Do you already have your panel(s)?
Here's a picture of a small 250 watt system I built for our greenhouse:
A schematic of a smallish off-grid system and link to the Homepower article:
https://www.homepower.com/articles/home ... it?v=printHomepower 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 ... 2efc65830dBeware 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 ... 2665942749Cheapo 12V charge controller with USB charging ports (working quite well):
http://www.ebay.com/itm/10-20-30A-USB-S ... 2319883770Get the 30 amp model.
Volt/amp meter: http://www.ebay.com/itm/New-100V-100A-D ... 43c5b7c26912 volt batteries (I used 4 in parallel):
http://www.ebay.com/itm/Razor-E100-E125 ... 5d503b5feeI 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. (24
DC, 27
DC), 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" 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.