Douglas Toltzman's posts

You are a wise man, Tom.

The grid tied inverter is synchronized with the grid AC voltage. I would think you'd have a problem interfacing your micro-inverters unless you found some way to sync their output waveform with the grid.

Hello, Tom. I'm not an expert, but I've been running a homegrown off-grid solar system to power SOME of my electric loads for about 10 years. The most difficult thing, if you're going to be completely off grid is sizing the components to suit your needs. It's relatively easy to add solar panels, but adding or replacing a charge controller or inverter can be expensive.

I have some friends who live entirely off of about 1kW of solar, but they run a pretty tight energy budget. Tom Mayrand was dead on about solar thermal for your heating needs; that knocks out a huge portion of your energy budget, and it's a lot cheaper to heat water directly than it is to generate the kW's you'd need to operate an electric water heater. You can even build your own solar collector(s), if you're up for it.

Based on my past measurements, you'll be limited to the current produced by the panel that is producing the least amount of current. In your case, it's probably the 3A panel, but it would also vary if one of them is in shade.

From what I've read, MPPT charge controllers require identical panels to work efficiently.

How you wire your panels is going to depend somewhat on your choice of charge controller and voltage of the panels. I've found that wiring the panels in parallel to the controller is better, because it allows the full current of each panel to reach the controller, at the nominal input voltage of the controller, when the panel voltage is matched to the charge controller.

Having said that, there may be cases where the charge controller can operate at higher voltages and a series configuration will work. I don't want to sound like a know it all, but I'm pretty sure you want a parallel wiring configuration. It's also better to be in parallel if it's possible for one panel to go into shade while others have full sun.

The rest looks Ok to me. You'll probably want some fuses and a lightning arrestor. I have a fuse between my photovoltaics and my charge controller that limits to the amperage to that of the controller. I also have a 300A fuse between the battery bank and the inverter.

The replacement sensor is installed. It appears the problem is resolved. We didn't have a lot of sun today, but the pump did run several times after I installed the replacement sensor and the readings all seem to be sensible.

I installed a 3rd sensor on the hot water pipe, leaving the tank. As long as I am using hot water, the reading on that sensor is comparable to the new one at the top of the tank.

Thank you, Sascha. I think we're getting it all sorted.

What's up in the customer support department? I can't get an answer, or a return call.

Also, in the time it's taking to get a return authorization, the website has dumped my shopping cart, so I have to hunt down the parts for my next order, again. I thought, if I was signed in, my shopping cart would be saved for me

I've been an Alt-E Store customer for over 10 years. This is not what I've come to expect from Alt-E. If I don't get a call back from customer service, the shopping cart issue is probably moot.

Thank you, Tom. I think you misunderstood my solution. I added a 10.5K resistor in parallel with the sensor to adjust it's reading up by around 10-12 degrees. That is just a temporary solution until I can replace the top sensor.

I am using an Eagle II controller, and there are 2 sensors, hooked independently. You can look at the video I posted and see them operating (back when everything was working right). I have one sensor at the top and one on pipe that exits the bottom of the tank (heat exchanger) to return to the collector. If I could have one in the middle of the storage tank, I would, but that's just not possible without fabricating something (which I may actually do, when it works it's way to the top of my priority list. One year into this, I've consistently had a surplus of hot water, so improving the system is not a priority).

As of right now, the system is working fine, with the parallel resistor installed to adjust the sensor reading upward. I'll acquire a new sensor after the holiday weekend.

Thank you, again, for your thoughts.

Thank you, for your time and expertise, Amy. You are the best. Here are the measurements I took this morning:

water temperature: 149F
sensor ohm reading (disconnected): 2560 ohms (137~138F)
When I hooked it back up with my 11K parallel resistor (actual value 10500 ohms), the Eagle II reads 150 degrees. The computed parallel resistance would be 2058 ohms, and that should read 149~150F, so the Eagle II appears to be reading correctly.

The good news is that my 11K resistor in parallel will provide a temporary solution. The bad news is that I'm going to have to RMA that sensor or buy a new one.

BTW: I also wrapped the exposed part of the sensor in another inch of fiberglass insulation and that made no significant difference. It might have raised the reading by 1F, but the error is closer to 12F. The entire tank has an R30 wrap around it.

Thanks again, for your help.

I got an idea, after I wrote the previous post. I have a spigot that will allow me to draw potable water directly from the tank (the house water goes through a mixing valve). I ran the spigot long enough for the water to get really hot and took out 16 ounces in a 32 oz measuring cup. I then added 16 oz of water at 80 degrees and checked the temperature with my darkroom thermometer (it only reads to 140F). The resulting temperature was 116 degrees. By my math, that means that the 80 degree water rose 36 degrees which should have taken the hot water down 36 degrees. Therefore, the  hot water started at 152 degrees. The sensor at the top of the tank reads 140. That means I have at least a 12 degree differential between the water coming out the nearby spigot and what the system thinks the maximum temperature is.

This is frustrating. It's hard to save any money on my utility bill when I keep having to put it back into new parts.

My system has been installed and working for just over a year. In that year, I've needed to use my electric hot water heater for less than 12 hours. I have not had much luck with sensors, though. I'm pretty sure the one I have in the top of my tank is not reading correctly, and it's not very old.

The heat exchanger/storage are configured as follows ...
The heat exchanger is a tank of potable water, inside an outer jacket that holds the mixture that flows through the collector loop. The tank has a fixture on the top where the temperature sensor is supposed to go. The trouble, from the beginning, was that the "dip stick" mounted on the fitting that screws into the top of the tank was too long for me to remove it from the tank without drilling a large hole in the ceiling, and the sensor wouldn't fit into the hole at the top.
My first solution was to shorten the "dipstick" by cutting it off, inserting the sensor inside the tube, and running just the wire through the small hole at the top. It was a great challenge getting that tube resealed so I could stick it back into the tank with the sensor inside. After a month, or so, the sensor quit working because a tiny bit of water was seeping into the tube and the sensor ended up in a few inches of water at the bottom of the tube, eventually.
So, I opted to screw a submersible sensor into the top of the tank, even though it would be reading the temperature at the hottest point in the tank. In order to monitor the bottom of the tank, I attached a sensor to the collector loop output pipe at the bottom of the tank. That isn't ideal, either, but I get a good idea of what the top and bottom temperatures are, between the two sensors.
Well, lately, the top sensor has been reading about the same or lower than the bottom sensor. Normally, the top sensor reading rises pretty fast when the sun is shining and the system is running. Now, the bottom temperature overtakes the top temperature, and the circulating pump runs a lot longer than it should. In the middle of the day, if I'm not using any hot water, the pump might run for an hour at a time. That leads me to believe that the top sensor is reading low.
I don't have any alternate way of testing the temperature at the top of the tank. The water is under pressure, so I can't just unscrew the sensor and stick a thermometer in there. Based on common sense, it has to be reading wrong. I checked for air at the top of the tank. There is an air bleeder that is working properly, and I unscrewed the sensor a little to let some water drip out before I retightened it.

So, are these sensors that unreliable? Could it be failing? Or is there another explanation I haven't yet considered?