What is the difference between a grid-tie and an off-grid wind energy system?

Here’s a basic overview of the three basic types of residential wind energy systems:A. Grid-Connect (Grid-Tie) Systems without Batteries: Grid-connect systems interface directly withthe electric utility grid via an inverter (provided with our grid-connect wind generators). A Voltage Clamp ( grid-connect controller) rectifies the wind generator’s “wild” (variable voltage & frequency) alternating current (AC) to direct current (DC) and limits the maximum output voltage in order to maintain the health of the inverter. The inverter changes the DC outputted from the Voltage Clamp into AC at the required frequency (60 Hz or 50 Hz, depending upon country) and synchronizes with the utility power grid, prior to sending energy produced by the renewable energy system to the household appliances and/or to the grid. Advantages: Grid-connect systems avoid the inherent inefficiency and vigilant maintenance requirements of batteries. Sizing a wind energy system for grid-connection is also simpler than with its battery-charging counterpart, because the utility grid can make up for mismatches between the electrical loads and the wind generator’s production capability.Additionally in many states, there are production incentives for renewable energy sent to the utility grid (while relatively few states provide renewable energy incentives for off-grid production).Disadvantages: If the utility grid shuts down, so do grid-connected renewable energy systems without battery back-up. In situations where continuous power is critical or where power outages are frequent, battery back-up equipment may be advisable.B. Battery-Charging Off-Grid Systems: Battery-charging systems feed through a charge controller and into a battery bank. This type of system is primarily used in remote locations where grid power is not available. When storing renewable energy exclusively in batteries, the renewable energy equipment and battery bank must be sized appropriately to maintain sufficientenergy to match consumption and maintain battery health.Advantages: Battery-charging systems provide their owners with energy independence. Thus, off-grid systems are unaffected by electric utility grid outages.Disadvantages: When insufficient energy is captured by a battery-charging system, the homeowners must curb their usage to match (since there is no infinite power source, such as the utility grid, to draw upon). Conversely, when the battery bank is full and renewable energy is being produced at a rate faster than loads are being fed, the excess energy is usually “wasted” by heat dissipation (this excess energy can optionally be put to use with water-heating elements in a hot water tank). Batteries require vigilant care and maintenance to keep water and charge levels adequate. Renewable energy batteries are expensive, and failure to properly maintain them can be a very costly mistake.C. Grid-Connect Systems with Battery Back-up: Grid-connect systems with battery back-up can be configured in several ways -with batteries filled from the utility grid or from the renewable energy system. This system functions similarly to the system described in letter A (Grid-Connect Systems without Batteries) above but continues to function via a back-up battery bank when the local utility grid experiences a power outage.Advantages: This system combines the best traits of the other two system types. The utility grid can be utilized to fill in energy consumption gaps or over-production surpluses, and they continue to operate (on batteries) if the utility power grid experiences an outage.Disadvantages: Since this type of system uses batteries, careful maintenance and attention to battery water and charge levels are required in order to maintain healthy batteries. Also, this is generally the most expensive of the three system types, because a more complex configuration comprised of both grid-connect and off-grid equipment is required.