaker size. However, since you are using four “strings” in parallel of four 6-volt batteries in series, each of these strings is only carrying 1/4 of the inverter current, so the lower cost #2/0 cables can be used as the battery to battery jumpers, as long as you use the larger #4/0 cables to supply the inverter.

Good Luck!

Jeff Yago

Off road truck campers

Hello Jeffrey,

I came aross your information in a google search. I own a rv rentals and sales company in Ireland called Vanderlust. I wish to expand my fleet to include off road truck campers as mentioned in your article. Do you know of any existing such business in your neck of the woods? The idea of off road trucks fully self reliant really appeals to me and I wish to investigate this avenue further.

Kind regards

Padraic O Brien

Padraic:

Stay tuned, we will have a more detailed article related to solar power and off road campers, and camping in general in an upcoming issue. (Scheduled for Nov/Dec, 2007) —Ed.

Jeff Yago

Stirling engines

Jeff,

I own forest land which I renewable harvest for heating my Alpine house. I am extremely frustrated as I wish to combine a Stirling engine with log-burning to produce green electricity via a generator. Nowhere have I found anything on the domestic scale. Toys and demonstrators and large-scale alternatives seem to exist but not what I seek. I want to be independent and not use fossil fuel for my power requirements. It seems to me that the technology exists and this is such an obvious application I cannot understand the causes of my frustration. Can you help?

John Newson
Julian Alps
Slovenia

John:

You are correct, a Sterling engine-driven electric generator that uses low level heat energy from either burning waste wood or solar thermal energy is a good way to solve your energy needs. Please note that there are many others working in this field even though you may feel frustrated in your search for information. This link will take you to a web site that sells detailed drawings and information on how to build your own 5 HP Sterling engine driven electric generator. This is not a toy or demonstration project.

This link will take you to a British Car Company’s web site describing their new packaged Sterling engine-driven home power-plant that provides both space heating and 15 Kw of electricity for a typical home.

Good luck!

Jeff Yago

Hydronic wood stove

Some 30 years ago I help install an hydronic system in a house in northeast Texas that used a similar system but went a lot farther: We ran hitemp PVC thru the slab and out into a coil (radiator) in a 10,000 gallon water tank. Then we hooked it up with black pipe to the fireplace by embedding it into the hitemp (stove) cement. Added a pop off valve at a low pressure (approx 110 psi) and a pump for backup.

This allowed the water to be heated from the fireplace and due to the temperature difference it move the water thru the system (slab and water tank) by itself. The water heated the slab and the water tank. Once the water was heated your house stayed warm and you had hot water for your home.

Come spring time you turn off the stove and switch the water coil in the 10,000 gallon tank to the sun concentrator to heat the water for the house.

All of this is not hard, just a lot of money!

Kevin Bradway

Keven:

As I mentioned in the article, we designed several systems that used a storage tank. Tank water was heated from the hydronic wood stove which was then circulated later at night to circulate to the home’s floor slab after the fire was out. Most of these tanks were under 1000 gallons since they would be located in the garage, and they took about 4 hours of a really big fire to heat up. If you had a 10,000 gallon tank, it must have taken days to get the water hot, but then you would be able to heat for days without a fire once it was!

We used standard 3/4″ copper which come in 60 foot rolls for our heat exchanger and placed two coils in the tank which kept the water that circulated through the stove and coils from mixing with the water that stayed in the tank. All of our systems required two pumps and three automatic zone valves to re-direct the flows since you need three separate operating modes: stove to tank, stove to house, and tank to house. If you were able to do all this without any pumps or valves, you must have had a really good thermo-syphen effect with your hydronic stove.

Thanks for the description of your very large system.

Jeff Yago

7 year old AGM Deep Cycle Batteries

Jeff:

I have about 20 batteries from a solar power unit that was installed in 1999. These are from Concorde Battery Corporation, 12 v, capacity of 255 AH @ 20 hr, and seriously heavy, 162 pounds. Could they still be good? How do I find out? Do you know who could use them?

Thanks,

Jimmy

Jimmy,

Based on your battery description and age, this is a Model #PVX-6220 Concorde “Sun-Xtender” VRLA sealed Battery. This is a “maintenance-free” absorbed-glass mat (AGM) battery, which means the acid is absorbed and cannot be re-filled.

Any quality lead-acid battery, sealed or open, will have several things that will affect its life. If it was maintained near a full charge most of the time, it should last 6 to 8 years. If it was located in an area that did not get too hot or too cold, it will last longer. If its normal charge and discharge cycle did not cause the depth of discharge to exceed 20% (80% charge remaining), it will last longer. If it regularly was discharged down to a total discharge state, or was left totally discharged for months, most deep discharge batteries will fail years before their advertised life.

If your batteries meet any of these conditions, I would say they are worthless by now. In addition, the “maintenance-free” sealed batteries are very sensitive to charging voltage since a lower quality charger that does not measure battery temperature can re-charge to quickly and over-heat them. Since they are sealed, this can cause a venting of gasses through the over-pressure safety valve and this loss of moisture cannot be re-filled since they are sealed. Sealed batteries usually dry-out and fail much faster than open type lead acid batteries (batteries with fill caps), even if they were properly maintained.

I suggest taking these to a battery re-cycler who may pay you something for the scrap lead which has really going up in price nationally in the past few months. In fact, battery prices have increased over 50% in many cases due to the high overseas demand for scrap lead.

Good luck!

Jeff Yago

Solar installer certification

Hey Jeff,

I’d like to become a certified pv solar installer. What would you recommend to someone like me who dosen’t have any experience {yet}?

Thanks,

Jeff Hall

Jeff:

Thanks for the question as I am asked this many times in person. The problem with getting into solar is the many different things you need to learn. For example, you need a good understanding of the sun and its movement through the sky, verses solar system mounting arrangements and shading effects. Estimating system loads requires a good understanding of the specific electric loads in a home or business verses their operating hours. Mounting solar modules requires an understanding of wind loads, structural requirements, and sealing roof penetrations. Sizing electrical wiring requires a very strong understanding of basic electricity and power wiring, and the differences between DC and AC wiring. Finally, to avoid burning down houses or electrocuting the occupants, you should really know the national electric code and how to apply it.

Unfortunately, many electricians have this knowledge and installation skills, but have no interest in getting involved with solar projects. I have met electricians who have never installed a battery bank or wired any DC power equipment in their entire lifetime as an electrician, nor have any desire to start. They also usually work only on utility grid connected power panels and do not usually work on wiring systems with capacity limitations.

However, if you install a grid-tie solar power system and intend to legally sell power back to the utility, you will need a licensed electrician to make the final wiring connections into the main house panel, who will certify in writing that the system meets all codes, and warrants the solar hardware installed meets the IEEE dis-connect requirements. In other words, the best path to being a solar installer is first becoming a licensed electrician, then taking the extra courses to become a NABCEP certified solar installer. The NABCEP certification is not easy, and it requires training in all of the subjects I mentioned above.

There are even a few trade schools and 2-year colleges now offering these programs. Being a NAPCEP certified installer is the highest rating I know of for anyone in this business and is your best way to open doors if you are just getting into this business. However, since full certification requires that you have already installed three complete solar systems, you will need to team up and assist someone already in the busiess as a way to gain this experience after completing the “book learning”.

Here is a link to the NAPCEP web site – check it out for more information: http://www.nabcep.org/

Good luck!

Jeff Yago

Solar light question

Dear Jeff:

I’ve tried the archives, but couldn’t find answer I was looking for. I am trying to buy, build or get plans for a very simple solar light to be used by developing nations without electricity or other power sources. If not Solar, perhaps a light running off a car or boat battery. Years ago we used to camp with a light wired to a smaller type vehicle battery, and a regular 60 watt bulb on end. I was a child, so I’m not sure how this was possible or made. If the people without electricity could use a re-chargeable vehicle battery, (12v??), perhaps that would be a sturdier power source, but solar is a choice I’d think would be best. The people I am trying to help don’t have any source of light at night, thus limiting them in so many ways. If you could help me figure a simple, doable solution for them, it would be great. I figure they don’t have access to many modern parts, or supplies once they got the light source, so I’d try and supply them with back up or something they could get if they needed to keep the “source” working. I did find some solar lanterns (most used for camping), but thought parts would be hard to get later for the people needing it. Maybe not.

Please feel free to truncate or shorten my ques, I wasn’t quite sure What I was asking for and was long winded. But found it necessary to get point across with my limited knowledge of alternative methods of powering a light source.

THANK you, I have also applied to join your terrific forums.

Sincerely,

Debbie

P.S. I found out that some soldiers in Afghanistan are requesting help for the friendly natives there who don’t have any source for lights at night. The soldiers in Afghanistan could use some easy light sources, too, but FIRST they asked help for the Afghan villages. I thought that was so thoughtful and self-less, that I’d try and help them. I’ve seen military care packages to Iraq and Afghanistan, but this seemed so humanitarian on the soldiers part, that perhaps I could do something from here to help. Thanks.

Debbie:

I am somewhat at a loss. You said you have tried everywhere and could not find any source for solar powered lighting. I admire your worthy goals, but you are really playing catch up here. First, every solar dealer in the United States sells solar powered lighting kits, solar modules, sealed batteries, and all kinds of DC lights. We have been selling low power solar-powered street lights for almost 10 years. Many companies sell new LED low voltage light “blocks” that are almost indestructible and sell these by the thousands to developing nations for lighting huts and rural farms.

I just purchased a sack of solar-powered walk lights from Lowes the other day that cost under $15 each and were very well made. Everywhere I look I can find solar powered lights, solar powered radios, solar powered laptop computers, solar powered water pumps, you name it.

Don’t try to re-invent the wheel, you just need to look in the right places:

www.backwoodshome.com/articles2/yago92.html

www.hollysolar.com/html/lighting.html

www.solarseller.com/dc_lighting.htm

www.etaengineering.com/lighting/lanterns.shtml

www.siliconsolar.com/DC-Lighting-System-p-16679.html

Good Luck!

Jeff Yago

Generator question

Jeff,

I have a home with a year around stream running beside it. I am sure I would not be permitted to dam the channel, but I am wondering if I were to have a 3″ pipe with about 8′ of fall suspended in the flow, and a 1/2 hp deep well pump mounted on it and driven by the water flow, would it act as a generator? the lowest flow is probably about 10 gallons/sec.

Dave Mckee
Oregon

Dave:

You cannot make an AC well pump generate electrical power no matter how fast you run water through it. The reason would take me 4 pages to explain but its due to the basic theory of operation of any AC type motor. It is possible to cause a DC motor to generate electricity if you drive its shaft, but I really doubt you have a DC well pump since these are only used with battery and solar power systems. In addition, most modern pumps, regardless of AC or DC operation, use a magnetic shaft drive to allow sealing the pump section from the motor section, and I am not sure how well this magnetic drive will work in reverse.

Now for the good news – If I lived right next to any stream that flowed 10 gallons per second, you can bet I would have already purchased a water turbine generator. There are many manufacturers who make many different sizes and types of these generators. If your stream and land has lots of fall, most people extend the pipe upstream as far as possible to achieve any more flow, since a lower flow at a higher head pressure is usually more effective in generating power than a higher flow of a lower head pressure. Again, lots of technical reasons why this is so, but if your stream really is year round and you can extend a pipe to a higher upstream position you should do this.

Here are a few sources for more information:

www.backwoodssolar.com/

www.utilityfree.com/hydro/

Good luck!

Jeff Yago

Solar question

Jeff:

I have 5W 12V solar panel charging 12V deep cycle battery. my question is, it seems that I only get 80% charge (12.5V) on a full sunny day. how can I get 100% charge? will it makes any difference if I connect another 5W 12V solar panel in parallel?

Thanks for the help.

Bassam

Bassam:

A 5 watt solar panel puts out about 0.3 amps of current. A typical deep cycle battery could have hundreds of amps capacity, and needs a charging voltage much higher than the battery voltage or you cannot “push” the charging current into the battery.

Your solar charger needs to be operating above 14 volts when charging to reach the higher charge level, and I bet it is dropping down to around 12.5 volts as soon as it is connected to the battery.

A 5 watt solar module is almost a “toy” when wired to a deep-cycle battery. You need a solar module in the 20 to 40 watt range to fully charge this size battery.

Good Luck,

Jeff Yago

Solar with Computer Center Using Laptops

Dear Jeff:

I have enjoyed reading your articles on Backwoodhome.com. I am a Sierra Leonean based in Atlanta, Georgia and Vice President of the Prince of Wales Alumni Association, Georgia Chapter. Ours is a Not-for-Profit Organization working to improve our Middle/High School in Freetown, Sierra Leone, West Africa. I have designed a Solar System for use with a New Computer Center at the Prince of Wales School (POW). In order to reduce the cost of the project, we have decided to use Laptop Computers that use Lithium Batteries. Our current design is for about 15 Laptops (rated at 65 Watt each), 2 Inkjet Printers and about 4 x 40 Watts fluorescent bulbs. I have summarized below the major equipment associated with our solar project;

1. 22 x 165 Watts Solar Panels

2. 1 x 2,000 Watt Outback Inverter/Charger

3. 12 Deka Batteries (265 Amp-hours each)

Since we are still raising funds, we are looking at various ways of reducing the cost of the system. One of our members who is an electrical engineer recommended that we supply the DC power directly from the solar panels to the Laptops Lithium battery which will eliminate most (~11) of the batteries and prevent us from “using a battery to charge a battery”. Although the concept looks good, I will appreciate any feedback you can give on this type of wiring. Is it practical? Do we need a charge controller? Do we still need an Inverter for the Laptops? What about the limitation on battery life for a Center that operates 8 hours per day? Do we still use the AC Adapter or we need a special Adapter to supply the Laptop directly with DC? Any suggested wiring will be appreciated

I will appreciate your answers to this questions.Thanks

Regards

Samuel O. Atere-Roberts, P.E.
Solar Project Manager

Samual:

Due to the many requests I receive each week for design assistance, we have only limited time to address each question and try not to get into specific sizing and equipment selection advice due to the many unknown factors for each specific site. However, I will give you some general comments that should point you in the right direction.

First, you say you want to limit costs, yet you start out with a very large solar array which represents about 70% of the total system cost. The limited number of laptop computers and lights you have indicated do not justify this large array, especially in a country with fairly good sun and mild temperatures year round. If you are not sizing this for larger future loads, my advice is to go with a smaller array and provide the ability to add more modules later as the electrical loads increase.

You cannot directly connect a solar array to a computer laptop battery or operate the computer directly from the solar array. There are many technical and safety reasons which I cannot go into in this limited forum, but don’t try. All solar arrays require a solar charge controller(s) which adjust the voltage and current of the array to the battery voltage and charge level to maximize the rate of charge. The solar array will be operating at much higher voltages than the 12 volt limit on most laptop computers operating directly from a car’s utility socket which is what they are designed for.

Your estimate of 65 watts per laptop seems high. Do NOT go by the nameplate data on any appliance, as these are for legal labeling requirements and are “worst-case” maximum values. Buy a $50 watt meter tester available from any solar dealer and actually test each light and computer for both their watt draw when turned “on” and also when turned “off”. Most will have a standby load when off, and this can be a major load since it will be for many hours of evening and night.

Your laptop computers should do OK with most inverters and power systems, but the printers are more sensitive to power quality and really need a “pure sine-wave” inverter. The Outback inverter is an excellent choice, but be sure to consider their “sealed” model for dusty climates. Years ago we always ran at least some DC lights and DC appliances directly from the batteries as this avoids the efficiency losses of an inverter. However, todays inverters are extremely efficient and reliable, and its far easier to just use standard 120 VAC lights and appliances, as long as they are high efficient brands.

Your list indicates 40 watt fluorescent bulbs. My guess is you were planning to use standard 4 foot 40 watt fluorescent lights. Please note these actually draw almost 50 watts due to the ballast load and are not good light quality . You should use 4 foot T-8 style fluorescent lamps as these require only about 32 watts each to run, will produce far more light than a standard 40 watt tube so you can get by with fewer lights, and their electric ballasts are high frequency with no light “60 cycle flicker”.

I cannot tell what type battery you are planning to use, but suggest you give this a lot of thought as it looks like this also does not appear to properly match the loads and solar input.

Finally, the charge controller is the most important item in the system and you really want a good quality model as it can reduce the number of solar modules you need, but you did not even mention this. The Outback MX-60 is a good choice for this application, but you may need more than one with this many solar modules. You all really need some engineering design assistance to get this right.

Good luck!

Jeff Yago

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