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
PORTA-BLE GENE-RATOR	Runs on gasoline, diesel, propane, or natural gas (depen-ding 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 profes-sional instal-lation 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 refuel-ing) unless hooked up to an external fuel source Very noisy No auto start Requires mainte-nance Burns fuel even when it idles	Must be run outdoors only Potential fire and carbon monoxide hazard if used improperly
STATIO-NARY STANDBY SYSTEM (WHOLE HOUSE GENE-RATOR)	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 black-outs and as the whole house genera-tor Typical transfer time with auto transfer switch: 10-30 seconds	Auto start option on many models Practi-cally infinite run time when connected to natural gas line	Expensive Requires profes-sionally installed transfer switch and fuel line Older homes may require a new higher volume natural gas meter Requires mainte-nance	Instal-led outdoors on a cement pad and connect-ed via a transfer switch
BATTERY BACKUP WITH DC-AC POWER INVERTER - CHARGER	Powers critical applian-ces via extension cords. May be perma-nently connected to the house wiring via a transfer switch Typical power for residen-tial use: 5-10 kW Auto start systems have response time 16-36 ms	No mainte-nance required Silent May be installed indoors Low power consump-tion at no load (consumes power according to the actual load demand)	Limited run time (typ. 2 to 12 hours) depending on the battery tank capacity	Look for a sealed deep cycle battery and a tempera-ture compen-sated charger with a trickle mode to avoid battery over-heating

BACKUP HOME GENE-RATOR VIA VEHICLE	Good for short outages and to power only essential loads Typical power 300 W- 5000W depen-ding on the battery capacity and inverter	Lowest cost No profes-sional instal-lation 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 electro-cution hazard
SOLAR PANELS with a BATTERY SYSTEM and DC-AC INVERTER - CHARGER	Photo-voltaic (PV) panels charge battery bank Produces electri-city 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-inter-active type of inverter with a transfer relay)	Utilizes renew-able energy Silent No mainte-nance required Defrays energy cost or even let you sell electri-city back to utility Federal and state incentives	The most expensive type Limited run time [depen-ding on the battery tank's capacity] Requires profes-sional instal-lation	In off-grid instal-lations it's worth to supple-ment the system by a diesel or a propane genset
WIND GENERA-TORS 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 Suitable only for rural areas	Uses rene-wable energy Federal and state incentives Defrays energy cost if you are on grid	The second most expensive type after solar Limited run time [depen-ding on the battery tank's capacity] Requires a tall tower Noisy	In off-grid instal-lations it's worth to supple-ment the system by a diesel or propane genset