Battery charging and feeding the grid at the same time

[stephendv1]

Looking at the specs for some commercial 48V turbines, it seems that there is some power to be harvested between 40V and 56V that might otherwise go to waste because the battery is at a higher voltage.  Would it be possible to connect a turbine directly to the battery through a blocking diode, and then connect a suitably low voltage GTI with programmable power curve to the other side of the blocking diode?

To my novice eye, it seems that this would allow the GTI to draw power from the lower voltages and then also charge the battery once the turbine reaches higher than batt voltages.  I'm thinking of using a 1.5kW max output 48V turbine with a 500W windmaster GTI.  Dumping surplus will then be done through a typical battery PWM controller and is not included in the sketch.

[stephendv1]

Looking at the specs for some commercial 48V turbines, it seems that there is some power to be harvested between 40V and 56V that might otherwise go to waste because the battery is at a higher voltage.  Would it be possible to connect a turbine directly to the battery through a blocking diode, and then connect a suitably low voltage GTI with programmable power curve to the other side of the blocking diode?

To my novice eye, it seems that this would allow the GTI to draw power from the lower voltages and then also charge the battery once the turbine reaches higher than batt voltages.  I'm thinking of using a 1.5kW max output 48V turbine with a 500W windmaster GTI.  Dumping surplus will then be done through a typical battery PWM controller and is not included in the sketch.  Will this work?

[Flux]

To be honest there is so little energy in low winds that you will never produce enough power to cover the cost of the GTI in a hundred years.  Below cut in to the batteries you are looking at watts or even milliwats depending on how the turbine is optimised for low winds.

Below cut in the prop is unloaded and will run as fast as it can before its aerodynamic losses stop it. Although not de4sperately efficient at runaway speed it will still attempt to charge the battery with what energy is available in the wind.

Only if the turbine is very badly designed or optimised to work in gales would you get any significant power before battery cut in, If this was in fact the case, a boost converter costing very little may be worthwhile an expensive GTI inverter would probably never get paid for.

Flux

[stephendv1]

Thanks.  I'm looking at a 2.8m diameter 1.5kW Huaya (aka exmork) turbine with attached power curve- turns out that curve is measured using their battery controller so upper voltage is clipped.  It shows that at 8m/s it produces 43 volts and 700W.
Another one is the futureenergy 1kW machine (1.8m blade) which shows at 400rpm it produces 40V and also about 700W.

Are you saying that if they were battery connected and the batt V was 53V then those 700W would be also be available at the higher voltage and the turbines would just spin faster till they reached that V in the same wind?

[Flux]

Just re read your post and you were not proposing what I originally though. I thought you were trying to get a bit of charge into batteries before the GTI came on line.

At this point I am not sure what you are trying to do. As shown, it will come on line as a GTI and track along its power curve until you reach battery volts, beyond this point the battery will clamp the volts and throw the GTI off power curve, you will get progressively more battery charging as the wind picks up but neither battery charging or power to grid will be mppt and the results will not be optimum.

Without knowing your intentions it is probably not a good idea for me to comment further.

Without the GTI those turbines will speed up and charge batteries directly but it will be a direct charging scheme and without mppt you won't get the full rated power of a mppt scheme.

Flux

[stephendv1]

Just re read your post and you were not proposing what I originally though. I thought you were trying to get a bit of charge into batteries before the GTI came on line.

I want to use a GTI's MPPT to get power from the turbine before the turbine reaches battery voltage.  The GTI I'm looking at will start at 30V, while my battery bank is 48V.  So between 30V and 53V (ish), can I pull power from the turbine using the MPPT of the GTI?

[Flux]

OK, I am not sure of the priority of battery chaging v grid feed.

You can optimise the GTI inverter for use up to battery volts. As I said previously there is little power in low winds so you may only get a watt ot so at 30v.

As you approach the higher voltages the GTI should make best use of the power but will go right off its curve when direct battery charging starts.

I don't know your battery priority but it may turn out thet you can get quite useful battery charging direct from the turbine even when its optimised input volts for the GTI is below battery volts.

How this would compare with charging the battery from a charger from the grid ( supplied by GTI) , I have no idea.

If the main priority is battery charging I would try the turbine direct first rather than spending money on the GTI.

If the ultimate priority is battery charging then something designed for the job such as the Classic would do a better job.

This seems an odd requirement and only you know your priorities. If you are restricting the GTI to the very low wind region, as I said previously it will probably never pay for itself but if it is to capture power regardless of cost then it may be justified.

Flux

[stephendv1]

If the main priority is battery charging I would try the turbine direct first rather than spending money on the GTI.

Thanks, I think that's what I'm going to do.  Sorry that I've hidden my ultimate goals so as not to muddy the waters.  The goal in both cases is charging the battery, with the GTI option it will feed into the output of a Sunny Island and backfeed that inverter to charge the batteries or supply the loads.  Going to try direct connection first, see how that works out and then play with MPPT down the line.

If the ultimate priority is battery charging then something designed for the job such as the Classic would do a better job.

Yeah the classic is an option, but since it's a buck converter it won't give any benefit for voltages lower than battery voltage.  Take your point that it may be a waste of time chasing power in low wind.