P110/120: Energy/Energy & Technology Fall 2015
Homework 05
1. Solar energy can be attractive not only environmentally, but also economically. If an electric clothes dryer has a power rating of 6000 W and is used for 1 hour per day, how much money can be saved in a month by using the "backyard solar clothes dryer" (see Fig. 6.37 in your text), assuming electricity costs 10 cents per kWh?
6000 W x 1hr/day x 30days/month x 1kW/1000 W x $0.10/kWh= $18.00/ month
So $18 a month for electric clothes dryer will be saved because it’s free to use a “backyard solar clothes dryer.”
2. Suppose you have solar radiation of 650 W/m2, and you can collect 20% of the energy that falls on the reflecting surface of a solar cooker. If you need 350 W for the …show more content…
What is the optimum angle of tilt (from the horizontal) for a solar collector located at 30 N latitude for the purpose of domestic water heating? For space heating?
The angle of tilt would be 30 degrees for both domestic water heating and space heating because the tilt is supposed to be equal to the latitude.
4. What are the disadvantages and advantages of locating solar collectors on a vertical, south-facing wall?
An advantage is that insolation is greater in winter because the sun is lower. The installation would be easy as well. A disadvantage would be in the summer the sun will be higher and need solar collectors to be horizontal.
5. What size flat-panel collector is needed to supply a family's domestic hot water needs in March in Denver, Colorado? Assume 80 gallons per day are needed (1 gal = 8.3 lbs) for the water and that the collector-heat exchanger system has an average efficiency of 40%. Assume a temperature difference of T = between the input water temperature to the soar collector and the output water temperature to be used for showering, washing dishes, etc. The collector tilt angle is equal to the latitude (see Appendix D).
Q= mcDeltaT DeltaT = 70 degrees
80gal x 8.3lbs/gal x 1Btu/lb/degrees x 70 degrees = 53100
Homework 05
1. Solar energy can be attractive not only environmentally, but also economically. If an electric clothes dryer has a power rating of 6000 W and is used for 1 hour per day, how much money can be saved in a month by using the "backyard solar clothes dryer" (see Fig. 6.37 in your text), assuming electricity costs 10 cents per kWh?
6000 W x 1hr/day x 30days/month x 1kW/1000 W x $0.10/kWh= $18.00/ month
So $18 a month for electric clothes dryer will be saved because it’s free to use a “backyard solar clothes dryer.”
2. Suppose you have solar radiation of 650 W/m2, and you can collect 20% of the energy that falls on the reflecting surface of a solar cooker. If you need 350 W for the …show more content…
What is the optimum angle of tilt (from the horizontal) for a solar collector located at 30 N latitude for the purpose of domestic water heating? For space heating?
The angle of tilt would be 30 degrees for both domestic water heating and space heating because the tilt is supposed to be equal to the latitude.
4. What are the disadvantages and advantages of locating solar collectors on a vertical, south-facing wall?
An advantage is that insolation is greater in winter because the sun is lower. The installation would be easy as well. A disadvantage would be in the summer the sun will be higher and need solar collectors to be horizontal.
5. What size flat-panel collector is needed to supply a family's domestic hot water needs in March in Denver, Colorado? Assume 80 gallons per day are needed (1 gal = 8.3 lbs) for the water and that the collector-heat exchanger system has an average efficiency of 40%. Assume a temperature difference of T = between the input water temperature to the soar collector and the output water temperature to be used for showering, washing dishes, etc. The collector tilt angle is equal to the latitude (see Appendix D).
Q= mcDeltaT DeltaT = 70 degrees
80gal x 8.3lbs/gal x 1Btu/lb/degrees x 70 degrees = 53100