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?