Building Solar Friendly Roofs

Transcription

1 Building Solar Friendly Roofs Presented by John Maissan Leading Edge Projects Inc. Yukon Housing Corporation Contractor Breakfast April 15, 2015

2 Presentation Outline Why solar Sun angles by time of day and month Building and pitched roof orientation Optimum roof pitches Additional dead and live loads Flat roof solar system mounting Wall solar system mounting

3 Why solar? About 50% of energy is available from November 1 to May 31 when hydro inflows are limited Even in the longest days of the year solar energy is supplied in the daytime when electrical loads are high, so a high percentage is useful in hydro system Solar PV (electricity) is simple no moving parts Gives homeowners a sense of empowerment and a chance to reduce emissions by reducing diesel (and LNG) generation on the margin

4 Sun angles in Whitehorse Chart in solar time, 12 PM = solar noon = 2:10 PM Pacific Daylight Saving time

5 Solar summary & data Best energy production when square to the sun Highest angle December 21 is 6 above horizon (114:12 pitch) Highest angle June 21 is 52 above horizon (10:12 pitch) Optimum winter position is 70 (33:12 pitch) Optimum summer pitch is 30 (7:12 pitch) Optimum all-year position is 50 (14:12 pitch)

6 Effect of roof/array angles off south 20 east or west of due south = 2% production loss 45 east or west of south = 12% production loss 67 east or west of south = 20% production loss 90 from south (due east or west) 30 % production loss

7 Building and Pitched Roof Orientation Best orientation of roof surface if no shading is due south If significant shading at either east or west sides then angling to open side would be helpful Large continuous surfaces best for solar Keep penetrations (chimney & soil pipe) on north side if possible With our low sun angles in winter shading from near-by buildings, trees, and even mountains is important significantly reduces energy capture

8 Optimum roof pitches A roof pitch in the range of 12:12 to 16:12 is good for flush mounted system annual ideal is 50

9 Takhini River CAFN / Habitat triplex 12:12 pitch facing due south, 20 modules each unit

10 Tilt mounted PV system on 5:12 pitched roof

11 Additional dead and live roof loads Flush mounted solar PV system will add about 3 to 4 psf (0.14 to 0.19 kpa) dead load Tilt mounted system will add about 4 to 5 psf (0.19 to 0.24 kpa) dead load Flush mounted system will add no live load Tilt mounted system will add live load both wind and snow load (array acts like a snow fence) Need some structural engineering advice on extra live loads 2015 NBC increases design live (snow) loading

12 Maissan house built in 2004 Design dead load 3 psf (0.143 kpa) Design live load 23.4 psf (1.15 kpa) Structural assessment: not adequate for additional dead or live loading Had to beef up trusses inside attic (not a fun job) Cheaper and easier to build with a larger capacity margin to start with

13 Snow needs to be taken into account Snow will not slide off shingle roofs, so can accumulate on flush mounted systems Metal roofing allows snow to slid off more easily better suited to flush mounted solar

14 Flat roof PV mounting systems Two main options: first, penetrate roof and tie into roof trusses Second, add extra aggregate protection cover to roof and place a self ballasted system on top Second option is generally preferred, but this adds to the dead load that the roof needs to be able to carry. Building orientation less important than in pitched roof buildings flexibility in array orientation In Yukon low winter sun angles requires very significant separation between rows

15 Flat roof ballast mounted solar (in US) Note the concrete blocks that are the ballast

16 Wall mounted solar Solar modules can be mounted on walls with appropriate hardware even tilted

17 Summary of vertical solar modules Facing due south output 17% less production than optimum tilt of 50 Facing 20 east or west of south, 18% less Facing 45 east or west of south 24% less Should be virtually no snow losses

18 CSA PV installation guideline CSA issued its Solar photovoltaic rooftopinstallation best practices guideline (SPE ) in 2014 YG building inspections are more particular than City inspections

19 Presentation summary The easiest time to prepare for solar friendly roofs or walls is at building design and construction Building orientation Roof pitch & penetrations Roof covering Additional dead and live load carrying capacity

20 Questions? Discussion?

21 Solar PV in Summer June PV output kwh; load scaled :00-01:00 01:00-02:00 02:00-03:00 03:00-04:00 04:00-05:00 05:00-06:00 06:00-07:00 07:00-08:00 08:00-09:00 09:00-10:00 10:00-11:00 11:00-12:00 12:00-13:00 13:00-14:00 14:00-15:00 15:00-16:00 16:00-17:00 17:00-18:00 18:00-19:00 19:00-20:00 20:00-21:00 21:00-22:00 22:00-23:00 23:00-24:00 kwh July load

22 Solar PV Summary Peak annual production in late spring / early summer when hydro output is low (~ 50% Nov to May) No production at night when loads are lowest Even June daily average production fits with summer daily load curve most of energy is useful Costs have declined rapidly in recent years Can be installed in small scale on building roofs and walls Simple no moving parts Energy costs $0.25 to $0.50 per kwh (decreasing) Disadvantages fluctuations, intermittent (daily cycle), and not dispatchable (also low output in mid winter)