Charge Controlling for Wind and Solar

[svh2obo]

If this thread is a repeat, then I apologize, but I could not find the answer to my problem.

I have a Rutland wind generator, 2 85W and 2 50W solar panels. I would like them to charge my 12V house bank of 4 golfcart batteries with a total capacity of 450 amphours. Currently I am using a Flexcharge nc25 to regulate the wind generator and two Flexcharg nc7 each with an 85 and a 50W panels connected in parallel with no blocking diodes. I don't think I am getting the full bang for my buck.

My question is: What is the most efficient/best way to do this. Is there one charge controller that will work? Should the panels be connected in parallel or series? Are blocking diodes needed?

I have searched the web but have found no definitive source of information.

Thanks in advance.

[Bash]

Originally Posted by svh2obo

If this thread is a repeat, then I apologize, but I could not find the answer to my problem.

I have a Rutland wind generator, 2 85W and 2 50W solar panels. I would like them to charge my 12V house bank of 4 golfcart batteries with a total capacity of 450 amphours. Currently I am using a Flexcharge nc25 to regulate the wind generator and two Flexcharg nc7 each with an 85 and a 50W panels connected in parallel with no blocking diodes. I don't think I am getting the full bang for my buck.

My question is: What is the most efficient/best way to do this. Is there one charge controller that will work? Should the panels be connected in parallel or series? Are blocking diodes needed?

I have searched the web but have found no definitive source of information.

Thanks in advance.

I like having separate controllers for wind and solar. I have mine set so that the wind generator shuts itself down about .25 volts lower than the solar array, so that if the state of charge is high enough that I don't need both systems working, the solar is responsible for topping off the batteries while the wind generator takes a rest.

[noelex 77]

The Flexcharge controllers appear to be very crude on / off controllers without even PWM.
You should get a much better result from a more sophisticated controller.

I agree with Bash that separate wind and solar regulators are a better option than one controller.
There is a lot of debate about series (MPPT regulators only) or parallel connection, but the differences in efficiency will be small. I would stay with a parallel connection give your panels are dissimilar.
Blocking diodes are not needed with most solar controllers, but check the handbook, or see if you are getting any discharge at night through the solar panel. Blocking diodes do cost a small amount of power during the day, if there is no discharge at night it is better not to fit them.

[cwyckham]

It's my understanding that there is a risk of the two controllers interfering with each other (Don Casey and Nigel Calder both caution about this in their books).

For example, the solar puts 14.4 V on the battery, but is only able to supply a small amperage because it is late afternoon and cloudy. The battery could absorb more, but the wind controller thinks the battery must be full due to the high voltage, so it shuts down the wind generator or pushes the output to a dump resistor.

I was looking at a blue sky controller that does both solar MPPT and wind regulation in one unit. However, it would be much cheaper to buy separate controllers (especially since I'm looking at the Breeze-X which has it's own internal controller.

I believe there is the same issue with the alternator, so Calder and Casey both recommend disconnecting the wind and solar when using the alternator.

I'm not clear if this problem would even exist during bulk charging, and float doesn't need much current anyways. Is this just an issue during absorption?

[noelex 77]

Originally Posted by cwyckham

For example, the solar puts 14.4 V on the battery, but is only able to supply a small amperage because it is late afternoon and cloudy. The battery could absorb more, but the wind controller thinks the battery must be full due to the high voltage, so it shuts down the wind generator or pushes the output to a dump resistor.

I am not sure what you mean by "the battery could absorb more". If the solar panels cannot output enough current for the batteries to maintain 14.4V the voltage will drop. When that happens the wind generator will start supplying current again (if this is where the regulation points are set).

Minor problems can occur if the wind generator has maintained a high voltage overnight and the batteries are fully charged. When some solar regulators start a new day they will maintain the absorption voltage for a set time which will be slightly overcharging the batteries,.
A solar regulator that monitors the net return amps and drops back to float when the net amps are low,( but the voltage is high) fixes this problem. The extra expense of this sort of regulation is not justified for most systems.

Many solar and wind regulators can be manually dropped back to float and this is worth doing if you know the batteries are near fully charged.

[cwyckham]

OK, then I'm totally confused. Totally ignoring wind vs solar interactions, what about solar vs alternator regulator? Why would Nigel Calder and Don Casey recommend a relay to open circuit the solar whenever the engine is running in order to prevent the solar controller from fooling the alternator regulator? Isn't that following exactly the same principle? Are they just out to lunch?

[noelex 77]

Originally Posted by cwyckham

OK, then I'm totally confused. Totally ignoring wind vs solar interactions, what about solar vs alternator regulator? Why would Nigel Calder and Don Casey recommend a relay to open circuit the solar whenever the engine is running in order to prevent the solar controller from fooling the alternator regulator? Isn't that following exactly the same principle? Are they just out to lunch?

I have not got Nigels excellent book on board so I cannot check the relevant section, but the last edition I read was written when solar controllers were much more basic. On my own boat I monitor our DC carefully and have seen any problems.
The only theoretical danger of multiple controllers is that each could leave the batteries at the absorption voltage for the allocated time (often 1hr). If there is no overlap in these times and the battery return voltage point is reached (or the controller does an automatic absorb cycle every 24hrs) it is possible with 3 different charge sources, if there was no overlap a full battery could be maintained at the absorption voltage for 3 hours, which is not ideal.

In practice this scenario would be rare, there is likely to be some discharge in between and there is a lot of debate about the ideal adsorption time from different manufactures with anything from 1-3hrs recommended.
This situation is often seen in boats with just solar anyway. When the boat is left with no load the solar controller will often start a new absorption cycle each day even though the battery is very close to fully charged. Many boats are left like this for months with a new absorption cycle every day.
If anyone can think of other theoretical conflicts please post them.

I think the main effect in turning off your solar panels when the engine is running would be to make your alternator and engine work a bit harder, increase your charging time, and of course the inevitable problem that you would forget to turn it back on

[twistedtree]

I think Noelex 77 is on the right path here. Any good charge controller has voltage set points, along with timers and current sensors that control how quickly the battery works through the charge stages. Here's my take on the risks and exposures in each of the charge stages:

Bulk: I can't see any conflict here. The more charge sources the better, as the goal is to dump as much current into the battery as possible. In theory you provide too much current, but I think it's very rare that a boat will have enough charging sources to exceed the typical C/5 max charge rate.

Absorb: As Noelex said, the biggest risk is that each charge source decides to run an absorb cycle and they happen back to back. This will result in one absorb cycle after the other, but I don't think this is a big deal at all. With a fully charged battery the absorb voltage will be reached very quickly (minutes), and the acceptance current will drop off very quickly. Any good charge controller will complete absorb when the current drops to around C/50, and that will happen very quickly. Also, keep in mind that this is exactly what happens every time you plug into shore power and turn on you charger, and every time you unplug and start your engine.

Back to the original caveat of "any good charge controller" - this is important and by itself a good reason to use quality controllers. With modern controllers, I would respectfully disagree with Calder and Casey

[Seahunter]

There are few charge controllers that can handle wind and solar. Outback makes a good one that can do both, albeit a wee pricey. You might find one here, wholesalesolar.com

[cwyckham]

Originally Posted by Seahunter

There are few charge controllers that can handle wind and solar. Outback makes a good one that can do both, albeit a wee pricey. You might find one here, wholesalesolar.com

I didn't find one on Outback's website. Blue Sky makes the SB3024 DUO which has an MPPT solar controller with integrated 20 A (upgradable to 60 A) PWM diversion style controller for hydro or wind generation.

Interestingly, you can switch the Blue Sky unit to a max diversion power mode that will also dump any excess solar power to the dump resistor if it's doing something useful (like heating your water).

It's only a $50 upgrade to convert a 3024 to DUO, and you get a coordinated 3 stage approach, so it may be a worthwhile option if you're looking at that controller anyways.

I'm considering a Breeze-X for wind, and that has an internal controller that will slow the blades instead of dumping to a resistor. I lose the hot water option, but I think the reduced noise and wear and tear on the generator make it a huge benefit to keep to separate controllers in this case.

[Seahunter]

Originally Posted by cwyckham

I didn't find one on Outback's website. Blue Sky makes the SB3024 DUO which has an MPPT solar controller with integrated 20 A (upgradable to 60 A) PWM diversion style controller for hydro or wind generation.

Interestingly, you can switch the Blue Sky unit to a max diversion power mode that will also dump any excess solar power to the dump resistor if it's doing something useful (like heating your water).

I agree, the Blue Sky option is a good one, especially if one isn't comfortable with Outback not supporting wind turbines, even though their MPPT chargers with a Mate will work with turbines. The "dump" feature is a good one. I've installed Outback MPPTs that divert the excess into a small electric hot water heater. Upgrade to the SB3024iL Duo as it can can manage other electrical sources including your genset. The only downside is that you'll have to make sure it's mounted in an absolutely dry space as it's neither ignition protected nor water resistant.

[Zakimimula]

Originally Posted by noelex 77

I am not sure what you mean by "the battery could absorb more". If the solar panels cannot output enough current for the batteries to maintain 14.4V the voltage will drop. When that happens the wind generator will start supplying current again (if this is where the regulation points are set).

Ok, I worried about the same issue; what happened if two regulators are connected to the same battery bank, won't they conflict?

I am not sure wht you mean when you say "If the solar panels cannot output enough current for the batteries to maintain 14.4V the voltage will drop". Why would that be? I thought a MPPT charge controller connected to a solar array providing (for example) 0.5A at 15V would maintain the battery voltage at 14.4V. My wind turbine regulator connected to the same battery would sense a "full" battery and dump any charge it might have, rather than combine it and increase the bulk charge to the battery.

Is that the case or will the two regulators add their charge together?

The issue has my concern because I'm about to sink serious $$$'s into solar panels to supplement my wind generators output. I can't see, from my probably limited understanding, how the two regulators will play nice... especially if my turbine regulator is capable of sensing another charge source and dumps its charge automatically.

Having said that, I email led Plasatronics with this concern. They said it was "a non-issue" but didn't clarify any further. Any light anyone could shed on this would help...

Cheers.

[noelex 77]

Originally Posted by Zakimimula

I am not sure wht you mean when you say "If the solar panels cannot output enough current for the batteries to maintain 14.4V the voltage will drop". Why would that be? I thought a MPPT charge controller connected to a solar array providing (for example) 0.5A at 15V would maintain the battery voltage at 14.4V.

Battery voltage is determined by the battery. A MPPT regulator connected to a solar aray producing 0.5A @ 15v could be expected to produce around 0.5 to 0.6A at the battery end. The voltage will depend on the battery. 0.6A might for example give a battery voltage of 14v for a small fully charged battery, but only 12.4v for a flatish medium sized battery.

[Zakimimula]

Thanks for coming back me so quick Nolex77; I'm sorry I haven't got back into Internet service range until now!

I'm a bit confounded by your reply, namely that the battery determines voltage while charging, not the regulator... That was news to me.

Here's how I thought I could experiment with that concept:
Tomorrow I'm going start the motor to charge our house batteries. I plan on having a look at the voltage while charging to see if I can see it "coming up". I'm hoping to see the ambient voltage steadily rise as the battery charges, in which case the battery is determining the voltage, and any other charge regulators on the same battery bank would see the same thing and continue to contribute their charge.

I'll let you know what I see...

Cheers!

[noelex 77]

The regulator can limit the current from the solar panels and therefore reduce or regulate the battery voltage to a set level, but it cannot increase**the battery voltage. If you put say 0 .5 A into a battery from any source the battery voltage is controlled by the battery, depending on its state of charge ,size etc. *