The Big E

The Big E
Vern's Stories fredhorn37@gmail.com

A small, simple, off grid solar electric system

 If you would like to have the capability to run a refrigerator, a freezer, a fan or two, some household lights, or recharge your phone, or charge some rechargeable AA batteries, consider a small offgrid solar electricity system.

It doesn't take a lot of solar panels. The battery system will probably be the biggest single expense.

Here are the major parts you will require, not including wiring and fusing:

  1. Solar Panels
  2. MPPT Charge Controller
  3. Battery Bank
  4. Pure Sine Wave Inverter 
1. Solar panels. 600 watts of solar panels will easily run your fridge or freezer. My 24 cubic foot fridge runs off/on all day. When I look at the power consumption my fridge typically pulls 130 watts when it is on. And that is usually for 5 minutes or less. On first startup for cooldown that will probably be a lot more. Here is a link to some solar panels on amazon: 

Renogy 12 Volt Solar Panel 100 Watt High-Efficiency Monocrystalline

2. MPPT charge controller. I specify a Maximum Power Point Tracking controller because this type has the capability to determine how many amps to put into the battery bank, thus making it the most efficient type of controller. I selected this 60A controller because it will take up to 780 watts input, where the lower expense 40A controller is rated at 520 watts. Here is a link to a good unit on amazon:

EPEVER 60amp MPPT Charge Controller

3. Battery Bank. This is probably the largest expense of your system. For my system, I chose a brand of battery called Deka. The reason I did this is because that is what my preferred local battery provider supplies. Other brands are available to order, but he stocks the Deka all the time. I chose Deka GC15 six volt flooded lead acid golf cart batteries. My system has 8 of these, wired series parallel to provide a 12VDC configuration. Here is a link I found online for these: 

Deka Pro Master GC15 Flooded 6V 230Ah Deep Cycle Battery

When I purchased the last set of 8 batteries in June of 21 I paid $140 each plus a $40 core charge per battery. I did not pay shipping because I picked mine up locally. If you order online you will pay a lot in shipping.

Regarding batteries, the flooded lead acid batteries require you to check water level on a regular basis. Other types of batteries which do not require as much maintenance are AGM(absorbed glass mat), sealed lead acid, LiFePo4. All of these are more expensive batteries, especially the LiFePo4. The upside is they last longer than FLA batteries.

4. Pure Sine Wave Inverter. Inverters typically come in a modified sine wave or pure sine wave inverter. The pure sine wave matches or exceeds the quality of electricity provided by your energy provider. That is why I chose that, it is better for electronics.

A 4000 watt inverter will easily power your refrigerator in your home, especially during the day when your solar panels are providing energy.

The charge controller I selected has a monitoring device, titled MT50. This device can tell you how much power is used. Just now, I checked my inverter display and it said the fridge and the fan I have connected to the inverter are using 160 watts of power. I looked at the MT50 unit and it said the pv panels were inputting 250 watts of power into the battery bank. What that means is, the battery bank voltage will stay relatively constant as long as more is going in than coming out.

Here is a link to a good 4000 watt pure sine wave inverter on amazon:

GIANDEL 4000W Heavy Duty Pure Sine Wave Power Inverter DC12V to AC120V with 4 AC Outlets with Remote Control 2.4A USB and LED Display

As I said above, these are the major parts required, not including wiring and fusing.

Regarding wiring, when talking about a 12vdc battery system, bigger wiring is always better. Bigger wire, and shorter length, means less resistance to current flow, resulting in less heat buildup and more flow to the unit.

I have found this out on my system. I installed a positive cable of 2 gauge wire 10 feet in length and the same for a negative cable from my battery system to my inverter. From my battery to the connections on the inverter, I have a 0.2 vdc voltage drop. I can remedy this by installing larger, shorter, cabling. But for the moment it works okay.

From the battery to the inverter the experts recommend a fuse in the wire. For 2 gauge wiring I found one chart that said I needed a 600 amp fuse, and one chart that said I need a 400 amp fuse. By my calculations, I should use a 300 amp fuse. On my system I have chosen to not install a fuse. I might be dancing with the devil, but that is what I choose. For now.

For connecting the batteries to each other, I used 2 gauge wire. I purchased a cable crimper from Harbor Freight and squeeze crimped cable ends onto the 2 gauge wire. That was much less expensive than having the cables made by someone else. Many experts and literature suggest the wiring should be bigger than 2 gauge. But for my system it works okay, and the heat buildup in the wire is negligible.

Now for the wiring from the panel to the charge control. I am using 10 gauge wire for that. For wire sizes, 10 gauge wire is smaller than 2 gauge wire. Each solar panel positive wire is wired individually to a small automotive fuse block. I am using 7.5 amp automotive style fuses there. From the fuse block I used a twistlock connector to tie all of the panel wires together and then ran a single wire to the charge controller.

The solar panel negative wire is done the same way, except it doesn't go thru a fuse block. 

From the charge controller to the battery, I am using the same size 10 gauge wire. Positive from the controller to battery positive, negative from the controller to battery negative. 

What I have just described is a basic, simple yet effective, off grid solar electric system. Before you purchase parts and start installing them, do your due diligence and do some studying. Youtube has some great videos about this.

If it appears I have forgotten something here, please let me know.





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