here comes the sun – applications of solar energyhere comes the sun – applications of solar...

Marc Rosenbaum, P.E. – South Mountain Company – West Tisbury, MA

Here Comes The Sun – Applications of Solar Energy

Learning objectives

1 – Participants will learn how to quantify the amount of sun reaching a surface 2 – Participants will learn how these energy flows compare with the loads of advanced buildings 3 – Participants will learn how to apply the sun’s energy to serve building loads 4 – Participants will have fun

Agenda

1 – Solar gain calculations with PVWatts 2 – Solar gain calculations with AVOTS 3 – Daylight factor calculations 4 – Case study

How much energy is in sunshine?

Introducing PVWatts http://www.nrel.gov/rredc/pvwatts/

PVWatts

PVWatts Output

Back to PVWatts – Pick the State

PV Watts – Pick the City

PV Watts Input Page

PV Watts Input Page

PVWatts

Solar insolation by orientation

-

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

45,000

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

BTU/ft2/month

South vertical

East vertical

North vertical

West vertical

Solar insolation by orientation

-

10,000

20,000

30,000

40,000

50,000

60,000

70,000

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov

BTU/ft2/month

South 42 degree pitch

Horizontal

South vertical

East vertical

North vertical

West vertical

Calculate Monthly Solar Gain

Insolation x 317 x days/month = BTU/ft2/month

Calculate Window Solar Gain BTU/ft2/month x ft2 x SHGC x 0.85 x % unshaded = BTU/month

Compare to Heating Load

Solar Hot Water

Compare to DHW Load BTU/ft2/month x ft2 x efficiency = BTU/month

Solar Electricity

Solar Electricity

kWh/kW

Solar Electricity

Clear Day Hourly

Introducing AVOTS http://www.pge.com/mybusiness/edusafety/training/pec/toolbox/arch/calculators.shtml

Clear Day Hourly

Clear Day Solar Gain

Daylighting with Toplighting

Daylighting with Toplighting

Simple Calculation of Effective Aperture for overcast period daylighting from above Inputs: -  Skylighting aperture (skylight area/skylit floor

area) -  Glazing visible light transmission (VLT) -  Well factor (WF) -  Dirt/screen factor of 0.85

Effective aperture = Skylighting aperture x VLT x WF x 0.85

Well Factor

How much light that enters a skylight well gets into the space below First calculate Well Cavity Ratio (WCR): WCR = 5 x H x (W + L) / (W x L) Say a skylight is 4’ x 4’ and the well is 3’ deep - WCR = 7.5

Daylighting with Toplighting

A WCR of 7.5 with a reflectance of 0.80 has a Well Factor of 0.68

Case Study – West Tisbury Project

South Mountain Company Photos Derrill Bazzy

Case Study – West Tisbury Project

•  3,000 ft2 multipurpose building – gallery, shop, greenhouse, solar electricity

•  Not heated, but high quality thermal envelope and very tight construction

Solar applications include solar electricity, solar greenhouse with remote thermal storage, daylighting

Solar Electricity

•  Estate usage of 36,000 kWh/year and objective of net zero electricity

•  Buildings are heated with propane; swimming pool converted from propane to a heat pump

•  Objective of providing power when the grid is down led to a bi-modal system with SMA grid-tied and off-grid inverters with battery banks

•  35 kW of Sunpower panels mounted on the standing seam roof – expected annual output of ~ 45,000 kWh

Solar Electricity

Solar Thermal

•  Solar greenhouse designed to keep plants at 50F or more through the winter without heating

•  Glazing is double low-e argon Cardinal 180 •  When greenhouse temperature is greater than thermal

storage temperature a blower turns on to transport heated air from the greenhouse to the basement level thermal storage

•  Heat retrieval during cold night time conditions is via passive natural convection

Solar Thermal

•  Clear day calculations on vertical and horizontal glazing to assess thermal storage need – final design has 300 five gallon water containers that store 125,000 BTU over a 10˚F rise – concrete in the basement adds significant additional storage

•  Peak hourly net gain calculation to size the blower

Solar Thermal

Solar Thermal

Solar Thermal

Solar Thermal

Daylighting

•  Both gallery and shop were designed with little sidewall glazing

•  Toplighting via a continuous ridge skylight was chosen to daylight these spaces

•  A Daylight Factor of 2% was the target •  Glazing is triple low-e argon Cardinal 272 – VLT

is 56%

Daylighting

Daylighting

Daylighting

Daylighting

Daylighting

Thank you

http://www.energysmiths.com/ http://thrivingonlowcarbon.typepad.com/ http://www.southmountain.com/