With this lesson, we continue our survey of energy industries based on energy sources. In this lesson, we will review two renewable energy sources, wind and solar.
By the end of this lesson, you should be able to...
The table below provides an overview of the requirements for Lesson 9. For details, please see individual assignments.
Please refer to the Calendar in Canvas for specific time frames and due dates.
REQUIREMENT |
SUBMITTING YOUR WORK |
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Read Lesson 9 content and any additional assigned material | Not submitted. |
Weekly Activity 9 | Yes—Complete Activity located in the Modules Tab in Canvas. |
Case Study--work with others on your Team to prepare Case Study, following course guidelines | Check Canvas calendar for all Case Study Due Dates. |
The technology and economics of wind and solar make it practical to install and use them over a wide range of scales--from single-household residential installations a kW or less in size to multi-MW power plants. In particular, the ability for electricity consumers to generate some or all of their own electricity invites new circumstances, needs, and opportunities for policy.
Both solar and wind can be used in situations with or without access to electricity from a utility company. When solar or wind is used to generate electricity at a site that is not connected to a local electricity transmission and distribution system, the installation is off-grid (also often referred to as a standalone system). An installation may be off-grid because it is in an area where there is no electricity infrastructure - typically remote areas - or because the wind or solar system is generating enough electricity to support the site, and electricity from the grid is not necessary. More often than not, it is due to the lack of local electricity infrastructure. Because wind and solar are intermittent energy sources - the wind doesn’t always blow and the sun doesn’t always shine - off-grid systems are almost always designed with on-site electricity storage, usually batteries and called "battery backup." Off-grid systems constitute a very small portion of total installed capacity worldwide (remember that capacity refers to the rated output of an energy-generating system, as opposed to generation, which refers to the energy output). In the U.S. the most frequent use of off-grid systems is for small-scale solar applications such as road signs and weather stations.
Solar and wind systems are most often installed at sites that do have access to electricity from the grid. These sites have a meter and are connected to local power lines from the utility company. These installations are on-grid and often called grid tied. (These systems may also have battery-backup, to provide power during times of grid outages.)
When a grid-tied electricity consumer generates some or all of its own electricity that it uses on site, it is called a behind-the-meter (BTM) installation. If you were to put a photovoltaic system on the roof of your home or small business, for example, and used some of it on-site you would have a BTM installation. And when you both buy electricity from others (through the grid) and generate some of your own electricity, you are sometimes referred to as a customer generator.
When wind or solar is used on the scale of a power plant where the electricity being generated is sold to other electricity consumers, the installation is a commercial generator (a power plant), in the same way that other power plants are, like the coal, nuclear, and gas generators we considered earlier.
In BTM generation, the site will use electricity it generates (from the wind or solar) and, when more is needed, draw additional electricity from the grid. If the site is generating more electricity than it is using, the excess electricity is sent out to the grid. Customers pay for the electricity they get from the grid and may get credit for the electricity they send to the grid. This credit may then be used to offset future electricity use. For example, a customer generator may generate more electricity than they use in the summer time which gives them “money in the bank” (kWh in the bank, really) with the utility company. In the winter, when the customer generator needs more electricity than it can generate, electricity is pulled from the grid and the credit is used. When the credit is used up, the customer once again buys electricity from the grid. This may also happen on a daily basis if a customer generates excess energy during some daytime hours and needs to purchase energy at other times. When the utility gives the customer credit for all energy the customer sends to the grid, it is called net metering. Net metering exists in most, but not all, states in the USA but the details vary widely.
Net metering gives the customer generator the opportunity to avoid electricity costs beyond what they have without it. The customer only pays for the “net” amount of electricity that is purchased, which means that the utility in effect pays customers for the electricity they generate and feed into the grid. Many states require utilities to pay "retail" rate for this electricity, which means they pay the same rate the customer pays to the utility. See the image below for an indication of which states have net metering policies. (This is the most updated listing of policies as of October 2017.) This map was taken from the Database of State Incentives for Renewables & Efficiency (DSIRE [1]), which is unequivocally the best source to consult if you want to find which energy incentives are available nationally or in any U.S. state.
Both wind and solar require substantial initial capital outlay relative to the long run operating cost. These systems have no fuel costs. Once built, the operating costs are generally low. Solar photovoltaics (PV, aka solar panels), in particular, have a low operating cost. In addition to components having long rated lives (solar panels are usually warrantied for at least 25 years), there are no moving parts (except in cases where mechanical trackers are used). Under normal conditions, wind turbines will last at least 25 - 30 years, though they require more maintenance than solar PV.
States and countries have implemented a variety of policies meant to incentivize or encourage private investment in clean, renewable energies. The most common of these policies are tax credits, grants/rebates, and performance-based incentives (PBI), including feed-in tariffs (FIT) and renewable portfolio standards (RPS).
A tax credit is just that, a credit. When an individual or business investor earns a tax credit it means that the amount of the credit will be subtracted from a future tax bill. For example, in the United States, we have a Federal Residential Renewable Energy Tax Credit [4] which provides a tax credit covering 30% of the cost of an installation. If you put a photovoltaic system in your yard at a cost of $30,000, you earn a $9,000 tax credit. The government doesn’t mail you a check for this amount. It means you get to deduct that amount from your next tax payment. To realize this money, you will need to have paid at least $9,000 in taxes, but excess credits can "generally" be carried over to future tax years. Note that even if you were owed a refund, this tax credit can be used to increase your refund, as long as you paid at least $9,000 in federal income tax throughout the year.
A rebate means that a government agency or other group (sometimes utility companies) will refund some of the investment. Pennsylvania used to provide a solar rebate program that provided rebates to investors based on the power rating of the system, $1.75/Watt, for example. The rebate was a check mailed directly to the investor (or their designate). Many states still have such programs such this solar PV rebate program in Oregon [5] (description from DSIRE of course!). Different states often have different program specifics. See DSIRE for more examples of programs.
Performance-based incentives (PBIs), also known as production incentives, provide cash payments based on the actual output of the system. For wind and solar electric, this is the number of kilowatt-hours (kWh) generated.
The case study for this course illustrates in detail how a renewable portfolio standard (RPS) policy works. To summarize, an RPS requires utilities to use renewable energy or renewable energy credits (RECs) to account for a certain percentage of their retail electricity sales. A REC is earned by a qualified grid-tied facility for every 1,000 kWh (i.e., 1 MWh) of electricity that is generated using a renewable energy resource. The RECs are then bought and sold through an auction where the market determines the price. The settlement price varies depending on REC supply and demand at any point in time, though special auctions with guaranteed pricing and incentives are sometimes used.
Another type of production-based incentive, a feed-in-tariff (FIT) pays grid-tied renewable energy generators a specified price for the electricity they generate and guarantees them this price for a specified amount of time. This type of policy is widely used in Europe, most notably in Germany, but less so in the USA. This may be changing.
Renewables are not the only energy source receiving government subsidies to keep costs down and encourage consumption. The International Energy Agency (IEA) provides this global assessment in their 2016 World Energy Outlook (released in November of 2016):
"The value of global fossil-fuel consumption subsidies in 2015 is estimated at $325 billion, much lower than the estimate for 2014, which was close to $500 billion... The decrease in the value largely reflects lower international energy prices of subsidized fuels since mid-2014, as the gap between international benchmark and end-user prices is closed by decreased international prices of energy, but it also incorporates the impact of pricing reform. Of the total, oil subsidies accounted for 44% of the total ($145 billion, covering an estimated 11% of global oil consumption), followed by electricity subsidies estimated at just over $100 billion (covering 17% of global electricity use). Natural gas subsidies were also significant, amounting to nearly $80 billion (affecting the price paid for 25% of gas consumption). Coal subsides are relatively small, at $1 billion in 2015"
International Energy Agency, World Energy Outlook 2016, p. 99.
The IEA goes on to address market distortion and their projection of the continued need for subsidies. (The New Policies Scenario is the IEA's baseline scenario, and assumes that countries will comply with policy commitments and plans. There is also a description of other IEA scenarios) [6]
"In the case of subsidies to renewables (examined in detail in Chapter 11), these continue to be necessary to incentivize investment in renewables over fossil-fuel alternatives, for as long as markets fail to reflect the environmental and health costs associated with the emissions of CO2 and other pollutants. But as technology costs come down and electricity and CO2 prices increase in several markets, more and more new renewable energy projects become economically competitive without any state support: in India, solar PV is competitive without subsidies well before 2030; for the world as a whole, most new renewables-based generation in 2040 does not require subsidies. The value of the subsidies paid to all forms of renewable energy peaks at $240 billion in 2030 in the New Policies Scenario and then falls back to $200 billion by 2040, remaining well below the today’s value for fossil-fuel consumption subsidies. The subsidy per unit of renewables-based electricity generation falls dramatically: subsidies to renewable-based generation rise by some 30% over the period to 2040, yet the electricity generated by non-hydro renewables increases by a factor of five over the same period."
International Energy Agency, World Energy Outlook 2016, p. 100.
It is difficult to put an objective number on the amount and distribution of energy subsidies in the United States, due to the complexity of the inner workings of our tax code. As one Forbes article [7] put it, "Just how taxpayer money gets doled out is mired in so much intricacy that is difficult to follow." (And that's from Forbes, "among the most trusted resources for the world's business and investment leaders!")
One can easily find news from credible sources saying that both in the United States and globally, fossil-fuels are subsidized more than renewables, and vice versa, depending on how you scope which subsidies and tax breaks to include and how you measure the amount (total $ or total $/BTU produced, for example). Regardless of the relative subsidy, a strong case can be made for reducing fossil-fuel subsidies, especially with regards to climate change. For example, in 2015, a coalition of eight governments (Costa Rica, Denmark, Ethiopia, Finland, New Zealand, Norway, Sweden, and Switzerland) calling themselves the Friends of Fossil Fuel Subsidy Reform submitted a communique "encouraging governments to prioritize the reform of fossil fuel subsidies," mostly in an effort to influence the recent Paris Climate Talks.
Via the International Institute for Sustainable Development [8], read "Fossil Fuel Subsidy Reform Communique [9]".
In any case, when electricity is generated at or near where it is going to be used (the “load center”), this is called distributed generation. Solar and wind are both widely used for distributed generation, but so are non-renewable sources such as diesel generators. The U.S. EPA [10] defines distributed generation as "a variety of technologies that generate electricity at or near where it will be used, such as solar panels and combined heat and power."
The diagram looks like a bulls eye with “Grid Services” in the middle. Going outwards, the rings are “Financial”, “Security”, “Environmental”, and “Social”. Each of the categories have text associated with them.
ALL information on this page through Wind Power comes directly from World Energy Outlook 2013 [13], pp 208 - 211
Unlike dispatchable power generation technologies, which may be ramped up or down to match demand, the output from solar PV and wind power is tied to the availability of the resource. (Electricity generation from (non-dispatchable) variable renewables, such as wind and solar, is weather dependent and can only be adjusted to demand within the limits of the resource availability.) Since their availability varies over time, they are often referred to as variable renewables, to distinguish them from the dispatchable power plants (fossil fuel-fired, hydropower with reservoir storage, geothermal and bioenergy). Wind and solar PV power are not the only variable renewables – others include run-of-river hydropower (without reservoir storage) and concentrating solar power (without storage) – but PV and windpower are the focus of this section as they have experienced particularly strong growth in recent years and this is expected to continue.
The characteristics of variable renewables have direct implications for their integration into power systems (IEA). The relevant properties include:
Variability: Power generation from wind and solar is bound to the variations of the wind speed and levels of solar irradiance.
Resource location: Good wind and solar resources may be located far from load centres. This is particularly true for wind power, both onshore and offshore, but less so for solar PV, as the resource is more evenly distributed.
Modularity: Wind turbines and solar PV systems have capacities that are typically on the order of tens of kilowatts (kW) to megawatts (MW), much smaller than conventional power plants that have capacities on the order of hundreds of MW.
Uncertainty: The accuracy of forecasting wind speeds and solar irradiance levels diminishes the earlier the prediction is made for a particular period, though forecasting capabilities for the relevant time-frames for power system operation (i.e., next hours today-ahead) are improving.
Low operating costs: once installed, wind and solar power systems generate electricity at very low operating costs, as no fuel costs are incurred.
Non-synchronous generation: power systems are run at one synchronous frequency: most generators turn at exactly the same rate (commonly 50 Hz or 60 Hz), synchronized through the power grid. Wind and solar generators are mostly non-synchronous, that is, not operating at the frequency of the system.
The extent to which these properties of variable renewables pose challenges for system integration largely depends on site-specific factors, such as the correlation between the availability of wind and solar generation with power demand, the flexibility of the other units in the system, available storage and interconnection capacity, and the share of variable renewables in the overall generation mix. The speed at which renewables capacity is introduced is also important, as this influences the ability of the system to adapt through the normal investment cycle. Elective policy and regulatory design for variable renewables needs to co-ordinate the rollout of their capacity with the availability of flexible dispatchable capacity, grid maintenance and upgrades, storage infrastructure, efficient market operation design, as well as public and political acceptance.
Generating power from wind turbines varies with the wind speed. Although there are seasonal patterns in some regions, the hourly and daily variations in wind speed have a less predictable, stochastic pattern. Geographically, good wind sites are typically located close to the sea, in flat open spaces and/or on hills or ridgelines, but the suitability of a site also depends on the distance to load centres and site accessibility.
For onshore wind turbines, capacity factors – the ratio of the average output over a given time period to maximum output – typically range from 20% to 35% on an annual basis, excellent sites can reach 45% or above. The power output from new installations is increasing, as turbines with larger rotor diameters and higher hub heights (the distance between the ground and the centre of the rotor) can take advantage of the increased wind speeds at higher altitudes. Moreover, wind projects are increasingly being tailored to the characteristics of the site by varying the height, rotor diameter, and blade type. Wind turbines that are able to operate at low wind speeds offer the advantage of a steadier generation profile, reducing the variability imposed upon the power system, but likely reducing annual generation.
Wind turbines located offshore can take advantage of stronger and more consistent sea breezes. Wind speeds tend to increase with increasing distance from the shore, but so too does the seafloor depth, requiring more complex foundation structures. Capacity factors are generally higher ranging from 30% to 45% or more, as distance from the shore or hub height increases. However, offshore wind turbines are more expensive to install because of the high costs associated with the foundations and offshore grid connections. Bottlenecks can also occur due to a shortage of specialized installation vessels.
Power generation from solar PV installations varies with the level of solar irradiation (irradiation is the amount of solar energy hitting a surface over a period of time) they receive. Irradiation is usually measured in kWh/m2/day or kWh/m2/yr. Geographically, solar irradiation over the course of a year increases with proximity to tropical regions and is more uniformly distributed than wind. Seasonal and daily patterns in output from solar PV systems can be fairly well forecast – on a clear day, solar will follow a consistent pattern, based on the path of the sun through the sky. The power received from the sun is called irradiance, generally measured in W/m2. The irradiance from the sun can be predicted with reasonable accuracy for a given location at a given time of year. Of course, local conditions (particularly shading) can significantly impact irradiance levels. A heavily-shaded area can result in near-zero irradiance levels.
A picture is worth a thousand words! Below are three examples of wind turbine of varying scales.
Please watch the following (4:18) video from First Wind, Where does Wind Power come from? Climbing Inside a Wind Turbine.
LIZ WEIR: Hey, I'm Liz from First Wind. Today, we're going to be doing something that anyone who's ever seen a wind farm is dying to do-- climb one of these bad boys. Let's go.
RYAN FONBUENA: Just hand over hand, and easy as she goes.
LIZ WEIR: All right, sounds good. See you guys up there.
RYAN FONBUENA: Right now, we are at the base unit section. This is at the top of the base section-- the midsection of the tower's bolted up. We're about 85 feet up in the air right now, and only 180 to go.
LIZ WEIR: Sounds good. Now, you're so much faster than the rest of us. About how often do you climb this thing?
RYAN FONBUENA: I try and climb a couple times a week. Not as much as I used to, but with practice, about a six-minute climb is average, for average technicians.
LIZ WEIR: Six minutes, all the way up?
RYAN FONBUENA: All the way up.
LIZ WEIR: Oh, my gosh.
All right, so Ryan, tell us where we are now.
RYAN FONBUENA: Well, where we are now, we're at the yaw deck of the turbine. This is just below the nacelle at the very top of the top tower section. What we have here, these are all the cables that allow the turbine to not only operate, but to communicate with the master control system in the bottom of the tower.
What we also have here are the power cables that delivers energy from the generator back to the grid.
LIZ WEIR: These guys are pretty smart.
RYAN FONBUENA: Yes, they are very intelligent machines. They're constantly tracking wind speed, wind direction, temperatures. They are very intelligent machines.
LIZ WEIR: All right, now we're heading up to the last leg of the trip, up to the nacelle.
RYAN FONBUENA: Yeah, I'll grab the ladder to get us up there, and we'll get the full tour.
LIZ WEIR: Sounds good. I’m smacking my head-- OK. Here we go. All right. Where to?
RYAN FONBUENA: So here we are at the nacelle.
LIZ WEIR: Now, exactly how many feet are we up in the air right now?
RYAN FONBUENA: We're proximately 270 feet in the air right now. So the wind is obviously going to be a lot stronger up here than it is on the ground.
LIZ WEIR: Can you tell us what we're looking at, in front of us?
RYAN FONBUENA: Yes, what's in front of us now is the main shaft. And this is what the rotor, or the hub, and all three blades are bolted to. The main shaft is running to our gear box here. And what the gear box does is take that low speed rotation, transmits it into a high speed rotation into the generator.
LIZ WEIR: So all the power that's coming from here goes right down through the cables we just saw, on a level before us?
RYAN FONBUENA: Yes, that's correct.
LIZ WEIR: All right, well I think what we're all looking forward to doing is heading up top. Think we can go?
RYAN FONBUENA: Yeah, we'll get up on top.
LIZ WEIR: All right, sounds good.
Oh, my god!
All right, so it's pretty cloudy up here today. But in actuality, how high up are we?
RYAN FONBUENA: We're about 275 feet off the ground now, being on top of the nacelle.
LIZ WEIR: Straight up in the air.
RYAN FONBUENA: Yes.
LIZ WEIR: And behind us, you see a weather station. Can you tell us a bit about what that measures?
RYAN FONBUENA: Yes, the met stations that's behind us measures not only the wind speed, but also the wind direction. So the turbine constantly knows where to point itself into the wind. And with the wind speed, to know when to pitch the blades to start capturing the wind, and when to pitch them out when the wind speeds either get too high, or too low.
LIZ WEIR: To learn more about wind power, please come and visit us at firstwind.com. I'm Liz, I'll see you next time.
Please watch the following (2:38) video from Puget Sound Energy.
PRESENTER: We're going to go ahead and climb a C3 wind turbine today. We're going up over 200 feet wind turbine mace wave because of the wind outside. You will be in the close proximity of high voltage cables. 34,500 volts.
PRESENTER 2: So we're set to go ahead and climb up the turbines. So there's a base section, a mid section, and a top section to each turbine. Right now we're in the yaw deck.
This is where the cell’s going to pivot. The gearbox weighs around 20 tons. The generator and air cooler are just less than 10 tons.
As described in the videos above, wind turbines convert the kinetic energy of the wind into mechanical energy that rotates a rotor, which then spins a generator, which generates electricity. This process (from wind to electricity) has a theoretical maximum efficiency of 59.3% (this is called the Betz Limit [22]), but in practice, turbines operate a significantly lower efficiency.
So where does the energy in the wind come from, and how much is there? Wind is caused by differences in pressure - air from high-pressure areas will naturally move toward areas of lower pressure. Pressure differences are caused by differential heating of the surface of the earth. All else being equal, cold air has a higher pressure than warmer air. There are many localized wind sources, but global wind circulation is caused by cold air from polar regions (relatively high pressure) moving toward warm air (relatively low pressure) toward the equator.
The power in the wind is given by the following equation:
Power (W) = 1/2 x ρ x A x v3
Thus, the power available to a wind turbine is based on the density of the air (usually about 1.2 kg/m3), the swept area of the turbine blades (picture a big circle being made by the spinning blades), and the velocity of the wind. Of these, clearly the most variable input is wind speed. However, wind speed is also the most impactful variable because it is cubed, whereas the other inputs are not.
Turbines are rated in terms of capacity, usually in kW or MW. As with other energy sources, this is not the amount of power that a turbine generates at all times - it is the peak output. At peak output, a 100 kW wind turbine will generate 100 kWh of energy over 1 hour (100 kW x 1 h = 100 kWh). To determine the output at different speeds, you need to look at the power curve. The power curve for the 95 kW Northern Power turbine (similar to the turbine in the picture above) is below. As you can see, the turbine will only generate its rated 95 kW with a very limited range of wind speeds. Note also that the turbine has a startup speed of 2 m/s.
Energy.gov's Wind Program gives this description of distributed wind generation:
The Wind Program defines distributed wind in terms of technology application, based on a wind plant's location relative to end-use and power distribution infrastructure, rather than size. The following wind system attributes are used by the Wind Program to characterize them as distributed:
Distributed wind energy systems are commonly installed on, but are not limited to, residential, agricultural, commercial, industrial, and community sites, and can range in size from a 5 kilowatt turbine at a home to a multi-megawatt turbine at a manufacturing facility. Small wind turbine technology, which includes turbines that have a rated capacity of less than or equal to 100 kilowatts, is the primary technology type used in distributed wind energy applications and is the focus of the Wind Program's technology R&D efforts for distributed applications.
Not required, but for more information on distributed wind generation see Distributed wind energy systems [24] and OpenEI's Small Wind Guidebook [25].
IEA Wind is the International Energy Agency's (IEA) Implementing Agreement for Co-operation in the Research, Development, and Deployment of Wind Energy Systems. "Founded in 1974, the IEA Wind Agreement sponsors cooperative research tasks and provides a forum for international discussion of research and development issues" (IEA Wind [26]).
Visit International Energy Agency (IEA) Wind [27] and open the most recent report, the IEA Wind 2015 Annual Report. [28]
In the Executive Summary, read:
Average wind speeds vary widely by geographical location. Take a few minutes to inspect the wind speed charts from the National Renewable Energy Laboratory below. Note the location of the greatest and wind speeds, and think about the physical characteristics of those areas (e.g. flat, mountainous, on-shore, off-shore, etc.). Click here for a larger version of the 30m wind speed image [29] and click here for the 80m image. [30]
In addition to variability being a barrier to wind deployment, the location of wind resources is as well. In general - and certainly, in the U.S. - the best onshore wind resources are not located near major population centers. Approximately 50% [31] of the U.S. population lives within 50 miles of the coast, but as you can see in the maps below, this is generally not where the greatest onshore wind is located. This is a problem because transporting electricity over power lines results in energy loss (as heat) due to electrical resistance in wires. The longer the electricity has to travel, the more energy is lost. To minimize this loss, large (and very expensive) power lines must be built. As you can imagine, this type of infrastructure is lacking in areas of the country that do not have large populations.
For an idea of how expensive building high voltage lines can be ($560 million to $720 million for 224 miles!) and to gain some insight on some interesting issues related to wind, hydro, and international energy issues, read the summary below.
Every single hour, the Earth’s surface receives more energy from the sun than the entire world's human population uses in a year. And, as far as fuel prices go, the price is right!
It is only natural that we have learned to work with the sun--to use it for our convenience and well being. We use energy from the sun in all sorts of ways, to heat water, dry clothes, warm spaces and generate electricity. Be they simple or complex, these designs and technologies all use “solar energy” for useful purposes.
This is the art and science of designing systems (typically buildings) to work in cooperation with the sun, without any mechanization. There are no motors, no fans or blower or switches, for example. Instead there are simple features, such as deep overhangs that provide shading in the summer, when the sun is high and temperatures are warm, but let the sunlight in in the winter, when the sun is low and the warmth is welcomed. If you would like more information, a good starting place is the Department of Energy's Passive Solar Design [34] page. (Clothes lines are another example of passive solar, and wind. A "renewable dryer" investment has a terrific return financially and environmentally!)
This is a broad term for systems that use energy from the sun to heat water (or other material) for a variety of purposes.
For clear understanding and communication, it is useful to keep in mind the broad meaning of “solar thermal” and to be specific regarding the technology of a given application.
These are systems that use energy from the sun to generate electricity. There are two general categories: photovoltaics (PV) and concentrating solar power (CSP).
Certain materials have the natural property of converting energy from the sun into electricity. When the sun hits these materials, electrons start to flow, creating a direct current (DC). This is the photovoltaic effect. Photovoltaic materials (semiconductors) are packaged into solar cells, which are appropriately wired and connected together into modules (also called panels) to collect the flow of electrons into a current and make it available for our use. If you have a solar-powered calculator, the little window is a small solar cell. The solar arrays that you may see on a roof top are an installed group of solar modules wired together. Systems that use photovoltaic components to generate electricity are photovoltaic (PV) systems.
The output of an array is primarily dictated by the amount of solar energy (insolation) hitting the panel. Insolation is highest when the panel is directly facing the sun, when the sun is at its peak in the sky (at solar noon, which is usually not the same as local noon), and when it is unshaded. Insolation is synonymous with irradiation, noted earlier in this lesson. Irradiance, on the other hand, is the amount of solar power (not energy) hitting a surface at any given moment, or the average power over a given period of time. This is typically measured in W/m2.
Like wind, a solar array's capacity is rated in power (usually kW, but larger ones can be rated in MW). Also like wind, solar panels only generate full capacity under optimal conditions, mostly having to do with panel temperature and irradiance level. Further, the capacity is what is directly generated by the panels, and does not include other losses. After generated by a panel, the electricity must travel through wires and (usually) an inverter. There are other factors that impact output, such as panel imperfections, loss of efficiency over time, and mismatch of panels in an array. All of this adds up to losses, usually in the range of 10% - 20%. All of these losses together are called the derating factor. A derating factor of 80% means that 20% of the energy generated by the panel is lost (to heat) before it leaves the PV system. Note that derating does not include losses associated with shading or imperfect panel placement! Finally, the hotter a panel gets, the less energy it generates, and the colder it gets, the more it generates (all else being equal). Because of this, it is not uncommon for a solar array to generate nearly as much electricity on a very cold, clear winter day as a hot summer day, despite the fact that irradiance is significantly higher in the summer.
When all is said and done, it is not unusual for an array to generate 20% - 30% less than its rated capacity, especially if the panels are not tilted at a perfect angle and facing an ideal direction (the compass direction a panel is faced is called its azimuth), and/or is partially shaded during certain times of the year/day.
A 1 kW array will generate 1 kWh of electricity over the course of one hour if it is operating at full capacity, but if it has a derating factor of 15%, it will only generate 0.85 kWh. If there is a 10% additional loss due to shading and other losses, the output would be 0.765 kWh (0.85 kWh x 0.9 = 0.765 kWh).
Systems that use mirrors (heliostats) to reflect (focus) the sun's energy onto a single point or area are called concentrating solar power or CSP systems. They use mirrors to focus energy from the sun to heat synthetic oil, molten salt, gasses, or other materials to high temperatures for purposes of generating electricity (by generating steam to turn a turbine or with a Sterling Engine.) The focused energy may be used to create very high temperatures for generating electricity (with a Sterling Engine or by creating steam to drive a turbine).
These systems use highly concentrated (focused) sunlight to generate electricity directly from photovoltaics. According to a December 2013 report (Concentrated PV (CPV) Report [42], from IHS), "After years of slow progress, the global market for concentrated photovoltaic (CPV) systems is entering a phase of explosive growth, with worldwide installations set to boom by 750 percent from 2013 to the end of 2020. CPV installations are projected to rise to 1,362 megawatts in 2020, up from 160 megawatts in 2013." For better or worse (despite promising research like this [43]at Penn State), the market for concentrated solar PV has yet to materialize, due in large part to the rapid drop in PV module prices.
Please review Canvas calendar for all due dates related to your Nonmarket Analysis Case Study.
Complete "Weekly Activity 9," located in the "Weekly Activities" folder under the Modules tab in Canvas. The activity may include a variety of question types, such as multiple choice, multiple select, ordering, matching, true/false, and "essay" (in some cases these require independent research and may be quantitative). Be sure to read each question carefully.
Unless specifically instructed otherwise, the answers to all questions come from the material presented in the course lesson. Do NOT go "googling around" to find an answer. To complete the Activity successfully, you will need to read the lesson, and all assigned readings, fully and carefully.
Each week a few questions may involve research beyond the material presented in the course lesson. This "research" requirement will be made clear in the question instructions. Be sure to allow yourself time for this! You will be graded on the correctness and quality of your answers. Make your answers as orderly and clear as possible. Help me understand what you are thinking and include data where relevant. Remember, numbers should ALWAYS be accompanied by units of measure (not "300" but "300 kW"). You must provide ALL calculations/equations to receive full credit - try to "talk me through" how you did the analysis.
This Activity is to be done individually and is to represent YOUR OWN WORK. (See Academic Integrity and Research Ethics [44] for a full description of the College's policy related to Academic Integrity and penalties for violation.)
The Activity is not timed, but does close at 11:59 pm EST on the due date as shown in Canvas.
If you have questions about the assignment, please post them to the "Questions about EME 444?" Discussion Forum. I am happy to provide clarification and guidance to help you understand the material and questions (really!). Of course, it is best to ask early.
In this lesson, you learned about renewable energy, specifically the use of wind and solar technology for electricity generation. We reviewed important concepts related to distributed generation and policies that work to support and incentivize these technologies, including on- and off-grid applications, net metering, rebates, tax credits, and performance-based incentives.
You learned:
You have reached the end of Lesson 9! Double-check the list of requirements on the first page of this lesson to make sure you have completed all of the activities listed there.
Links
[1] http://www.dsireusa.org/
[2] http://www.dsireusa.org/resources/detailed-summary-maps/
[3] http://www.forbes.com/sites/uhenergy/2016/03/16/the-solar-net-metering-controversy-who-pays-for-energy-subsidies/#3ed99bca6291
[4] http://programs.dsireusa.org/system/program/detail/1235
[5] http://programs.dsireusa.org/system/program/detail/936
[6] https://www.iea.org/publications/scenariosandprojections/
[7] http://www.forbes.com/sites/kensilverstein/2013/12/06/energy-subsidies-fan-the-flames-but-all-sectors-share-in-the-federal-pie/
[8] http://www.iisd.org/media/governments-call-removal-harmful-fossil-fuel-subsidies
[9] http://www.iisd.org/sites/default/files/publications/FFSR_Communique_17_4_2015.pdf
[10] https://www.epa.gov/energy/distributed-generation
[11] http://www.rmi.org/elab_empower
[12] https://www.e-education.psu.edu/eme444/sites/www.e-education.psu.edu.eme444/files/A%20Reveiw%20of%20Solar%20PV%20Benefit%20and%20Cost%20Studies%20-%20RMI.pdf
[13] http://www.worldenergyoutlook.org/publications/weo-2013/
[14] http://www.windenergy.com/products/skystream/skystream-3.7
[15] http://images.nrel.gov/viewphoto.php?imageId=6327147
[16] http://www.northernpower.com/wind-power-products/northern-power-100-wind-turbine.php
[17] http://images.nrel.gov/viewphoto.php?imageId=6326642
[18] http://www.4coffshore.com/windfarms/arklow-bank-phase-1-ireland-ie01.html
[19] http://images.nrel.gov/viewphoto.php?imageId=6311802
[20] https://www.awea.org/wind-power-101
[21] http://energy.gov/articles/how-wind-turbine-works
[22] http://www.reuk.co.uk/Betz-Limit.htm
[23] http://www.northernpower.com/wp-content/uploads/2015/02/20150212-US-NPS100C-24-brochure.pdf
[24] http://energy.gov/eere/wind/how-distributed-wind-works
[25] http://en.openei.org/wiki/Small_Wind_Guidebook
[26] http://www.ieawind.org/index.html
[27] https://www.ieawind.org/annual_reports_PDF/2015.html
[28] https://www.ieawind.org/annual_reports_PDF/2015/2015%20IEA%20Wind%20AR_small.pdf
[29] http://www.nrel.gov/gis/images/30m_US_Wind.jpg
[30] http://www.nrel.gov/gis/images/80m_wind/awstwspd80onoffbigC3-3dpi600.jpg
[31] https://woodshole.er.usgs.gov/project-pages/newyork/
[32] http://www.nrel.gov/gis/wind.html
[33] http://www.businesswire.com/news/home/20161116006518/en/Presidential-Permit-Paves-Minnesota-Power%E2%80%99s-Great-Northern%C2%A0Transmission
[34] http://energy.gov/energysaver/passive-solar-home-design
[35] http://energy.gov/articles/energy-101-solar-photovoltaics
[36] https://www.scientificamerican.com/article/why-china-is-dominating-the-solar-industry/
[37] http://www.nrel.gov/gis/images/map_pv_national_hi-res_200.jpg
[38] http://www.nrel.gov/gis/solar.html
[39] http://energy.gov/eere/videos/energy-101-concentrating-solar-power
[40] http://www.npr.org/sections/thetwo-way/2016/02/04/465568055/morocco-unveils-a-massive-solar-power-plant-in-the-sahara
[41] https://www.wsj.com/articles/a-solar-project-worth-watching-in-morocco-1473818401
[42] http://press.ihs.com/press-release/design-supply-chain/concentrated-photovoltaic-solar-installations-set-boom-coming-year
[43] http://news.psu.edu/story/474813/2017/07/17/research/rooftop-concentrating-photovoltaics-win-big-over-silicon-outdoor
[44] http://www.ems.psu.edu/current_undergrad_students/academics/integrity_policy