Wednesday, July 12, 2017

Doing some research on photovoltaic systems

So, I have a degree in physics and some experience with electronics, but when I set up my solar power system (photovoltaic system) I payed more attention to the amount of money I had to spend and getting the best options available in my price range than setting things up for maximum efficiency.

In retrospect it would have been a lot better to do a little more research and spend a little more money.

If you are new to solar power I'd recommend watching the Tin Hat Ranch off Grid Solar Videos on youtube. They are great videos for explaining all the basics and how to set up a simple and inexpensive, but effective system.

This guy's setup is pretty good, but I wonder if that's a 10 amp DC breaker he used in the electrical box between the panels and the charger. It looks kind of like an AC breaker and it seems like that could cause some issues.

Also, there's some misinformation here about batteries. He says that they are too expensive and hazardous to ship, but you can easily find good batteries on Amazon and eBay.

Also, I would avoid flooded lead acid batteries and go with sealed AGM deep cycle batteries. They are safe to store inside a home in a battery box, they don't need to be vented and are superior in virtually every way in how they charge and discharge. They are a little more expensive but well worth the price difference.

I use three of these batteries in parallel. I've read that a parallel configuration isn't optimal and it is better to have them in series configurations for efficiency and increased battery life, but on a budget a parallel configuration of 100amp hour batteries seems to be the most cost effective solution. It's extremely important to use very high gauge wire and make sure each wire connecting the batteries together is the exact same length. I ended up going with this 2 gauge welding wire and crimping battery connectors onto it: 
12V 100AH BATTERY FOR SOLAR WIND DEEP CYCLE VRLA 12V 24V 48V - Mighty Max Battery brand product

Ideally I should have bought 4 100ah batteries, but I didn't only because I'm dirt poor.

Also, in the beginning I just went with the crappy PWM solar charge controller that comes with the Renogy 400Watt kit, but I'm upgrading to an MPPT controller and switching my panels into series configuration instead of parallel.

I would strongly encourage you to use an MPPT charge controller of a PWM charge controller for the following reasons:

PWM controllers often only charge the batteries when the optimal amount of sunlight is hitting the panels. If too much light is on the panels they either don't charge the batteries at all or clip the voltage at just above 17 or so volts so they are only using part of the available power from the panels. Also, if it is too cloudy and the panel voltage drops below somewhere around 14ish volts (which happens very frequently) then no matter how many panels you have the charge controller does absolutely nothing.

With an MPPT controller you can wire the panels in series not only avoiding the need for those annoying and expensive parallel couplers, but you're also drastically increasing the efficiency in many ways.  A series circuit increases the voltage and decreases the current traveling through the wire which drastically decreases the power loss over the wire. It also makes it way safer to transmit power because the wires don't give off as much heat.

The biggest benefit I can see to an MPPT controller is it can take input voltages from around 14 to 150 volts (depending on the controller) and use that to charge your battery bank. This means that if you wire 4 100 watt 12 volt panels (which actually produce more like 18 volts on sunny days) and wire them in series then even on very cloudy days your batteries will charge and this is why: Even if each panel is only producing 9 volts because it's cloudy 9v x 4 = 36v which is still way above the 14 volts required to charge your battery bank. The MPPT controller can take that extra voltage and convert it into current for charging the batteries.

So right now this is the setup I'd recommend on a budget if you're going to live off grid and I wouldn't go with anything less than this:

  • 4 100 watt 12 volt Renogy solar panels ($547)
  • 4 Mighty Max 100Ah AGM batteries wired in parallel using equal length 2 gauge welding wire. It's important that your batteries are identical and the same age if you are wiring them in parallel. Wiring in parallel increases the available current. Wiring them in series only increases the voltage. ($740 for batteries and cables)
  • 10 amp inline DC circuit breaker between the panels and charger ($12)
  • SolarEpic MPPT 40A Solar Charge Controller 150V PV input Tracer 4215BN Negative Ground with display and usb cable and temperature sensor ($232)
  • 30 to 50 amp inline breaker between the battery bank and the charge controller
  • AIMS Power PWRIX120012S 1200W Pure Sine Inverter with Transfer Switch ($143)
    • I've looked at a lot of pure sine inverters out there and this is the best one in the price range also AIMS has a great warranty on these. I blew mine (totally because I screwed up) and they replaced it without issues. Also, you hardwire these and there is a pass through feature that allows you to easily hook up a generator to your power grid.
  • 150 amp breaker between the batteries and inverter ($29)
    • I like breakers instead of fuses because you can use them as off switches and they last way longer.
Total cost is around: $1550 if you include other wiring.

Again there are less expensive ways to do this, but for a stable system I'd recommend not going any lower than this.

This provides me with plenty of power for my lower power home. I'm currently only running on 3 batteries which I'd rather not do, but wiring old batteries with new ones is a very bad idea as it will significantly lower the life of your batteries. I'll probably end up building a new battery bank when I get the money and just build in a switch to switch between the two banks.

Also my panel stands totally suck right now.... I'm in the process of designing one that can easily rotate for tracking the sun.

This is also a great video with a lot of important basic considerations:

There's also some useful information about battery charging here in this video and I really wish I learned more about lead acid battery charging before I set up my system. I really ignored some really important things:

There is currently a big problem with my PV system that I've known about for a while, but foolishly ignored. 12 volt solar battery banks should not be drained below 11.8 volts, but the AIMS 1200 watt inverter for some stupid reason only shuts the inverter off at 10 volts or lower, but even my charge controller shuts off at a higher voltage meaning if my batteries are drained by the inverter then they won't charge back up and my batteries will pretty much be ruined.  The 10 volt disconnect is under a load so the load does cause a voltage drop across the battery meaning after the load shuts off the battery voltage will be slightly higher than 10 volts. Meaning if I had a large load on the battery when the inverter shut off it may have been at something like 11.8 volts, however if I had a smaller load it would be closer to 10 volts.

So, I can either find an inverter with a higher cut off voltage, or buy a voltage disconnect that can handle 100+ amps, but these are super hard to find for some reason, or design a circuit to shut off the inverter at 11.8 volts.

After much searching I found this voltage disconnect for $60 and ordered it off Amazon:
Image result for Victron Battery Protect 12/24V-100A

Victron Battery Protect 12/24V-100A

Only time will tell how well this works, but it had great reviews and looks like a solid product.

Also, here's a video on how to correctly make battery cables:

But I made my cables more like this guy (except I used a huge pair of channel lock pliers and didn't do such a sloppy job):

Make them like the first guy: I was just being an idiot because I didn't have a crimper. So, don't be an idiot, buy the correct crimper.

Also as a side note please make sure your panels and equipment is properly grounded otherwise you've spent a lot of time and money on something that can easily be destroyed by a little lightening.