Solar Battery Maintenance Guide
Batteries are one of the most important aspects of this DIY system. The more batteries that are added, the more storage there will be for off-grid use.
A typical household needs 20 kilowatts-hours to 40 kilowatts-hours of battery storage, which can be as much as 30 batteries or more. The batteries must also last on days when the weather is bad and there is minimal solar energy available.
Using air conditioning, washer, dryer, dishwasher, large TVs, or other electronics can drain energy significantly. When dealing with a battery system, you will want to be very conservative with energy use.
This DIY system has a manual switch to choose electricity from batteries or the grid. The more electricity that I use at the farm, the less I can use my batteries. AGM batteries are the best type of batteries for use with solar and wind storage systems.
There are only a few choices for batteries with DIY off-grid solar or wind systems.
Lead-acid batteries are the best choice, especially sealed lead-acid batteries. Lithium ion batteries, as of 2014, are still much too expensive to consider for a DIY off-grid system.
There are 2 types of lead acid batteries that require little to no maintenance, which are gel cell and absorbed glass mat (AGM) batteries.
AGM batteries were chosen because these batteries did not require us to fill the batteries periodically with battery acid or water, and also the high number of charge cycles for the price.
The main advantages for AGM over gel batteries are that the AGM type is cheaper, can last longer, and AGM does not need a special type of charge controller.
If you were to purchase gel batteries, you would typically pay more versus an AGM battery as well as see a shorter life cycle. Special charge controllers are needed for gel batteries over AGM batteries.
All of these disadvantages led to the decision to choose AGM over all other types of batteries. We carefully researched the first set of AGM batteries for the system before making a purchase. Six of the first 12 batteries were purchased at Batteries Plus for $200 each, a franchise store that sells batteries in Florida.
Most Batteries Plus stores are franchise owned, so if you do find one you can talk with the owner of the store and try to negotiate a discount.
Also if you are buying several batteries at the same time, you are more likely to get a discount. Often times you can find coupons in the newspaper or online from either Batteries Plus or another battery supplier. After 2012, battery prices dropped across the market as solar became ever popular.
Sam’s Club, a large member-only supermarket warehouse chain, started selling deep cycle batteries for cheap. The later AGM Duracell brand batteries were bought from Sam’s club for $150 that are rated for 100-amp hours.
A cheap battery tester was purchased to test the quality and charge of the batteries for battery maintenance. We use this battery tester every six months to make sure none of the batteries are going bad.
Battery jumper cables are required to connect each battery. Each of the battery jumper cables seen in the pictures is expensive; most are at least $15 to $20 now. In the beginning of the project they were $20 each. We have used a total of 22 of these battery jumper cables.
Ventilation is also very important for the batteries. The batteries do need air to help cool while charging or discharging, so a fan was built into the shed that blows hot air out of the shed. Since the Florida sun will often bake the shed with temperatures above 85 degrees Fahrenheit, the fan greatly assists in keep the temperature lower in the shed.
At lower temperatures, the AGM batteries will last longer and have a greater number of discharge cycles over the life of the battery.
A main battery disconnect switch was also installed. This switch allows for the circuit that the batteries are on to be immediately turned off for maintenance on the batteries or in the event of the emergency.
This is a highly recommended to have a disconnect switch in a battery system since the entire battery bank can be turned off in almost half a second.
Why Not Feed Electricity into the Grid?
The battery system was designed as a back-up system for the farm, and to provide electricity at night. This system is integrated into the 120 volt AC grid all across our property. A common question that is asked is “Why didn’t you sell the electricity to the power company or get net-metering to lower your power bill?”
The main reason we opted for a battery DIY system was that the local electrical company here in Florida would not recognize solar photovoltaic systems (it is a co-op electric company), and it would be difficult to obtain an interconnection agreement.
If you desire to feed electricity into the electrical grid (your electric utility company), then you must first contact your local electrical company.
Each electric company has different requirements for connection to the grid using a solar system or wind system.
A solar system must also be installed by a licensed solar contractor in the State of Florida, along with proper permits that need to be filed, depending on your county or city codes.
When connecting to the grid with an electrical company, the electrical company will often send a representative to visit with you to determine all requirements. In some states, you can actually “net meter”, which means that the electrical company can compensate you on the electrical generation from your solar panels.
The electric company will credit this energy generation on your electrical bill. In this case, you would not need to have a battery system. In our case, we choose to have batteries since we are in a very rural area that has constant power surges, blackouts, etc. over and over again. A decision was made to eventually go off-grid and be completely sustainable on our farm.
12 Volt System
A 12 volt system was designed as the DC side of the system because 12 volts is the standard voltage for much of the equipment available such as inverters and battery chargers. Designing a battery system at 12 volts allows more flexibility in just simply adding one battery at a time in parallel to the battery array.
A 36 volt system and 48 volt system was investigated before building this system, but due to the much higher price of a DC to AC inverter from a 36 volt/48 volt battery bank, a 12 volt DC battery system was chosen.
The final design has several 12 volt batteries in parallel so that the voltage stays at 12 volts, while the amp-hours reserve increases of the system. Each battery is about 100 Ah (amp-hours) rated, so with 10 batteries in parallel, I technically have 1000 Ah available from the batteries. Each solar panel that was purchased was also 12 volts, but if a 24 volt panel were obtained, it could be added in series in another string of solar panels.
Each string of solar panels cannot exceed about 120 volts DC due to the MidNite Solar charge controller requirements.
Several strings can be connected to the MidNite Solar charge controller, so we have future wiring already in place for the future strings when we buy more solar panels. This is always a good idea to run future wiring for adding future solar panels.
Since we have a ground mount system, there are extra 10 gauge sized wires in the electrical conduit buried in the ground near where the future solar panels will be mounted.