Reply
 
Thread Tools Display Modes
 
Old 08-17-2008, 03:38 PM   #1
Site Team
 
crazycal's Avatar
 
Join Date: Feb 2007
Posts: 4,087
Re: Solar Power Conversion questions

Here is 400 watts delivered to your door for 569.99. 400 watts of solar would probably cost you between $1500-2000 today. It seems that solar is getting more expensive not cheaper.


http://www.costco.com/Browse/Product...=1&topnav=&s=1
__________________
I'm hungry!

You Gotta Let Me Fly
crazycal is offline   Reply With Quote
Old 08-18-2008, 10:54 AM   #2
Bus Nut
 
Join Date: Dec 2006
Location: downriver, detroit mi
Posts: 794
Re: Solar Power Conversion questions

michael, thanks for the response, i responded yesterday with the thought that air and electric heat don't fit the solar power profile and then posted it into cyberspace.
thanks again
paul iossi is offline   Reply With Quote
Old 08-18-2008, 11:30 AM   #3
Hex
Skoolie
 
Hex's Avatar
 
Join Date: Jul 2008
Location: Buffalo, New York
Posts: 190
Year: 1995
Coachwork: Bluebird, Model 3800
Chassis: International
Engine: T444E
Rated Cap: 42
Re: Solar Power Conversion questions

Quote:
Originally Posted by busnutz
“Cheese” I have a question for you … why would you install 60-15 watt panels, why not just install larger 130 watt and up panels. That would be quite a bit cheaper in the long run and 100% easier to install.
One thing that I can see with that set-up is that with more, smaller panels you're less likely to lose efficiency from a cell in one of the big panels being shaded. Even one cell shaded (or a number of cells half-shaded) can drop your efficiency by 50% ...

At least as I understand it from my investigations ...

Though I'm looking at the bigger panels for my potential system so that I can get as much power as possible - we're in a low insolation area and I want to maximize the efficiency of the area ...
Hex is offline   Reply With Quote
Old 08-18-2008, 11:33 AM   #4
Skoolie
 
Jerry Campbell's Avatar
 
Join Date: Dec 2003
Location: Summit, Oregon
Posts: 117
Year: 1975
Coachwork: Crown
Chassis: Supercoach
Engine: DD 6-71N
Re: Solar Power Conversion questions

Hi,
I have a roof full of solar panels (1580 watts) and 1000 lbs. of batteries (1680 amps), a 3000 watt sine wave inverter and a 400 watt wind generator and a 2000 watt gas inverter generator/120 amp charger for backup and I can't do what you want to do.
A/C and electric heaters draw way too much for consistant use. They are Luxury items. You can forget those.

For camping, it takes very little electricity BUT for living there is NO SUCH THING AS TOO MANY solar panels on a bus. Even if we had the space we could not afford enough. In 2002 my system cost was about $12,000. Since then the price has almost doubled. Don't be discouraged. Do a load analysis. Do what you can now and add more later. During the process you will learn what you need to know.
Good Luck
Jerry
Jerry Campbell is offline   Reply With Quote
Old 08-18-2008, 12:38 PM   #5
Hex
Skoolie
 
Hex's Avatar
 
Join Date: Jul 2008
Location: Buffalo, New York
Posts: 190
Year: 1995
Coachwork: Bluebird, Model 3800
Chassis: International
Engine: T444E
Rated Cap: 42
Re: Solar Power Conversion questions

Thanks Busnutz!

That makes lots of sense. I hadn't thought of multiple controllers for the panels, however, I had thought of potentially getting an extra controller to put on the 'in' line from the alternator in order to insure that the batteries wouldn't over-charge while traveling ...

How's that sound?
Hex is offline   Reply With Quote
Old 08-18-2008, 02:04 PM   #6
Bus Nut
 
SeanF's Avatar
 
Join Date: Nov 2004
Location: Tucson, AZ
Posts: 524
Year: 1993
Coachwork: AmTran
Chassis: IHC
Engine: Dt360
Rated Cap: 19
Re: Solar Power Conversion questions

I agree, lose the A/C & electric heat, then start your analysis from there.

1. Estimate your average electric needs per day. This should result in some number in watt-hours, and will tell you your battery bank size. You don't want to completely discharge your battery bank every day, or when you have a string of cloudy days, so your battery bank capacity should easily be 2x what your max daily needs are.

1a. Fewer, bigger batteries are better than a bunch of smaller batteries for the same reason that a few, bigger panels are better than a pile of smaller ones -- fewer connections, easier maintenance, to name a few. Do you want to tilt 4 big panels or sixty small ones? (And you'll likely want to tilt your panels in the winter.)

2. With your battery bank size (capacity) estimate, you can use your geographic location's average solar insolation to estimate the number of panels you'll need to keep them charged. You'll want to size for the shortest day of the year, i.e., 22-ish December. If your panel array seems like it will be too expensive doing it this way, you can also do calcs to see how much money you'll spend on a generator & fuel to take up the slack on short winter days & long strings of cloudy days.

3. Using the size of your panel and battery arrays, you can get an idea of the charge controller capacity, wire size, etc.

All in all it's not a trivial task to make your system the right size; it takes a lot of research and number crunching. I've not paid an electric bill, or had to be tethered to "the grid" for over two years. Worth it? Hell yeah.
__________________
Bus conversion/info here
SeanF is offline   Reply With Quote
Old 08-20-2008, 09:47 AM   #7
Bus Nut
 
SeanF's Avatar
 
Join Date: Nov 2004
Location: Tucson, AZ
Posts: 524
Year: 1993
Coachwork: AmTran
Chassis: IHC
Engine: Dt360
Rated Cap: 19
Re: Solar Power Conversion questions

IMO, what you want to do can be done for an non-outrageous price if you use small loads, especially for the 24x7 stuff - very efficient DC refrigeration, LED lights, flat panel monitors for your surveillance equipment & computer(s), laptop computers over desktop models, digital recording rather than physical media, etc.
__________________
Bus conversion/info here
SeanF is offline   Reply With Quote
Old 08-22-2008, 05:57 PM   #8
Skoolie
 
Lady Franklin's Avatar
 
Join Date: Feb 2008
Location: Regina, Saskatchewan, Canada
Posts: 130
Year: 1989
Coachwork: Thomas
Chassis: 3800
Engine: 7.3 International Diesel
Rated Cap: 72
Re: Solar Power Conversion

Hey I read these books on solar and found them very helpful check them out. The RV solar battery charging is right up your alley. These would be a great resource for your research. I have read both cover to cover and still need to do more research before I buy my set up. Pay close attention to the estimated usage worksheet, this will give you an idea of how much your going to need. But as mentioned earlier your AC and heating desires are not practical but there are alternatives. Good Luck.

Book 1 RVers' Guide to SOLAR BATTERY CHARGING 12volt DC-120 volt AC Inverters
By Noel and Barbara Kirkby ISBN: 0-937948-08-X

Book 2 The Complete Idiots Guide to Solar Power for Your Home
By Dan Ramsey with David Hughes ISBN: 978-1-59257-643-2
Lady Franklin is offline   Reply With Quote
Old 01-30-2010, 04:39 PM   #9
Bus Crazy
 
Join Date: Jan 2008
Location: Upstate NY (Mohawk Valley)
Posts: 1,096
Re: Solar Power Conversion questions

Quote:
Originally Posted by CHEESE_WAGON
I can't seem to find the answer to the two main questions on my mind...... forgive me if this has been mentioned before, sometimes I'm lucky if I can remember what someone said five minutes ago.

Question 1)

If I were to have a 3,000 watt inverter with a 4,500 watt surge capacity..... at a given load of 70% capacity......

How do I calculate the current draw on the battery bank? Would it vary with the AC load on the inverter, or would the inverter have a steady load on the bank, no matter the load?
The the amount the inverter will draw is equal to the output wattage plus any losses due to wire heating and converter efficiency, and varies with changes in the load. Figure using 11 amps at 12 volts DC for every one amp at 120 volts AC if the inverter is 90% efficient.

3kW x 70% = 2.1 kw load at 120 VAC. Divide watts by volts to get 17.5 amps AC. Multiply by 11 to figure roughly 192.5 amps at 12 volts DC. Since battery amp/hour capacities are usually rated at a 20 hour discharge rate, you should have a 3850 Ah 12-volt battery bank to run this much load in a steady state. In 10 hours you will reach 50% discharge. You can obviously run peak demand for short periods of time on a smaller bank if the battery wiring is big enough.

For this much power usage, it might be better to use a 24-volt battery bank and 24-volt inverter. The current would be down to 96.25 amps and the storage required would be 1925 Ah. Though the number of batteries in series-parallel would be the same, the lower current would mean less loss in heated wiring, and less fire danger from a corroding connection starting to get hot.

Quote:
Originally Posted by CHEESE_WAGON
Question 2)

If it does vary with load, with a 70% load, how do I calculate how many solar panels I would need to generate enough power to overcome that drain and provide a small charge?
Calculate solar availability in watt-hours by multiplying array capacity times the standard hours of insolation for the season and the area. Compare this with your estimate of watt-hours to be drawn. Standard insolation hours figure in the fact that early morning and late afternoon are less productive than right around noon. Standard hours vary from about 4 in the north in winter, to I guess 6-10 in the south in summer.

Array wattage is specified at peak output, which is generally a higher voltage and lower current than you get connecting direct to the batteries. For 12-volt panels, the peak is usually around 17 volts. If you wire the array through an MPPT charge controller, which lets the panels run at their best output, multiply the specified wattage times the insolation. If you wire the array directly across the battery bank, and use a controller that disconnects the array when the batteries are full, then use the battery voltage times the short-circuit current (Isc) for the wattage and multiply this times the insolation. This is usually about 30% less.

I don't have a figure for how much extra capacity to add for losses in battery charging. You will not have 100% of the electricity you put into a battery available for withdrawal, so be sure to add more than the minimum.

Quote:
Originally Posted by CHEESE_WAGON
One other thing I thought of was to put certain portions of the load on its own bank and inverter (several small banks and inverters), I would think this would help in both troubleshooting and helping to keep one bad battery from taking out ten or twelve.
There are two schools of thought on this - one big expensive inverter, or several small ones. If inverters are left in idle waiting for a load, instead of removing power from them, there are small amounts of idle current drawn. When you have multiple inverters, this begins to add up. Also, if you had one big load to power for a while, no one of the small ones may be capable of handling it.

On the other hand, with one big inverter, if it goes out you are in the dark. With multiple small ones, you could transfer a critical load to an inverter in place of a non-critical load, and keep on keepin' on. (Just like "Genghis Khan and his brother Don.") Multiple medium-sized battery wires would spread out the heat compared to one set of extra-large ones. With this option you would pretty much use 12-volts, as small 24-volt inverters are rarer.

A compromise is usually one big inverter, plus one or more smaller ones for critical loads. You might have a refrigerator or some medical equipment on its own inverter, so you could put the big one to sleep when you aren't up and active and still not lose the important item. You wouldn't lose the critical load if you tripped off the main inverter trying to run a circular saw or something, either. Or, you could install a small pure sine wave unit for delicate electronics, and make the big one a cheaper modified sine wave unit.

It sounds like you were thinking of multiple battery banks for multiple inverters. This could get overly complicated. With good battery maintenance, you should not need to do this. Just don't mix old batteries with new, or mix different sizes together. If one string has a battery that is weak and runs out first, the good batteries will run down trying to recharge their wounded comrade.
__________________
Someone said "Making good decisions comes from experience, experience comes from bad decisions." I say there are three kinds of people: those who learn from their mistakes, those who learn from the mistakes of others, and those who never learn.
Redbear is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Solar power 3forward2back Conversion General Discussions 1 09-07-2012 12:56 PM
Solar power vent fan lornaschinske Electrical, Charging and Solar 2 03-24-2012 09:09 PM
Solar power questions... ezbme Electrical, Charging and Solar 54 07-30-2009 01:42 PM
Solar power and usage drchefscott Skoolie Conversion Projects 7 02-07-2009 08:22 AM
Solar power rolecall timecrash Conversion General Discussions 4 08-19-2007 08:25 PM

» Virginia Campgrounds

Reviews provided by

Powered by vBadvanced CMPS v3.2.3

All times are GMT -5. The time now is 09:41 PM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2017, vBulletin Solutions, Inc.