Urine powered generators

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tallgirl

Senior Member
Location
Great White North
Occupation
Controls Systems firmware engineer
Amp-hour counting will not keep up with the battery state of charge either.

It's significantly more accurate than watt-hour counting.

The greatest inaccuracies, in my experience, are dealing with absorption and adjusting for self-discharge. When batteries are in absorption, a growing amount of energy is converted to heat. With self-discharge, it just disappears.

With watt-hour counting, charging watt-hours have to be adjusted by voltage elevation from high rates of charge, and discharging watt-hours have to be adjusted by voltage depression. Using amps instead of watts adjusts for both of those scenarios pretty well.
 

tallgirl

Senior Member
Location
Great White North
Occupation
Controls Systems firmware engineer
I take your point but the purpose of a battery is to store energy, energy that is available to do work.
Take electric vehicles for example. The stored energy is converted to mechanical output to propel the vehicle. The Ah does not tell me what that energy is but stored kWh does. And that's the figure that EV manufacturers generally give.

From various sites:

Tesla Roadster - Battery 53 kWh (Lithium-ion battery)
Nissan Leaf - 24 kW?h lithium ion battery

Wiki

I understand that completely, and I often quote my own battery capacity at around 25kWh.

However, the "kWh cycle efficiency" -- kWh Out / kWh In -- is dependent on the charge and discharge rates moreso than the "Ah cycle efficiency" -- Ah Out / Ah In.

The monitoring software my company makes includes the ability to calculate battery voltage at various rates of charge and states of charge.

What you see when you look at the curves is the energy needed for a given change in state of charge INCREASES with the rate of charge. That is, to go from 80 to 90% state of charge requires more energy if you're charging at, say, C/10 than if you're charging at, say, C/20.

If you naively assume the time to go from 80 to 90% is halved at the higher rate (it isn't -- it takes longer than half as long due to a decrease in efficiency and increased thermal losses), the voltage elevation alone means it takes more energy to go from 80 to 90%. Using amp-hours "fixes" the voltage elevation problem, though it does solve the thermal loss problem.
 

bullheimer

Senior Member
Location
WA
using a potato as a battery would make more power than p. lame-o idea if you ask me, with all the animal poop they could gather up and make power with that. otherwise, with all the beer i drink, i could power the universe.:dunce:

one liter of p would probably equate to a nano watt. as was said previously, p on a generator wheel and you will make more power than this 3rd world brainfart. sorry.
 

bullheimer

Senior Member
Location
WA
sorry about that...too late to edit. but speaking of brainfarts, if you could put a tiny windmill on the outside of each ear......:lol:
 

Besoeker

Senior Member
Location
UK
I understand that completely, and I often quote my own battery capacity at around 25kWh.

However, the "kWh cycle efficiency" -- kWh Out / kWh In -- is dependent on the charge and discharge rates moreso than the "Ah cycle efficiency" -- Ah Out / Ah In.

The monitoring software my company makes includes the ability to calculate battery voltage at various rates of charge and states of charge.

What you see when you look at the curves is the energy needed for a given change in state of charge INCREASES with the rate of charge. That is, to go from 80 to 90% state of charge requires more energy if you're charging at, say, C/10 than if you're charging at, say, C/20.

If you naively assume the time to go from 80 to 90% is halved at the higher rate (it isn't -- it takes longer than half as long due to a decrease in efficiency and increased thermal losses), the voltage elevation alone means it takes more energy to go from 80 to 90%. Using amp-hours "fixes" the voltage elevation problem, though it does solve the thermal loss problem.
I quite understand the charge and discharge cycles, rates, temperature dependence etc. We design and manufacture battery chargers and have made systems up to 3,600A so it is reasonably familiar territory for me.
My simple point is that Ah does not give you stored energy.
 

tallgirl

Senior Member
Location
Great White North
Occupation
Controls Systems firmware engineer
I quite understand the charge and discharge cycles, rates, temperature dependence etc. We design and manufacture battery chargers and have made systems up to 3,600A so it is reasonably familiar territory for me.
My simple point is that Ah does not give you stored energy.

Correct, because amp-hours aren't energy.

However, you cannot calculate, a priori, the amount of energy stored in a battery bank. Peukert's will help some, but even Peukert's is measured in terms of ampere rates of discharge and total amp-hours to some voltage under load.
 

tallgirl

Senior Member
Location
Great White North
Occupation
Controls Systems firmware engineer
Indeed that was the simple point I was making.
The energy storage capacity of a battery system is a determining factor in the potential performance/range of EVs.

Nope, that's simply not true either, and I own an EV (and a PV system and a company that monitors PV systems ...) and would be more than happy to explain why that isn't true. Though G-d knows I've tried several times now.

To understand why energy is about as useless as it gets, read this --

http://www.smartgauge.co.uk/peukert_depth.html

You'll notice that "watts" and "watt-hours" don't appear on that page. More significantly, the calculation of the voltage at the battery terminals, which would be required to calculate either watts or watt-hours isn't based solely on amp-hours removed, it is based on the instantaneous state of charge, charge or discharge rate and battery temperature (assuming all other factors, such as battery age and condition, are equal).

That's the heart of the problem -- the inability to know the battery terminal voltage prior to actually charging or discharging. Since watts = volts * amps, not knowing the voltage means you just don't know the watts or watt-hours.
 

kwired

Electron manager
Location
NE Nebraska
If we are talking about "running water" waste systems, it could possibly be more efficient to place turbines in the system and "recover" energy from flowing water to drive generators, and you could still harvest methane or other gases eventually when you get to a treatment plant, and power additional generators.

I doubt the generator shown in the article in the OP is all that effecient of a method of utilizing what gases they have produced. Looks like a portable generator with internal combustion engine designed to run on gasoline.
 

Besoeker

Senior Member
Location
UK
If we are talking about "running water" waste systems, it could possibly be more efficient to place turbines in the system and "recover" energy from flowing water to drive generators,
Probably not. Most, in my experience, are pumped systems. Put a turbine in the flow and the pump has to work harder to make up energy extracted by the turbines - plus losses.

I doubt the generator shown in the article in the OP is all that effecient of a method of utilizing what gases they have produced. Looks like a portable generator with internal combustion engine designed to run on gasoline.
Quite.
 

kwired

Electron manager
Location
NE Nebraska
Probably not. Most, in my experience, are pumped systems. Put a turbine in the flow and the pump has to work harder to make up energy extracted by the turbines - plus losses.

The water supply system is pumped, the waste water system is dependent on gravity (with exceptions at lift stations). If you were to put turbines in this gravity system you are basically recovering energy that was needed to lift the water to its utilization point as it flows through the wastewater system. The equipment and other costs very well may not be worth the return on investment but the energy recovered is essentially free, left over, already paid for, however you want to look at it.
 

Besoeker

Senior Member
Location
UK
Nope, that's simply not true either, and I own an EV (and a PV system and a company that monitors PV systems ...) and would be more than happy to explain why that isn't true. Though G-d knows I've tried several times now.

To understand why energy is about as useless as it gets, read this --
What determines the range of your EV if not available energy?
Joules. Not Ah. The charge/discharge Ah will be the same whether it is one battery or a dozen in series. The stored energy, you must allow, might just be a wee bit different.
I know that charge/discharge rates have a significant bearing on available Ah. And on available energy.

That's the heart of the problem -- the inability to know the battery terminal voltage prior to actually charging or discharging.
You mean you can't actually measure and monitor it? With respect......
One of the usual criteria for determining the point at which a UPS shuts down is battery array terminal voltage.

And, since you mention them, PV array outputs are usually given in W or kW. Not Ah.
As for Peukert's law, boiled down to the basics it says that if you discharge at a higher rate there will be more losses than at a lower rate - self-evident one would have thought. No?
 

mivey

Senior Member
It's significantly more accurate than watt-hour counting.
It is not very accurate except for certain short time operations where the error accumulation is relatively small.

The greatest inaccuracies, in my experience, are dealing with absorption and adjusting for self-discharge. When batteries are in absorption, a growing amount of energy is converted to heat. With self-discharge, it just disappears.

With watt-hour counting, charging watt-hours have to be adjusted by voltage elevation from high rates of charge, and discharging watt-hours have to be adjusted by voltage depression. Using amps instead of watts adjusts for both of those scenarios pretty well.
Adjustments are needed for amp-hour counting as well. You seemed to imply that amp-hour counting is accurate without keeping up with what goes on in the charge-discharge cycle.
tallgirl said:
You'd have to know the entire history of the charge and discharge cycle to know the state of charge if you use watt-hour counting.

It is simply a matter of fact that amp-hour counting alone is only useful for certain short time operations where the error accumulation is relatively small. To be accurate, amp-hour counting must be supplemented with other measurement and book-keeping tasks. These can include stabilized voltage measurements, EMF measurement/determination, table comparisons, or other techniques to re-synch with the battery's real status. Additional adjustments must frequently be made for changes in capacity, self-discharge, charge/discharge efficiencies, memory effects, etc. as well as other battery model parameters that change during the usage and life cycles.

In order to make an accurate book-keeping system, amp-hour counting must be part of an adaptive system.


Battery capacity is the battery?s electrical energy content expressed in ampere-hours.

In battery mangement, key items including charge control, capacity monitoring, run-time status, and charge-cycle counting but the two most important tasks are optimizing the use of the energy in the battery and preventing battery damage.

Monitoring is a sub-set of functions that supports the over-all battery management. State-of-charge indication is just one function used to manage the energy in the battery. Outside of determining delivered/recieved power, amp-hour counting alone is a useless function and one should recognize the underlying purpose is to monitor the battery capacity and prevent battery damage.

The other monitoring functions include state-of-health and remaining run-time. The remaining run-time is an estimate based on loading and is a function of remaining battery capacity (the energy we can expect to get out of the battery).

In addition to current and time, other measurements are used to determine the battery's remaining capacity including voltage, impedance, temperature, etc.
 

mivey

Senior Member
Nope, that's simply not true either
That simply is true. For power loads (like an EV) it is the remaining energy that is important and we use watt-hour calculations. For current loads we use amp-hour calculations.
 

Besoeker

Senior Member
Location
UK
The water supply system is pumped, the waste water system is dependent on gravity (with exceptions at lift stations).
It may be different there but here, waste water from flushing the loo, washing your hands, showering, dish washing, laundry, etc. ends up in the sewerage system. If that just flowed downhill by gravity it would end up in river, lakes, and all in the sea eventually. Raw, untreated. That is not permitted. It goes to sewage treatment works where it is, well ....treated. This involves pumping, aeration and, I suppose, a few other processes.
 

mivey

Senior Member
To understand why energy is about as useless as it gets, read this --

http://www.smartgauge.co.uk/peukert_depth.html
Very nice website with a lot of good info, including:
So, whilst we can praise amp hours counters for certain functions, the simple fact is, they are all but useless for the purpose of monitoring the state of charge of deep cycle batteries. They simply do not do what is required.

as well as a few more:

This is one of the problems with amp hours counters. An amp hours counter would actually calculate that the same load uses more current when the battery is in a lower state of charge. This is, as we have shown above, correct. But it doesn't use more power or energy. And at the end of the day, it is the remaining energy that we are really interested in.

So attempting to show the available charge remaining in a battery purely from amp hours available is bound to fail as the available energy depends upon the battery voltage as well as the charge status.

The result of this is that when relying on an amp hours counter, the same power consumption apparently shows different amounts of power being used depending upon the state of charge of the batteries. Which is obviously ludicrous.

SmartGauge displays the charge status as the remaining energy available in a battery which cures this problem and gives a far more accurate measure than remaining amp hours.
 

kwired

Electron manager
Location
NE Nebraska
It may be different there but here, waste water from flushing the loo, washing your hands, showering, dish washing, laundry, etc. ends up in the sewerage system. If that just flowed downhill by gravity it would end up in river, lakes, and all in the sea eventually. Raw, untreated. That is not permitted. It goes to sewage treatment works where it is, well ....treated. This involves pumping, aeration and, I suppose, a few other processes.

It does simply flow downhill, with occasional exceptions where a lift station is necessary. The lift station is nothing more than a surge tank that is pumped when a predetermined level is reached, but once pumped, the water begins to flow again with gravity being the only force making it move. At some point a treatment location is reached, but until then most movement between user and treatment facility is by gravity.
 

tallgirl

Senior Member
Location
Great White North
Occupation
Controls Systems firmware engineer
Very nice website with a lot of good info, including:
as well as a few more:

Yes, they are correct on a number of points, but please keep in mind that they are trying to sell a product.

And no, they don't actually show the available energy (watt-hours). They show a state of charge based purely on battery terminal voltage and time.
 

tallgirl

Senior Member
Location
Great White North
Occupation
Controls Systems firmware engineer
It is not very accurate except for certain short time operations where the error accumulation is relatively small.

Adjustments are needed for amp-hour counting as well. You seemed to imply that amp-hour counting is accurate without keeping up with what goes on in the charge-discharge cycle.

It is simply a matter of fact that amp-hour counting alone is only useful for certain short time operations where the error accumulation is relatively small. To be accurate, amp-hour counting must be supplemented with other measurement and book-keeping tasks. These can include stabilized voltage measurements, EMF measurement/determination, table comparisons, or other techniques to re-synch with the battery's real status. Additional adjustments must frequently be made for changes in capacity, self-discharge, charge/discharge efficiencies, memory effects, etc. as well as other battery model parameters that change during the usage and life cycles.

In order to make an accurate book-keeping system, amp-hour counting must be part of an adaptive system.


Battery capacity is the battery?s electrical energy content expressed in ampere-hours.

In battery mangement, key items including charge control, capacity monitoring, run-time status, and charge-cycle counting but the two most important tasks are optimizing the use of the energy in the battery and preventing battery damage.

Monitoring is a sub-set of functions that supports the over-all battery management. State-of-charge indication is just one function used to manage the energy in the battery. Outside of determining delivered/recieved power, amp-hour counting alone is a useless function and one should recognize the underlying purpose is to monitor the battery capacity and prevent battery damage.

The other monitoring functions include state-of-health and remaining run-time. The remaining run-time is an estimate based on loading and is a function of remaining battery capacity (the energy we can expect to get out of the battery).

In addition to current and time, other measurements are used to determine the battery's remaining capacity including voltage, impedance, temperature, etc.

So, what you're saying is that watt-hours are more accurate than amp-hours for doing all of those tasks?

Just a "Yes" or "No".
 
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