Chapter 17 Quiz: Solar, EV Chargers, and Whole-Home Generators

Multiple Choice

1. Why does a standard grid-tied solar system stop producing power during a utility outage?

a) The panels are damaged by the power surge that causes the outage b) The inverter detects loss of grid voltage and shuts down for safety, preventing back-feed to utility lines c) Grid-tied systems automatically switch to battery backup mode d) Solar panels require grid power to operate their internal electronics

Correct answer: b This is a required safety feature, not a flaw. If grid-tied inverters continued operating during outages, they would back-feed power into de-energized utility lines — creating an electrocution hazard for utility workers. The solution for backup power is battery storage with an island-mode inverter.

2. The federal Investment Tax Credit (ITC) for residential solar systems provides:

a) A tax deduction that reduces your taxable income by 30% of system cost b) A direct payment from the IRS of 30% of system cost c) A dollar-for-dollar reduction in federal income tax owed, equal to 30% of system cost d) A 30% reduction in utility bills for the first 10 years after installation

Correct answer: c The ITC is a tax credit — a direct reduction in tax owed, not a deduction. A $20,000 system generates $6,000 in tax credits. This requires having sufficient federal tax liability to fully utilize the credit; those with low tax liability may not be able to use the full amount in one year (though unused credits can sometimes be carried forward).

3. Level 1 EV charging (standard 120V outlet) typically delivers approximately how many miles of range per hour?

a) 15–20 miles per hour b) 10–12 miles per hour c) 3–5 miles per hour d) 30–40 miles per hour

Correct answer: c Level 1 provides 1.2–1.9 kW, delivering roughly 3–5 miles of range per hour. A typical 30-mile daily commute requires 6–10 hours of Level 1 charging — adequate for overnight charging with a normal evening-to-morning window, but insufficient for high-mileage drivers or those who need to recharge quickly.

4. Level 2 EV charging requires which electrical configuration?

a) A standard 15A, 120V household outlet with a special adapter b) A dedicated 240V circuit, typically 40–50 amps c) A three-phase 208V commercial service d) A standard 20A, 120V circuit with a special Level 2 adapter

Correct answer: b Level 2 uses 240V — the same voltage as electric dryers and ranges. A dedicated circuit is required (not shared with other loads), typically sized at 40–50A. This requires a licensed electrician to install from the main panel to the garage or parking area.

5. For generator sizing, why must you consider "starting watts" in addition to "running watts"?

a) Starting watts determines how much fuel the generator consumes b) Electric motors draw significantly more current when starting than when running; the generator must supply the surge or it will bog down or cut off c) Starting watts is a safety rating that determines whether the generator meets code requirements d) Running watts applies to resistive loads only; starting watts applies to lighting

Correct answer: b Inductive loads (motors) draw 3–7 times their running current during start-up. A well pump rated 750 watts running may draw 2,800 watts for the first second of starting. If the generator can't supply that surge, it stalls or shuts down. Generator sizing must account for the largest starting surge plus total running loads.

6. A whole-home standby generator differs from a portable generator primarily in that:

a) Standby generators produce cleaner electricity suitable for sensitive electronics b) Standby generators run on natural gas or propane and start automatically when power fails, without any manual action required c) Standby generators don't require a transfer switch d) Standby generators are more fuel-efficient but produce less power

Correct answer: b The defining feature of a standby generator is automatic operation — it monitors utility power continuously, starts automatically upon power failure, transfers loads via an automatic transfer switch, and shuts down when power is restored. Portable generators require manual starting and manual load connection.

7. What is the MINIMUM distance a portable generator must be placed from your home's doors, windows, and vents during operation?

a) 5 feet b) 10 feet c) 20 feet d) 50 feet

Correct answer: c The 20-foot minimum is the standard safety recommendation from the Consumer Product Safety Commission. Carbon monoxide from a generator can migrate toward and into a building even from some distance, particularly under certain wind conditions. Further is better.

8. "Back-feeding" a generator through a wall outlet using a "suicide cord" is dangerous primarily because:

a) It can damage the generator's electronics b) It violates equipment warranties c) It energizes the home's full wiring and the utility lines — creating electrocution risk for utility workers and bypassing all circuit protection d) The generator can overheat without proper load balancing

Correct answer: c Back-feeding energizes the utility lines that workers may assume are de-energized, creating a potentially fatal hazard for utility crews. It also bypasses the panel's protective devices and puts uncontrolled generator power on all circuits simultaneously. This is illegal in most jurisdictions for exactly these reasons.

9. The "derate factor" used in solar production calculations (typically 0.75–0.85) accounts for:

a) The reduction in panel output expected over the 25-year warranty period b) Real-world losses including temperature effects, wiring resistance, inverter efficiency, and soiling c) The percentage of time the system will be down for maintenance d) Local shading and cloud cover adjustments

Correct answer: b Solar panels are rated under Standard Test Conditions (25°C, perpendicular sunlight) that are never achieved perfectly in practice. Temperature above 25°C reduces output; wiring resistance loses some power; inverters operate below 100% efficiency; dust and soiling reduce output. The derate factor (typically 0.80 as a rule of thumb) accounts for all these real-world factors.

10. An automatic transfer switch on a standby generator serves which critical safety function?

a) It regulates the generator's voltage output to match utility standards b) It prevents the generator and utility power from being connected simultaneously, avoiding back-feed to utility lines c) It monitors fuel level and shuts down the generator before it runs dry d) It distributes generator power equally across all circuits

Correct answer: b The automatic transfer switch disconnects the home from the utility before connecting generator power. This prevents the generator from back-feeding the utility lines — the same hazard that makes portable generator suicide cords dangerous. The ATS is not optional; it's the safety mechanism that makes standby generator use legal and safe.

Short Answer

Short Answer 1: Priya Chen-Williams receives a solar quote with an estimated annual production of 12,000 kWh from a 7.5 kW system in a mid-Atlantic location. She runs the same numbers on PVWatts and gets an estimate of 9,200 kWh. What should she make of this discrepancy, and how should it affect her evaluation of the quote?

Model answer: A 30% discrepancy between the installer's production estimate and an independent PVWatts calculation is a significant red flag. PVWatts uses National Renewable Energy Laboratory data on local solar resource — it's a well-validated, conservative estimate used by the industry. Installer estimates 20%+ above PVWatts typically indicate optimistic assumptions (possibly unrealistic shading assumptions, overstated irradiance data, or inflated derate factors). Priya should use the PVWatts figure for her payback calculation rather than the installer's number. She should also ask the installer to explain in specific technical terms why they're projecting production higher than PVWatts. If they can't provide a clear technical justification, she should be skeptical of the quote overall.

Short Answer 2: Dave Kowalski's rural property frequently loses power for 1–3 days after ice storms. He has a generator but hasn't been using it correctly — he's been running it in his garage with the garage door open. Explain why this is dangerous and what the correct procedure is.

Model answer: Running a generator in a garage with the door open is dangerous because CO is denser than air and can accumulate at floor level even with a door open. Wind can carry exhaust back into the garage, and exhaust can enter the house through gaps around the door or duct openings. The CPSC and emergency responders consistently find CO poisoning victims in homes with "open" garages where generators were running. CO is odorless and colorless — people become incapacitated without warning. The correct procedure: run the generator outdoors, at least 20 feet from any door, window, or vent, with the exhaust pointed away from the house. Dave should also install CO detectors on every level of his home, with one outside each sleeping area, and test them regularly.

Short Answer 3: What is the difference between a tax credit and a tax deduction, and why does this distinction matter for the 30% solar ITC?

Model answer: A tax deduction reduces taxable income. If you're in the 22% tax bracket and take a $10,000 deduction, you save $2,200 in taxes. A tax credit directly reduces the tax you owe. A $10,000 tax credit reduces your tax bill by $10,000, regardless of your tax bracket. The solar ITC is a credit — so for a $20,000 system, the 30% credit equals $6,000 off your tax bill, not $6,000 times your marginal rate. This makes the ITC significantly more valuable than a comparable deduction, and the value is the same for taxpayers in any bracket. The practical limitation: you must owe at least $6,000 in federal taxes to fully use a $6,000 credit in one year. Taxpayers with lower tax liability may need to carry unused credits forward.