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Energy, Energy Measurement and Calculations Energy: the ability to do work - movement, heating, cooling, manufacturing Types: Electromagnetic: light – solar power - photovoltaics Thermal: Heat – geothermal Kinetic: motion – turbines Nuclear: breaking apart nuclei Electrical: energized particles (electrons) Chemical: coal, oil, natural gas, galvanic cells (batteries) Sources of Energy: Renewable and Non-renewable: Non-renewable: Oil Coal Natural Gas Oil Shale Fissionable Material (Nuclear) Renewables: Solar Wind Water: Hydroelectric dams, tides Geothermal Biomass Biofuels Net Energy Definition: The total useful energy available from the resource over its lifetime minus the amount of energy used (1st law of energy), automatically wasted (2nd law of energy) and unnecessarily wasted in finding, processing, concentrating and transporting it to others. Measuring Energy HEAT: 1 Food Calorie = 1 kilocalorie (1 kCal or 1 Cal) = 1000 calories 1 calorie = the amount of heat required to raise the 1 gram of water 1 oC As a measure of heat 1 calorie = 4.186 Joules 1055 Joules = 1 BTU (British Thermal Units) Measuring Energy Electrical Power = Watt = amps x volts Amp = the number of electrons flowing through the wire = current 1 amp = 6.241 × 1018 electrons passing a point at one time Volts = the force of the electrons (pressure) Watt = Joules/sec Watts (the work done) = Amps (the resources consumed) times Volts (the strength of the resource units) The amount of worked performed by a circuit today was 100 watts. It did it with 100 amps. It didn't take much force since it had so many amps. It only took 1 volt. If there were only 50 amps, it would take twice as much force. It would take 2 volts. If there were only 25 amps, it would take four volts. ............................ My men lifted 100 lbs today (watts). Their labor contract said they were only allowed to lift 1 pound each (amps). It took 100 men (1 volt each) to lift the 100 pounds. The labor union renegotiated, and they can now lift 2 pounds each (amps). It now only takes 50 men (2 volts each) to lift the 100 pounds. I'm trying to renegotiate for them to lift 4 pounds each (amps). That way, it will only take 25 men (4 volts each) to lift the 100 pounds. Electrons do the work and the more that come through a gate and the speed at which they pass through, the more work (watts) can be done. The gate restricts how many electrons can pass through at the same time. The gate (wire) size dictates this number and think of this number as amps. Now the electrons can flow through the gate at different speeds (voltage) and the faster they go through, the more energy or power they impart (Watts). Watts = Amps X Volts It helps me to think of the electrons moving through the wire as I can see that amperage capacity is then a function of wire size (how many electrons can fit in the gate or tunnel cross section) and then I visualize the speed at which they are moving as the voltage or velocity. To use this analogy further, consider a resistor or resistance as speed bumps [img]images/icons/grin.gif[/img] The electrons are slowed down at this point and a voltage drop occurrs. As the electrons hit the speed bumps and are slowed, energy is lost. Another reason I like to think of voltage being the velocity of the electrons is that I can visualize electrons speeding through a wire and if they come to a gap in the wire, the faster they are moving, the farther I can see them successfully jumping across this gap (arc). The greater the voltage, the greater the arc. Utility companies usually measure in kilowatts 1 kW = 1000 W Electricity is billed by the amount used (demand) and the time it was used (kWh) Understanding Electricity Billing Watts The rate of electrical use at any moment is measured in watts. For example: A 100-watt light bulb uses 100 watts or 100 J/s. A typical desktop computer uses 65 watts or 65 J/s. A central air conditioner uses about 3500 watts or 3500 J/s. Watt-hours To know how much energy you're using you have to consider how long you run your appliances. When you run a 1-watt appliance for an hour, that's a watt-hour (Wh). One 100-watt light bulb on for an hour is 100 Wh One 100-watt light bulb on for five hours is 500 Wh Five 100-watt light bulbs on for an hour is 500 Wh Why is 100 Wh a measure of power? Watt = J/s # Watts X 1 hour (3600 sec) = # Joules Kilowatt-hours 1,000 watt-hours is a kilowatt-hour (kWh). For example. One 100-watt light bulb on for an hour, is 0.1 kWh (100/1000) One 100-watt light bulb on for ten hours is 1 kWh (1 bulbs x 100W x 10h= 1000Wh = 1 kWh) Ten 100-watt light bulbs on for an hour, is 1 kWh (10 bulbs x 100W x 1h= 1000Wh = 1 kWh) Ten 50-watt light bulbs on for an hour, is 0.5 kWh Ten 100-watt light bulbs on for 1/2 an hour, is 0.5 kWh Running a 3500-watt air conditioner for an hour is 3.5 kWh. Note the difference between kilowatts and kilowatt-hours. kilowatt = rate of power at any instant kilowatt-hour = amount of energy used for a given amount of time A light bulb doesn't use 60 watts in an hour, it uses 60 watt-hours in an hour. Since utilities measure usage for an entire building, they use kilowatts or thousands of watts. Utilities refer to the monthly kW reading as demand. Demand is the actual wattage consumed. Most utilities charge residential and small commercial customers only for the energy, or kWh, they use in a month. However, for larger commercial and industrial customers, most utilities will base the charges on both the energy and the monthly demand reading. Utilities base the demand charge on the highest fifteen or thirty minute average demand that occurs during a month. Sometimes a rate schedule is set up to include a " billing demand". The billing demand is the highest of either the current month's demand or a percentage of the highest demand from the previous eleven months. How much does electricity cost? The cost of electricity depends on where you live, how much you use, and possibly when you use it. There are also fixed charges that you pay every month no matter how much electricity you use. For example, $6/mo. for the privilege of being a customer of the electric company, no matter how much energy used. Most utility companies charge a higher rate when you use more than a certain amount of energy, and they also charge more during summer months when electric use is higher. As an example, here are the residential electric rates for Austin, Texas (as of 11-03): First 500 kilowatts hours 5.8¢ per kilowatt hour (kWh) Additional kilowatts hours (May-Oct.) 10¢ per kilowatt hour Additional kilowatts (Nov.-Apr.). 8.3¢ per kilowatt hour These figures include a fuel charge of 2.265¢ per kWh. An additional charge based on the maximum amount of electricity you draw at any one time. This is called a demand charge. The following chart from Wisconsin Electric illustrates the concept. The shaded area is how much electricity you used, and you know you get charged for that. But the black bar on top is the demand, how much energy you "demanded" at any given point throughout the day. If your utility company has a demand charge (ask them), then you can save money by spreading out your electrical use. For example, run a washing machine and dryer one after the other rather than at the same time. And better yet, run them when you're not using much electricity for other purposes (such as at night when the air conditioner is off). Calculating Energy Costs and Savings Example 1 A small commercial customer replaces 100 60 watt incandescent lamps with 100 - 15 watt fluorescent lamps. The lamps operate eight hours per day, five days per week, year round. Their utility charges them $0.08/kWh. To calculate the energy savings, just figure the difference between the existing energy usage and the proposed energy usage. Existing Energy Usage 100 lamps times 60-watts per lamp 8 hours per day Five days per week 52 weeks per year 1000 watts per kilowatt The Proposed Energy Usage 100 lamps 15-watts per lamp Eight hours per day Five days per week 52 weeks per year 1000 watts per kilowatt The Cost Savings To calculate the cost savings, just multiply the annual energy savings times the charge per kWh for electricity (eight cents in this case). Example 2 Let's take this same scenario, but this time let's assume there is an additional demand charge of $9.75/kW. Demand Savings equals existing demand minus proposed demand Existing demand 100 lamps times 60-watts 1000 watts per kilowatt. Proposed demand 100 lamps 15-watts per lamp 1000 watts per kilowatt Demand savings per month and per year Example 3 If a customer's maximum or peak demand occurs at 2:00 PM because of air conditioning, and the lights are operating on a time clock from 6:00 PM to 6:00 AM, then the lights do not contribute to the peak demand. Making a change to the lighting demand does not affect the customer's demand charges. For example, the previous situation of 100 lamps being changed would save only energy costs, not demand if these lamps are located outdoors and operate only at night.