Bench Degree·SOLAR POWERchapter
Appendix A: The Bench
The whole volume’s kit in one place. Every experiment in this book is on this list, so you should never have to stop mid-chapter and wait two days for a delivery. Each chapter names what it needs when it needs it and points back here; if you would rather order once and be done, order from this list.
Chapter 1 costs about $20, and nineteen of that is a multimeter you will use for the rest of your life. The starter set that carries you through Chapter 6, which is the entire physics of the subject, is about $130, and some of it is already in the house.
Nothing here is specified by brand or by part number. Every item is described by function, range or rating, so the list stays orderable from anyone, anywhere, for as long as the book exists. Suppliers change and a printed link dies permanently. A specification does not.
Bought new, all at once, the whole volume comes to roughly $760. Nobody should do that. About half of it is three instruments that are better borrowed than owned, and Section 4 says which.
Section 1: The starter set, for Chapters 1 to 6
| Item | Specification | Rough cost |
|---|---|---|
| Multimeter | The one instrument this book cannot do without. Must read DC volts, DC microamps and ohms. A second one, however cheap, is worth having by Chapter 7, because voltage and current want reading at the same instant. | $20 |
| One LED, any type | A clear 5 mm (0.2 in) red or green one from a junk drawer. Chapter 1 turns it into a solar cell. | pennies |
| Small photovoltaic panel | 10 to 50 W, 12 V nominal, with a junction box or flying leads. The workhorse of the volume. Chapters 1, 4, 6, 8, 9 and 13 all use it. | $30 |
| A 12 V bulb and a few resistors | 100 Ω, 1 kΩ, and one or two power resistors of 1 to 3 Ω. Loads for Chapters 1, 6 and 7. | $8 |
| Clip leads | A set of ten. | $5 |
| Black poly tubing | 15 m (49 ft) of 13 mm (0.5 in) irrigation tube, plus a board to lay it on. Chapter 2’s solar thermal collector. | $12, or owned |
| Two thermometers | Reading to 0.5 °C (1 °F) resolution, probe type. Chapter 2 needs an inlet and an outlet at once. | $8 each |
| Measuring jug and a stopwatch | A kitchen jug and a phone. Together they are your flow meter. | owned |
| Copper sheet | 150 mm square (6 in square), 0.5 mm (0.02 in) thick, sold as roof flashing. Enough for several attempts at Chapter 3’s cuprous oxide cell. | $8 |
| A clear glass jar and table salt | Chapter 3’s electrolyte, and the closest thing in print to Becquerel’s 1839 apparatus. | owned |
| Old selenium exposure meter | The photographic sort with a grille of windows, a moving needle and no battery compartment. Flea markets and camera shop junk boxes. Chapter 3. | $10 to $25 |
| A CD and a DVD | Chapter 4 splits sunlight with the track pitch. Already in the house, and a scratched one is fine. | owned |
| Cardboard box and a craft knife | For the Chapter 4 spectrometer. | owned |
| Television remote | Chapter 4 finds the infrared edge of the silicon response with it, and a phone camera to see the beam. | owned |
| Enamelled copper wire | 50 m (164 ft) of 30 AWG. Chapter 5 uses it as a metal whose resistance rises with heat. | $9 |
| NTC thermistor | 10 kΩ. The semiconductor that disagrees with the copper. | $2 |
| Diodes | One silicon, such as a 1N4148; one germanium, such as a 1N34A; one white LED. Chapter 5 reads three band gaps off three forward voltages. | $6 |
| 9 V battery and a AA pair | Chapters 5 and 6. | owned |
| Graph paper and a sharp pencil | Chapters 6, 7 and 9 ask you to plot readings. Do it on paper; the shape is the point. | $4 |
Starter set total: about $130, or nearer $95 if you already own a multimeter and a length of black hose.
Section 2: Added for Chapters 7 to 15
| Item | Specification | Rough cost |
|---|---|---|
| Wirewound rheostat | 50 Ω, rated 50 W or more. The instrument that makes Chapter 7 possible: it sweeps the load from short circuit to open circuit so you can trace a curve by hand. It gets hot enough to burn at the low-resistance end, because it is eating the panel’s whole output. | $20 |
| Second multimeter | Volts and amps at the same instant, on the same curve. Borrow one if you can. | $20 |
| Irradiance meter or reference cell | Chapter 8 cannot compute an efficiency without knowing what arrived. A cell of known rated short-circuit current does the same job for less. | $0 to $35 |
| Infrared thermometer | Chapters 7, 8, 9 and 15. Non-contact, and cheap ones are fine for comparisons. | $20 |
| Thermocouple thermometer | Taped to a panel’s back, it separates temperature from irradiance in Chapter 9. | $15 |
| Second identical panel | Chapter 8 runs one panel loaded and one open circuit, side by side, to catch the energy going the other way. | $30 |
| Four small panels, 10 W each | Chapter 10 wires them three ways and Chapter 14 lets an accomplice sabotage them. These four earn their keep more than anything else on this list. | $18 each |
| MC4 connectors or screw terminals | Enough to make up and break down strings. | $10 |
| Wire, two gauges | 60 m (197 ft) of 18 AWG for the string experiments and 30 m (98 ft) of 20 or 22 AWG to make voltage drop obvious. | $20 |
| PWM charge controller | Chapter 7’s comparison needs the cheap kind as well as the good kind. | $15 |
| MPPT charge controller | The thing that finds the knee of the curve for you, sixty times a second. | $60 |
| 12 V battery | Lead-acid or lithium iron phosphate, partly discharged. An old car battery is ideal and often free. Chapters 7 and 12. | owned, or free |
| Two plug-in AC energy meters | Chapter 12 measures round-trip efficiency, which needs energy in and energy out. One meter used twice will do. | $15 each |
| Shunt-based DC energy meter | Reads amp-hours and watt-hours at the battery terminals. Chapters 12 and 13. | $20 |
| Logging DC energy meter | For Chapter 13’s week of readings, unless you are willing to write them down by hand. | $25 |
| Cheap 300 W inverter, and a pure sine inverter | Chapter 11 compares the waveforms. The cheap one is the point of the experiment. | $25 and $70 |
| 12 V AC wall transformer | Run backwards, this is your isolation between a mains-voltage waveform and your oscilloscope. Do not skip it. | $8 |
| USB oscilloscope | Or a borrowed bench scope. Chapter 11 only. | $50 |
| DC clamp meter | Reads a live string’s current without touching a conductor, which is the only safe way to measure a working array. Chapters 11, 14 and 15. | $90 |
| Protractor or inclinometer app | Chapter 13 sets five tilt angles in one day. | owned |
Second set total: about $630 if you buy every line new. It is not meant to be bought that way. The four small panels, the rheostat, the second meter and the shunt meter come to about $150 and cover most of what is left in the book.
Section 3: Free, and worth more than most of what is above
| Item | Where | Chapter |
|---|---|---|
| A junction box from a scrapped module | Any installer’s skip. They replace panels and the dead ones are waste. Cut one open and the bypass diodes are right there. | 9 |
| A cracked or delaminated panel | Same place, and often free for carrying away. It still produces, and it is the only safe thing to practise on. | 14 |
| An old car battery | A garage’s core pile. Half dead is better than new for Chapter 12, because you are measuring what it has lost. | 12 |
| A thermal camera, borrowed | A building surveyor, an electrician, an energy assessor. Ten minutes of their time is the whole experiment. | 14 |
| Somebody else’s array, and permission | A neighbour, a farm shed, a village hall, your own workplace. Chapter 15’s final examination is nothing but a notepad and a nameplate. | 11, 15 |
| One accomplice | Chapter 14 asks somebody to break your string while you are out of the room, then times you finding the fault. This is the best experiment in the book and it costs nothing. | 14 |
Asking is the skill. Every measurement on a real system in this volume needs somebody’s permission rather than somebody’s money. Bring the question and no tools, ask before touching anything, and accept a refusal without argument.
Section 4: The one expensive thing, and whether you need it
A thermal camera. A phone-attachment unit is about $300, a poor standalone imager about $150, and a good handheld one is well past $1,000.
You do not need one. It appears in exactly one box, Chapter 14’s survey of a working array, and the whole point of that box is that a bad cell runs hot. Borrow the camera from a surveyor or an electrician, spend ten minutes, and give it back. Nothing else in this volume needs it, and the fault-finding experiment in the same chapter works with a clamp meter and a piece of card.
The one you should actually buy is the DC clamp meter at about $90, and it is the instrument that changes what you can do. It reads the current in a live string without contact, which means every measurement on a real installed system in Chapters 11, 14 and 15 becomes safe and legal for a person with no qualification. An instrument that lets you measure something you must not touch is worth more than one that measures something you already own.
Two things worth borrowing rather than buying. An oscilloscope, for the single afternoon of Chapter 11. And an irradiance meter, for the single afternoon of Chapter 8, though a small cell of known rated short-circuit current gets you within a few percent for nothing.
Section 5: What you already own more of than you think
Every LED in your house is a solar cell. Not an analogy. A light-emitting diode is a photodiode built backwards, and Chapter 1 has you point one at the sun and read a few hundred millivolts off it with a meter. There are perhaps fifty in the room you are sitting in.
Your phone camera sees light your eyes cannot. Chapter 4 aims a television remote at it, finds the invisible flash, and uses that to bracket the long-wavelength edge of the silicon response. The remote and the camera are both already in your pocket.
A freezer and a hairdryer are a temperature laboratory. Chapter 9 measures a panel’s temperature coefficient with those two and a plastic bag, and gets a number within a fraction of a percent per degree of the manufacturer’s own figure.
A black garden hose on a board is a solar thermal collector, and Chapter 2 measures its efficiency properly, in watts per square metre, against a photovoltaic panel of the same area on the same afternoon. One of the two wins by a factor you will not guess.
Your kitchen stove makes semiconductors. Chapter 3’s cuprous oxide cell is grown on a ring at red heat, and it works, at a fraction of a percent, which is about what Charles Fritts had in 1883.
And your own roof is the last chapter’s worked example, whether or not anything is on it. Chapter 13 sizes an array for a real house from a real electricity bill, and the bill is in a drawer already.
Section 6: The experiments, and where they are
Thirty-one, and the whole list fits on the kit above.
| Experiment | Chapter | What it costs |
|---|---|---|
| The LED in reverse | 1 | $20, and that is the meter |
| One thumb, most of the output | 1 | $30 above the meter |
| The hose collector, measured | 2 | $30 |
| Head to head, same sun, same area | 2 | $70 |
| Build an 1883 solar cell | 3 | $10 |
| Hold Adams and Day’s result in your hand | 3 | $10 to $25 |
| Split the sun with a disc | 4 | $5 |
| Find the edge with a television remote | 4 | nothing |
| Two components disagree about heat | 5 | $12 |
| Watch a diode’s forward voltage give away its band gap | 5 | under $5 |
| A solar cell is a diode in the dark | 6 | under $10 |
| Slide the curve with sunlight | 6 | nothing more |
| Trace your own I-V curve by hand | 7 | $30 |
| MPPT against direct, same panel, same day | 7 | $100 |
| Measure your own panel’s efficiency | 8 | $35 |
| Catch the energy going the other way | 8 | $80, or nothing with two panels |
| Measure your panel’s temperature coefficient | 9 | $20 |
| One day, one panel, two effects separated | 9 | nothing |
| Find the diodes, then confirm what they do | 9 | nothing |
| Four panels, three ways, one wire | 10 | $95 |
| See the voltage drop, and prove it goes as the square | 10 | $10 |
| Look at an inverter’s output, safely | 11 | $170 |
| Measure a real inverter’s efficiency curve | 11 | $90 |
| Measure round-trip efficiency properly | 12 | $50 |
| Find out what a battery of yours can really hold | 12 | $20 |
| Five tilt angles, one day | 13 | nothing |
| Log a week, then check your own prediction | 13 | $25 |
| Thermal-image a working array | 14 | free, or up to $300 |
| Have somebody break it, then find the fault | 14 | $90 |
| The final exam, on somebody else’s array | 15 | nothing |
| The whole book in one afternoon | 15 | $90 |
The five in bold are the ones to do if you do only five. The first turns something in your junk drawer into a solar cell and delivers the whole thesis for the price of a meter. The second measures a solar thermal collector so honestly that Chapter 2’s conclusion about it stops being an opinion. The third builds a working cell on a stove ring for ten dollars. The fourth draws the curve that every other chapter refers back to, by hand, one point at a time. And the fifth is the only experiment here that tests you rather than a panel.
Eight of the thirty-one cost nothing at all beyond the starter set, and two more need only permission. This is a cheap subject to learn honestly, and the expensive half of it, which is the installed array on somebody’s roof, is deliberately left to be measured and read rather than built.
The safety gear, which is not optional
Wear this for the experiments the book says to wear it for. The reasons are on the Before You Start page at the front, and in the chapter that owns each experiment.
| Item | Specification | Cost |
|---|---|---|
| Eye protection | Any impact-rated safety glasses. Worn for the stove work in Chapter 3 and any time a battery is on charge. | $8 |
| An opaque cover for a panel | A bin bag, a towel, a sheet of cardboard. This is the isolator for the whole book and it costs nothing. | free |
| An inline fuse holder and fuses | 10 A and 20 A, for any experiment with a battery in it. | $6 |
Section 7: Kits
A single collection covering the starter set and the four small panels, ordered once, is the obvious convenience and it is being worked on. When it exists it will be at benchdegree.com/kit/solar-power, and that address is deliberately the only place it will be published: suppliers and product listings change, and a link printed in a book cannot be corrected. The specifications above can be taken to any supplier and will still make sense in twenty years.
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