Solar power production calculator in Australia

 

The calculator below provides power production numbers for polycrystalline panels.

Monocrystalline and Half-Cell panels with lower temperature coefficients and improved design to combat minor shade would be expected to produce 1-4% more.


To use the table, simply enter in the total kW of panels you have for each roof orientation in the second column...

e.g. If you have 11 x 300W panels on East and 11 x 300W  panels on West then enter 3.3 to the right of the E and W rows.

 

Under the table is a second calculator that works out your electricity bill savings based on the data you enter in the first table and under that is an explanation about WHEN in the day the power is made.

 

One of the things that really surprises most people is how little power is made after 3pm...even on a West facing roof in Summer. So the idea of putting extra panels on West to catch the sun in the late afternoon is actually remarkably ineffective. For instance, 3.3kW of panels over Summer (Dec 1st to Feb 28th) in Perth on a West facing roof produces a daily average of 19.2kWh but only 1kWh of that is produced after 3pm. By comparison, the same 3.3kW of panels on North produces 20.3kWh in the day but only 0.5kWh of it after 3pm, and even an East facing roof with 20.6kWh for the day manages 0.26 kWh after 3pm.

 

Download this Excel spreadsheet that breaks down the power production for any roof orientation in Summer, Autumn, Winter and Spring for Dawn to 7am, 7am to 11am, 11am to 3pm and 3pm to 7pm. (Perth only at this stage).

Select a City :

Perth
kW of panels (e.g. 5.5) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual Avg. Per Day % to N

Export Price :

Electricity Price :

Annual electricity bill savings

Daytime power consumption Savings Year 1 Savings Per Bill


Solar cells degrade in output every year by about 0.6%, you will need to factor this in for an older installation.

What is more important to your hip pocket than just overall production, is when you USE power. If you come home from work/school and switch on lots of things, then an afternoon sun West facing roof might be better for you, financially, than North.

Under the power production figures is a calculator showing what your cost savings would be if your daytime power use was 5,10, 15, 20 or 25 kWh per day.
This is based on electricity prices of 26 cents for units of solar power used and 7 cents for units of surplus power exported back into the grid. We will soon be adding the facility for you to enter your own rates.
Please note that this is your DAY power use, not Total. Solar only works when the sun is shining, so you either use it, as it is made, or it is exported back to the grid.
When batteries become affordable, then the surplus solar can be stored and used at night, greatly improving the financial return. Not yet though.

The next thing we look at is how the sun transits across the sky through the seasons and WHEN during the day solar power is made.

Most people know that the only two days of the year that the sun actually rises due East and sets due West are March 21st and September 21st, but it surprises a great many people how FAR South East the sun rises in Summer, and sets in the South West. In fact in January the sun is due West at about 3.30pm !!

You can also see that the arc is narrow, meaning the sun is more 'overhead' than the Winter picture shown underneath. It barely gets above Northbridge in the picture.

July image below. The Sun is rising in the East North East and setting West North West.

Notice how low in the sky the sun is with the top of the arc at Noon stretching up as far as Landsdale in the North in this picture.

Being so low in the sky greatly reduces solar production.

The tables below show WHEN the solar power is produced, every two hours, from dawn until dusk.

East facing roof

86% of the solar production is achieved, on average across the year by 2pm and over 97% by 4pm
Summer power production is quite evenly spread from dawn to 4pm

Winter power production is very concentrated to between10am and 2pm

 
Dawn to 8am
8am to 10am
10am to Noon
Noon to 2pm
2pm to 4pm
4pm to 6pm
6pm to Sunset
Jan
15%
23%
25%
21%
13%
3%
0%
Feb
12%
23%
25%
21%
14%
4%
1%
Mar
8%
25%
28%
23%
13%
2%
0%
Apr
7%
26%
30%
24%
11%
12%
0%
May
1%
26%
36%
27%
9%
1%
0%
Jun
1%
15%
39%
34%
10%
1%
0%
Jul
0%
15%
33%
35%
14%
3%
0%
Aug
3%
26%
33%
26%
10%
2%
0%
Sep
3%
24%
34%
26%
10%
3%
0%
Oct
7%
21%
33%
23%
13%
3%
0%
Nov
16%
25%
26%
21%
11%
2%
0%
Dec
17%
23%
24%
21%
12%
2%
1%
 
Ave
7.55%
22.75%
30.49%
25.06%
11.64%
2.33%
0.18%
Cum
7.55%
30.3%
60.79%
85.85%
97.49%
99.82%
100%

 

North facing roof

As with the East facing roof, North produces virtually no power after 6pm year round,
and virtually nothing before 8am in Winter

Production is very evenly spread, year round, from 8am to 4pm

75% of daily power, on average, is produced before 2pm, and 95% before 4pm

 
Dawn to 8am
8am to 10am
10am to Noon
Noon to 2pm
2pm to 4pm
4pm to 6pm
6pm to Sunset
Jan
5%
18%
24%
24%
20%
9%
1%
Feb
4%
17%
23%
24%
22%
9%
1%
Mar
3%
17%
25%
27%
20%
8%
0%
Apr
3%
17%
26%
27%
21%
6%
0%
May
1%
15%
29%
30%
22%
3%
0%
Jun
0%
15%
30%
31%
21%
4%
0%
Jul
0%
14%
30%
31%
22%
3%
0%
Aug
1%
17%
30%
31%
18%
3%
0%
Sep
3%
18%
28%
28%
16%
6%
0%
Oct
6%
20%
28%
27%
17%
2%
0%
Nov
7%
21%
27%
26%
16%
2%
0%
Dec
7%
19%
24%
24%
19%
7%
0.%
 
Ave
3.36%
17.23%
27.16%
27.45%
19.51%
5.11%
0.18%
Cum
3.36%
20.59%
47.75%
75.2%
94.71%
99.82%
100%

 

West facing roof

Worried about late afternoon shade from trees hitting your West roof after 6pm ?

Don't be...Only 0.45 % of your production happens after 6pm, whereas 2.88% HAPPENS BEFORE 8AM.

Over 40% of your average production happens before mid day and 90% by 4pm.

 

 
Dawn to 8am
8am to 10am
10am to Noon
Noon to 2pm
2pm to 4pm
4pm to 6pm
6pm to Sunset
Jan
5%
15%
22%
23%
21%
12%
2%
Feb
3%
15%
23%
26%
22%
10%
1%
Mar
2%
14%
23%
26%
22%
12%
1%
Apr
2%
14%
25%
28%
21%
10%
0%
May
1%
14%
27%
30%
22%
7%
0%
Jun
0%
13%
29%
26%
19%
13%
0%
Jul
0%
15%
29%
30%
22%
4%
0%
Aug
1%
4%
28%
30%
20%
8%
0%
Sep
2%
14%
25%
28%
21%
9%
0%
Oct
4%
15%
24%
27%
22%
9%
0%
Nov
5%
17%
24%
25%
20%
9%
0%
Dec
7%
10%
16%
28%
24%
13%
1%
 
Ave
2.88%
14.05%
24.58%
27.09%
21.39%
9.57%
0.45%
Cum
2.88%
16.92%
41.51%
68.59%
89.98%
99.55%
100%