reply to post by Pilgrum
When I was typing that post up, I was thinking about the older homes in this area that still use 100A services (a few are still 60A, but they're
getting rare). So no, not taking anything wrong; I even posted that if one were to drop the power requirements, the cost would drop considerably.
I tend to over-design... that means two things: First, that the cost is a bit higher initially, and second, that what I design never stops working.
My concern over the peak power requirements is in the electronics used to transform the DC into AC power. This is a typically hot process anyway (the
power ratings are based more on cooling ability for the components than anything else) and the heat produced by a sudden short will overheat
components. The question is how much and for how long. Most equipment has some measure of resilience to overload, but continued overloads are not
advised at all. Thus, I want the maximum peak power to be either at or above the rating of a main breaker, which here is standardized at 200 amps.
If you are using a 100A breaker, you can cut my power figures in half for the inverter, and that alone will save some big bucks. If you are sure of
your average energy usage, you can make similar adjustments as well to both the solar array and the batteries needed. In the end, all those
calculations are based on what is typical here, and based on your season-to-month statements it is apparent you are not in the Northern Hemisphere and
thus not in the US.
You also need to verify, then, the frequency of your standard AC line; appliances and other gadgets are designed for use with a specific frequency of
power input. Putting 60 Hz into a device designed for 50 Hz can have unpleasant consequences depending on the device.
I am steadily working on a design to get myself off the grid as well, of course over-designed as I mentioned above, but with different electrical
input than solar. The common need is an inverter, and I am playing with a design that uses a variation of a switching power supply and multiple
floating voltage references to produce the AC supply directly. If that works out, I'm sure everyone on ATS will see it.
Incidentally, I am working with a 30-battery bank of 8-Ds, giving me 360V nominal (potential for 430V) for a minimum back-up of 15 hours plus...
acceptable with a steadier source of DC power. I am also not interested in tying my system back into the grid; I will probably just install a 100A
breaker in my box to be used as input rather than output. One major caution with this idea for anyone reading:
Never, ever, have the auxiliary and
main breakers on at the same time! 180 degrees out of phase would show a dead short and you have no simple way to know what the phase relationship
is without expensive monitoring equipment.
TheRedneck
