In event of power failure, the critical loads in a house can be powered by an emergency power system. This can be done using an electric or hybrid vehicle. The main loads are the heating system, the refrigerator (and maybe freezer) and for some, a sump pump.
If a house has a gas fireplace, the house can be heated in the winter without need for Alternating Current (AC) power. Also a gas stove can be used for cooking without AC power. For homes with gas furnaces, AC power is needed to operate the controls and circulation fan. At night, low power LED lights can be used.
AC Power from Vehicles
In order to provide 120 Volts AC power from a battery, an inverter is required. It can be connected to the 12 V battery in a vehicle. Electrics and hybrids usually have a 12 V battery to run the instrumentation and lighting in addition to the main high voltage battery power pack. The inverter takes the 12 Volts Direct Current (DC) and produces alternating current and an increase in voltage. Solid state devices are quiet and efficient. Two types are available on the market. The less expensive produce alternating current which is not equivalent to the household electrical grid supply. It is referred to as “dirty” or “wild” AC power. The form of the alternating current is not a pure sine wave. This means certain electronic devices and controls may not work properly and can even be damaged. Most manufacturers of these types of inverters give a list of products that can be powered by the device. Lights, pumps, heaters, coffee makers, some power tools and some devices which use an AC adaptor to convert to DC such as laptop computers are usually included.
For other devices which incorporate computer controls such as modern appliances and desktop computers, a pure sine wave inverter is required. Several models are given below.
To power a sump pump, a non-pure wave inverter can be used. These pumps use about 250 Watts (1/3 HP) and the total power consumed depends on how long the pump runs. A 300 Watt inverter with start-up surge provision would be adequate.
Newer refrigerators use about 400 Watts with 3.5 amps and maximum draws of up to 650 Watts. In winter, food can be put in the garage or outside when temperatures are below freezing (0F/-18C) for the frozen food or at 40F/4C for refrigerator food. It can be disconnected if the sump pump needs to run. The daily load is 1.65 kWh or about 4 hours of run time, or about 3.5 x 4 = 14 Amp-hours. The refrigerator should have pure sine wave AC to ensure operation of the electronic circuits.
Other devices have power ratings identified on them. LED lights consume about 2 to 12 Watts each.
The minimum power requirement of an inverter during a power failure would be about 300 Watts. For most, a preferred level of comfort would be a 1000 Watt unit. A rule of thumb for cost of inverters is about $1 per Watt retail and discounts are available. So a 1000 Watt unit would cost between $750 and $1000.
Car and Inverter
To use a vehicle to power equipment, an extension cord can be run to the device from the inverter connected to the vehicle’s 12 V battery terminals under the hood. The Prius and other hybrid cars are designed to run the gas engine only when needed. If all accessories are off, it should only run when the inverter drains the car battery to the recharge level. The 12 V power outlets inside the car should not be used as they are rated at 10 Amps maximum and are not capable of running a refrigerator which requires 400 Watts/12 Volts = 33 amps. The Inverter can be connected directly to the battery at the jumper terminals under the hood. The Prius would operate until the gasoline runs out. This would take several weeks.
For all electric cars, the inverter can be connected in a similar way but attention is required for operating time. With a full charge, the electric vehicle will produce power for a given time depending on the requirements of the appliance. For example, a Nissan Leaf has battery capacity of 24 kWh which can be a variety of combinations of kiloWatts and hours. If we look at a 400 Watt refrigerator or 0.4 kW, it would operate for 24/0.4 = 60 hours. As mentioned above, the refrigerator runs about 4 hours a day so the car would provide power for 15 days before needing recharging. This is quite unlikely as most power outages are less than a week. If longer, there is the possibility of driving the car to a charging station while the refrigerator is not opened.