Batteries Storing Renewable Energy “Chemical engines used to push electrons around”

Basic Terms Voltage – Electronic pressure Current – Flow of electrons Power – Amount of energy being generated

How it Works Cells Contain –Electrochemical Couples Two materials which react chemically to release free electrons –Electrolyte Transfers the electron between electrochemical couples Sometimes electrolyte participates in reaction (lead-acid) sometimes not (nickel -cadmium, nickel Iron)

How it Works Polarity – One part of couple is electron rich and other is electron deficient While discharging electrons flow from the electron rich negative cathode pole to the electron deficient positive anode pole While recharging process is reversed

Lets Look at the Atom Chemical bonding is the sharing or exchange of electrons Sodium and Chlorine are chemical elements When combined they become something different – salt Chemicals made during the discharge process are broken by the charging process

Battery Capacity Measured in ampere-hours (amp-hours) at a given voltage Depends on two factors: –How much energy is needed and –How long the energy is needed Example 350 amp-hour battery can provide: 35 amps for 10 hours or 100 amps for 3.5 hours

Important!!! A battery based alternative energy system will not be effective if it is not sized correctly

Life Expectancy and cost At least 5 years Often over 10 years or 1500 deep cycles Shipping is expensive

State Of Charge Percentage which represents the amount of energy remaining in the battery A battery is “deep cycled” when it reaches 20% or less state of charge A shallow cycle (car battery) will withdraw less than 10% State of discharge is opposite so a battery is “deep cycled” if it is at discharged to 80%

Rest Voltage vs. State of Charge

Temperature Batteries get sluggish at cold temperatures Usable capacity drops radically below 40° F Self Discharge happens rapidly above 120° F Keep them between 55° F 100° F

Hydrometer Measures density of liquid with respect to water The electrolyte has greater specific gravity at greater states of charge So voltage can be an indicator Careful opening cells, contamination of the electrolyte solution is possible

Rates of Charge and Discharge 50 amp load for a 100 amp battery is large But for 2000 amp battery – no problem So we combine current pulled (or added) with capacity to get a rating scheme –If it take 10 hours to fill a completely drained battery then – C/10 charge rate –If it takes 5 hours to drain a battery then C/5 discharge rate

Rates of Charge and Discharge Recommended rates are C/10 – C/20 Using a C/5 rate will cause much more electrical energy to be loss as heat This heat can damage battery plates Example – –440 Ampere-hour battery –How many amps added for a C/10 –How many amps added for a C/20

Equalizing Charge After time individual cells vary in their state of charge If difference is greater than.05 volts – equalize Controlled overcharge at C/20 rate for 7 hours Turn off voltage sensitive gear before equalizing

Self Discharge Temperature greater than 120° F results in total discharge in 4 weeks At room temperature loss is 6% and will discharge in 16 weeks Storage Fully charged 35 ° F - 40 ° F

Capacity vs. Age If a battery is supposed to be good for 5 years – This means it will hold 80% of its original capacity after 5 years of proper use

Battery Care Don’t discharge beyond 80% C/10 – C/20 rate Always fill up when recharging Keep batteries at room temperature Use distilled water Size batteries properly Equalize every 5 months or 5 charges Keep batteries and connections clean

Connecting Cells Power in battery can be increased by arranging the cells in two ways –Series One path for electrons to follow Connect + to –’ Increases voltage –Parallel Multiple paths for electrons to follow Connect (+ to +) and (- to -) Increases amperage

Series Each cell in lead acid battery is 2.1 volts Nickel-Cadmium is 1.25 volts Flashlight batteries are 1.5 volts each A lead acid battery is typically 6 volts –This is 3 – 2.1 volts cells wired in series

Parallel Increases Capacity Trojan L-16 are 350 amps and 6 volts Wire them in parallel and you will get 700 amps Wire two of these “700 amp batteries” in series and you get one 12 volt, 700 amp battery

One Trojan L-16

Where to connect?.

Right

Where to connect?...

Right

How to connect?.....

Right

Wire Sizing for DC Applications Voltage drop is caused by a conductors electrical resistance This voltage drop can be used to calculate power loss

VDI Voltage drop Index Easier method for determining wire size What you need to know –Amps (Watts/volts) –Feet (one-way distance) –Acceptable % volt drop –Voltage

How to Use Formula and Chart Example: 1 KW, 24 volt system, 60 feet, 3% drop Amps = 1000 watts/ 24 volts = amps VDI = amps * 50 feet = % * 24 volts

VDI Chart 2 AWG wire That’s pretty big wire What if we make it a 48 volt system?

How to Use Formula and Chart Example: 1 KW, 48 volt system, 60 feet, 3% drop Amps = 1000 watts/ 48 volts = 20.8 amps VDI = 20.8 amps * 50 feet = % * 48 volts

VDI Chart 8 AWG wire That’s better

Practical Considerations Lighting Circuits –10% drop in incandescent leads to 25% drop in light output –10% drop in fluorescents results in 10% loss in light output –Suggested acceptable loss 2-3%

Practical Considerations DC Motors –Operate at 10-15% more efficiently –Minimal surge demands –Some motors will fail to start if drop is too great (Sun Frost)

AC Motors Exhibit high surges when starting

PV Battery Charging Circuits Need to be higher than battery voltage so they are wired to be around 16 volts A voltage drop of 1 or 2 volts is significant A 10% drop will result in 50% loss of power in some cases 2-3% loss is recommended