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System Design

Introduction

There are two primary steps to designing a renewable energy system.

1. Determine how much energy must be produced to meet the expected electrical loads. This is called an energy budget.
2. Assess the amount of energy available from various resources and select the right equipment to capture available energy and store it for later use. Please see the sections on PV, wind or micro hydro design.

Power Consumption
The most important factor to consider in designing a power generating system is knowing the amount of power that will be consumed. It is critical to know where the power is going. A poorly designed system will produce too little or too much power. In order to get the best value for your money it is important to compile accurate information on how the power will be used. This is done with an energy budget.

Energy Budget
An energy budget is used to assess the electrical loads in a residential renewable energy system. An energy budget requires you to depart from our traditional concept of electrical supply. An energy budget is a list of all your electrical appliances and the energy they use

Electricity must be viewed as a finite commodity like flour, firewood, or money.

Conservation
You may want to prepare your energy budget a few times to see if you can reduce your projected energy needs. The most cost effective method of conserving energy is by using energy efficient appliances.

A 15 watt compact fluorescent tube will produce the same light intensity as a 60 watt incandescent bulb. The energy you save by using the 15 watt compact fluorescent tube for three hours is equivalent to the daily output of one 45 watt solar module.

Energy conservation is less expensive than energy generation.

Our ConServ and Sunfrost refrigerator / freezers may seem expensive initially, but when you compare that to the number of solar panels required to run a conventional appliance, it becomes much more favorable.

Rated Watts
To complete your energy budget you will need to know the rated watts of the appliances you plan to operate. If you do not know the rated watts of an appliance, try looking at its nameplate usually located near the power cord.

The nameplate (generally located on the bottom or by the power cord of an appliance) may list the power consumption of the device in amps instead of watts. Multiply the amps by the voltage to determine rated watts.

For example, if your blender says 4.5 amps and 120 volts AC on the back, then multiply 4.5 by 120. The rated watts of the blender is 540 watts.

Watts = Amps x Volts

Loads and Operating Time
To assess the viability of large intermittent or small constant loads, the concept of load vs operating time is essential. The energy consumed by an appliance is a factor of the load in watts multiplied by the run time. For example, operating a large load like a microwave at 1000 watts for six minutes is the same as operating a 50 watt light bulb for two hours.

Fine Tuning
If you use your electrical system only on weekends and holidays, your energy budget will have a much lower average daily load than a full time system. The system has an entire week to charge in preparation for your weekend holiday.

There may be some loads you prefer to operate from a generator, such as a washing machine or large power tools. These loads should not be listed in the energy budget because they will not be drawing energy from your storage battery. Watch out for appliances that have built in clocks or instant-on features. These will continue to draw power even when you think they are turned off. We call these "phantom loads".

Phantom Loads
Many people do not realize that most appliances consume electricity even when they are "off" Many electronic products such as stereos, TV's, clock radios, computers and items with wall cube transformers draw constant power. This is generally a result of poor electronic design - cheaper components generally use more power and are less likely to have power saving features such as automatic power off. Multiply this by millions of households, and we have significant power that is being wasted on these poorly designed products. Connecting these items to a power bar and turning it off can help reduce this wasted power.

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