How Long Can Your System "Coast"?

Symbioquine said:

We'll call the time where a system is neither all the way full nor too close to empty: "coasting"

IMHO, time spent coasting is one measure of how well an off-grid system is balanced in terms of production capacity, storage capacity, and usage.

Lots of ways to look at this, but;

• If your production capacity is too large you'll spend a lot of time full and not getting the full value out of your solar panels (or wind/hydro/etc).
• If your storage capacity is too small (relative to production) you'll spend a lot of time either almost empty or full and either not have power to use or room to store power for the future use respectively.
• If your usage is too large or too small (relative to storage and production) you'll also spend a lot of time either almost empty or full and either not have power to use or room to store power for the future respectively.

So, post your numbers/graphs. I'm feeling pretty good about ~26 days "coasting" without generator and ~33 days including generator use. 43 kWh storage, 5.75 kW PV, Avg ~7 kWh/day usage.

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Obviously, you can game this metric by limiting usage to match production so I bet some folks "coast" all winter... Kudos to you, tell us about it!

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Rocketman said:

I think everyone has the wrong idea about winter- if you are not getting enough sun in the winter to keep the battery full - go south - that’s what those big black tires on your MotorHome are for.

Winter in Arizona or Baja provides plenty of sun…

Oops - I think I missed the point.

In my MotorHome I don’t have a big enough battery 544ah - 12v - only eight of the big blue cells… and only 1400w.
I can have one bad solar day, but if there is another the generator gets it’s exercise.

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Mattb4 said:

It helps if you live where it is rare to have more than 1 or 2 really crappy days in a row. Partly lousy days can still develop some power if you have enough panels. Places like the West coast of Washington State that have only 1 or 2 days in a row of good weather is a whole 'nother ball game. I grew up in the PNW and we would travel across the mountains to Eastern Washington just to see the sun (or that strange yellow orb in the sky as I used to refer to it as a child).

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