Advice on best way to go with my system

[RichardB]

Hi,

I'm at a bit of a crossroads in my design and would be grateful for some experienced advice please:

The site:
2.8L/s currently coming down the pipe.
550m of 50mm ID Poly pipe
Gross head 101m
Net head calculated as 84.5m
Hydraulic power potential as about 2200W
Therefore I calculated the power generation potential as 1560W (although in the real world I'm guessing this could be closer to 1400W)

The current system:
There is currently a 24V 440Ah battery bank, but I would consider going up to 48V bank if really needed.
The current turbine is, undersized, poorly built and inefficient, generating around 600W. It uses old smart drive washing machine motor attached to a home built turbine. There is a lot of vibration in the system and the NSK bearings usually only last about 6 months. This part of the system will be completely replaced.
There are also 6 x 120W solar panels connected to an Outback FM60.
Dump load is into the hot water cylinder via 2 x 28V 1000W elements and controlled by a PowerMaster 60A Charge Controller.

My requirements:
Run a normal household
Run workshop tools when needed (usually only in short bursts). The most powerful tool I have is a single phase welder which pulls 4800W at full power, but again only in short bursts and seldom used at full power.
Dump to hot water cylinder up to 75 deg C and then switch over to an air dump load. In summer the hot air will be allowed to escape to atmosphere and in winter will be blown into the house to reduce our reliance on the wood burner for heating.
Happy to remove the solar completely (as the hydro should be generating plenty) or possibly keep as a backup.

I have one of those sites that is in the middle ground (not big enough for running directly off an AC  single phase turbine, but hopefully enough constant power at 1400W to power a household and workshop with a suitably sized inverter and battery bank).

The questions:
I'm stuck trying to decide which way to go with the generator and batteries.
Will inverters typically use an AC source first and draw additional current requirements from the battery bank? Can the AC source be a hydro? If that is the case, then would I be better off using a single phase 240V generator?
This is the inverter I had in mind
http://www.aimscorp.net/8000-Watt-Power-Inverter-Charger-48-volt-to-120-240vac.html or http://www.aimscorp.net/6000-Watt-Pure-Sine-Inverter-Charger-24-Volt.html
Alternatively I could try source a 80V three phase generator (which might be much harder to come by), connect that to a three phase clipper and classic and use that for charging the batteries.
What size battery bank am I likely to need at 24 or 48V?

I've done a lot of reading, but no closer to making up my mind which way to go! Any help and advice much appreciated.

Thanks
Richard

[Westbranch]

As Corporal KLINK (Hogans Heroes) would zay: I Know NU-ZINGK!... about them personally...

go here http://forum.solar-electric.com/search?adv=&search=AIMS+inverter&title=&author=&cat=all&tags=&discussion_d=1&discussion_question=1&discussion_poll=1&comment_c=1&comment_answer=1&within=1+day&date=

[mike90045]

You better back up, and study your last line:

What size battery bank am I likely to need at 24 or 48V?

To size a system, you must first determine your loads. Even that can break down into several parts:
Steady load, peak load, daytime load, nighttime load. 

Your battery bank should be about 3x your daily KWh, so if your daily loads total up to 8 Kwh, you need a 24Kwh (24000wh) battery
Volts x Amps gives you KW  x Hours      or  V x Ah = Kwh
24V x 100ah = 2400wh battery  Too Small
48V x 200ah = 9600wh still too small
48V x 500ah = 24000wh  Just right.   You can have one cloudy day before you have to run the genset on the 2nd cloudy day. If you forget, day 3 comes along and finishes off your batteries.

Now you have low batteries, and a sunny, 3 hour day coming up tomorrow, how much solar do you need to recharge, or do you want to rely on using some genset power to charge with ?

[RichardB]

As Corporal KLINK (Hogans Heroes) would zay: I Know NU-ZINGK!... about them personally...

go here http://forum.solar-electric.com/search?adv=&search=AIMS+inverter&title=&author=&cat=all&tags=&discussion_d=1&discussion_question=1&discussion_poll=1&comment_c=1&comment_answer=1&within=1+day&date=

Thanks, any suggestions for suitable inverters in the reasonable price bracket?

[RichardB]

You better back up, and study your last line:

What size battery bank am I likely to need at 24 or 48V?

To size a system, you must first determine your loads. Even that can break down into several parts:
Steady load, peak load, daytime load, nighttime load. 

Your battery bank should be about 3x your daily KWh, so if your daily loads total up to 8 Kwh, you need a 24Kwh (24000wh) battery
Volts x Amps gives you KW  x Hours      or  V x Ah = Kwh
24V x 100ah = 2400wh battery  Too Small
48V x 200ah = 9600wh still too small
48V x 500ah = 24000wh  Just right.   You can have one cloudy day before you have to run the genset on the 2nd cloudy day. If you forget, day 3 comes along and finishes off your batteries.

Now you have low batteries, and a sunny, 3 hour day coming up tomorrow, how much solar do you need to recharge, or do you want to rely on using some genset power to charge with ?

It's hydro not solar, so same 1400W coming in 24/7 ... it's more the peak load that is going to be the deciding factor for me.

[vtmaps]

It's hydro not solar, so same 1400W coming in 24/7 ... it's more the peak load that is going to be the deciding factor for me.

Then what you need to do is figure out how much your load's peak wattage will exceed your hydro wattage, and for how long, and how often.

example:  you want to draw 5500 watts for 30 minutes.  Your batteries will need to supply 5500 - 1400 = 4100 watts for 30 minutes.  That is 2050 watthours.  (actually more because I am ignoring inefficiencies). 

But what size battery?  That's a really tough question for several reasons.  First we have to know how often these deficits occur... If this deficit occurred just once a day, you could get by just fine with a 6 kwh battery.  If these deficits occur X times per day, your battery will run out of cycle-life X times faster than a typical RE battery subject to daily cycling.   This situation argues for a larger battery.

Another major issue is Peukert factor.  The amphour rating of most RE batteries is a 20 hr rate.   If you are drawing 4100 watts at 48 volts, that is 85.4 amps.  A battery that can put out 85.4 amps for 20 hours is a 82 kwh battery. 

If your typical deficit loads are high wattage but relatively short duration, that may argue for AGM or Lithium batteries.  These types of batteries have low Peukert factor and are suitable for higher current than other batteries of the same energy capacity.

--vtMaps

[RichardB]

It's hydro not solar, so same 1400W coming in 24/7 ... it's more the peak load that is going to be the deciding factor for me.

Then what you need to do is figure out how much your load's peak wattage will exceed your hydro wattage, and for how long, and how often.

example:  you want to draw 5500 watts for 30 minutes.  Your batteries will need to supply 5500 - 1400 = 4100 watts for 30 minutes.  That is 2050 watthours.  (actually more because I am ignoring inefficiencies). 

But what size battery?  That's a really tough question for several reasons.  First we have to know how often these deficits occur... If this deficit occurred just once a day, you could get by just fine with a 6 kwh battery.  If these deficits occur X times per day, your battery will run out of cycle-life X times faster than a typical RE battery subject to daily cycling.   This situation argues for a larger battery.

Another major issue is Peukert factor.  The amphour rating of most RE batteries is a 20 hr rate.   If you are drawing 4100 watts at 48 volts, that is 85.4 amps.  A battery that can put out 85.4 amps for 20 hours is a 82 kwh battery. 

If your typical deficit loads are high wattage but relatively short duration, that may argue for AGM or Lithium batteries.  These types of batteries have low Peukert factor and are suitable for higher current than other batteries of the same energy capacity.

--vtMaps

Cheers.
I'm not doing large scale manufacturing, welding is more of a hobby.
At most I would weld for an hour (during that hour maybe 15-30 minutes would be actual welding). As to how often, once a day would be a lot, once a week more likely.
Most of my other tools are around 2000W max and also used in short bursts, so these should not cause much drain on the system. Only one tool gets used at a time.

[zoneblue]

With hydro the battery is only there to buffer your load profile. In practical terms this (likely) means that it just needs to be big enough to support the inverters surge. The general rule there is for (FLA) 100Ah per kilowatt of inverter. If your inverter is say a 6kW unit, then you need 600Ah at 48V of battery. If you use AGM or LiFePo4 you can use less. For AGM, lets say 400Ah, for lithium at 1C discharge rate, 125Ah. Working backwards, assuming the hydro is running at 1400W, and the welder is drawing 4000W continously, 125Ah lithium bank will drop to 20% SOC in :
- net power = 4000/0.85-1400= 3300W
- net current= 3300W/48V = 69A
- time to LVD= 125Ah/ 69A*0.8= 1.4 hours

1400W is a really decent output, and enviable head you got there.  Thats 33kWh/day enough to power the average amercian home. If a guy cant power a place with that, hes nuts.

Some inverters do accept ac input in such a way as to augment the battery, its called gen support, and the inverters are called hybrid inverters. However the frequency needs to be in really tight bounds, and unless your turbine is sophisticated enough to have the necessary speed governers in it, it will all be not worth the hassle, so id forget it.

Suggest you stay away from AIMS. Stick with name brand UL listed gear, the big 5, Outback, Schneider, Magnum, Victron, SMA. Do it once do it right.

[zoneblue]

One other thing, some people here use the Classic 200 with pelton turbines with no diversion load required. The classic can handle the free spin turbine output. Just a thought. Of course the 200s are less efficient.

[RichardB]

With hydro the battery is only there to buffer your load profile. In practical terms this (likely) means that it just needs to be big enough to support the inverters surge. The general rule there is for (FLA) 100Ah per kilowatt of inverter. If your inverter is say a 6kW unit, then you need 600Ah at 48V of battery. If you use AGM or LiFePo4 you can use less. For AGM, lets say 400Ah, for lithium at 1C discharge rate, 125Ah. Working backwards, assuming the hydro is running at 1400W, and the welder is drawing 4000W continously, 125Ah lithium bank will drop to 20% SOC in :
- net power = 4000/0.85-1400= 3300W
- net current= 3300W/48V = 69A
- time to LVD= 125Ah/ 69A*0.8= 1.4 hours

1400W is a really decent output, and enviable head you got there.  Thats 33kWh/day enough to power the average amercian home. If a guy cant power a place with that, hes nuts.

Some inverters do accept ac input in such a way as to augment the battery, its called gen support, and the inverters are called hybrid inverters. However the frequency needs to be in really tight bounds, and unless your turbine is sophisticated enough to have the necessary speed governers in it, it will all be not worth the hassle, so id forget it.

Suggest you stay away from AIMS. Stick with name brand UL listed gear, the big 5, Outback, Schneider, Magnum, Victron, SMA. Do it once do it right.

Thanks very much, I appreciate the advice.