Here's what you need to make a basic, affordable off-grid solar electric system for your home. We have to say, this is a lot simpler and cheaper than we thought possible!

While you could start with just a battery and a solar panel, the basic system described here is a complete system. Because it’s not tied in to existing house wiring, you’ll also need extension cords and power strips.

1 – 100 watt solar panel from solarproductswarehouse.com $113
1 – Battery, deep-cycle, 12v, 100ah locally from Costco, SAMS or WalMart $86
1 – Battery box locally from Costco, SAMS or WalMart $19
1 – Charge Controller, PWM, 30a from solarproductswarehouse.com $50
1 – Inverter, PSW, 300 watts from solarproductswarehouse.com $144
1 – Meter/Switch assembly (DIY): parts from Jameco.com $18
1 – 40 amp circuit breaker NAWS store $10
Misc wire, connectors, fuses, hardware various sources $20
Total starter system cost: $460
The starter system, as described, can provide 450 watt hours per day or more. You may be far from your goal (1,500 to 3,000 watt hours), but it’s a good start. You’ll be able to charge cell phones and portable electronic devices. You’ll have an abundance of light, using LED or CFL bulbs. You might use a table-top fan, power a TV, cable box, game machine, and a wide range of other devices.

I’ve listed a 30 amp charge controller, while a less expensive 10 amp charge controller would be just fine. I suggested the larger controller so that it doesn’t have to be replaced when installing additional solar panels. A 30 amp charge controller will handle the current for up to 4 – 100 watt solar panels.

Make sure that the wire you use can handle the expected current, and that all circuits are properly fused. A single solar panel might produce 6 amps of current at 12 volts, so a 15 amp automotive fuse will work fine. Fuses, and in-line fuse holders, are available from any auto supply store. 10 gauge wire can handle the solar panel current. For battery interconnects, and wiring from the battery to the inverter, use 7 gauge or heavier wire, and a 40 amp breaker. If you can’t find wire that heavy, consider cannibalizing a set of automotive jumper cables. For best performance, keep wires as short as possible. For roof mounted solar panels, ground the frames, and a lightning-protection device is recommended.

The battery box is oversized for the battery you will be using, and it includes a spacer. This extra space provides plenty of room for the charge controller, and fuses. The battery box is properly vented, and should be located outdoors, in close proximity to the solar panel. The manufacturer is listed as NOCO, and it’s called a Snap-Top HM318BK Group 24-31 Battery Box.

For roof mounted solar panels, ground the frames, and a lightning-protection device is recommended.

The Meter/Switch assembly is optional, but highly recommended. The meter displays either the battery voltage, or the output from the solar panel(s), selectable via a two-position switch. This allows you to get the most out of the system, and tells you what you need to know in order to protect the battery. The parts can be ordered from Jameco.com. Part numbers are: 2152323, 2135857, and 675489, for the meter, switch, and enclosure. You’ll also need some 3 conductor wire.

Knowing the battery state of charge (SOC) at any particular time is important for two reasons.

To make sure that the battery is fully charged, each sunny day.
To avoid over-discharging the battery.
Chronically undercharging, or over-discharging the battery can shorten its life. Unfortunately, measuring the battery SOC is not a straight-forward process. However, after observing the system over time, and with a little practice, it’s not difficult. First of all, what we consider a 12 volt battery is not really a 12 volt battery. It’s a 12.7 volt battery. When a battery is neither charging, nor discharging, it is considered to be “at rest”. With that in mind, here’s what to look for:

When the solar panel voltage is significantly higher than the battery voltage, it’s an indication that the charge controller is doing its job, and the battery is fully, or nearly fully, charged.
Expect the fully charged battery reading to be 12.6 to 12.7 volts, while at rest.
When the at-rest voltage drops below 12.1 volts, the battery is considered to be about 50% discharged.
While charging the battery, and for a period of time soon thereafter, expect to see a battery voltage reading far above the “normal”, fully charged reading, perhaps in excess of 13.0 volts. This is normal. It’s called “surface charge”. However, it makes determining the actual state of charge a bit more difficult. You can “burn it off” by applying a load for a short time, or simply wait until it dissipates.
The load (devices drawing power from the battery), affects the voltage reading. Determine the SOC when no load is connected, and when the battery has been at rest for 1 hour or more.
Copy this chart, and place it near the meter:

Battery Voltage Load Approximate SOC Comment
12.8 or higher None unknown Battery is charging
12.6 to 12.7 None 100%
12.4 None 75%
12.1 None 50% Do not connect load
For best results, battery should be at rest for 1 hour before taking voltage reading. Readings are taken at night, when solar panels are not generating power.

Your results may be different than that listed above because your batteries may be different than the ones I use, and temperature has an effect on battery voltage. Until you’re comfortable with determining battery SOC by reading the meter, it’s best to estimate SOC based on usage, as explained below.
If you start with a budget of $50.00 per month, you’ll have a complete, and substantial system in about 9 months, and a more powerful system in about 14 months.

Another way to determine approximate battery SOC is by monitoring the load. With one 100ah battery, the expected usable storage capacity is about 450 watt hours. (More about determining battery capacity later in this article). If you add all of your loads, multiplied by the hours of use, you can determine how much of that 450 watt hour capacity you’ve used. For example, if your load includes only a 35 watt fan for 12 hours, and a 10 watt light bulb for 4 hours, the total drain on the battery is: (35 x 12 = 420 and 10 x 4 = 40) or (420 + 40 = 460), exceeding the recommended shut-down limit by 10 watt hours. Until you’re very comfortable using the meter to determine battery SOC, it’s best to use this method instead.

Is this system something you would consider building?

If you start with a budget of $50.00 per month, you’ll have a complete, and substantial system in about 9 months, and a more powerful system in about 14 months. This system will power AC-operated devices, up to a maximum of 300 watts. The AC will be “clean” power, allowing you to run devices without performance problems, and without the fear of damage to sensitive devices. With a budget of only $50.00 per month, you could have a system that meets all of your needs (1,500 to 3,000 watt hours per day), in less than three years.

So what do you think? Would you build this solar system? Do you use solar polar, and if so what kind of system do you use? Share your thoughts in the comment section below!

Article Source: The Prepper Journal