Text 7957, 90 rader
Skriven 2005-03-24 07:12:25 av David Drummond (3:640/305)
   Kommentar till text 7895 av Michiel van der Vlist (2:280/5555)
Ärende: Solar energy
====================
Michiel van der Vlist -> David Drummond wrote:

 DD>> Although I've read of grid-connected systems, I've never seen
 DD>> one. This seems odd as there is so much solar energy falling on
 DD>> the ground in this neck of the woods.

 MvdV> Most of the solar systems here are connected to the grid. Same for wind
 MvdV> power.

 DD>> The building at my country estate is 100 metres or so from the
 DD>> road in the bush. Running mains would be a fairly expensive
 DD>> proposition - maybe more than the solar set-up cost me, and I
 DD>> would be subject to the vagrancies of the power company.

 MvdV> Over here the power companies are required to connect you for the
 MvdV> standard fee. No matter hoe far one is from the nearest line. I guess
 MvdV> that would make them go broke in Australia. ;-)

The "standard fee" only reaches 20 metres from the supply. That's where my tree
line starts. Eucalyptus trees are renowned for dropping, sometimes quite large,
branches for no apparent reason. This makes the life of strung of power lines
rather short. There is layer of rock just under the surface for 20 metres or so
too which would make the digging of a trench to the regulation depth
difficult/expensive.

If people live hundreds of metres into their properties, running the mains in
can be *very* expensive. Some of the sites I've visited in "the outback" rely
on diesel generators although solar power is making inroads.

 MvdV>>> What is the storage capacity of your battery?

 DD>> There seem to be many ways of measuring this - but I reckon its
 DD>> 450 amp hours at the 100a rate.

 MvdV> Ten times the capacity of my car battery. Hmmm.. that's a big one.

Over 120Kg.

 MvdV>>> What type of battery do you have?

 DD>> I have six x 2 volt deep discharge gel cells, specifically
 DD>> developed in Australia for Australian (warm) conditions. I chose
 DD>> gel cells due to the lower maintenance.

 MvdV> Gell cells are nice, but be aware that they are vulnarable for
 MvdV> overcharging. You have overcharge protection?

I have an "intelligent" regulator in the circuit, all power into, and out of
the battery is under its control. It is programmable (has a small processor of
some type in it) and has settings for the requirements of gel cells. It uses
PWM to regulate the charge current.

If it determines that the battery voltage has dropped too low (programmable) it
disconnects all loads.

 MvdV>>> I have an ordinary car battery in my caravan, but starter
 MvdV>>> batteries do not do very well in stationary applications. One
 MvdV>>> should actually use batteries designed for lower amps over
 MvdV>>> longer time. But those are two to three times more expensive
 MvdV>>> than car batteries with the same nomimal amp-hour rating...

 DD>> Yes, I know. A 40 amp hour car battery is $50ish here. My
 DD>> 450AHour cells cost about $1200.00

 MvdV> Wow... expensive too.

A little dearer than comparable wet cells. Although I usually visit once every
three weeks, it can sometimes be six weeks. I figured that a gel cell would
need the "topping up" that a wet cell would.

 MvdV>>> Matter of supply and demand I suppose.

 DD>> The car battery has a two year warranty, the deep discharge has
 DD>> a 15 year warranty.

 MvdV> If it actually lasts that long, it may not be a such a bad deal after
all.

The cells are guaranteed for that long, they should last longer.

The solar panels have a 20 (or was it 25) year guarantee.

-- 

regards

David

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