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Newbie looking for some info

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Posted by Jack Pagel on February 14, 2011, 6:43 am
I have been looking at the solar cells and panels for years, but that
was as far as I went with it so far. But I am considering to install a
small system for my hobby room. How can I estimate how large of panels
and batteries I would need? Most of the appliances would be low current
draw such as the receivers and lights, but there are high current
transceivers (amateur radio) that draw up to 20 amps with full output.

Posted by you on February 14, 2011, 9:48 pm

You would be better off asking on a Ham Radio forum than here as there
are specific to that arena, rather than generic like we talk about

Posted by Martin Riddle on February 15, 2011, 1:06 am

Some starting points..

PVwatts <http://www.nrel.gov/rredc/pvwatts/version2.html>
Homer <http://www.homerenergy.com/>
Homepower <http://homepower.com/webextras/>
      Load sizing <http://homepower.com/files/webextras/loadcalc.pdf>

Steve's Site

And some outdated work before NEC implemented the codes, but still
Wiles Code corner Articles
Or here

Most of these are for AC loads, but you can correlate them to DC loads
as well.
I had a simplified spread sheet but can't find it at the moment.

Hope that helps.


Posted by Randy on February 15, 2011, 4:22 am

I can't resist!
You need Four evergreen 200 watt panels for total 800 watts
Wire them in parallel using a pv combiner box with breakers.
Run a lets say set of 8 gauge wires to a Morningstar MPPT 45 amp Charge
controller, from there to a pair of L-16 batteries in series for twelve
Hook up an Outback VFX2812 (with a fw250 beaker box on each end to make it
easy and safe) and a mate to make the adjustments needed for your operation
and the output to a wall outlet from the fw ac beaker(s) following outback's
good instruction manuals.
This is rather simplified as you will find many other components needed
(such as which breakers) as you search.
Feel free to make any changes as this is my little stab at it.
Remember, Safety first and it is good to have a licensed electrician around.
Also beware of the code and inspector fiends, they may be friend or foe.
I don't work for these guys, but they are sure nice to me:
However there are a few other guys out there who are awesome as well.
Take care and Enjoy!

Posted by Ron Rosenfeld on February 15, 2011, 1:21 pm

This is very generic, and lacking considerable detail, but should provide an
outline of how to approach for an off-grid system.   See some of the URL's
provided by others for more detail.

First, determine amount of electricity to be generated:
1.  Determine exactly how much electricity your components consume per day/week
and whether there are any seasonal differences (i.e. using it more in winter vs
summer).  Do actual measurements (there are inexpensive meters available for
2.  Determine what percentage of your daily use you want to supply using PV.
3.  If you will be using AC for all or part of your needs, factor in inverter
inefficiency (e.g. if inverter is 85% efficient at the point where it will be
running most of the time, divide your daily use by 0.85)
4.  Losses in battery storage will add another 20% or so to electricity
generating requirements, so multiply the above by 1.2 (or whatever you figure).

How many panels:
1. Insolation, or "effective sun hours per day"  (ESH) can be obtained for most
places from web resources.
2. Determine "worst month".  If there are no seasonal use differences, this will
probably be December if you are in the northern hemisphere (month with the
lowest ESH).
3. Divide electricity requirements by ESH to obtain panels you need in watts.
You'll eventually convert this to amps once you decide on a system voltage.

Battery considerations:
1.  How critical is the application?
2.  How long might you go without sun?
3.  How deeply can you safely discharge the batteries you will be purchasing?
4.  For mid-latitudes, and a non-critical application (or one with a non-PV
backup, like a fossil-fuel generator), 5 days of storage is often sufficient.
So, if your daily requirement is 1kWh, then you need 5kWh storage; if you can
safely discharge your batteries to 50%, then you'll need 10kWh of battery

On the other hand, if you are grid-connected, then you can consider the "grid"
as your battery storage; you can eliminate the 20% factor for battery losses,
and your battery sizing consideration will be merely that required to provide
power for the longest power outage you wish to account for.

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