background paper -- solar electricity

Background Paper: Solar Electricity

Yukon Energy Charrette

2011 March 6-9, Whitehorse

Developed by

Gordon Howell, P.Eng.

15006 - 103 Avenue, Edmonton T5P 0N8

Voice: +1 780 484 0476

Fax: +1 780 484 3956

E-mail: [email protected]

Background Paper: Solar Electricity Yukon Energy Charrette

DESIGN AND DEVELOPMENT SPECIALISTS IN SOLAR-ELECTRIC SYSTEMS

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1. Brief Overview of Electricity, Energy and Power

Discussions about electricity need to include both energy and power. Many myths and mis-understandings abound regarding electricity, energy and power. It is critically important to not mix these all up, but many people do, including some engineers and including some people in the electric industries. These are very important basics for everyone in the charrette to understand well in order for the discussions to be focussed on the well-grounded subject matters.

Energy is the ability to move an object over a distance. It can take many forms, such as chemical energy, thermal energy, mechanical energy, kinetic energy, potential energy, electrical energy, atomic energy, light energy – but it is all just energy and it is measured in joules (J).

Power is the rate (or speed) at which energy flows. It is not electricity. It can be seen as the amount of energy being used in a moment of time. It is measured in joules per second (J/s), which has been encapsulated into another term called a watt (W). 1 J/s = 1 W.

Electricity is electronic charges. It is not power – the public gets immensely confused when electricity is referenced as “power”. Electricity is not energy either, but it contains energy (as do all objects and materials) and we know how to extract the energy from electricity in order to make it do useful work.

A useful analogy between energy and power is with distance and speed, as follows:

Analogous with: Energy is the ability to do work Distance is the ability to get somewhere Power is the rate at which energy flows Speed is the rate at which distance passes by

Measured in Measured in Energy: joules Distance: metres (or km) Power: joules per second (= J/s = W) Speed: metres per second (or km/h)

Then, for example, when we take a light bulb using 100 joules of electricity energy per second (= 100 W) and operate it for 10 hours we know it uses 100 x 10 watt-hours (or watts x hours = Wh) of electrical energy = 1000 Wh = 1 kWh (= k x W x h).

kWh is merely another energy unit in parallel with joules. kW is a unit of energy flow (= power). Many people mix up kWh with kW, which seems to leave them confused about the subject. In comparison we don’t mix up distance (km) with speed (km/h).

In simplistic terms, when electric utility companies decide the size (or capacity) of electrical generating, transmitting and distributing systems they largely only need to consider the maximum energy flow (= maximum power not total energy) over the year. (though many other complex electrical engineering factors related to the stability of these systems are considered also) When we know we can meet this maximum flow, then we know we can meet the lesser energy flow needs of the electricity consuming devices at all the other moments in time.

We only need to consider the annual amount of energy needed (not energy flow) when we are looking at the amount of energy resource that is available to generate the energy over a year.

We as electricity customers don’t buy electrical “power” (in kW); we buy electrical energy (in kWh). Electricity is priced as ¢/kWh of electrical energy, not as electrical power in ¢/kW. Commercial, farm and industrial customers may also be charged an electrical energy-flow fee, but this fee is actually based on a peak energy flow and is intended to discourage simultaneous energy flow from a number of electrical loads, which would require the system’s electrical infrastructure to be upgraded at great expense but for little energy revenue.



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2. Resource Capacity – Solar Energy

Solar energy is the energy contained in the light emanating from the sun. The amount that can be generated depends on the intensity of the solar radiation. Solar-electric system generating capacities are rated at intensities of 1000 W/m2, which is an extremely bright second with not a cloud in the sky. Such conditions can occur any day of the year including winter.

Solar energy is not “discovered” in the same way as other energy sources are prospected. Though measuring solar radiation at proposed generating-plant sites can be useful, it can easily be determined for most performance modelling and site feasibility purposes from many sophisticated software models available and from the many detailed satellite measurements that have been co-related with ground-based measurements at some of Environment Canada’s weather stations.

Many people think that northern Canada has little solar energy potential compared to the south, which is not well founded. Table 1 provides brief details of the minimum and maximum annual amount of solar energy available in Whitehorse. The minimum is shown by the global radiation on a horizontal surface (column B); the maximum is shown by the radiation available to a 2-axis tracking system (column E) and the monthly variation of horizontal global (column I) and 2-axis tracking (column J). It also compares Whitehorse with some Canadian cities and with some desert locations where solar energy is actively under development.

The amount of energy in solar radiation incident on the Yukon’s total surface area every year is 1.2 million times more than the 375 GWh that the Yukon generates in electrical energy. Of course this is an impractical comment but it indicates the size of the solar resource. Eliminating the area for lakes, rivers, towns and farms, and assuming that 90%(?) of the land area is in accessible due to mountainous leaves 6% of the land area available for solar generation. On this land then, the available solar radiation is 80,000 times more than the Yukon’s electricity generation. This provides the basis for the discussion about the solar energy resource.

However, usually the power resource, not the energy resource, is the critical point for energy system design and planning. The power resource is the ability of the technologies to deliver the energy as immediately needed, and which is strongly related to its ability to store energy. The delivery on demand and the energy storage is the key to the implementation of all energy technologies. However, it is the generation of energy, not power, that causes damage to the environment and thus needs to be of grave concern in choosing the source for generating electrical energy.

3. Solar-Electric Generating Technologies – What Are They?

Electricity generated from solar energy can typically be categorised into two technologies: solar photovoltaic (known as PV) and solar thermal-electric 1. These are distinct from solar thermal technologies that convert solar energy into heat for the purposes of heating buildings, potable water, and industrial processes.

Though this background paper will provide a brief overview of solar thermal-electric technologies, its major focus is on solar PV because it is the most wide-spread, most developed, most readily available and is the sole focus of my professional work.

1 Informative overviews of solar electric technologies can be found on Wikipedia at Solar_thermal_energy,

Concentrating_solar_power, Photovoltaics and Concentrated_photovoltaics.



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Table 1. Comparison of average annual solar radiation in several cities 2

(A) (B) (C) (D) (E) (F) (G) (H) (I) (J)

Solar data shown in kWh/m2/day Horizontal

Ratio of diffuse

Compared to Whitehorse 3

Ratio of monthly max. to min. 3

Location Global Clear

sky Diffuse 2-axis

Trackingto 2-axis Global 2-axis Global

horizontal 2-axis

tracking

Whitehorse 2.8 4.1 1.4 3.5 41% 100% 100% 28 10

Edmonton (Namao)

3.2 4.6 1.6 3.6 43% 114% 106% 10 5

Vancouver (Harbour)

3.4 5.1 1.6 3.6 44% 120% 105% 6.5 4

Medicine Hat 3.6 5.0 1.6 4.0 41% 126% 116% 6.9 4

Toronto 3.6 5.3 1.5 4.0 38% 125% 115% 4.6 2.5

Mojave Desert, America

5.3 6.1 1.3 7.0 19% 188% 203% 3 1.9

Andalusia, Spain

4.9 5.7 1.4 6.2 22% 172% 179% 3.6 2.4

Morocco 5.0 5.9 1.5 6.0 25% 175% 174% 3 2

Solar Thermal-Electric The development of solar thermal-electric technologies, also called concentrating solar power (CSP), is rapidly progressing, along with major cost reductions. They consist of a number of technologies at the utility-scale only:

• solar power towers using thousands of heliostat mirrors to heat molten salt;

• parabolic troughs that concentrate solar radiation onto a thin oil-filled pipe;

• concentrating linear Fresnel lens reflectors; and

• dish Stirling engines.

2 These data were obtained from the NASA Langley Research Center Atmospheric Science Data Center.

They were downloaded from http://eosweb.larc.nasa.gov/PRODOCS/sse/table_sse.html. Global horizontal data and 2-axis data were selected to show the extremes of the worst and the best angles for mounting any solar electricity generating devices. The actual mounting angles would be at some point between these.

3 The numbers in columns (G), (H), (I) and (J) equal their respective numbers for a location in the table divided by the numbers for Whitehorse. Columns (I) and (J) compare the minimum and maximum of the monthly averages. Daily, hourly and day to night ratios are much larger.



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They all involve concentrating the solar radiation in order to heat liquids to very high temperatures. The first three technologies use oil or salts to absorb the heat to boil water to produce steam to drive standard turbine-based electricity generators. Dish Stirling receivers use the heat to drive external-heat-source Stirling engines, which drive electricity generators.

Most concentrating solar technologies need to track the sun in order to be effective. In addition, CSP systems, as well as concentrating solar photovoltaics (CPV), are most effective in desert-like areas, which receive much more solar radiation directly from the sun’s disc instead as of diffused (scattered) radiation from the atmosphere. Diffuse radiation, which occurs in cloudy and overcast conditions, cannot be concentrated. The ratio of diffuse solar radiation to horizontal is shown in Table 1 to compare Canada with desert areas. However, a 1 MW CSP project is being developed in Medicine Hat, Alberta now, and the diffuse component of its solar radiation is just as high as Whitehorse.

Figure 1. 10 MW “Solar One” solar power tower in the Mojave Desert

Solar parabolic-trough plants are the most numerous of the solar thermal-electric technologies and range from 1 MW to 354 MW. In total there are 26 operational solar thermal-electric plants of all technologies in the world today totalling 1265 MW, 29 under construction totalling 1934 MW, and 61 under development totalling 17,500 MW.

As of 2009 September, the cost of building a CSP generating station was typically US$2.50 to $4 per watt. A 250 MW CSP station would cost US $600 million to US$1 billion to build and would generate electricity at a price of 12 to 18 US¢/kWh.

A study done by Greenpeace, the European Solar Thermal Electricity Association, and the International Energy Agency investigated the potential of CSP. It found that CSP could account for up to 25% of the world's energy needs by 2050 and that improving technologies would drop prices from the current range of 15 to 23 €¢/kWh down to 10 to 14 €¢kWh by 2050. Other organizations expect CSP to cost 6 US¢/kWh by 2015 due to efficiency improvements and mass production. In 2009 September, Google expected that the price to be 5 US¢/kWh in 2011 or 2012.



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The price of electrical energy from such systems in the Yukon could be double these price estimates due to lower solar radiation levels and higher transportation and living costs.

Some solar thermal-electric technologies are able to store energy from 3 to 10 hours. This is a significant advantage over solar photovoltaic generating technologies.

Figure 2. Schematic of solar power tower

Figure 3. Solar parabolic trough system



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Figure 4. Schematic of solar parabolic trough system

Figure 5. Tracking concentrating dishes that produce solar heat for a Stirling engine generator



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Another technology, called a solar updraft tower, is in its early stages of development. This heats air and concentrates it through an extremely tall stack, which drives an air-turbine electricity generator.

Figure 6. Concept of the solar updraft tower that generates electricity

Solar Photovoltaics Solar PV cells are an electronic semi-conductor that utilise the photovoltaic effect to convert solar radiation into electrical energy. They operate most efficiently in colder temperatures and in concentrated sunlight.

The market and deployment for solar photovoltaic (PV) technologies is growing rapidly. The International Energy Agency reports an average growth of 46% per year over the last 17 years. System costs are plummeting. Solar photovoltaics consist of two major configurations:

• systems using concentrating PV modules known as CPV, which are largely utility scale only; and

• systems using flat-plate PV modules, which are widely scaled including residential, commercial, municipal, industrial and utility sizes and applications.

Solar Photovoltaics – concentrating Low concentration intensities of 2 to 100 suns are cooled through passive ventilation and if there is a sufficiently high solar acceptance angle then active solar tracking is not required. To achieve cell efficiencies of 30 to 40%, CPV systems concentrate a large amount of solar radiation, usually by using a Fresnel lens, onto a very small area of solar photovoltaic material.

Concentration rates of 100 to 300 suns, require two-axis tracking and cooling of the cells (whether passive ventilation or active water circulation). High concentration systems concentrate sunlight to intensities of 300 suns or more. The solar cells require high-capacity heat sinks to prevent thermal



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destruction and to manage performance losses. Cell efficiencies of 40% (and system efficiencies of 30%) have now been reached in production.

Diffuse light, which occurs in cloudy and overcast conditions, cannot be concentrated. To reach optimum maximum efficiency, CPV systems are located in areas that receive plentiful direct sunlight, which primarily occurs in desert areas.

CPV systems are traditionally less expensive to produce than flat-plate systems because a much smaller area of expensive solar cells are used. The relative costs are changing considerably however with the reduction in PV cell costs.

There are some suggestions that CPV could be close to reaching grid parity in America, but I have no first-hand information from expert colleagues on this.

Figure 7. Array of Concentrating Solar PV Modules

Solar Photovoltaics – flat plate The balance of this background paper will focus on flat-plate solar PV systems.

Solar-electric systems using flat-plate solar PV modules are the most common and most recognisable of the solar-electric technologies. The object of primary visibility in a solar PV system is the solar PV module, which consists of some 72 to 96 solar PV cells mounted behind glass and in an aluminum frame. A number of solar PV system terms and components are shown in Figure 8 and Figure 9.

As per Figure 9, a system consists of an array of solar PV modules mounted on a rack, connected in various electrical series and parallel configurations to a grid-dependent inverter connected to an electrical panelboard connected to the electric distribution system. Larger systems merely have more modules and inverters along with combiner boxes, fuses, circuit breakers and monitoring instrumentation.



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Figure 8. Solar PV components of a solar PV system

Figure 9. General electrical configuration of a grid-connected solar PV system of any size

4. Technology Strengths

The strengths of solar PV include:

• zero operating emissions;

• payback of system manufactured energy and emissions of between 1 and 4 years;

• very low maintenance requirements;

• reliably generates electrical energy and significantly reduces the emissions of existing fossil-fuelled generators;



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• robust equipment and product standards;

• rapid development of new products;

• design configurations can be very flexible to meet aesthetic, space and energy requirements;

• can provide voltage and VAr support when operating;

• plummeting equipment prices;

• eager competitive national and international equipment suppliers;

• rapidly growing contractor development;

• highly valued and sought after by the public; and

• imminently flexible and scalable from systems with one solar PV module to systems with 10,000,000 PV modules, from small remote or local off-grid to house-sized systems to huge centralised generating plants covering 1000 acres, from pilot-scale to operational.

5. Technology Weaknesses

The weaknesses of solar PV include:

• does not store energy;

• takes up large areas of land, typically 5 to 6 ha/MW (12 to 14 acres/MW) depending on the spacing between the rows of PV modules;

• does not generate reliable electrical power, so needs to be combined with highly flexible electricity generators such as hydro, diesel gensets or gas turbines in order to provide the “firm” generating capacity required by the grid;

• has higher capital costs, though decreasing rapidly; and

• has little wide-spread experience by governments, electric utility industry, regulators, and inspectors, though this is changing rapidly.

6. Potential Electricity Generation

All of the Yukon’s electrical energy could technically be generated from solar radiation. No-one should choose 100% solar electricity however, until all manner of electrical energy efficiency has been implemented because energy efficiency is much cheaper. So (as with all energy sources) the most important option is to achieve significant levels of electricity efficiency first before generating more.

Solar electricity on available land area in the Yukon could generate some 1100 times more electrical energy than the Yukon presently generates 4. A solar photovoltaic system to generate only 100% of the Yukon’s annual electrical energy would have the capacity of 470 MW and be located on 27 km2 of land surface. Though a system of this size is not practical with likely existing energy storage technologies and transmission lines, this shows what is possible with the technology.

The electricity from a plant this size could not be readily supplied into the Yukon’s existing grid because this is four times the capacity of the generators (and likely the transmission lines) presently connected to the main grid.

4 With 9.5% solar PV system efficiency (for example) (including snow cover and various electrical losses),

17% area coverage to allow for access and inter-row shading, and 10% electric distribution system losses.



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Though technically 100% of the Yukon’s total electrical supply (375 GWh in 2009) could be supplied by solar photovoltaic systems, likely in practical terms, only 9% or less could be supplied (as a guess) without any energy storage.

Other large systems:

• There now are over 1000 solar PV systems around the world in 31 countries that are over 2 MW in generating capacity. 5 Some have been operational since the early 1980s in California.

• There are 150 PV plants around the world that have over 10 MW of capacity.

• The current largest plant is in Sarnia, Ontario, with a capacity of 80 MW. (see Figure 10) It became operational in 2010. It will soon be eclipsed by plants that are 150 to 225 MW. The largest two in the world under development are 2000 MW in China and 3000 MW in India.

• The Sarnia plant covers 465 ha (1,150 acres), will generate 120 GWh per year and will displace over 22,000 tonnes of carbon dioxide emissions per year.

Figure 10. 80 MW PV generating plant in Sarnia

7. Capital Cost and Electricity Price

Typical prices for solar PV electricity range from 20 to 60 ¢/kWh depending on the size of the PV system, financing charges and whether owned by a person or business. A 470 MW solar photovoltaic system to generate 100% of the Yukon’s annual electrical energy would cost $1.5 to $2 billion and generate electrical energy at a price of between 20 and 28 ¢/kWh 6.

5 See http://www.pvresources.com/en/top50pv.php 6 Based on an 800 hour per year system yield (9% capacity factor), 50-year plant life, 0.3% per year

maintenance costs, 15-year inverter change-out, 0.5% per year PV module performance degradation, 2% financing charges, 50% accelerated capital cost allowance, 16% marginal business tax rate.



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The capital cost of PV systems ranges from $3/W to $8/W depending on the size of system, as installed in southern Canada and in America. America is developing a plan to reduce the installed cost of PV to $1/W by 2020 at a utility scale.

The only on-going cost associated with solar PV is an annual maintenance cost estimated at 0.3% of capital cost that pays for re-commissioning the system plus any costs for insurance and security. There are no fuel or water costs.

Figure 11. 80 MW PV generating plant in Finsterwalde, Germany

8. Complementary Applications

Though flat-plate solar PV modules do heat up because they are in the sun, no widely-available technology has yet been developed to use that heat. A building-integrated Solarwall/PV system that heats ventilation air for buildings is in the prototype stage.

Concentrating PV and solar thermal (called CPVT), also sometimes called combined heat and power solar (CHAPS) is a cogeneration technology starting to be developed using CPV that both generates electricity and produces heat. The heat may be employed in district heating, water heating and air conditioning, desalination or commercial processes.

9. Time to Market

My guess is that the 80 MW PV system in Sarnia took perhaps 2 to 3 years to build (?). In comparison, a system that generated 10 GWh/year would have a capacity of 13 MW; 20 GWh/year would be generated by a 26 MW system; and 50 GWh/year would be generated by a 63 MW system.



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10. Probability to Market

With the number of systems being developed and constructed around the world every year (growing at over 6000 MW per year now), along with the number of suppliers available to bid on large systems, I can’t imagine much of a completion risk (generating electricity in the Yukon on time and on budget) from the supply chain. There would be several international PV system project developers and contractors that would be very capable of supplying and constructing systems of this size.

11. Regulatory Issues

If the electric utility owned the PV system I don’t see what the regulatory issues (during both construction and operations) that could be showstoppers.

I am not familiar with the Yukon electric industry regulatory governance in order to comment fully on any regulatory issues. I’d be interested in discussions to clarify this so that I could respond better.

12. Environmental Issues

Since it is the generation of energy (not power) that damages the environment, then solar PV electricity reduces the atmospheric and water emissions of standard fossil-fuelled generators. Solar PV electricity has zero operating emissions (apart from people driving to the site for security reasons, to admire it or to show it off). The payback from the emissions and energy expended in its manufacture and installation is typically one to four years depending on where the system is installed.

The solar electricity generation is easily quantified. The resulting reduction in emissions from reducing the operation of the grid’s standard generators can be verified if the baseline emissions from these generators can be verified. Thus any carbon credits arising from solar PV would be saleable.

13. Seasonal Nature

Solar PV systems only generate energy and do not have firm capacity. Solar PV is not dispatchable. It can provide significant energy contribution to an existing generating system that has sufficient firm capacity to meet the entire moment by moment power load.

A PV system’s power output is roughly a linear function of the intensity of solar radiation, with increased efficiencies with colder temperatures. As a result it is not operational at night. In heavy-cloud weather, the radiation intensity can be 100 to 200 W/m2 and so the output at 10% to 20% of rated capacity. Though there can be moments of solar radiation intensity at the rated levels of 1000 W/m2 in any month of the year, it is rare to have PV systems operate at their rated capacity unless there are bright sun hours, cold temperatures and snow reflection. Typical system yields in Whitehorse could be in the order of 800 rated operating hours per year or an annual capacity factor of 9%.

Existing grid generators need to be able to ramp up and down at a rate that matches the net load on the grid (which is the difference between the variable moment by moment loads with the variable PV generation) in order to accommodate the significant changes that can occur in moment by moment PV output. Hydro, Diesel and gas turbines would likely be able to provide this flexibility.



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14. Other Considerations

As Yukon Energy chooses among the various options presented, I suggest that it is critically important for it to make its decision based on:

• a sustainable diversity of generating technologies and efficiency measures;

• full life-cycle cost analyses for the technology including all societal costs and all environmental effects;

• payback of the embodied energy and emissions expended due to manufacturing, transportation and installation;

• the effect on the environment of a technology’s complete full fuel cycle, from cradle to cradle (no technology graves allowed);

• technologies with existing proven designs and performance records; and

• technologies that can guarantee installed capital costs.

I am confident that the very competitive international solar PV industry can deliver on these.

+Gordon Howell, P.Eng. Principal Solar PV Engineer

background paper -- solar electricity

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