Questions on Solar Panels

[gr8njt]

My electrical plan includes the use of solar panels to "float" and "equalize" the house batteries when the bus is on "hybernation status". I also figured that it may be a good source of free power to run the pro-heat DC pump during the colder weather.

Foreword: I know they are quite expensive and it will take years to recoupe the expense to set up the system anyway, here are the questions for the solar gurus:
a.   Any one of you have such a system in your bus conversion?
b.   What brand/make of solar panels can be easily configured into a 24 volt system?
c.   Any experiences on the "flexible panels"? I sort of like them because they seem to be able to be be glued directly unto the curved MCI9 roof. Any undue complications if I glue them directly to the roof?
d.   What solar charge regulators do you use/recommend?
e.   Is a set of four (4) 15 watt 12V panels enough to do the float on a 24V bank during the winter or other colder months? I am not as worried in the summer and warmer months because I will be driving the bus from point A to point B and the Proheat would be running less.
Thank you.

[ChuckMC8]

I have this setup on my MC8 with Zantrex C-35 controller configured to 24 volts. Email me if I can provide more specifics-hth Chuck
http://groups.msn.com/July2004Busphotos/shoebox.msnw?action=ShowPhoto&PhotoID=70

[Sean]

a.   Any one of you have such a system in your bus conversion?

Yes.

b.   What brand/make of solar panels can be easily configured into a 24 volt system?

I use Shell Solar (now SolarWorld, but panels in the pipeline are still widely sold as Shell).  These panels are 24v nominal, so you can run an odd number of them (I have three, 110 watts each).  If you get a (more common) 12-v panel, you will have to run them in series pairs.

c.   Any experiences on the "flexible panels"? I sort of like them because they seem to be able to be be glued directly unto the curved MCI9 roof. Any undue complications if I glue them directly to the roof?

They are very small (wattage-wise) and very inefficient compared to regular laminated panels.  Also very expensive on a per-watt basis.  You'd have to cover about twice as much roof with these than with laminate panels, and it will cost you more than double.

d.   What solar charge regulators do you use/recommend?

Without question, Blue Sky.  I have their smallest 24v controller, the 3024i.  That's rated for 30 amps, which would be over 700 watts of panels, twice as much as I currently have, and certainly more than I can fit on the roof.  The MPPT technology maximizes the amount of charge available under all solar conditions.

e.   Is a set of four (4) 15 watt 12V panels enough to do the float on a 24V bank during the winter or other colder months? I am not as worried in the summer and warmer months because I will be driving the bus from point A to point B and the Proheat would be running less.

That depends on how large your bank is (in Amp-hours) and what parasitic loads will remain connected while your bus is sitting.  It also depends on whether or not you intend to tilt the panels to the south while parked, or leave them flat on the roof.

The 60 watts worth of panels you are looking at could generate, under ideal conditions (meaning a bright, sunny, cloudless day with the panels aimed directly at the sun) a little over two amps.  Under more realistic conditions, your panels would average about 1 amp during the solar sweet-spot (9:30am to 3:00pm).  As long as your parasitic loads and "self-discharge" rate average less than 6 amp-hours or so per day, you'll be fine on sunny days.  However, remember to figure in what percentage of days are sunny in the place you'll be.

I don't think you'll ever get an equalization charge with this setup, though.

HTH,

-Sean

[H3Jim]

Figure on spending about $4.50 to $5.00 per watt of power for the panels themselves.  I just bought 4 panels, made by BP for a total of 600 watts.  The panels are 31" x 62" by 2".  The hard panels are more efficient at power generation which means if you are trying to get a lot of power on your roof, and space is an issue, these amorphous silicon panels give more power per square foot than the flexible ones.  The issue with configuring panels is to just get panels with a voltage of 33 to 35 volts for a 24 volt battery system.  The panels can only charge the batteries if they are a higher voltage than the batteries.  If you get two 17 volt panels, you can wire them in series to get 34 volts.  Its pretty straight forward.  Panels come in a large variety of wattages and sizes. You will be most interested in voltage and wattage.  I would stay with a big brand name in case you ever have to replace one, or want to add another panel later.  That way you can be relatively sure you can find an identical panel.

You can just get or make L brackets to mount the panels to the roof.  Dichor is an unbeatable sealant.  The installer I bought my panels from has used Dichor for thousands of installations and never had a leak.  You can get fancier with the mounts so you can tilt up the panels.  This might be a good way for you to go in the north so you can angle the panels toward the small amount of sun you get.  The down side to tilting your panels is you have to get up there to tilt them, not something you want to do with snow or ice on the roof.

controllers. Blue Sky invented a technology that provides maximum power transfer from the solar panels to you batteries.  MPPT.  They license it to Heliotrope, but I don't thin anyone else uses it.  Highly recommended to get the most from your panels, especially in lower light situations.  Their web site is  http://www.blueskyenergyinc.com/products.htm  While they are the manufacturer and do not sell direct, they are very helpful people with a great product.  I bought the 3024i controller.  Good for up to 30 amps of power at 24 volts.  It will also trickle chare a second set of batteries when the main set is full – I use this for my start batteries so that even when the bus sits for a while the start batteries are always full too.  You can get two flavors of remote panels for this controller too, one comes with a shunt so you an monitor total amp hours in and out of your house batteries instead of just voltage level.  While you should always use the same panel, not mix and match since the voltage output of the panels must be the same, with the 3024, if you late want to add a different voltage panel you can add another controller and gang them together to charge the same set of batteries.  Probably not too useful for us bus nuts, but you never know.

As for how many watt you need, you have to do the calculations on your system.  Power in  / power out.  I have several friends that have the solar, one has 300 watts and is full by 10 am ( in Yuma) the other has 800 watts and is full by noon.  He has a larger battery bank and runs lots of electrical from it.  60 watts seems a little small for what you want to accomplish, especially if you are running a pump for your preheat.  You will need to calculate the amp hours you expect to use to see if you proposed wattage is enough.

[gr8njt]

Chuck, Thanks and I sent you an eMail.
Sean, as usual your responses are direct to the point and very concise.
H3Jim, Thank you. Very informative post!
With a 400-600Ah 24V bank, what wattage do you recommend to "float" this bank IF the total parasitic loss is (Just a guesstimate on the consumption of a 12V proheat pump) less than 10A (24V) per day?  TY

[H3Jim]

"They" say that you should have 50 watts for every 100 amp hours of battery as a minimum.  But that is sized more for battery capacity than load.  Rest assured, you will probably want more panels / wattage after you start using them.  So plan ahead with what you buy and with how you mount them for space utilitzation.

You might start out with that 60 watts and see if its enough.  I suspect it won't be, but some is better than nothing, and it will give you experience.  Depending on your budget, I might try a single panel in the 150 watt range.

Arizona has no sales tax on solar panels / systems.  Of course  mail order from another state, or ordering from a state that has no sales tax also give you the savings.

[tekebird]

I got two Pannels from Solarpath.com

just use them as trickle charge on the 4104, works great, have not had to charge or jump in the 6 years since I put them on.

[niles500]

Grant - I have (and will) put off this purchase waiting to hear how the Holographic panels work in our use - Since our uses move its hard to 'hardwire' for best efficiency and some how adjustable panels don't seem to be an answer for us - Maybe you could be the Guinea Pig? If the hype is correct 1 panel will do the work of 2.

[rv_safetyman]

I am bringing this to the top again.  We were at the FMCA in Redmond, and as vendors we don't get to the bus enough to have the generator bring the batteries up.  At the end of the show we were not in good shape.  Part of the problem is not enough batteries (8 golf cart) and a house fridge.  So, I think I need to crack out and get a solar system going.  BTW, in terms of justifying the cost, FMCA now charges $160 for marginal electrical power for each main event.  Diesel for the generator is not cheap either.  We will not be able to afford enough panels to keep the batteries topped off, but I would like to start with a system that will keep me from going too far into the hole (probably three 125 watt panels)

So, as I did my search on this board, I found this thread that seems to be the most pertinent.  I have some additional questions:

1) Anyone want to suggest a good on-line source?

2)  Sean went with Shell and Jim went with BP.  My quick look on http://www.wholesalesolar.com shows they are both a bit over $5 per watt.  I assume that both are quality panels

3)  On another general RV board someone brought up the possible issue of conflict with the alt. (I have a dedicated alt. for the house batteries).  Does the Blue Sky system take care of that?  are both charging the batteries when driving down the road?

Thanks for the help.

Jim

[luvrbus]

Northern Arizona Wind and Sun has a good web site for solar information also

[H3Jim]

There is no sales tax in Arizona for solar equipmpent.

I think its  a good idea to go with a major brand / model panel so if you want to add more later, they will be available.  If there is too much difference in the volatage, capacities of the panel, the one with the higher voltage will do all the work and the lower one will not be  providing you current for your $.

I called Blue sky in Vista, Ca.  (north San Diego) They are wholesalers only and won't sell to you directly. I talked to the wife of the inventor / ower - they invented the technology that everyone else has to license).  She talked with me for 20 minutes, and was very helpful and supportive.  She gave me the names of their high volume distributors, I went that route so I knew I was using a high volume, committed dealer.

Yes the controller and the alt will be charging at the same time, possibly. Each is controlled by the battery voltage.  If one is charging at a higher voltage, it will keep the other from doing any real work.  No harm though.

I bought the version of the controller that keeps track of all amp hours in or out, so I know more than just voltage.  Very handy if you are using the bus often, as it takes several hours of non usage for the voltage to stabilize enough for it to be a reliable gauge of your state of charge.  Use the shunt monitor, you'll thank yourself (or me)

[rv_safetyman]

Jim, thanks for the information.  After our discussion about battery "state of charge" last year when I was at your place, I did a lot of research.  I ended up getting a Bogart Engineering TriMetric battery monitoring system:   

http://www.bogartengineering.com/

It has the shunt system to measure the amperage in and out.  I have been playing with it and it seems to be a great system.  I do want to check the calibration by using a hydrometer, when I can get the bay emptied and get to the battery box.

It was this meter that convinced me that I need to get some solar going for those times we are away from the bus for major parts of the day.  Later, I will upgrade batteries, but it just does not make sense to throw my current golf cart batteries away.

Jim