[VAC] Re: Solar panels mounting on roof

[Jim Dunmyer <jdunmyer@xxxxxxxxxxx>]

Sarah,
 You're correct about panels' orientation making a big difference in
output. My first solar "installation" can be seen on my Airstream pages,
the second on the Avion pages. The first was just a frame so I could set
the panel alongside the trailer and orient it however I wanted. After
getting it all connected, I hooked up an ammeter and experimented, just
to see the effects.

The panel definitely wants to be at right angles to the Sun. However,
there's not much power available early in the morning or late in the
afternoon, so you can point the panel to the South and be mostly OK. Of
course, there's also not as much power available in the Winter, so it's
hard to depend on solar at all. If you were trying to use your solar
system in Winter, you'd probably want to be able to tip the panels up
quite a bit from 'flat'.

Home-based solar systems nearly always include provisions for adjusting
the tilt angle during the changing seasons. Many include trackers to
wring out the last watt-hour available; trackers are usually cheaper
than just throwing more panels on the rack. Unfortunately, this isn't
real practical in an RV environment.

Now, for a real-life report:

Each of my panels, rated at 75 watts from the manufacturer, will give
right at 4 amps under optimum conditions: clean (very important!), cool,
and oriented towards the bright sun. The 2 of them, mounted as shown on
the Avion, will sometimes hit 6 amps when the sun is very bright, but 4
is much more common. So, I've lost nearly 50% of my theoretical output
by paying no attention to panel orientation. This is actually the norm
in the RV world, as it's not very practical to install panel aiming
devices and you can't always orient your rig in the optimum direction.
You make up for it by oversizing your array.

Remember also that there are other tradeoffs: The Silicon panels give
significantly more output than Amorphous on a per-square-foot basis.
However, Amorphous panels can be mounted on a flexible substrate and
aren't affected quite as much by partial shading or clouds. All of them
to my knowlege are negatively affected by heat, but mounting them right
down against the skin of the trailer for better looks might be an
acceptable tradeoff for Bob. There is NO 'right solution' for everyone,
and you really, really need to start with your NEEDS and work through
the storage (batteries), and only lastly to the source (panels). Doing
the opposite may well result in spending a lot of money and getting an
unsatisfactory result.

As we all know, hands-on experience is worth more than all the books/web
sites/whatever in the world. If someone is seriously interested in solar
power, I'd urge them to do a bit of study on several of the many web
sites, then BUY a panel. A 20-30 watt panel isn't too expensive, yet is
large enough to give usable amounts of power. You should already have a
DVM (digital volt meter), which has an ammeter function, so you can
connect the panel to your battery and have some fun. (please use a fuse
in one of your battery leads!!!!) If you want to get serious, yet save
some $$$, go to the Dayton Hamvention and find the guy who sells
'seconds', that's where my panels came from, and they were about half
the price of 'retail'. He's always buddied up with a fella who has
controllers, and they're also inexpensive.

                                         <<Jim>>