THE BASICS OF BACKUP POWER:



REVIEWS AND COMPARISON OF DIFFERENT SYSTEMS FOR HOME AND COMMERCIAL USE



A blackout can happen at any time. Often the grid may be down for days or even weeks. Backup power systems can supply electricity to critical loads or entire house when the grid is down. There are various kinds of emergency backup devices depending on the type of energy source they are using to produce electricity. When you are choosing your system, the main things you get to decide are: the amount of electrical power you may need during a blackout, the length of time you want to produce it, and of course your budget.









To properly size your system see our sizing guide. When you do the sizing you may want to add 10 to 20 percent safety margin for system derating and to prevent false tripping of its circuit breaker. Note, since many appliances have surge current exceeding their steady state current, you need to make sure your backup system has sufficient surge capacity to accommodate all the loads at start up. This is especially important for automatic home generators. If you choose a manually activated system, you can always turn off your loads before starting the backup source and then turn them back on sequentially. The table below provides basic features of the main types of power back up sources. Electric gensets are generally the least expensive source of power. For a short-term blackouts an emergency portable generator is the most popular low-cost solution. For a long-term emergency a natural gas or propane-powered stationary home generator with a transfer switch is probably the most cost effective solution. Such a system can provide electricity for as long as it has fuel. Home battery backup is less common because it is suitable only for short term outages. And unlike portable generators that can be manually refueled, a battery needs a source of electricity to recharge. Alternative energies, such as photovoltaic energy are becoming increasingly popular due to various incentives and rebates. However, they are still more expensive types of home backup. Because of their intermittent nature they have to be supplemented by another power source, or you will need a humongous battery bank.

BACKUP POWER SOURCE MAIN FEATURES PRO's CON's NOTES
PORTABLE GENERATOR
  • Runs on gasoline, diesel, propane, or natural gas (depending on the model)
  • Power range: 500-17,500 W
  • Gasoline models are good mainly for short-term outages
  • Multi-fuel models running on LPG or NG may provide long-term power
  • Can be moved from place to place
  • No professional installation is needed [unless you want to connect it to the house wiring via a manual transfer panel and/or to an external fuel source]
  • Limited run time (less than a day before refueling) unless hooked up to an external fuel source
  • Very noisy
  • No auto start
  • Requires maintenance
  • Burns fuel even when it idles
  • Must be run outdoors only
  • Potential fire and carbon monoxide hazard if used improperly
STATIONARY STANDBY SYSTEM (WHOLE HOUSE GENERATOR)
  • Connects to the home wiring via a transfer switch
  • Runs on diesel, propane or natural gas (depending on model)
  • Highest power range (6kW -100's kW)
  • The best type during long blackouts and as the whole house generator
  • Typical transfer time with auto transfer switch: 10-30 seconds
  • Auto start option on many models
  • Practically infinite run time when connected to natural gas line
  • Expensive
  • Requires professionally installed transfer switch and fuel line
  • Older homes may require a new higher volume natural gas meter
  • Requires maintenance
  • Installed outdoors on a cement pad and connected via a transfer switch
BATTERY BACKUP WITH DC-AC POWER INVERTER / CHARGER
  • Powers critical appliances via extension cords. May be permanently connected to the house wiring via a transfer switch
  • Typical power for residential use: 5-10 kW
  • Auto start systems have response time 16-36 ms
  • No maintenance required
  • Quiet
  • May be installed indoor
  • Low power consumption at no load (consumes power according to the actual load demand)
  • Limited run time (typically 2 to 12 hours) depending on the battery tank capacity
  • Look for a sealed deep cycle battery and a temperature compensated charger with a trickle mode to avoid battery overheating

BACKUP HOME GENERATOR VIA VEHICLE
  • Good for short outages and to power only essential loads
  • Typical power 300 W- 5000W depending on the battery capacity and inverter
  • Lowest cost
  • No professional installation required

  • Engine must be ON all the time to avoid car battery discharge
  • Power is limited by the rating of vehicle parts
  • Limited run time
  • Exhaust fumes present potential hazard
  • Hybrid and electric cars batteries have the highest capacity, but you need a special inverter rated for high input DC voltage; dealing with high voltage poses electrocution hazard
SOLAR PANELS with a BATTERY SYSTEM and DC-AC INVERTER/ CHARGER
  • Photovoltaic (PV) panels charge battery bank
  • Produces electricity only on bright days
  • Can power stand alone AC loads or can be connected to the house wiring (in which case it requires a grid-interactive type of inverter with a transfer relay)
  • Utilizes renewable energy
  • quiet
  • No maintenance required
  • Defrays energy cost or even let you sell electricity back to utility
  • Federal and state incentives
  • The most expensive type
  • Limited run time [depending on the battery tank's capacity]
  • Requires professional installation
  • In off-grid installations it's worth to supplement the system by a diesel or a propane genset
WIND GENERATORS with BATTERY and DC-AC INVERTER
  • A wind turbine converts wind energy into electric energy. Includes a battery bank, charger and grid tie DC-AC inverter with auto transfer switch
  • May be used primarily in rural areas
  • Uses renewable energy
  • Federal and state incentives
  • Defrays energy cost or even let you sell electricity back to utility
  • The second most expensive type after solar
  • Limited run time [depending on the battery tank's capacity]
  • Requires a tall tower
  • In off-grid installations it's worth to supplement the system by a diesel or propane genset