Energy & Its Impact on Global Society Jerome K. Williams, Ph.D. Saint Leo University Dept. Mathematics & Sciences

Chapter 6: Solar Energy Active vs. Passive Solar Heating Solar Systems: Cost-Benefit Analysis Energy Conservation (DHW) Passive & Active Solar Space Heating Thermal Energy Storage Materials

Active vs. Passive Solar Heating Core components of System – Collection Device – Storage Facility – Distribution System

Active vs. Passive Solar Heating

Active solar heating system uses pump or fan to circulate fluid (water or air) that Sun heats Passive solar heating system does not use external power but allows fluid (water or air) that Sun heats to circulate by natural means

Active vs. Passive Solar Heating Active solar heating system: heat swimming pools & hot water heaters Passive solar heating system: space heating home. – System can save up to 50% heating costs for 1-5% increase in construction costs: drawback is you must incorporate system when house is built

Solar Systems: Cost-Benefit Analysis Three Types of Solar Domestic Hot Water (DHW) Systems – Flat-plate collector (FPC) – Batch Water Heaters (Bread box) – Passive (Thermosiphoning)

Solar Systems: Cost-Benefit Analysis Flat Plate Collector (FPC) Systems – Most common system for DHW & pools – Expensive system ($ $5000) – Payback (Break Even Point)15-30 years Time interval dependent upon variables (rebates, tax credits, net metering, etc.)

Solar Systems: Cost-Benefit Analysis

Batch Water Heater(Figure 6.25) – Commonly called bread box heater – Inexpensive system($500 - $1000) – Older technology; been around over a century – Break even point: 5-10 years

Solar Systems: Cost-Benefit Analysis

Solar Water Heater: Do It Yourself MTL4 MTL4

Solar Systems: Cost-Benefit Analysis Thermosiphon Method – Passive Solar System – Water flows from collector to tank under natural circulation – Storage tank situated above collector – Commonly used in Asia, particularly China

Solar Systems: Cost-Benefit Analysis

Energy Conservation (DHW) To further reduce water heating bill: – Reduce thermostat temperature to 120 F – Insulate water heater (R-19 fiberglass) – Use reduced flow shower heads and low flow aerators for sinks

Passive & Active Solar Space Heating Passive solar space heating system: House acts as solar collector and storage facility Object: let sunlight enter (large windows; south side) and store energy inside structure using material of house itself

Passive & Active Solar Space Heating Essential elements passive solar system – Excellent insulation – Solar collection (large South-facing windows) – Thermal storage facilities

Passive & Active Solar Space Heating Passive Systems: Three Categories – Direct Gain – Indirect Gain – Attached solar greenhouse

Passive & Active Solar Space Heating Direct Gain System – Sunlight enters house (South side; large windows) – Thermal storage material placed inside house to absorb solar radiation (daytime) & radiate it outward at night – Concrete, slate, stone, brick

Direct Gain: Solar Home Heating

Passive & Active Solar Space Heating Indirect Gain System – Sunlight enters house (South side; large windows) – Thermal storage material placed near window. – Idea: Collect & store absorbed solar energy inside material. Use heat transfer (convection/radiation) to distribute heat – Trombe wall

Indirect Gain: Solar Home Heating

Passive & Active Solar Space Heating Attached Greenhouse – Sunlight enters greenhouse (South side) – Entire structure acts like “large thermal storage wall” – Serves dual function: food and heat production – Concrete floors & water filled drums common energy storage devices

Attached Solar Greenhouse: Solar Home Heating

Passive & Active Solar Space Heating Active Solar Space Heating – Been around for long time; not commonly seen in US due to cost issues

Thermal Energy Storage Materials Recall heat energy absorbed or released is governed by equation Q = mcΔT See Table 6.5 for Thermal Energy Storage Data

Problems 3, 5, 24, 25