A step toward completely off grid! - Page 2 - Fuel Economy, Hypermiling, EcoModding News and Forum

thingstodo · 05-20-2013, 01:11 PM

Quote:

Originally Posted by MPaulHolmes

All you do (during the bulk charging phase) is adjust the PWM duty to maximize the output current! You don't need to maximize the product of the input current and input voltage (input power)! Just the output current!

I'm not quite following ... do you have a fixed output voltage, and that's why the output current is the only thing that you need to maximize?

MPaulHolmes · 05-20-2013, 01:39 PM

DISCLAIMER: This made sense to me last night, after being in the sun all day, so I could be wrong. haha:

Yes, since it's feeding a 48v battery bank, the voltage is approximately constant. Well, higher current into the batteries causes the battery bank voltage to go up slightly because of the internal resistance. Am I thinking about this wrong?

thingstodo · 05-20-2013, 01:50 PM

Quote:

Originally Posted by MPaulHolmes

DISCLAIMER: This made sense to me last night, after being in the sun all day, so I could be wrong. haha:

Yes, since it's feeding a 48v battery bank, the voltage is approximately constant. Well, higher current into the batteries causes the battery bank voltage to go up slightly because of the internal resistance. Am I thinking about this wrong?

I guess charging a battery bank is close enough to constant output voltage. It will be a narrow range of output voltage ...

So maximizing output current ... will maximize the input V * I for the buck converter ... that follows!

I don't know how you have the PV arrays wired. Do you need a buck/boost circuit for cloudy days ... wait ... you said Arizona. Never mind!

MPaulHolmes · 05-21-2013, 01:21 AM

My wife had made the pictures set to private. dang it. But she has some pictures of her nursing on there too, lol, so I guess I understand. Here's one picture anyway:

I was up at 3:40am, and worked until around 8pm. And it was like 95 degrees outside today. But it's getting close to done:

Two 3/8" x 3" lag bolts to connect the "superstrut" from home depot to the 4x4:

NachtRitter · 05-21-2013, 01:47 AM

Quote:

Originally Posted by MPaulHolmes

I was up at 3:40am, and worked until around 8pm. And it was like 95 degrees outside today. But it's getting close to done:

Still rather cool there, eh? Don't you have another 20 - 30 degrees to go?

MPaulHolmes · 05-21-2013, 02:00 AM

hahaha. Yes. We moved here in December, and I was dying from the heat by the time February hit. It just keeps getting hotter!! And it's MAY!

elhigh · 05-21-2013, 10:12 AM

I was thinking that if you're up to it - and you certainly appear to be - you could mitigate a lot of the heat load your house experiences by shading the house with the solar panels.

That would sharply reduce how much air conditioning you need. Sure, you give up a lot of power generation by foregoing tracking, but I think you get it back in reduced weathering on your roof, reduced cooling load, etc.

redpoint5 · 05-21-2013, 10:02 PM

I would think the clay tiles would reject more solar heat than the PV panels since they are lighter in color and do not conduct heat as well, but I'm no expert on the subject. I'd use landscaping to provide shade on the house, as it appears there is none at the moment.

Tracking is absolutely crucial to getting the most performance per M^2 out of a PV array. However, the pictures of the rack don't suggest a method of adjusting the vertical tilt seasonally, and they certainly don't pan east to west.

Still, I'm sure the setup is more efficient than if I were to install the same M^2 PV on a tilt and pan tracker in the Pacific NW. It seems insane to me that people install PV up here, when there would be a better return by installing it in AZ. Essentially leasing out the PV system to those that can better take advantage of it.

MPaulHolmes · 05-22-2013, 02:17 AM

A solar tracker would be much better. It's actually really simple. You can have a photo diode that only has a small slit for light, and each time it gets dark, a motor turns on until the peephole gets sunlight again. One hard thing was making the mounting strong. We get CRAZY winds around here. My neighbor used to have 21 chickens, and after the monsoon season in July/August, he only had 1 chicken left. haha. So, I was just afraid it would break if I tried to get tricky on the first draft.

(My son wanted to click the face with the tongue sticking out)

MPaulHolmes · 05-23-2013, 08:43 PM

OK I went with photobucket. I think they'll show up now...

I just used some square washers that are 1/4" thick to squash each panel down at 4 different points. I should get a picture of that part.

There were about 15-20 mph winds today and there's not even a hint of wobble. I think they will be fine in really really fast winds, at least I hope.