Off-grid Solar With Battery Backup

When powering a remote island retreat, off-grid solar with battery backup is often the only option!
When powering a remote island retreat, off-grid solar with battery backup is often the only option!

Yesterday was a pretty good day at work.It featured a boat ride, an exclusive remote island, some old school solar stuff, and a bright sunny day. Sure, I had to sweat it out in a 100 degree battery room, but it’s all worth it when there isn’t an alternative for power and you can help out a new friend.

When we say “off-grid solar” we are referring to a location where utility power is not available. There are many places where people have access to utility power, but want to have autonomy. These systems are called solar with battery backup. Off-grid systems all have batteries, as do battery backup systems of course. However, off-grid systems can only charge batteries with solar panels or a generator. Battery backup systems with a utility connection can charge batteries using utility power, solar power, or generators.  We do not refer to true off-grid systems as battery “backup,” because batteries are the primary source of energy. The battery is the heart of the system.

Off-grid homes require three major components to work effectively.

  1. A source or sources of electricity production, which can include solar, wind, generator, or other energy sources.
  2. A storage system, which is almost always a battery.
  3. An inverter to convert DC electricity to usable AC electricity in the home.

Source – Solar Power

In most cases in Florida, off-grid homes use solar power as the primary energy source with a propane or diesel fueled generator for backup. While solar power can be used exclusively, there is a balance to be struck because all of the solar power produced must be stored for use when the home’s occupants demand it. Solar power needs to recharge batteries, power electrical loads during the day, and produce enough exceess energy to get through nights and periods of poor weather. The number of solar panels is calculated by how much power is needed under the worst case scenario, with respect to available space and variability in usage. If generator power is available, it is often most cost effective to plan for solar delivering something less than 100% of the energy needs. On rare occasions it is more cost effective to just run a generator. This balance is something that needs to be discussed between the owner and a solar professional to come up with the ideal energy source mix.

Storage – Battery

The battery is typically made up of many battery cells strung together in series and parallel. Most off-grid battery banks operate a nominal voltages of 24V or 48V, with 48V being most common for all but the most modest homes and cottages. Batteries today are almost all lead-acid, with some being Absorbed Glass Mat (AGM), Valve Regulated Lead Acid (VRLA), or Gel. Lithium Ion is coming onto the scene, and the new Tesla Powerwall is making big waves. The capacity of the battery dictates how long your home can run without any charging source. As you use energy, you draw from the energy reserve in the battery. Eventually it needs to be recharged with either solar power or a generator. The battery is the heart of an off-grid solar energy system, and often the most expensive component by far. Proper use and maintenance of the battery is key to a successful and long lasting system.

An off-grid inverter system powers a remote island home with solar power.
An off-grid inverter system powers a remote island home with solar power.

Use – Inverter

Unless you have compatible DC lighting, pumps, and appliances, you can’t use energy stored within the battery. An Inverter is needed to convert DC power to AC power for use with standard electronics and appliances. Because AC powered appliances are far more common and affordable, an inverter is used on almost all off-grid homes. The rating of the inverter(s) dictates how much power you can use at a given time. You might have a massive battery bank and tons of solar panels, but if your inverter is not big enough, you can’t use all of that energy. The inverter is sized to meet your greatest expected demand. For example, if there is a chance that your water pump, refrigerator, and air conditioner will all run simultaneously, you will need to size your inverter to handle the total power requirements of these electrical loads.

Balancing an Off-Grid Solar Energy System

The source, storage, and use of energy for you off-grid home is a very complex issue. Properly identifying your usage patterns helps solar professionals identify components that will work together to maximize your enjoyment and convenience while minimizing your costs (initial, maintenance, and replacement).

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