SBM Solar Panel are rated differently based on power
-258W=30.6V ; 150W/140W = 18V; 130W=17V
-Charging Current for Battery = (1/10)*Ah level
-Need to find Voltage output from solar panel
(http://www.circuitstoday.com/lead-acid-battery-charger)
http://www.electronics-lab.com/blog/?p=6232
(8Amps )
 Lead acid Classification
o SLI Batteries
 Up to 2 yrs useful service in small stand alone PV systems
 Maximum allowable depth of discharge is limited to 40-60%
 Not designed for long life deep cycle service
o Motive Power or Traction Battery
 Designed for deep discharge cycle service
 Very durable
 Used in PV systems for deep cycle, long life, durability
o Stationary
 Designed for Backup power to un-interruptible supplies
 Occasional use, limited cycle service
 Types of Lead Acid (commonly used in PV systems)
o Lead-Antimony
 Advantages
 Greater mechanical strength, great deep discharge, high discharge rate
 Limit shedding of active amterial, better lifetime than lead-calcium (at
high temps)
 Disadvantages
 High self-discharge
 Frequent water addition(maintenance?) due to necessary overcharge
 Good for PV case deep cycle and ability to take abuse,
 Water additions can be minimized
o Lead-Calcium
 Advantages
 Greater mechanical strength, low self-discharge, reduced gasing (lower
water loss/maintenance)
 Disadvantages

Poor charge acceptance after deep discharges, shortened batter life for
high temps and high depth of discharge
 Flooded Lead-Calcium, Open Vent Not good
 Flooded Lead-Calcium, Sealed Vent
 -120 ampere-hrs in 12V unit
 Intolerant of overcharging, high operating temps, deep discharge
 “Maintenance free” but limits useful life
 Must be carefully charged to achieve maxium performance and life
 Will probably have short life in most PV systems
o Lead-Antimony/Lead Calcium Hybrid
 Capacity of over 200 amper/hrs
 Deep cycle, low water loss, long life
 Stratification and sulfation will be problem
 Used in PV systems with larger capacity and deep cycle req (Exide Solar Battery
Line)
o Capactive-Electrolyte Lead-Acid Battery (VLRA)
 Intolerant of excessive overcharge!!
 Populer for PV because of spill proof, easily transported, low maintenance
 Sensitive to overcharge in high climates
 Less susceptible to freezing
 Gelled electrolyte designs (AGM batteries)
 Nickel-Cadmium Battery
o Long life, low maintenance, survivable for excessive discharge, good at low temp,noncritical voltage reg
o High cost and limited availability
o Sintered Plte
 “memory effect” will limit further discharge (loss of capacity)
o Pocket Plate
 Water additions
 Deep discharges, good at extreme temps
 High intial cost but long lifetime
 Definitions
o Ampere Hour: transfer of one ampere over one hour
o Capacity: Ability to store or deliver electrical energy
o Cutoff voltage: lowest voltage battery system can reach
o Cycle: Discharge to given depth followed by full recharge
o Open circuit voltage: voltage when battery is at rest
 Charing/Discharging:
o Allowable DOD (depth of discharge) determines maximum discharge limit (set by low
voltage load disconnect in controller)
o Battery more likely to freeze when discharged
o Autonomy: Time a fully charged battery can supply energy to system with no energy
supplied
o Longer Autonomy leads to lower average daily DOD
o Self discharge rate: open-circuit mode reduction in state of charge (higher at high
temps, almost 0% at low temps)
o
Battery proportional to average state of charge if battery is not
overcharged/overdischarged
o Prolong battery by limiting average daily DOD
 Temp Effects
o High temps: accelerate corrosion
o Low Temps generally increase battery life but will reduce capacity
o Battery should be stores in insulated enclosure
 Important to have charge voltage regulation to prevent overcharge (temp compensated)
 Under and over charging will result in premature battery failure
 Overcurrent and disconnect Req
o Over current can cause explosions/fires
o All PV systems need proper dc rated overcurrent and disconnect protection
o Ampere interrupt rating (AIR) must be taken into account for overcurrent
o Disconnects required for ungrounded systems
 Enclosures
o Enclosures are generally required for safety standards.
o Protect battery from extreme temps
o Some kind of ventilation for battery gasing
 Maintenance
o Flooded lead-antimony battery require most
o Sealed lead-acid battery (gelled or AGM) remain ‘clean’ during operation
 Battery Charge Controllers
o Want to maintain highest state of charge while protecting overcharge and overdischarge
o Controller will: Prevent batter overcharge/discharge, and provide load control functions
o
o
o
Prevent overcharge by interrupting or limiting current flow from array (Voltage reg set
point)
Low voltage regulation for overdischarge protection
O