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Solar Panel Store Blog — Off-grid Solar

Which type of battery is best for solar applications?

Which type of battery is best for solar applications?

There are several types of batteries that can be used for solar power systems, but the best type of battery will depend on your specific needs and circumstances. Some common options include lead-acid batteries, lithium-ion batteries, and nickel-metal hydride batteries. Each of these types of batteries has its own advantages and disadvantages, so it's important to consider factors such as cost, performance, and maintenance requirements when choosing the right battery for your solar power system.

Lead-acid batteries are the most common type of battery used in solar power systems. They are relatively inexpensive and have a long life span, but they can be heavy and can lose their charge quickly if not used regularly. It's common to use sealed or wet style batteries for renewable energy applications. 

The main difference between sealed lead-acid batteries and wet lead-acid batteries is the way in which the electrolyte solution is contained. In sealed lead-acid batteries, the electrolyte solution is absorbed into a sponge-like material, whereas in wet lead-acid batteries, the electrolyte solution is held in a separate compartment within the battery.

Sealed lead-acid batteries are also known as "maintenance-free" or "valve-regulated" batteries because they do not require regular maintenance or the addition of electrolyte solution. Wet lead-acid batteries, on the other hand, require regular checking and topping up of the electrolyte solution to ensure that the battery remains in good working order.

Sealed lead-acid batteries are generally more expensive than wet lead-acid batteries, but they are more convenient to use and require less maintenance.

Lithium-ion batteries are becoming increasingly popular for use in solar power systems because they are lightweight, have a high energy density, and can hold their charge for a long time. However, they are also more expensive than lead-acid batteries.

Nickel-metal hydride batteries are similar to lithium-ion batteries in that they are lightweight and have a high energy density. They are also relatively inexpensive, but they may not last as long as lithium-ion batteries.

The team here at SolarPanelStore.com has been working with batteries for off-grid and grid-hybrid systems for many years, and we have a lot of experience that we are happy to share with our customers. Please feel free to contact us for questions about batteries or to help with any kind of solar application!

SPS Project Spotlight – Small Hunting Cabin Solar System

SPS Project Spotlight – Small Hunting Cabin Solar System

SPS Project Spotlight - Small Hunting Cabin Off-Grid Solar System

Yesterday a customer came into our office looking for a nice power solution for his hunting cabin. Initially, he had some questions about a pre-configured portable solar kit that he had noticed online. These plug and play solar kits can be a great choice for particular applications, but after speaking with him for a few minutes, the custom design wheels started to turn in our heads!

After  reviewing the customer's expected loads (what he planned to power), showing the customer some solar system components and examples of a few of our off-grid solar charging systems in our warehouse, we were able to get a great idea of exactly what he needed. Keeping low cost and high reliability in mind, our first system design ended up being a 540 Watt pole-mounted system with a 1000W 24VDC -  120VAC inverter. After providing him a quick quote and basic custom wiring diagram, we look forward to the next step with this customer and his installer to see if he would like to look into other options, such as using a larger inverter or possibly an inverter/charger for automated generator use.

As with many off-grid systems, there will probably be a few tweaks to our first design, but we are more than happy to work with our customers until they get exactly what they need and leave with a smile on their face and an extremely reliable system that won't leave them in the dark!

Here's the skinny on what we quoted for this customer, and some notes on what the customer can expect from the system.

Small Hunting Cabin Off-Grid Solar System - Parts List:

QTY: 2 - Peimar 270W 60 Cell Poly Solar Panel SG270P
QTY: 1 - Side-Of-Pole Solar Mount 2X 60-Cell Panel (SOP-Y)
QTY: 3 - HelioLug U Lug PV Lug with Hardware UL 2703
QTY: 1 - 50 ft MC-4 PV Cable Extensions
QTY: 1 - MidNite Solar 3 Circuit Combiner
QTY: 1 - MNEPV 20A PV Breaker
QTY: 1 - MidNite Baby Box
QTY: 2 - MNEPV 30A PV Breaker
QTY: 3 - Two Wire Cable Grip 6mm
QTY: 1 - MidNite Kid 30A MPPT Charge Controller Black MNKID
QTY: 1 - Samlex PST-1000-24 1000W 24V Inverter
QTY: 1 - 2-0 Inverter Cable 48in Red
QTY: 1 - 2-0 Inverter Cable 48in Black
QTY: 1 - Samlex DC-FA-200 Battery Post Fuse Block

Off-Grid Solar System Description.

This is a pretty straight forward 540 Watt 24 Volt system. The two solar panels will be mounted on a side of pole mount from our friends at General Specialties, one of the top-notch U.S. made racking companies we've happily worked with for a number of years. The panels are wired in series, so only a single solar panel extension wire will be required and the panels are fused at the array inside a Midnite Combiner box. The 20A PV breaker is intentionally oversized, the solar panels do have a max series fuse rating of 15A, but here in CO we have seen odd breaker issues in the winter time on pole mounted systems due to the high irradiance and an anomaly we call snow bounce. This 20A breaker is installed inside the Midnite Combiner. Not included in this parts list or wiring diagram, but something that we will also recommend is a lightning suppressor, which would also be installed at the combiner. Our favorite lighting arrester or surge suppressor for this is also made by Midnite Solar, the MNSPD-300-DC.

Wires from the pole will land in the Midnite Baby Box, a handy indoor breaker enclosure, which holds the two 30A breakers for the solar input and output from the MPPT Charge controller. An MPPT charge controller was used not only to step down the voltage from the panels wired in series, but will be better for wintertime production, which is generally when these small hunting cabins are utilized the most. This will feed a 24V battery bank, which the customer currently has but may be interested in upgrading, I'll make some notes below on a couple battery banks that would pair up nicely with the kit.

A 1000 Watt 24V - 120VAC Pure Sine solar inverter from Samlex can power their AC loads, and can either be hardwired to their electrical panel or used standalone with its two standard GFCI receptacles.

A system like this should charge around 1500 - 2700 Watt Hours into the battery each day in the winter time, this is assuming proper panel orientation and 3-5 hours of good sunlight.

We recommended a nice starter battery bank for this cabin solar system that includes four Trojan T105 225Ah 6V batteries. These would be wired in series for a 225 Amp Hour 24 Volt bank, with a total storage capacity of 5,400 Watt Hours.

Off-Grid Solar System - Wiring Diagram

Here's the wiring diagram we worked up for them to give them an idea of how all of the parts work together, we like to keep our parts list in basically the order you see them in our diagrams to make things as easy as possible!

We hope that this customer project spotlight will help inspire your own solar project!  Give us a call to explore what kind of custom solution we can provide for you!

Thanks for reading!

Battery Maintenance

Battery Maintenance

Battery Maintenance

To get the most life and performance out of your solar system's batteries, regular battery maintenance is key.   In this article we cover some basic principles of flooded deep cycle battery maintenance. Please keep in mind all battery systems are different and you should consult your battery data sheet for information specific to your batteries.

Battery Basics.

Voltage.  What is your battery bank voltage? Typical battery voltages include 12V, 24V and 48V, 36V is also found in some instances. Remember that series wiring (positive to negative) will increase voltage while keeping amperage the same. Parallel wiring (positive to positive and negative to negative) will increase amperage, while keeping your voltage the same.

Battery Type. What type of battery are you using? Common battery types include deep-cycle flooded, AGM and gel batteries. Lithium batteries are not yet as common for off-grid applications due to the cost, but they are becoming more popular. AGM, Gel, and Lithium batteries are sealed,  maintenance-free, and more expensive than flooded deep cycle batteries.  Because this article is about battery maintenance, we won’t focus on these other battery types.

Capacity.  Battery capacity for solar systems is measured in amp hours based on a C/20 discharge rate.  The faster a battery is discharged, the less capacity it has.  C/20 is a slower discharge rate that approximates the typical discharge time period of a solar system.  While amp hour capacity can vary by the battery case size, it is common to see 12 volt batteries around 100 amp hours and golf cart style 6 volt batteries around 225 amp hours and L16 size 6 volts around 400 amp hours.  Also if you convert capacity into watt hours you can better estimate how much capacity you need to power the loads you have.  Because Ohm’s law tells us that watts = volts x amps, a 12 volt 100 amp hour battery is 1200 watt hours.  Because the maximum discharge level for deep cycle batteries (“dept of discharge”) is generally 50%, that means that a 1200 watt hour battery only has 600 watt hours of usable capacity.

Tools.  Below is a list of tools you’ll need to do your battery maintenance:

  • Eye protection
  • Gloves
  • Wrench
  • Voltmeter
  • Baking Soda
  • Battery Post Cleaner
  • Distilled Water
  • Hydrometer
  • Vaseline
  • Notepad

Visual Inspection.

The first step is a visual inspection.  But before you do,  ALWAYS be sure to wear eye-protection and gloves when working on a flooded deep cycle battery bank!  And wear old clothes!

A visual inspection includes checking all the batteries. Be sure to look for cracks or irregular bulges. Check for any fluid on or around the batteries. Cracked or leaking batteries will need to be replaced. Also be sure to inspect cable lugs and battery terminals. These should be clean of fluids, dirt and corrosion. Inspect cable connections for tightness.  All connections should be at the proper torque value, which can be found in your battery’s data sheet. Be sure to not over-tighten connections as this can lead to battery damage and hot spots. While connections that are too loose result in poor conduction and hot spots.

Make regular visual inspections of your battery bank a habit. Early problem detection can save a lot of time, money and headaches down the road. Shoot for monthly inspections until you get a good idea of how your batteries perform. Over time you may find that monthly inspections are too frequent, or not enough!  How frequent really depends on how hard they are working.  

Battery Tests.  

After you finish visually inspecting your batteries, there are two important tests you should do as part of regular maintenance:  1) Open Circuit Voltage Testing and 2) Specific Gravity Testing.  Performing these tests each month will provide you with important information about your batteries’ health, age and charge level.  They will also help you detect problems like overcharging, undercharging and overwatering. Finding these issues early is key to keeping the entire battery bank strong.

Specific Gravity.

Testing the specific gravity of a battery’s electrolyte solution with a hydrometer is an accurate way to measure a battery’s “State of Charge”.  As a lead acid battery discharges, sulfuric acid floating in the electrolyte binds back to the charging plates (forming lead sulfate), which makes the electrolyte more water-like and less dense and causes the Specific Gravity to go down.  The reverse is true when the battery charges (Specific Gravity goes up as lead sulfate from the plates changes to sulfuric acid in the electrolyte solution).  Also if your battery’s electrolyte level gets too low, the density goes up and Specific Gravity goes up.

  1. Don’t add water at this time, If your batteries are low on water you should add water and let them go through a complete cycle before testing.
  2. Fill and drain your hydrometer at least 3-4 times before taking your test sample.
  3. Take a sample, you should have enough liquid to completely support the float.
  4. Take a reading and record it. Return the sample to the cell.
  5. Move to the next battery cell and repeat the above 3 steps.
  6. Be sure to check all the battery cells.
  7. Replace all battery caps and clean any liquid that may have spilled in the process.
  8. Correct the readings to 80 degrees fahrenheit by: 
  9. Adding 0.004 for readings 10 degrees fahrenheit below 80 degrees
  10. Subtract 0.004 for readings 10 degrees fahrenheit above 80 degrees
  11. Compare the readings.
  12. Check the state of charge using the below table.

Readings should be at factory specifications of 1.227 +/- 0.007. If any specific gravity is reading low follow the below steps.

  1. Check and record voltage levels.
  2. Put batteries on a complete charge.
  3. Take specific gravity tests again.

If after reading specific gravity you find cells registering low you may try the below steps.

  1. With your voltage meter check voltages again.
  2. Proform an equalization charge.
  3. Take specific gravity tests again.

After your equalization charge has finished and your still getting lower voltage readings than factory specifications you may have one or more of the below conditions:

  1. The battery was left too long in a state of discharge.
  2. The battery was over-watered during the last maintainence procedure.
  3. A weak or bad cell is developing inside the battery.
  4. Electrolyte was spilled or has leaked from the battery.
  5. The battery is reaching the end of its life.

If you are showing signs like those above you may want to take your battery in to a specialist, or consider replacing the battery.

Open Circuit Voltage.

When testing open circuit voltage,  batteries should remain idle with no charging or discharging for 6 hours.  It is best to let them sit idle for 24hrs.

  1. Disconnect all loads from batteries.
  2. Measure voltage using a DC Voltmeter (or a Multimeter set to DC voltage)
  3. Check battery state of charge with the below table.
  4. Charge the battery if it registers 0% to 70%

If your batteries are registering below the table 1 values, the batteries may have been left too long in a state of discharge, or the battery may have a bad cell. In this case it is best to take the battery to a specialist or replace the battery.

Battery Watering.

All flooded batteries use distilled water as a key component of their electrolyte solution.  While not everyone loves checking and adding water to batteries, because flooded batteries are a lot less expensive than sealed batteries, it is worth doing, and doing right.  There are some battery watering products on the market today such as the Trojan Hydrolink, and the BWT system by US Battery that are not within the scope of this article, but make the battery watering process easier and quicker.   

Distilled water should be added after the battery has been fully charged.  However, the water level should at least cover the battery plates before charging. That will ensure that the water levels are sufficient during the different states of charge.  Also, keeping your battery plates covered will keep them from being exposed to air, which can cause corrosion to the plates.

It is also important not to overfill the batteries with water.  Overfilling can result in the battery overflowing and losing battery acid which will degrade the capacity of the battery. Battery acid is a highly corrosive liquid and can cause damage to anything it touches. Battery containment trays can help avoid damage as they provide a safe place to catch any overflowing acid-containing electrolyte. You should use a distilled or deionized water for watering because these liquids have very low mineral counts. Because the battery electrolyte is a mixture of water and battery acid, always wear protective gloves and eye protection when handling or maintaining batteries to protect your skin and eyes from damage.  It’s also best to wear old clothes!

Steps to adding water to a battery:

  1. Put on your protective eye protection and gloves.
  2. Remove vent caps and check the inside fill wells.
  3. If the battery plates are exposed add just enough water to cover these plates.
  4. Put your batteries on a complete charge before adding any additional water.
  5. After your batteries are have finished charging open vent caps and check the fill wells.
  6. Add water until the water level is about ⅛ below the bottom of the fill well.
  7. Clean and replace the vent caps.

You should never add battery acid to a battery.

Below is an example of the Trojan Battery fill wells and where your water level will need to be.

Battery Cleaning.

Regularly cleaning your battery terminals ensures that current will flow through your battery bank smoothly which, in turn, helps make sure all your batteries receive an equal and full charge.

Steps to battery cleaning.

  1. Put on your eye protection and gloves.
  2. Make sure all vent caps are tight.
  3. Clean the battery tp with a cloth or brush with a solution of baking soda and water.
  4. Clean battery terminals and lugs with a post cleaner.
  5. You may want to use a protective coating of anti-corrosive spray or silicon gel.
  6. Clean the area around the batteries this should be a dry organized area.

Keeping a small notebook as your maintenance journal can be helpful to record your maintenance dates and test results so you can compare readings and determine the best maintenance schedule.

Batteries and Solar.

The goal with any battery-based solar system is to maximize the health and life of your battery bank.  Why?  Because the battery bank is often the most expensive component of your system.  So be sure to charge your batteries completely after use. Batteries that are not fully recharged soon suffer from reduced charging capacity and a shorter life span.  If you are going to store the batteries for an extended period of time you will want to charge them fully every three to six months. Flooded batteries can be expected to self-discharge up to 15% each month. This self-discharge rate can depend on the age of the batteries and also the temperature they are stored at.

It is also important that you size your solar array to be large enough that it will fully recharge your battery bank in 4-5 hours during an average sunny day.  That will help your battery bank stay fully charged as often as possible to ensure long battery life.

We hope you found this article helpful.  Following these recommendations should help you keep your deep cycle, flooded batteries healthy and extend their life and your investment for years to come.