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Sustainable Energy and Energy Systems: Balance Spread Sheet Approach

Sustainable Energy and Energy Systems: Balance Spread Sheet Approach. Lectures 3 ECE 4502/6502 Dr. Carl Elks. Talk about the Semester Project (30 minutes). District Scale PV Plant for UVA – Bring Project document to class everyday… Goals of the Project:

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Sustainable Energy and Energy Systems: Balance Spread Sheet Approach

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  1. Sustainable Energy and Energy Systems: Balance Spread Sheet Approach Lectures 3 ECE 4502/6502 Dr. Carl Elks

  2. Talk about the Semester Project (30 minutes) District Scale PV Plant for UVA – Bring Project document to class everyday… • Goals of the Project: • To understand complex issues of social, economic, and environmental impact of a Renewable Energy project. • Provide credible science and engineering based information to UVA sustainability office for future plans. • To research on a given topic and find evidence to support (or refute) own arguments. • To understand a range of concerns and values held by other people. • To articulate both sides of a story. • To improve group communication skill.

  3. Working Model of Source, Transmission, and Consumptions Sources and Consumption

  4. Model for “Systems” Level View - Balance Sheet Approach: Simplistic but puts things in perspective for “out of the box thinking” • Basic Metrics • Energy Density • Utility • Land use • Water use • Resources • Conversion Efficiency • Energy Consumption Sources • Residential • Industrial • Lighting • Transportation • Etc.. The Renewables Energy Transport: Distribution and Management Non-renewables: Gas, coal Nuclear

  5. Balance Sheet Approach We’re going to make two stacks. In the left-hand, red stack we will add consumption production up our energy consumption, and in the right-hand, green stack, we’ll add up sustainable energy production. We’ll assemble the two stacks gradually, adding items one at a time as we discuss them.

  6. What do we tally in the Boxes • The Red Box • People = How many people per region or country are using power. • Going back to power, I like to use KWhr/d/person as starting point for energy consumption. • We relate to people and energy dependent things in we use. • We add other metrics as needed like Co2 Emissions per sources/ per person. • In the red stack, we’ll estimate the consumption of a “typical middle-income person;” Later on we’ll also find out the current average energy consumption of Americans, Europeans, Asians, etc….There is a big difference. • The aim is not only to compute a number for the left-hand stack of our balance sheet, but also to understand what each number depends on.. Assumptions are important and controversial in Energy analysis – so we need to be clear. • We can do this for each energy consuming sector (residential, Industrial, transportation, etc…)

  7. What do we tally in the Boxes • The Green Box • The green box is what we need to produce to meet our demands for energy. • The green box is more complex because we need to account for impacts related to environment and use. For now we will keep it simple: • Power density - Express power densities as quotient of the flux power with respect to a surface area (W/m2) • Utility - For a sustainable energy plan to add up, we need both the forms and amounts of energy consumption and production to match up. You don’t power your toaster with gas. • Land use – How much Land do we need to generate “x” amount of power – Power density per acre of land or W/m2/person • Water use – How much water is used in the process of making energy. Water is becoming a valuable resource not only human habitation, but ecology as well. • Resources – What do we give up or gain in natural resources for energy production

  8. Calculations and AnalysisStep 1: List all of your energy services and sourcesAs Example:

  9. Calculations and Analysis: Example Transportation Personal Driving Some basics Let’s look at our 30MPG car. A gallon of gasoline contains 36.6 kWh of heat energy when combusted, in this case taking us 30 miles down the road in the process. So this car uses 1.2 kWh per mile. Example: • 5 mi daily from UVA to Downtown (round trip) • 10 mi * 4 days/week = 40 mi / week • Your car: MPG - 30 miles / gallon • A gallon of gas has 36.6KWh of heat energy (87 octane) • KWh/week = 1.33 gallons/ week = 1.33 x 36.6Kwh =48.6kWh/week • Carpool: 48.6KWh/ 2 = 24.3KWh/week (2 people) What if you ride the bus Busses • 1.6 kWh/ mile for each passenger (half full bus) – Based on a 60 person bus • .6 KWh/mile for each passenger (almost full bus)

  10. Hot Water Consumption Heat Energy • Q = m x cp x (T 1 – T2) • cp : specific heat constant, 4190 J / kg C • T 1 : temperature of the hot water • T 2 : temperature of the cold water Example (overly conservative) Carl uses 50 L of hot water per day from an electric hot water system. The water is heated from 18C to 60C. (note this is normal figure for a family of three) The heat energy contained in the water, Q = m x cp x (T 1 – T2) Q = 50 kg x 4190 x (60 C – 18C) Q = 8.8 MJ / day Q = 61.6 MJ/ week Efficiency of Electric Water Heater is 0.7 to 0.8 61.6 MJ / 0.8 = 77 MJ (Efficiency of Gas Water Heater is 0.6 to 0.75) So, 1 KWh = 3.6MJ Q = 77MJ/3.6MJ = 21.3 KWh Alterative method: Most Hot water heaters run for about 3 hours out of every 24 hours. The heating element in the tank is rated in wattage: Normally 2000, 3500, 5000. There are normally 2 elements per tank. If the tank is heating it is consuming energy at the rate of (heating element wattage rating)x(*2) / time. Example: Tank is on for 3 hours a day (2000) x(2)/3 = 1333.3 = 1.333Kwh /day - factoring in efficiency of .7 Q = 1.904 Kwh/day

  11. Household Heating • Roughly speaking, space heating consumes about 10-30% of the total energy used in a household, whereas air conditioning takes up around 20%. • Residence- area heated: 25-170 kWh/m2 • Residence- area cooled: 5-15 kWh/m2 • Residence- total used area: 50-110 kWh/m2 • Residence- Electricity: 40-75 kWh/m2 • The conversion units for the direct energy uses were calculated from EIA (Energy Information Agency) data, the Residential Energy Consumption Survey (RECS) • Large variances due to energy efficiency

  12. Household Heating – Basic Model It is typically modeled in terms of conduction although infiltration through walls and around windows can contribute a significant additional loss if they are not well sealed. Source: http://hyperphysics.phy-astr.gsu.edu

  13. Household Heating – Basic Model (2) I. Calculate wall loss rate in BTUs per hour. For a 10 ft by 10 ft room with an 8 ft ceiling, with all surfaces insulated to R19 as recommended by the U.S. Department of Energy, with inside temperature 68°F and outside temperature 28°F: II. Calculate loss per day at these temperatures. Heat loss per day = (674 BTU/hr)(24 hr) = 16168 BTU Note that this is just the loss through the walls

  14. Household Heating – Basic Model (3) • III. Calculate loss per "degree day“ • This is the loss per day with a one degree difference between inside and outside temperature. • If the conditions of case II prevailed all day, you would require 40 degree-days of heating, and therefore require 40 degree-days x 404 BTU/degree day = 16168 BTU to keep the inside temperature constant

  15. Household Heating – Basic Model (4) • IV - The typical heating requirement for an Atlanta heating season, September to May, is 2980 degree-days (a long-term average). • The typical number of degree-days of heating or cooling for a given geographical location can usually be obtained from the weather service.

  16. Household Heating – Basic Model (4) • V. Calculate annual heating cost. • Calculate heat loss per heating season for a typical insulated southern house in Atlanta (2000 sqft). • 15,000 to 30,000 BTU/degree-day. Choosing 25,000 BTU/degree-day: • Assume natural gas cost of $6per million BTU in a furnace operating at 70% efficiency. • = $638.57

  17. Some Numbers for a “typical” Home US EIA website for More current data!

  18. Some Numbers for a “typical” Home

  19. Miscellaneous Loads and Modes

  20. Example: Laptop

  21. TV’s – LED vs Plasma

  22. Consumption Side Analysis (Carl Elks Profile) This is far below the 250 KWh/day/person for the US that was used by David Mackay e.g. (RNE – without hot air). Current Consumption (84Kwh/day) Electrical Stuff 18Kwh/day Heating and cooling (26Kwh/day) Transportation 40-50KWh/day Why the big discrepancy? Mckay uses total energy divided by population This is includes industrial, commercial, Infrastructure support, jet transportation, etc…. The individual energy consumption per person is somewhere between 92Kwh/day and 250Kwh/day – It’s more likely around 150Kwh/day/person.

  23. Generation Side: Solar PV • Let’s take a look at the production side: • The solar constant – radiation that reaches area perpendicular to the incoming rays at the top of the atmosphere – at 1,366 W/m2. If there were no atmosphere and if the Earth absorbed all incoming radiation then the average flux at the planet’s surface would be 341.5 W/m2 (a quarter of the solar constant’s value, a sphere having four times the area of a circle with the same radius: 4πr2/πr2). • At ground level. But the atmosphere absorbs about 20% of the incoming radiation and the Earth’s albedo (fraction of radiation reflected to space by clouds and surfaces) is 30% and hence only 50% of the total flux reaches the surface prorating to about 170 W/m2 received at the Earth’s surface, and ranging from less than 100 W/m2 in cloudy northern latitudes to more than 230 W/m2 in sunny desert locations near the equator.

  24. NREL Solar Insolation map Central Virginia about 4.0Kwh/day (best case with a 1 or 2 axis tracker) Power density = 135 W/M2

  25. What's the PD ? • For an approximate calculation of electricity that could be generated on large scale by photovoltaic conversion it would suffice to multiply that rate by the average efficiency of modular cells. • Let’s use the working efficiency of copper mountain PV cells transposed to Virginia(14%). • Research PV cells are over 30% • Copper Mountain PD is 135w/M2 x .14 = 19W/M2 (cheap and off-the shelve) • Cutting edge – PD = 135w/M2 x .23 = 31W/M2 (Costly and limited availability)

  26. What’s the Land use for Various Plant Sizes (rough Est) Copper Mountain layout • Let’s use direct and indirect land use. • Direct is what occupies the PV plant. • 300 MW Plant in Charlottesville • 300MW/19 W/M2 = 15.7M m2 • or 15.7Km2 (Now High grade 14% technology) • 300 MW Plant in Charlottesville • 300MW/ 31W/M2 = 9.6M m2 • or 9.6Km2 • (cutting edge or near future 23% • technology) Indirect land Use is about 10-15% added on top od these numbers Why 300MW Plant size – The size of Power plant needed for 100-200K size city

  27. How does this Square with NREL Planning Numbers. 8.3 acres x 300 MW = 2400 acres = 9.7Km2 Capacity weighted – real size is larger Capacity factor = Real output over time/rated output

  28. Land and Water Uses • If we talk about a dedicated PV power plant then the use of the land is governed by the needs of the PV arrays, distribution, invertors, etc.. • Difficult to have duel use, but not out of the question. • Distributed PV is a different story, but requires smart integration (smart grid and Virtual Power Plants) to interconnect. (latter Topic) • PV does not use water, direct conversion to Electrical energy. • Summary, we would need a very large PV plant that has variable energy capacity to supply all of Charlottesville's Power needs. We need to think about a mix of energy sources that can seamlessly work together. • Albemarle county is 1800 Km2 of which about 800Km2 are flat. • We need to think of an Integrated solutions for next time…

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