Newbie question

Re: Newbie question

First, regarding the traction battery--They are designed to discharge to 50% or deeper (if you routinely only discharge by 25% to 50%, and avoid going deeper than 50% very often, and never below ~20%, your batteries will last longer). Automotive/truck batteries are designed to discharge by only 15% or so. Marine are supposed to be somewhere between starting and deep cycle--But they are not recommended for deep cycling.

There are lots of ways of looking at power from the solar array and how it gets to your loads... But from a 50,000 foot point of view, the equation would look something like this for a flooded cell, AC Inverter system (conservative power estimate):

1,000 watt panels * 0.52 overall system efficiency * 4 hours of sun per day = 2,080 Watts minimum of "useful" AC power per day (typically ~9 months of the year)

So, if you have 5,280 WH of storage and discharge a maximum of 50%, the amount of "useful" AC power would be:

5,280 watts * 0.50 discharge * 0.85 inverter efficiency = 2,244 WH per day

Of course, if you do not have enough panels/sun to fully recharge the bank for the next day's use--Then you will have less energy for the next day's use (unless you take the battery further into discharge--"deficit charging", or have a backup generator to assist).

Note that, typically, we use the C/20 (20 hour discharge rate) for most of our work here... However, if you have heavy loads (well pump, etc.), the battery when discharged at C/10, C/8, C/5 discharge rates will appear to have less AH capacity. You can read about Peukert below:

Peukert's Equation. A quick explanation of the equation.
Peukert's Equation (Peukert's Law) properly explained (and correctly).
A Peukert Calculator spreadhseet (extremely useful program).
The 50% rule for deep cycle batteries.
More on the effects of Peukert.

The general rules of thumbs work pretty well because they give conservative results, and most people/homes, on average, are a mix of loads... Not a set of loads that run 100 watts * 24 hours per day, or 4,800 watts for 30 minutes a day.

For folks with "unusual loads and profiles", then we do need to look closer to see that the system will meet expectations.

So, yes, your 110 Watt load * 24 hours per day = 2,640 Watt*Hours per day. But when you start looking at the details (inverter losses, and overall losses from panel ratings of 81%, controller at 95%, flooded cell battery at 80%, and inverter at 85% efficiency--You multiply all this together and get 0.52 or 52% efficiency--It turns out that you don't get exactly that amount. Also, for most people, they will see a mix of ~3-5+ hours of sun per day (seasonal). And there will be days/weeks of bad weather where you may see less than a 1/2 hour equivalent sun per day. So--Either you need to be flexible (i.e., postpone washing) or have to have a back up genset to cover your loads on days with poor power production.

-Bill