Inverters vs Generators

Erasmus :  This web page is about portable energy production and portable energy storage.

Kinkajou : The only portable technology that I can think of is the electric generator.

Erasmus : Probably two technologies come easily to mind: Electric generators and inverters. But we will discuss a lot of other fuel cell type technologies as well later.

Kinkajou : These are almost the same thing aren’t they?

Erasmus : I think many people use these terms almost interchangeably, but there is a difference. Generators are old technology. Essentially a fuel source (typically a hydrocarbon fossil fuel such as diesel or petrol or natural gas), powers a motor attached to alternator that produce electricity. The motor runs at a constant speed usually around 3600 rpm, producing typical electrical AC output in the range 120 to 240 V AC at 60 Hz.

Inverters are a relatively new invention. Typically an inverter uses electricity derived from the DC power source such as a car battery or a solar panel. The circuitry in the inverter process the DC power by “inverting” it into AC power.

Inverters are a recent development arising from electronic circuitry advancements in the development of better magnet technology. Typically they output three phase AC current, convert this to DC, and then invert this back to clean single phase AC power at the required voltage (120 to 240 V AC) and frequency (typically 60 Hz).

Kinkajou : But don’t inverters also have a fuel source?

Generator Inverter

Erasmus : Inverter generators generally have more fuel-efficient engines, largely due to their ability to adjust engine speed to the load required. Conventional generators run about 3600 rpm regardless of the load. Their output is constant. Inverter generators have a more limited fuel capacity, but their greater efficiency means they can often run longer and therefore require less fuel storage and less fuel processing technology.

This efficiency translates into most inverter generators being smaller and more lightweight than conventional generators. Conventional generators are heavy but their greater mass does limit their portability substantially. I have a generator myself. However, I built a small wheeled trolley to move it. I’ve also been very careful in lifting the generator into my car, as it is so heavy you do need to protect your back to prevent straining your spinal discs while lifting.

Inverter generators are generally designed to be quiet. For a start by not running constantly at full speed, sound output will be reduced.

 Inverters, on the other hand, can adjust the electrical characteristics of the power produced using microprocessors and special electronics. This means that the engine can throttle back when the load is light, saving fuel and substantially reducing noise.

Our sample generator for this discussion,the Yamaha EF2000iS, for example, produces just 51.5 decibels of sound when running at ¼ load (about the same as human conversation), and only about 60 decibels when running at full load. (An electric razor is rated at 68 decibels!) In contrast, many conventional generators are rated at 65 to 75 decibels – the same range that includes chain saws and jet engines!

Noise Warning Sign

Erasmus :However conventional generators can be built on a huge range of sizes, perhaps up to hundred and 50 kW. Inverter generators due to the electronic design and focus on quietness and portability often have outputs in the 1 kW to 4 kW range.

 
Inverter generators due to their inbuilt electronic processing technology have excellent regulation of their output power, resulting in much more consistent and purer power output (“pure sine waves”), which is independent of the engine speed. This means that many of our daily devices incorporating electronic circuitry are less likely to be damaged by the dirty quality of the electricity arriving at the appliance.

The other advantage lies in that an inverter generator can be paired with another identical unit, using special adapters, to double the output wattage and amperage. Although inverters are much more complex than typical generators, experience to date has not demonstrated any significant reliability issues in comparison with traditional generated designs.

Currently, pricing is a battleground of trade-offs. Larger conventional generators may cost more due to their size, but inverter generators may cost more due to the complexity of the circuitry.

 

 

Parallel Operation

Many inverters, can be paired with another identical unit to double power output (in watts)

Inverters operating in Parallel

Conventional Generators vs. Inverter Generators

The Battery

Kinkajou : So where to from here?

Erasmus : This web page is about portable energy storage and portable energy generation. The key existing technology for portable energy storage is the battery. The key technology for portable energy generation is the fuel cell. These devices, namely battery versus fuel cell, have very different operating parameters.

Erasmus : I think to understand were going we need to understand where we are. Current battery technology is awesome. A patient with an implantable pacemaker has a battery which can last anywhere between 5 to 15 years. Most implantable pacemaker batteries are lithium-based; draw 10–20 microamperes and last 5–10 years. Unfortunately, when the battery begins to fail, the device must be surgically replaced. While this is not difficult because the pacemaker is often implanted just under the skin of the chest wall, a better solution may well involve fuel cells.

Many hearing aid batteries are also primary batteries with a capacity from 70 to 600mAh, good for 5 to 14 days before replacement. This is amazing considering their size.

The rechargeable version offers less capacity for its size and lasts for about 20 hours between charges. The ability to recharge will save money in the long run.

 

Primary batteries are not rechargeable. Primary Batteries

Rechargeable batteries are also known as secondary batteries.

 

 

Kinkajou : Why not just create a battery that can charge itself from externally applied RF or magnetic field frequencies? We probably just haven’t got around to doing yet.

Erasmus :  I think the answer lies in much the same vein as the inverter versus generator battle. In short, Technology is progressing.

There may be other reasons as well.  To recharge the battery, would require rechargeable battery technology i.e. a secondary battery structure. In this application (inside the human body), such an architecture would likely result in increased maintenance requirements. Secondary batteries have lower lifetimes and less stable discharge characteristics.

There are also some concerns about the biological effects of long-term exposure to EMF fields. Lying in bed and charging your pacemaker, may not be a good idea.

Kinkajou : So in the pacemaker application, the question then becomes why a battery versus why a fuel cell?

Erasmus : The current solution for the pacemaker scenario is of course the primary battery. However an organic fuel cell fuelled by glucose, may well be a better long-term solution being more considerate of the needs of the people afflicted by heart conditions requiring pacemakers. Such a fuel cell may well be able to be surgically implanted once, and run for the remainder of the life of the patient.

Kinkajou : So what is driving the interest in fuel cell technology?

Erasmus : The high energy density and energy capacity of the “fuel” used for fuel cells suggests the ability to produce a lot of energy over a long time, far in excess of the limited capacity of the battery. Remember when you do your numbers, metals are heavy, so efficiency per weight characteristics will suffer, just due to structure issues.

Initial fuel cell concepts focused a lot on the use of hydrogen which is a super “clean” fuel. Hydrogen burns with oxygen to create water, hence defining the ultimate green combustion and green fuel process.

Specific environments may well benefit from the use of new tech fuel cells. For example, an organic fuel cell burning glucose derived from the bloodstream just looks much more sustainable and “green” than implanting a “dirty” alkaline battery within the body.

 

 

 

 Kinkajou : So when we are considering batteries, what are the main features we look at?

Erasmus :

• Energy storage: time and capacity
• Power output:
• Environment
• Efficiency
• Charge time versus fuel time
• Operating cost
• Disposal

Erasmus:  Primary batteries such as alkaline cells can hold their charge for up to 10 years with minimal losses. Secondary (rechargeable) batteries are much less stable. Typically these batteries (Lead-, nickel- and lithium-based batteries) would lose a significant portion of their charge within the first month. Rechargeable batteries also typically hold less energy per unit weight.

 

 

Kinkajou :   Power output:

Erasmus :  Batteries in general have a wide power bandwidth. They are able to deliver power as required to a range of devices under a range of load conditions.  Different loads do however result in alterations in the battery lifetime. Typically, batteries last longer if a small constant low current is drained from the battery. For example, when an alkaline camera battery has discharged sufficiently to fail, it is often still capable of running a low load device such as a clock for up to a year.

Fuel cells typically are built to match a specific energy load. They may be either matched to the camera load or the clock load but typically not both.

Batteries are also typically heavy. For example a one hundred kilogram battery may produce approximately 10 kWh of energy where an internal combustion engine (burns fuel, though heavy as well) of the same weight could well generate a hundred kilowatts of power and for an extended time, (so perhaps 1000 kWh of energy).

Another difference between batteries and fuel cells lies in the responsiveness. Batteries are generally able to turn on and function at near full capacity in seconds. Power flows from the battery within a fraction of the second of the battery being turned on. There is no warm-up. A fuel cell may well require minutes to build up enough heat to enable efficient production of electricity for power.

 

 

Kinkajou : Environment

Erasmus : Sealed batteries can operate in any position and are very tolerant of shock and vibration they are clean and cool and have no exhaust. Fuel cells and the internal combustion engine by comparison have more complex operational requirements. The need to feed fuel to the engine means there must be a storage tank of fuel in an appropriate position to drain into the engine. Fuel cells and the internal combustion engine require air for combustion and have an exhaust, with a thermal component. They cannot operate in a sealed compartment in the same fashion as batteries can.

Batteries require relatively less maintenance than fuel cells or the internal combustion engine. Typical battery maintenance requirements are:

• the need to maintain water in lead acid batteries
• the need to prevent excessive discharge via the safety circuit of lithium ion batteries
• the need to properly discharge the nickel cadmium (NiCad)  batteries to prevent “memory” issues

Fuel cells in the internal combustion engine by virtue of their multiple complex components i.e. fuel storage, carburettor, combustion chamber, exhaust and control circuitry are likely to require much more maintenance. This complexity also makes miniaturisation difficult, and you would expect that a fuel cell is larger than a battery for a given power output.

Batteries operate very poorly in cold environments. However fuel cells and the internal combustion engine will warm up with operation. So once started they can rapidly approach optimum operating temperatures. Batteries do not warm-up with operation. Also, if they are maintained at a higher temperature, the performance is increased but at the cost of accelerated ageing of the batteries structure.

Notebook Battery Power

 

Kinkajou :   Efficiency

Erasmus : The battery is highly efficient. Below 70 per cent charge, the charge efficiency is close to 100 per cent and the discharge losses are only a few per cent. In comparison, the energy efficiency of the fuel cell is 20 to 60 per cent, and the efficiency of thermal engines is 25 to 30 per cent. (At optimal air intake speed and temperature, the GE90-115 on the Boeing 777 jetliner is 37 per cent efficient.)

Kinkajou :   Charge time versus fuel time

Erasmus :  Fuel cells in the internal combustion engine by their nature take less than minutes to fuel to a state ready to operate.   Lithium- and nickel-based systems take 1 to 3 hours to charge; lead acid typically takes 14 hours. Battery technology can be adjusted to allow for fast charging. For example some electric vehicle batteries can be charged up to 80% in less than an hour on a fast charge high power outlet.

Battery Recharger

Primary batteries such as alkaline battery cells can maintain their charges for long periods of time. However rechargeable batteries have a much shorter service life and degenerate even when not used. In many consumer products a rechargeable battery life span of 3 to 5 years is adequate. However new applications such as electric vehicles and solar voltaic assemblies require rechargeable storage batteries with significantly longer battery life, hopefully of the order of 8 to 10 years.

The comparable life expectancy of a fuel cell is the expected maintenance free operation time. For a fuel cell this could reach up to 5000 hours of operating life. But this is still a much shorter lifespan than the 5 to 10 years which could be achieved by large stationary storage batteries.

Kinkajou :   Operating cost

Erasmus :  Lithium- and nickel-based batteries are best suited for portable devices. Lead acid batteries are economical for wheeled mobility and stationary applications. Cost and weight make batteries impractical for electric powertrains in larger vehicles. The price of a 1,000-watt battery (1kW) is roughly $1,000 and it has a life span of about 2,500 hours. Adding the replacement cost of $0.40/h and an average of $0.10/kWh for charging, the cost per kWh comes to about $0.50. The IC engine costs less to build per watt and lasts for about 4,000 hours. This brings the cost per 1kWh to about $0.34.

 

Kinkajou : Disposal

Erasmus :  Nickel-cadmium and lead acid batteries contain hazardous material and cannot be disposed of in landfills. Nickel-metal-hydrate and lithium systems are environmentally friendly and can be disposed of with regular household items in small quantities. Authorities recommend that all batteries be recycled. 

Erasmus : Batteries are a very simple and robust technology. They all derived from single basic simple format.

Battery Disposal

 

 

 

Kinkajou : So how are batteries organized / constructed

Erasmus :  Battery Building Blocks

An electrochemical battery consists of a cathode, anode and electrolyte that act as catalyst. When charging, a build-up of electrons forms on the anode, creating a voltage potential between the anode and the cathode. “Release” is by a passing current from the positive cathode through a load and back to the negative anode. On charging, the current flows in the opposite direction.

A battery has two separate pathways; one is the electric circuit through which electrons flow to feed the load, and the other is the path where ions move between the electrodes though the separator that is an insulator for electrons.

 

Erasmus :  Anode and Cathode

The electrode that releases electrons on discharge through oxidation is called the anode. The anode on a battery is always negative and the cathode positive. The chemical reaction and hence the polarity designation could be seen as reversed on charge, but the terminal assignments on a battery never change.
Because the anode is negative, negative charges are created there.
Because the cathode is positive, positive charges are created there.

Anions >>     OH– , SO4 2–, CO3 2–, Cl– , Br– ,I– , NO3 –
Cations  >>    H+ , Ca2+, Cu2+, Fe3+, Fe2+, NH4

Battery Anode Cathode

Erasmus :  Electrolyte and Separator

On a flooded battery system, the electrolyte flows freely between the inserted electrodes. On a sealed system the electrolyte is normally added to the separator in a moist form to promote the movement of ions from the cathode to the anode on charge and in reverse on discharge. Ions are atoms that have lost or gained electrons. Being electrically charged, they pass freely between the electrodes through the separator. To electrons, however, the separator is an isolator that has no electrical conductivity.

 

 

 

 

Kinkajou :   Why is the cathode positive in chemistry but negative in physics?

Erasmus :  In chemistry, a cathode is the electrode where reduction (gain of electrons) takes place. So for it to gain negative electrons, it'll have to be positive. 
In physics, a cathode is a source of electrons (already been reduced) so it'll be classed as negative.

RE: 
Why is the cathode positive in chemistry but negative in physics?

In cathode there is an accumulation of electrons 
In Electrolytic cells it allows the electrons in to the solution 
In Electrochemical cells it receives the electrons. Therefore the sign of cathode is positive (positive will always attracts the negative)

 In an electrochemical cell, cathode is the positive electrode because at cathode reduction occurs (i.e. gain of electrons).Thus the electrons flow from the anode (where oxidation occurs) to cathode due to this, anode is considered as the negative (-ve) electrode (terminal).

In electrochemical cells the cathode is + ve & in electrolytic cell it is -ve. The cathode simply acts as sink of electrons so depending on the type of cell its sign changes. Chemically it’s always reduction that occurs at cathode.

Cathode is actually an electron rich negatively charged end which attracts the positively charged ions or molecules present in the system

Goo: That is something I have never realised my whole life. It is very confusing, but obviously difficult to remember.

 

 

Primary Batteries

Kinkajou : So tell us about Primary Batteries!

Erasmus : Common battery technologies include:

• The carbon zinc battery, (now little used), (one of the cheapest batteries).
• The alkaline battery, (originally known as the alkaline manganese battery)
• Several lithium batteries,
• (One variant technically known as the lithium iron disulphide battery), (this is probably the most common lithium battery type).
• (Another variant being the lithium thionyl chloride battery).
• (Another variant being the lithium manganese dioxide battery).

Alkaline	Cathode (positive)	Anode (negative)	Electrolyte
Material	manganese dioxide	zinc	aqueous alkaline

Figure Composition of primary alkaline battery

All batteries are prone to rupture their seals and cause corrosion. However, the new battery technologies are less prone to leakage than the carbon zinc battery.

Erasmus :  There are many more primary battery types that we have mentioned above. The above list however covers the bulk of battery is used by consumers in the public arena.

Alkaline batteries are able to sustain higher load currents for a longer time delivering more energy than a compatible carbon zinc battery. They also deliver up to 40% more energy than the average lithium ion battery, but are slower to deliver power on starting up.

Lithium iron disulphide batteries are capable of delivering 3 V and higher but have been modified structurally to deliver 1.5 V to make them compatible with the existing AA and AAA battery formats. They have a flatter voltage output curves than alkaline batteries which ensures longer term performance under moderate to heavy load conditions as may be found in the use of a digital camera. They can be stored for up to 15 years at ambient temperatures. Unfortunately lithium is a restricted chemical. Air regulations ban passengers from carrying more than about two lithium cells on flights. These batteries include a safety device which limits the current at high temperatures. Recharging can cause a leak or explosion, hence the only suitable for use as primary batteries.

Lithium thionyl chloride can deliver higher power outputs than the lithium iron disulphide batteries. If used inappropriately that can be hazardous so this type of battery tends to be used in specific applications are not in public consumer devices.


Figures 1 and 2 compare the discharge voltage and internal resistance of Alkaline and Li-FeS2 at a 50mA pulsed load. Of interest is the flat voltage curve and the low internal resistance of Lithium; Alkaline shows a gradual voltage drop and a permanent increase in resistance with use. This shortens the runtime, especially at an elevated load.

Figure 1: Voltage and internal resistance of alkaline on discharge.

The voltage drops rapidly and causes the internal resistance to rise.

Alkaline Battery On Discharge

Figure 2: Voltage and internal resistance of Lithium on discharge.

The voltage curve is flat and the internal resistance stays low.

 

Batteries Under Load Discharge

Erasmus :  The key role of primary batteries is in situations where recharging a battery may be impractical or impossible. Their stability and long life makes them suitable for remote or inaccessible locations. The disadvantage is their intolerance of high load currents. This means they are predominantly more suitable for light loads such as flashlights, use in micro consumer devices such as MP3 players and remote controls as for TV or DVD applications.

They are relatively environmentally friendly when disposed. However it is still a recommendation to attempt to recycle all batteries, rather than simply dispose of them

Kinkajou : In many critical applications primary batteries are replaced prior to each use, to guarantee performance. This can substantially increase the cost of using these types of batteries, as batteries are discarded well before the energy capacity for discharge is reached.

 

Lithium Battery

 

Erasmus : Advantages of Primary Batteries

Figure 1: Specific energy comparison of secondary and primary batteries
Secondary batteries are typically rated at 1C (coulomb); alkaline batteries use much lower discharge currents.

Batteries generally give lower performance than these graphs would indicate. This is because the capacity on consumer grade primary batteries is measured with a very low output current of 25 mA. Higher load currents give substantially reduced life expectancies. In measuring the capacity of a consumer grade battery, a voltage threshold the .8 V is used to define that the battery is discharged. This is substantially below the nominal rated voltage of a battery of 1.5 V.

 
Primary Battery vs Secondary for Discharge

Figure 2 compares the performance of primary and secondary batteries as “Rated” and “Actual.” Lead acid, NiMH and Li-ion are secondary batteries, while alkaline and lithium are primary. Rated refers to the specific energy when discharging at a very low current;

Actual is with a 1C discharging, the way most secondary batteries are rated. The graph clearly shows that the primary alkaline performs well with load requirements for most entertainment devices, while the secondary batteries are more resilient for industrial use. A long-life alkaline (not shown) will provide better results.

 

 

 

Figure 2: Energy comparison under load. ”Rated” refers to a mild discharge; “Actual” is a load at 1C. High internal resistance limits alkaline battery to light loads.

 
Energy Of Battery Under Load

One of the reasons for low performance under load conditions is the high internal resistance of primary alkaline batteries, which causes a voltage collapse under load. This was evident in the previous graph. The internal resistance also continues to rise as the battery depletes.

This makes alkaline batteries impractical for high load applications such as battery power tools. Digital cameras form a borderline case.

 

Table 3: Alkaline specifications. The discharge resembles entertainment devices with low loads.

Table 4 compares carbon-zinc, alkaline, lithium, NiCad, NiMH and nickel-zinc and the AA and AAA cell sizes.

	Carbon-zinc	Alkaline	Lithium (Li-FeS2)	NiCad	NiMH
Capacity  AA                 AAA	400-1,700 ~300	1,800-2,600 800-1,200	2,500-3,400 1,200	600-1,000 300-500	800-2,700 600-1,250
Nominal V	1.50	1.50	1.50	1.20	1.20
Discharge Rate	Very low	Low	Medium	Very high	High
Rechargeable	No	No	No	Yes	Yes
Shelf life	1-2 years	7 years	10-15 years	5 years	5 years

Table 4: Summary of batteries available in AA and AAA format

Note that double a battery cell has roughly double the capacity of the smaller Triple-A battery. Also, there can be a substantial difference between the performances of different branded alkaline batteries. So not all batteries in the same size format such as AA, will deliver the same performance.