Re: Off-Grid vs. Grid Tied Efficiency
The data that BB Bill posted above, gets you to the 50-ish percent figure.
An additional inefficency results from a desire to use solar input to fully charge the battery bank on 90% (or so) of the days in a year. This dictates a significantly larger solar array, which means that on most days there is a large excess solar power which can be used for heating, cooking, managing A/C, water heating or pumping, clothes washing and so on.
Almost all of these tasks are manually driven. They can take a lot of a person's time to manage, and often need monitoring or intervention, so one's attention needs to be directed onto these activities. If one makes a run to town, or is away at work, some of the above can run beyond the excess solar use, into running these things from battery power, if the "excess" power is taken from an inverter, as opposed to running from the DC output of the solar array.
Most of the advanced solar Charge Controllers have a useful function that indivates when there is excess solar power available -- CC in Float mode. This would help atuomatically manage the use of excess solar input, but it is up to the person who manages the off-grid system to implement a more automated system to use this information from the CC, applying the excess onto a pritorized list of uses for this excess power (as an aside, the Xantrex XW SCC has lacked this important function).
An alternative to having a lot of this excess solar power capability, is to run a generator more often when the demands on the off grid sysem for power exceed the PV power available. This type of system could be viewed as being more efficient, and it is much easier to automate, with Automatic Generator Start, but, of course it would use more non-renewable energy.
Trade-offs, always tradeoffs ... . Vic
Off-Grid, Sys1: 1280 AH 48 V bat, 3.150 KW STC PV, MX-60, Xantrex Stacked SW+ 5548s; EU6500isa, 21KW Kubota diesel gens, misc Honda Eu gens
Sys2: 1280 AH 48 V 4KS25 Surrettes, 5.88 KW STC, Two Classic 150s, MN SPDs, Stacked X SW+ 5548s; Kohler 18 KW LP, EU 3000isa gens, HB DC Charger, Midnite Breakers/boxes. Thanks for this great Forum!