Feb 102012
 

Electricity for the home can be generated in a number of ways depending on the energy source. Below we will review your main options and power generator types.

ENGINE GENERATOR SET

The most common type of backup power source for the home is a set consisting of an electric generator and an engine, also known as genset. It contains a small engine (motor) that runs on a fossil-based fuel, such as natural gas, propane or gasoline. The motor drives an alternator that produces AC voltage. Electric power generators are available in a wide range from 500 watt to tens of kilowatt, so you can always find the right size for your power demand. These devices can generate electricity for as long they are supplied with fuel. This can be both an advantage and a disadvantage. On one hand, if you have a continuous fuel supply, such as a natural gas line, you can be getting emergency power practically indefinitely. Such a permanently connected genset is the only type of system suitable for long-term blackouts. On the other hand, unlike renewable energy, fuel supply to a genset can be interrupted, in which case it becomes is useless.

SOLAR POWER

Solar powered generators use sunlight as “fuel.” The energy carried by sun rays can be converted to electricity in photovoltaic (PV) cells. It is known that regardless of size and technology, the output of a single-junction cell is always less than 0.7V. Therefore, many cells have to be interconnected into panels to yield higher voltages. Most commercially available panels are rated between 50 and 300 watt. To produce power sufficient for an entire home, multiple panels in turn have to be interconnected into arrays. PV cells can produce only DC voltage. The DC voltage from a PV array is converted into conventional AC by electronic devices called inverters. If there is excess of generated energy, it can be stored in batteries and used for power backup. Today’s an average installed cost of a complete solar system with a grid-interactive inverter is about $7,000 per kilowatt. For a homeowner, more than half of this cost can be offset by various incentives and rebates. There are even programs with free installation. Note that because of the low energy density of the batteries, the backup time is usually low – probably a few hours, unless your electricity consumption is really low. Therefore, this type of generator is not very helpful during lengthy outages.

WIND POWER

The main component of wind-powered systems is a wind turbine. Just like gensets, it includes an alternator that converts mechanical energy to electrical energy by using electromagnetic induction. The difference is that in the turbine the mechanical energy is produced by blades that are driven by wind. Residential grade wind turbines normally produce non-regulated AC voltage with variable frequency and magnitude. This voltage is then has to be rectified and converted into a regulated fixed-frequency household AC by solid-state inverters.
The average installed cost of a complete residential wind power system is $4,000-6,000 per kilowatt prior to credits and rebates.

Just like in solar systems, a portion of the wind energy can be stored in batteries and used for short-term backup purposes. Although, unlike sunlight, winds can blow both during the day and at night, they are still intermittent by nature and can’t be relied upon in an emergency. Therefore, wind systems alone just like solar ones generally are not useful during long-term outages. Those who live off-grid normally supplement them with another power source, such as an electric generator.

BATTERY BACK UP

For a few hours, electricity to the home can be provided by a battery backup system. Its main components are an inverter, a battery charger, and transfer relays. The charger will maintain the batteries under normal conditions. When the power goes out, the inverter will provide electricity to selected lines or the whole house. Unlike all other types of power generators, all parts of such systems can be installed indoors. This is big advantage. Many power interruptions happen during winter. You don’t want to drag a portable genset through a 2-feet snow! Unfortunately, as mentioned above, batteries have relatively low energy density. Therefore battery backup systems may be useful in case of short-term rolling blackouts, or if you want to maintaine only small critical loads with very light power consumption. However, it is impractical to store enough energy in batteries to supply an entire house for days. That’s why battery-based systems are rarely used in residential homes.