Converting from AC generator to DC storage or better ideas welcome

4 Posts

Jul 8, 2007 02:06 pm

I own an off-grid resort and working ranch in Costa Rica. Currently we generate all our power using a 3 X 24amp old AEG generator hooked up to a water turbine but our water only allows us to generate what I estimate to be about 6-10KMH based on which nozzle we use. Because of power fluctuations due to demand and the need for additional and stable power output, I am considering adding an array of PV panels, exchanging the generator for a large alternator, adding battery banks and an inverter to continue to use AC power through out. Since my installation so far has been pretty simple and I'm a real novice, I've been able do handle it. Now I need major advice as to whether I'm doing the right thing or if there are other approaches that make more sense. The distances are also an issue since the complex were we are using the power at is about 10 acres of a 400+ acre ranch. Specific questions: what is the maximum distance I could have between my PV cells and hydro system (battery bank distance?), how do I measure exactly what I'm currently generating in KWH, how do I estimate the effectiveness of PV panels in an area were there are no maps (middle of the rainforest), is there a way to make my hydro system more effective without going to the PV system. More water, head or larger nozzle is not an option at this time. I am using a 14 inch pipe with 80 feet of fall at a 45 degree angle and reduced to a nozzle of 2 inches. When water levels drop me reduce the nozzle to 1.5 inches to keep the tube full. For further info check out www.ranchomargot.org. Thanks in advance

Ken Hall

351 Posts

Jul 8, 2007 07:11 pm

Re: Converting from AC generator to DC storage or better ideas welcome

"using a 3 X 24amp old AEG generator hooked up to a water turbine"

What do you mean with 3 X 24 amp Generator ? Is that a 3 phase generator with 24 amps per phase ? (What is your generation voltage and how many rpm ?)

If so, how are you keeping the phases balanced, load wise? Part of your problem could be having the majority of the demand on a single phase, at any given time. The generator probably will not produce 24 amps on one phase with minimum draws on the other two.

Running some rough numbers for 80 feet of head and about 120 feet of 14 inch pipe, I get about 750 gpm with the 2 inch nozzle and about 6100 watts. With the 1.5 nozzle, that drops to about 400gpm and 3200watts.

A new single phase alternator would solve the imbalanced 3-phase problem, but you will still be limited to what you can generate with a 2 inch nozzle, or about 6100 watts.

My guess is that your system was originally designed for a larger use. Something on the order of a 3.4 inch nozzle at about 2000 gpm.

Anyway, 3.2kw would give you up to 76.8kWh a day if everything was constant. My guess is that your system runs at a constant water flow, and then the excitation is varied to produce the power required. If that is the case, you may have a lot of un-used generation during periods of low demand. So adding batteries and an inverter could store this unused power, for periods that it is needed, with or without PV.

As far as measuring your generation, a power monitor would do it. Or, a watt hour meter like the one on a house. You might need three, if they are single phase and you are generating 3-phase.

Juan Sostheim

4 Posts

Jul 8, 2007 08:11 pm

Re: Converting from AC generator to DC storage or better ideas welcome

Thanks for your reply Ken. You are right about the generator being three phase and most of our equipment is single phase. We do however attempt to balance the phases and often have an unbalanced load. The generator is designed for larger water flows and at optimum it probably would generate 24 KWH. The generator is designed to run at about 1600-1800 rpm and we are well within the range with 0 load. Our output is between 100 and 130 volts. Do you think an alternator generating DC would have advantages going straight to the battery banks? Can the excess electricity be stored by converting AC to DC or is it more effective to do the opposite? Running straight from the battery banks would certainly have the effect of stabilizing the current and avoid the phase balancing act. We are using current regulators to keep some of our equipment from getting overloads but when a heavy piece of equipment starts up it is lowered to unacceptable levels.

Juan Sostheim

4 Posts

Jul 9, 2007 09:48 am

Re: Converting from AC generator to DC storage or better ideas welcome

If I can get 90 feet of head at a 45 degree angle or 150ft of 14 inch pipe with a nozzle of 2 1/8 inch, what would I be able to generate and what about same head with 1.5 inch nozzle. Ken if you could provide me the formula I'd very much appreciate it.

Ken Hall

351 Posts

Jul 10, 2007 02:14 am

Re: Converting from AC generator to DC storage or better ideas welcome

Juan:
AC generation is far superior to DC for your system. You can convert AC to DC with a battery charger if you do go with battery banks.

I don’t think that you want to try to put your entire system through a battery. The cost of batteries, inverters, etc would probably be prohibitive.

A simple formula for calculating power is liters per second X head in meters X 9.81 X system efficiency. Using the 750 gpm (47.32 L/sec) and 80 feet of head ( 24.38m) the formula would be 47.32*24.38*9.81*0.54= 6111.407 watts
If you increase the head 10 feet it becomes 47.32*27.43*9.81*0.54= 6875.96 watts
So, you would pick up about 765 watts simply by increasing the head 10 feet.

If you increase the nozzle size to 2.125 inches at the 90 foot level, it will increase your water flow to about 840 gpm (about 90gpm more than you are currently using). The formula then becomes 53*27.43*9.81*0.54= 7701.307. So you pick up about 825 watts from the increased nozzle size/flow.

By the way, what is the diameter of your wheel ? And what size breakers do you have on the phases ?

Before making any dramatic or costly changes to your system, I would take a look at time shifting some of the loads to time periods where more generation is available. And Energy conservation where possible. Also, you mentioned some large equipment hammering your system. Is that equipment automatic, or is someone operating it. What about your water system, are there any large pumping loads or water heating loads ? If so, are they falling during the overloaded periods ?

Ken
PS The calculated numbers are based on balanced phases. With the imbalance you are experiancing, your net gain could be 1/3 of the numbers shown.

« Last Edit: Jul 10, 2007 01:22 pm by ken hall »

Juan Sostheim

4 Posts

Jul 14, 2007 05:46 pm

Re: Converting from AC generator to DC storage or better ideas welcome

Ken, as always, thank you. The wheel has a diameter of 70 cm. We go from the generator with 3 phases + neutral to a distribution box with a 3 way switch to switch between hydro and diesel generator (61 KWH Fiat). I estimate my daily consumption when fully operational at 300-350 KWH. I could add a battery bank and charge the batteries 3-4 hours/day while we use heavy loads, or use solar panels. I don't like running diesel even if it's biodiesel. Our consumption is almost all refrigiration, power tools by day, lighting by night. No thrills. From the distribution box we go to 8 different panels with the closest being 80 meters and the farthest 400 meters away from the generators. We use 100AMP circuit breakers at each panel. At night we have 250, 13 watt bulbs turned on and what will amount to 5 walk in coolers and one walk n freezer. Some small appliances, Coffee maker 1.8KW, computers, musikbox, etc. Any ideas, do's and don'ts there all welcome at this point. My concern with the current system is that we don't store the overproduction to help in peak periods and that the power is unstable when heavier loads start up. I need a steady 110-120V or I blow chargers and compressors. It needs to work perfectly! Any thoughts?
Juan

My electrician says we have one phase at 15amp, another at 13amp and the third phase at 6 amp.

« Last Edit: Jul 14, 2007 05:50 pm by Juan Sostheim »

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