On 30/04/2019 11:34, Tim Lamb wrote:
In message , John
Rumm writes
On 30/04/2019 08:15, wrote:

How realistic are the manufacturers claims for energy produced by
their solar pv panels. If they claim 2kw howlikel is this to be
true/realistic ?

Its likely to be a true reflection of the maximum power delivery of
the panel when in full midday sun in the summer.

In peak summer you might get a load factor as hight as 20% in the uk.
In the winter it will be down in low single digits. Averaged across
the year its usually estimated to around the range of 10% - 12%. Also
peak delivery never aligns with peak demand.

Hmm.. My grazing tenant is considering solar PV panels for an unattended
cattle watering set up.
12V bilge pumps seem readily available and adequate for the head and
flow required. Lead acid battery not a problem but...

how much panel do you need for Hertfordshire sunshine May to October?
Hot weather conveniently requires more water which, last summer, was
around 600litres/day at a head of around 5m.

OK this is entirely guesswork, so make what you want of it...

If we work it out from the work required for that lift of water... So
Force x Distance = 600 x 9.8 x 5 = ~ 30kJ of energy.

Now that ignores the losses associated with the motor, pump, and battery
cycling etc. So let's make a few wild stabs... say 60% for the motor,
80% for the battery charge cycle. Pump efficiency is harder to call -
could be 50 to 70% for a smaller one. Lets go with 60%.

so we could do 30,000 / ( 0.6 x 0.8 x 0.6 ) = ~105kJ Energy input
required from the panels.

Let's say a typical roof top sized panel can give approx 250W peak.
That's perhaps 1.2 kWh per day in summer (20% load factor). 1.2kWh in J
is 4.3 MJ. In winter is could be 0.18 kWh (3% load factor) or ~650kJ.

That sounds like it ought to be plenty, although the variation from
cloud cover can be significant - so some days you may only get a tenth
of that - so you would still be relying on the battery to provide
potentially several days worth of support worst case in the winter. (and
if you have snow cover, then all bets are off!)




--
Cheers,

John.

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