Renewable Energy Systems Midterm 1

Which of the following will have an impact on your annual cash flow chart? (Select all that apply) PTC incentive ITC incentive Discount Rate Maintenance Cost

PTC incentive ITC incentive Maintenance cost

Annual production of oil and gas

Peak oil is the point in time when the maximum rate of global petroleum extraction is reached after which the rate of production enters terminal decline. Will get too expensive

Select all the true statements about electricity on the grid

Peaking power plants are used only when there is high electricity demand -High voltage is transmitted on the grid to minimize losses

Power

Power is active: something is happening -energy is being used at a particular rate, how many seconds does it take to burn up the barrel of oil? -power is the rate at which energy is used, energy is produced, work is done, or energy is transformed over some time period -Power= energy (J)/ Time (s) = WATT

Which of the following represent the components of an LCA model? Processes Environmental impacts Inputs System boundary Outputs

Processes Inputs System boundary Outputs

Transmission of Electricity

Production->step up transformer to higher voltage-> transmission lines->transmission substation->power reduced->sub transmission lines->distribution station transformers reduce voltage->business or if going to home reduced further before getting to home

Power (electricity)

Rate at which electrical energy is transferred by an electrical circuit P=V x I = Watt -amount of work that is done in the circuit per unit time -measure in watts, depends on amps and volts Watts= volts x amps

The discount rates for Gary and Sandy are 5% and 3% respectively. If they both receive a similar payment in 10 years from now, from an investment made today, whose investment has higher present value?

Sandy If they both had 100$ today the one with the lowest discount rate would have the least amount in the future (kind of like having lower interest). Now we need to do this in reverse - if they have the same amount in the future the one with the higher discount would make more "interest" so started with a lower amount today.

What is a power grid?

The high-voltage electric current is carried through the power grid to a substation. A power grid is a network of wires for transmitting electricity. Transmission lines have evolved into three major power grids in the 48- states

Payback Period

The number of years required to recover a project's cost, or "How long does it take to get our money back?" -number of years required for cash inflows to just equal cash outflows, measure of liquidity rather than a measure of profitability

Circuits

The path a current takes, must be a complete loop, an incomplete circuit will not conduct electricity. -Power source->conductor-> load -> power source -Direct current: electrons move in one direction -Alternating current: wire rotates past magnet causing a shift in direction, happens times each second, cycles per second= Hertz alternator moves, most electricity we buy AC

The Net Present Value is best described as:

The sum of all of the initial and ongoing cash flows (costs and income) adjusted to 'todays' value.

If you are given a unit of POWER (such as a kW) what information do you need to calculate ENERGY production or use?

The time period (duration) of power production or use

Why does the power grid use "peaking" power plants?

They respond quickly to changes in demand

AC vs DC grid

U.S AC powered, 60 hz in US, big debate in 1880s -need high voltage for efficient transmission of electricity AC easier/ cheaper -some rethinking due to semiconductor needing DC

Levelized Cost of Electricity

Used to compare costs among energy sources, or to compare the cost of energy from variations in the same technology -some limitations in its application -only good for electricity -constant unit cost (per kwh or mwh) of a payment stream that has the same present value as the total cost of building and operating a electricity generating project over its life -units=money/energy -LCOE= total life cycle cost/total lifetime energy production -its main function is to provide a way to compare the relative cost of energy produced by different energy generating sources regardless of project scale or operating time frame -factors: costs, incentives, energy -used to inspect sensitivity to different cost factors

Other power units

Watt Horsepower Btu/hour Pferdestarke calories/second Tonne refrigeration

A small residential wind turbine generates 5 MWh annually and is installed in a location with a 30% Capacity Factor. What is the nameplate capacity of the wind turbine in kW? Use 2 significant figures.

X * 0.30= 5MWh x=16.67Mwh -> wh 16.67Mwh/8760hrs= 0.0019 MW x 1,000= 1.9 KW

Capacity factor example

You buy a 2 MW windmill, 2MW nameplate capacity, if you install the windmill in a location where it is predicted to have a 0.25 capacity factor you would likely predict to produce 0.50MW of electrical power -25% is likely an annual CF and 0.50MW is the average annual power produced

If calculated cash flow is negative in a particular year it means that...

Your Cash outflows (investment, operating costs. loan payments, etc) exceeded you Cash Inflows (energy sales income,savings in avoided energy) in that year

How does the average per capita power consumption in North America compare to the world average?

about 4 times higher

Where does our renewable energy come from?

almost all energy forms on earth start with the solar radiation that reaches us, or in other words sunshine. -exceptions: Geothermal gets it energy from heat in the inside of the earth. Most of this heat is from residual heat from the earth formation or from radioactive decay of elements. Tidal energy comes from tides which are created due to gravity bulges that occur when the earth rotates. Nuclear energy comes from fission of heavy elements (sorry no fusion on earth yet)

Select the following true statements about techno-economic analysis: -Defines return on investment (ROI) of a project -Evaluates physical and economic properties of a technology (e.g. renewable energy) to determine its feasibility -Reduces environmental Impacts of a project -Applies to only new technologies -Investigates cash-flows over the lifetime of a project

-Defines return on investment (ROI) of a project -Evaluates physical and economic properties of a technology (e.g. renewable energy) to determine its feasibility -investigates cash-flows over the lifetime of a project

Electric Generation Basics

-Electricity is produced when a conductive wire passes rapidly through a magnetic field (except for PV) -Bulk electricity cannot be stored- it must be produced to match customer needs -generation that matches load demand is the most valuable to the system (midday peaks and summertime) generating electricity closer to users load reduce line losses

LCA can provide outputs for environmental impacts including: Net Present Value Greenhouse Gas Emission Answer Net Energy Return Annualized Operational Impact Eutrophication Potential

-Greenhouse Gas Emission -Net Energy Return -Eutrophication Potential

What affects capacity factor?

-Inherency in technology: sun not shining at night, wind does not always blow, ground temp for geothermal -Location: energy resource availability -Downtime: running a power plant only some of the time (peaking), maintenance

Mark all the true statement about levelized cost of electricity (LCOE): -LCOE is affected by programs that increase the price of renewable electricity. -Answer LCOE is used to compare costs among different energy sources without taking into account purchased power price -LCOE provides a way to compare the relative cost of energy produced by different energy-generating sources regardless of project scale or operating time frame -LCOE has units of money (dollars) per project lifetime.

-LCOE is used to compare costs among different energy sources without taking into account purchased power price -LCOE provides a way to compare the relative cost of energy produced by different energy-generating sources regardless of project scale or operating time frame

capacity factor of a power plant

-Ratio of the actual (energy) output of a power plant over a period of time and its potential output if it had operated at full nameplate capacity the entire time -total amount of energy the plant produced during a period of time, divide by the amount of energy the plant would have produced at full capacity -should not be confused with- availability factor (hrs/year that the plant could operate-downtime for repairs/maintenance) Efficiency (conversion factor from fuel to power)

Mark all the true statement about real discount rates -Real discount rate takes into account both risk and inflation -The real discount rate will be higher than nominal discount rate. -SAM modeling uses the real discount rate for some of its calculations. -The real discount rate avoids purchasing power erosion through inflation, investors consider the real interest rate, rather than the nominal rate -A real discount rate refers to the discount rate before taking inflation into account

-Real discount rate takes into account both risk and inflation -SAM modeling uses the real discount rate for some of its calculations. -The real discount rate avoids purchasing power erosion through inflation, investors consider the real interest rate, rather than the nominal rate

Parts of LCA

-System boundary: how far upstream and downstream to go. beginning-cradle, end-grave, anywhere along the way-gate -outputs: main product, co-products, emissions. Main=any good/service produced in system co-products=byproducts -inputs= direct and upstream. direct: inputs from a process inside the system boundary direct: inputs from a process outside the system boundary -processes: how inputs transformed into outputs -functional unit= unit of product by which impacts will be measured -metric= measure based on the functional unit

Non-renewable vs renewable capacity factors

-both systems have CF -in general most fossil fuel plants are quite high, these plants run near their plated capacity -why not a CF=1.00? -easier on equipment, scheduled downs, fuel costs, energy demand (peaking vs baseload)

Conversion efficiency vs coefficient of performance

-conversion efficiency is typically used for most conversion of energy forms (kinetic to electrical, potential to kinetic to electric) -heat transfer (thermal energy from hot to cold objects) is a special case -in some renewables like geothermal we are not converting energy but rather just moving thermal energy -typically use coefficient of performance (COP) not conversion efficiency

Return on Investment

-measures the efficiency of an investment -quotient of the difference between the gain from an investment and the cost of investment, and the cost of investment -if you have one investment at time zero then ROI=NPV/investment at time zero

Net present value

-most-used method -found by discounting all cash inflows and outflows to the present time at an appropriate discount rate (typically the MARR) a positive NPV for an investment project means that the project is acceptable (satisfies the MARR) the larger the NPV the larger the projected profit

Discount vs interest rate

-not all money for projects comes from the bank -companies or investors can provide money from existing businesses or cash on hand -investments typically should exceed the returns the existing business can garner (minimum acceptable rate of return) -the rate then used to discount $ is then called a discount rate instead of an interest rate as no loan is involved

What is energy?

-property that must be transformed to an object in order to perform work on (or heat) the object. -Can be converted in form, but not created/destroyed -Energy= amount of work= Force x Distance -SI Unit= Joule -work= force x distance force=mass x acceleration Energy=mass x acceleration x distance Joules= newton x meter = (kg m/s2)*m

Tax credits

-some investments can be deducted directly from due income taxes -certain investments may be treated as expenses and deducted from income -some investments can be depreciated over a period of years -some income can be treated as capital gains and can be taxed at a lower rate -amount that is deducted from the project's income tax

Potential Energy

-stored energy: gravitational potential energy PE=mgh m=kg -potential energy in springs & deformed media

Assistance with capital

-two primary types of incentive -investment tax credit (ITC) is an upfront credit against the capital expense used to build out your project. typical for solar, usually 30% federal -production tax credit (PTC) credit over time based on the amount of energy produced- typical for wind ~0.02/kwh -either/or not both, some states/utilities also have grants for projects

If the company installed 20 modules how much surplus of electricity would they be able to sell to the grid (in kW-h per year, at least 3 significant figures)?

.24 kw for one panel x 20 panels= 4.8kw 4.8kw x 8760hours= 42048 kwh 42048 kwh- 15000 kwh= 27,048kwh excess

Use the same rock at the top of the same building as in the previous question. This time you tie a parachute to the rock so that some of the potential energy is not converted to kinetic energy due to friction. If the efficiency of conversion from potential to kinetic energy is now 75%, how fast will the 3 kg rock be moving (in m/s) when it hits the ground 10 meters below?

.75 x 294= 220.5 220.5= .5 x 3 x v^2 v= 12m/s

A hydroelectric dam has 805 kg of water go through its turbine per day. All of the water goes through the intake and enters the turbine at a velocity of 8 m/s and leaves the turbine at 4 m/s. The water spins the turbine and the generator produces electricity by converting the change in kinetic energy (KE in - KE out) into electrical energy. If the turbine has an efficiency of 100%, how much electricity in kJ does the hydroelectric dam produce daily? Use 2 significant figures.

0.5 x 805 x (8^2 - 4^2)= 19320 joules = 19 kJ

A hydro turbine has a maximum power output of 0.5 MW. If it ran at full capacity for one year how much energy would it produce in that year?

0.5MW x 8760 hours in a year = 4380MW-h

You have a 0.8 MW rated wind turbine that is installed in a location that has a capacity factor of 0.37 based on the wind resources. Assume you can sell wind energy to the grid with the following rates: 9 cents/kWh for 12 hours per day - peak rate5 cents/kWh for 12 hours per day - off-peak rate What is the predicted income from the turbine over a year (in $)? There are 100 cents per US dollar. Answer with at least 3 sig figs.

0.8 MW x 1,000= 800KW*8760hrs= 70080000kwh 70080000kwh*0.37= 2592960kwh 2592960kwh/2= 1296480kwh 1296480 kwh * .09 cents/kwh = $116,683.2 1296480 kwh * .05 cents/kwh = $64,824 $181,507.2 total

How much thermal energy do we collect if the conversion efficiency of the collector is 55%? 1 KWh

1 KWh total solar radiation energy input*55%= 0.55 kwh = 1.98MJ

A solar panel array project, rated at a nameplate capacity of 10 kW installed in an area with a capacity factor of 25%, is expected to cost $61,800.00 over its lifetime of 18 years. What is the levelized cost of energy (LCOE) of this project (in cents per kWh)? 3 sig figs.

10*.25= 2.5 2.5*8760= 21900 kwh per year x 18years= 394200 kwh $61800/394200 kwh= $.157 or 15 cents per kwh

Let's say that it takes 100 kj of mechanical energy to drive a car from home to work, if the efficiency of transforming chemical energy to mechanical energy is 30% how much primary energy does the car consume?

100 kj is the output 100/0.3= 333 kj (input)

A battery provides power to the motor in an electric car. The motor "pushes" the car with 106 kN of force and moves the car 23 meters every 9 seconds. How much power, in kW, is the battery providing to the motor? Assume 100% energy conversion. Power = ____kW

106kN x 23 m= 2438 kjoules 2438 kjoules/ 9 seconds = 271 kW

You have installed a wind turbine at your rural home. About 1/2 of the energy generated by the wind turbine is used directly by your household and 1/2 is sold to your electric utility. Your normal purchase cost of electricity is 10 cents/kWh. You get paid 6 cents/kWh for the energy you sell back to the grid. What is the value (to you) of the energy generated by your wind turbine?

10cents/kwh+6cents/kwh divided by 2= 8 cents per kwh

Let us consider that a family's annual electricity consumption is 11,000 kW-h. What is their average power consumption (in kW, with at least three significant figures)?

11,000 kw-h / 8760 h= 1.256kw

What would be the maximum income the company be able to obtain selling the excess to the grid (in $ every year, at least 5 significant figures), if they install 20 modules? Assume they get $0.12/kWh during the peak hours $0.05/kWh during the non-peak hours. Hint: you may assume the solar panel generate power during peak rate hours - which generally coincide.

27,048 kwh x $.12 during peak hours= $3,245.76

A school has a photovoltaic solar panel array that captures 288 kWh of energy each day. The school uses 80% of the energy from the array and sells the remaining 20% to an electric utility. Purchasing electricity from the electric utility costs the school 10 cents/kWh. Selling energy back to the utility earns the school 7 cents/kWh. How much money does the school save each day by generating 288 kWh of energy? Answer in $/day with 3 significant figures. There are 100 cents per US dollar.

288*.80= 230.4kwh*.10cents/kwh= $23.04 288*.20= 57.6kwh*.07cents/kwh= $4.032 $27.07

How much energy have you applied to 3 kilogram rock when lifting it 10 meters from the ground to the top of a building? (to the nearest 2 significant figures, assume 100% efficiency and acceleration of gravity = 9.8 m/s2).

3 x 10 x 9.8= 294 290 joules

If you drop the 3 kg rock you lifted to the top of the building, how fast will it be moving (in m/s) when it hits the ground 10 meters below. Assume that the conversion from Potential to Kinetic Energy is 100% efficient? (answer with at least 2 significant figures)

3 x 9.8 x 10 = 294 joules PE = KE KE= 294= .5 x m x v^2 294= .5 x 3 x v^2 v= 14 m/s

You have installed a wind turbine at your rural home. The turbine generates 698 kWh of energy in one year. Your household uses 403 kWh of the energy generated by the wind turbine and sells the rest to the electric utility. You can purchase electricity from the utility at a price of 10.9 cents/kWh and you are paid 5.5 cents/kWh for the energy you sell back to the grid. How many cents/kWh should you value the energy generated by the wind turbine? Answer with 3 significant figures.

403kwh* 10.9cents/kwh= 4392.7 698-403= 295kwh sold= 295kwh * 5.5cents/kwh= 1622.5 6015.2 cents / 698 total kwh = 8.6 cents per kwh

The same 0.5 MW capacity hydro turbine as in the previous question is installed on a river that has a capacity factor of 0.66 how much energy does it produce in one year?

4380MW-h * 0.66= 2890MWh

A wind power plant has a rated power capacity of 5 GW and a Capacity Factor of 25%. What is the estimated annual energy output in GWh?

5 GW * 0.25= 1.25GW 1.25GW * 8760hrs= 10950 GWh

Transmission Lines

500 kV to 161 kV subtransmission lines-138-55kV -distribution lines-33kV

You can sell 100 kWh of wind energy for a given day to the grid at $0.06/kWh with half of the time (12 hours) receiving the 'on peak' rate and the other half of the time $0.03/kWh at the 'off peak' rate. What is the approximate value of the energy produced in dollars (assuming steady production for the whole day)?

50kwh*0.06= $3 50kwh*0.03= $1.5 about $4.5

If electricity going into a transformer is at 513 V and 142 A and exits the transformer at 101 V and 432 A, what is the efficiency of the transformer?

513x142=72846 watts 101x432= 43632 watts 43632/72856= 0.598

A hydro turbine has a maximum power output of 1 MegaWatt. If it ran at full capacity for one year how much energy would it produce in that year?

8760 megawatt hours

Transformers

A device that is used to change on value of voltage and current to another value of voltage and current -energy conserved (except for heating loss) -power in=power out -Vin x A in = V out x A out -higher voltage = lower amperage

The discount rate is best described as:

A factor used to normalize money's worth as a function of time using an estimate of the 'opportunity cost' of money

Select the following true statements about what an energy model can provide: -Avoids costs of having to build a prototype of the system -Simplify calculations and quantify energy and economic inputs and outputs -Generate figures and tables to help communicate findings -Run simulations of alternative technologies or systems

All of them

Grid Control

Baseload generators on all the time, some "spinning reserve" generators are kept running below their full load to cope with unexpected load demands -peaking generators are loaded or unloaded automatically if needed the load voltages can be reduced to lower demand or even some consumers temporarily disconnected

Why is capacity factor a big deal?

Convenient way to determine power produced specific to a location/scenario -ex: if you buy a windmill you know what is is rated at (nameplate capacity) the capacity factor can convert the nameplate capacity to actual power produced (or likely power that will be produced) -for energy products you pay for capital and ongoing costs like fuel -for renewable energy, typically the fuel is low cost/free but capital is not -so cost effectiveness for these projects really is dependent on cost of capital per energy produced -solar panel costs the same in sunny place as cloudy, sunny place delivers more energy

Which of following devices is essential to connect PV panels to the grid?

DC-AC inverter

Renewable energy- an engineering approach

Define problem (new energy requirement, environmental concern, others) -Characterize boundary between system and environment (project purpose, scale, key input and output variables, determined by expertise of modeler/designer/engineer) -inputs: physical/technical-resource availability, appropriate technology for the region, design criteria for energy deficit/environmental need -Financial: borrowing, capital and operating costs, taxation -outputs: energy generated, system sizing, cash flow, return on investment (ROI), may include environmental impacts- often requires lifecycle assessment (LCA)

Electricity Market

Electricity supplied or consumed during periods of high demand is worth more than periods of low demand. -Since electricity can not be stored, the electricity market contains a time-basis. We need to produce what is being used -power plants feed the grid -North America targets at a frequency of 60 Hz, 50 Hz common in the rest of the world -consumers draw their power demand from the grid supply-transmission losses= Demand

Electrical energy

Energy delivered by an electric circuit, ,energy supplied by the combination of electrical current and electric potential that is delivered by the circuit potential x current x time = electrical power volts x amps x sec = joules

Techno-economic assessment

Evaluates physical and economical properties of a technology (renewable energy) to determine its feasibility, investigates cash flows over the lifetime incorporates regional economic incentives, defines return on investment (ROI) applies to new or retrofitted technologies

Inflation impact on interest

Federal reserve raises interest rates when they feel that the rate of inflation is increasing, protects savings -one way to approximate the effect of inflation is to call the "true interest" rate the actual interest rate minus the estimated inflation rate -if you don't adjust for inflation it is called "nominal interest rate"

Steps in getting electricity to customers

Generation- converting a source of energy to produce electricity Transmission- using high voltage line from the power plant to send electricity across long distances Distribution- using lower voltage wires to deliver electricity to local customers

Please mark all of the following that do NOT obtain the originating energy from solar radiation? Wind Energy Biofuels Geothermal energy Hydropower Solar Thermal

Geothermal

Which type of organization is likely to accept the lowest discount rate on a renewable energy project?

Home owners in a residential energy project (others want to make more money)

Which of these renewable energy sources is the most "dispatchable" (i.e. most likely to be available when we need it)?

Hydro

Ohm's Law

I=V/R V=IxR relationship between voltage, current, and resistance -amount of current that can be pushed through a conductor depends on resistance and voltage, greater distance means increased resistance

The following information is to be used for the next 3 questions. A small company is considering installing solar panels to bring their electricity costs. The system consists of solar panels, an inverter, and a battery. The company electricity usage is 15000 kWh/year. The panels are rated at 1.0 kW per module and the area they live in has a capacity factor of 0.30. The system does lose some energy after the modules (from storage at night in batteries, converting from DC to AC, and transformation to the correct voltage). Combined, these are accounted for as energy conversion efficiency of 80.0%.

If the goal is to offset current energy consumption using solar PV, how many modules would need to be installed? (give answer as whole modules, can't buy a half module) --1500kwh x 1year/8760 hours= 1.712 kw 1 panel= 1kw 1kw*0.80*0.30= .24kw 1.712kw/.24kw= 7.13-> 8 panels

Project incentives

In the US incentives for getting renewable energy such as solar and wind power installed are available at both federal and state level -lots of variation between different states and their local commitments, most states have federal tax rebate of 30%

Which of the following is biggest limitation of using the payback period (years to recoup project costs) as a measure of financial success?

It ignores the size of project's profit potential.

energy efficiency

Its taking a lot less energy to produce goods, we're getting much more energy efficient, energy getting more expensive-> businesses more interested in become efficient

Energy SI Energy Units

Joule= kg*m2/s2 1 kilojoule= 1,000 joules 1 exajoule 1x10^8 joules, used for world energy use

Other energy units

Joules----------- Footpound kg*m2/s2 -------Horsepower-hour kilowatt-hour---- Kiloton(explosive) Quad ------------Gallon of Gas Btu ---------------Tonne Coal Therm------------ Tonne Oil Calorie Nutritional Calorie

Select all the TRUE statements about LCA -LCAs can only determine environmental impacts for energy systems -Life cycle assessment is the investigation and valuation of the environmental impacts of a product or service -The output of an LCA will tell you definitively if a process is sustainable -There is only one correct way to perform an LCA -LCAs are governed by ISO standards

Life cycle assessment is the investigation and valuation of the environmental impacts of a product or service -LCAs are governed by ISO standards

Which of these describe "base-load" electrical generation facilities?

Low cost or production and respond slowly to changes in demand

Power v Energy

Mathematical relationship= derivative -Power= change in energy over change in time -something is happening: energy is being used/produced or changing form -Joules/second= watts= kg*m^2/s^3 -converting between power and energy: power x time= energy -watt x second= joules= kg*m2/s2, for using simple division we are assuming a constant or average

When does electric energy have the highest economic value in the US market?

Mid-afternoon in summer months

Interest

Money paid for the use of borrowed capital or money gained from the use of loaned capital -borrower wishes to minimize rate of interest; lender wishes to maximize -actual interest rate is a compromise based on the availability of capital, investment opportunities and degree of risk of loss of capital

Who sells electricity?

Most people buy electricity from a electric utility company -Utility companies sell the electricity that power plants make -utilities have to provide and repair power lines, keep supply steady, keep cost affordable, meet government rules

Where do renewables fit?

Most renewable energy dam power, projections show more renewables

What is electricity?

Movement of charges, electron flow, secondary energy source, conversion from other sources of energy

EROEI (energy return on energy investment) EROWI (energy return of water invested)

have to invest electricity to build a plant or keep it running, ratio needs to be above 1 to make sense

What are measures of power?

horsepower/ btu per hour

Generation- renewable fuel types

hydroelectric, solar, biomass, wind, geothermal- resource determines capacity factor

Compound Interest

if both the principle and the interest earned accrued interest, the investment is known as compound interest and a $100 investment at an effective annual interest rate of 5% will grow to $105 the first year, $110.25 in the second year and $115.76 in the third year -the effective annual interest rate, ie, can be calculated from the interest rate per period using the following formula where m is the number of compounding periods per month ----ie=(1+i)^m -1

Simple interest

if only the principle (i.e original investment) accrues interest, the interest is known as simple interest and a $100 investment at an effective annual interest rate of 5% will grow to $110 in the second year and $115 in the third year and so on

Assistance with rate

incentives with pay rates -small projects (homeowners) typically must rely on programs for selling rates, larger projects will negotiate a power purchase agreement with utilities. Utilities typically have programs to pay higher rates for renewables, more typical when a state is behind its renewable portfolio standard (RPS) state by state and have either current minimums or goals for future minimums- not all states have this

Inflation

inflation offsets interest; deflation adds to interest costs -inflation is associated with operating costs, maintenance costs, energy prices, etc -generally the interest rates are slightly above the overall inflation rate

Where LCA is used

inform consumers -guide researchers and policy makers ex- environmental policy: low carbon fuel standards

Resistance

interference to flow of electrons or the opposition to the flow of charges. Electrical resistance is conceptually similar to mechanical friction -symbolized by R, unit is ohm -opposition to current flow in the circuit. Resistance is measured in ohms can be the load or work circuit doing

Technology output vs peak demand

intermittent technology: solar only during day which is usually peak demand and wind can run night and day Steady technology: biomass day and night can increase in day for peak, geothermal day and night, hydro day and night and can increase in day in storage scenarios

Life Cycle Assessment

investigation and valuation of the environmental impacts of a product or service, not an exact science -net energy, global warming, acidification potential, eutrophication potential -governed by an iso standard

Energy is passive

it is not doing anything, it is the capacity to do something in the future or it has done something in the past-> like chemical energy stored in a pile of coal -work is a specific form of energy transfer (both have same units)

A Madison-area water tower holds 3800 cubic meters of water at an average height of 51 meters. (Assume the water has a density of 1000 kg/m3). How much potential energy in MJ is stored in the water? Use 4 significant figures.

mass= volume x density 3800 x 1000 = 3800000kg 3800000x9.81x51= 1901.178 MJ

Electric field strength

measured in volts/meter -typical level in homes: 4-60v/m electric fields from transmission lines at 200ft 10-50 v/m

Consider a turbine producing electricity that is then used in an electrical motor to spin a wheel. Select the best answer that describes the conversion of energy

mechanical to electrical to mechanical

Kinetic energy

motion- energy of mass in motion KE=.5mv^2 m=kg rotational- energy of a mass at a radius (r) from the center of rotation -rotating with an angular velocity radians/time= units per seconds

Current

movement/ flow of electrical charges. Electrons in motion symbolized by I, unit is the Amp (A) -amount of electricity that flows in the circuit, measured in Amps more current= higher amps -pushed and pulled by voltage, produces heat

Renewable energy- low GHG

only large scale, low cost, low carbon energy sources can reduce GHG, provide energy security and improve nations long term prosperity -only GHG involved in renewables is building structure

Problems with power lines

people generally not excited about high voltage transmission lines through their properties -effects of generated electric fields

Chemical energy stored in Biomass:

photosynthesis, energy use in a biological system. Simplified case of glucose oxidation

Conversion efficiency

ratio between the desired output to the total energy input -conversion efficiency= useful energy output/total energy input -second law of thermo- conversion efficiency is less than 100% there is no perpetual motion machine -ex: electric motor 90% efficient (electrical ->rotational energy)

Capacity Factor

ratio of actual energy output in a year to potential energy output in a year, if it were possible to operate at full power for the entire year -Capacity factor=actual energy output in a year/potential energy output in a year -not the same as availability (fraction of the year it is not shut down for maintenance or repairs) or efficiency (conversion efficiency from one form to another)

Why LCA is needed

renewable energy has historically cost more than fossil fuels -fossil fuels bear externalities that renewable fuels dont -LCAs can quantify those externalities -LCA enables apples to apples comparison among fuels across different metrics

Models allow us to

simplify and quantify problems, run simulations, generate figures and tables, make prediction

Triple bottom line

social sustainability: concerns for people involved in a enterprise (labor, community, etc) economic sustainability: is enterprise profitable environmental sustainability: minimizing the impact to natural resources, environment and biological community

The availability of which of these renewable energy sources is more coincident with electrical demand?

solar

Electromagnetic energy

solar radiation travel through the vacuum of space -visible light and other frequencies/wavelength -solar constant: solar radiation that falls on an area above the earth's atmosphere at a vertical angle

AC vs DC power generation

some systems naturally produced AC and some DC you can use transformers to convert between the two (some loss) if the system has rotation it generally is producing AC (wind, water & stream turbines) if the system is generating using PV or chemical generally, DC (solar, batteries)

Systems analysis

the act or process of studying an activity typically by mathematical means in order to define its goals or purposes and to discover operations and procedures for accomplishing them most efficiently

The rated capacity of an renewable energy system (wind turbine, solar panel, etc) is

the amount of energy that an energy installation will provide under ideal conditions of operation

Internal Rate of Return

the discount rate that makes the NPV of an investment zero -the most widely used rate of return method for performing engineering economic analysis, if IRR for a project is greater than the MARR, then the project is acceptable -interest rate that equates the equivalent worth of an alternatives cash inflows (revenue) to the equivalent worth of cash outflows (expenses) -also called breakeven interest rate

Thermal Energy

the energy required to raise the temperature of a mass or the ability of a mass to release heat energy to the environment -T.E= specific heat * mass * change in temperature -Thermal energy transfer: heat transfer occurs between two bodies which are at different temperatures. Heat is to thermal energy as work is to mechanical energy heat moves from hotter object to colder objects until thermal equilibrium the amount of energy transferred is the amount of heat energy exchanged

The rated capacity of a power production facility is..

the maximum power that the facility is able to produce under optimal conditions

Time value of money

the principle that a dollar received today is worth more than a dollar received in the future -factors affecting time value of money: interest, inflation, discount rate, tax credits, cash flow

Power is best described as

the rate of energy production or use

Cash flow

the sums of money recorded as receipts or disbursements in a projects financial records are called cash flows -negative cash flow generally exists during the early stages of design if product successful it will later cover this lost money plus interest plus profit

If too much power is being generated on the grid

then the extra power will cause the whole grid including all generators to speed up -there is a lot of inertia on the grid so the acceleration is not fast -conversely the grid frequency will drop if there is excessive demand

What are measures of energy?

tonnes of coal, barrels of oil, Btu

Electromagnetic Induction

turbine turns coils of wire in a magnetic field to produce a current

Net Metering

typical for smaller consumers who generate some or all of their own electricity, important with non-dispatchable technologies (wind, solar) -allows project owner to use power generated later without a storage system policy measure the "net" amount of power sold and power produced rolling over excess in either kwh or money on monthly or annual basis -in essence allows you to get paid same rate you buy electricity at

Coefficient of Performance (COP)

units of thermal energy moved/unit of energy to do the work of moving -ex: COP for a heat pump would be the ratio of heat energy moved to the input electric energy used in the process -refrigerator is an example of a heat pump. If it takes 1khw to provide 3.5kwh of cooling load the COP would be 3.5/1.0= 3.5 -COP can be and typically are >1 or 100% where conversion efficiency usually less than one -2nd law of thermodynamics limits that theoretical max COP as function of the temps between the two COP

Electrical voltage

voltage is the electromotive force. It is the force or push on electrons in the circuit, referred to as potential difference. Potential to do work but does nothing by itself, measured in volts (V)

Current energy consumption

~500 EJ/ year

Environmental impact

clean air, clean water (oil spills, water behind dams changing temp) resources (only so much land for biofuels) world water stress, food prices and ethanol production, nutrients (nitrogen going up per year) -dead zone in gulf of mexico due to agricultural runoff

Generation- non-renewable fuel types

coal, oil, natural gas, nuclear -human choices determine capacity factor

Why not renewable energy?

cost of electricity: as a whole not as cost competitive as some fossil fuels (coals) costs are expected to come down -environmental impacts: area requirements; some of them take a lot of area wind and biomass a lot of area -other impacts: siting (visual, noise, smell) habitat impact, water use, rare earth elements

Life-cycle cost

defined as the sum of all the PW (present worth) of all the cost components in the energy system

Generation

electricity is produced in generators. Generators require other sources of energy, conversion of mechanical energy into electrical energy

The case for energy models

energy is very contentious/ political -how do you inform deeply-ingrained opinions and conventional views with science? -need for comparing and quantifying strategies

What is a computational model?

"simplistic" representation of a real-world system, quantitative, aids in our understanding, helps inform and communicate avoids having to build a prototype -all models are wrong, but some are useful Time

Let us consider that a family's annual electricity consumption is 11,000 kW-h. Assuming the energy expenditures of the family totaled $ 1,500 per year, calculate the unit price of energy (in $/kWh, with at least 4 significant figures) charged by the utility company.

$1500/11,000= .13/kwh