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Solar Power Storage: Battery Banks & Solar Generators [DIY Mini Course 4/6]

Long lasting off-grid solar power is only made possible by utilizing battery storage.  In an off-grid solar power system, the electricity generated by the solar panels is sent through the charge controller to some form of solar battery bank.  Once the energy is stored in the battery, it can be used to power the inverter and your electronic devices whenever you need it. 

Solar Power Storage: Battery Banks & Solar Generators [DIY Mini Course 3/6]

Standalone solar batteries are available in a wide range of sizes and capabilities.  First time DIYers may have difficulty finding the right solar battery and may even want to explore solar generators as an all-in-one storage and deployment option.  In this lesson, we are going to outline everything you need to know about solar power storage including different types, pros and cons of each, how to size a battery bank and more!

Types of Off-Grid Solar Power Storage 

When it comes to storing solar energy, there are two main types of battery technology:  Lead Acid & Lithium.  Whereas traditional lead batteries have been used for a variety of purposes for many decades, lithium technology is quickly becoming a popular option for home and off grid solar power storage.  

What is a Deep Cycle battery?

Unlike a car’s starter battery that is designed to release a large amount of power at once, a deep cycle battery is a storage device that can be used to release a steady current over a long period of time.  Because of this, deep cycle batteries are perfect for off grid solar energy storage systems that power many devices for varying amounts of time.  

Traditional Lead Acid Batteries

Lead acid batteries are traditionally used to store electricity in devices such as golf carts, sump pumps, boats, and more (this is why golf cart batteries are popular option for off-grid solar power systems).  Lead Acid technology is a tried and true way to store solar electricity, and, until very recently, was the only option available.  There are two distinctive types of lead acid batteries:  Sealed (AGM & Gel) and Flooded.  

Flooded Lead Acid Batteries 

Flooded lead acid batteries are the original and generally the least expensive option for lead acid batteries.  They require careful maintenance, as the user must keep distilled water levels within the battery topped off for optimal performance and lifespan. It's important to note that flooded lead acid batteries must also be installed and kept upright as they have the potential to leak if spilled over.  

Sealed Lead Acid Batteries

Sealed lead acid batteries are similar to flooded lead acid batteries, except that the interior cannot be accessed and users do not have to maintain water levels.  Instead, the battery is designed to provide a maintenance free life of a predetermined amount of cycles.  

In solar, most sealed lead acid batteries are either Absorbed Glass Matt (AGM) or Gel.  Both AGM and Gel batteries can be mounted in any direction and do not require ongoing maintenance.  AGM batteries tend to be a bit more popular for DIY off grid solar, because they are generally less expensive, less sensitive, and can achieve higher charge and discharge rates than Gel batteries. 

Lithium Batteries & Powerwalls

Beyond lead acid batteries, lithium technology has become an extremely popular “premium” option in large solar power storage systems.  Consumers may be most familiar with Tesla’s “Powerwall” which can be used to back up a grid tied residential solar system (if the grid were to fail, the home would use the power from the Powerall).  The Powerwall uses lithium ion technology to store a tremendous amount of solar energy.  

Lithium ion & lithium iron polymer (LiFePo4) batteries utilize new technology, but deliver advanced results.  Lithium batteries can be found in small and large capacities, and are also built-in to some high end solar power generators.  Below, we will outline the critical pros and cons of lithium batteries as they relate to solar storage.  

AGM vs Lithium Batteries 

AGM batteries rely on trusted technology to deliver affordable solar energy storage.  However, we recommend all DIY solar installations consider upgrading to a lithium battery (or battery bank) eventually.  Here are the main advantages & disadvantages of choosing a lithium battery. 

Pros of Lithium Batteries (vs. AGM)

    1. Longer Warranties & Life Cycles- Most high quality AGM batteries are warrantied for between 3-5 years.  Lithium batteries tend to have much longer warranties.  For example, the Lion Energy Safari UT 1300 has a lifetime warranty and a 3,500 cycle guarantee.
    2. Less Weight & Size - Lithium ion batteries are lighter than lead acid batteries (generally about ⅓ the weight) and also usually take up less space.  If you are installing an off grid solar system in a van or RV, every bit of room you can save is valuable, and less weight also means better fuel efficiency. 
    3. Increased Usage Capacity - One of the most important things to understand about lithium batteries, is that they can be discharged at must higher rates than AGM batteries.  With an AGM battery, users can generally only draw roughly half of the power without potentially damaging the system.  Systems with Lithium ion & LiFePo4 batteries can typically use between 80% and 95% of the total battery capacity.  
    4. Efficiency - Lithium batteries are the premium option because they increase the efficiency at which solar power is stored.  Lithium batteries tend to increase storage efficiency by 10% to 15% more than AGM batteries.  

Cons of Lithium Batteries (vs. AGM)  

  1. Higher Upfront Cost - If you cannot afford a Lithium ion battery, then unfortunately your options will be limited to cheaper storage components.  However, it is important to see your battery as a long-term investment rather than just purely an expense.  
  2. Developing Technology - Although they have experienced rapid adoption, lithium ion and LiFePo4 batteries are still considered a new technology.  Some people may not trust a new technology or may be worried about its likelihood to remain compatible with existing system components. 

How to Size Your Off-Grid Solar Power Battery Bank 

When it is time to design your DIY solar power system, finding the right size battery bank can be very intimidating.  Batteries are one of the most expensive parts of an off-grid solar energy system, which makes many people want to cut costs with a smaller battery.  However, this could lead to power outages due to lack of battery capacity or performance.  

Calculating Required Battery Capacity 

Solar battery capacity is generally measured in watt hours (wH).  In order to correctly choose the right size solar battery, you need to calculate how many watt hours your appliances and electronic devices will require when being powered by your battery.  

Most electric appliances have their “wattage” listed on the product or packaging (i.e. 100 watt laptop or 500 watt blender).  After the sun goes down, if you plan to watch 3 hours of TV on a television that requires 50 watts to power, that device will require 150wH (50 watts x 3hr) of battery capacity.  

To make it easy, you can use our solar load watt hour calculator to figure out what your total load in watts will be.

Small Loads

If you are sizing a battery bank for a relatively small amount of electricity, then you can probably get away with one standalone battery for all of your solar storage.  If you are keeping it simple inside of your van, RV, or cabin, you may only need to power your lights, phone, and laptop for a few hours each night, while running your fan and fridge on battery power until the morning.  

For small loads, we recommend a lithium ion battery such as the UT 700.  If you are setting up your off grid solar to power a light, sump pump, or other standalone system, you may want to consider a deep cycle AGM battery such as this one from Renogy.

Medium Loads

Medium size solar loads are typical of small cabins and RVs.  If you want to enjoy the luxuries of television, kitchen appliances, and even a small air conditioning unit, then you will need to purchase a larger capacity battery, or connect a few in a series.  For example, if your daily electricity requirement exceeds 2 kWh (2,000 watt hours), then most standalone lithium batteries will not be large enough for your system.  By connecting two 1300 wH batteries in a series or parallel, you can increase your solar storage capacity to 2600wH.  

Large Loads

For big, permanent solar installations, large load capacities may only be sufficed by large, wall-mounted solar batteries.  For full-home systems or modernized cabins, “power walls” or “power banks” are the best solar batteries for off grid and hybrid solar systems.  High power LFP batteries such as this one from Simpliphi start at 3200 watt hours and can be scaled for systems large enough to fulfill any residential electricity requirement.     

How Much Solar Do You Need to Recharge your Battery Bank?

So you’ve figured out your required battery capacity, great!  Now it is time to determine what solar panels to install to charge your battery.  Depending on where you live, there are only a certain amount of sun hours per day.  In the United States and Canada, there are between 3 to 5 “peak sun hours” per day, so the rule of thumb is to aim for between 5 to 7 hours of full sunlight to recharge your battery. 

To calculate how long your battery will take to charge, simply divide the total watt hours of your battery bank by the total watts of solar power installed. So if you have a 1300wH battery and 200 watts of solar panels (1300wH / 200w), then your battery will charge in approximately 6.5 hours.  Although this would work just fine, if you have the room in your budget or on your roof, we would recommend adding an extra solar panel for even faster charging and to account for the fact that it's extremely rare to generate 100% of the potential watts from your solar panels. 

Solar Generators as a Battery Bank (and more!)

Solar generators (or portable power stations) are becoming an increasingly popular, portable (or even stationary) solution for solar power storage and use.  Solar generators typically combine a battery, an inverter, and charge controller into one easy-to-use package popular among campers, vanlife enthusiasts and for emergency preparedness.

How to Use a Solar Generator as a Battery Bank

Generally speaking, solar generators are known as a “plug-and-play” option.  In order to charge the battery within your solar generator, the process may be as easy as plugging in an MC4 cable from a solar panel.

Solar Generator Pros

  1. Convenience - Above all, solar generators are convenient and user friendly.  Having all of your solar components together in a small, lightweight, portable package is a dream for those who are not interested in the technical aspects of setting up a DIY off grid system.  
  2. Alternate Charging - Solar generators are often labeled as portable power stations because they can be charged in multiple ways.  Unlike standalone solar energy systems, many solar generators can be plugged into an electrical outlet or a vehicle's DC outlet in order to charge their batteries.  This can come in handy in an RV or in an area with limited sunlight.

Solar Generator Cons

  1. Inseparable components - In a traditional solar system, if a component malfunctions, you can replace that piece of equipment.  In a solar generator, however, if a component in your generator needs maintenance, you will likely have to either send it back to the manufacturer to repair or replace it or open it up to fix it. 
  2. Low Power Potential - In order for an inverter and battery to be large enough to power a home, it must be very large.  Although some solar generators such as the Titan are powerful enough to run an entire home’s electricity, the size and weight of the system compromise its portability.  So in this case, users may find it more cost efficient to install the components separately.  

Conclusion

For many, batteries can be the most intimidating part of an off grid solar power system.  We hope that this lesson helped explain the different options, technologies, and sizes available for solar batteries as well as helped you choose what is right for your DIY solar power system.  If you have any questions about your off grid solar system, feel free to contact us today.      


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