Practical PV Power, by Graton

Even though I have been dabbling in solar power since about 2008 I hesitated to share my experiences because I felt totally incompetent about the subject. I still feel that way in large part, even though my “knowledge” has increased dramatically.

One of my first projects was setting up a solar-powered well for a friend’s cattle where obtaining grid power would have been financially prohibitive. The equipment included a Grundfos 11 SQ-Flex 2 pump, 6 solar panels, Midnite Solar 60 charge controller, golf cart 48-volt battery bank, etc. You may have noticed that there is no mention of an inverter because this Grundfos will run off any source of power, AC or DC, without any modification. I had already built a wood rack to hold the solar panels with an enclosed area underneath to hold the solar equipment. I was amazed that we were able to install the pump and install all solar components and get it running in one day. We had a scary moment when we turned it on and nothing happened. Before pulling the pump I checked all of the above-ground connections and found a loose wire in the charge controller. It was quite exhilarating when we heard water gurgling and had full water flow, just seconds later.

Years later — around 2015 — I decided that my prepping would not be complete without at least a minimum availability of electricity if grid power was not available. I also wanted to build a workshop and decided that would be the perfect location for solar panels and the rest of the equipment. At that time I felt the size of the project was beyond my capabilities and started the search for someone to provide me with a turnkey solution. Looking through a couple of quotes I realized the proposals left a lot to be desired in terms of power provided versus cost. I decided that I would have to do a lot of studying and learn how to accomplish the project myself. This turned out to be very confusing and I often had to sift through conflicting statements from manufacturer’s manuals and their tech support and retailers.

I received no compensation of any kind from any of the companies mentioned nor are they even aware that I am writing this article. It is just to alert SurvivalBlog readers to some products I used and how this turned out for my purposes. I am sure other products out there are as good or even better. Before choosing a place to purchase my system components I did some research and found a lot of positive comments about Backwoods Solar, near Sandpoint, Idaho. I have not been disappointed with that choice.

A caveat is that it helped that I didn’t realize how much time I would spend studying and the angst involved due to having limited knowledge and conflicting advice. Also, this is a good time to say that the return on investment (ROI) for solar is not great, especially if you opt for a battery storage system. Any savings will likely be used up completely when your batteries require replacement. With that said, a system without batteries will not allow most appliances to work due to the minute-to-minute variability of solar alone. The huge plus is having at least some power if the lights go out.

I hired an electrician to wire my shop and he agreed to sign off on the grid-tied solar system if I helped and took responsibility for the technical side of the solar installation. He had no prior knowledge of photovoltaic (PV) power installations.

The following is a list of components that I used:

  • 24 mono-crystalline 260-watt solar panels = 6,240 watts
  • 1- Schneider Conext XW+ 6848 inverter with PDP
  • 2 – Conext MPPT 60 150 charge controllers
  • 1 – Conext System control panel [most programming and status can be done here]
  • 3 – MNPV3 combiner box and breakers
  • 3 – MidNite Solar MNSPD300-AC Surge Protector
  • 3 – MidNite Solar MNSPD300-DC Surge Protector
  • 24 – Concorde SunXtender PVX-9150T Sealed AGM 2V 915Ah batteries for the battery bank
  • A simple aluminum racking system for roof mount.

I used 2/0 welding lead cables to do series connections between the batteries and 4/0 ten foot cables were included with the inverter PDP for the battery-to-inverter connection.

I used 6 gauge multistrand wire for connections between MNPV3 and charge controllers and inverter. I have a subpanel that contains only the breaker for my submersible well pump as it is the only thing I want automatically powered if the lights go out. All other breakers are in the main panel and would have to be toggled manually if the power was out, long-term.

I also ran solar power to my home next to the shop. There the sub-panel contains most of the 110 VAC  breakers which automatically receive power during an outage so there is no interruption. The main panel contains all the 220 CAC breakers plus a few odd 110 VAC breakers. They would have to be addressed manually in case of a long-term outage. The system automatically disconnects from the grid when it senses a power outage, so there is no danger of backfeeding power through the grid lines. The transfer time is about 8 milliseconds so the only way that we know power has been interrupted is when the clock on the stove goes out.

The system above has been in operation since 2015 — about 8 years. In that time I have experienced no significant problems. The longest grid down that has occurred was about 8 hours with multiple outages of shorter duration. Everything has worked flawlessly so that we don’t even have to reset clocks when grid power is interrupted. This system also handles 220 VAC, so that the submersible well pump automatically remains powered up. What I have failed to do so far is disconnect completely from the grid and make power available to all the 220 VAC items in the main power panels to be certain that it all works out as expected.

Like all things, this system has limitations. The inverter is limited to providing 60 amps continuously, and up to double that for a minute. If more amps are desired, then multiple inverters can be piggybacked. But with 60 amps I can run a hot water heater plus one other 220 VAC load simultaneously along with all my 110 VAC  loads. My battery system should carry me for about 3 days without depleting them below 50%. I prefer limiting that to 20% in order to prolong the life of the batteries. I have read that 50% depletion versus 20% depletion would result in about halving the life of your batteries.

It is very rare that we have more than 3 days without enough sunshine to fully recharge the batteries. If such was the case — as during winter — then I would turn off the hot water heater and avoid using any other 220 VAC loads until the weather improved. Another thing we would practice would be to do all power-hungry operations by 2PM to be sure batteries can recharge before dark. A pleasant surprise has been that even after 8 years the battery voltage in the morning before daylight triggers solar charging, remains at 51.0 to 51.5 volts. According to my battery supplier that means that the battery system remains practically new because it retains full power overnight. He told me he would expect me to get at least another 8 years out of these batteries. That is much better than expected, based on my previous experience with flooded-cell golf cart batteries. I am a devotee of the Concorde SunXtender AGM batteries and so far don’t see any real advantage to lithium or other alternatives.

One bit of info that I am having trouble pinning down is the conversion from DC amps to AC amps. If your battery system has a total of 900 amp hours @ 24 hours and you want to limit yourself to a 20% draw, you would have about 180 amp hours available. But when you convert those DC amps to AC amps would that equation be 48DC/110AC or about 50%? I believe this is the case even though I have not been able to find much info on this question. Perhaps a reader with expertise could give us a definitive answer.

Reader Alex B. immediately chimed in:

“Answer:  Amps don’t know whether they’re being used for AC or DC loads.  
When the ultimate source of power is a battery bank, the amp draw will always be found by dividing watts by the battery voltage. 
1,000 running watt DC load / 48vdc battery system = 20.83 amps. 
Run it for one hour and it will use 20.83 amp-hours. 24 hours will use 499.92 amp-hours and so on.
1,000 running watt AC load / 48vdc battery system through an inverter = same 20.83 amps + inverter tax*. 
The real question being posed is how to understand how much power is being used so as not to run the batteries too low. This is something like a “master amp-hour calculation for off-grid battery system.”
Basically, all that needs to be done is understand the “average” wattage needs by doing this calculation for all the electrical demands. 
It’s not an exact science because most electrical loads aren’t running all the time. A refrigerator or window air conditioner for example. Off, on, off, on. 
Let’s say the 1,000 watt load above only runs 60% of the time. In a 24-hour period, it would use (499.92×0.60) = 299.95 amp-hours. 
There are some other nuances that complicate it further but if the battery system is oversized by a responsible margin, they’re irrelevant.
*The “inverter tax” is measured as efficiency in decimal form, for example .96, that makes the tax 4%. It can vary between manufacturers and how much work the inverter is doing compared to its maximum output.”


Photovoltaic power is definitely not cheap, but when I considered the time and work involved in going to a creek with two buckets to get water that would then need filtration or treatment to make it potable, I decided we needed to squeeze our budget in order to afford it. Plus, consider refrigeration, lights, etc. Another factor is the increasing unreliability of the grid plus the rapid increase in price. The ROI of solar is improving rapidly because of price increases.

At present, this system provides about 50% of our electrical consumption. About two years into owning this system as I was still studying how it all worked I ran across a mention that the inverter could be programmed as to whether the battery charging was from the grid or using DC directly from the panels to the batteries without converting to AC. It involved having a trigger set for recharge to initiate when the battery voltage dropped below 52 volts on the charge controllers, but setting the inverter trigger at 51 volts before charging occurred from the grid. This meant that charging would automatically begin as soon as any power was produced at the panels in the morning, since the morning voltage was usually around 51.5 volts. This small change increased my power fed back to the grid by at least 50%.

The maximum panel wattage of the inverter is 6,800 watts. However, no harm is done by having more wattage installed with a larger solar array. One of the most cost-effective changes I could make would be to increase the panel array to 9,000 watts. That would give extra power to charge batteries independently from the inverter and would therefore increase my feedback to the grid, further decreasing my net cost of electricity. It would also provide a better chance of getting maximum inverter power on days of limited sunshine. No harm is done by the extra wattage even if the system has no capability of utilizing that extra power. If I added extra panels on a ground mount on the west side of the shop it would be a fairly easy upgrade. Another change I would really appreciate would be having a second system control panel inside my house so that monitoring the system would not require me to go outside to the shop.

The lifetime of this system is not infinite. The batteries will probably be the weakest point, but even though storage capacity will decline I believe it would be a long time before I could not run refrigeration and a few lights at night. Most other electricity demands could be postponed to daylight hours, thus solving most of that problem because power would just flow through the batteries. The inverter and a lot of other components are microprocessors and transformers for the most part and I have read of systems that have been running for more than 20 years. I will add some spare parts, as finances permit.

One aspect that I did not realize at first is the value of solar capability as a great barter currency in a TEOTWAWKI situation. Even though this system only reduces my bill by 50%, there are many days of great sunshine where my production exceeds my utilization. In a grid-down situation, once your batteries are topped off, there is no place for your excess power. Without the feedback to the grid to act as a de facto battery, this excess will be lost unless you use it as it is produced. With planning and proper attention, this excess can be used in my shop for welding, machine lathe, milling machine, sharpening, woodworking, and a myriad of other operations that will rise exponentially in value when electricity becomes rare.

Another barterable service would be recharging batteries for tools and flashlights for neighbors. I feel that it will be possible to trade refrigeration in exchange for some beef and pork. And a full chest freezer is more efficient than one that is half empty. The owner of the meat, not paying for the refrigeration, could then barter a 2-day supply of meat to someone for an item that he needs. As space permits, ice could be traded to someone for use in an ice chest for preserving fresh foods.

I once read a comment from a machinist who had just finished a lengthy and complicated description of the steps in machining a part.  He said: “I probably told you more than I know, but I haven’t knowingly lied.”  I realize there are many unanswered questions in this article but I am hoping to encourage others to take the plunge and start studying in order to construct their own system. I am glad that I made the effort to learn about it and do some of the hands-on work, because if a problem does occur, then I will hopefully be in better shape to find and implement a solution.

We are glad that we made the sacrifices needed to allow us to have the funds to achieve a higher level of self-sufficiency.