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300W Micro-PV for fun - any advice?

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300W Micro-PV for fun - any advice?

Unread postby Zarquon » Thu 02 Feb 2017, 12:29:50

Last year I've begun reading about photovoltaics; out of interest, not any particular use in mind. Just the basics first - photons, wavelengths, absorption curves etc. Today there are some amazing online resources for beginners, going as much into the details as you like. I haven't finished my PV 101 studies yet, especially the part about electrical installations, but I'm thinking about building a mini-PV on my balcony this year, whenever I find the time.

A few hundred Wp, cheap, just to experiment with it and learn a few practical skills. I'll find some tools to calculate potential yield, build the thing, collect some data and see where I end up. I'd need only a way to feed a laptop computer and perhaps a few LEDs with it.
(Disclaimer: I don't intend to save Mother Earth, I don't intend to feed the grid, and I know that it won't pay for itself in a hundred years.)

I know that some of you here have experience with their own PV setups. Can you share some advice on where to start, common newbie mistakes, useful planning tools, how to hook up a system to my computer to collect data etc.?
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Re: 300W Micro-PV for fun - any advice?

Unread postby KaiserJeep » Thu 02 Feb 2017, 13:06:15

Here's an example of some kits on eBay: http://www.ebay.com/bhp/home-solar-panel-kit

That's everything you need for the panels, the DC charger (12v) and/or the AC inverter, depending on which way you want to go. These kits assume you already have the battery, as they are add-ons for boats and such. An inexpensive deep cycle marine battery is about another $90 to $150 at a local auto parts store, depending upon size.

For monitoring the performance you can get an inexpensive Raspberry Pi cloud data logger with the sensors you need for voltages, currents, temperatures, etc. Start here: http://docs.fluentd.org/v0.12/articles/raspberrypi-cloud-data-logger

The data acquisition part will be more expensive and complex than the Solar PV. You will have to have a Raspberry Pi nanocomputer ($29), some flavor of Debian Linux (free) and some voltage/current/temperature sensors (?). Off-the-shelf data loggers could be used, but cost hundreds or thousands of dollars.

Edit: As with anything purchased on the Internet, let the buyer beware. Another source which would let you pick it up would be Home Depot: http://www.homedepot.com/b/Electrical-Alternative-Energy-Solutions-Solar-Panel-Kits/N-5yc1vZcdro
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Warning: Messages timestamped before April 1, 2016, 06:00 PST were posted by the unmodified human KaiserJeep 1.0
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Re: 300W Micro-PV for fun - any advice?

Unread postby GHung » Thu 02 Feb 2017, 14:17:52

Do you already have your panel(s)?

Here's a picture of a small 250 watt system I built for our greenhouse:

Image


A schematic of a smallish off-grid system and link to the Homepower article:

Image
https://www.homepower.com/articles/home ... it?v=print

Homepower magazine is a goldmine for learning PV and other alt energy systems. Look for their older articles on DIY PV systems.

A small PV system consists of:
=>PV panel
=> fuse or breaker (PV disconnect)
=> charge controller (controls volts/amps to battery)
=> battery (another fuse or breaker is recommended between charge controller and battery)
=> loads (inverter, DC loads, etc.).

For a 300 watt system (what voltage?) you may want an MPPT controller ($$). I use Outbacks for the house system, but have tried one of these cheapos with success on smaller systems:
http://www.ebay.com/itm/20A-MPPT-PV-Sol ... 2efc65830d

Beware that many cheaper so-called MPPT controllers aren't really MPPT controllers. If you are using a higher voltage panel (24+ volts) to charge a 12 volt system, you must use an MPPT controller (reduces higher voltage to ~12 volts) PWM controllers must be used with a panel that matches the battery voltage. 12 volt panels usually put out around 17 volts (open circuit) which a PWM controller will do fine with.

I recently built a small system for charging devices out of some parts I had laying around. Here are some links to various parts I used, mostly from Ebay:

30 watt PV panel: http://www.ebay.com/itm/30W-30-Watt-Sol ... 2665942749

Cheapo 12V charge controller with USB charging ports (working quite well):
http://www.ebay.com/itm/10-20-30A-USB-S ... 2319883770
Get the 30 amp model.

Volt/amp meter: http://www.ebay.com/itm/New-100V-100A-D ... 43c5b7c269

12 volt batteries (I used 4 in parallel):
http://www.ebay.com/itm/Razor-E100-E125 ... 5d503b5fee

I used standard automotive fuses and fuse holders. Oversize your wiring (I used 10 gauge) for efficiency.

Shop around ebay for parts from the US, but I've had good luck ordering cheap stuff from China as well. Takes a couple of weeks, but saves a few dollars. You can also use a regular deep cycle (RV/boat) battery from Walmart, etc. (24DC, 27DC), but the little AGM scooter batteries last longer for small systems in my experience. I built an essentially identical system for a long-range wifi repeater which has been working flawlessly for almost 3 years. I run the wifi repeater directly off of the charge controller's USB port.

You can buy one of those pre-packaged systems for about the same cost, but they don't include batteries or meter. Besides, where's the fun in that?

Note: If you add a small inverter remember that a 120 volt inverter pulls 10 times the amps from a 12 volt system (120/12=10), so a 300 watt inverter at full output is sucking 25 amps+ from your batteries. Best to keep things DC if possible. Always remember that watts= volts x amps (Watt's law)!

As for monitoring performance, many charge contollers with digital display will tell you what you need to know, including accumulated kWhs, amps, voltage. Another not-too-expensive meter is the "Tri-metric" from Bogart Engineering, or the upgraded "Pentametric" which can log to a PC:

http://www.bogartengineering.com/products/trimetrics/

https://www.altestore.com/store/meters- ... or-p11865/

There are also cheap Chinese knock-offs, but I haven't tested them. I have two Tri-metrics working well after 18+ years. About $150 per. The Pentametric with input unit and PC interface, about $260. Shunts are an additional ~$25. The Pentametric can also have a display console. It can monitor multiple points in your system (PV output, battery in/out/totals, inverter draw/cumulative usage, etc.)

I monitor and log our household system using Outback's data "Hub" and software from RightHandEngineering. I have years of data; handy when the naysayers come around to insist; "this shit doesn't work" :lol:

Another good source for deeply discounted panels (also have "Grade B & Grade C" panels really cheap; fine for the hobbyist) is Sun Electronics. It's a wholesaler in Miami:
http://www.sunelec.com They frequently have discounted inverters and batteries as well. They're moving to a new warehouse, so their site may be a bit quirky right now.
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Re: 300W Micro-PV for fun - any advice?

Unread postby GHung » Thu 02 Feb 2017, 19:32:46

baha wrote:There are two types of inverters, pure sine wave inverters and the cheap ones. My hobby system has a 350 watt and a 750 watt cheap inverter from Wal-Mart. They work fine for lights or motors (like a freezer compressor) but they will burn up the power supply in a PC or TV in no time. If you want to power electronics you will have to spend real money.


Sort of..... Many inverters have been built that are "quasi-sine wave" inverters. Our first big inverters were (are) Trace SW4024s that aren't pure sine wave; they have a 54(?) step wave that 'mimics' a true sine wave and have performed well; one going into its 18th year of constant operation. We've had few issues that could possibly be related to their wave pattern. That said, most of our possibly sensitive loads have been on an Outback inverter for about 10 years that is a true sine wave inverter. No point in risking my vintage hifi equipment on a non-sine wave inverter 8O

I agree that you get what you pay for. We've budgeted to replace our old Trace inverters with Outbacks in the next few years.
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