New England Solar Electric, Inc.

Introduction
In the past, most of our business has been with people powering off-grid homes. Recently more and more people have begun to consider an alternative power supply for their homes in case of power grid failure. Supplying backup power for a home tied to the power lines is an entirely different problem than supplying primary power for an alternative energy home. In the next few pages we will try to describe how to provide emergency power for the necessary items in your home--usually central heat, refrigeration, water pumping and lighting.

Solar Power/Wind Power
Many people hope that solar panels or a wind turbine can provide backup power for their homes. They are crestfallen when we tell them that this probably won't work for them. A typical home connected to the power lines consumes about 25 kilowatt hours per day on average. This does not include electric power for hot water, space heating or air conditioning. Making 25 kW-hrs of electricity per day is nearly impossible using alternative energy methods. In the northern latitudes $6500 worth of solar panels produce 6 kW-hrs a day, on average in the summer and only 3 kW-hrs a day in the winter. That's little more than one-tenth the power required for an average American home. A normal refrigerator uses roughly 2kW-hrs a day. A central heating system may use as much as 3 kW-hrs a day just for pumps and motors.

An alternative energy home is designed to use only a small amount of electricity. Cooking, hot water heating and space heating all utilize some form of energy other than electricity. In the northern latitudes most people must use a gas refrigerator. Once these major electrical loads are shifted to another energy source, the remaining necessary electrical loads are made as efficient as possible. Compact fluorescent lighting is used throughout the home. A water pump is sized just large enough to do the job. Appliances are chosen for their frugal use of electricity. Nothing is left on when not being used. Appliances with phantom loads such as TV cathode heaters and digital clocks are placed on switched outlets. With a little extra effort one can actually live quite comfortably on alternative energy.

Alternative Power for the Conventional Home
Unfortunately most homes in the U.S. are not designed with frugal electrical use in mind. So how does the homeowner provide an alternative power source for a conventional American home when the grid fails? The first step is to decide which items need to be powered when the power grid fails. In limited situations solar modules may be used, i.e. to run a water pump and some lighting. Some may even want to add a freezer, TV, and a computer. (Keep in mind electric heat, electric hot water and air conditioning are really not possible for an affordable backup power system to deal with. One could buy a very large generator and run it 24 hours a day, but this isn't really practical unless you have unlimited means.)

The only practical way to provide emergency backup power is with the use of a generator and an inverter/battery system. This combination is called a Generator/Charger System. Despite its lack of "greenness" a generator is the only affordable way to produce the 4 to 8 kW-hrs a day necessary to power the essential items listed above.

Generator Selection
The first step is to pick a generator. A 4 kW to 10 kW generator should do. Fuel choice is the next variable. Gasoline generators are the least expensive and probably the easiest to procure. They are usually portable and easy to move. But gasoline has its drawbacks. It may not always be available when you need it. Additionally, storage of gasoline is difficult and dangerous.

LP gas (propane) or diesel generators perform well in a home backup situation, but they are much more expensive than portable gasoline generators. Commercial grade (1800 rpm) generators will last much longer than a gas generator. They can be remotely started and they can usually be configured for full 120 volt output, a benefit when used in conjunction with an inverter. Fuel can be stored in underground tanks in the case of LP gas or in large above ground tanks for either fuel.

We recommend a small portable gasoline generator for our alternative energy customers who are living mainly on solar and/or wind power. They will probably need it only a few times each winter and can easily move it to different locations for other uses during the year. This type of generator is a good choice for alternative power for the home as long as it is sized large enough to power the necessary loads.

For our customers who run businesses in their homes which would use more energy than the typical household, we usually recommend commercial grade LP gas or diesel generators for their longevity. Likewise, those homeowners who want to power relatively large loads during power outages may want to consider a larger, commercial grade generator, especially if cost is not the main factor.

Inverter Selection
An inverter is a device that converts DC electricity stored in batteries to the AC electricity we use in our homes. The inverter provides the back up power most of the time. The generator is run only 2 to 3 hours a day to recharge the batteries. The charging process is performed basically by running the inverter backwards as a battery charger. Since selecting an inverter can involve many different variables, its best to discuss that topic in detail on an individual basis. The discussion below is meant to give you an idea of how this process might evolve.

There are two basic kinds of inverters and a full range of sizes. The AC loads you want to power--both their size and type--will determine which inverter you choose.

Typical inverters range in size from 1500 watts to 5500 watts. The need to power a water pump usually determines how large an inverter you would need. If powering a water pump is not necessary you may be able to provide backup power to your home with as little as a 1500 watt inverter. On the other hand if you have a one horse power submersible pump you'll need a 4000 watt (4kW) inverter. The most common household water pump is a one-half horse power submersible pump. This pump would require at least a 2400 watt inverter, or a larger one if you hope to run both a refrigerator and freezer as well as the pump.

The type of inverter you choose will depend on what kinds of loads you want to power. There are two types of inverters: a sine wave inverter and a modified sine wave inverter. Sine (pronounced 'sign') and modified sine refer to the type of wave form each inverter produces. Sine wave power is the type of power the grid supplies. Therefore a sine wave inverter is the 'best' type and is at least twice as expensive as a modified sine wave type.

Fortunately a modified sine wave inverter will power most necessary household loads including refrigerators, freezers, pumps and all motors, most TV's and stereos, PC computers and of course lighting. Central heating controls might be a problem when run on a modified sine wave inverter. Laser printers and personal copiers most likely will not work properly, and in some cases may even be destroyed by modified sine wave inverters! Other than central heating controls, some of the above equipment isn't really necessary in an emergency back up situation. And after talking with other vendors, it seems most Honeywell heating controls will work on modified sine wave inverters. A sine wave inverter produces electricity very close to power grid quality and so will power anything the grid is able to power.

We recommend using a sine wave inverter if you can (or want to) afford one. They have the advantage of being able to power anything, both now and in the future. If its just basic back up of a water pump, refrigerator, lighting and possibly a central heating system that you want to power, a modified sine wave should do just fine. They have the advantage of being much less expensive than a sine wave inverter. Consult the adjacent chart for other differences between the two inverter types. Also consult the Inverter section of this catalog on pages 50-53 and the Generator/Charger Kits on pages 46-49 for more detailed information.

Equipment Installation
Once the equipment is selected, it must be installed so it can safely provide back up power to your chosen loads. In almost all cases this installation will be performed to National Electrical Code Standards. It is important for you to understand what this entails. There are several methods possible for equipment installation, all of which will most likely require the services of an electrician. Diagrams are provided for the most common system designs. These should help both you and your electrician understand how an inverter is installed in a home back up system.

The first thing to consider is system voltage. An inverter is a 120 volt device. Most of the appliances and systems you want to provide emergency power for also require 120 volts. The one exception is the water pump. It is usually a 240 volt device. This problem can be solved either by using a transformer to convert the 120 volts to 240 volts or by purchasing a second inverter. Two inverters of the exact same model can be "stacked" together to provide 120/240 volt power. In some instances, depending on the size of the pump and the type of generator being used, this might be the preferred method. Using a transformer is a less expensive and more common solution.

It is very important when supplying emergency power to your home not to supply it back to the power grid! This is an obvious danger to any lineman working on the power lines. Needless to say, it is also illegal and violates the electrical code. Conversely, if grid power is directed to the inverter's output, the inverter will be permanently damaged.

Three devices, either alone or in combination with one another, may be used to integrate the inverter and generator into your electrical system. They are a generator switch, a sub-panel or a device known as a Gen-Tran. The generator switch disconnects your main AC distribution panel from the power lines and reconnects it to your inverter/generator power supply. The switch must be thrown manually when loss of grid power occurs. A Gen-Tran (stands for generator transfer) performs much the same function, only with a few selected circuits in your main AC distribution panel instead of switching the entire panel. The use of a sub-panel is in many ways the most elegant solution. All the device and system circuits to be backed up would be moved from the main AC distribution panel to the sub-panel. The inverter would literally be wired between the two panels getting its input from the main AC panel and feeding its output to the sub-panel. Under normal circumstances the inverter would simply transfer the grid power from the main panel to the sub-panel. If grid power was out for only a day or two, most likely you wouldn't need to run your generator--the battery bank and inverter would be able to provide the emergency power necessary. When the power grid was re-energized, it would automatically recharge your battery bank. If, however, the power was off for a longer period of time, the generator would be connected to the inverter. Then it would be run to recharge the battery bank as needed--normally only 2 to 3 hours a day.

There are different reasons to use different combinations of the generator switch, Gen-Tran, and sub-panel. The size of the generator, the number of inverters involved, and the type of loads to be emergency powered are some of the determining factors. The drawings below are meant to give some idea of the various combinations possible. You are certainly welcome to consult with us to help you decide which equipment to use and how to integrate it into your electrical system. We urge you to consult with an electrician before attempting any rewiring of your home.

Advantages:

• Least Expensive
• Auto AC Switching
• Auto Battery charging

Disadvantages:

• Selected Circuits Only
• Only 120V Operation
• Need transformer for 240V Pump
• Only one AC Input at Inverter

Example #3: Generator with Switch to AC Main Panel Inverter Feeding AC Sub-Panel

Advantages:

• Generator can Power Entire House
• Auto AC Switching at Sub-Panel
• Auto Battery Charging

Disadvantages:

• Backup Selected Circuits Only
• Only 120V Operation at Sub-Panel
• Need Transformer for 240V Submersible Pump
• Only 1/2 Generator to Charge Battery bank
• Expensive Equipment and Installation Costs

Advantages:

• Generator can Power Entire House
• Can Use Two Small Inverters to Power Large Loads
• Auto AC Switching at Sub-Panel
• Auto Battery Charging
• Full 120/240V Operation
• Can Use Full Generator Output

Disadvantages

• Backup Selected Circuits Only
• Expensive Equipment and Installation Costs

Advantages:

• Generator can Power Entire House
• Inverters Can Power Entire House
• Full 120/240V Operation
• Can Use Full Generator Output

Disadvantages

• Manual Switching
• No Automatic Battery Battery Charging(Must Run Generator)
• Expensive Equipment Costs

Advantages:

• Least Expensive Installation
• Least Disruptive of AC Wiring
• Extra Equipment Out of Circuit Path

Disadvantages

• Manual Switching
• No Automatic Battery Battery Charging(Must Run Generator)
• Selective Circuits Only
• Can Use Only 120V Power from Generator
• Need transformer for 240V Pump
• Manual Battery Maintenance

Advantages:

• Least Disruptive of AC Wiring
• Extra Equipment Out of Circuit Path
• Full 120/240V Operation
• Can Use Full Generator Output

Disadvantages

• Manual Switching
• Manual Battery Battery Charging(Must Run Generator)
• Selective Circuits Only