Deep Cycle Battery vs. Starter Battery
The electricity generated from your home solar panels can be stored either in car batteries or solar batteries. Storing electricity is just a normal charging process and as long as the charger’s DC voltage meets the batteries charging requirement the batteries will be charged without any problems.
If car batteries can be used to store the solar electricity, can we use them to power our solar inverters? Unfortunately no, we can’t use car batteries to feed the inverters. Car batteries are designed to deliver a great amount of current for a short time frame to turn the engine during starting. After the engine turns there will be no more current drained from a car’s battery because the alternator will take over the job and provide the power needed by the car, including charging the battery to top up the current. The car’s battery will never deliver more than 20% of its total capacity to start the engine.
Car batteries have thin and porous lead plates inside to deliver sporadic current spikes to the engine. This plate design however limits the battery ability to be deeply drained. Frequent deep draining will damage the battery permanently.
Deep cycle batteries on the other hand use solid lead plates to enable them to constantly deliver a certain amount of current over a long period of time. Due to this design a deep cycle battery can be deeply drained up to 80% of its total capacity over several cycles, making the battery ideal for home solar system. Solar inverters need a constant supply of current to provide AC power for household appliance.
A deep cycle battery is designed to withstand several hundred of discharge and recharge cycles. This is different from car batteries which can’t be totally discharged.
Although we can discharge 80% of the total capacity of a deep cycle battery, heavy discharging to this limit may shorten the battery’s life. To play safe it is recommended not to drain more than 60% of its total capacity.
Different Behavior in Aging Batteries
Starter batteries can supply high current (CCA or cold cranking amp) through most of their lifespan and suddenly drop quickly towards the end.
Deep cycle batteries will gradually decrease in capacity as they age. While a new battery is designed to deliver 100% of its capacity, this capacity will steadily drop over the period of use. You should monitor this to decide when you need batteries replacement.
the SolarCost admin
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