The Power of Inverters

Should you decide to use your Solar Array to power your electronics and appliances, you are going to need an inverter.  An inverter simply takes the DC (Direct Current) power produced by your solar panels or battery bank and inverts it into AC (Alternating Current) power.  While this seems easy enough, there are items you need to be aware of when selecting an inverter.  Here is a short list for you:

1)      Inverters come in different output types.

The two most common types of inverters are Pure Sine Wave and Modified Sine Wave.  Pure Sine Wave inverters best emulate your existing Utility Grid.  In most cases, the power from a Pure Sine Wave inverter is cleaner than the Grid.  This type of inverter is best suited when sensitive electronics are going to be used.  A Modified Sine Wave Inverter does not produce as clean of power as a Pure Sine Wave inverter.  However, a Modified Sine Wave can be more economical when power is your sole focus.

2)      Inverters are rated by Power Output

You need to select an inverter with at least the same output wattage as your maximum wattage needs.  The inverter Wattage Output is the maximum power you can get from that inverter.  For example, a 2000W inverter will output up to 2,000 watts worth of power continuously.  If you need more power than the output wattage rating, you need to choose a bigger inverter.

3)      Input DC Voltage

 The Input DC Voltage of the inverter must match the output voltage of your battery bank.  If this is not the case, the inverter will never run properly and cause damage to the inverter or the battery bank.  If your battery bank is 24 volts DC, than your inverter must have a 24 volt DC input rating.

4)      Inverter verses Inverter/Charger

Even though your goal is to solely charge the battery bank using your solar array, you may need an inverter/charger.  This type of inverter will allow you to utilize Grid power to charge your battery bank when the solar array isn’t producing energy.

Planning your project will allow you to choose the right products to meet your needs.  

Fully Charge your Batteries for Max Life

As you may have noticed, several of our articles state to always fully recharge your batteries.  In this article, we are going to explain why this process is critical to battery maintenance.   

During normal discharging, soft lead sulfate crystals form on the lead plates inside a lead-acid battery.  As the battery is recharged, these soft lead sulfate crystals are removed from the lead plates.  If a battery is left in a discharged condition or simply being undercharged, the soft lead sulfate crystallizes into hard lead sulfate.  Unfortunately, hard lead sulfate cannot be removed during recharging.  Thus, the surface area of the lead plates becomes reduced.

The storage capacity of a battery is based on the available surface area of the lead plates.  As that surface area reduces, so does the storage capacity.  Eventually, the surface area can become so reduced, that a battery will no longer accept a charge, rendering it lifeless.

Failing to fully recharge a lead acid battery is estimated to cause approximately 85% of deep cycle lead-acid battery failures.  When it comes to battery maintenance, this is a priority.

As always, take care of your off-grid array and it will serve you well for years.

The Power of Batteries

When it comes to batteries, a common problem is a misunderstanding of the actual power available from the battery.  Unfortunately, clever marketing can perpetuate misleading information.  Before you invest in an off grid array let’s take a minute to discuss the real power of batteries.

All batteries are generally rated by their maximum capacity.  For example, a battery with a voltage of 12 and an ampere-hour (Ah) rating of 100 will be listed as having 1.2kWh (kilowatt-hours) worth of capacity.  This is the accepted practice to standardize the way in which batteries are rated.  However, this rating doesn’t mean that this is the capacity available for use.

Depending on the battery type we choose, our battery will not be able to produce its maximum rated capacity.  Let’s use a lead-acid battery for off-grid solar as an example.  Remember from our earlier article, “Top 5 Battery Mistakes” we do not want to go below 50% depth of discharge. We do this in order to insure our batteries last as long as possible. Therefore, using our battery example above, using a 50% depth of discharge we have roughly 600Wh (watt-hours) worth of capacity available for use.

Here is where most off-grid designs fall short.  Even though we aren’t overtaxing the batteries on paper, we have left out a very important detail.  That detail is how we plan on consuming the power from the battery.  It is true that our battery from above has a rated capacity of 1.2kWh.  But, what we must realize is that the rating is based on a C/20 rate or 20 hour charge rate.  In simple terms, this means that we have 1.2kWh if we consume that capacity over the course of 20 hours. That gives us roughly 60Wh worth of power each hour for 20 hours.

This nuance of batteries generally catches people off guard.  If we consume more than 60Wh each hour, the available capacity of the battery reduces.  We have to remember that batteries use chemical reactions to produce and store energy.  When we speed up the chemical process, we reduce the efficiency of the reactions.  This means our battery’s true capacity will be reduced during higher power draws.  If we consume our power over the course of 10 hours, the battery capacity will reduce down to around 90% of its rated capacity.  In our case, our 1.2kWh battery is now a 1.1kWh battery.

The biggest change we will see in a battery’s capacity is when we consume the bulk of our power in a single hour.  When a battery is required to give the bulk of its energy stores in one hour, its capacity will reduce to around 60% of its stated rating.  This is a significant change in the battery’s capacity.  The same 1.2kWh battery from above is now an 864Wh battery.  Remember, we still do not want to consume more than 50% of the available battery capacity.  Therefore, we have now effectively dropped our consumable power from 600Wh down to 432Wh.

By better understanding how batteries capacity is affected by our energy consumption, we can prolong the life of the battery.  Most early battery failures are the result of over-discharge.  Take care of your batteries and they will reward you with long lasting life.