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Week 1: Introductions

1/23/12

Most of your projects at ITP have an on button and a power supply – they are active energy users. Your projects are possible because computation has become extremely efficient – and abundant and cheap. The things you create may help make technology irresistible, an increasing part of daily life; the consequence of the on button is magnified.

But if you’ve ever smelled that “hot electronics” smell from a frying TIP120 or LM7805, you’ve been closer than most to tackling questions about energy directly. And because of your work at ITP, you are in a good position to understand energy in a precise and nuanced way – an understanding generally all too lacking.

In this first class we begin the adventure of looking at the world – from the scale of an individual electronics project to the scale of the universe – in terms of energy. We introduce (or reintroduce) some of the few terms and units we will rely on throughout the semester: watts, joules, work, power. We’ll meet your new best friends – the first and second laws of thermodynamics.

The first class serves as an introduction to some of the larger themes we will pursue over the course of the semester. We look at the origins of the course and the relevant parts of my background, and hear from you about your experience and expectations.

Reading: 

• An excerpt from Vaclav Smil’s earlier work: Energies: An Illustrated Guide to the Biosphere and Civilization. 1999, MIT Press, online here [pdf, 2.2mb]

Week 2: Kinetic energy

1/30/12

We’ll quantify kinetic energy, and see how it is converted into electricity (accounting for almost all of the world’s electricity generation).

 

Energy is either waiting to happen – potential – or is happening. When you look closely enough, everything happening is kinetic energy –  things in motion. Sometimes we can’t look closely enough, so we invent terms like “heat” or “sound”, which are names for patterns of kinetic activity too small and complex to observe directly.

In our pendulum experiments last week, we saw the almost perfect oscillation between potential energy and kinetic energy and back, but also observed energy leaving our system to its surroundings at a slow rate. We were introduced to the SI unit for energy and work – the joule – and its definition as force through distance (1 joule = 1 newton * 1 meter). A newton is a unit of force, defined as a that force necessary to accelerate a kilogram by 1 meter per second each second. If we lift an object, we do work moving its mass against the acceleration of gravity (9.8 m/s/s), and thus store energy in the elevated mass. A review of all this is found in Kinetic Energy 2012 (pdf).

This week we’ll take a whirlwind tour of energy throughout the history of the universe, and arrive at some of history’s first useful “heat engines”, devices for turning the stored chemical energy of fuels into heat, and from heat into motion. The proliferation of these devices has shaped our modern world. We’ll also look at electromagnetic induction, the phenomenon exploited by electrical generators, by which moving current can induce a physical force and vice versa. Heat engines alone or as the input for generators account for a huge slice of our (non-food) energy use.

To really get induction, we need to have a good understanding of the dual nature of electricity/magnetism. About the best, and most fun, reference I’ve found is this entry in the excellent Cartoon Guide to Physics by Larry Gonick and Art Huffman. Buy it! Note in particular how Lenz’ law relates to the conservation of energy. MIT created a series of applets and videos that help visualize this relationship that we’ll look at in class.

For our purposes, just about any motor is a ready-made generator. We’ll try some out, look at the basic circuits needed to condition their output (rectification via diodes, maybe a little smoothing with capacitors, maybe regulation), and try to assess their electrical performance.

Materials used in class:

• Kinetic Energy 2012 (pdf)
• 5 Minute Energy Tour (pdf)
• Magnetism comic and applets
• Circuit
• Kinetic/Electrical one-sheet

Reading:

• Smil, Energy, a Beginner’s Guide Chapters 1 and 2
• Energy Scavenging for Mobile and Wireless Electronics, Paradiso, Starner, 2005.
• Extra credit: listen to this analysis of the energy themes in the President’s state of the union address.

Week 3: Small solar

02/06/12

We’ll see how solar panels work and use small ones in simple circuits.

Last week we saw what a central role heat and heat engines play in planetary energy flows. Looking at Lawrence Livermore Lab’s analysis of US energy use, we saw that most of our energy use is either direct combustion of fossil fuels (for transportation), or using fuels as a heat source for thermal electricity plants. (Fuels, especially natural gas, are also used directly for space heating and industrial processes).

The electrification pathway is significant. The California Council on Science and Technology looked into the feasibility of reaching the state’s goal of reducing emissions to 80% below 1990 levels. The study included two significant points: 1) as much as possible California’s economy and energy use would need to become electrified, including space heating and transportation, and 2) that that electricity generation would have to be de-carbonized.

The carbon-neutral electricity generation methods available to us pose different problems. Large scale hydro electricity is already developed in many of the places it could be used, and in any event comes with an environmental footprint that is not immediately obvious. Wind power has seen intense recent development in the US thanks to the 1603 Treasury Grant Program providing production tax credits for wind power, but that program is set to expire at the end of 2012, and this has already affected plans for new turbines. The gargantuan megawatt turbines that are the most cost-effective also face aesthetic opposition in some prime wind areas. To date, no one has solved the problem of storing the by-products of nuclear electricity production, and the recent Japanese tsunami and subsequent Fukashima Daiichi crisis have shown the difficulty of securing nuclear facilities from unforeseen events.

All these methods of electrification are also somewhat indirect. A nuclear plant is a coal plant with a different hot side; wind and hydro electricity rely on the sun to drive the water cycle and energize the wind. But electricity can be generated directly from the sun. This is done via photovoltaic (PV) materials – materials that produce an electrical potential when exposed to light.

Solar works! Our modern world would not be the same without our solar-powered communication satellites, and PV is the only power supply that could operate reliably and for long durations in the extreme and remote environment of earth orbit. PV also works closer to home, powering equipment wherever grid electrification is infeasible. The proliferation of battery-powered mobile devices and mobile lifestyles has been accompanied by increasing interest in PV for consumer products. With silent operation and no moving parts, PV is the ultimate long term technology, and, contrary to some beliefs, becomes energy-positive within four years. This, combined with it’s attractive carbon profile, has resulted in global installed PV increasing exponentially in recent years. Recent drastic fluctuations in the cost of electronics-grade silicon (from $400/kg to less than $40 since 2008) and the unprecedented scale of Chinese solar manufacturing coming online make this an interesting moment for solar.

We’ll get our hands on some PV materials this week, measure their performance, and power some small circuits with PV.

Class materials:

• Solar Notes
• Sparkfun lipo charger
• Beam bots and info site

Discussion:

• Sean McIntyre, Solar powered sensor networks or energy analysis of two or three off-the-grid communities.

Week 4:  Useful connections

02/13/12

The bulk of this class will be given to catching up with hands-on time with materials such as solar panels, generators, and related peripherals. We’ll start with solar, including a review of what the department has available to you. We’ll quantify the output of panels under different lighting conditions by measuring the open circuit voltage and short circuit current, and we’ll power test loads.

We’ll charge up some capacitors and see how they can play a role in at least smoothing the (usually variable) output of our energy converters. Much larger capacitors – on the order of a farad or more – can be used as battery replacement (low energy density, very high power density, and high cost).

We’ll also look at two methods for providing a steady voltage for our loads – simple linear voltage regulators such as the LM7805, and more efficient and flexible (and expensive and harder to source) step-up or step-down DC to DC converters.

Finally, we’ll talk overall strategy for thinking about energy projects. We’ll approach the problem from a few different angles. For example, we can think generally about the kinds of energy conversions we are using. While we’ve focused particularly on the kinetic- and solar-to-electrical conversion pathways, we’ll remember that in fact there are many others, and we’ll take a second look at Smil’s conversion grid. We’ll think in terms of available inputs (Smil again, and Paradiso) – if you needed a 20W power source, what are your options? What about 5W? 100? We’ll discuss measuring or at least approximating a load – if we want to run a computer, or a phone, or an arduino, how much power do we need? And how would you know when to use any of the tech bits (regulators, smoothing capacitors, etc.) we’ve seen in class? We’ll look at a decision tree for sorting that out.

(As came in Sean’s discussion last week, there are packages available for energy harvesting that could simplify this design process for some very-low-energy projects – usually they’re geared towards the kinds of distributed sensor networks we saw last week. The department should have some if they can be found. Here’s a write up by a former student.)

And of course, we’ll see your midterm schematic drawings, hear the one line descriptions, and learn your projects’ names.

Discussion:

• NA

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Presidents Day 02/20/12 – NO CLASS!

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Week 5: Limits

02/27/12

We’ll look at fundamental limits to how useful energy can be to us. These concepts won’t help you build anything, but are part of being energy literate.

One easy-to-understand limit is the Betz’ law relating to maximum possible turbine efficiency. A turbine is a machine for extracting kinetic energy from a moving column of fluid such as air or water. First we need to know the maximum amount of kinetic energy we’re going after. Just as every moving mass has kinetic energy, so does a moving column of fluid. Our turbine will have a diameter, and we can imagine a column of fluid flowing through our turbine at a given speed. In a given period of time (say, one second) a column of a certain height will pass through our turbine. We can derive the volume of the column from the height and diameter. Then we can derive the mass of fluid passing through our turbine per unit of time using the volume and the density of the fluid (e.g. y 1.225 kg/m³ for 15C air at sea level). We now have mass and velocity, and the kinetic energy is 1/2 mv². That energy was per unit of time, so we can divide by time to also know instantaneous power.

Now we can imagine a perfect turbine – one with no central rotor, mass-less blades, etc. – no dead weight, only a perfect theoretical machine for extracting kinetic energy from a moving fluid. Any of the messy “real-world” engineering issues we will inevitably encounter will only lower the efficiency of our ideal machine.

Finally, we can imagine a set of boundary cases. What if our turbine extracted no kinetic energy from the fluid? In that case it wouldn’t be a very good turbine! The efficiency is 0. But what if it extracted all the kinetic energy? Good, right? 100% efficient. But wait – the fluid behind the turbine is now not moving, and no new fluid can enter to turn the rotor. By trying to extract all the energy, we immediately end up in a condition where we can do no further work – 0% efficiency again! In other words, at least some of the incoming kinetic energy is not available to us because it must remain to allow the turbine to keep functioning.

In between these two extremes there is a sweet spot, and that’s what Betz (and some others working independently) calculated. The Betz limit for a turbine is:

Betz’ limit: 59.3%

And remember – that’s an ideal limit. Other approaches that consider more real-world effects place maximum efficiency much lower. Be suspicious of turbine designs that claim to approach, let a lone surpass, the Betz limit.

Similar limits exist elsewhere. In 1824, when heat was believed to be an actual fluid that could be passed from one object to another, Sadi Carnot derived the maximum efficiency of an ideal machine for converting heat into work. The Carnot efficiency is:

Carnot efficiency: 1 – (TC / TH)

where TC and TH are the absolute temperatures of the cold and hot sides of the engine, respectively. Absolute as in relative to absolute zero, the temperature at which molecular motion stops. So in our real world, where ambient temperatures dictate the available cold side of a heat engine, the maximum efficiency has a low upper limit – the ratio of TC/TH cannot approach 0 because TC has a relatively high value. And again, this is an ideal limit. Any real-world instance of a heat engine will have lower efficiency.

The best we can do is make TH as high as possible. That’s hard to do in small, mobile applications like car engines – making an engine strong enough to withstand extreme temperatures makes it heavier and larger. So small engines tend to have low thermal efficiencies – around 20% actual, 37% theoretical maximum. Diesel engines operate at higher compression and temperatures, so have a slightly higher efficiency. For stationary applications, the Carnot efficiency favors massive power plants with low surface-area-to-volume ratios that can operate at extreme temperatures.

I’m told (by wikipedia) that the limit for a single-junction solar cell is 37.7%, and for an infinite series of ideal junctions 86%.

In the preceding discussion the concept of the ideal and the real came up a lot. It is always tempting to wish away the real world. The energy is there, if only we could get it! But this is the real world. As you work on your midterms, consider the role that cost, complexity and time play in keeping you from getting every last joule of available energy from a given system. These are limits too. Eventually gathering up the crumbs becomes too difficult to make a return on the effort invested.

Discussion:

• Monica Bate

Week 6: Midterm projects

03/05/12

Congratulations on your midterm presentations. Enjoy your break, but while doing so, consider your final projects, which we will discuss concepts for on 3/19.

In previous classes, the following four criteria have been developed for considering what constitutes a successful project. A good project will:

1. Meet the requirement for “weak sustainability” – project gets all energy for operation from its users or the surrounding environment (no primary batteries, no plugs).
2. Quantify its energy usage in terms of input, storage, and output, with efficiencies at each stage.
3. Use energy concepts as an explicit and essential part of the conceptual underpinnings of the project.
4. Make a positive difference.

These begin with the specific and easy, and end with the nebulous and very difficult – how many projects can be said to make a difference. That said, I think perhaps you are in a class like this because you’ve decided to try. This post by Mike Monteiro summed it up in the first resolution: “Choose better problems to solve.” Everyone likes your sandwich.

Spring Break 03/12/12 – NO CLASS!

 

Week 7: Big kinetic – wind

03/19/12

Discussion:

• Ingrid Gabor

Week 8: Big solar – field trip

03/26/12 

Weather permitting, we will go from class to Washington Square Park with the portable solar kits. 

Discussion:

• Allison Berman, superconductivity.

Week 9: Guest crits; special topics

04/02/12

You present your final project concepts and progress. Clare Miflin of Kiss+Cathcart Architects, and Tom Igoe of ITP join.

Discussion:

• Guiherme Costa

Week 10: Monitoring, horizons, special topics

04/09/12

If Edison or Tesla were still alive, they would recognize most of today’s electrical grid as similar to what they invented. The megastructure that delivers electricity to homes and businesses cannot be updated quickly – it is too large – and so we mostly have to live with solutions that were engineered a century ago.

Today we hear a lot of talk of the “smart grid” – a sort of sensor overlay to the existing grid that will enable the grid to be more nimble and resilient. At the home and building level, this takes the form of more precise and real-time electricity metering. Continuously monitored per-circuit or per-outlet sensors augment the per-building, once-a-month meter already in place. This allows users to see the immediate energy impact of actions like unattended vampire loads, and allows utilities to progress towards variable time-of-day pricing that more closely match the cost of electricity with the moment-to-moment demand.

Today we’ll see consumer hardware like the Kill-A-Watt (modified into the Tweet-A-Watt) and the EnergyHub Dashboard (EnergyHub is based in Brooklyn).

Most larger solar includes some kind of monitoring. Our roof-top panel uses this slightly-more-advanced charge controller than the ones in the solar kits, and this one has a RS-232 port on it. On occasion, the data has been scraped and logged here. Some solar projects log their data to publicly available sites – see for example NYC-based AltPower. Often logging is integrated with the inverters that connect solar installations to the grid.  For example, SMA supplies a networked Web Box that can push data to the web, or provide data via FTP. Data looks like this file from Riverhouse on 2010-04-27.

Whether solar or not, many buildings use what is called a “Building Management System” or BMS; Johnston Controls is a major example. They have built-in UI’s; other companies provide better-looking and/or more flexible “dashboards.” Monitoring, along with other retrofits, can have major energy savings. The Empire State Building recently undertook a major energy overhaul financed entirely by the projected energy savings.

Negawatts (energy efficiency) will only go so far though. Billions of new “non-legacy” (i.e. no inherited grid or energy infrastructure) are coming online and, no matter how efficiently, will be new energy consumers. Without the ability to cheaply store renewable energy, there is a low limit to how much they can help. Storage is key.

Daniel Nocera thinks he has a solution in the form of a cheap, robust catalyst that can store renewable energy supplies by electrolyzing water into hydrogen and oxygen (note – his solution still requires solar panels and a fuel cell, ponts missed by much of the mainstream reporting on the work). In these short and long talks he summarizes his work, and addresses the viability of other energy sources along the way.

 

Discussion:

• Danne Woo

Week 11: Workshop

04/16/12

Discussion:

• Sam Galison, chemical reactions (e.g. potato clock), tesla, resonant frequencies

Week 12: Final Presentations

04/23/12   4/30/12

Final presentations are now a week later, on 4/30.