Back in 2014, my wife and I installed a 9 KW solar system. The system is an off-grid with battery backup. After about 18 months of use we do like the system, despite the cost and complexity of installation.
I spent about a year doing research on which type of system best met our needs and settled on a grid tied system with battery backup, since it would give us the ability to use grid or off-grid power. With most grid tied-only systems, you will be outta luck once SHTF; grid-tied-only systems shut down as a safety precaution. The off grid capability is really valuable. One lesson we learned the hard way with anything grid-tied is to investigate which type of insurance your power company requires and how much (if any) tariff will be charged. Our homeowner’s insurance does not offer the liability protection required by our utility, so we had to search for a new policy. Also, the utlility charges a $40 monthly tariff. These two requirements by the utility make grid tied solar not very practical for small systems, in my opinion. In the end, we only switch the system off grid when the sun is shining and are on grid power otherwise. It was purchased primarily as a backup SHTF power system, so we are only moderately disappointed. I have no doubt that if I had fully researched the utility’s requirements ahead of time, I could have saved some money! Try your best to get everything in writing so you’ll have the documentation, should it become necessary. When you generate your own power and try to sell it back to the utility, they treat you as a competitor rather than like a customer, in my opinion. YMMV!
Another consideration before purchasing is where you will put the system (ground or roof mounted). We chose a ground-mounted system. I have more on this at the end.
After SHTF, I assume we will have more than just the two of us living on our farm, so we need a large system. With potentially three additional families living with us at least temporarily, we knew we would need a lot of capacity. We started thinking about critical loads: water wells, fan, air conditioner, space heater, et cetera. Our system is sized accordingly. One thing we found out quickly is that when we are running in off-grid mode, cloudy days reduce our power output substantially and the batteries provide us with a fairly large power reserve. We have two water wells (2 HP and 3/4 HP), so knowing how to determine current draw from motors is important. From my research, I found that motors can draw up to four times their running wattage at startup. Our 2HP well takes about all the power we can produce just to start. Running wattage for the 2 HP well is about 2,900 watts. The 3/4 HP well is around 1,300 running watts. (We have a Simple Pump alongside the 3/4 HP well as a backup.) One device, which can lower your startup current draw significantly, is a Soft Start unit. Schneider Electric makes several types, but I don’t own one. If you have or are considering a well, look into a larger pressure tank (or tanks) in order to give yourself a reserve water supply on cloudy days.
My brain “thinks” better in watts than amps, and I determined that what we needed was a system that could supply 8-10KW. Solar panels are usually rated in watts of power output, but when building your system you need to utilize Amps and volts, A/C and DC power. It can get complicated.
Here is a helpful chart for a simple off grid setup: Sunlight (Photons)==> Solar Panel (absorbs photons, emits electrons) ==>Charge controller (collects power from panels and converts it to the required voltage your system can handle) ==> Inverter/Batteries (Inverter provides 120 or 240 volts as needed; batteries are charged automatically) ==> Load (refrigerator, pump, et cetera)
Once I determined how much power I needed, I had to find a supplier. The one I settled on was Wholesale Solar from a web search and got some quotes on systems I could afford. Our final system price was around $4 per watt. You might need something totally off-grid and much simpler. Wholesale Solar provided me with a wiring diagram along with the matching components. You can probably find some youtube videos of how to match your components. My wife and I did the “grunt” work ourselves to save money and had a contractor recommended by Wholesale Solar to hook everything up. We set posts, trenched for conduit to the house, attached the panels to the racks ourselves, and probably saved $1500 or more. If you aren’t able to set posts in concrete and run wire, et cetera, find someone to do it for you. The component hookup was too complicated for me, so having someone who does it for a living was great. Not knowing what you’re doing can get you or a utility lineman killed.
Our system utilizes 36 Astroenergy 260 Watt panels, two Midnite Solar Charge controllers, and two Outback Radian Inverters. Charge controllers keep your batteries charged and run your inverter. The charge controllers must be sized correctly with your solar output and battery bank. Sometimes both units run at once, while other times only one is required. They run in a master/slave orientation. Our system is 48 volts with lead-acid batteries. After SHTF, you’ll need to figure out how to distill your own water to maintain the batteries. Maintenance free batteries are available but cost more and have a lower storage capacity. The batteries are six volts each and wired in series (6×8=48). Cleanliness around the batteries is a must. Also, you can assume that they will be emitting hydrogen gas, so avoid smoking, open flames, or sparks to avoid igniting the hydrogen. The inverters seem to run in a master/slave orientation. Both are required to start the 2HP well, but after startup, only one appears to be running.
Some odds and ends
We are located at roughly 32 degrees latitude, so 32 degrees south facing is the recommended panel tilt angle. After a lot of thought, I installed our panels at a 22 degree angle. This reduced angle will have less wind resistance in the winter when we can have 40+ MPH north winds, and it gives us a little more power in the summer. In hindsight, I wish we could have added a few panels facing due west to take advantage of late evening sunlight. I have no experience with roof mounting a system. That sounded like a bad option due primarily to the number of roof penetrations required and the fact that our house has too many tall trees around it. If you decide to go with a roof mount system and your roof develops a leak, who’s going to fix it? You can bet that anywhere you penetrate your shingles or metal, your warranty against leaks would be voided. As far as components go, you might as well get the best you can afford because after SHTF, there probably won’t be a lot of spare parts for these systems. One thing you’ll have to get used to is a gradual decline in power output of your solar panels over the expected lifetime of the panels. Each manufacturer should specify how much power (wattage) will be reduced over the expected lifespan of the panels. You’ll need to size your system for not only the possibility of greater future power demands but lower future power output. I have noted a very slight output drop from this time last year. Generally speaking, cold sunny days produce a lot more power than hot sunny days. Even on cloudy days we can generate at least 1 KW. Higher ambient temperatures will yield higher battery storage capacity but will shorten battery life. Our system’s efficiency is greatly reduced in August when temperatures over 100 degrees cause the inverter and charge controller fans to run full speed. I have had to add a ventilation fan to the inverter shed to help keep it cool in the summer. Whenever possible I tried to oversize the components (wire and inverters, for example) of the system to give us the ability to add on in the future if necessary. This is not a maintenance free system. I check water levels in each battery cell at least monthly and more often in the summer.
If we were to run all of our critical loads simultaneously, they would quickly overwhelm the system. So when the time comes, we will have to choose which loads to use.
Here is what I have found some of our loads to be:
- Stove– each burner, 2KW, all four burners = 8KW
- 2HP well– startup, 9KW, running, 2.7KW
- 3/4 HP well– startup, 6KW, running, 1.3KW
- Skilsaw– startup, appx 3.5KW, running 1.5KW
- Minisplit A/C– 400Watt-1.0KW
- Space heater– 700Watt-1.3KW
- 24 cu ft refrigerator– startup ?, running watts, 200
- Washing machine– 300 Watts-1.0 KW, depending on cycle.
With a finite amount of power, we had to choose which appliances we could do without. We chose the water heater and the oven. We can work around these two appliances with difficulty. Modern LED lighting and a very reliable DeWalt CFL flashlight will give us night lights.
Finally, speaking of OPSEC, I couldn’t think of too many ways of disguising our system. It’s sitting in the only place that made sense for maximum power generation. I know there are flexible panels available that could be mounted in various places, but they seemed to be pretty expensive.