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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1. Solar Batteries
2. Electric Solar System – Calculating the Power
3. Solar Inverter

Most of 12 volt-rated electric solar panels produce 16 – 20 VDC. The average voltage needed by solar batteries to get fully charged is around 14V so without proper regulation the batteries will be damaged from overcharging.

You may also find solar batteries with 24 volt or other voltage rating; therefore it is important that the charge controller match the battery’s voltage.
When the batteries are fully charged the controllers – also known as regulator – will stop the batteries from getting further charged. A charge controller that has a low voltage disconnect (LVD) facility will also disconnect any load connected to the DC load terminal when a certain low voltage is detected to prevent the battery from draining down too far.

The quality of the charge controller may affect your battery’s lifespan. There are generally three types of solar charge controller:

- Simple controllers (1 – 2 stage controllers). This type controls the voltage in one or two steps by means of shunt transistors or relays. Basically they just short or disconnect the electric solar panels once a certain voltage is reached. Because they don’t have many components they are not easy to fail. This type is considered old but you may see some of them still running.

- 3-stage or PWM (Pulse Width Modulation) controllers. Unlike the simple controller that gives a steady output to the batteries, the PWM controller delivers a series of short charging pulses to the solar batteries. These charging pulses work as a very-rapid on and off switch. When the batteries are fully charged without load the controller will send its short pulse every few seconds but when they are discharged the controller will deliver very long pulse almost continuously or even work in fully “ON” mode. The PWM controller determines how long the pulse shall be and how fast it should send it by constantly checking the batteries charge status between pulses and do the self-adjustment when necessary. Due to these pulses the PWM controllers can easily emit noises that affect your TV, radio or other electronic devices.

- MPPT (Maximum Power Point Tracking). This type of controller is the most expensive one and can give up to 98% efficiency and can deliver up to 30% extra power to the solar batteries. When a solar panel is connected to a battery, the battery will limit the voltage output of the solar panel. Based on this condition you normally see two voltages listed on the back of your solar panel: The open circuit voltage, which is the panel’s voltage output in a full sun and the panel operating voltage which is the voltage of the panel after being connected to the solar battery. Panel operating voltage is lower than open circuit voltage. The reason why MPPT can boost the power up to 30% is because it can ‘fool’ the panels by eliminating their view of the batteries in the system so the panels will not drop the voltage output to the panel operating voltage.

the Solar Cost Admin

Related posts:

1. Solar Inverter
2. Solar Batteries
3. Solar Kits

There are three types of solar inverter available:

- On-grid or grid-tie inverter, used to complement the utility grid with solar panels electricity. To allow the solar power integration into the grid power this grid-tie inverter should produce AC electricity that matched phase with the grid power sine-wave. For safety reasons during utility power outages the inverter should shut down automatically. If you experience loss of utility supply often and want to back it up with solar power generator this type of inverter will not help you. The main reason why people use this inverter is because they prefer not to purchase the solar batteries and instead they use the utility grid to bank the excess electricity generated by the home solar panels. They don’t mind having no backup power during utility outages. If utility supply doesn’t trouble you much in your area then you may consider this option because this system is less expensive than the others.

- Battery backup solar inverters. These inverters are also connected to the utility grid, similar with the grid-tie inverters, but they are designed to draw the electricity from a battery and control the battery charging by means of a solar charge controller and send the excess electricity to the power grid. Because this system store the solar electricity in the battery, the solar inverter can draw DC electricity from the battery bank and still produce the AC power during power outages. To fully comply with the safety regulation these inverters are required to have anti-islanding protection. Without this protection during a power blackout the utility workers may experience a hidden electrical shock hazard because they don’t know that the solar power generator is still injecting power to the grid.

- Stand-alone or off-grid inverters. These inverters are used in remote or isolated areas with no power lines available. The solar inverter will draw the DC electricity from the batteries charged by the electric solar panels and/or other sources such as fossil fueled generators, wind turbines or hydro turbines. Some of these inverters are also equipped with integral battery chargers to replenish them from the AC power when available. Because these inverters are not necessarily connected to the utility grid they don’t have to be equipped with the anti-islanding protection.

Depending on its type, the lifespan of a solar inverter may vary from 5 years to 15 years. Consult with the solar company you are dealing with in case you are in doubt. While home solar system are said to have a long lifespan people sometimes forget that the only one part of the solar kits that may reach 20 more years lifespan is the photovoltaic panels.

the Solar Cost Admin

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Three types Solar Batteries

A.    Flooded (Wet) Lead-Acid Batteries

Lead-Acid batteries are the cheapest type available. They also have longest lifespan compared to the other types; if the battery maintenance is properly done it can serve your system up to ten years.  Despite of the benefits lead-acid batteries also have their drawback:

-    Routine maintenance is needed, including adding water, cleaning the terminals and battery top, voltage monitoring and equalization charging.

-    When overcharged heavily lead-acid batteries will release hydrogen. Due to this issue you should keep them in place that has good air circulation / ventilation.

Can we use automobiles batteries to store the current? The answer is NO. Batteries used in automobiles are of the shallow cycle batteries. They can only discharge a large amount of current in a short period (i.e. during engine start up) but they can take mild overcharge without loss of electrolyte problem. This type of batteries is designed to discharge current at maximum rate of 20% only. Repeated discharging the battery for more than the maximum limit above will shorten its life.

Solar batteries should stand repeated discharge current up to 80% of the total battery capacity. They are categorized as deep cycle batteries. Although they can be discharged up to the maximum limit above, please note that discharging them at shallower cycle will prolong the lifespan of the batteries.

B.    Sealed Deep-Cycle Lead-Acid Batteries

These batteries – aka AGM batteries – are more expensive than the flooded lead-acid batteries because they are maintenance free and need no equalization charge. They are very ideal for unattended solar generators. The drawback of this type is shorter lifespan compared to the wet lead-acid batteries and extra cost.

C.    Sealed Gel Cell Batteries

Sealed gel cell batteries use gelled electrolyte that has high viscosity. Although they are relatively maintenance free they can’t be charged exceeding the voltage charging limit. One time overcharging the battery for a long period is enough to reduce its life or even kill it forever. Pick a solar charge controller that can be adjusted to prevent overcharging the solar batteries beyond their safe limit.

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2. Solar Charge Controller
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