What happens to excess solar energy if the house battery is fully charged? I assume the charge controller is not going to go through its normal recharge cycle, since all voltages for the various phases of the recharge are going to be met very quickly. So what happens to the excess power generated?
excess solar energy
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DC Fuse
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While power is still produced your charge controller eliminates it so as to not overcharge batteries.
This is where you could "Sink" that excess power into a hot water heating element or pump water from a well for example.
This is where you could "Sink" that excess power into a hot water heating element or pump water from a well for example.
What do you mean by 'eliminates it', does it just disconnect from the Solar panel, or dump it into some kind of load, or something else?DC Fuse said:
I was thinking that I could divert it to something, charging the starting battery was what came to mind.
SternWake
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Lot of charge controllers have a load diversion feature, for when the solar is making more energy than the house battery needs to be held at such and such a voltage, it diverts it elsewhere, like to the other battery, or the electrical water heater element or some other load..
Lots of charge controllers to not have this feature.
If you care to monitor it and disconnect when appropriate, you can hook jumper cables between the batteries, or bridge the solenoid or other isolation device between the two batteries if your charge controller does not have this feature and you find that wasting solar electrons to be irritating.
When I have extra solar electrons available, beyond what my battery needs, I crank up my fridge, charge laptop, or charge anything. But in general I don't stress wasting the extra, anymore.
Lots of charge controllers have large heat sinks to dissipate extra solar energy as heat.
Lots of charge controllers to not have this feature.
If you care to monitor it and disconnect when appropriate, you can hook jumper cables between the batteries, or bridge the solenoid or other isolation device between the two batteries if your charge controller does not have this feature and you find that wasting solar electrons to be irritating.
When I have extra solar electrons available, beyond what my battery needs, I crank up my fridge, charge laptop, or charge anything. But in general I don't stress wasting the extra, anymore.
Lots of charge controllers have large heat sinks to dissipate extra solar energy as heat.
DC Fuse
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anm, I should have been more clear but yes your DC panels are still putting out power but the circuit in the controller is open so this power just "Dead ends", no place to go. Just disconnects from panel(s).
If my bank is full and I turn on the microwave for example, I can see the reading on the panel go from say 100w (float plus whatever minor loads are going) to 1000w to cover what is being drawn. I have way too much extra power, so I have decided that instead of a 12v step down (I have a 24v bank) I'm just going to add a charger and another 12v battery to power all 12v items, this way when I have too much power I can put it someplace useful. I may put the charger on a timer even since I'm rarely in it when the sun is out.
It sounds like we're thinking along similar lines. I've been thinking of putting in a switch (solenoid?) so I can charge the starting battery from the solar panel when it's producing excess. It's a pity my charge controller has no control for such a solenoid, so I would have to switch it manually.
I wish I had a small fridge, that sounds like a good idea.blars said:
Maybe having a second battery that can be charged when there is excess and discharged when there is a need... it doesn't sound too good for the battery though, suppose it gets discharged and there is no excess solar for a week, can the battery be left discharged that long?
I suppose the best idea is to try and match battery size to solar size....
I was thinking about getting one of these to charge when the battery is near topped off:
Portable Charger Aluminum 12000mAh Power Pack and External Battery Bank
Of course you need something that can be charged using USB ports but the price isn't too bad.
Portable Charger Aluminum 12000mAh Power Pack and External Battery Bank
Of course you need something that can be charged using USB ports but the price isn't too bad.
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You can't size your battery bank to your panels properly, it's impossible!
In Phoenix AZ there is a 4 hour difference in the amount of time the sun is above the horizon from Summer to Winter Solstice. The further north you go in the country, the more hours a day difference there is. In Seattle, there are more than 8 hours more sunshine on June 21 than there was on Dec 21.
If you size your system properly for winter, you will have way too much in summer.
Bob
In Phoenix AZ there is a 4 hour difference in the amount of time the sun is above the horizon from Summer to Winter Solstice. The further north you go in the country, the more hours a day difference there is. In Seattle, there are more than 8 hours more sunshine on June 21 than there was on Dec 21.
If you size your system properly for winter, you will have way too much in summer.
Bob
What just occurred to me as driving while overcast, is that if I was concerned about a solar over-charge all I have to do is cover the solar panel (or drive around until I find some clouds!)...
So how does one size the system correctly? Batteries more than able to take my max demand, and more than enough solar panels to recharge them?akrvbob said:
SternWake
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People who try and size their solar exactly to their expected needs with no excess, are simply shooting themselves in their foot. Unless you have acreage of roof space, just put as much as you can on the roof.
Your needs will increase, the more amps the batteries receive early in the day, when depleted, the happier they will be. The controller's job is to make sure they are not overcharged. Extra is not wasted, having extra means the batteries are more likely to reach that elusive 100%.
Most electronic indicators of full charge, are simply wrong. That last 5% of charge makes a huge difference in battery life, and 'excessive' solar is the best way to fill that last 5%, as it takes time, not just charging current, but time for the battery to absorb it.
Get a charge controller which can adjust absorption and float voltages. This ability will pay for itself in much extended battery life and possibly within the first year.
Your needs will increase, the more amps the batteries receive early in the day, when depleted, the happier they will be. The controller's job is to make sure they are not overcharged. Extra is not wasted, having extra means the batteries are more likely to reach that elusive 100%.
Most electronic indicators of full charge, are simply wrong. That last 5% of charge makes a huge difference in battery life, and 'excessive' solar is the best way to fill that last 5%, as it takes time, not just charging current, but time for the battery to absorb it.
Get a charge controller which can adjust absorption and float voltages. This ability will pay for itself in much extended battery life and possibly within the first year.
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I think you are making too big a deal of the "wasted power" issue. I consider it a total non-issue. You size your system for the worst case and then luxuriate in the excess of plenty of sun. Seems very good to me!
But, if it is going to drive you crazy I think I have a solution. Buy an extra battery that is only for good times when there is excess power. Because t will be a different age and condition than your main bank you can't wire it in with it--they will all suffer if you do. Instead, run a wire from the controller to an A-B switch and from the A-B switch to the main battery bank as A and the back-up as B. When their isn't enough sun you turn it to A and the backup battery isn't taking power from A, it gets it all, and they are happy! When there is excess power and A is full and happy, switch it to B and it will fill up.
I've never done this but I must admit it's a good idea. Sternwake is so much smarter about this stuff maybe he will explain exactly how to do it. I might do it myself!
Sternwake, I would be concerned about sending a spike through it if there is power on it it when you turn the switch.
Would you suggest a circuit breaker between the controller and the A-B switch?
Bob
But, if it is going to drive you crazy I think I have a solution. Buy an extra battery that is only for good times when there is excess power. Because t will be a different age and condition than your main bank you can't wire it in with it--they will all suffer if you do. Instead, run a wire from the controller to an A-B switch and from the A-B switch to the main battery bank as A and the back-up as B. When their isn't enough sun you turn it to A and the backup battery isn't taking power from A, it gets it all, and they are happy! When there is excess power and A is full and happy, switch it to B and it will fill up.
I've never done this but I must admit it's a good idea. Sternwake is so much smarter about this stuff maybe he will explain exactly how to do it. I might do it myself!
Sternwake, I would be concerned about sending a spike through it if there is power on it it when you turn the switch.
Would you suggest a circuit breaker between the controller and the A-B switch?
Bob
SternWake
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I think the idea has merit, except a good switch is gonna cost 30$. A cheap toggle switch could get overloaded when a 14.4v battery is connected with a 12.0v battery.
I would not hook the additional battery to the charge controller and put a switch between the other battery and the solar controller, I would hook it to the other batteries.
With the depleted battery sucking power from the batteries that were in float and wasting those precious solar electrons, their voltage will drop, causing the controller to go back into bulk mode where it sends as much juice as it can into all the batteries.
I do not like this as once the battery is in absorption stage, It needs to stay there for a certain amount of time, and paralleling a depleted battery at this point will drop the voltage out of absorption stage and defeat the goal of trying to get to, as best as possible, 100% every day before the next discharge cycle begins.
Another issue with this is the manual factor/human error factor, and old batteries should not really be discharged or rested in parallel with newer ones, and there can also be issues charging an older battery in parallel with newer batteries. with the newer batteries gobbling more current due to having less internal resistance
I'd keep the batteries from being paralleled through the solar controller which is what would happen if there was a switch between controller and additional battery.
Also solar controller wire inputs do not really like having multiple wires inserted into them as they seem to be made too small for just one wire. One of my pet peeves with insert bare stranded wire. Tighten screw connectors.
Always come back and retighten the screws after an hour or two. You might be surprised how easy it is to get another half turn or more on the screw.
I use 3 manual switches for ignition, loads, and solar, and basically have the option of sharing solar current to my other battery whenever desired.
Wiring should always be fused to protect the wire in case of overload/ short. neither a fuse or a circuit breaker is going to protect from Spikes, they only open the circuit when the fuse rating is exceeded which happens when passing too much current through the fuse, or short circuiting it.
Lot of extra steps and complications just to avoid wasting any free power. Just crank up the fridge, and charge other things when there is a lot of sunlight and extra solar. All this trying to figure out exactly the solar amount and not one watt more is kind of ridiculous. I used to worry about wasting extra power too, so I understand the desire to not waste anything, but I got over it.
I would not hook the additional battery to the charge controller and put a switch between the other battery and the solar controller, I would hook it to the other batteries.
With the depleted battery sucking power from the batteries that were in float and wasting those precious solar electrons, their voltage will drop, causing the controller to go back into bulk mode where it sends as much juice as it can into all the batteries.
I do not like this as once the battery is in absorption stage, It needs to stay there for a certain amount of time, and paralleling a depleted battery at this point will drop the voltage out of absorption stage and defeat the goal of trying to get to, as best as possible, 100% every day before the next discharge cycle begins.
Another issue with this is the manual factor/human error factor, and old batteries should not really be discharged or rested in parallel with newer ones, and there can also be issues charging an older battery in parallel with newer batteries. with the newer batteries gobbling more current due to having less internal resistance
I'd keep the batteries from being paralleled through the solar controller which is what would happen if there was a switch between controller and additional battery.
Also solar controller wire inputs do not really like having multiple wires inserted into them as they seem to be made too small for just one wire. One of my pet peeves with insert bare stranded wire. Tighten screw connectors.
Always come back and retighten the screws after an hour or two. You might be surprised how easy it is to get another half turn or more on the screw.
I use 3 manual switches for ignition, loads, and solar, and basically have the option of sharing solar current to my other battery whenever desired.
Wiring should always be fused to protect the wire in case of overload/ short. neither a fuse or a circuit breaker is going to protect from Spikes, they only open the circuit when the fuse rating is exceeded which happens when passing too much current through the fuse, or short circuiting it.
Lot of extra steps and complications just to avoid wasting any free power. Just crank up the fridge, and charge other things when there is a lot of sunlight and extra solar. All this trying to figure out exactly the solar amount and not one watt more is kind of ridiculous. I used to worry about wasting extra power too, so I understand the desire to not waste anything, but I got over it.
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Sternwake, I'm sorry but I didn't describe it well.
There would only be 1 wire coming off the charge controller and it would go to the A-B switch.
A wire would come off the A terminal and to Battery Bank A and a wire coming off the B terminal to battery bank. They would never be parallel unless you wanted them too be which I wouldn't.
It's true it would introduce the need for manual user control, I think that could be done.
Here is a simple diagram:
There would only be 1 wire coming off the charge controller and it would go to the A-B switch.
A wire would come off the A terminal and to Battery Bank A and a wire coming off the B terminal to battery bank. They would never be parallel unless you wanted them too be which I wouldn't.
It's true it would introduce the need for manual user control, I think that could be done.
Here is a simple diagram:
Since I have a 24v bank and run many 12v loads this was a huge area of thought for me in terms of how to properly address it. A+B battery switches are bad news, I would avoid them at all costs personally. I would instead go for two disconnects, this will allow you for a moment to go from having battery A on to having battery A+B on to having battery A off and only B on. Since charge controllers are not happy about being hooked up to a solar source without a battery attached this solves that issue as you would otherwise need to cut off your solar, switch battery banks and turn the solar back on.
In the end, this was far too much trouble to mess with for me, I simply got a 4amp charger to hook up to my inverter, this allows me to charge my 12V battery at any time and not have to deal with all the issues of doing it any other way.
As for too much solar, that's silly, you can either size your bank to have a few days of backup or you can size your panels to always refill your bank, even in the worst of conditions.
I'm currently in Seattle and watching as 3.5 minutes of daylight disappears every 24 hours, even in the rain I'm still getting my bank back to 100% without troubles but I have a 6,000 watt bank, 1,380 watts of solar on my roof and I'm not draining the bank under 85% ever. In the winter and with more usage, I'm sure it would get tougher. Really, you can't have too much, that would be like calling the spare tire in your car excess, I guess, sure but I call it insurance.
In the end, this was far too much trouble to mess with for me, I simply got a 4amp charger to hook up to my inverter, this allows me to charge my 12V battery at any time and not have to deal with all the issues of doing it any other way.
As for too much solar, that's silly, you can either size your bank to have a few days of backup or you can size your panels to always refill your bank, even in the worst of conditions.
I'm currently in Seattle and watching as 3.5 minutes of daylight disappears every 24 hours, even in the rain I'm still getting my bank back to 100% without troubles but I have a 6,000 watt bank, 1,380 watts of solar on my roof and I'm not draining the bank under 85% ever. In the winter and with more usage, I'm sure it would get tougher. Really, you can't have too much, that would be like calling the spare tire in your car excess, I guess, sure but I call it insurance.
SternWake
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Quality ABboth switches are not bad news. The human error factor is the bad news.
Only when approaching their load limits with undersized wire will a quality switch present problems, and it will need a huge or multiple alternators and a huge depleted battery bank to reveal issues with them.
I've been using them for 13 years without a single issue. the first one did start wearing out after 12 years and about 5000 switchings under load, which is acceptable. My newer switches are rated for 150 more amps ( if properly cabled) and more cycles than the one which was worn but still fully functional.
If such a manual AB switch is employed just for the main isolator device, meaning no isolator or solenoid oR ACR, then the Solar controller could be wired directly to the battery 2 stud. When the switch is on battery 1( engine) the solar feeds only the house battery(2), and the two batteries are separated. When switched to BOTH, then solar current is shared between both batteries and both batteries see alternator current or starter loads, charge and discharge together. When switch is turned to battery 2 solar goes only to battery 2, engine starts from battery 2, all alternator current goes to battery 2, and battery one is completely isolated from everything not wired directly to it .
Lots of room for human error, if this makes it bad news, then so be it, but the products themselves, properly employed are themselves not bad news, and the un-forgetful and aware, should not fear them.
Everybody else can run for the hills in the presence of one.
Bob, in your diagram, basically add the alternator/starter to the solar controller side of the battery switch, and that is how my system was set up for the first 13 years.
Know how many times i ran both my batteries so low it could not start the engine? Zero
Know how many times I turned the switch to off with the engine running, and destroyed my alternator?
Zero.
I had failed alternators, but only because they were remanufactured junk that could not handle charging such depleted batteries.
I've not had an alternator issue since getting solar. but watch it explode tomorrow
Murphy was an optimist.
Only when approaching their load limits with undersized wire will a quality switch present problems, and it will need a huge or multiple alternators and a huge depleted battery bank to reveal issues with them.
I've been using them for 13 years without a single issue. the first one did start wearing out after 12 years and about 5000 switchings under load, which is acceptable. My newer switches are rated for 150 more amps ( if properly cabled) and more cycles than the one which was worn but still fully functional.
If such a manual AB switch is employed just for the main isolator device, meaning no isolator or solenoid oR ACR, then the Solar controller could be wired directly to the battery 2 stud. When the switch is on battery 1( engine) the solar feeds only the house battery(2), and the two batteries are separated. When switched to BOTH, then solar current is shared between both batteries and both batteries see alternator current or starter loads, charge and discharge together. When switch is turned to battery 2 solar goes only to battery 2, engine starts from battery 2, all alternator current goes to battery 2, and battery one is completely isolated from everything not wired directly to it .
Lots of room for human error, if this makes it bad news, then so be it, but the products themselves, properly employed are themselves not bad news, and the un-forgetful and aware, should not fear them.
Everybody else can run for the hills in the presence of one.
Bob, in your diagram, basically add the alternator/starter to the solar controller side of the battery switch, and that is how my system was set up for the first 13 years.
Know how many times i ran both my batteries so low it could not start the engine? Zero
Know how many times I turned the switch to off with the engine running, and destroyed my alternator?
Zero.
I had failed alternators, but only because they were remanufactured junk that could not handle charging such depleted batteries.
I've not had an alternator issue since getting solar. but watch it explode tomorrow
Murphy was an optimist.
