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D.I.Y Solar Calculator Rough Guide

Work out what size PV system you need in 7 simple steps?

D.I.Y solar poer calculator rough guide

  1. Find your Power bill
    Choose three power bills if possible – Winter, Summer, Autumn/Spring
    The idea is to get an average usage of power throughout the year
  2. Add together the amount charged on each bill
  3. Divide this amount by 3 or 2 if only 2 power bills
  4. Multiply by 6.
    This is your average yearly cost for your electricity
  5. Divide the yearly cost by 365
    This is your daily power average cost
  6. Divide the daily average amount by .22
    This is the daily average amount of electricity units used for domestic usage. Commercial divide by .30
  7. For daytime use with no intention to add batteries divide this number by 2
  8. Round up to the nearest number

D.I.Y solar calculator rough guide_power bill calculation


  1. Power Bill ;
  2. Summer $600, Winter $520,  Autumn or Spring  $160 = $1280
  3. $1280 divide by  3 = $426.66
  4. Multiply $426.66 by 6 = $2560 (average yearly power bill)
  5. $2560 divide by 365 = $7.01 per day
  6. Divide  $7.01  by .22 = 31.8
  7. Divide 31.8 by 7 = 4.55
  8. Round up to 5

A 5kw system is the best size to suit a power bill of $1280 a year, however, part of the power used will be used during the day, and part will be used during the night.
A 5 kw system is big enough to handle the total electricity needs for both night and day.

If power is only required for daytime use, then the system size can be reduced for the amount of daytime usage.

To make an easy calculation lets say half the power is used during the day, therefore the size of the PV system can be halved and rounded up to the nearest full number
Example 5kw divided by 2 equals 2.5kw rounded up to 3kw

Battery Storage

To look ahead and set up a system that can look after daily power usage, but have the option to upgrade later, a 5kw inverter can still be used, but only put on 3kw of panels.

There is the economic advantage of saving money on installing less solar panels, but at the same time the downside is that there will be an extra installation charge to add the extra panels when the time comes

How much will it cost to set up the Solar System ?money

Actually, it is cheaper than you think, but..!
You do get what you pay for, in other words, if the system is very cheap, then there is no certainty that it will be trouble free. Systems are cheap for a reason.

For an average Solar PV system, you could use the rule of thumb, $1000 a kw installed.
A system around this price would be reasonable quality and trouble free,

For a high quality top of the range system, the price would be around $1500 a kw installed.

When will the Solar PV system pay for itself ?money_2

We will use the average priced system of $1000 a kw.
Based on the example system above, needing a 3 kw system during the day, and a 5kw system for day and night.
An average 3kw system would cost $3,000

The power bill for the example above was $2560 a year.
Being as how we are setting up 3kw for the daytime, the amount we will be saving will only be half – $1280 a year

$1280 divided into the cost to set up the system – $3000 = 2.34 years to pay back original investment.

Adding Battery Storage

When the system is paid off, it would be a good idea to add Battery Storage.
The total amount of savings would now be the entire power bill – $2560 a year.
A rough guide on price for Batteries would be about $1200 a kWh.
Based on the example above, we would require about 15 kWh.
With a conscious approach to using electricity, the kWh needed could come down to about 10kWh
This would mean an investment outlay of $12000 to set up the battery storage.

Future Savings … The

With a total saving on $2560 per year on the Power bill, now that Battery Storage has been added, will pay off the $12,000 investment in 4.68 years.
(5 years).Depending on the battery the life cycle will range from 2,000 – 6,000 cycles which is about 4 – 15 years depending on the depth of discharge and temperature.
An average lifetime would be about 5,000 cycles which equates to about 10 years.

The Batteries will be paid in 5 years and will still have 5 years of life in them before they need replacing.
With the power bill in the above example of $2560 a year, after 5 years the batteries are paid off which now creates an investment saving of $16706.
That is the $12650 over 5 years compounding @ 7% interest with 2.5% inflation = $16706
This means that when the batteries need replacing, which will be cheaper and more technologically advanced in the future, there will be enough money saved to pay for new batteries to now create a real saving of 100% for the life of the new batteries.

These are very conservative figures, but they are better than investing your money in the bank.

If you cant afford to set up a system, call us, and we can arrange finance for you, then you can start saving right away and use the money you save on power to pay off the loan.


contact usCall us on 0401405442 or drop into the office at unit 2 / 31 Christable Way Landsdale to discuss any questions you have about Solar Power, or use the Contact form to send off an email and we can get the ball rolling, even if it is just giving you helpful advise on how to get started to work out what type of system you. need.


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