Negative power bills?? or are my calculations way way off?

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Negative power bills?? or are my calculations way way off?

Postby zoeeoz » Fri Dec 09, 2016 2:31 pm

Hi :)

I''m looking at getting a solar system for my grid connected home, either a 4.2kw system or 6.4kw system, on east and west facing roofs, very little shading on north coast NSW - cost is $4600 for smaller system, $5500 for larger (parts are fronius inverter and canadian tier 1 panels, which seem decent quality). We don't use much power, only ~6.5kw/day, and its probably more in daylight hours than most folk. My energy provider will do a 10c solar feed in tariff from the end of the year. By the calculations I've done, the bigger system will pay itself off far sooner because of the feed in tariff (12 years to pay off smaller system, 6 years to pay off bigger one). The thing is, I've been reading that it makes more sense financially to get a smaller solar system, and that expecting negative or no power bills is unrealistic. Is there something I'm missing in my calculations? :? I'm happy to be putting up extra solar for the benefit of others too, but just don't want to find that I'm lumped with bigger power bills than I thought plus paying off solar because my calculations are somehow way off..

A rough sketch of my calculations in case it helps:

4.2kw system: If I use 3kw per day from solar, use 3.5kw/day from grid at $.2662/kw, daily power supply charge of $1.5, and export average 10.4kw/day at $.1.. then I'd be charged $1.39/day or $507.97/year for power. In comparison to current charges of ~$900/year, I'd save ~$390/year and take ~12 years to pay it off.

6.4kw system: If I use 4kw per day from solar, use 2.5kw/day from grid at $.2662/kw, daily power supply charge of $1.5, and export average 22.8kw/day at $.1.. then I'd be charged -$0.11/day or -$42/year for power. In comparison to current charges of ~$900/year, I'd save $940/year and take ~6 years to pay it off.

Do those figures sound plausible?

Thanks heaps! :D
zoeeoz
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Re: Negative power bills?? or are my calculations way way of

Postby APR » Sat Dec 10, 2016 11:53 am

Hi zoeeoz, That Enova Energy is a good outfit. I like their community spirit.

I am in northern NSW with panels split east and west, and have done a few calcs using your proposed panel wattages and the $ charges you indicate. I have used the kWh production I have achieved for each kW of installed panels over the last 12 months to do the calcs. My production has been 1,389kWh per kW of panels.

On my calcs, you may still pay a few dollars for power each year with the 6.4kW system, but your calcs are in the ballpark.

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2 x Goodwe GW5048D-ES Hybrid inverters, 13kW panels, 20kWh LiFePO4
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Re: Negative power bills?? or are my calculations way way of

Postby APR » Sun Dec 11, 2016 11:41 am

Hi zoeeoz, looking further at your calcs you have stuffed up with the 4.2kW system. You would pay a few dollars over $390/year for electricity with the 4.2kW system, not save $390. Your saving with the 4.2kW system would be more like $765/year.

Also, the currrent charges you quote of $900/year are out of whack with the usage and daily service charge you suggest for your system analysis. In your calcs you use $900/year for electricity, but the usage you suggest calculates to around $1,179/year. I have edited and added to my calcs, and you can see them below.

Image


Image
2 x Goodwe GW5048D-ES Hybrid inverters, 13kW panels, 20kWh LiFePO4
Mk2 PV Router feeding excess solar generation to a 3.6kW 250 ltr HWS
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Re: Negative power bills?? or are my calculations way way of

Postby zoeeoz » Sun Dec 11, 2016 5:27 pm

Thanks so much APR :D Good to know what you get up here..

And yes, thanks for picking that up, I confused myself trying to keep my post and calculations as simple as possible since it was already complex enough.. in reality I currently already have a 1kw system that I could add an extra 3.2kw to as a side by side set up, or replace entirely with a 6.4 kw system.. so I left off the 4.2kw calculations the kw I already get from current system.. and the $900 is what I've been paying with the 1kw system already running. With my previous power company. And then there's how long my current 1kw inverter will last. And what I could get if I sold it. Too many variables!! :) :)

Right - here goes, with all that in mind I reckon I'll get the bigger system! :D
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Re: Negative power bills?? or are my calculations way way of

Postby Gordon-Loomberah » Fri Dec 16, 2016 2:54 pm

EM have a solar and battery calculator here, which may help you determine what size PV system and battery you want. The load "Profiles are average for an year in the location ... are based on AEMO and include 8760 data points" although it certainly doesn't match my load profile very well with its 9pm demand peak.

http://www.energymatters.com.au/solar-c ... ulator.php
http://gunagulla.com Loomberah weather and astronomy including live solar radiation intensity and UV + Gunagulla aquaponics, organic eggs and cherries
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