Stephen is Thinking Solar

And 2000 pound monsters.

I got this comment from Stephen. I’ll let you take a look at it and then I’ll comment, OK?

“Well I’m a new-b, & an old fart, I wanted to start this process a long time ago, but for the dollars…
I’m interested in learning more of the availability of these 2000lb. Monsters, though I really need some education on the basics like …If I Install 11,500 watts of panels on my clear view roof, do I need to buy ( 3) 4048 inverters & then split the panels over 3 separate systems?? Sometime in the future I may purchase a nice 20kw diesel standby gen. w/ ags. Probably will take a while $$$again.”

OK, here we go. No worries about being new. Every day is a new day with solar. Every morning I read a half dozen or more solar and energy newsletters and there is always something new. As far as being an old fart goes, Old Guys Rule! Step away from the rocking chair! And as far as the $$$ go, you are already ahead of the game if you’ve found Sun Electronics. I look at some of the pro systems going in around me and OMG the prices! My system will blow most of them away at a fraction of the cost.

Now, you ask about “2000 lb. Monsters”. I assume you are talking about my forklift batteries. 540ah at 48v is a good start and I figure 4 of them will put you in good shape. However, there’s that 2000 lb. bit to consider. The more modular battery systems are easier to handle and many require little or no maintenance. The forklift batteries can be a super deal, though. Probably the best ones are coming off a 2 year lift truck lease. For some reason, these leasing companies pull the 2 year batteries and install new. You can find these on Ebay. There are forklift companies and battery companies in most cities and they can be a source. It could be good to buy locally and cultivate a relationship because your battery may need service some day. THEY can change a cell or rejuvenate a tired battery, but I don’t think they do house calls. Maybe, though. There is a funny numbering system for these monsters that tells you the volts and amp hour ratings, but you have to know the code. And since we are talking about batteries, I assume we are not talking about grid tie.

Dragging 2000 pound monsters on a sled is not so hard. Scooting them against the wall and onto a pallet with a jack and a pry bar is when it gets fun. Old Guys Rule!

Grid tie can be quickest and cheapest to install, but most folks like having their lights stay on when the grid goes down? I hear that happens. You can still have the grid and run it in with the solar in a hybrid, interactive system so you can avoid fees and all manner of unpleasantries that some power companies impose.

I’m not sure how, but somehow you came to the conclusion that you want 11,500 watts of solar panels on your roof. That’s actually a pretty good number for a typical American home. That’s over 200 amps of current in a 48 volt system, so you need a pretty hefty battery bank to soak it all up without causing problems. You note you have a clear view from your roof….to the south? That’s great for maximum production, but we are finding that it is actually pretty good to have some panels facing the west. I know my a/c is running in earnest late in the afternoon and the sun is toward the west at that time. After success with a small experiment, I am putting in a 10 panel array in a westerly orientation. North is not a good direction, but pretty much everything else will work.

Next you mention 3-4048 inverters and I am not sure why. Because 3 x 4048 adds up to pretty close to that 11,500 watts of solar? That isn’t how it works. Your modules are going to connect in blocks of, say, 3. Those blocks meet up in Combiner Boxes, as appropriate, and all that combined electrical goodness goes into a charge controller. Most of these charge controllers I use have an input of 130-160 vdc. 3 panels in series, generally add up to that. There are exceptions, so check the data sheets and think ahead. I also have a 250v input charge controller that will handle 5 x 60 cell modules or 4 of the higher voltage 72 cell modules. In addition to those volts, you need to keep up with the watts, as well. A 60 amp charge controller is good for around 3000 watts. I say “around” because folks have different takes on how mathematics works. In my motley collection, the 60 amp controllers range from 2800 to 3200 watts. Some are more tolerant than others to the occasional aberration. Read the data sheet, watching for gotchas.

There are bigger charge controllers, like the FM300, but I kind of like the idea of having a little redundancy. I have 6 charge controllers on the main system, but 4 would be plenty. By now you have guessed that if you are using 3000 watt charge controllers, YOU will need 4 of them to cover all those watts flowing off the roof. Now, do as I say and not as I do, here…my system didn’t just happen, it evolved. I have several varieties of charge controllers, so they can’t share a communications system if you like to chuckle over charts and graphs of power production.

Now we have all of those solar watts tamed and being shoveled into our monster battery pack. Let me tell you about a fellow who fed a similar amount of power into a not-quite-monstrous battery pack of 400 ah. First, that was not enough to do much good on a whole house system. Second, cramming 200 amps into a small battery pack is just going to cook the batteries. He had some nice AGM batteries, but not for very long. 60 amps for the set should have been the limit. I have some AGM batteries of twice the size and the data sheet says don’t exceed a charge rate of 40 amps. I have 4 strings of those and the monsters and two electric vehicles to soak up well over 200 amps without exceeding the limit on the charging rate of the delicate AGMs.

Better still, a forklift battery or any other variety of flooded lead acid or FLA battery is pretty tolerant of a hard charge, though you might have to water more frequently.

OKAY, back to the 4048 inverters. You apparently broke the code, here. 40=4000 watts and 48=48 volts. Why 3? What you need to consider for inverters is how much do you need? Being careful, I have run everything but the electric stove and clothes dryer, including one of the central a/c units with a 5048. I don’t have an electric water heater. At the present 10,000 watts I could pretty much run it all if I had a heavy enough cable. (That’s a project for another day) My old partner, Tom, did well with a 12kw inverter. Then it broke and he ran, I think, an 8kw, one of those nice Outback GS units that Roberto has. It was not quite enough, but you can run two of them in parallel for 16kw, so he was in good shape and if one failed he could get by while repairs were being made.

There are myriad features in today’s hardware. Many 4048 inverters I have seen, like the old Xantrex or Trace or Sunny Island are 120 only. You connect two with a combiner to make 120/240 for normal household operation. I am presently cabling in a pair of Sunny Island 6048 units that work the same way. You gotta have two of them and 3 would be just weird. The combined 12kw would be overkill for me. Right now I use them for welding, so they are pretty tough. My homebuilt 10k48 puts out 110/220 on its own, but has no tricks. The Outback GS8048 makes 110/220 standalone and you can stack it to double the power. It can also do lots of nice tricks, like hybrid, grid tie or automatic transfer. The beauty of the 8048 over the smaller size is that you get twice the power for just a grand more.

Now what? How are we going to do this? I’ve mentioned some really versatile gear, so we have options. If you want to go off grid, you are good to go. If you want to keep the grid for backup or because you use a lot of power, how about a hybrid setup? This is especially handy if your power company hates solar (charges fees and makes onerous rules). The aforementioned Tom connected his inverter to the house through a transfer switch, like he used with his generator. The grid had a separate line down to the barn where it entered the secondary input of the inverter. During the day, and as long as his batteries were above the threshold he set, the inverter provided power to the house. On warm summer nights, the a/c would draw down the battery and the system would shift back to grid. There were no extra fees and no selling electricity to the power company for 3 cents and then buying it back at night for 13. His big limitation was his tiny battery bank. With 2000 amp hours, I suspect a changeover to grid would have been rare.

I have simplified things here, of course. You’ll need to throw in some surge protectors and circuit breakers. There are the mounting racks for the panels and the cables and gadgets to comply with the new “rapid shutdown” rules to let the fireman shut down the panels before spraying water on the roof, in case of fire.

Finally, a 20kw generator? Diesel is a great choice. Today’s gasoline just won’t keep. There are natural gas and propane units that may be a good choice, too, but I am a fan of diesel. I normally keep enough diesel and jet fuel around that I could run a generator for a year. Many years ago when we had a 5 week outage I had an old 15kw diesel that ran at 1200 rpm. It was meant to run continuously and had 3 phase. I brought 2 legs in through one of the external a/c disconnect boxes and ran the whole house. It came in through a 30 amp breaker, so I could only use around 7000 watts and we did fine. It would charge my battery backup, run the stove, laundry and water heater while I was getting ready for work and then we’d shut it down. (This was back when I was willing to work for a living.) Lights and fridge and such ran off the battery backup except during breakfast and supper.

So I guess the point is that 20kw is probably more than you need. My recent generator addition is an 11kw Kubota LoBoy with 113 gallon fuel tank and autostart. I can’t imagine needing more than that. Oh, and by the way, the smart inverter is taking that power and passing it to the house and/or charging the battery as needed. Boy, these inverters are smart, but the manual will blow your mind. You actually have to think, which I suppose is usually the best plan.

Did I cover it all? Get busy, Stephen!

-Neal