Which one is the correct answer for it?

Question

A typical residential hot water system that uses approximately 10 kWh(e)/d is replaced with an electricity-boosted solar hot water system that uses an average of 170 watts (W) of electrical power. Use this information to evaluate the following statement:

"Installing a solar hot water system can reduce household water heating costs by up to 60%."

Answer:

a) The statement is inaccurate: installing a solar water heater reduces electricity costs by much more than 60%


b) The statement is accurate: installing a solar hot water heater reduces electricity costs by around 60%


c) The statement is inaccurate: installing a solar hot water heater reduces electricty costs by much less than 60%

Answer 1

Sean,

 

10 kWh/d is really 10,000 W/d, so the electrical reduction is

10,000 - 170 = 9,830 W/d,  9,830/10,000 = 0.983 decimal which is really 98.3% electrical usage reduction per day

 

Then answer (a) is correct if I understood your units correctly in kWh(e)/d.

 

Of course, this is an incomplete and unfair comparison since you need to add in the daily costs of buying, transporting, and installing each of these two systems.  For example, what are the daily payments for the bank loans taken out to pay for them and their installations.  There may also be some small additions for any maintenance or servicing that the systems require during their useful lives.  For example, do you need to clean your solar panels periodically to get the dirt off the glass in order to restore efficiency? The point is, in any real comparison, all costs must be included.  And in comparing environmental impacts, the impacts of getting their raw materials, manufacturing them and transporting them to your site should be included, not just when they are operating.