Final Flashcards
1
Q
A cost-effective micro-CHP system should be:
A
run constantly
2
Q
The efficiency of a large-scale fossil fuel burning power plant not utilizing CHP would likely be closest to:
A
40%
3
Q
The majority of the distributed generation units in the U.S. today are:
A
small fossil fuel generators
4
Q
What is the primary purpose of the buffer tank in a micro-CHP system?
A
to temporarily store all of the thermal energy produced
5
Q
What is usually the biggest problem to overcome in designing an economically viable micro-CHP system?
A
low heat demand
6
Q
Which of the following buildings would be the best candidate for micro-CHP?
A
dormitory
7
Q
Which of the following conditions are usually found where large-scale CHP exists?
A
- colder climate
- the need for electricity
- higher building density
8
Q
Which of the following is most accurate regarding PURPA?
A
PURPA forced the utilities to allow Independent Power Producers to connect to the grid.
9
Q
Which of the following would not be an economically viable use for the thermal energy produced by micro-CHP?
A
cooking stove
10
Q
Why is CHP not utilized at most large-scale U.S. power plants?
A
The power plants are remotely located.
10
Q
What is the abbreviation used to describe the simultaneous production of both electricity and heat from a single fuel source?
A
CHP
11
Q
The primary advantage of a typical micro-CHP unit is that it does not use any fossil fuel.
A
False
12
Q
A dam has a spillway to prevent what?
A
overtopping
13
Q
A large hydro plant with an inconsistent water supply would likely have a:
A
low Capacity Factor
14
Q
Advanced Hydropower strives to achieve what at an existing dam site (choose all that apply)?
A
higher environmental performance and higher electrical output
15
Q
Itiapu Dam (India) has a capacity of 14 GW. Approximately how many average sized coal power plants is that equivalent to?
A
20
16
Q
The biggest obstacle to the dam removal movement is:
A
lack of money
17
Q
The highest percentage of U.S. electricity that hydro achieved was approximately:
A
40%
18
Q
To get from the intake to the turbine water flows through the:
A
penstock
19
Q
Which of the following parts of a dam is not an electrical component?
A
turbine
20
Q
Which of the following statements is most true today?
A
Hydro produces 60% of U.S. renewable energy.
21
Q
How much electricity per year, in TWh, will a 700 MW hydro plant produce if it operates with a capacity factor of 25%? Provide only the number.
A
1.533
(x TWh / (700 MW * 8760 hours) = x / 6,132,000 MWh = 0.25 or 25% capacity factor
x = 6,132,000 MWh * 0.25 capacity factor = 1,533,000 MWh = 1.533 TWh)
22
Q
Most dams in the U.S. produce power.
A
False
23
Q
North Carolina is part of the Tennessee Valley Authority Coalition.
A
True
24
Pumped Storage Hydro creates more electricity than it uses to operate.
False
25
In order to produce electricity a micro-hydro site needs which two characteristics?
water flow and pressure head
26
Which type of turbine must be used on a site with a head of less than 10 feet but with adequate flow?
Reaction
27
The maintenance on a micro-hydro system is most significantly related to:
the amount of water handled
28
The most difficult part of a micro-hydro system installation with significant capacity will usually be the:
penstock
29
What function does a dump load perform in a micro-hydro system?
It diverts power to something else when there are no operating loads.
30
What is the static pressure of a penstock that has 175 feet of head?
76 psi
31
When a full penstock begins to flow the pressure at the outlet of the pipe will:
fall
32
When does the maximum flow rate in a penstock occur?
when net pressure is 2/3 static pressure
33
Where should a powerhouse be placed in a micro-hydro system?
as close to the water return as possible
34
Which of the following is required on both a DC and an AC off-grid micro-hydro system?
dump load
35
Which of the following pipe materials would you likely use for the bottom portions of a penstock under very high pressure?
steel
36
Given a wind shear exponent of 0.14 and an average wind speed of 14mph at 35 feet, what will the approximate wind speed be at a turbine height of 60 feet?
15mph
((60/35)0.14 x 14 = 15.09mph)
37
The causes of wind turbine noise include which of the following? Select all that apply.
mechanical operation and aerodynamics
38
The minimum size of a site for a small turbine should be:
1 acre
39
The most important factor in power production by a wind turbine is:
wind speed
40
The U.S. state with the highest wind energy capacity is:
Texas
41
Which of the following would likely be the best site to locate a wind turbine?
a site with constant high winds
42
What country is the leader in installed wind turbine capacity?
China
43
The capacity of a wind turbine indicates the amount of power produced whenever the wind blows.
False
44
The U.S. has a higher wind capacity factor than solar PV.
True
45
Wind turbines cause more bird deaths than every year than pollution, buildings, and cats combined.
False
46
A barrage tidal generation plant is closest in terms of technology to a:
hydroelectric dam
47
All other things being equal, which of the following wind turbines will likely produce the largest annual energy output?
rated output of 1 kW at a rated wind speed of 20 MPH
48
Based on wind speed, on a site of which Wind Power Class would be the best to build a wind turbine?
Class 5
49
Currently, most distributed generation units in the U.S. are:
fossil fuel generators
50
If the static pressure in a microhydro penstock is 100 psi, the optimum net pressure for maximum flow will be closest to:
70 psi
51
In terms of wind power, the U.S. is the world leader in:
electricity produced
52
On which of the following sites could a vertical-axis wind turbine be considered over a horizontal-axis turbine?
on a tight urban lot with severe noise restrictions
53
The largest hydro capacity in the U.S. is found in which region?
Pacific Northwest
54
The largest source of renewable electricity in the world is:
hydroelectricity
55
The maintenance on a micro-CHP unit is most similar to the maintenance on a:
car engine
56
What is a primary advantage of an AC microhydro system over a DC system?
smaller wire sizes
57
What is the approximate swept area of a horizontal-axis turbine with a rotor diameter of 16 feet?
201
(swept area = πr2, so
3.14159 * (8)2 = 201.06)
58
What is the capacity factor of a hydroelectric dam with an installed capacity of 1,000 MW producing 180,000 MWh in a 30-day month?
25%
180,000 MWh / (30 days * 24h per day * 1,000 MW) = .25 or 25%
59
What is the most common means of rotor control for small wind turbines?
horizontal furling
60
What is the most effective way to stop a small wind turbine from spinning out of control?
During a break in the wind, apply dynamic braking.
61
What is the most important consideration when selecting a small wind turbine?
annual energy output
62
What is the purpose of a tail vane on a wind turbine?
to passively yaw the turbine into the wind
63
What is the static pressure in a microhydro penstock with a head of 300 feet?
130 PSI
The static pressure is the highest pressure achieved at the bottom of the penstock when it is full of water and not moving. 2.31 vertical feet of head is equal to 1 PSI of pressure. Therefore:
300 / 2.31 = 130 PSI
64
When designing a microhydro system, which of the following will likely result from an increase in the flow of intake water?
increased intake maintenance
65
When does the dump load kick in on a stand-alone DC microhydro system?
whenever the battery bank is fully charged
66
Which is the largest hydroelectric dam in the world?
Three Gorges Dam
67
Which of the following are an advantage of hydroelectric dams over other forms of energy generation from renewable sources? Select all that apply.
Systems have an ability to provide both baseload power and peak power., Power production scales exponentially., Systems generate electricity using one of the most abundant chemicals on earth.
68
Which of the following are an advantage of microhydro over other forms of energy generation from renewable sources? Select all that apply.
Power production scales exponentially., Systems generate electricity using one of the most abundant chemicals on earth., Systems can be configured and installed in a DIY fashion.
69
Which of the following are an advantage of wind turbines over other forms of energy generation from renewable sources? Select all that apply.
Power production scales exponentially., Systems can be configured and installed in a DIY fashion.
70
Which of the following are likely to be found on a large wind turbine but not on a small wind turbine? Select all that apply.
transmission, yaw motor
71
Which of the following are the primary goals of Advanced Hydropower? Select all that apply.
increase power capacity, increase environmental performance
72
Which of the following buildings is the best candidate for a micro-CHP generator?
a hotel with a natural gas supply
73
Which of the following countries is not among the world leaders in large wind turbine manufacturing?
the United Kingdom (UK)
74
Which of the following is an advantage of combined heat and power (CHP)?
Systems burns fossil fuels more efficiently.
75
Which of the following is an advantage of tidal generators over other forms of energy generation from renewable sources?
Systems harness natural cycles that occur twice per day.
76
Which of the following is not a characteristic of a self-supporting wind turbine tower?
It is less expensive than a guyed tower.
77
Which of the following is not an advantage of offshore wind?
proven reliability
78
Which of the following power plant types is always built as a baseload plant?
nuclear plant
79
Which of the following renewable technologies is a viable large-scale alternative to hydroelectric power?
wind turbines
80
Which of the following sites would be the best candidate for significant power production using microhydro?
Head: 180 feet, Flow: 60 GPM
81
Which of the following technologies will likely have the highest capacity factor?
hydroelectric dam
82
Which of the following would need to be increased in order to create the most significant increase in the power of a wind turbine? Select all that apply.
wind speed, rotor area
83
Which renewable energy source creates the most electricity in the United States?
hydroelectricity
84
You want to install a Southwest Windpower Air X turbine on your 1-acre lot. Your house is 30 feet tall and there are no trees on the lot. You want to order the shortest tower that will still get your turbine into the unobstructed winds. Which of the following towers should you order?
75 feet
85
A hydroelectric dam can be easily turned off and on quickly to provide spot electricity.
True
86
A microhydro site with high head would most likely use an impulse turbine.
True
87
A pumped hydro storage plant pumps uphill when grid demand is high and produces power when grid demand is low.
False
88
All areas off the coast of North Carolina are available for offshore wind turbine development.
False
89
An effective wind turbine uses more lift than drag to turn its rotor.
True
90
CHP is not utilized at most large-scale U.S. power plants because the power plants are remotely located.
True
91
Most dams are built to create electricity.
False
92
Most large utility-scale wind turbines have a tail vane.
False
93
Most large-scale U.S. power plants utilize CHP.
False
94
A machine that extracts heat from ground water and transfers it to domestic hot water is called a:
water-to-water heat pump
95
How many coaxial coil heat exchangers are located in a water-to-air ground source heat pump equipped with a desuperheater?
2
96
In a geothermal heat pump the coaxial coil heat exchanger replaces what?
the outdoor coil
97
In North Carolina, if the outdoor air temperature in summer is 85 degrees the ground temperature 6 feet below the surface will be:
cooler
98
What is the primary advantage of an open loop over a closed loop in a geoexchange system?
more efficient heat exchange
99
What is the primary reason why polyethylene pipe is used in a ground source closed loop?
The joints between the pipes are strong.
100
What primarily determines the capacity of a horizontal ground loop (select all that apply)?
soil type, the length of the pipe
101
What two qualities define an effective refrigerant (select all that apply)?
At low pressure it boils at a very low temperature., At high pressure it condenses at a very high temperature.
102
Which of the following closed loop systems would be most appropriate for a condo in downtown Raleigh with a small accessible courtyard?
vertical
103
Which of the following criteria define the best location for a ground source heat pump (select all that apply)?
moderate ground temperature, mixed climate
104
Which of the following increases your HVAC load in the summer but not in the winter (select all that apply)?
lighting, humidity, solar gain
105
A warm spring could be effectively be used to generate what?
district heat
106
The Geysers uses treated wastewater to:
replenish the aquifer
107
What will occur if the source aquifer of a geothermal energy plant is depleted?
The capacity of the plant will be reduced.
108
Which of the following can be found in heated groundwater used for geothermal energy?
methane, dissolved metals, hydrogen sulfide, ammonia
109
Which of the following is the least complicated type of geothermal energy plant?
dry steam
110
Which of the following natural phenomena is not a visible source of geothermal energy?
aquifer
111
Which of the following U.S. states has the largest geothermal energy potential?
Nevada
112
Geothermal energy is a pollution free source of electricity.
False
113
Compared to a gasoline-powered vehicle, a fuel cell vehicle using hydrogen from natural gas reforming is:
quieter, NOT carbon neutral, and costs more
114
Hydrogen kept at -163ºF would be in the state of a:
gas
115
Which of the following describes a possible relationship between a wind turbine and a fuel cell?
Excess electricity from the wind turbine can be used to create hydrogen to be used later by the fuel cell.
116
Why is hydrogen liquefied?
to minimize its volume
117
Hydrogen gas has a very high energy density.
False
118
A 40-pound bag of wood pellets has a heat content of approximately:
340,000 BTU
119
A face cord of wood is:
43 cubic feet
120
A primary advantage of wood pellets over bulk dry wood for heating is:
consistency
121
A site with severe groundwater quality issues should use which of the following types of geothermal loops?
vertical closed loop
122
Advantages of fuel cells include which of the following? Select all that apply.
high reliability due to no moving parts, scalable, pollution-free
123
Binary cycle geothermal energy plants can be considered:
less polluting than steam-based plants
124
Biomass as a fuel source can be considered to be carbon neutral under which of the following conditions?
new planting replaces the harvested material
125
Compared to oil and natural gas, uncompressed hydrogen has an energy density that is:
lower
126
Four fuel cells stacked together would produce a voltage closest to:
3 volts
127
Fuel cells can utilize which of the following inputs? Select all that apply.
biogas, propane, natural gas, hydrogen gas
128
Heat always moves from:
hot to cold
129
In terms of conversion to ethanol, select the answer that is in order from easiest to hardest to convert.
sugarcane, grains, cellulosic material
130
In terms of energy content, lignin is most similar to:
coal
131
In the evaporator of a heat pump the refrigerant is transformed into:
all gas
132
North Carolina currently has the resources to easily meet which percentage of its energy needs with biomass?
10%
133
Of the following, the primary problem preventing the widespread use of residential fuel cell units is:
cost
134
Substituting 10% of gasoline with ethanol (making E10) will result in:
up to 20% worse fuel economy
135
The component of a heat pump where heat is released to the ambient environment is called the:
condenser
136
The United States produces more ethanol annually than:
Canada, China, India
137
What component keeps the refrigerant moving in a heat pump?
compressor
138
What is the most important reason why a geothermal ground loop needs to be sized correctly?
Because a geothermal loop cannot be easily changed
139
What is the primary purpose of a desuperheater?
to provide hot water
140
When do the electric heat strips on a heat pump turn on?
Whenever the heat pump cannot extract enough heat from the ambient environment to meet the heating load
141
Which country in the world has the most installed geothermal energy electricity capacity?
United States
142
Which country in the world produces the most electricity from geothermal energy?
United States
Slide 22 of the "Geothermal Energy" lecture notes that the US has the highest installed capacity in the world. I realize a lot of students chose Iceland; that was not included with the purpose of tricking you, but to help you understand the difference in scale.
143
Which of the following are an advantage of biodiesel? Select all that apply.
can be made at home, availability of source material, biodegradable
144
Which of the following are an advantage of fuel cells over other forms of renewable energy generation? Select all that apply.
Systems have an ability to provide both baseload power and peak power., Systems generate electricity using one of the most abundant chemicals on earth.
145
Which of the following could be considered an energy crop?
trees
146
Which of the following geoexchange systems is considered an open loop?
standing column well
147
Which of the following heat pump systems would likely give the best performance at the lowest operating cost?
system sized for 100% of the heating load and 125% of the cooling load
148
Which of the following is a byproduct of biodiesel?
glycerol
149
Which of the following is a form of heat loss in a building?
conduction
150
Which of the following is an advantage of geothermal heat pumps over other forms of energy generation from renewable sources?
Systems might be cost-effective on almost every home in the United States.
Remember that the temperature of the ground at the depth where a GHP would be used is relatively constant and as such, GHPs are not limited to areas where conventional geothermal energy generation would be used. This means that unlike solar, wind, and hydro - the suitability of which changes by location - GHPs might be used everywhere with similar cost and efficiency.
151
Which of the following is not a potential source of biogas?
used motor oil
152
Which of the following is the best location for a ground source heat pump?
a site with equal heating and cooling needs
153
Which of the following is the most common sources of hydrogen for use in fuel cells?
natural gas
154
Which of the following types of geothermal energy plant has the least issues with air emissions?
binary cycle
155
Which of the following would be considered an advantage of geothermal energy? Select all that apply.
low cost of fuel
156
Which of the following would be the approximate length of a horizontal closed loop for a 4-ton geothermal heat pump?
2,000 feet
157
Which one of the following is not found in a geothermal heat pump system?
outdoor unit
158
What is the COP of a heat pump with a 34,000 BTU/hour capacity and 2kW input power? Round your answer to the nearest whole number.
5
Coefficiency Of Performance (COP) = hh / hw
where hh = heat produced (BTU/hour)
where hw = equivalent electric energy input (BTU/hour) = 3413 * Pw
where Pw = electrical input energy in kW
COP = 34,000 / (3413 * 2) = 4.98
159
From what source is the majority of the United States' ethanol made?
corn
160
Name one of the two main types of biofuel.
ethanol
161
Biomass is the largest renewable energy source in the United States.
True
162
Compared with Iowa, North Carolina has a more varied mix of biomass resources.
True
163
Fuel cells are one of the most scalable renewable energy technologies.
True
164
Hydrogen has no smell, but odorants are added to help detect leaks.
False
No odorant is light enough to travel with hydrogen.
165
Hydrogen is the most powerful power source on Earth.
False
166
In general, the temperature of rocks within the earth increases with depth.
True
167
More than half of the United States' corn crop is used to make ethanol.
False
168
Most small fuel cell units utilize hydrogen storage technology.
False
169
Refined biogas and natural gas can be used interchangably.
True
170
The EROI of cellulosic ethanol is higher than corn ethanol.
True
171
A clear solar window means that an array remains unshaded between which hours?
9:00 AM through 3:00 PM
172
A PV module that is 10% shaded will most likely see what drop in performance?
90%
173
A PV mounting system that adjusts every day for altitude but not azimuth is called a:
single-axis tracker
174
In the northern hemisphere the days are longer in the summer and shorter in the winter primarily because of:
the tilt of the Earth
175
Perpendicular to the sun is called:
normal
176
The most important factor governing how much insolation falls in a particular location is:
latitude
177
The sun will always be highest in the sky at:
solar noon
178
To maximize the amount of insolation on a surface the angle of incidence between the surface and the sun should be:
90º
179
Which of the following are the primary problems with tracking systems? Select all that apply.
cost, maintenance
180
Which of the following factors will likely be your lowest concern in the installation of a residential rooftop PV array?
vandalism
181
Which of the following statements is most accurate regarding world manufacturing of PV panels?
China's share of PV manufacturing has gone from almost none to almost the majority.
182
Which of the following will not be able to be determined using Google Earth when performing a preliminary solar assessment?
whether the site has a clear solar window
183
Using the information below, determine how much insolation, in kWh/m2/day, this array would receive in March at a fixed latitude tilt? Provide only the number and round to one decimal place..
5.2
97% x 5.4 = 5.238 kWh/m2/day
The correct answer is: 5.238
184
It is necessary to determine the electrical load and design month for a grid-tied PV system.
False
185
The Solar Pathfinder only shows the obstructions that occur during the solar window.
False
186
After 20 years the efficiency of a PV module drops off due primarily to:
weathering
187
Before it can induce the photovoltaic effect, pure silicon must be:
doped with impurities
188
What is the power output at VOC?
zero
189
What is the efficiency of a PV module that produces 200W and is 1m x 1.5m in size? Provide only the number and round to two decimal places if necessary.
13.33
1.5 square meters x 1000 W/m2 = 1500W max irradiance
200 ÷ 1500 = 13.3%
190
What is the rated power output (in watts) of a module with VMP of 17.1V and IMP of 2.5A? Provide only the number!
42.75
191
What should the actual tilt be, in degrees, for a stand-alone PV array located in Nome, Alaska where the critical loads are in the winter? Provide only the number and round to one decimal place.
79.5
The coordinates for Nome, Alaska are 64.5039°N, 165.3994°W (this is easy to find, Google will tell you this). Therefore:
64.5° latitude + 15° tilt (critical loads are in the winter!) = 79.5° actual tilt
192
This is a Sharp PV module rated at 240W. Approximately how much annual energy, in kWh, would a grid-tied fixed array containing 8 of these modules produce in area with an insolation value of 5.2? Provide only the number and round to the nearest whole number.
2733
240W panel rating (STC) x .75 de-rating factor = 180W AC
8 modules x 180W = 1,440W for the array
1,440W x 5.2 insolation = 7,488 Wh/day
7,488Wh/day x 365 days per year = 2,733,120 Wh/year
2,733,120 Wh = 2,733 kWh/year
193
Assuming an average of 2W, what is the approximate wattage of this PV module? Provide only the number. (32 cells)
32
Since wattage ranges from 1-3 per module, accepted answers include:
1 x 32 = 32
2 x 32 = 64
3 x 32 = 96
194
ISC is always higher than IMP.
True
195
A 100 AH battery provides:
2A for 50 hours
196
Advantages of microinverters include which of the following? Select all that apply.
smaller wiring, higher efficiency, allows for individual module tracking
197
DC to AC efficiency is typically around:
90%
198
How many AH per day is required in a 1200Ah battery bank for a DOD of 50%?
2,400
1200Ah per day / 0.5 = 2400Ah per day
199
How many AH would a 400Ah battery bank need for 5 days of autonomy?
2,000
400 Ah/day * 5 days = 2,000Ah
200
How many days of autonomy should be allocated for non-essential uses or for systems with a backup generator?
2-3
201
Which of the following are characteristics of a battery? Select all that apply.
direct current, contain both an anode and a cathode, maintain a voltage, even when "dead"
202
Which of the following functions do PV system batteries provide? Select all that apply.
stores excess electricity produced, provides electricity at night, establishes a consistent voltage across the system, powers larger loads than the PV array by itself
203
How many amp-hours (Ah) per day is needed in a battery bank to meet the needs of a system requiring 7,092 Wh/day at 18V? Please provide only the number.
394
Watts = Amps x Volts
Amp-hours (Ah) x Voltage = Watt-hours (Wh)
Ah/day = (Wh per day / system voltage)
7092Wh per day / 18 volts = 394Ah
204
What is the total energy load, in kWh, for the following? Please provide only the number.
120W of lighting for 8 hours per day
2000W stove for 30 minutes per day
200W TV for 4 hours per day
70W laptop for 2 hours per day
2.9
960 + 1000 + 800 + 140 = 2900 watt-hour/day = 2.9 kWh
205
A battery that is frequently and quickly discharged will have less capacity.
True
206
It is good practice to oversize a PV battery bank relative to the array.
False
An oversized battery bank will remain in a state of partial charge and will not be fully recharged, especially during cloudy weather. This will shorten life and capacity. An undersized bank will be charged up too fast, shortening battery life.
207
Regardless of type and rating, new batteries should never be added to an existing battery bank.
True
New batteries must be added in parallel to maintain system voltage. Excessive "paralleling" increases the chance of failure from a bad cell. Even though the rating might be the same, the new batteries will have a different capacity than the old, requiring different charge rates. The internal cell resistances will be different.
208
When designing a system utilizing batteries, a DOD of 50% is typically used.
True
209
A DC-to-AC de-rating factor of which percentage is commonly used?
75%
210
A solar thermal storage tank must be sized to meet what?
summer output of collector
When sizing a solar thermal system, you need start by choosing tanks that can handle what the collectors are actually producing. See slide 20 of the Site Assessment Solar Thermal PP.
210
A solar thermal system designed to provide space heating should use which type of collector?
evacuated tube
210
About how much more output will a single-axis tracker give a PV system over a fixed tilt?
20%
211
All of the following are viable methods of dumping heat in a glycol system except:
draining the glycol back to a tank
During the lecture, it was noted that water is almost always used as the heat transfer fluid in drainback systems; especially when using glycol, evacuated tubes are almost always used. See slide 14 of the Components and Operation Solar Thermal PP.
212
An expansion tank is found only on which type of solar thermal system?
glycol
213
An inverter is always required on which of the following PV systems?
grid-tied
214
Direction conversion of photons to electricity is known as:
photovoltaic effect
215
Fixed-tilt PV systems that are grid-tied or designed for year-round loads should have a tilt equal to:
latitude
216
How does the heat transfer fluid flow through an evacuated tube collector?
It flows across the top header of the collector., It does not flow to the collector at all.
217
How many 24V/200Ah batteries will be required for a 24V system with 3240 Wh/day loads and 2 days of autonomy?
3
3240 Wh per day / 0.9 efficiency from DC to AC = 3600 Wh actually needed
3600 Wh / 24 volts = 150 Ah per day needed
150 Ah per day * 2 days of autonomy = 300 Ah per day
300 Ah per day / 0.5 DOD limit = 600 Ah per day total needed
24 volt system / 24 volts per battery = 1 battery in series
600 Ah per day needed / 200 Ah per battery = 3 battery in parallel
1 battery in series * 3 batteries in parallel = 3 batteries total
218
How many days of autonomy should be allocated for critical loads or no backup?
5-7
219
How many of the batteries in the image below will be needed in a bank designed for 1200Ah per day at 24V?
To get the number of batteries required in the series: 24 volts required / 12 volts per battery = 2 batteries per series
To get the number of batteries required in parallel: 1200 Ah per day / 50 AH = 24 batteries
2 batteries in series * 24 batteries in parallel = 48 batteries total
220
How many volts does the average PV cell produce?
0.5 volts
221
How much irradiance would a PV module with 25% efficiency capture?
250 W/m2
222
If a flat plate collector is sloped to one side, what type of system is it?
drainback
223
Relative to due south, what is the loss of performance, in percent, of a solar thermal hot water system that faces southeast?
3%
Relative to due south, southeast or southwest orientation will only reduce the energy produced by 3%. SE is preferred to SW because it is sunnier. See slide 14 of the Solar Thermal 2 PP.
224
The controller constantly manages what?
the temperature of the water in the tank relative to the temperature of the collector
225
What are the primary advantages of a net metered PV system? Select all that are correct.
PV power is credited at the retail rate., Backup power is provided during nights and inclement weather.
226
What are the primary advantages of a variable speed pump over a constant speed pump? Select all that apply.
It does not short cycle., It is more efficient.
227
What does a parabolic dish receiver have that a parabolic trough system does not?
external heat engine
228
What is the cost of power produced, in dollars per watt, of a panel with a peak DC wattage of 400W that cost $2,400?
$6 per watt, $8 per watt
400W (STC) * 0.75 de-rating factor = 300W AC
$2400 / 300W = $8 per watt
229
What is the maximum theoretical capacity factor of a concentrating solar power system without storage?
50%
230
What is the primary advantage of a thermosyphon system over a batch system?
insulation is added to the tank
231
What working fluid is most commonly used in a drainback solar thermal system?
water
Glycol CAN be used, but it was made very clear at ~14:35 of the second Solar Thermal lecture (slide 22 of the PP), that water is by far the most common.
232
When does glycol turn acidic and corrosive in a solar thermal system?
when it overheats
233
When does the control open the diverting valve in a solar pool heater?
when the collector is sufficiently warmer than the pool
234
Which day of the year should be used to determine the worst-case scenario for a shading analysis?
December 21
235
Which of the following components would not normally be purchased in the installation of a solar pool heater?
new pump
236
Which of the following contributes to increased voltage drop? Select all that apply.
longer wires, smaller wires, higher ambient temperature
237
Which of the following houses is likely the best candidate for solar thermal hot water in terms of economics?
6-person family home with an aging electric water heater
238
Which of the following is an advantage of a stand-alone AC system over a stand-alone DC system?
Standard household loads and appliances can be accommodated.
239
Which of the following is an advantage of flooded lead acid batteries (wet cells)?
can supply high surge current
240
Which of the following is true regarding how quickly a PV panel will "use up" its stored electrons?
PV panels do not store any electrons.
PV panels are a perpetual converter, rather than a battery, so they do not have any electrons to "use up".
241
Which of the following would be a load powered by a Day Use PV System?
DC pump
242
Which of the following would be considered a hybrid system?
PV + wind turbine
243
Why are open loop solar thermal systems discouraged in most cases? Select all that apply.
possibility of corrosion and scale, possibility of water contamination, inadequate freeze protection
244
Why can’t a solar thermal passive batch system be used in North Carolina?
it contains no freeze protection
245
Why do solar pool heaters use unglazed plastic collectors?
because only low heat is needed
246
How many Ah per day is needed in a battery bank to meet the needs of a system requiring 9,576 Wh/day at 12V? Do not factor in DOD or Days of Autonomy. Provide only the number and round to the nearest whole number if necessary.
887
Watts = Amps x Volts
Amp-hours (Ah) x Voltage = Watt-hours (Wh)
Ah/day = (Wh per day / system voltage)
9576Wh per day / 0.9 efficiency from DC to AC = 10,640Wh actually needed
10640Wh per day / 12 volts = 886.67Ah
247
How many AH per day is required in a 400Ah battery bank for a DOD of 50%? Please provide only the number.
800
400Ah per day / 0.5 = 800Ah per day
248
How many AH would a 300Ah battery bank need for 3 days of autonomy? Please provide only the number.
900
300 Ah/day * 3 days = 900Ah
249
Use the information below to determine how much energy, in kWh/m2, a fixed latitude-tilt PV system can capture in July in Wilmington, NC. Provide only the number.
5.5
Under the "Fixed array" category, go to the "Latitude" line and find the "Jul" column.
250
Using the module in the image below, what is the maximum amount of power (as a whole number) the module can produce? Provide only the number.
185
Pmp = Vmp * Imp
37.5V * 4.95A = 185W
251
A parabolic trough system operates as a closed loop.
True
252
A solar pool heater can be used to cool a pool as well as heat it.
True
253
An AC pump can be run directly from a PV panel.
False
254
As heat builds up due to temperature increase, the voltage in a PV module decreases.
True
255
Concentrating solar thermal is economically viable throughout the majority of the U.S.
False
256
Current increases at lower temperatures, but battery life decreases.
False
257
Frequently shallow-cycling a battery will result in a longer life and higher reserve capacity.
True
See slide 26 of the Batteries PP.
258
Overcharging shortens the life of the battery while overdischarging causes a potentially unsafe loss of electrolyte.
False
259
Polycrystalline cells handle higher temperatures better than monocrystalline cells.
True
260
PV panels do not usually work on cloudy days.
False
261
