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Thread: can i use a solar panel without using battery

  1. #1

    Post can i use a solar panel without using battery

    My question is
    can i use a solar panel in daytime directly to supply electricity my home appliances without using battery.

    i mean

    one solar panel and then inverter and then load.

    is it possible?
    what possible safety measure should i have take into account to protect my appliances from overcurrent.

  2. #2
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    If you're planning an off-grid system,it wont work. The inverter input has to be within a certain range ,and the panel voltage is above that range during most of the day.

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    No it will not work.
    MSEE, PE

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    Are you trying to describe a "grid tie system" where a very special type of inverter takes power from a string of PV panels, and feeds that into the grid? In that case, the grid acts as the battery.

    Somewhere, you need a battery, either the "grid" or a bank of batteries.

    Panel and load only works for some special water pumps with expensive control modules.
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    This was one of my main questions I wanted to ask before I start buying equipment. And it will be off grid.

    With the EXTREMELY high price of batteries now, which from my research, now way surpasses the cost of panels factoring in life of product, it doesn't seem logical to have a large battery bank if the majority of electrical use will be during sunlight. I will still have batteries, but I was thinking something like 2 6v 390Ah batteries for minor use after sundown.

    Figuring you sleep 6-8 hours at night and here in Arizona you've got say, at least 9-12 hours of sunlight a day. And I don't understand why people wouldn't put some panels on a "fairly simple" pole mount which can be moved by motor or hand. Wouldn't you then get pretty much the full amount of "sun power" sun up to sun down?

    That being said, there must be a way to pretty much bypass the batteries during the day, instead of spending thousands of dollars on batteries. Seems like an awful waste to have to use the batteries as a go between, unless it doesn't affect their life, which leads me to another question. Does it? When you have say 1000 watts of sun power and you use less than that at any given time while the panels are producing that, does the power just kinda pass through the battery without degrading life?

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    The thickness of the soup we call "atmosphere" really does block a lot of power from the sun in the dawn-10am, and 3pm - sunset. The 4 hours around noon[+2,-2], are the productive ones, so an "ultra tracker" won't help much outside those hours.

    You don't "bypass" batteries in the daytime, you have to recharge them, and then, use "opportunity" loads in the afternoon, after the batteries have begun the absorb part of the cycle, and you have some spare PV to run the washer and maybe air conditioner.

    If you feel you can get by with only small loads at night, great. I won't tell you to spend $ needlessly, but if you discharge batteries too deeply, you shorten their lifetimes.
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    So, again if you have fully charged batteries and say you have 1000 watts of panels capable of producing that and you start using 7 100 watt light bulbs, does the power come from the batteries or pretty much straight from the panels? In that scenario, which I think for me would be typical of most daylight hours, would the power usage affect battery life?

    And I know my knowledge with all this is very basic and beginning, but I just took out my 30 watt panel and did some tests.

    Directly aimed at the sun, it was at about 24v and .95A. Set on a flat surface, it was 1-2 volts less but the current was .35.
    That was measured at 4:30pm Arizona time. Am I wrong to assume that could be 3 to 1 power difference?

    From what I know so far, I can't tell the watt output until I put a load on it and bring it down to 12v then do the measurements, right? And any easy way of doing that?

    Oh, I just looked up the specs, for my uni-pac 30, and the short circuit specs were 2.1A, which is what it was when I measured it a month or so ago at high noon. So, does that mean it would put out about 15watts when I measured it facing the sun 20 minutes ago?

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    Quote Originally Posted by themaxx69 View Post
    So, again if you have fully charged batteries and say you have 1000 watts of panels capable of producing that and you start using 7 100 watt light bulbs, does the power come from the batteries or pretty much straight from the panels? In that scenario, which I think for me would be typical of most daylight hours, would the power usage affect battery life?
    Why would you burn 7 light bulbs in the day time ?

    What you haven't picked up on is the batteries, or the grid, level out the power supply.

    Panels don't produce a nice, even steady flow of electricity like a generator does ( heck, even they bog down when you load them up )....a fixed panel produces a little at sunrise, then the most around noon, then tapers off again in the afternoon as the sun angle falls away from perpendicular to the face of the panel. Also, weather conditions GREATLY affect the output. Cloud moves over, output falls WAY off.

    In the case of incandescent light bulbs, say a cloud moves overhead.....they would simply dim. But what happens if you're using a motor ? Brown out....or your system tries it's best to pull it out of the small battery bank.

    In a IDEAL world, your attempt "might" work....if you could sit there all day and match your power use to the output of the panels every given second ( or maybe split second )....but I know I sure don't have time to do that......so I pull my excess needs ( wife flips on the oven, or the dryer, or a hair dryer, or anyone of a dozen other things ) from the grid, if the grid is up, and from my batteries ( on limited circuits.....she's just flat out of luck with the oven or the dryer....ahahahaaa ) if the grid is down.

    Then, when we have excess power the house is NOT using, the meter turns backwards as we put it back on the grid. In off grid situations, if the battery was fully charged, and you weren't using the full power the panels produce, power simply wouldn't BE produced.....the panels just sit there at idle until a load occurs.

    That's the WHY of what these other guys are trying to tell you when they say "It won't work"......because it won't work.

  9. #9
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    Quote Originally Posted by TnAndy View Post
    Why would you burn 7 light bulbs in the day time ?

    What you haven't picked up on is the batteries, or the grid, level out the power supply.

    Panels don't produce a nice, even steady flow of electricity like a generator does ( heck, even they bog down when you load them up )....a fixed panel produces a little at sunrise, then the most around noon, then tapers off again in the afternoon as the sun angle falls away from perpendicular to the face of the panel. Also, weather conditions GREATLY affect the output. Cloud moves over, output falls WAY off.

    In the case of incandescent light bulbs, say a cloud moves overhead.....they would simply dim. But what happens if you're using a motor ? Brown out....or your system tries it's best to pull it out of the small battery bank.

    In a IDEAL world, your attempt "might" work....if you could sit there all day and match your power use to the output of the panels every given second ( or maybe split second )....but I know I sure don't have time to do that......so I pull my excess needs ( wife flips on the oven, or the dryer, or a hair dryer, or anyone of a dozen other things ) from the grid, if the grid is up, and from my batteries ( on limited circuits.....she's just flat out of luck with the oven or the dryer....ahahahaaa ) if the grid is down.

    Then, when we have excess power the house is NOT using, the meter turns backwards as we put it back on the grid. In off grid situations, if the battery was fully charged, and you weren't using the full power the panels produce, power simply wouldn't BE produced.....the panels just sit there at idle until a load occurs.

    That's the WHY of what these other guys are trying to tell you when they say "It won't work"......because it won't work.
    Thank you for that intelligent and well worded answer
    Rich
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    NABCEP certified Technical Sales Professional

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    Default panel output verses time of day

    Here is an attached "bell curve" of an imaginary 120w panel and its aprox outputs over the daylight hours.. Obviously it wont be exact for every location ,its just to give an idea even though there is "daylight" its not not enough to produce much power except for a comparatavly short period of the day
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