Below is an introduction to "The Alternate Power Calculator." The calculator is an educational tool that will help you understand the requirements and limitations of using alternate energy sources such as solar or wind power. How to use the calculator: The Load Table 1. You can input up to 10 loads. The entries must be in watts. If you have more than 10 loads you can always add similar loads together. Three 100 watt lights are the same as a 300 watt load. Note that surge loads have to be combined with other surge loads. 2. Next to the load inputs there will be a radio button. Select this button only if the loads are surge loads. Remember surge loads are appliances such as florescent lights, motors, pumps, and air conditioners. 3. Select the button labeled “Next.” Calculator screen 1. Enter your battery voltage. 2. Enter your total load run time in hours. 3. Enter the distance between the battery bank and the inverter (inverter/charger) in feet. The answer will be the distance “ONE WAY.” 4. Check the box if you require a true sine wave inverter. 5. Record the results (press "Ctrl P" to print screen). Solar Panel Sizer The DC load watts and run time (Hours) are carried over from the “Inverter Sizing” portion of the program. You must enter the “Average Peak Sun Hours” for your location. The “Average Peak Sun Hours” for your location can be found on various websites. I included a reference site below. Next, you must enter the size (in watts) of the solar panels you plan to use. The program will provide the minimum number of solar panels required to run your loads. NOTE: Since you cannot have a partial solar panel, the program rounds up. The result will be the lowest integer above the calculated value. If the calculated value is an integer (very rare) an "n+1" result may occur. Wind Turbine Sizer The internet has many great sites, such as the Iowa Energy Center, dedicated to wind power and I was able to research a formula for wind turbine power in DC watts. Many sites state the base formula: Power (Watts) = ½ (air density * rotor swept area *(wind velocity) ^ 3) Where air density is found by the formula: p = (1.325 * pressure in inches mercury) / temperature (Fahrenheit + 459.69) And where rotor swept area is found by the formula: A = π * (rotor radius) ^ 2 However, these formulas are for a perfect world and lack the inefficiencies of power conversion. In 1919, a German physicist named Albert Betz stated that you can only capture a maximum 59% (0.59) of the wind power available. This is known as the Betz Limit or coefficient of performance (Cp) and typical results are 35% - 45%. Eric Eggleson states in his 5 February 1998 article “How can I calculate the amount of power available at a given wind speed?” that the efficiencies of the gear box and generator should also be included in a wind power formula. Even though some sites had simplified formulas, I decided to use the formula listed below. Power (DC Watts) = ½ (air density (kg/m^3) * rotor swept area (m^2) * (wind velocity (m/s)) ^ 3) * Betz Limit (coefficient of performance) * gearbox efficiency * generator efficiency In my program you can calculate the missing value, such as rotor swept area, if you have all the other values. My present program will require you to know the air density and rotor swept area. A future program may also allow you to calculate these values. As with any formulas used in this program, if you have a concern, please send me an email. References Danish Wind Industry Association, “Wind Turbines: Energy from the Wind” Eric Eggleson (5 February 1998) “How can I calculate the amount of power available at a given wind speed?” www.awea.org Practical Action, The Schumacher Centre for Technology and Development “Wind electricity generation” www.energy.iastate.edu , Iowa Energy Center www.flexploring.com www.omafra.gov.ca Micro-Hydro Size Calculator Testing stage: To be released shortly The latest feature is the micro hydro size calculator and is presently in testing stage. I used the formula: Power (kW) = Flow (m^3/s) * Gross Head (m) * gravity (9.8 m/s^2) * efficiency (0.5) The formula as well as test data was provided by National Resources Canada. However, National Resources Canada’s website states efficiency at 0.77 to 0.88, but their publication Micro-Hydropower Systems: a Buyer’s Guide (2004) states efficiency at 0.5 for small systems. As my program is an educational program, I used the lower efficiency. If anyone has any comments regarding the efficiency or formula, drop me an email. The program finds “Gross Head” and “Flow” based on known data. The program has one known glitch which I have not solved yet. The inputs for the calculator require a specific format. All decimal values less than "1" will require "0" placed in front of the decimal. i.e. 0.59. Also, all integers must have a decimal and "0" placed after it. i.e. 1.0 or 5.0. Related Terms Voltage: Electrical pressure. Alternate energy typically is available in 12, 24 and 48 Volts. Household appliances typically use 115 or 220 Volts. Alternating Current: Electrical current found in most homes and allows most household appliances to operate. Alternating current cannot be effectively stored. Direct Current: Electrical current that can be stored in batteries such as those in your car. Sources of Alternate Energy: These can be wind generators, solar panels or anything that can create a DC power source. Charge Controller: An electronic current and voltage regulator used to convert raw alternate energy, such as solar, so that you can effectively charge a battery. Load: An electrical appliance or motor is called a load. Loads are typically rated in watts. IE 100 watt light bulb. Surge: Certain electrical loads such as florescent lights, motors, pumps, and air conditioners have start up surges. Each load will have a different surge but my experience is that surging loads will surge 4 times their ratings. IE a 1000 watt air conditioner will surge 4000 watts. Battery: A device that can store direct current (DC). Most batteries used in alternate energy applications are lead acid batteries. Battery Bank: More than one battery in series or parallel. Amp hour: Batteries are rated in amp hours. An 8 amp hour battery can run a 1 amp load for 8 hrs. However it is standard practice not to deplete a lead acid battery lower than 50%. Series: Two batteries placed in series doubles their voltage but their amp hour rating is maintained. IE 12VDC/ 8 amp hours + 12VDC/ 8 amp hours = 24VDC / 8 amp hours. Parallel: Two batteries placed in parallel doubles their amp hour rating but their voltage is maintained. IE 12VDC/ 8 amp hours II 12VDC/ 8 amp hours = 12VDC / 16 amp hours. Power Inverter: An electronic device that takes DC power stored in a battery bank and converts it to AC power to operate house hold appliances. There are three types of inverter outputs, square wave, modified sine wave and true sine wave. Square wave is rarely used anymore and will not be discussed further. Inverters have operating input voltages and typically have automatic shut offs when the input voltage gets too low (battery dies). Inverters typically will handle load surges 2 times their rating. IE a 1000 watt inverter will handle a surge of 2000 watts. True sine wave inverters generally handle surges better than modified sine wave inverters. Modified Sine Wave: A close replica of the electrical output from your utility company. They will operate most but not all loads properly. CHECK WITH THE LOAD'S MANUFACTURER OR THE INVERTER'S MANUFACTURER BEFORE USING A MODIFIED SINE WAVE INVERTER ON A SENSITIVE OR IMPORTANT LOAD. True Sine Wave: An exact or near exact replica of the electrical output from your utility company. True sine wave inverters are required for loads such as some battery chargers and some medical equipment. Battery Charger: An electronic device that converts AC power to DC power. Batteries can only store DC power. Inverter / Charger: An electronic device that works as an inverter when DC power is applied and as a battery charger when AC power is applied. Voltage Drop: Even the best cables placed between your batteries and your inverted will have a voltage drop due to resistance in the cables. It is best practice to limit your voltage drop to below 0.2 volts by using the right size cables. Too small of cables will create an excessive voltage drop which will shut off your inverter or limit your load's run time. Using too large of cables will just decrease voltage drop. Cable Size: Cable sizes are given in units of CMA and more commonly used AWG. Related Formulas Watts = volts * amps Total watts = watts 1 + watts 2 + watts 3 +watts n DC Amps = Total watts / (battery voltage * 0.85). The 0.85 is to compensate for system efficiency. Surge of load = load watts * 4 Surge of inverter = inverter watts * 2 CMA = DC amps * feet (one way) * 2 * 11.1 (constant for copper) / 0.2 (recommended voltage drop) CMA to AWG / MCM 0 - 1620 = 18 AWG 1621 - 2580 = 16 AWG 2581 - 4110 = 14 AWG 4111 - 6530 = 12 AWG 6531 - 10380 = 10 AWG 10381 - 16510 = 8 AWG 16511 - 26240 = 6 AWG 26241 - 41740 = 4 AWG 41741 - 66360 = 2 AWG 66361 - 83690 = 1 AWG 83691 - 105600 = 0 AWG 105601 - 133100 = 2/0 AWG 133101 - 167800 = 3/0 AWG 167801 - 211600 = 4/0 AWG 211601 - 250000 = 250 MCM 250001 - 300000 = 300 MCM 300001 - 350000 = 350 MCM 350001 - 400000 = 400 MCM 400001 - 500000 = 500 MCM Solar Sizer Formulas (Beta) I used formulas that I researched from a government website listed below. Watt Hours = Watts * Runtime Hours Number of Solar Panels = Watt Hours / Average Peak Sun Hours / De-rating value of 0.77 / Panel Wattage. NOTE: Some websites use a de-rating value of 0.7, but they did not list their references. Please comment if you feel a de-rating of 0.7 is a better variable. References http://www.nrel.gov/gis/solar.html rredc.nrel.gov Disclaimer The information used in this program is believed to be correct. The program was designed as an educational tool. The creator, distributor and retailer take no responsibility for any loss of property (money), injury or loss of life from the use of this program. Please consult component manufacturers and appropriate laws regarding all limitations and operating parameters before developing an alternate or back up power system. All electrical components should be used under supervision of an adult. All electrical components should be installed by professionals and operated as directed by the component's operating manual. Copyright: 2005-2007