My Solar Project !!! (Questions)

thanks I did see those videos.  My question was if i can connect those pv panels that are rated for 18v to 12v charge controller, or does it have to variable charge controller?

"My question was if i can connect those pv panels that are rated for 18v to 12v charge controller, or does it have to variable charge controller?"

Most any 12 volt charge controller will handle 18 volts input. Some panels have 21-22 open circuit voltage. It's the current handling ability of the controller that's important.

no, I believe that you and mr. abel are confusing a couple of things. 

for mr. abel, you are confusing nominal voltage with voltage at max power.  it is true that 12v (nominal) charge controllers will handle 18v (vmp - voltage at max power) inputs.  however, mr. rzeszotko was referring to an 18v nominal module with vmp at 29v, which is not capable of being handled by a 12v nominal pwm or shunt controller.

for mr. rzeszotko, switchable does not mean voltage converting.  while for example, a xantrex c40 or morningstar tristar is "switchable" to the choice of 12/24/48 volt NOMINAL systems, the controller is NOT capable of down converting an array voltage of a higher nominal voltage down to a battery bank of a different nominal voltage.  if using a pwm or shunt controller, the nominal voltage of the array should match the nominal voltage of the battery bank.  the switching only allows for the controller to be adjusted for 12v, 24v, or 48v nominal operation under the assumption that the array nominal voltage matches the battery nominal voltage.

here is an article that may clear some things up.

http://www.altestore.com/howto/Solar-Power-Residential-Mobile-PV/Solar-Components/Solar-Panels-PV/Solar-Panels-PV-and-Voltages/a98/

hope that helps, thanks for contributing to the thread.

james
altE staff

well, not quite.

you need to know these two variables first

1. what is my array nominal voltage?

2. what is my battery bank (aka system) voltage?

with those two questions answered, you could move on.  if the answer to Q1 and Q2 are not the same, then you are forced into an mppt controller.  if they are the same than a pwm controller is an option.

given that your answers force you to have an mppt controller you would then ask yourself these questions.

A. is there a controller that can down convert for the parameters i set out in Q1 and Q2?

B. if there is a controller that meets question A, does that controller meet my requirements for ampacity (current) as well?

- so this is a simplification, but this is where some of the mppt string sizing tools, or a solar professional would step in and make sure everything is correct.

regarding the most recent post,   if the answers to question 1 and question 2 were the same, AND you selected a pwm controller with field selectable voltage settings, then YES, you would select the appropriate voltage (same as you answered in Q1 and Q2) on the controller, usually with a jumper of some type.

if however you selected an mppt controller, there is generally no selecting done at all.  all the math is done beforehand, and the controller can auto-detect the battery bank voltage without human intervention in the case of most mppt controllers.

for most new folks, the question of "what am I trying to do?" is the most essential, yet most overlooked.  with this as a guide, a solid solar pro can help somebody along to a functioning system to reach an end goal.  all too often I get calls and emails after somebody has a hodge podge of stuff bought on sale that does not work together.  i would encourage any new folks to get a system goal and a system design on paper before selecting any individual components.

all that being said, this forum is for education and sharing, so if you have specific questions on components, feel free to fire away, usually the community is eager to help.

james
altE staff

because at least 80% of the market is grid tied, where they dont care what your batteries like.  so if you make modules, which market segment would you serve? 

there are still 12v and 24v nominal modules around for battery based systems, but they are often smaller in size and higher in cost per watt.

now that there are controllers that can deal with other voltages, in does not matter as long as there is a solid system designer.  what is often the case is that the cheaper larger modules require mppt controllers for battery use, and often require truck shipping, all but eliminating the savings $/watt savings that attracted the new folks with smaller system goals to begin with.

james
altE staff

something in the 5 watt range.
let me explain. i started my system with a single 5w module, a 7ah sla battery, and a 150w inverter. then i found that my system was out of balance. after a bit, i ended up adding 2 more batteries, a charge controller, another module. wired things wrong, but nothing blew up and i learned quite a bit. now i am working on fusing, proper wire sizes, grounding.
this little system is now used just for little things, like charging the cell phone or my rechargeable batteries. running the stereo constantly through the summer (really non stop!). it has given me an idea of what i can expect. summer i can run the batteries constantly and they just suck up sunshine the next day. winter they must be babied, production drops to nearly zero. shading, proper angle and orenation , voltage drop, mid summer cleaning, etc. so much easier to fry a $20 charge controller and $60 or 70 in batteries than to add a zero or two to those numbers.
evergreen makes nice modules for offgrid stuff. i think that they make nice modules period. i also like kyocera. not to partial towards bp. not because of quality, more that they are a giant oil co. just my two cents. -m

OOps.. Mybad! I didn't follow the link to the panel. Thanks Jim.. 

 Mr Rzeszotko;

  Mr Cormican, is asking these questions (I think)
 because ,it is very important to know what you expect to get out of the system you are trying to build.That way he can save you costs and mistakes,that sometimes turn out to be frustrating and costly.

 If you live in an area that pays you for the power you may add to the grid, that may be a better option,than a non grid tied system.400 watts of a non grid tied system may not run what you want it to,although, it can help you save on your existing electric bill if you use it for some appliances.

 If, you have an outside storage for batteries you can use acid filled, if they have to be inside you need to use sealed batteries and they need to be as close to the inverter as possible.If you are tied to the grid without battery back up you will not have power when the grid goes down,to add batteries to a grid tied system , you add a bunch more money to the system.

 Off grid system means at night you will only be working off of the batteries, you may need 8 or more and then,you also need to know what kind of load you are planning at night...do you have enough battery backup?

 Inverter choice is important.  off grid systems with enough power but not enough surge time from the inverter may,run your washer but not your spin cycle. Instead of one second surge You may want to get a five second surge capability,better for starting motors, wanting a big load.
 The one thing which I,did not think about,so I have to plug into the grid for spin cycle,no big deal to me but to some they would be disappointed (actually guess i was disappointed initially, missing this one little detail).An inverter that uses a minimal amount of power when on is a plus also.

 An off grid system of 400 watts will not run your waterheater,stove,or dryer.

 The systems really are fairly simple but having the RIGHT system is critical for your happiness,thats why you must really take some time ,even write it down on paper,your goals and try to plan your expansion and how you wish to go about it..the cost difference in several of the individual parts/grid/off grid
can be substantial.The learn center here on this site is great and you can also look at the off grid systems on how they are wired and different features.I ,studied and thought for a couple months before deciding exactly what I, could afford and what I wanted to do and it really paid off.

 No final decision was made though until I called AltE personally at their store.At this time they made a few points about ground fault breakers and electrical code and grounding.. to make sure I knew what the latest electrical code was on that particular issue.

 Rechecked the disconnect panel and controller wiring one more time before throwing the switch and yes..... I,found one wiring mistake I made,fixed it ,a look see one more time
 and she has been humming ever since.

 A very happy customer
 AltE,James and the rest of the crew go beyond the call to help people,they want them to be happy and knowledgeable
 with what they are getting and how to use it.

 All the best to you and your, soon to be new system.
 Rob
 

Marcin, I'm a little curious.  What do you want from your system.  Or stated another way, what benefits are most important to you?  I ask because I started out with a system barely big enough to keep one CFL bulb burning for a few hours.  My goal at the time was a backup system to serve in the event of power failures.  I thought of other things of course, like cooking, heating, and refrigeration, but I didn't want my small budget to keep me from getting started.  I now have a system that will do all of those things, with limitations of course.  I've never regretted starting small.  If I had waited until I had the finances to build a system big enough to meet all my goals, I'd still be waiting.  You're right, of course, to learn as much as you can before taking the plunge, but once you get a system up and running you'll really start to learn.

John

I would suggest to start off with an off-grid system and think about grid-tie later.  After we come out of this proverbial eye of the economic storm, we could be in for some very rough sailing, including loss of basic utilities should hyperinflation hit.  Los Angeles and New York both independently suffered power outages recently even without such an impetus!  Having a back-up system is more important than ever, even if it's only powerful enough to charge your cell phones and flashlights and radios.  Have that battery bank now and worry about tying it into the grid later.

As for the charge controller, get yourself an MPPT capable one right off the bat.  I use the Outback MX-60, which has worked great.  For one thing, the MPPT controller will maximize your power output in the morning and the evening when otherwise you might not get enough voltage.  Also, if you want to add new modules to your system later, you may find that putting them in various series and parallel configurations requiring a higher voltage is the only way to make it work.  Plus, if you put your modules in series to begin with (18Vx2=36V), the higher voltage makes for more efficient transfer (less voltage loss) through wires.  It would also be better to put your batteries in series (12Vx2=24V, or 4Vx6=24V) and then down-convert at your load panel if you want to run 12V appliances, or else just send that directly into your inverter.