hydro

ws9876

I was reading an article in HomePower about hydro. At one point he says that DC to DC hydro units can only use MPPT controllers
if they are low voltage because the open line voltage on a DC generator is twice the output voltage and its too high for most MPPT.
First... most hydro units are wild AC to DC ,so is this an issue????
2 why is a DC generators open line voltage higher than its output voltage??? how does that work??

waynefromnscanada

Re: hydro

ws9876 wrote: »

Why is a DC generators open line voltage higher than its output voltage??? how does that work??

Similar to open circuit PV voltage, it's higher than the normally loaded voltage. With hydro, unload it and it speeds up, raising the voltage.

ws9876 wrote: »

DC to DC hydro units can only use MPPT controllers
if they (the turbine/genny combo) are low voltage because the open line voltage on a DC generator is twice the output voltage and its too high for most MPPT.

Same as above, an unloaded hydro unit will speed up, easily doubling it's normally loaded RPM, and in turn doubling the voltage, which, depending on that voltage, could easily smoke the controller. In some cases, hydro powered by a high enough head, could over-rev and destroy itself. These cases can only be used with load diverting controllers, so when the battery can't use the power, it's diverted to heaters or whatever to maintain a load on the turbine, thus preventing it's destruction. I'm lucky with my low head system, it can't over rev and can actually be paralleled with some of the PV on the same controller.
You don't have to use MPPT, but if you don't, you'll be throwing away a lot of power, as the MPPT will seek out the best, most efficient load on the hydro generator, thus harvest the max power. A non MPPT controller can't do that and will only work with whatever amps the hydro is producing, and can't take advantage of the extra voltage otherwise available.

Surfpath

Re: hydro

waynefromnscanada wrote: »

You don't have to use MPPT, but if you don't, you'll be throwing away a lot of power, as the MPPT will seek out the best, most efficient load on the hydro generator, thus harvest the max power. A non MPPT controller can't do that and will only work with whatever amps the hydro is producing, and can't take advantage of the extra voltage otherwise available.

Hi Wayne,
Agreed, regardless if a MPPT or PWM controller is used, a DC (Generator) to DC (Battery Bank) hydro setup that has the head (or flow - basically the power) to exceed that battery bank's capacity may result in generator damage is unless a diversion load is set up.

I am aware that MPPT works for you. However (for example), a 48V DC Hydro generator should, by design, typically only produces voltage compatible with a 48v bank (ie in the 48v - 64v range). In other words when a 48v Hydro Generator experiences greater flow then amps simply increases. The MMPT high voltage 'advantage' is therefore minimal(?).

In that way, for most DC to DC (Hydro/wind) set ups (where power transmission distance is not an issue) surely there is not much efficiency difference between PWM and MPPT? 10% percent more efficient for MPPT?


I'm just a student here, trying to get my head wrapped around the concepts.
-SP

ps. For generator systems where power transmission distances are an issue I can certainly see how MPPT can increase efficiencies....

From HomePower Hydro: With the DC-to-DC conversions in the MPPT controllers, it is possible to operate the hydro at high voltage to keep the amperage low, minimizing line losses on long-distance wires. The MPPT units also allow the hydro turbine to run at the speed and voltage that produces the most power. Some small hydros allow varying the strength of the magnets to better match the varied flow of a stream, but the MPPT will unload the unit to let it speed up, and do the adjusting automatically. The problem with using these units is they are designed for solar-electric arrays that put out a defined high-voltage limit that isn’t too much higher than the system’s running voltage. However, in a DC hydro turbine, the open-circuit voltage is twice the running voltage. So using an MPPT controller directly with a hydro turbine is limited to low-voltage systems.

One “bleeding edge” method is to connect the hydro in parallel with a solar-electric array at about the desired voltage, and the array will “clip” the peak voltage at about 10% above its rated open-circuit voltage. The modules act like giant zener diodes protecting the MPPT controller in high-voltage conditions. Many small hydro systems are on seasonal creeks that dry up in the summer, so a PV array is already a part of the off-grid hybrid system. The MPPT controller gets the maximum output from both components of the renewable energy system.

BB.

Re: hydro

Surfpath wrote: »

One “bleeding edge” method is to connect the hydro in parallel with a solar-electric array at about the desired voltage, and the array will “clip” the peak voltage at about 10% above its rated open-circuit voltage. The modules act like giant zener diodes protecting the MPPT controller in high-voltage conditions. Many small hydro systems are on seasonal creeks that dry up in the summer, so a PV array is already a part of the off-grid hybrid system. The MPPT controller gets the maximum output from both components of the renewable energy system.

I would never suggest doing that... Sounds like a good way to cook your array or even start a fire.

With wind turbines, where you have a fairly large RPM range (hardly turning to gale force winds), an MPPT controller can substantially increase the harvest (something approaching 3x improvement during Midnite solar testing--As I recall from one post a few years ago???).

With water turbines, if your RPM is more matched to the job--Perhaps a MPPT controller is of less use (unless you want to increase water flow/RPM to gain output power without installing a new/rewound alternator--my guess).

-Bill

waynefromnscanada

Re: hydro

Surfpath wrote: »

I am aware that MPPT works for you. However (for example), a 48V DC Hydro generator should, by design, typically only produces voltage compatible with a 48v bank (ie in the 48v - 64v range). In other words when a 48v Hydro Generator experiences greater flow then amps simply increases. The MMPT high voltage 'advantage' is therefore minimal(?).

In that way, for most DC to DC (Hydro/wind) set ups (where power transmission distance is not an issue) surely there is not much efficiency difference between PWM and MPPT? 10% percent more efficient for MPPT?

The huge advantage of a GOOD MPPT controller with hydro is that the max efficiency of the turbine may well not be at the battery voltage, rather some voltage substantially above that. My hydro with no load runs up about 55 VDC, but the MPPT controller finds the max efficiency point at roughly 35 VDC, which happens to be very close to that of my PV. With a PWM controller, the hydro voltage is clamped to battery voltage of 12.4 to 14.8, which loads down the turbine too much, slowing it to below it's max efficiency range, lowering it's wattage output and in my case, badly overheating the alternator windings. In my case the MPPT gives roughly 50% more wattage than PWM.
Furthermore, even if the turbine/alternator combo matched the voltage (under load) of the battery voltage, that same alternator would produce near twice the voltage if left to run unloaded. This is because of mechanical inefficiencies and electrical resistance losses under load.

Surfpath

Re: hydro

waynefromnscanada wrote: »

The huge advantage of a GOOD MPPT controller with hydro is that the max efficiency of the turbine may well not be at the battery voltage, rather some voltage substantially above that.....

However, it appears that many of today's turbines are custom-built to match the paired battery bank. There seem to be a lot of options:

"Each unit is built to match site specifications. When ordering, specify battery voltage, transmission line length and size, flow, pressure, pipe size and length".

That way you can ensure a more efficient match?

waynefromnscanada wrote: »

Furthermore, even if the turbine/alternator combo matched the voltage (under load) of the battery voltage, that same alternator would produce near twice the voltage if left to run unloaded. This is because of mechanical inefficiencies and electrical resistance losses under load.

Yes, for sure.