Re: Sourcing energy storage capacitors in the UK
From: Ian Stirling (root_at_mauve.demon.co.uk)
Date: 06/09/04
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Date: 09 Jun 2004 13:06:42 GMT
John Beardmore <wookie@wookie.demon.co.uk> wrote:
> In message <40c522f4$0$551$ed2619ec@ptn-nntp-reader02.plus.net>, Ian
> Stirling <root@mauve.demon.co.uk> writes
>>John Beardmore <wookie@wookie.demon.co.uk> wrote:
>>> In message <40c4e1e5$0$551$ed2619ec@ptn-nntp-reader02.plus.net>, Ian
>>> Stirling <root@mauve.demon.co.uk> writes
>>>>John Beardmore <wookie@wookie.demon.co.uk> wrote:
>>>>> In message <10c9adjsalv87ab@corp.supernews.com>, Tim Wescott
>>>>> <tim@wescottnospamdesign.com> writes
>>>>>>John Beardmore wrote:
>
<Snip>
>>20 tons a day, let's say it's running for 5 hours, so that's
>>4 tons an hour, or about a liter a second. (this implies fairly good
>>insolation and a fixed panel, or a slightly less good panel with a tracker.
>>
>>Ok...
>>You later say the head is 4m, so that's 40W of 100% efficiant pump.
>>160W would probably be a reasonable worst-case guesstimate for the 'right'
>>AC centrifugal pump.
>
> Yes. Provisionally I'm assuming perhaps 320W of PV, a 357W single phase
> 250V pump and a 500W sine wave inverter.
<snip>
>>You have looked at the various solar FAQs, and got the information for
>>your location as to expected solar gain?
>
> Didn't know there were any FAQs on this in general. Then again, it's
> been a long time since I looked, and usually I'm writing them not
> reading them.
alt.solar.photovoltaic.
There are sites where you can look up the location, and it'll give
you the optimal tilt, and average power output for the correctly tilted
panel, and average power for a tracker, taking into account weather
conditions.
<snip>
>>I'd want to keep the battery over 75% charge, so you want to size the
>>battery so that a really bright day can charge it up to 100%, and then
>>it'll keep going a bit during the night until the voltage drops below
>>a threshold
>
> This is OK up to a point, but our assumption is that batteries will
> start to sulphate when discharged by as little as 10%.
The idea is to be able to use all the energy the solar panel provides,
and one way of ensuring this is to (probably better to discharge just
before the morning) discharge enought that you can store the excess
that may build up over an especially good day.
>
> We thus aim to charge up to 100%, then discharge to 90%.
>
> 100% charge can be determined by terminal voltage under charge, and 90%
> discharge assumed after running a known load for a know time, though
> perhaps with a low voltage cut off just in case.
Batteries do have a temperature coefficiant, which you probably need
to look at if you haven't already, it alters the set-points a bit.
>
> I'm assuming we can always use more energy that we generate.
Hmm, I see where you'r going.
This would need a significantly smaller battery, but has the problem that
a significant proportion of your energy is going to go into and out of
the battery, incurring losses (some 30-40% IIRC) along the way.
You'r also going to be charging and discharging the battery quite hard,
something which is not good for life.
>
> This way, the battery will only have to hold its charge for a few
> minutes, and will never be left over night at less than 90% charge.
>
>
>> (lead-acid will have best cycle life if kept partially charged,
>>75% may be conservative.)
>
> As I understand it, % discharge without sulphation is a bit of marketing
> issue. 10% seems to be accepted in the academic community, do for
> example you can safely take 10AH out of a 100AH battery.
>
> Sometimes however, a say 200AH battery might get marketed as 100AH, but
> able to accept 20% discharge without sulphation.
>> (read the sci.chem.battery.electrochem FAQ)
>
> Thanks ! Didn't know there was one !
Probably an idea to ask about charge philosophies there too.
<snip><
> Yes, though the far that we'll be up a 15 meter mast with an existing
> yaw bearing makes it more appealing than it might be !
Is this mast partially underwater, or is the pump at the base?
>
>
>>Yes it might allow you to shave a few hundred dollars off the solar panel
>>price, but it's not going to be free.
>
> No, though it could be as simple as
<snip>
It could be, but can you ensure that it can take several thousand cycles
when exposed to wind/rain/...
>>You probably want a peak-power tracker with battery charger,
>
> Yes. (Assuming you mean an 'optimal power point tracking (OPT)
> regulator' ?)
>
I do.
>
>> something
>>to cut out the pump when the battery voltage gets too low
<snip>
> Possibly, and many inverters will shut down if the input voltage is too
> low.
You certainly don't want to take the battery down to the non-changable
cut-off points of many inverters. (10.6V is common)
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