SHI Research Methods & Evidence-Based Practice 2 — Questions and Answers
Question 1: A solar installer wants to compare two collector brands using field data. Which statistical measure best indicates consistency of energy output across multiple test runs?
- Arithmetic mean
- Standard deviation (Correct answer)
- Median absolute deviation
- Interquartile range
Correct answer: Standard deviation
Standard deviation quantifies how spread out individual measurements are around the mean, making it the primary indicator of output consistency.
Question 2: In an evidence-based solar system audit, what does a high coefficient of performance (COP) value indicate?
- High heat loss through the collector
- Efficient energy conversion relative to energy input (Correct answer)
- Elevated stagnation temperature risk
- Excessive glycol concentration in the fluid
Correct answer: Efficient energy conversion relative to energy input
COP is the ratio of useful heat output to the energy input, so a high COP confirms efficient system performance.
Question 3: Which type of study design provides the strongest causal evidence when evaluating a new solar collector design?
- Cross-sectional survey
- Case report
- Randomized controlled experiment (Correct answer)
- Retrospective cohort analysis
Correct answer: Randomized controlled experiment
Randomized controlled experiments eliminate confounding variables through random assignment, providing the strongest causal evidence.
Question 4: A technician reviews a manufacturer's solar collector efficiency curve. The curve shows efficiency vs. reduced temperature difference (Tm*). What does an X-intercept on this curve represent?
- The collector's peak optical efficiency
- The operating point where collector gains equal losses (zero net gain) (Correct answer)
- The stagnation temperature of the fluid
- The maximum flow rate through the absorber
Correct answer: The operating point where collector gains equal losses (zero net gain)
The X-intercept is the reduced temperature difference at which heat losses exactly cancel solar gains, yielding zero net useful output.
Question 5: When reviewing published solar irradiance data for system sizing, what is the purpose of using Typical Meteorological Year (TMY) data?
- To identify the single best weather year on record
- To provide a statistically representative annual weather dataset for long-term performance prediction (Correct answer)
- To calculate the worst-case shading scenario
- To determine peak demand in winter months only
Correct answer: To provide a statistically representative annual weather dataset for long-term performance prediction
TMY data is assembled from long-term records to represent typical annual conditions, making it the standard for predicting long-term system performance.
Question 6: An installer notices that two separate studies on solar water heater performance report conflicting results. The most appropriate evidence-based next step is to:
- Accept the older study as more reliable
- Conduct a meta-analysis or systematic review of all available studies (Correct answer)
- Choose the study with the larger sample size and discard the other
- Apply the results from the local climate study only
Correct answer: Conduct a meta-analysis or systematic review of all available studies
A systematic review or meta-analysis aggregates data from multiple studies to resolve conflicts and produce more reliable conclusions.
Question 7: In solar thermal research, what does 'incidence angle modifier (IAM)' data help an installer determine?
- How collector efficiency changes as sunlight strikes at non-perpendicular angles (Correct answer)
- The pipe insulation R-value needed for the climate zone
- The minimum glycol concentration for freeze protection
- Whether the collector meets SRCC certification standards
Correct answer: How collector efficiency changes as sunlight strikes at non-perpendicular angles
The IAM quantifies the reduction in collector efficiency as the solar beam angle deviates from perpendicular, which is critical for accurate annual yield calculations.
SHI Research Methods & Evidence-Based Practice 2
A solar installer wants to compare two collector brands using field data.
Which statistical measure best indicates consistency of energy output across multiple test runs?