Engineering: Solar House Design Trade-Offs
Balancing energy, cost, comfort, and constraints in a solar home
Engineering: Solar House Design Trade-Offs
Balancing energy, cost, comfort, and constraints in a solar home
Engineering - Grade 6-8
- 1
A team is designing a small solar house. List three goals the team should consider besides making as much electricity as possible.
Think about what a family living in the house would need every day.
The team should consider goals such as keeping costs reasonable, keeping the house comfortable, making the design safe and strong, using materials wisely, and fitting the house on the available site. - 2
A roof can hold either 8 high-efficiency solar panels that each produce 350 watts or 12 standard panels that each produce 250 watts. Which option produces more power, and by how much?
The 8 high-efficiency panels produce 8 times 350, or 2,800 watts. The 12 standard panels produce 12 times 250, or 3,000 watts. The standard panels produce 200 watts more power. - 3
A south-facing roof gets strong sunlight for 6 hours each day. An east-facing roof gets strong sunlight for 4 hours each day. If the same 500-watt solar array could be placed on either roof, how much more energy would the south-facing roof produce in one day?
Energy in watt-hours equals power in watts times time in hours.
The south-facing roof would produce 500 times 6, or 3,000 watt-hours. The east-facing roof would produce 500 times 4, or 2,000 watt-hours. The south-facing roof would produce 1,000 watt-hours more in one day. - 4
A design choice adds extra insulation to the house. It costs more at first, but it reduces heating and cooling needs. Explain the trade-off.
The trade-off is higher construction cost in exchange for lower energy use over time. Extra insulation may make the house more comfortable and reduce electricity bills, but the team must decide if the savings are worth the added cost. - 5
A window design uses very large south-facing windows to let in winter sunlight. In summer, the same windows may overheat the house. Name one design feature that could reduce overheating while still allowing winter solar gain.
The Sun is usually higher in the sky in summer and lower in the sky in winter.
A roof overhang, shade awning, adjustable blinds, shade trees, or low-emissivity glass could reduce summer overheating while still allowing useful sunlight in winter. - 6
A student says, "We should cover every part of the roof with solar panels because more panels is always better." Explain why this may not be the best engineering decision.
Covering every part of the roof may not be best because some areas may be shaded, face the wrong direction, be hard to maintain, or add too much cost or weight. Engineers must compare the extra energy gained with the extra cost and possible problems. - 7
A solar house has a daily energy need of 18 kilowatt-hours. Its solar panels produce 12 kilowatt-hours on a cloudy day. How much extra energy must come from a battery or the electric grid?
Subtract the energy produced from the energy needed.
The house needs 18 kilowatt-hours and the panels produce 12 kilowatt-hours. The extra energy needed is 18 minus 12, or 6 kilowatt-hours. - 8
Compare these two wall materials for a solar house: Material A costs less but has low insulation. Material B costs more but has high insulation. Which would you choose for a cold climate, and why?
Material B would usually be the better choice in a cold climate because high insulation reduces heat loss. Even though it costs more at first, it can improve comfort and lower heating energy use over time. - 9
A design team must choose between placing solar panels on a roof or on a ground rack. Give one advantage and one disadvantage of each option.
Think about space, sunlight, safety, cost, and maintenance.
Roof panels save yard space and can be closer to the house wiring, but roof angle, shade, or repairs may be limiting. Ground-mounted panels can be easier to aim and maintain, but they take up land and may need extra supports or wiring. - 10
A battery system costs $4,000 and stores enough energy to power the house at night. Without the battery, the house must use grid electricity at night. What are two benefits and one drawback of adding the battery?
Two benefits are that the battery can store daytime solar energy for night use and can provide backup power during outages. One drawback is that the battery adds a large upfront cost and may need replacement after years of use. - 11
A house design includes a tall tree on the west side. The tree shades the house on hot afternoons, but it also shades some solar panels. Explain how this creates a trade-off.
Shade can be helpful in one place and harmful in another.
The tree can reduce cooling needs by shading the house, which saves energy and improves comfort. However, if it shades the solar panels, the panels produce less electricity. The team must balance cooling savings against lost solar production. - 12
A team has a budget of $10,000. Solar panels cost $7,000, better insulation costs $2,500, and smart energy controls cost $1,200. Can the team include all three choices? If not, how much over budget would they be?
The total cost would be 7,000 plus 2,500 plus 1,200, which equals $10,700. The team cannot include all three choices because they would be $700 over budget. - 13
A solar panel works best when it is not shaded. Look at this situation: a chimney casts a shadow on the roof from 2 p.m. to 5 p.m. each day. What is one design change that could improve performance?
Changing panel location can sometimes improve energy production without adding more panels.
One design change is to move the solar panels away from the chimney shadow. Another possible change is to place panels on a different roof section or use panel wiring that reduces the effect of one shaded panel. - 14
Rank these design priorities from most important to least important for a solar house in a storm-prone area: lowest cost, strong roof structure, maximum window area, secure panel mounting. Explain your ranking.
A reasonable ranking is strong roof structure first, secure panel mounting second, lowest cost third, and maximum window area last. In a storm-prone area, safety and durability are the most important because the house and panels must withstand wind and weather. - 15
A final design produces enough solar energy in summer but not in winter. Give two reasons this might happen and one possible improvement.
Seasonal changes affect both sunlight and home heating needs.
This might happen because winter days are shorter and the Sun is lower in the sky. Snow, clouds, or shading can also reduce solar production. One improvement is to adjust the panel angle, add more panels if space and budget allow, reduce energy use, or improve insulation.