Introduction to Small-scale Photovoltaic Systems (including RETScreen case study)

Q&A Session

Q: Can RETScreen be used to optimise a design for a given area and also be used if the energy policy is based on imports & exports not feed-in tariffs?

A: Yes, you can run as many scenarios as you wish, then finding the optimal configuration for your particular case. See also the distance between panels in Annex of presentation. RETScreen provides an electricity production estimation. From there you can extract your imports and obtain the net export with the applicable fee.

Q: What should be the tilt angle for pv ?

Depending on latitude there is an optimal angle, which is close to latitude value. You should choose your angle depending on what you need to optimize : winter production, summer production or yearly production. The software provides the production on monthly basis for the various angles you try, then you decide which angle maximizes your function.

Q: Have you considered the effects of performance degradation effects?  If so, what are the most important equipment performance degradation processes?

The most important degradation process is relative to PV panels: account 1% per year (loss of efficiency). In 20 years (guaranteed lifespan) the efficiency will be 20% lower. The cause is a loss of properties in materials (glass transmitivity, PV cells efficiency). Inverter can also reduce its performance in the time.

Q: Is the degradation the same for CPV?

www.isfoc.es will be providing this return of experience in the coming months.

Q: How can Retsreen program help me in take the decision?

By providing an expected electricity generation and then an expected return of your investment.

Q: What is the average cost per watt using photovoltaic system nowadays?

For fixed systems should be around 4-5 €/W and decreasing.

Q: How does the ambient temp effect on pv performance?

Account a loss of 0,5% of power per ºC.

Q: PVs generally have a long payback period, how long would you estimate a panels lifespan would be before a replacement would be warranted?

Manufacturer’s guarantees currently run up to 20 years. Current feed-in tariffs allow a payback period around 10 years.

Q: A local installer places panels vertically on the wall of a house. They run cooler and do not accumulate snow. I'm assuming this works well with a low winter azimuth. But will the indirect angle in summer significantly reduce energy input?

You can simulate its behaviour using RETScreen module. Indeed, vertical panels are more optimized for winter generation than for summer.

Q: What about a system in which the bracket does allow for a change in angle for the summer, where the panels block sun from the window (shading the window)?

As RETScreen makes a production estimation on monthly basis you can run each tilt angle for the corresponding months and determine the annual generation.

Q: What is the difference in power output between fixed and Tracking systems?

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