The Holey Story begins....

We were out in the boonies…far out in the boonies….and Paul was daydreaming

“I have a dream” gushed Paul “a dream of football”

“ooooookay” I responded, trying my best to sound supportive. Clearly we’d been spending too much time out here and Paul was going nuts…but I thought it safest to humor him at this point.

“No, no, no”, he answered excitedly (and with a bit of crazy eye in his expression, I thought). “You don’t understand”. “My dream is to watch 3 football games in one day while boondocking and using the internet without draining the batteries…and I think we can do it” he chirped, skipping happily around the RV

Paul putters around tilting panels out in the AZ desert

Several things fell into place in my noggin at once. The fact that it was football season (that would be American Football for my European friends -> where they carry the ball, believe it or not), the fact that Paul had been doing covert solar calculations for several days, and the fact that he’d been grumbling about needing more Amps. At least he wasn’t going crazy…in the normal sense I mean.

As a fellow geek I was immediately interested. Not in the football, mind you, but in the concept of the usage plan. Paul explained that he wanted to watch 3 football games in a day (so, TV/satellite on) plus have the internet on all day (because knowing me well, he knew I would need something to do), plus normal boondocking usage….all fully supported by our solar system…and with the least extra expense. Now, that was an interesting problem, from a geek point of view.

It's a question of Amps, my dear Watson...

In order to fully understand the scale of this dream I’m going to throw some numbers at you. Those of you of technical persuasion will no doubt be gripped with excited interest at this point. For the rest of you, go ahead and skip to the bottom-bottom line at the end, and spend the rest of your day blissfully math-free until tomorrow’s post.

In numbers terms Paul’s dream was about a management of Amps that needed to follow the universal and oft-quoted rule of “what goes in must come out”. In this case our generation (from solar) would have to match what was going out (to usage). Ideally we wanted to end the day with fully charged batteries too, but that was what we in the business call a “stretch goal”.

The Generation Model

Panel tilting is very exciting stuff!

Our system has 600Watts of Solar Power. Using solar flux models (see our post on panel tilting HERE and the model HERE), Paul calculated the approx. solar generation we would expect in January in the SW desert with 45-degree tilt of the panels.

Approx. solar  flux in SW in Jan at 45-degrees tilt = 5.95 kWhours/m2
Our measured solar surface (6 total panels) = 6 x 0.78 = 4.68 m2
So, total expected generation on a sunny day = 5.95 x 4.68 = 27.85 kWhours

Our panels/system are ~10% effecient (this is very typical of solar systems in general. Panels only really convert ~10% of incoming flux)
So actual generation = 2.785 kWhours = 2,785 Watt Hours
This translates into ~232 Amp Hours (divide the above by 12V)

Bottom Line = We expect to generate ~232 Amps Hours of solar energy from our panels on a good, sunny day. Lots and lots of assumptions in here, but it’s a decent, simple start.

The Usage Model

Here’s where we get into the really fun stuff. We calculated our potential usage model, and backed it up with measurements done at night with our Xantrex LinkLITE monitor (LOVE that thing).

(i) Our Inverter is a Magnum ME2012
(ii) For TV/satellite we have Direct TV, a satellite dish on our roof and a Sharp Aquos 32-inch LCD TV
(iii) For internet we use a Verizon modem, MBR1000 Router, Wilson RV Antenna and Wilson amplifier (see our full set-up HERE).
(iv) We have 2 computers which each run ~3 Amps
(v) This is a “fudge factor” which includes anything else we might want to do during the day (e.g. run lights, a bit of microwave, a few hours of furnace etc.)

Bottom Line = In this usage model we expect to use ~360 Amp Hours in a full day (24 hours)

The Bottom-Bottom Line

If you put it all together this is what you get

Total Solar Generation in one day = 232 Amp Hours
Total Usage in one day = 360 Amp Hours
Total Drain on the Batteries = 232-360 = -128 Amp Hours

In search of Amps....

Now, that’s the number we wanted to be zero, ideally, and clearly we were WELL over. We have 440 Amp Hours of AGM batteries (=220 usable amp hours if you don’t go below 50% discharge, which should always be your goal with deep-cycle batteries) so we can handle the load, but it’s not where the dream wanted us to be. Clearly this needed some creative geek-thought, especially if we didn’t want to pay out the wazoo to get it done.

Coming Next -> The Final Chapter. How we solved the elusive 128 Amp Hour Gap….

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21 Responses to The Holey Story Part I -> Dreaming Of Football In The Boonies

  1. Marty & Roz Hill says:

    Do I hear a generator running in the background (to supplement the solar)?

  2. Jeff says:

    I feel an new appliance going into that hole. I have an old 22″ CRT for football and was looking for something less glutonous. Replacement will require cabinet re-design so it got places on the wait-list.
    Happy Travels.

  3. Terry says:

    Hmm…you propped up the bicycle and connected it to a hand crank generator and peddled your a..er ah, buns off to generate power while watching the game! Right?

  4. I’m starting to think getting solar panels would be a bad thing… just what Keith needs – another thing to get his geek mind going. ;) Really though, it sounds cool & I can’t wait to read the results!

  5. Daryl says:

    We are really wanting to instal solar and all the accoutrements, not only to boondock, but also to replace some of our electrical when we are t our home base in Ontario. Will be reading all about your solar setup.

  6. Denise says:

    **** Eyes glazing over ****
    Oh how I wish I understood any of that !! I try – I really do – and I read and read and read – but my poor old brain will simply not accept the data that is being read. Oh well !!

  7. jil mohr says:

    Do I see a beer and a bar in your future:)

  8. Our quick answer would be get a generator. But that’s not geeky enuf! We’ll await your resolution.

  9. Bob says:

    Possibly one less football game?

  10. Don Rose says:

    Hi,

    You might save about 20 amp hours by going to an inverter with less overhead. Mine is 0.5 amps per hour.

    I don’t understand why the internet “costs” 2.5 amps per hour. My cradlepoint MBR1200 router only draws 4 watts.

    I’m sure interested in how you make up the shortfall in energy production. One possible way would be to use some sort of reflective material to “bounce” more sunlight onto the panels.

    • libertatemamo says:

      Hi Don,
      Regarding the internet cost. The reason ours is higher is that we include our amplifier and antenna in the set-up(as detailed in item (iii) above). This is our standard set-up in the boonies. The 2.5 Amps was actual measured usage (per our Xantrex LinkLITE) for the entire lot.
      Regarding your ideas…you’re definitely on a track that we considered :) All will be revealed soon!
      Nina

  11. Terry says:

    How about a fuel cell tied into the black tank. Power production proportional to bean consumtion.

    • libertatemamo says:

      Fabulous! If you could make that baby work you’d become an instant billionaire. Think of all that wasted black tank fuel out there!
      Nina

  12. [...] ask me). The second point being this was ALSO exactly what Paul envisioned last year when we wrote The Holey Story Part I -> Dreaming Of Football In The Boonies (and wherein the RV was caught lamenting ”Oh, where art thou [...]

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