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kitestrings

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Managing opportunity and dump loads
« on: February 06, 2015, 12:55:34 PM »
Hi,

I'm still messing about with opportunity diversion loads and dump loads.  Our current system consists of 3.2 kW of PV, and our 15' axial.  I had previously configured an opportunity diversion to a water pre-heat tank using the aux diversion setting on the PV controller, an OB MX60.  This is to a Marathon 40 gallon tank with 2- 1,250w 48VDC elements via SS relays.  Aside from wishing the tank was a bit larger, this arrangement has worked very well for several years now.

When we got the turbine up and running, I added another pair of control wires from one of the non-PWM aux outputs from the Classic.  Currently this is set for “PV High – On”.  Above a set voltage  - about the point that our second controller starts to see load - we add some load to the bank in similar fashion to the PV set-up.  But wind is fickle, as we all know, and I've been wanting to increase the available diversion load particularly when the winds are gusty.   So, I recently reconfigured the water heater control such that:

1)   when the PV is diverting nothing is change, the elements are interlocked (max load 1x 1250w, ~22A)
2)   when the WIND is diverting both elements are firing, assuming they are calling for heat (max load 2x 1,250w, ~45A)

The logic was that often the wind is sporadic, though shorter in duration, and the added available load would help keep the voltage moderated while doing something useful.  I'm further looking to move this to the PWM output of the second controller (there are two for the turbine), so it can be a bit smoother.

I should mention that the above arrangement is separate from our 3-phase load bank, or home-made ‘clipper,' used for protection of the wind system.  There, we close in on a resistor bank above a higher preset voltage, adding the equivalent of about 4+ kW of load on the 3-ph input to managed input voltage.

What I'm trying to figure out is how best to manage things when the ‘opportunity' is not there.  I could add another air heater for when the water heater is satisfied and the wind resource is still high.  I've also considered setting the dump/clipper to engage once float is reached, or alternatively automate the manual furling (with an actuator).

Generally we want to (in descending priority):
1)   protect things
2)   recharge the battery bank
3)   leverage opportunity loads that are useful, but not have unnecessary were and tear

Up until now I've been managing with a bit of manual intervention; close down the turbine on a sunny day when we're away at work.  Opening it back up when we get home.  Predicting the weather some days is a challenge.

Ideas & cold beer welcome.  ~ks

SparWeb

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Re: Managing opportunity and dump loads
« Reply #1 on: February 07, 2015, 01:43:44 AM »
Have I shown you this before?



When the batteries are full (your criteria 2), due to either wind or sun, the device detects that the resistors in the diversion load are on.  That triggers it to close a power relay.  What that power relay turns on in your system, is entirely your choice (criteria 3).  I used a 1200W water heater.  Failure of this device in any way results in the system you already have (criteria 1).
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kitestrings

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Re: Managing opportunity and dump loads
« Reply #2 on: February 09, 2015, 12:22:40 PM »
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Have I shown you this before?

Not that I recall.  You remind of another tool that I keep forgetting.  The inverter also has it's own aux logic, so I could add, as you've suggested, something on the (single-phase) AC side of things.  I probably will add something either there or directly on the 48DC bank, so the diversion is always available (in the case where the water heater is satisfied).

Each of the Classics has two aux outputs, one PWM and one relay control.  I'm currently only using two.  What I'd like is for the wind to assist getting us to float, as it does, but then close down the turbine if there's nothing useful for it.  This could be either in the form of latching in the (3-ph) load bank, or furling the tail.

SparWeb

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Re: Managing opportunity and dump loads
« Reply #3 on: February 15, 2015, 08:01:43 PM »
Sorry for the delay getting back to you.

My little box had a relay inside to keep the DC isolated from the AC.  Any time the charge controller switched to diversion load, a wire (high impedance circuit) would conduct a signal to a little board with a FET driving the relay.  The AC going through the box was just plug-in receptacles like any other standard receptacle.  The DC side required access to 24VDC supply, and of course a long wire to "smell" what the diversion load was doing.  The trigger circuit would latch ON for 2 minutes (adjustable) so that the system would cycle on/off repeatedly, nor would it get stuck on unnecessarily.

If one of your Classics has a relay control output available, then you can do the same with it as the timer I built (provided that you can program it to turn ON when the diversions turn on).  That would be enough to close a relay (or FET+relay, depending on what that output can do) on any AC load you want.  You could even make a latch timer to "drop-out" the relay after a fixed period of time. 

No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
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SparWeb

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Re: Managing opportunity and dump loads
« Reply #4 on: February 15, 2015, 08:17:32 PM »
Can't find the forum thread where we came up with it.
Here's a photo:

No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
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SparWeb

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Re: Managing opportunity and dump loads
« Reply #5 on: March 23, 2015, 10:23:51 PM »
KS,

Somebody at Home Power magazine must be reading the forum.  This month's issue has an article about diversion loads.
No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
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kitestrings

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Re: Managing opportunity and dump loads
« Reply #6 on: March 24, 2015, 04:01:01 PM »
Funny, I was just reading that article.

I'm working with MS right now trying to sort out a problem with my Classic set-up.  We have two Classics (250's).  Basically, everything works well up to the point that the aux diversion begins, then the first unit (which is pretty heavily loaded) "sees" the load, for a split second, as a short on the battery side of things.  Reportedly happens when the input voltage is real high and there is either a large load on the inverter, or the battery cables undersized and/or shared with the load; neither true in our case.  It appears as an "OCP error" - you can google on MS forum if interested - and the unit effectively goes into "resting" which is not a very desirable result in high winds.  I welcome any thoughts.

Gotta sort it out before we put ours up higher.  I've been glad it has been just on the "test tube" (stub tower) so we can keep an eye on it.

BTW, I liked your recent pics on "remembering Zubbly" post.  Regards, ~ks


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Re: Managing opportunity and dump loads
« Reply #7 on: March 26, 2015, 01:08:22 AM »
I was hoping the article would lead to some ideas.

Switching spikes?  Unsuppressed coils?  Need something like a "soft-start" on your diversion?
If OCP means "over current protection" like I think it does, then what are the loads, exactly?  Do they add up to more than the limit (presumably limited by the system's design but maybe a system variable that you can alter)? 

Back in the old days, fuses and circuit breakers needed time to trip.  Electrical engineers would look at the I/t curves to determine the tripping time rather than just rely on the spec current rating.  Nowadays stuff has electronics that can switch in microseconds, and current sensors that detect switching spikes and respond to them as if there's a fault on the line.  They can trip the system much faster than any mundane over-current protection will notice, because those rely mostly on I2R heat.
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kitestrings

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Re: Managing opportunity and dump loads
« Reply #8 on: March 26, 2015, 09:15:23 AM »
Here's a link to the discussion on this so far:

http://midnitesolar.com/Forum/index.php?PHPSESSID=a70bdacfde4e86812c021c1e02501170&topic=2257.0


It's proving to be a real challenge, and there aren't many people who using multiple Classics on wind (two as near as I can tell).  The diversion load is a pair of DC water heater elements.  They pull a little over 40A DC (48V nominal bank) when energized and calling for heat.  I've moved them to the aux2 on our second unit, so in effect it has the ability to very the load up to that point.

A couple of subsequent changes to note: 1) I correct a suspected wiring issue, which was increasing the gage of the jumper between the DC bus and the pos+ lug in the DC breaker panel.  2) I've moved the water heater source so it comes directly off the battery pos+ terminal.

OCP is over current protection as you surmised.

I captured it on my iPhone video.  In the video, the first controller loads to about 35A (it's limit is set at 40A), in the next frame the output goes to -0- and the unit clicks out, and goes into resting.  It attempts to reconnect, then does.  When the dust settles - all in about 1-2 mins. I'd estimate - the OCP error displays.  Now I understand that as the battery V rises and the wind is high, the controller will force the input voltage to climb.  However, we've been well below the 'clipper' (homemade, 3-ph resistor bank) when this occurs.  It seems to be triggered by the DC load diversion which is set to quite a bit lower V (~120V).  Fortunately, it has only been in brief periods, with high gusts, but it is not an acceptable outcome as you can well imagine.

Frankly, I think the OCP, as currently configured, may just be too sensitive for wind (and diversion).  I think it 'sees' the diversion for a split second as a short.  It's fast, but maybe too fast.  And I could be wrong.

~ks


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Re: Managing opportunity and dump loads
« Reply #9 on: March 26, 2015, 02:36:10 PM »
Interesting story, good read for someone (like me) thinking about a Classic + wind. 

Auto-Reset...  <shudder>

So, do you think the inverter wire replacement is enough to prevent it from happening again?

One thing I realize now, though, is that where I've talked a bit about the "aux diversion" downstream of the battery, you are not. 
You must have set up the two Classics to add diversion loads on-line with the turbine during peak periods. 

That's a totally different ball of electrons.
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kitestrings

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Re: Managing opportunity and dump loads
« Reply #10 on: March 26, 2015, 05:38:13 PM »
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So, do you think the inverter wire replacement is enough to prevent it from happening again?

I'd hoped that was it; unfortunately no, it has done it since.  The inverter cables are 3/0 CU.  It was actually the 10-12" jumper in the PSDC (Outback's DC panel) that connects the positive bus bar to the lug of the inverter breaker.  Originally I had just our solar, so a piece of #4 CU was fine.  With the potential of up to 80+A from the wind, I bumped this up to 2/0.  Everything else is pretty hefty.

We have two separate loads involved both on aux2 (PWM capable) outputs.  On the DC side, we're simply diverting to an electric water heater with DC elements.  I should mention we've done this with our MX60 for several years now on the solar side, with no issues.  On wind, the Classic is diverting based on input volts "PV-V on Hi" at ~118V.  Unlike the solar, it doesn't slowly ramp up and stay there.  A big gust of wind roles by and the voltage can rise very fast.  Even with the PWM, at times it is an all or nothing load.

On the second unit is our homemade clipper.  This puts a balanced 3-phase load on the turbine input to hold the voltage to a reasonable level. Similarly, it is triggered on input voltage.  Currently I have at about 130V, but I've moved this down in lieu of the OCP issue.  This load bank also is tied to an Omron voltage sensing relay, which monitors the AC input should, for any reason, the Classic(s) fail.

Overall I've been very happy with the Classics, and MS's support has been good.  Clearly, there are more people using them with solar, so there's uncharted territory.  I only wish it could be one unit, or that they had the option to share the load - would be much simpler.

We definitely got to solve, or we're sunk.  ~ks

kitestrings

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Re: Managing opportunity and dump loads
« Reply #11 on: March 26, 2015, 06:27:21 PM »
I have a few questions for MS - I think we all collectively thought that the wiring issue might solve this - when we can discuss again:

Something I recently got to thinking about...in the charge "Limits" where you set the amp limit for the controller, there is also a voltage limit.  The default is 63.2V.  Seems fine, and well above any recorded highs during the events I've seen.  I wonder though, if during an accelerated wind gust, this voltage limit might trumping other functions?  I don't think so, because it always seems to be an adverse reaction to the diversion load when it occurs, but the two are not far removed in time sequence.

I wonder if the OCP feature can be de-sensitized, or defeated (probably not recommended) through firmware?

Mary B

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Re: Managing opportunity and dump loads
« Reply #12 on: March 26, 2015, 09:00:58 PM »
Soft start relay for the heater off the wind. It is a resistor/relay combo that ramps current up slowly then the relay drops in to make the circuit direct instead of through the resistor. If I can locate a schematic I will post it

SparWeb

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Re: Managing opportunity and dump loads
« Reply #13 on: March 27, 2015, 12:21:28 AM »
Here they are:


I went back to your "upright and turning" thread from last year to get a sense of what they look like and how it's all set up.
Frankly you're in the best hands talking to MS as you are.  They're more likely to figure it out that me: I don't have a pair of Classics!

Though, I do have a thought that these peaks could be a result of something the turbine is doing during the gusts.  So far I haven't considered that.  The typical way to think of a "matched set" of wind turbine and MPPT controller is to under-size the prop, which drives a generator that is just too stiff for the prop to turn at optimum TSR.  It's the MPPT function of the controller, to modulate the current in the circut, which unloads the generator just enough for the prop to turn at optimum TSR like it should.  Sounds simple though it isn't really...

What could be happening that would interfere with the behaviour of the turbine - in such a way that would cause the controller to need to protect themselves?  One thing I can think of is stator heating.  If significant enough, it could increase the resistance in the circuit, which lets the turbine run a little too fast. 

Another thing is the furling tail and its ability to keep the turbine tucked in as the gust passes.  There is always a lag as the gust front arrives, passes the blades first, then passes the tail, and the time required for the increase in thrust force to move the rotor around and furl... the blades can be accelerating their speed until that is complete. 

One last thought, back to the electronic side, is a possible source of capacitance in the circuit that you haven't intended to have.  True, the stator coils are the opposite; inductance, but there are many other components in your system. 

In many ways, I am not prepared to take the OCP error message at face value.  It's probably my background troubleshooting all sorts of crap, some of it built and programmed by me, that's not working and not telling me why it's not working.  Without knowing more about the innards, the firmware, etc. I wouldn't just chalk it up to an over-current fault.  The error could be a catch-all message, or not programmed to report the actual fault correctly, so out comes this instead.
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kitestrings

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Re: Managing opportunity and dump loads
« Reply #14 on: March 27, 2015, 02:46:43 PM »
Mary, Spar,

You've hit on some possible complications and contributors.  On the mechanical front, my furling is definite later, less responsive than I'd like it to be.  The tail came in a bit heavier than forecast, and the hinge angle is too steep - in part it has a 3 degree error from what was intended/calculated - something I plan to alter this summer.  That is, this is all happening well shy of the allowable speeds/voltages.  I never seen over 160V.  This problem occurs about 100-120V.

Electrically, I originally had the water heater on a aux1 (non-PWM) output.  I moved it to aux2 thinking this would soften the introduction of the load.  At the same time, however, I speculated that the diversion load was perhaps too light - the wind is kickin' out say 50A, and the diversion only calling for only 22A - so I changed the configuration so that rather than having the elements interlocked, as they had been (1 x 1,200w), I now have they pair energizing together (2 x 1,200w).  I may have moved it in the wrong direction.  In either case when a sudden gust hits, it often becomes an all or nothing diversion.  The challenge with any sort of soft-start is that delaying the load, when it is needed, means the input voltage ultimately gets pushed up faster (somewhat defeating the positive influence of the diversion).

Heat in the stator I wouldn't think would be a factor.  At peak output it is only about 20A on 2-in hand 14#.  The wire run is a bit longer than it will be in the final install.

Ryan at MS similarly has suggested that the OCP is an interpretation of what's going on; not necessarily what's going on.

~ks

kitestrings

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Re: Managing opportunity and dump loads
« Reply #15 on: March 29, 2015, 09:06:40 AM »
I'm trying a slightly different approach.  Perhaps it may shed some light on things.  I've changed the aux 2 water heater diversion to the "Waste Not Hi" mode, aka "Louie-Louie"  ('Ui-Loi', Use It Or Lose It).  From observation, the controller seems to have heartburn when the input voltage from the turbine is very high relative to the batteries.  In effect we're trying to respond to a sharp up tick in input voltage, over a very narrow window, and hopefully moderate it with the diversion load.  Comparatively, the input voltage from the turbine is very volatile, in our case it can fluctuate from 59-60V at cut-in to about two and half times that near the upper limit output.

The "Waste Not" diversion is a battery relative mode which allows you to divert excess/opportunity load relative to the system charge stage at any time (absorb, EQ, or float).  My thought is that the battery voltage is inherently more stable.  If were well a set-point, absorb for example, the higher current flows will be welcome.  As we approach the set-point, the diversion will begin, and we will allow the 'clipper' to respond as before.  We'll see.

I've been messing with the settings a bit with sunny conditions.  There will be some trial and error, but it is pretty slick.  I've read some related articles on MS forum to see what others are using.  I've started with an off-set of -1.0V, and a width of 1V.  If I understand correctly if the absorb is say 59.2V, the PWM will start to become active at 58.2V, and become fully active - no longer pulsing - at (58.2 + 3.0 =) 61.2V.

kitestrings

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Re: Managing opportunity and dump loads
« Reply #16 on: March 30, 2015, 11:24:18 PM »
Well the verdict is still out on the wind, but I thought I'd share that the PV harvest pulsing both elements was much, much higher.  I expected it would be a bit better.  On the MX60 my diversion was to one of two interlocked 1200w elements.  With the speed (or lack of) switching, I was concerned if I had too much load it would often be bouncing the voltage below the intended set point in less than full sun; a "coup de fouet" I think I've seen it described.  With aux2 I don't need to worry about this.

Anyhow our normal high days on PV (3.2 kW) are around 14-16 kWh, mostly the summer.  Sunday (cold clear, snow cover), after programming it to Waste Not we logged 20 kWh!  I don't think I've ever seen that high.  The highest day in the last 30-40 days has been about 14 kWh.

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Re: Managing opportunity and dump loads
« Reply #17 on: April 01, 2015, 11:08:52 PM »
So by tweaking one setting you get 25% more energy?
20 kWh out of a 3.2kW array is roughly 6.25 hours in full sun.  Accounting for taper-up in the morning and taper-down in the evening, the PV would be at its peak efficiency for about 9-10 hours. 
...In March. 
This is a fixed array, right?
Jeepers

You won't be needing that nice wind turbine any more.
I'll give it a good home.
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kitestrings

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Re: Managing opportunity and dump loads
« Reply #18 on: April 02, 2015, 08:40:25 AM »
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So by tweaking one setting you get 25% more energy?

No.  The gain was mainly from changing to a larger available load.  On the MX60, the diversion was non-PWM so we had the elements (2 x 1,200w) interlocked, like on a conventional system.  The logic was that is the load was too larger, there would be times when the diversion would be frequently 'bouncing' the voltage below desired set-point.  It's functional, but comparatively very slow.  Mid-day, sunny-day, the diversion was continuously "on", but only about half of the available array output.

With the Classic I could move the diversion to aux2 (PWM) and have full-range, 0-2.5 kW, of the connected load with the elements in parallel.  Now during the mid-day period there is ~2.5 kW being diverted (assuming no other significant loads).  I thought it was a fluke, but we did another 18.1 kWh just yesterday.

I was pretty happy with it before.  Our LPG drops precipitously in the summer period since we started "opportunity diverting".  Especially when we're gone for the day - work, school - the opportunity, with only a 40 gallon tank, is *((170-55 delT)*40 gal*8.33# =) 38,000 BTUs, or about 11 kWh.  Functional storage; cheaper than batteries; simpler than DHW solar.

Yes, it is a fixed array.  45deg at same lat.




*This is not a typo.  We're heating to the allowable temp of the tank 170degF, then we temper it down.  It doesn't normally get this high, but it gives us the potential for a bit more storage.

~ks
« Last Edit: April 02, 2015, 08:44:40 AM by kitestrings »

kitestrings

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Re: Managing opportunity and dump loads
« Reply #19 on: April 02, 2015, 09:57:21 AM »
Quote
You won't be needing that nice wind turbine any more.

We pretty much don't need it from now (with a few exceptions) thru September or October.  It's November thru February where the PV output is pretty low - ranging 80 or 90 kWh to maybe 150-175 kWh/mo. - and a lot of -0- days.  Fortunately, the winds return late fall, good thru the winter, and exceptional in the spring.

I'm curious, do you run your turbine year-round?

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Re: Managing opportunity and dump loads
« Reply #20 on: April 03, 2015, 01:21:19 PM »
Winter winds trade off with summer sun in Alberta, so we are a lot like what you just described.  In the spring we get lots of both wind and sun, so as I write now, the turbine is shut down and the battery cabinet is opened to cool off.  I came home on Wednesday to find the batteries 10C warmer than in the shed.  The season to keep them insulated is over, but I also suspect a bad temp sensor connection.  The past 3 days have been unusually windy too.  Once the jetstream settles down (May) the wind goes into the doldrums and we rely on sun to keep batteries topped off.  Until September it's mostly storms that keep the wind numbers up, not continuous breezes worth collecting.  If I ever move to the off-grid life I will opt for lots and lots of solar.

I don't usually shut down the turbine, even if the power isn't needed in the summer.  This is mostly psychological.  I'd rather see it working than see it waiting, even if it isn't doing much.  Not much wear and tear in the summer, so not much wear is saved by idling it in the summer.
No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
System spec: 135w BP multicrystalline panels, Xantrex C40, DIY 10ft (3m) diameter wind turbine, Tri-Star TS60, 800AH x 24V AGM Battery, Xantrex SW4024
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