Frequent Questions: Batteries

How many batteries do I need? 
Batteries come in a variety of types and sizes.  Batteries are like gas tanks, in that some are bigger than others.  A better question would be “How many Amp hours of capacity do I need?”  

When dealing with lead-acid batteries you will want between 0.5 and 1.0 Amp hours for every 1.0 watts of solar panels.  If you have too much battery capacity your batteries may not be able to reach a full charge frequently enough to prevent sulfation.  Additionally, battery charging inefficiency will eat up an increasing amount of solar production as you add to your battery bank.  But, if your battery bank is too small, you will reach a full charge early in the day while there is still plenty of sunlight.  Solar panels connected to a fully charged battery bank cannot produce power and therefor become expensive roof decorations.

With lithium batteries you don’t need to worry about full charging or inefficiencies.  Get as much lithium battery capacity as you can afford as long as you have enough to store a full day’s solar production.

What is better, 6V or 12V batteries? 
If you are comparing similar battery types, from a chemistry perspective, there is no difference between 6V batteries and 12V batteries.  The only difference is that 12V batteries have twice as many of the same type of cells as 6V batteries.  In other words, aside from smaller plates, a 12V battery is just two 6V batteries in the same enclosure.  People choose one type over another based on space constraints and costs.  Two 100Ah 6V batteries connected in series will have the same electrical characteristics as a single 100Ah 12 battery.

Are lithium batteries worth the upfront cost? 
Many customers that factor in the longer lifespan and improved performance of lithium batteries conclude that in the long term they are cheaper than AGM batteries.  You can learn more about the advantages of lithium batteries on our Batteries page. 

What should I do to keep my AGM batteries healthy? 
The challenge with AGM batteries is managing the build-up of sulfate on the internal plates.  This accumulation of sulfate on the plates is a natural side effect of the battery discharging, but getting that sulfate off the plates and back into the electrolyte solution is an often-overlooked aspect of battery management.  If the sulfate isn’t regularly removed from the plates it will harden and reduce the conductive area of the plates, which will reduce the capacity of the battery.  

In order to remove the sulfate, the battery has to be fully charged.  But, if the battery is over charged the electrolyte will boil off.  A careful balance has to be maintained in order to get the most useful life out of your battery bank.  A well-tuned charge controller system can automatically regulate the charging cycle of your batteries.  

All systems installed by AM Solar are tuned specifically to optimize your battery bank.

To learn more about battery management check out our Batteries page.

How long will my batteries last? 
Batteries have varying lifespans depending on how they are used.  AGM batteries may last up to three years.  Lithium batteries are warrantied out to five years but can last longer than ten years.

What does Bulk, Absorption, Acceptance, Float & Equalize mean? 
These are all terms pertaining to the various stages of lead-acid battery charging.  

Bulk:  This is the stage where the battery gets about 80% of charge and where it can handle the highest current and voltage.

Absorption (also known as Acceptance):  This stage can be described with an analogy of pouring beer into a glass.  After the main pour (bulk stage) you have a lot of bubbles in the top part of the glass and you have to slow down the pour rate to keep from overflowing the glass.  The absorption stage is essentially a slower charge than the bulk stage.

Float:  The float stage is a very slow charge rate and how batteries are maintained long term when they are full.  Back to the beer analogy, the float stage would be like slowly replacing beer that evaporates as a glass sits full for a long time.

Equalize:  A battery is composed of cells that may not always be at the same charge level.  An equalization stage is a brief overcharge that brings all the cells to full (equal charge) to remove the accumulated sulfate on the battery plates.  In terms of beer, it would be like having several closely spaced shot glasses with a pitcher pouring beer all over them and only stopping when the last shot glass is full.  Some shot glasses will fill quickly and overflow, but in the end they will all be equally full.

To learn more about battery management check out our Batteries page.

How should I dispose of old batteries? 
Lead-acid batteries have lead cores that need to be recycled after they are spent. Most battery shops will accept lead cores, and some will even charge an extra fee if you purchase a battery without returning a spent core. Also, check with your local recycling centers to see which centers are willing to receive spent cores.

When lithium batteries have reached the end of their lifespans, they will also need to be recycled. We’re not quite sure what that will look like 10 years down the road, but we know lithium technology today should not be disposed of in the landfill.  Check with your local reclamation centers for additional information.

Frequent Questions: Inverters

What size inverter should I get? 
Inverter capacity is measured in Watts which should be higher than the total watts of all the devices that you plan on running simultaneously.  For example, if you have a 1500 watt microwave oven, a 300 watt refrigerator and maybe another 200 watts of lights, cell phone charging and misc., you will need at least 2000 watts of inverter capacity.  If you only have a 2000 watt inverter and you try to run all of that equipment plus a 1000 watt blender it will overload your system and your inverter will turn off.  

The size of an inverter system has nothing to do with how many solar panels you have or how much battery capacity you have, it is only relevant to the size of your AC loads.

Learn more about inverters on our Inverter page.

What is the difference between pure and modified sine? 
A pure sine inverter is universal and works with all AC appliances.  A modified sine inverter is usually less expensive and does not work well on devices with moving parts.  The output of a pure sine inverter is smooth and constantly changing as its output goes from negative to positive.

Learn more about different wave forms on our DC, AC, Pure Sine page.

What kind of efficiency would I get on an inverter? 
A typical inverter used in RV applications would have an efficiency of around 90%.  In mathematical terms, this means Voltage out x Current out x 0.9 = Voltage in x Current in, or if an inverter is driving a 2000W load, you would see 120V x 17A x 0.9 = 13V x 141A.

In addition to power conversion inefficiency there is also an idle wattage consumption of around 7 watts, just for having your inverter turned on.  A consumption of 7 watts over a 24 hour period works out to 168 watt hours, which is about half the daily production of a single 100 watt solar panel.

What extra features might I want on my inverter? 
Many inverters will have an option for a built-in DC charger for your 12V system when you are plugged into shore power or running from your onboard generator. Other inverters may have an option for a pass-through AC function that enables shore power (or generator) to bypass the inverter when you’re “plugged in.” Some inverters may even have both of the options described above. Of course, the price point changes with the addition of these options.

Is my inverter a good match for my panels? 
A better question would be “Is my inverter capable of supporting my load?”.  The solar panels and charge controller determine how quickly the battery bank charges.  The inverter determines how quickly power can be drawn off the battery bank and converted to Alternating Current.  The two systems don’t have any contact or influence over each other.

What happens to the onboard converter/charger when I install an inverter/charger combination? 
In our shop, we typically disconnect the onboard converter/charger from the circuit breaker in the AC distribution panel. We do this in order to prevent a feedback loop between the two chargers. Most often, we leave the onboard converter/charger in place, as a backup, in case the inverter/charger fails. For this contingency, you may want to leave the wiring intact, but label the circuit breaker to remain OFF at all times.