Concentrating Solar Power: A Viable Option For Desert Regions

It has been reported for more than 2000 years that Archimedes used mirrors to concentrate sunlight and set Roman ships afire during the seige of Syracuse in 213BC. While much evidence has been presented to refute this claim, it is probably too powerful a legend to die. Nevertheless, the legend supports the saying heard often in the early days of modern solar energy that if solar had been a weapon of war it would have been fully developed by now.

Following the Arab Oil Embargo of 1973-74 and increased U.S. interest in energy issues, the U.S. Department of Energy started a concentrating solar power project called Solar One. It involved hundreds of ground-mounted reflecting mirrors, called heliostats, that followed the sun and directed their sunlight to a water receiver at the top of a 400-foot centrally-located tower.

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The heated water was converted into steam and fed into a steam-turbine electricity generator. Construction of Solar One was completed in 1981 and was operational from 1982 to 1986. It was then redesigned to incorporate molten salt (60% sodium nitrate; 40% potassium nitrate) as the thermal collection and storage medium and relabeled Solar Two. The redesign was needed to address the instability of Solar One when sunlight was disrupted by passing clouds. Solar Two was successfully tested at 10MWe using molten salt but operation was eventually discontinued in the mid 90’s when the industry was unwilling to share further development costs with DOE. The Solar Two tower was eventually demolished in 2009; the heliostats are now being used for astronomy research.

CSP also comes in two other ‘flavor’s, parabolic trough and dish-Stirling, both of which are discussed in the attached PowerPoint (‘Concentrating Solar Power’) that I presented in 2010 to a meeting of utility executives. I did so for two reasons, to make sure the executives were familiar with CSP (which had been of limited visibility for a number of years) and to catch up on the current state of the technology which was beginning to reappear.

Concentrating Solar Power

I will end this blog by emphasizing one of CSP’s major advantages over intermittent renewable energy sources such as PV and wind – it comes with storage. The major barriers to its greater utilization are its requirement for unscattered (direct normal) radiation (you can’t focus scattered sunlight), cost, and the need for cooling (water or air). Deserts, which usually have few clouds and therefore little scattering of sunlight, are natural venues for CSP power plants. Unfortunately, deserts are also known for their lack of water. These issues are discussed in the PowerPoint.

Solar Energy: The Unstoppable Transformative Technology

As most readers of this blog will know solar energy comes in two broad categories: photovoltaics (PV) and concentrated solar power (CSP). The latter category includes concentrated solar thermal power (as in parabolic troughs, …) and concentrating photovoltaics (CPV). This blog will focus on PV; concentrated forms of solar energy will be discussed in a subsequent blog.

PV is a now a well-known and widely deployed form of renewable energy in which radiation from the sun is converted directly into electricity via panels of solar (or PV) cells. They can be roof-mounted or ground-mounted, as shown below, or used in many other ways to provide smaller amounts of electricity to handheld calculators, roadside telephones, battery chargers, remote microwave relay stations, solar lanterns, water pumping, and numerous other applications. It is a modular technology that can be scaled up in kW size as needed. It also lends itself to integration with various building and other materials – e.g., as roof tiles, building facades, blankets, clothing, and other flexible materials. There is an extensive and rapidly growing literature on PV – one hardly knows where to start. One useful starting point I would recommend is
http://wwww.eia.gov/kids/energy.cfm?page=solar_home-basics-k.cfm
Another useful source of information is the web site of the Solar Energy Idustries Association: http://www.seia.org

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Roof-mounted PV

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Ground-mounted PV

There are two energy technologies that I consider transformative (some people prefer the term ‘disruptive’), i.e., they change the way we generate and use electricity. These are fuel cells, which use hydrogen as a ‘fuel’ to generate electricity, water and heat (and will be discussed in a future blog), and PV, the focus of this blog.

PV is transformative because it can be used wherever the sun is shining (e.g., in space to power satellites and space stations, and even on Mars to power robotic vehicles), it can generate power where it is needed without the need for power lines, it is modular, and its cost is coming down significantly as more and more PV is manufactured. Our infrastructure is already highly dependent on PV – think about satellites used for wireless telephony and GPS, and terrestrial PV that increasingly is supplying electricity to individual homes and businesses as well as utilities.

i would also note that our use of terrestrial PV is only beginning. An industry that started in 1973 in the U.S. (PV had been used earlier for space applications) now employs more than 120,000 people in the U.S., will add more than 4 gigawatts (yes, I said gigawatts) in the U.S. alone in 2013, on top of 8.5 GW already installed in the U.S. and 102 GW worldwide. Global additions in both 2011 and 2012 totaled 31 GW, and PV today is, annually, a multi-billion dollar industry and growing.

The above discussion clearly indicates that PV is an unstoppable energy technology, as the German electric utilities have learned and U.S. utilities will eventually learn as well. The problem that PV presents to utilities is its decentralized nature and the fact that PV generation is maximum at peak periods of electricity demand when utilities are used to charging higher than average kWh prices. If this peak demand on the utility systems is reduced by home- or business-generated electricity then utility revenues are adversely affected based on current utility business models.

It seems clear that this business model will have to change, and, based on experience, that utilities will resist this change as long as they can. The German utilities faced this problem first because the German government introduced a feed-in-tariff (FiT) for PV in the 1990’s, stimulating a massive deployment of PV in Germany ever since. Today Germany leads the world in PV deployment with about 30 GW installed. I would even note that on one very sunny summer day last year more than half of Germany’s electrical demand was met by PV. When faced with this reality German utilities got into the PV business and are now even offering energy storage services to the German public.

The U.S. federal government has not yet seen fit to offer a FiT to the American public but several states are taking the lead in stimulating PV and other renewable energy use. U.S. utilities are clearly behind the German curve and some are resisting the new PV reality by making hookup to the grid unnecessarily complicated, by proposing extra charges for homes that install PV and battery storage systems, and not incorporating PV into their own generating systems. This will change, hopefully sooner rather than later, as utilities take advantage of these new business opportunities.

The Role of Government vs. That of the Private Sector

This is a topic that applies to more than just the energy sector, but it is one that I wrestled with as a U.S. DOE official with significant budget responsibilities. Where does the government fit into the research, development and deployment (RD&D) of emerging energy technologies and where is it appropriate to turn these responsibilities over to the private sector? Where do government interests differ from and overlap with private sector interests? How does one balance the two?

In some ways addressing these questions were some of the most difficult decisions of my DOE management career. My immediate staff, aware of the decisions I faced, often said: “That’s why you get paid the big bucks.” If only that were true!

My thinking on these issues was strongly influenced by my familiarity with the DOE renewable energy program at the end of the Carter Administration. I had been a political appointee in that Administration until leaving in 1979 but I had kept in close touch after that with my former DOE colleagues. Something that burned into my memory was the experience the DOE wind energy program had with the Boeing Corporation. After the oil embargo in 1973-74 there was increasing attention to and budget support for renewable energy programs like wind, solar and others. Boeing was supported by the wind program to develop wind turbines for commercial application, a logical approach given Boeing’s experience with aviation propellers, turbine generators, and related technologies. The problem was that Boeing put up none of its own money in this effort, being fully supported by DOE. As we like to say: they had ‘no skin in the game’.

With the arrival of the Reagan Administration this funding situation changed and 100% support from DOE was no longer possible. In fact, the Reagan Administration tried its best to eliminate DOE’s entire renewable energy program, and even DOE. When this loss of total support became known to Boeing they dropped their participation in DOE’s wind program, and I drew a conclusion that guided my future decisions when I returned to DOE as a senior manager in 1991: no RD&D funding to companies that will not do cost-sharing with the government, with the degree of cost-sharing being a function of the level of risk faced by the private sector concern in carrying out its RD&D responsibilities. Thus, when I was in a position in the 1990’s to make such budget decisions my guiding rules were: at least 25% cost-sharing by the private sector when the risk was high in the early stage of a technology’s development; 50% during most of a technology’s development; and 75% when a technology was approaching commercial application. With respect to this latter point, I believed that the government could help get demonstration units into the field for evaluation and confidence building but that the government had no role in commercialization.

I also believe that government should work closely with the private sector to expedite transfer of emerging technologies to the commercial marketplace. This does not mean that government goals overlap completely with private sector goals, as some may believe but I do not. I see government’s RD&D role as ‘looking down the road’, seeing what’s coming, and doing what’s necessary to protect the public’s longer term interests. In addition, our economic system has assigned the private sector the role of maximizing financials returns to investors. Given this latter assignment of responsibility, private sector goals are of necessity shorter term in nature than those of the federal government. Thus, I see it as governnment’s responsibility to set policy and create a financial environment in which government and private sector goals can overlap to the extent possible. They will never be the same, but this is one place where government officials can earn ‘the big bucks’.

I will conclude by noting some recent public discussion of the private sector’s role in serving the public as well as its shareholders. This has been motivated by several corporations, e.g., IBM, making public their primary goal of maximizing shareholder returns. I leave a discussion of whether this is appropriate for another time and for others to discuss.

Flywheels: A Way To Change the Utility Business Model?

Flywheels and other energy storage systems have the potential to change the way electric utilities operate. A while ago I put down my thoughts on flywheels in a 2010 article I share below in this blog.

The context for my thoughts is that the large central station model for utilities is changing as we move toward more decentralized power generation (think renewables). People are also beginning to react to the vulnerability of the current system to outages, whether accidental or deliberate, that leave thousands of people without power for extended periods of time.

Storage of energy, whether electrical or thermal, can reduce this vulnerability and allow greater use of variable (intermittent) renewable energy sources such as solar and wind. Pumped hydro, compressed air energy storage, and batteries have received the most attention to date. For batteries the major barriers have been insufficient storage capacity, purchase and maintenance costs, space requirements, and the inconvenience of replacement of heavy batteries.

Lead acid batteries have been used in cars, boats, buoys, aircraft and other applications requiring portable electricity sources for many years, and will be used for many years into the future. An interesting aspect of lead acid battery use was their powering of electrical vehicles in the early decades of the 20th century when electric vehicles were the dominant form of personal transportation. In fact, Mrs. Henry Ford drove an electric vehicle. This situation changed because of limited range then available with existing batteries and the advent of high energy density liquid petroleum fuels.

This may be changing today with the emergence of more energy dense and lighter lithium ion battery technologies, but cost is still a major consideration. While cheaper lithium ion cells are coming and lithium ion battery packs are being explored actively for a wide range of applications, including electric vehicles and utility power storage, I would like to suggest that flywheels may also have a role to play in our electric utilities’ future. This idea has been swirling around in my head for many years, and has been mentioned by others, but with the advent of advanced flywheels in recent years I believe it is time to take a serious look at using flywheels in individual homes.

An additional consideration is that as decentralized power systems such as solar roofs become more widely accepted, and utility intermediate- and peak-power sales are reduced, utilities are having to think about getting into the solar energy and energy storage businesses, as is already happening in Germany. I expect this to happen in the U.S. as well.

Using Flywheels to Supply Residential Electricity Demand (July 2010)

Flywheels have always appealed to me as an interesting and potentially widely useful energy storage technology. For many years I have thought about using flywheels at individual homes to supply residential electricity demand during waking hours, using less expensive utility electricity at night to recharge the flywheel (i.e., get it up to maximum rotational speed and stored energy). Limitations have been the physical stresses on flywheel components at the high rotational speeds needed to store appreciable amounts of energy (i.e., tens of kWh) and cost. The use of advanced carbon-fiber materials may now have addressed the first limitation, and cost reductions will be associated with large scale manufacturing of the devices (still to come). The purpose of this note is to explore the feasibility and stimulate discussion of such an approach ( a few others have discussed this possibility as well), which has the potential to reduce utility peak power demands, reduce consumer costs by taking consumers off the grid at peak periods, and transform the nature of utilities. It is offered as a personal thought and does not reflect my responsibilities at the U.S. Department of Energy (2013 note: from which I am now retired).

I start by looking at residential consumer demand. According to the U.S. Department of Energy’s Energy Information Administration: “In 2008, the average annual electricity consumption for a U.S. residential utility customer was 11,040 kWh, an average of 920 kilowatt-hours (kWh) per month. Tennessee had the highest annual consumption at 15,624 kWh and Maine the lowest at 6,252 kWh.” This corresponds to an average daily demand of 11,400/365 = 31.2 kWh. Flywheels that can store 25 kWh are commercially available today (see www.beaconpower.com), and it is not unreasonable to assume that slightly larger flywheels could be easily manufactured. Thus, the idea of a flywheel providing a residence’s daily electricity demand is not unreasonable.

How do flywheels work? To quote from the Beacon Power website (there are other flywheel manufacturers as well): “Flywheel energy storage works by accelerating a cylindrical assembly called a rotor (flywheel) to a very high speed and maintaining the energy in the system as rotational energy. The energy is converted back by slowing down the flywheel. The flywheel system itself is a kinetic, or mechanical battery, spinning at very high speeds to store energy that is instantly available when needed.

At the core of Beacon’s flywheel is a carbon-fiber composite rim, supported by a metal hub and shaft and with a motor/generator mounted on the shaft. Together the rim, hub, shaft and motor/generator assembly form the rotor. When charging (or absorbing energy), the flywheel’s motor acts like a load and draws power from the grid to accelerate the rotor to a higher speed. When discharging, the motor is switched into generator mode, and the inertial energy of the rotor drives the generator which, in turn, creates electricity that is then injected back into the grid. Multiple flywheels may be connected together to provide various megawatt-level power capacities. Performance is measured in energy units – kilowatt-hours (kWh) or megawatt-hours (MWh), indicating the amount of energy available over a given period of time.

Beacon’s Smart Energy 25 flywheel has a high-performance rotor assembly that is sealed in a vacuum chamber and spins between 8,000 and 16,000 rpm. At 16,000 rpm the flywheel can store and deliver 25 kWh of extractable energy. At 16,000 rpm, the surface speed of the rim would be approximately Mach 2 – or about 1500 mph – if it were operated in normal atmosphere. At that speed the rim must be enclosed in a high vacuum to reduce friction and energy losses. To reduce losses even further, the rotor is levitated with a combination of permanent magnets and an electromagnetic bearing.”

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An obvious issue associated with flywheels is catastrophic failure. With rotors moving at high rotational speeds and the flywheel structure experiencing large physical stresses, what would happen if a flywheel flew apart? The industry’s answer is that they’re designed for safety, which is probably correct, but people will need additional reassurance, at least for a while. Thus, my proposal would be to place the flywheel unit under garage or carport concrete floors with a removable protective cover, to allow maintenance as needed. Flywheels can also be shielded in other “containers” as well.

Issue #2 is how long does it take to charge up a flywheel at night from full discharge? First we note that there is an energy loss associated with charging/discharging flywheels, and round-trip efficiencies have routinely been quoted in the 70-85 percent range. Recent literature quotes over 90 percent, and for purposes of calculation I shall assume 85 percent as a reasonable number to start with. Thus, to have 31.2 kWh available for useful discharge we will have to supply 31.2/0.85 = 36.7 kWh to the flywheel. A dedicated 40-amp 220 volt circuit provides power at 8.8kW. Thus, fully charging the flywheel from full discharge would require a little more than 4 hours, and this power would be purchased at low overnight rates when utility demand is lowest (at least at present). This could all change, obviously, if charging of hybrid-electric and electric vehicles, and flywheels, becomes widely used. In any case, overnight rates should be lower than daytime rates, especially peak rates.

To utilize a flywheel generator for a home a reliable control system will be required. Much design effort is going into control systems at present (e.g., for hybrid electric vehicles and smart grids), and this application would benefit from these efforts, but it would be an extra cost for the residential customer. Such costs, in addition to the cost of the flywheel and its enclosure and related electrical costs, would have to be balanced against the savings from using cheaper electricity at night. An important counterbalance is the potential set of savings to the utilities of reduced peak demand and the savings from using their currently underutilized generating equipment more fully at night. This raises the possibility of a utility advancing the costs of a flywheel system to its customers, based on its long term savings, as was done with customer installation of ground source heat pumps that also reduced utility peak demand. The advance is then paid back to the utility as an additional charge on the customer’s bill that is reduced by the use of the flywheel.

These are just initial thoughts that I hope will stimulate lots of additional thoughts and reactions. I await your feedback.

(Note: this blog was re-published in the August-September 2013 issue of The Alternative Energy eMagazine, which can be found at http://altenergymag.com/emagazine.php)

Vulnerabilities of U.S. Infrastructure: We Need To Pay More Attention

U.S. infrastructure is highly vulnerable to natural disasters and sabotage and needs increased attention from all levels of government. It is an issue that first caught my attention in the 1980’s and continues to concern me. This blog is my first attempt to write down my thoughts on what I consider a scary subject.

‘Infrastructure’ is defined by Wikipedia as “basic physical and organizational structures needed for the operation of a society or enterprise, or the services and facilities necessary for an economy to function. The term typically refers to the technical structures that support a society, such as roads, bridges, water supply, sewers, electrical grids, telecommunications, and so forth.”

My first exposure to the complexities of maintaining infrastructure came in 1985 at a meeting of the Council of the National Academy of Engineering (NAE). I was then a staff person at the NAS/NRC. Part of the discussion was in response to a Council member’s suggestion that the NAE undertake a study of the vulnerability of the U.S. power distribution network, in response to several instances of power blackouts. Pros and cons of such a study were discussed for about half an hour until it was agreed that the topic was too complicated to undertake a study. I remember that discussion like it was yesterday and have never stopped thinking about it. Hopefully, lots of people today are giving much more thought to that issue, along with other national vulnerabilities, but is it enough?

Let me be specific about my concerns:
– most of our electricity supply today comes from large, centralized power plants that are not terribly well protected if at all (nuclear power plants are protected, but how well is a good question), and most power is distributed over above-ground power lines that are subject to falling trees, storm damage, or sabotage. In my opinion it wouldn’t take much to disable a portion of our electrical grid that removes power from large numbers of people and other utility customers. This concern is exacerbated by our increasing computer control of the grid and its vulnerability to malevolent hacking. Given today’s level of protection against such hacking I am very worried.

Another vulnerability of our power system, one that has received some increasing attention of late, is the impact that an electromagnetic pulse from a solar flare could have on that system. The power line system can act as a giant antenna that captures solar flare energy that overloads the system and burns out power lines and transformers (Note: this happened in the 1860’s and burned out many telegraph lines). While physical components can be replaced it takes time, during which most people will be without power unless they have a backup generator. This is especially true for replacing the large power transformers in the system that are quite expensive and not routinely inventoried.

– another area of concern is the U.S. water supply. In fact, immediately after I learned of the 9/11/2001 attacks in New York City, and in my capacity as a DOE official, I immediately placed a call to one of DOE’s Power Administrations with responsibility for water reservoirs that serve as hydroelectric power as well as domestic water sources. My question was: What are you doing to make sure nobody is poisoning that water supply? We could not discuss that on the telephone, but it was my first thought about how else can a terrorist disrupt our country. I see our water supplies as poorly protected, with a critical need for sensors that can detect even small amounts of contamination. This latter topic is now getting some attention at DOE’s National Laboratories.

A disrupted water supply also has major implications for food production and public health, along with other potentially impacted areas of national life.

– I will end this blog by mentioning only one other area of concern out of the many others that could be discussed, telecommunications. Our communication systems today (telephone, internet, GPS, weather forecasting, ….) are highly dependent on solar-powered satellite links and any disruption to these links, whether inadvertent or deliberate, can disable critical aspects of our society. As a ‘renewable energy advocate’ I am particularly sensitive to the suggestion that we place large (multi-gigawaat) solar power satellites in synchronous orbit around the earth and beam the power down via microwaves. This concept has some strong advocates but I’m not one of them. While the cost of putting large solar arrays in orbit is an obvious concern, I worry most about the vulnerability of such a large array to technological failure (there are micrometeorites up there and things do break, don’t they) and deliberate military attack. One proposal I read about, and never got over, was to put a 10-gigawatt array in orbit above New York City, whose peak demand is about that size. In my opinion, and apparently that of many other people, that’s crazy and I don’t mind saying so.

Nevertheless, reasonably-sized earth-orbiting solar-powered satellites are an important part of today’s world and provide unique and invaluable services. Their vulnerability to failure due to wearing out, micrometeorites hits and solar flare radiation place many services on which we depend at risk.

I see this issue – the vulnerability of our infrastructure systems – as requiring significantly increased national attention, debate and financial support. Please join me in being part of this debate.

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