Grid Tied with Battery Backup

Grid Tied Solar Electric Systems w/Battery Back Up

Emergency Solar Backup Power for your home or small business can come in handy when bad weather or other conditions interrupt the utility electrical service. Home or business owners can find themselves unable to power critical load appliances and lights. This situation can be serious if critical applications such as medical devices, telephone, home office computers, sump pumps, or refrigeration are threatened. The Solar Store's emergency backup power systems are some of the best values currently available on the market.

When a emergency blackout happens at your home or business, the AC pure sine wave inverter instantly starts powering critical loads from the batteries until the power comes back on. (If you have the unit hardwired to a critical load subpanel)  The backup power unit will then automatically re-charge its batteries and go into a standby mode. When the power goes out, lights, refrigerator, computers, television, alarm systems, automatic gate or garage openers, all continue working during a emergency blackout. When the power comes back up, the unit switches over and starts recharging the batteries for the next time. All our home backup power kits come with an easy-to-use monitoring system so you can check your power supply anytime of day.

Hardwiring Your Backup Power System to Your Home or Business. 

When you are working out the details of how your emergency solar backup power kit is going to work in your home or business, the first step is to decide what loads are critical to you during a blackout. If you choose to hard-wired your backup power kit, the power needs to be sent to a critical load sub-panel that is not directly connected to your home or businesses main AC utility service panel. The two panels may be connected only by using the AC inverter that comes pre-wired with the backup power battery cabinet. The way it works is you will have an AC power in conduit coming from your main service panel that is connected to the “AC” in-port on the emergency solar backup power panel. You then connect an “AC” out-port that is connected to your critical load sub-panel box only which is not connected to your home or business main service panel. What happens during a utility blackout is power will only be supplied to the critical load subpanel from the backup power unit which is wired to several important independent outlets or switches in your home or business. To make this happen in this scenario, you either need to relocate specific critical load circuits or install new ones near where you need the power during an emergency power outage. There are some very goods reasons why you have to do this. The first is called islanding, which is illegal and dangerous. Islanding means you are sending power back to the grid. Imagine, if you will, a utility worker responding to the power outage in your neighborhood. He or she thinks the power is down and starts working on the line and is injured because power is back flowing from your home. The second very good reason this backup power system needs to be wired this way is when the grid is up, power will be flowing to the AC out-port connected to the backup power center. This creates a condition where the state of charge on the bank of batteries is not regulated and you will fry the batteries. Wired correctly, when the utility power is working, electricity will flow from your main power panel through the backup power kit to power the critical circuits that you moved to your sub-panel. Keep in mind you must limit the continuous power to your critical load circuits to no more than 80% of the output of the inverter. If you need more continuous power we can parallel multiple inverters to increase the current flow. But if you choose to do that without increasing your battery bank you will simply drain the batteries faster. Better to just decide on a few “have-to-have” loads and stretch the draw down on the batteries in the backup power center.

AC Coupling of Existing Grid Tied Solar Systems

Grid connected solar systems do not require batteries to operate because the excess energy produced is in effect stored with the utility company in the form of NET metering. What many homeowners fail to realize when they purchase a standard grid tied system is when the grid goes down, so does the power being produced by the solar panels. Why? The IEEE-1547 standard requires that utility interactive inverters cease to export power (Means your meter spinning backwards) if the voltage measured at the Point of Common Coupling (PCC) (That mean your homes electric service meter) exceeds +10% or -12% of nominal. If that were not the case, the result would be an unintentional island of power generation that would energize a portion of the utility power grid that the local utility has de-energized. The importance of grid connected home solar systems is clearly recognized, but as home systems continue to make inroads into America’s utility grid, national guidelines were needed to stipulate how homes and businesses could connect to to the grid. To this end, the Institute of Electrical and Electronic Engineers (IEEE) worked with the United States Department of Energy (DOE) to develop the IEEE 1547 standard, which provided in 2003 a set of requirements in America for the interconnection of home solar systems into the utility power grid. When the grid goes down, most homeowners with an existing solar system quickly become frustrated because the potential power that is readily available nearby is useless. MidNite solar, Magnum Energy, SMA and Outback have long recognized this void in the market place that will allow existing solar customers and new customers to utilize the AC energy that is normally back fed through to the utility company to now be used to in a home or business and still be in compliance with the IEEE-1547 standard.

AC coupling kits for existing grid tied and emergency power battery based applications during utility blackout’s. In ac-coupled home solar systems, these on grid systems are integrated with battery-based on grid inverter systems. AC coupling uses grid tied inverters networked to one or more centralized battery-based inverters. This configuration allows AC electricity to either go directly to AC home loads, bypassing the batteries, or to charge the batteries via the battery-based inverter. Regulation is controlled on the AC side of the system by limiting the output of the grid tied inverter (Enphase(inverters) or SMA Central Inverter) when the batteries are fully charged or bleeding off the unused AC electricity created by the solar panel AC inverters via a relay driver. The Relay Driver is a logic module which provides high level system control functions such as high / low voltage alarms, load control and generator start. The product controls AC relay driver outputs by reading digital data inputs by reading battery voltage.

When the utility power goes down during a storm or blackout, the on-grid inverter and utility interactive SMA central inverter or Enphase (inverters) stop exporting power to the grid. Once this occures, in less than a 60th of a second the on-grid inverter automatically starts pulling power from the battery bank to continue to power the homes backup loads. Since the utility based AC inverter is connected on the home side of the on-grid inverter, the utility inverter will have a frequency synchronization witht he on grid inverter and begin to produce power. The cycle time for the utility AC inverter to begin operating again is about 5 minutes with most inverters.

The utitiliy AC inverter is now operating again using the on-grid battery based inverter and is producing as much power that is available safely through the homes solar system. This electricity is used by all the loads in the home with the excess electricity being used by the on-grid inverter/charger to recharge the home’s battery bank. The amount of power that is allowed to be produced is regulated by either an high voltage AC relay which sences the voltage of the battery bank interrupting the AC electricity being produced by the AC utility inverter.

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