An "alternative coupling"?

MarkC

Is it possible to "couple" (typically) grid tied and off-grid equipment at the DC PV panel connection(s)?  Is there equipment that would allow simultaneous/parallel connectivity of both a typical off-grid charge controller AND an on-grid inverter to the same set of panels.  This is not a theoretical musing as it is being done in the electric vehicle arena to provide V2G functionality - for bi-directional energy transfer to/from large EV batteries from solar and back to grid.  

jonr

Some (but perhaps not typical) controllers have ways to disable the MPPT tracking feature that may cause interference between controllers.

Dave Angelini

It may be possible to run both a grid inverter and a CC in parallel at the same time but,
Many brands would not like it and you would have to test it.
The lower DC input might not share power with the higher DC input of the other. It could be erratic.
Equipment damage and certainly not approved by Fire and Homeowners insurance.
Why can't you switch it? One on, the other off?
 

MarkC

Dave Angelini said:

It may be possible to run both a grid inverter and a CC in parallel at the same time but,
Many brands would not like it and you would have to test it.
The lower DC input might not share power with the higher DC input of the other. It could be erratic.
Equipment damage and certainly not approved by Fire and Homeowners insurance.
Why can't you switch it? One on, the other off?
 

I'm actually set up to "switch".  I'm asking Midnite first, but I'm quite sure the answer will be similar to yours - test at your own risk and potential destructive consequences!  Sort of hoping someone has come up with a clever solution to send the DC power to the battery cc load preferentially.  

jonr

You could connect the panels only to a grid-tie inverter and then run a  240VAC battery charger.  If net metering rates aren't attractive, then switch on the charger only when the sun is shining.

mcgivor

@MarkC Do you have grid available? I've been thinking along similar lines and think I have a solution, but it would need the grid, so without rambling on thought I would ask a simple question first.

MarkC

mcgivor said:

@MarkC Do you have grid available? I've been thinking along similar lines and think I have a solution, but it would need the grid, so without rambling on thought I would ask a simple question first.

Yes - actually two separate GT systems.  The "signature" describes my hardware quite well.  Much of the equipment is somewhat "experimental" in nature as there are likely simpler ways to achieve the functionality (the PriUPS system as an example).  I would like to experiment with "coupling" a grid tied inverter with a high quality style charge controller (my Midnite Classic) at the PV panels DC outputs.  The near term goal is to prove out a method that would preferentially push PV DC energy to my Classic/battery bank.  This will power my level II Nissan Leaf charging system.  Meanwhile ANY energy that is not used by the Leaf charging system, I would like to automatically flow to the grid. 

Can you explain your solution?

jonr

Somehow, you want the Classic to come up with a Vmp that is slightly lower than the one that the SMA finds.   If you can do that, it will get priority.

Maybe by setting the MPPShdw.CycTms/Cycle time on the Sunny Boy to a value much higher than the Classic.

mcgivor

My idea is somewhat different to sharing the DC output from the panels which would more than likely cause conflict between the GT inverters  and the CC. How about using  using an inverter charger which has grid support,   the grid/GT would  charge the backup battery and  pass through current  charges the Leaf, when both are fully charged, the only load would be what is required for float on the backup battery. Since it would be taking from the grid, which you are feeding into, the net result would be what you are seeking, this however would mean a new piece of equipment, which perhaps is not what you had in mind. My situation is sort of the reverse of yours, I have the inverter charger and want to push excess production into the grid but it's not hybrid, so was thinking of ways  to accomplish that.

MarkC

mcgivor said:

My idea is somewhat different to sharing the DC output from the panels which would more than likely cause conflict between the GT inverters  and the CC. How about using  using an inverter charger which has grid support,   the grid/GT would  charge the backup battery and  pass through current  charges the Leaf, when both are fully charged, the only load would be what is required for float on the backup battery. Since it would be taking from the grid, which you are feeding into, the net result would be what you are seeking, this however would mean a new piece of equipment, which perhaps is not what you had in mind. My situation is sort of the reverse of yours, I have the inverter charger and want to push excess production into the grid but it's not hybrid, so was thinking of ways  to accomplish that.

The use of the arduino could possibly be a solution? - if you can get to data in your inverter/charger and use this develop an algorithm to divert the excess energy.  Since I'm not sure of your setup, not sure it can help about getting energy back to the grid - but likely this link will lead you to the answer:

http://midniteftp.com/forum/index.php?topic=2511.0

The author - Will is quite knowledgeable about communicating with the Midnite equipment - maybe something similar with your inverter/charger is available.

In my situation, the "PV coupling" is the first step in essentially bi-directional energy to/from the Leaf - and is one of the choices - but would seem to be a very efficient choice.  Since I don't have a "hybrid" set up, I don't believe I can do what you are suggesting?

MarkC

jonr said:

Somehow, you want the Classic to come up with a Vmp that is slightly lower than the one that the SMA finds.   If you can do that, it will get priority.

Maybe by setting the MPPShdw.CycTms/Cycle time on the Sunny Boy to a value much higher than the Classic.

I'm going to look deeper into your suggestions.  Apparently, much data can obtained from the Midnite CC's via RS-232 protocols, but not sure of any "adjustments" to MPP tracking.  I don't even have communications set up with my SMA's - so will need to talk with SMA first about adjusting the MPPT cycling times.  

I do wonder about the basic electrical characteristics of the two pieces of equipment (potential variations in resistance that each equipment dynamically exhibit to the the PV panels under actual energy production - and will that be unstable or even destructive?).  If either the CC or GT inverter could "backfeed" seems that could be problematic - or maybe useful, depending upon the functionality needed!  

Dave Angelini

The "destructive part" is where I would really think the whole idea needs to be thought out and is it really worth the risk?

 I did an insurance claim for a system that had pictures taken during a pre-inspection of the house/garage. The after the fire pictures show quite a bit of extra solar equipment that was not really installed correctly. They did settle but I doubt these folks will ever have home insurance again. If you are doing the work as an owner builder you still need a permit if you have a claim.
 If you hired someone,

Qualified personnel have

training, knowledge, and experience in:

• Installing electrical equipment

• Applying all applicable installation codes

• Analyzing and reducing the hazards involved in performing electrical work

Pessimists usually have more data, unfortunately.

bill von novak

MarkC said:

Is it possible to "couple" (typically) grid tied and off-grid equipment at the DC PV panel connection(s)?  Is there equipment that would allow simultaneous/parallel connectivity of both a typical off-grid charge controller AND an on-grid inverter to the same set of panels.  This is not a theoretical musing as it is being done in the electric vehicle arena to provide V2G functionality - for bi-directional energy transfer to/from large EV batteries from solar and back to grid.  

Morningstar has a switch that allows switching an array between a charge controller and grid-tie inverter.  You would not want to connect them both simultaneously; they will tend to confuse each other.

BTW that's not how V2G works.

MarkC

Dave Angelini said:

The "destructive part" is where I would really think the whole idea needs to be thought out and is it really worth the risk?

Dave;
I agree, no it is not worth the risk unless the equipment manufacturers explain why (or why not) it can be done - or someone has come up with an innovative (and safe/tested) way to do it (however, seems that is how we have made much of our progress).  What got me interested is that an innovative manufacturer is actually doing it (V2G) with their equipment - as described.  But I don't have their equipment.

Dave Angelini

When I can buy something like this from my supplier or the store here is "when". Most all quality electronics has an intended use statement in the beginning of a decent manual.  Insurance companies are not happy when there is deviation. 

I probably will lose my homeowners policy because of the ridiculous amount of money they want where I live. It is a gut check to self-insure but in many ways it is better as it forces you to address every issue. We go through this insured and not insured. The last time they used Google earth to check the slope of the mountain/hill. Now they don't even do that, they just look at a zip code. Even the Military USAA policy that I had will no longer insure this zip code. 

Good Luck on whatever you decide!

jonr

The Classic has many settings to change MPPT behavior.    

Any PV->battery or PV->grid device that backfeeds anything towards the PV array doesn't make sense to me - does anyone know of such behavior?

Estragon

Insurance companies are in the business of collecting and investing premiums. They are not in the business of paying claims beyond a level that induces people to keep paying premiums.

They know odds better than you or I do, and over a large enough sample, insurance is always a losing bet - no different than a casino.

It is a gut check to self insure, especially for risks that are potentially life altering. On the other hand, a lot of folks are functionally self insuring, but don't know it. My father died some months ago in a house I own. It had to be insured as a rental as it wasn't owner occupied, and rates were accordingly higher. After he died, it took some time to clear stuff out and get the place ready to be sold. I took the usual steps of shutting off water, collecting mail, etc while vacant. It sold recently, so I contacted the agent about the date to end coverage. Apparently there can be issues where a delay in transfer of title can leave the property still at vendors risk after closing, so on the lawyer's advice I asked about extending coverage for a week or two after close. The answer was that; they would not cover after close, because the property would be vacant until close, an extra fee would apply for the period to close, and the property was effectively uninsured from date of death to the date the extra fee was paid. They would not, however, rebate premiums for the uninsured period. I was functionally self-insured for ~6mos and didn't know it. In hindsight, I should have been truly self-insured (and not paying premiums) instead.

jonr

Condolences about your father.  Insurance has so much unintelligible fine print that I'm surprised that they ever have to pay a claim.

Estragon

They have to pay some claims, or nobody would pay premiums.

Solray

Insurance is just like any other contract, you have to read it all or have your attorney read it and advise you of the terms before you sign up.

Dave Angelini

Estragon said:

Insurance companies are in the business of collecting and investing premiums. They are not in the business of paying claims beyond a level that induces people to keep paying premiums.

They know odds better than you or I do, and over a large enough sample, insurance is always a losing bet - no different than a casino.

My point was really that they do not know the odds. One company came out 5 years ago and saw that there was 16000 gallons of water, a fire pump, 200 feet of weed wacked perimeter, limbed trees up 15 feet, a power system that would not go down when the utility shuts down, metal roof and cement siding, and good roads. 

They insured us until they just decided not to. We went 3 years without and then got a decent offer.  The houses they do insure have none of what many of my offgrid clients do. It is a stupid business model and has been going on for a very long time.

Estragon

I can relate to that. They threatened to discontinue coverage a few years ago on the house because a porch door didn't close properly! The main door to the house was fine, so it's not like the place was insecure.

Dave Angelini

Yes that is unreasonable. Another one for you, on the other side of my hill there is a house without any of the safety gear, no one is living there, and they pay almost nothing for insurance because it is a vacation home on their main policy. Tall dead grass growing right up to the porch.

Estragon

Bah! I guess it's easier to have someone drive around in a city finding a porch door open a crack than to find an obvious total loss waiting to happen in a more remote area.

Maybe the underwriter has a brush clearing clause buried deep in the legalese.

nickdearing88

Not to derail the thread but one more....

I could not insure my home when I first purchased. Reason: the railings on either side of my back steps were made of different materials - one white vinyl and the other unpainted wood. I painted the wood railing white and called them back to take pictures, then the policy started.

Crazy.

Solray

It's all about the demographic and the odds. When I was a young man, I paid a huge amount for auto insurance, I now have 5 cars worth more than my house was at the time and I pay a lot less. Go figure.