Connecting Wind to Multiple Systems

[(unknown)]

I'm interested in building or buying a wind turbine (2-10Kw) and having it supply power to multiple off-grid systems.

For instance we have a cluster of houses each with its own solar system and we would like to provide a wind supplement to these systems and share it among the 3 houses. They are all within 100 feet of each other. I've considered a micro-grid style system but for social reasons prefer not to have everyone on the same battery bank so each house can manage its own loads and storage.

I'm also interested in eventually having an electric vehicle charging station which has the additional feature of the battery bank sometimes being off running about town and not available for charging.

Can anyone suggest a system for splitting the power between multiple off-grid systems?

I've thought about some sort of time based system, where the wind is switched between system A, B, or C every hour, ideally with some automated timer. This would be acceptable but is not very intelligent as it wouldn't take into account when one of the systems is full and another is not. Also I have no idea how to find or create such a switch.

Any ideas?

Thanks,

Tony

[sdscott]

If your existing systems are 12volt, maybe this logic will work?

[Flux]

This is a messy one without special equipment.

Scott's idea will work if you can get suitable turbines to suit your battery voltage. You would need a dump regulator across each battery with the mill feeding direct.

For a turbine of the same voltage as the battery it is even more messy. I would split the turbine leads into 3  with identical resistances and connect the things in parallel to share the current. If you do it on the dc side then the batteries will back feed, if this is an issue then each battery will need a blocking diode. At the cost of more wires and rectifiers you could parallel the ac connections with a 3 phase rectifier at each battery. Again each battery needs its dump regulator.

The parallel scheme is not in any way ideal. If one battery is fully charged you really need to take it out of circuit rather than run it in parallel dumping 1/3 of your wind machines power.

Series control regulators are risky on wind schemes unless you really know what you are doing and you would most likely have to do your own design.

The series option seems easier if you can get a suitable turbine ( build your own then you can have what you want).

Flux

[tanner0441]

Hi

We had a similar system on some of the larger boats, batteries charged from either engine using blocking diodes. then distributed to different systems again via blocking diodes.

The .6 volt drop from the alternators is not a problem because the regulators compensates. The problem I can see is the low voltage shut down on the inverters will come in early.

Brian

[Flux]

In this case I see each battery having its own inverter so diodes would only be needed for the mill.

Flux

[scottsAI]

Tonyrabbit,

Some out of the box thinking.

Were talking 3 homes.

Generate the power in 3 phase.

Rectify each phase separately (single phase). Each home gets a phase, thus getting its share of power. Requires all battery systems to be nearly equal. A significantly lower charged system could use more than the others are getting. But is limited somewhat.

Electric vehicle must connect to the homes DC bus to keep things fair. NOT A DIRECT CONNECTION! Connecting two batteries must use a current limiter between them.

Reality; expect vehicle DC is much higher...

Have fun,

Scott.

[Ungrounded Lightning Rod]

I'd use separate rectifiers for each house and equal resistance wiring between the common point and each house.  Rectifiers can be either at the common point or at the house, provided you do it the same way for all three.

The lower batteries will still pull somewhat more than their share of available power - though not in proportion to their excess usage.  But at least you won't have them sucking charge directly out of the less energy-consuming houses.

Simple stuff like this is non-optimum:  You'd like to remove the load when batteries are fully charged so more charging is available for those that are still low.  But that risks unloading the mill when everybody's full.  The voltage drop on the wires to the houses fouls the communication for controlling a common dump load.  Haven't thought of a good way to get the most out of the mill without back-communication of the state-of-charge from the houses to some common point.

[(unknown)]

Thanks for the input so far.

For reference, all systems are 48V. Windmill could be 48V or could be higher voltage (eg whisper 500HV) or even 120 or 240AC (eg like Skystream or with an inverter at the base of the tower (eg SMA Windyboy).

Some systems have outback charge controllers and inverters, others have Trace.

The Skystream and outback people show diagrams connecting the Skystream to the Outback Inverter (FX series) which includes a battery charger. Seemingly it would charge batteries from the mill like it would from a generator or grid power.

Electric Vehicle could be 48 V but many are 96 from what I've seen.

I like the idea of the 3-phase as far as equal sharing but it would not allow sending extra power one way or the other if one system were already full.

[hydrosun]

I was looking at a similar setup to share a hydro between three houses, but not equally. The owners house would be hooked up directly. It would have a load diverter to take up the extra power if all the batteries were full. The other two houses would be connected with a diode to prevent backfeed. I had planned to use an Outback MX-60 already hooked to a solar array (the solar panels clamps the voltage from going too high) to convert the 48 volt hydro output to the 12 volt systems of the other two houses. When the batteries were full the MX60 would disconnect. This system was designed to add a little boost to these other houses in the winter when their solar panels are putting out very little and a fossil fuel generator is the backup. One house is over 1500 feet away so would only get a few amps through a   10-2uf wire. But 2 amps at 50 volts is 2.4 kw a day, plenty for these very frugal solar only systems. I'm still waiting for them to give the go ahead to actually build the system. I'm sure someones generator will die soon to give a higher priortity to this project.

Something similar could be used for your wind system. One diversion controller and two solar disconnect controllers. If the wire resistance is equal  the power will flow mostly equally until the batteries are full.

Chris

[esc]

What if you used a standard generator design and did the time based switching.  Equal time slices, minutes, maybe even seconds, but any battery bank with a high voltage would skip a turn.

If it were managed by a micro-controller, like a PicAxe, most of the hard work is already done.  I have not personally done this sort of thing, yet, but it doesn't seem like it would be that hard.

This way the only non-standard item is the code in the controller, which is WAY easier to modify than hardware.

[laskey]

It would cost more, but you'd be better off delivering 3 phase to each house, and using a three phase rectifier at each battery bank.  You'd need a charge controller at each battery bank.  You probably don't need to worry about dump loading until all three banks reach full.  You should have a single large dump load to kick in when all banks are full.  

You definitely don't want to split the phases amongst each house.  If/When one bank gets full first and stops drawing it will likely cause a terrible impedance imbalance that will probably manifest itself in the destruction of your gen.  The three phases need to be in very close balance or ugly things happen.

Cya,

Zir

[laskey]

I think You're making it too hard on yourself there.  The mill isn't interested in the battery state of charge.  It only cares that it's loaded enough not to freewheel.  You can pick what that threshold is, and control your dump by sensing the total current being drawn from the mill, and kicking in the dump load when the total current drawn falls too low.  In the worst case, you might need to work out a 3 Phase "large" current sensor, but that's not that hard a task is it?

Cya,

Chris

[wooferhound]

I was thinking something like you are.

wind each coil '3 In Hand' and rectify it as three separate 3 phase outputs, one to each house.

[SparWeb]

This would be a fascinating design project for an engineer / contractor who could accomplish it.  The integration of multiple RE systems basically begs the creation of a "mini-grid" among the homes.  It may be possible, though I am far from sure, that what you want to do could be accomplished at the 120VAC level.

Since each house has its own solar system already (I assume) then there can also be many differences between the houses.  Not just in battery state-of-charge, but in the capacity of each battery bank, the solar array at each home, the type of inverter used at each, too, and so on.

To try to fairly provide energy to each home, you need something that can't be fooled the the apparent SOC of any particular house's battery.  I would avoid building a DC network.  The Outback and Xantrex inverters have many features that can make this work at 120VAC, so that would be my natural starting point.

When installing the wind turbine, install a full battery bank at the windmill, a big dump load, and a BIG inverter.  In your case, however, your windmill's inverter BECOMES THE GRID.  Now feed that among the houses at the Grid input to their inverters.  Those inverters will synchronize to the grid, they will charge their batteries from your "grid", and (maybe) can "sell back" to your grid when the sun fills up their batteries.

If the wind hasn't blown in a long time, and the windmill's battery bank gets low, the "grid" goes down, but the houses should manage okay, because they have inherent battery back up!

The Xantrex inverters can also start generators, which in your case could be wired to just "flip on" the grid charging from the windmill's AC output.  In your case, the house's inverter would just turn on a relay that makes the wind "grid" inverter's AC available.  When the house's inverter detects its battery is full, it would shut off the "generator", which would otherwise just be turning off that relay.

I have probably missed something because it shouldn't be so simple....

[Ungrounded Lightning Rod]

The problem is that if you set up the house batteries to disconnect from the mill at full charge (to maximize charging current for the other houses that are still low), when all the houses come to full charge you have no load.  A dump controller on the mill will then go wonky, with the voltage going 'way up when the load is off, turning it on, then going down below the setpoint and turn off.  Back and forth, with a hard "whang" to the mill's shaft every turnon.

You could cover for that with an extra set of batteries at the mill - big enough to accept the charging current but mainly there to float and stabilize the voltage.

[GWatPE]

One way of ensuring a balanced system is to use a normal diversion load on the windmill, set at the maximum system voltage and connected with a separate rectifier from the mill AC.  Each of the houses is supplied with AC and rectified at each battery bank.  The controller for each house would be a series disconnect type, loke a solar controller. This ensures the house systems do not interfere, and the max power gets to the loads.

Gordon.

[Madscientist267]

2 cents possibly worth less -

It would seem to me that somewhere youre going to invoke conversion losses in the process of making sure that each house can get the energy it needs. They might as well be in the ideal locations. The micro grid with the mill's own battery system seems the best, as long as you can afford the conversion losses that arise from it.

This way you have better control over how much power goes where, and the mill can have it's own dump load, so that regardless of the SOC of each house, the mill is protected.

Mill charges its own bank and a master dump load, inverter at mill distributes power to houses, chargers in each house top batteries independent of each other.

Getting into time based controls and all that just adds complexity - remember the rule - KISS

Steve

[jondecker76]

If I were looking to do what you are proposing, I would make a custom PLC controller that could be set up to equally spread out the power between the 3 houses. (I have done several RE projects using inexpensive PLC units with great success)

For example, lets say we make a user-adjustable setpoint and call it SwitchingKWH. Lets also say that we set this variable to 50 KWH.

Now just have the PLC start on house "A", and use that circuits battery bank and dump controller. Once the 50 KWH has been pushed to house A, switch to house B, and use that battery bank and dump controller. Again, once 50 KWH has been pushed to that house, switch to house C, and so on. This would ensure that each house got their fair share of the electricity produced.

The key is setting it up so that the SwitchingKWH variable is adjustable so that the system can be fine tuned.. For example, set it to 5 KWH for each house in the summer and there is less wind.. Then you can set it to a larger value in the winter when there are better winds.

Even better, if you do a PLC-based control scheme like this, you can have a different SwitchingKWH variable for each house individually if you wanted to. The possibilities would be endless.