Help me make wise decisions - First timer

Cariboocoot wrote: »

You definitely do not want to run an array of 100+ Volts unless it is necessary due to wiring distance considerations: the higher the array Voltage is in respect to the system Voltage the less efficient the controller is because of having to do more work to down-convert the higher Voltage. Usually you don't go more than 2X system Voltage (as in a nominal 48 Volt array on a 24 Volt system).

Read the links I gave you and I think you'll figure it out.

vtmaps wrote: »

In both configurations, you left out the combiner box.

Another consideration is the battery bank. A single string of batteries is optimal. Therefore, on that basis I would recommend the 48 volt configuration. One thing in favor of a 24 volt system, is the potential to have fewer cells. This makes for fewer connections and easier maintenance, but you will be using larger, more expensive cells (not GC batteries). Fewer cells also means a longer lasting battery bank. explanation:

No two battery cells are identical (half of all cells produced are below average!) There's virtually no chance that a 48 volt (or even a 24 volt) battery bank will be entirely composed of above average cells. Having even 23 of 24 cells above average does you no good because a battery bank is only as good as its weakest cell. So you can't realistically hope to have a battery with all above average cells, but what really matters is avoiding those outlier cells in the lowest percentiles. The more cells you have in your battery bank, the greater the chance of having an outlier cell, and the more likely your battery bank will have a below average lifespan. Statistically, the longest lived battery bank will have the fewest cells. Of course a 2 volt system voltage is impractical.... a good design compromise is to use a single string of cells at the lowest voltage that is practical for your power needs.

Regarding the inverter, you will be much happier with an inverter/charger. Not just because of the charger, but these inverters have many more features. You have grid available... read a little about hybrid inverters before you invest.

Where will you mount your panels? You should have your combiner box with a lightning arrester outside your home. btw, if you go with a 48 volt system, three panels in series will be OK. I wouldn't do three in series with a 24 volt system.

Take a look at Midnite's ePanel and download their ePanel wiring diagrams. You will learn a lot about the buses, breakers, shunts, and bypasses that you will need. They sell the ePanel as a kit with all components needed for the particular inverter/charger that you want.

Finally, how will you integrate your system into your present house wiring? Will you set up a separate AC distribution panel? Depending on what you do, you may need some transfer switches to keep your inverter and the grid apart. Inverter/chargers have built-in transfer switches.

--vtMaps

Cariboocoot wrote: »

There's no such thing as "too much array for the batteries" as the charging is regulated. So you can spend too much on the array, but it won't cook the batteries. A 1050 Watt array on an MPPT controller should be good for 34 Amps @ 24 Volts, more than enough for a single set of GC2's.

When you go up in array size and increase current potential you can program a good controller to limit its output current to an amount less than maximum. So the array might be capable of 60 Amps @ 24 Volts but the Classic 150 (for example) is set to only put out 30 Amps at most. Why do this? Because the sun doesn't shine all the time. In areas where clouds compete for the sky putting up a larger than typical array can help on those less-than-perfect days.

And keep in mind we are talking about peak, not constant, current and that most flooded cells can take 20% of their capacity for a maximum.

Since you are looking at 300 Watts output rather than 3000 you can definitely go down in size and save more money. 1kW 24 Volt inverter is about as small as they get: http://www.solar-electric.com/sa1wa24vosiw.html There are smaller inverters, but they are nearly always 12 Volt. Might as well find a good compromise between smallest and largest, eh?

Cariboocoot wrote: »

Yes: that would be 220 Amp hours @ 24 Volts and the array could provide 33 Amps @ 24 Volts.



I think you'll find four (one string) more than adequate. My battery bank is 232 Amp hours @ 24 Volts and it runs everything at the cabin including refrigerator.



The Kid will work fine. Current over 30 Amps will just be 'clipped' and the overage is likely to be no more than 10% at that.



Were it not for the big hit of the motors I use a 1kW inverter would work for my system as well. Most of the time it idles along at <500 Watts output. The surge capacity of the 1kW unit should allow the 'frige to start (they can demand over 1kW easily), if all the wiring is sound and there aren't many other loads on.

That Samlex has a "power save" mode which reduces its own consumption when there is no load demand on it. Although the minimum start-up trigger is 20 Watts. It draw 0.15 Amps then, or 0.75 when active. Otherwise conversion efficiency is 92% at full load (meaning 1000 Watts AC demands 1087 Watts DC plus the inverter's own 18 Watts - pretty good rating).