Off Grid All Together

Off-Grid Solar Systems

An off-grid solar system (off-the-grid, standalone) is the obvious alternative to one that is grid-tied. For homeowners that have access to the grid, off-grid solar systems are usually out of question. Here`s why:

To ensure access to electricity at all times, off-grid solar systems require battery storage and a backup generator (if you live off-the-grid). On top of this, a battery bank typically needs to be replaced after 10 years. Batteries are complicated, expensive and decrease overall system efficiency.

 

Advantages of Off-Grid Solar Systems

1. No access to the utility grid

Off-grid solar systems can be cheaper than extending power lines in certain remote areas.

Consider off-gird if you’re more than 100 yards from the grid. The costs of overhead transmission lines range from $174,000 per mile (for rural construction) to $11,000,000 per mile (for urban construction).

 

2. Become energy self-sufficient

Living off the grid and being self-sufficient feels good. For some people, this feeling feeling is worth more than saving money. Energy self-sufficiency is also a form of security. Power failures on the utility grid do not affect off-grid solar systems.

On the flip side, batteries can only store a certain amount of energy, and during cloudy times, being connected to the grid is actually where the security is. You should install a backup generator to be prepared for these kinds of situations.

 

Equipment for Off-Grid Solar Systems

Typical off-grid solar systems require the following extra components:

• Solar Charge Controller
• Battery Bank
• DC Disconnect (additional)
• Off-Grid Inverter
• Backup Generator (optional)

Solar Charge Controller

Solar charge controllers are also known as charge regulators or just battery regulators. The last term is probably the best to describe what this device actually does: Solar battery chargers limit the rate of current being delivered to the battery bank and protect the batteries from overcharging.

Good charge controllers are crucial for keeping the batteries healthy, which ensures the lifetime of a battery bank is maximized. If you have a battery-based inverter, chances are that the charge controller is integrated.

Battery Bank

Without a battery bank (or a generator) it’ll be lights out by sunset. A battery bank is essentially a group of batteries wired together.

DC Disconnect Switch

AC and DC safety disconnects are required for all solar systems. For off-grid solar systems, one additional DC disconnect is installed between the battery bank and the off-grid inverter. It is used to switch off the current flowing between these components. This is important for maintenance, troubleshooting and protection against electrical fires.

Off-Grid Inverter

There’s no need for an inverter if you`re only setting up solar panels for your boat, your RV, or something else that runs on DC current. You will need an inverter to convert DC to AC for all other electrical appliances.

Off-grid inverters do not have to match phase with the utility sine wave as opposed to grid-tie inverters. Electrical current flows from the solar panels through the solar charge controller and the bank battery bank before it is finally converted into AC by the off-grid-inverter.

Backup Generator

It takes a lot of money and big batteries to prepare for several consecutive days without the sun shining (or access to the grid). This is where backup generators come in.

In most cases, installing a backup generator that runs on diesel is a better choice than investing in an oversized battery bank that seldom gets to operate at it`s full potential. Generators can run on propane, petroleum, gasoline and many other fuel types.

Backup generators typically output AC, which can be sent through the inverter for direct use, or it can be converted into DC for battery storage.

Here's another diagram with more of the parts filled in.

More complete off-grid system diagram.

The added parts are as follows:

• solar array - If there are multiple solar panels in a system then they're collectively referred to as a solar array.
• battery bank - Multiple batteries in a system are referred to as a battery bank.
• disconnect switches - Throughout the system there are switches that are normally closed but are in place in case a part needs to be isolated for repairs and to prevent a short circuit in the system from damaging parts. For example, the charge controller has disconnect switches to either side of it.
• inverter bypass switch - If the solar system can longer supply power to the loads then this allows the generator to take over while the solar system is repaired.
• lightning arresters - Lightning arresters are on any wires that may bring damaging electrical current into the system from lightning. For example, if lightning strikes the solar panels then the panels will be damaged but the lightning arrester at the charge controller should protect it.
• combiner box - Depending on the number of solar panels and how they're wired up, it may make sense to have a box near the panels that combines many of the wires coming from them into just a few wires for the long distance to the charge controller.
• display and control unit - Some systems allow networking of their components so that they can be controlled and monitored from a single box, usually with an LED display. For example, OutBack's MATE and Magnum Energy's Remote Control.
• shunt - Part needed if you're going to be using an amp hour meter or battery monitor of some sort. Allows for monitoring of current going into and coming out of the battery bank.
• amp hour meter - A device that monitors the battery's state of charge (SOC) by measuring the electrical current going in or out of the battery bank. Also referred to as a battery monitor.
• automatic generator starter - If the batteries are low and there is no sun then the generator is run to top up the batteries and take over supplying power to the loads. This can either be done manually or be done automatically as a feature of the inverter, charge controller, display and control unit (e.g. OutBack's products) or a standalone automatic generator starter box (e.g. Magnum Energy's Auto Generator Start Controller.)

And of course you need wires that are appropriate sizes both for safety reasons and to make sure you get the required performance. For the latter, see the page about sizing wires to maintain the necessary voltage over long distances such as from the solar array to the charge controller by calculating the voltage drop.