Is aux/alt charging recommended for solar systems/batteries?

suecosueco Registered Users Posts: 22
I now have 8 solar panels (4x125W and 4x85W) and 8 batteries: 4/4 for my office, and 4/4 for the garage/pantry (small appliances). Right now, they are both 12V, but I'm getting ready to move the garage/pantry to 24V.

When I read about the care of the batteries, it says to top them off (to about 15V) regularly.

So, trying to be a good girl (yes, it's painful), I try to top off my batteries. What happens, the controller starts adding about 10-20W of power to the batteries, to top them off.... slowly. ALL DAY!

So, yes, the batteries need to be charged up slowly at the top of their charge. HOWEVER, the most expensive part of my set-up - the solar panels - are effectively doing nothing during this time.

I could go into a long song-and-dance about all the different arrangements I've tried to get the perfect usage so charging for topping off could occur slowly.... However, the bottom line is, I think it MUST be more cost effective to have an alternative way to top off your batteries - even if it's electric (?) (don't make me take this to the grid).

Thoughts? Am I missing something? Do they make something (efficient) just for topping off your battery bank.

I am in the process of building a stationary bike (out of an old bike) with a 300W generator, to charge in the evening. I guess I'm ok to exercise my butt off to top off the batteries. Still, I'm thinking that they make ?something? just for this purpose, so you're not wasting your high-dollar solar panels.

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Is aux/alt charging recommended for solar systems/batteries?

    Without knowing all the details of your system, such as the capacity of the batteries and the type of charge controller, it is difficult to say if there's anything wrong or imbalanced.

    However, standard charge profile of batteries is a lot of current at first bringing the Voltage up quickly. Then less current over a long time to finish charging. You might want to read through the battery FAQ's, especially this point: http://www.windsun.com/Batteries/Battery_FAQ.htm#Battery%20Charging

    For a 12 Volt system, 15 Volts is usually the equalization point not the charge point.
    And yes, the bane of off-grid systems is all that potential power that doesn't get harvested because the batteries are full and the sun is still shining brightly on the panels. That's what load shifting is all about; turning on whatever you can to make use of the otherwise untapped power potential.
  • suecosueco Registered Users Posts: 22
    Re: Is aux/alt charging recommended for solar systems/batteries?

    It's a general question, targeted at those who have experience with off-grid solar systems. For those in the know: if you set up a solar system, do you GENERALLY include some kind of auxiliary charging device, especially for topping off the batteries? Or would you say that an off-grid solar system runs it's best - or just as well - without this?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Is aux/alt charging recommended for solar systems/batteries?
    sueco wrote: »
    It's a general question, targeted at those who have experience with off-grid solar systems. For those in the know: if you set up a solar system, do you GENERALLY include some kind of auxiliary charging device, especially for topping off the batteries? Or would you say that an off-grid solar system runs it's best - or just as well - without this?

    I think I meet the qualifications for answering. :roll:

    We generally include an auxiliary power source such as a gas powered generator for when the sun doesn't shine enough to charge batteries. Mostly it is used to supply the Bulk charge stage, as gens are rather inefficient for supplying that last bit of power needed for the Absorb stage. One the whole you try to balance the panels and battery capacity against loads so that you have predictable power capacity on sunny days at least.
  • suecosueco Registered Users Posts: 22
    Re: Is aux/alt charging recommended for solar systems/batteries?

    I hope you weren't offended by my comment - I believe you are quite knowledgeable. And I know you know more than I do. I was trying to emphasize I was coming to you for a general answer, not so much a specific answer.

    Also, I have 2 morningstar controllers, and I know there are problems with those topping off the batteries. But, I didn't want to get into that discussions (separate thread).

    I do try to balance the load. This is hard for me because I'm retrofitting solar into a 35 year home, while TRYING to not impact the existing wiring too much (as it is a beautiful home I hope to sell when the market get's back to normal - if that happens).

    I am hoping to set up a resource (nonprofit) in Kansas City to assist "the average joe" to ADD solar to their homes. I'm trying a BUNCH of different things to see what is doable/affordable/safe/non-invasive, as well as what is BEST for this niche. I do believe this is doable, and getting more and more so all the time. I'm trying to keep the total cost under $5,000, while maximizing the solar aspects.... and, for now, I'm just learning!

    Thanks so much for your help.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Is aux/alt charging recommended for solar systems/batteries?

    I'd be remiss in my duties if I didn't point out that solar is an expensive way of getting power. You should include that fact in any advice given out. Some locations have incentives to help offset the capital costs, but it still comes to a pretty penny. It may technically save on your electric bill, but the price will be generating your own electric at several times that of the utility.

    The usual method of adding solar to an existing house is via grid-tie, which more economically feasible but not always allowed (depending on location and utility involved). Where it can be done it requires cooperation of the utility and local officials, complete with plans and permits. Another caution that must be included is that DIY solar can be a short path to burning your house down. It's electricity; it's dangerous. Batteries have enough current potential in them to weld steel. Solar panels can produce their maximum current continuously across a dead short. Get the wire sizing wrong, forget the fuses, and you have an almost certain impending disaster. Grid-tie arrays are typically 300 or more Volts, which is enough to stop your heart permanently.

    Homemade panels, BTW, are something to be avoided for actual household use. It's impossible to build them yourself to a standard that would meet UL approval, or even meet reasonable longevity expectations.

    I'm not trying to discourage you, but it is absolutely necessary to understand the dangers as well as the benefits involved. They are manageable; many of use deal with this stuff every day. I have yet to electrocute myself in 50 years, despite many well-founded attempts. :p
  • suecosueco Registered Users Posts: 22
    Re: Is aux/alt charging recommended for solar systems/batteries?

    No home made panels.

    I understand that it's a $dollar loss - that was the first solar knowledge I acquired. I tell everyone that up front - you will not even break even.However, I do think that small systems can be successful - I already feel good about what I've done, even though it's not quite perfect yet, it's doing something.

    I'm trying to stay away from grid-ties. Right or wrong, I looked into them first, and decided there were several complexities there I wanted to avoid - one of which was hiring an electrician. I want to be able to safely do EVERYTHING I do, and be able to say "I did this myself without incurring harm to myself or my home, and it works".

    As a side note, I've fixed several wiring errors in both homes that I've owned, which had been put there by a professional electrician, and any one of them could have burned the house down.

    All this to say, what is the BEST way to configure a small solar system for an amateur wanting to do SOMETHING, even something small.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Is aux/alt charging recommended for solar systems/batteries?

    It would depend on the particular home, of course. Being able to get good insolation is important; some houses just don't have the exposure to make the panels work well.

    Then there is the application. For one thing, a separate power system shouldn't be tied to the utility at all, save through perhaps and auxiliary plug to provide AC in and power circuits (if critical) when the sun doesn't cooperate.

    There's some posts on here about stand-alone, portable power systems. Search for "monolith" ought to find most of them. This is Mike90045's portable power project: http://www.mike-burgess.org/PVinfo_1.html

    What you do with the power once you get it is up to the individual. You could power your patio lights and stereo for parties by the pool. You could run a cord to your TV and save on viewing costs. You could keep your refrigerator going during a power outage. Maybe not very economical, but it can be done.

    Many of us run whole houses off solar, and the key is minimalism. Icarus wins the gold there, as his whole place is run from 400 Watts of panel. No electric heating of anything, btw. :p
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