200Voc or higher charge controller

aj164

Anyone heard any rumors of a 200Voc or higher voltage charge controller? I realize there is probably a good technical reason why this cannot be made to be efficient.

Otherwise, why isn't there a charge controller available that can take a high voltage PV string input (e.g. 500VDC) and output 24V or 48V to a battery pack? It sure would save on wiring!

-AJ

mike95490

Re: 200Voc or higher charge controller

Midnight is coming out with one that can take 250VDC input. Still in beta test.

stephendv

Re: 200Voc or higher charge controller

Apollo Solar do a 200V controller.

halfcrazy

Re: 200Voc or higher charge controller

Midnite solar has 250 volt units in beta now they will actual operate at 250 volts and safe to higher then that. It will not be a far step to go to string voltage but they really want to get there 3 models to market then they will tackle the really high voltage.

RCinFLA

Re: 200Voc or higher charge controller

In a conventional single coil buck switcher, ignoring Rs losses of coil, the duty cycle is about the ratio of the voltages. For 25 vdc output from 250 vdc input there is about a 10% duty cycle where the series pass input MOSFET conducts for 10% of the time.

This also means the current has to be quite high through the MOSFET during that short 10% conduction cycle to charge the coil. These means very low Rs MOSFET is required if efficiency is not going to suffer. Also coil Rs must be low because of peak currents. This also means larger coil core to avoid saturation of core material, which cost more.

Generally the accepted limit on this type of buck switcher is no less then a 5% duty cycle to maintain a safe stability margin on the system.

This makes achieving a 95% efficiency tough. The greater input voltage means higher breakdown voltage rating required on the MOSFET, and the bigger the semiconductor die. The lower the Rs of the MOSFET the larger the semiconductor die. Both these means higher cost. Also larger die means more equivalent gate driving capacitance which means the driver circuit consumes more power. This drive power becomes a significant piece of power consumed at low illumination currents so efficiency gets worse when sun intensity is low.

It's all do-able but likely at an efficiency hit.

A high frequency transformer can be used but this requires total flush of transformer current between cycles. This makes the ferrite core content much larger (cost).

AntronX

Re: 200Voc or higher charge controller

RCinFLA wrote: »

A high frequency transformer can be used but this requires total flush of transformer current between cycles. This makes the ferrite core content much larger (cost).

I was going to post something about using HF transformer too, instead of buck circuit. I don't think cost will be high, because there are switch mode power supplies available that operate on 220V input, producing 12V output. I thought about possibility of modifying such power supply with MPPT control electronics to turn it into 220V input charge controller. The only problem I think will be, is that lower PV to controller wiring loss will be offset by higher loss in voltage conversion process. In other words, it is not worth pursuing from efficiency point.

boB

Re: 200Voc or higher charge controller

RCinFLA pretty much has the right ideas here...

All designs have compromises and High input V with low output V is no exception.

But we try to make those compromises with the smallest impact as possible for the application. So far it's working very well. ~almost~ there now.

Sponge boB, Square-Wave

niel

Re: 200Voc or higher charge controller

wouldn't that be sponge boB, sine wave? you don't want to downgrade yourself.:D

dsp3930

Re: 200Voc or higher charge controller

Apollo makes a 200voc MPPT controller. (Apollo Solar T80HV)
It is a little more $$ though. ($700+)

solarix

Re: 200Voc or higher charge controller

I'd really like to add small battery backed systems to grid tied ones. People buying a $$$ solar system always hate the fact that they are going to be out of power during outages. I'd like to be able to add on a small package like the Xantrex powerhub 1800 to keep a fridge etc alive, but it needs a way to charge off the high voltage grid-tied array. I don't care if it isn't the most efficient as it is only utilized during outages. Maybe a manual switch to tie in the array when the grid goes down. This could be done at a very reasonable cost if only a suitable charge controller was available - and could be a large market.

stephendv

Re: 200Voc or higher charge controller

If the system is for 99% grid tie (i.e. you want maximum efficiency to sell to the grid) and 1% backup in case of power failure, then an AC coupled system makes sense. Apparently a firmware update for the Xantrex XW will allow it to work this way. And the SMA sunny Island and sunny boy have worked this way from the start.

techntrek

Re: 200Voc or higher charge controller

In case you missed it, Schneider/Xantrex just announced a high-voltage charge controller. Scroll to the bottom of this thread:

http://wind-sun.com/ForumVB/showthread.php?t=9275

Doesn't appear to be MPPT, but since it would only really be used during grid outages I don't think that's a big problem. I think it would be best to use a high-efficiency AC battery charger while the grid is up.

KeithWHare

Re: 200Voc or higher charge controller

techntrek wrote: »

In case you missed it, Schneider/Xantrex just announced a high-voltage charge controller. Scroll to the bottom of this thread:

http://wind-sun.com/ForumVB/showthread.php?t=9275

Doesn't appear to be MPPT, but since it would only really be used during grid outages I don't think that's a big problem. I think it would be best to use a high-efficiency AC battery charger while the grid is up.

Since the first line of the description is "Xantrex high voltage charge controller XW MPPT – 80 - 600", I think the new Schneider/Xantrex offering might be MPPT.


Keith

techntrek

Re: 200Voc or higher charge controller

Dave added "MPPT" and the MPPT voltage range after I made my post above. Glad to see it is.

KeithWHare

Re: 200Voc or higher charge controller

techntrek wrote: »

Dave added "MPPT" and the MPPT voltage range after I made my post above. Glad to see it is.

Sorry, I didn't verify the message timestamps before I responded.

In any case, the availability of several different MPPT charge controllers that support relatively high input DC voltages is going to be useful for off-grid and grid-tie installations.

In addition to the ability to use smaller wire for the runs between the PV array and the charge controller, it should be possible to get usable voltages earlier in the morning.

This is cool stuff!

Keith

Solar Guppy

Re: 200Voc or higher charge controller

KeithWHare wrote: »

Sorry, I didn't verify the message timestamps before I responded.

In any case, the availability of several different MPPT charge controllers that support relatively high input DC voltages is going to be useful for off-grid and grid-tie installations.

In addition to the ability to use smaller wire for the runs between the PV array and the charge controller, it should be possible to get usable voltages earlier in the morning.

This is cool stuff!

Keith

It makes no difference if you have a 48V array or a 400V array, its the exact same energy available to harvest. HV does have benefits as you mentioned , it also has some disadvantages, namely efficiency losses are higher and I would guess its probably double the cost of the current 150V controllers, we shall see soon!

Dave Angelini

Re: 200Voc or higher charge controller

KeithWHare wrote: »

Sorry, I didn't verify the message timestamps before I responded.

In any case, the availability of several different MPPT charge controllers that support relatively high input DC voltages is going to be useful for off-grid and grid-tie installations.

In addition to the ability to use smaller wire for the runs between the PV array and the charge controller, it should be possible to get usable voltages earlier in the morning.

This is cool stuff!

Keith

The best way to get early morning harvest is still the old fashioned way. The panel needs to be pointing at the sun!

BB.

Re: 200Voc or higher charge controller

I agree with Dave---"Panel Voltage" is not something that improves harvest with higher voltage strings... Vmp-array is achieved pretty much when weak direct sunlight (or lots of "sky glow" hits the panel (and near zero current).

Increasing sun (watts per square meter) increases current.

The comment about pointing to the sun is Dave's oft repeated recommendation for trackers--especially for off-grid systems where tracking increases the time on charge by quite a bit.

-Bill

Dave Angelini

Re: 200Voc or higher charge controller

Thanks Bill,
Even old dogs can change and my last 2 installs were fixed SE and SW arrays with the winter tweek to due south. Nothing wrong with the tracker but the panels are less pricey and if you have access to materials a pole mount is pretty hard to beat.

There is however the wow factor and the educational aspect of a dual axis tracker.
I have some Doc's with trackers who just keep sending me checks! Wow!

I have really like your Battery posts BTW.

BB.

Re: 200Voc or higher charge controller

Thank you Dave--And I appreciate when you and everyone else works to widen my perceptions too.

Sincerely,
-Bill