[aprssig] TAPR Dayton Solar Talk

Bob Bruninga bruninga at usna.edu
Sun May 22 10:56:39 EDT 2011

The AMSAT/TAPR banquet talk at Dayton was about Solar and emergency power for Ham radio.  In preparation, here are three ideas that amazed me that might amaze you:

1) This week by googling solar panels, I found PRIME home solar (UL approved) 220 Watt panels going for $1.39 per watt! (compare that to $6/w contractor installed systems 2 years ago...)

2) Even if you want to use bargain panels and bargain micro-grid-tie inverters, one way, is to pay a contractor to install the smallest fully approved and electrical-permitted solar system you can buy.  This  gets you fully legal, connected, grid-tied etc.  Then add as many panels and additional plug-in micro-grid inverters at your own DIY cost!

Just remember, to connect + to + in parallel, and + to - in series... and just plug in the DIY microinverters to the wall outlet.  (Note, the UL approved microinverters should be connected to a standard 20 amp breaker in your breaker box by a master electrician).

3) Amazing angles!  No-longer does SOUTH matter!!!

I hope everyone here has had the fun of playing with the on-line PVWATTS for computing annual solar ouput over any conceivable arrangement of azimuth and elevation angles.  I just compared a pure EAST/WEST facing roof to the optimum South facing, just to see how bad it would be.   AMAZING!  Here is the PVWATTS page:

DRUM ROLL:  A DUE EAST facing roof (with a 20 degree tilt) will produce 85% of the annual power as the ideal tilted southern array.  Amazing...

BUT!!!  SO does the WEST side of the same house!  So, unlike the southern home that can only use HALF his roof for power*, the EAST/WEST facing homeowner can generate 170% more power than the sourthern facing owner because he has twice the room to put the panels!!!  (Roof size and shade are the #1 limits to homeowner 100% production of their annual electrical needs).

*But wait, there's more!  Next for grins, I used PVWATTS to tell the power output from the NORTH FACING side of the South Facing house.  Who would ever even think of doing this?  But if the ROOF tilt is the typical low profile 20 degrees, guess what?  The NORTH side of the roof can produce 60% (annual) of the south side!  So the homeowner with his low-profile southern roof maxed out with solar, can now increase his total annual output by 60% (with a double sized array (on a low tilt roof)). He produces nearly zero in the middle of winter from that side, but makes up the full 60% of his total capacity for that array in the summer!

Many hams who know that SOUTH IS BEST find it hard to accept this.  But do the PVWATTS calculations yourself.  Remember, the SUN comes up in the NE and sets in the NW during the summer when the days are 14 to 16 hours long.  This means that for the 3 hours in the morning and 3 hours in the evening, the IDEAL Southern array is not even seeing the sun.  Sure, an east facing array will produce little in the winter, but for GRID-TIE, the ONLY thing that matters is ANNUAL total power.  and all these other directions make up for their poor winter performance by making MORE power in the other months.

Even laying flat on the ground will produce 80% of the annual power (but be a maintenance issue... Any panel should be at at least 10 degrees to assure rain-cleaning).

Back to the EAST/WEST facing house... Doubling the array to get the added 160% may not have been cost effective in the past, but with DIY panels at $1/watt and DIY plug-in micro-grid inverters at about $0.30/W, it's so cheap to expand your array into less productive angles, why not!  DIY panels and added plug-in DIY microinverters can double the size of your "approved" array for probably 1/4 the original cost of your contractor installed system.

Putting panels on EVERYTHING until you get to 100% of your annual electrical load is the goal.  You can do it!  Look outside the "southern" box.  (But shade remains the #1 killer of even the greatest solar ambitions.  But as costs are so low, look again...)

Don't forget, the economics of homeowner solar is all due to GRID-TIE.  There is not a single battery in the system.  Off-grid battery systems can only deliver about 33% of annual energy for the same $ investment plus the added burden of lifetime maintanance.  GRID-TIE is the only way to go (if you are on the grid)... Please see:


Oh, and the BIGGEST FACTOR by far is the almost 50% Government Credits, Rebates and Grants that come right off the top of your installation costs.  I would bet these are going to be gone in a year or two (my state has already reduced theirs by 1/3rd), beacuse the cost of home-solar produced power is now LESS than utility power (with the 50% incentives) and so EVERYONE is jumping into solar.  With tight budgets at all governmnet levels, do not expect these incentives to last.

Next week, I'll post slides from the AMSAT/TAPR solar talk.

Oh, and please come join the SolarDIY at yahoogroups.com discussion group made up mostly of HAMS going solar.


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