need help sizing solar panel..

 
Hello...
I want to run a pond pump in my backyard
as well as a couple of circuits of landscape 12 v lighting
(probably 60 watts each circuit)

The pond pump is 145 Watts AC
the landscaping lights are

The pump is to be run all day 24x7
and the lights only at night for about 5 hours

I plan on getting two 12 volt marine deep cycle batteries
to store the energy...

what do i need to buy in terms of solar panel (how many watts
should cover this scenario)

and do i need a converter or inverter for the AC pump

thanks in advance

turin
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  Jimmy Reza de la Turin wrote:

Pump 145W x 24 = 3480Wh/day

Lights 60W x 2 x 5h = 600Wh/day

Total daily load = 4080Wh

The thought crosses my mind that 18 - 80 Watt panels may just be a bit more than
you care to invest in.

I would suggest that you look at an automotive electric fuel pump and led lights
for your project.

Example: 13 - 18 led lamps draw 2.34 amps or 28 watts as apposed to your choice
at 120 watts (10A)

--
Posted via a free Usenet account from http://www.teranews.com

 On Tue, 10 Jul 2007 06:24:28 +0000 (UTC), turin@soda.csua.berkeley.edu
(Jimmy Reza de la Turin) wrote:


Let's see. The maths isn't too hard (except for quite a few
unknowns!).
But anyway, that aside for a moment

145 watts for 24hr is  3480 watt-hr. Add about another 600 watt-hr for
the lights and you have over 4kwh per day.
Now we know nothing about where you live/ whether it matters if the
pump and lights stop working when there hasn't been enough sun or
whether you have backup power available.
And does the pump actually use 145 watts all the time it is working?
(It may depend on the head to which you are pumping).

In most temperate climates with "average" sun - you will probably need
to generate the 4 kwh in about 4 hours (average) of each day - though
it will vary according to time of the year and other factors..
But let's say a 1kw array is unlikely to be big enough. And the
battery will probably need to be no less than 8kwh storage to be of
any use. Deep cycle marine batteries might store about 1kwh each, so 8
might be a minimum. Even then, the excessive deep discharges will
likely shorten the life of the battery.

Yes, you would need an inverter for that pump, and it might need a
good surge capability to start it, so it will be big enough to be
significantly lossy, unless you spend a lot of money for an expensive
one.

All of the above is NOT an indication of the design size (we would
need more information to begin with).
Its just to indicate that you are looking at a very large system for a
"pleasure" project (many people would consider the above more like a
small off-grid house system).

If you already have grid power available - it would be a far better
option.
If you DON"T have grid power, and still want to doing something like
you describe- you would need to go back and look at a much lower-power
pump - probably 12v, and efficient lights.

(Personally I wouldn't even consider running 4kwh per day for such a
project - not even from the grid. I think there are better ways of
doing something similar that use much less power)


Eric Sears

 On Tue, 10 Jul 2007 06:24:28 +0000 (UTC), turin@soda.csua.berkeley.edu
(Jimmy Reza de la Turin) wrote:


You omit some of the specifics needed to make the calculations.

However, I note from a subsequent post that you are in the SF Bay Area.

To size a standalone system that will work year-round, you need to consider
the "effective sun hours" or solar insolation during your worst month.  For
that area, the value is 4 hrs/day.  Part of that is due to shorter winter
days, but you must also consider that the sun is not directly overhead all
day long.

I am also going to assume that your landscaping lights are DC.

First -- energy requirements.

Lights
    60W x 2 circuits * 5 hrs/day = 600 watt-hours/day DC Load

Pump
    145W x 24hrs = 3480 watt-hours per day
Factor for inverter inefficiency (you will need one for the Pump) 0.85

Total AC Load = 4094.12 watt-hours/day

Total Load = 4094.12 + 600 = 4694.12 Wh/day

Let's assume that you will set up a 12V system (although I would probably
set up a 24V system for this capacity -- but you mentioned two (2) marine
batteries). One reason to use a higher voltage system would be to be able
to use smaller wires for the run between the panels/batteries/inverter.
But your power consumption will be about the same.

Total Load in Ampere-hours/day = 391.18Ah

Factor for system losses (battery charge/discharge) and inefficiencies =
20%

Adjusted load = 489.41 Ah/day

Worst month solar insolation = 4 hrs/day

Required array current = 117.35 A

Kyocera makes a 12V 130W panel that puts out 7.39A.  You would need 16 of
these to produce your required output (about $9,500 - $10,000 just for
panels).

Battery capacity will depend on how long you want the system to be able to
run if the amount of sun is inadequate.  If you purchase very high quality
batteries, that can tolerate an 80% depth of discharge, you could figure
about 6.6kWh/day of reserve (549Ah).  If your batteries will only tolerate
a 50% DOD, then figure 10.55kWh (879Ah) per day of reserve.

For whole house systems off-grid, 5 days of reserve is common.  But you may
choose fewer or more, depending on your requirements.

By the way, the reason my numbers are higher than others is related to my
including inefficiencies and losses in the system, inverter, and battery
charging.  That would have to be done if you were going to go ahead with
this.

In addition to panels, you would need to purchase mounts, wiring, a
controller to optimally charge the battery and an inverter.  Depending on
how much of that you did yourself, and how much was contracted out, and how
much battery capacity you want, the total bill could easily be $15-$20,000.

If the system is grid-tied, it could be smaller, and you might qualify for
a state rebate.

Perhaps you could find a more efficient pump and/or lighting system?
--ron