Calculating Payback Time for Solar Cell Panels: GCSE kWh Question

  • Thread starter Thread starter Mukilab
  • Start date Start date
  • Tags Tags
    Gcse
Click For Summary

Homework Help Overview

The discussion revolves around calculating the payback time for solar cell panels based on a household's electricity usage and installation costs. The problem involves understanding the cost of electricity from the National Grid and the implications of the solar panel installation costs.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the original poster's calculation of payback time and question the assumptions made regarding the cost per kW versus kWh. There are attempts to clarify the relationship between the number of hours of sunlight and the expected output of solar panels.

Discussion Status

The discussion is ongoing, with participants exploring different interpretations of the problem and questioning the provided information. Some guidance has been offered regarding the importance of units in the calculations, and there is a recognition of potential ambiguities in the question itself.

Contextual Notes

Participants note that the question may lack sufficient information, particularly regarding the expected output of the solar panels based on their capacity. There is also mention of previous questions from the same exam paper that may have been problematic.

Mukilab
Messages
73
Reaction score
0
The question: Electricity supplied from the National Grid costs 8p per kWh.
A householder is considering installing solar cell panels. The household uses 4000 kWh of electricity each year. The cost of installing a solar cell panel is £6400 per kW
What is the payback time?

The answer is 40 years however I got 20 by doing the following.

I first worked out the total cost which I got as £320 = 4000kWh * £0.08 , this is per year

Then I just did £6400 / £320 to get 20 years.

How can you get 40? And where did I go wrong? I'd be very thankful for any help.

On another note... how do I use Latex in this forum? It just comes up with a box... do I have to do the latex tags myself?
 
Physics news on Phys.org
Welcome to PF!

Hi Mukilab! Welcome to PF! :smile:
Mukilab said:
Electricity supplied from the National Grid costs 8p per kWh.
A householder is considering installing solar cell panels. The household uses 4000 kWh of electricity each year. The cost of installing a solar cell panel is £6400 per kW
What is the payback time?

Always look carefully at the units in the question …

in this case, the cost is per kW, not per kWh. :wink:​
... do I have to do the latex tags myself?

Yup! :biggrin:
 


tiny-tim said:
Hi Mukilab! Welcome to PF! :smile:


Always look carefully at the units in the question …

in this case, the cost is per kW, not per kWh. :wink:​


Yup! :biggrin:

I tried dividing the kWh by the number of hours in a year and it doesn't work.
 
Mukilab said:
I tried dividing the kWh by the number of hours in a year and it doesn't work.

hmm … yes, it goes the wrong way, doesn't it?

The question seems to expect you to instal 2kW of panels, yet with about 9000 hours in a year, that seems totally unnecessary. :confused:
 
tiny-tim said:
hmm … yes, it goes the wrong way, doesn't it?

The question seems to expect you to instal 2kW of panels, yet with about 9000 hours in a year, that seems totally unnecessary. :confused:

It's from an AQA GCSE science module paper... and it's not the first that has been dodgy. I'll wait for anyone else to see if they can figure out why it works.
 
The only way I can see it working is if there's only about 6 hours of daylight a day.

Since that's only half the actual amount (of 12 hours), maybe there's some reason for taking half, eg that the sun spends most of the day at the wrong angle? :confused:
 
tiny-tim said:
The only way I can see it working is if there's only about 6 hours of daylight a day.

Since that's only half the actual amount (of 12 hours), maybe there's some reason for taking half, eg that the sun spends most of the day at the wrong angle? :confused:

Sounds too complicated for GCSE :(
 
Mukilab,how was the question worded exactly and have you left out any information?
 
Dadface said:
Mukilab,how was the question worded exactly and have you left out any information?

no left out information at all.

Copied it exactly, word for word.
 
  • #10
Mukilab said:
no left out information at all.

Copied it exactly, word for word.

What year and what course was it from?
 
  • #11
June 2008 Physics AQA GCSE Core Science Past Paper Module exam higher tier.

If you look at it, also please look at the dodgy question on meter readings.
 
  • #12
Back again.I did a search on the AQA website to look at past papers for 2008 but could not find the questions you referred to.
 
  • #13
Dadface said:
Back again.I did a search on the AQA website to look at past papers for 2008 but could not find the questions you referred to.

Here: http://store.aqa.org.uk/qual/gcse/qp-ms/AQA-PHY1AP-W-QP-JUN08.PDF

Question 8C

The dodgy meter one is 6C
 
Last edited by a moderator:
  • #14
Question 8 is about drying?
 
  • #15
8C of the higher paper.

That paper contains two parts: foundation and higher tier. Scroll down to page 14 or so to get higher.
 
  • #16
yes page 14.
 
  • #17
Mukilab if you look at question 8a there are two bar graphs and the one on the left informs us that a 1kW panel produces 2000 kWh per year.That information needs to be carried across to 8c.
 
  • #18
Dadface said:
Mukilab if you look at question 8a there are two bar graphs and the one on the left informs us that a 1kW panel produces 2000 kWh per year.That information needs to be carried across to 8c.

Really? Usually it mentions that in the question e.g. 'using graph x as evidence'...
 
  • #19
You will often find that information provided in earlier parts of questions is needed for later parts of questions.Part c on its own does not give enough information.
 
Last edited:
  • #20
Dadface said:
You will often find that information provided in earlier parts of questions is needed for later parts of questions.Part c on its own does not give enough information.

thank you for the help
 

Similar threads

What is the PV panel surface area?
  • · Replies 2 ·
Replies
2
Views
2K
An interesting GCSE question: Why are electric lamps connected in parallel in house wiring?
  • · Replies 14 ·
Replies
14
Views
851
How Many Square Meters of Solar Panels Are Needed for Household Usage?
  • · Replies 6 ·
Replies
6
Views
2K
Could we make a practical solar fridge?
  • · Replies 30 ·
2
Replies
30
Views
4K
Is Wall-Mounted Solar Production More Efficient in Winter at High Latitudes?
  • · Replies 15 ·
Replies
15
Views
2K
Considering Earth ground vs floating ground in off grid solar
  • · Replies 13 ·
Replies
13
Views
7K
Self excited induction generators and grid connected solar inverters?
  • · Replies 9 ·
Replies
9
Views
2K
Calculating the cost of electricity
  • · Replies 6 ·
Replies
6
Views
7K
High School Calculating Output of Solar Cells in KWH
  • · Replies 3 ·
Replies
3
Views
4K
Almost Plausible Solar Takeover Plan
  • · Replies 108 ·
4
Replies
108
Views
13K