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Old 11-10-10, 04:06 PM   #1
bennelson
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Default Incremental PV Solar Setup

Hey Folks,

I would really like to get more serious about solar, but still have plenty to learn. I want to stay as DIY and affordable as I can.

I also have some other limiting factors, such as -

1) I'm OK with spending a fair amount of money on solar, but not all at once.
2) I have only OK, not great solar access.
3) I own my own home, but might move in a couple of years.

So, what I am interested in doing is slowly building a PV system, but how do I do that in such a way that I don't have to replace one part with another more expensive part down the line?

How do I incrementally increase the size of the system?

From what I know of PV so far, I get that the inverter is often the limiter to system size, SO it seems like you need to size that to the biggest that you think the system will ever get to. BUT, what if I never put up that many panels? Just wasted a bunch of money then!

I already have a number of (used) deep cycle gel and AGM batteries from my electric car projects, so it would be nice to use those as a battery backup system. I also already have a 48V computer UPS. Basically, it's a 2000 watt inverter, with very clean AC waveform.

So, I already have half what I need for a battery backup system. However, it's not good enough for running my whole house off of in general use (essentially take my house off-grid)

I think a grid-tie system would be great, in that it simply reduces how much power I would have to pay for from the electric company every month.

A homebrew solar system that would charge my batteries, and then kick over to power a grid-tie system would be pretty slick. On the other hand, the UPS already has a battery charger built into it. I could charge those batteries from the grid while the sun is charging (and the solar panels are making power) and then use them whenever I want later (such as in a blackout)

Some of those basic Chinese grid tie inverters are very inexpensive.

But back to the incremental part. Let's say I wanted to buy a $500 solar panel for X-mas every year. I want to be able to expand the system as I go. What's the best way to do it?

I have heard good things about the Enphase microinverters. Basically, you put one each on every PV panel. Very simple, expandable. Saves some costs (you get rid of combiner boxes and DC disconnects.) Microinverters are also supposed to be better for shading issues as well.

They aren't real cheap, about $2 per watt. But that probably figures out to not much different than just one big inverter.

I was also thinking that instead of buying used, discount, or closeout PV panels, that it would be best to pick a popular brand and a model of panel that should be around for a while. That way, I could get a panel at a time, and know that I could get more in the future.

I am hoping to rebuild my garage this next summer. If that happens, the plan is to "rotate" the roof 90 degrees so that it faces south. I would like to do a standing seam metal roof (as they are recyclable, unlike traditional shingles) and standing seam has some nice attachment systems for PV panels.

With the metal roof, it should be possible to add one panel at a time with minimal problems.

So, anyways, I am trying to keep it affordable, but expand the system as I can afford too.

Your thoughts?

-Ben

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Old 11-10-10, 04:26 PM   #2
Daox
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Couldn't you break out a circuit or two and run that only off of solar? Say, wire the fridge to run off of the solar battery bank?

I'd definitely go with the micro inverter route if you want to build as you go.

Don't you have some 48V panels too?
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Old 11-10-10, 05:31 PM   #3
bennelson
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I HAD several 48V solar panels.
The neat thing about that was that I could wire one directly up to the 48V battery pack (through a charge controller.)

I actually ended up selling BACK the panels to the guy I bought them from (for exactly what I paid for them originally.) It was sort of a closeout/pallet deal. He was working on a big solar installation using the exact same panels, and they were short the same number of panels that I happened to have!

Anyways, I got to help out as a volunteer on that PV install. Here's a photo.

That's only one of the TWO banks of panels they had. It was well over 100 panel total.

Anyways, the downside of those panels is that they are VERY bulky for their rated wattage. With my limited solar space, mono or poly panels would be better.

I like the Evergreen panels. They are US-based (I'm not sure where the manufacturing is though!) and they use a different process that more or less makes a polycrystaline panel, but with much less embodied energy.

I have no idea how I would make just one or two dedicated circuits in my house.

The PV would be mounted on the (detached) garage.
I don't have much space around my circuit breaker in the house. It isn't in a basement or anything. It's right in the kitchen between the wall and the door. Not enough room to put in an automatic transfer switch or anything.

To do a dedicated circuit, the easiest thing to do would be to just take my entire garage off-grid, which I sort have been playing with, but haven't had enough PV to make that work of any great amount of time.

If I got four 12V panels right away, it would be easy to wire them in series for 48V to charge the battery pack. I possibly could locate an inexpensive 48V grid tie inverter (ebay, china made, etc.)

Four 12V panels would maximize flexibility, as they could be seriesed or paralleled for 12, 24, or 48V systems.

The trouble with those 48V panels that I had was that they couldn't be used with ANYTHING 12V.
The other think I found out is that solar panels have fancy, dedicated power connections on them. They are named MC3 and MC4. Buying cables that go from the solar panels to a charge controller or anything else get expensive real quick.

All the solar panels have "male" and "female" connectors on them. To set them up in series, you just plug one panel into the next. That's it. Then get the fancy cable just to connect the two far ends to the rest of the system.

With the 48V panels, I had to get a pair of fancy cables for EVERY panel I wanted to hook up.

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