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PV providing power for a small pc, with mains powered 12v backup

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yyrkoon:
Ah, forgot to touch on the 12v vs 24v issue,

Overall 24v is more efficient. Less line losses if going long distances. Cabling is/can be cheaper( less copper )

However, one caveat would be battery cost. Battery cost is one of if not the biggest cost in any RE system. It is also the only reoccurring costs if your equipment is well maintained, and good quality.  So, as an example. You halve your current requirement for total power output, So if you use 12v batteries there is really no added cost. But, if you use 6v batteries, you're going to need at minimum 2 just to reach your voltage requirement. 2V batteries ( which is what we use ) you would need 12 minimum. Our batteries cost $326 each . . . So cost of admission for just batteries alone would be approaching $4000. Versus $2000. So there can be some trade-offs, where good/bad is concerned.

I would recommend that you research all you can before diving into something like this. Price per kW as it stood a few years ago. You could never beat your local power company in cost moving to solar / wind ( here in the USA anyhow ). However, there can be a lot said about being completely liberated from your local power company. More than the satisfaction of being the only house in the neighborhood with lights on during a brown out ;)

[EDIT]

And once again . . .  apparently I missed the meaning of your post. Got it now, after reading all of the post in the thread here.

Why not run off the batteries continually for the computer you speak of. Have a voltage sense device watch for a certain voltage on the batteries, Where it could then kick on a charger powered by the mains until either a) you're getting enough solar power coming in, or b) the batteries have reached a decent SoC? I do not know of one off the shelf, but it would be very easy to implement. Could even be a fun project. Personally, I would have the mains kick on to charge the batteries before they hit 70% depth of charge. But do some research on lead acid batteries to see what I mean.

Again, lead acid batteries have electrolyte in them that needs mixing. Which short of picking them up and physically shaking them yourself. Is done by charging the batteries enough to a point where they start bubbling. This also helps keep the plates clean.


For your 6kW array, 24v is going to be better. If that turns out to be an option. 48v would be even better yet.

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