NEW 10/14/21: I'm spoken to a growing number of people that can't run their system at full capacity because there aren't suitable inverters available. I know of two efforts to provide a solution to this problem. We should get more information in the coming months. This facebook group seems to be the best place to connect at the moment: https://www.facebook.com/groups/559492874643037
There is a weird breed of solar panel made by an defunct Minnesota company called Ten K Solar. They operate very differently from the standard solar panel. Every now and then I see a post on the internet asking about these, so I'd like to share what I know about them.
I know this is probably going to help nobody on a battery forum, but some people might get here on a google search or whatever and I wanted to get this information out somewhere.
If you're from the North-Central US and you just got your hands on a second-hand, weird-looking solar panel, then you've come to the right place. For everyone else, this write-up is entirely useless but might be an amusing anecdote.
Ten K Solar (AKA tenksolar or just TenK) was a solar company founded in 2008 in Minnesota, USA. Leveraging some “interesting” design choices, they grew out of the start-up phase thanks to some state incentives in place at the time. I joined the company in 2015, and left just before they shut down in 2017. (Many reports claim that Tenk went out of business due to the unreliability of the inverters. While there were definitely inverter troubles, the real issue was simply the difficulty in maintaining cost-competitiveness.)
Since I left before the shutdown happened, I don’t know what happened to all the company’s assets when they stopped operation. Specifically, the company owned a lot of unique IP which may be lost forever for all I know. I didn’t have the forethought to secretly take a copy of the source with me so the following is based on what I remember.
The short version of TenK’s design is “put it all in parallel”. Specifically regarding the latest 500W “Apex” modules:
Cells: half cells in a 25s8p configuration. The parallel cells are from bottom to top and series from left to right; this way if the bottom row is shaded (as they often are in order to get panels close together), it doesn’t interrupt the string.
Internal electronics: The plastic housing contains a MPPT boost converter to go from the ~15V cell voltage up to ~56V. The converter itself is an 6-unit interleaved boost converter (6 converters in parallel).
String connections: Around 10-15 or so modules are wired in parallel. The limiting factor is the amount of current that the wire can handle. #2 aluminum wire was the most common.
Inverters: The string of modules were wired to 10-12x ~700W micro-inverters wired in (you guessed it) parallel. The inverters were off-the-shelf units modified by the OEM to run in constant voltage mode (instead of MPPT).
Because of the integrated electronics, the TenK modules can’t be used in normal solar systems. In order to even get the module to produce power, it needs to be presented with a valid load. A load can be either:
A voltage source, such as a battery, or another module that has already started up. I forget the exact voltage requirements but I think anything between 20-55V would be acceptable.
A large (1000 uF+) capacitor, such as would be present on the input stage of a microinverter. There's a precharge step so the anything connected to the cap will need to wait a couple seconds before drawing power
So options for using these panels:
Find a Modified micro-inverter. This might be hard since they're not made anymore and they weren't perfect even when they were. LeadSolar and APS built them. Some of the companies that own the arrays do get inverters as replacements and I have a contact at one of them, so it may be possible to get some at full price.
Use a Standard Microinverter. You’d need something with a 60V input voltage. The interaction between the inverter MPPT and the panel electronic’s output tends to be unstable. It may be possible to improve it with some filtering between the two devices but we never experimented with this.
Use a battery. One of the less-frequently-used but fully-supported use of the panels is to directly charge a battery. The panel electronics double as a charge controller; you can simply hook up the panels directly to the battery to be charged.
One caveat: the end voltage is programmed by default to around 56V, which is too high for a 13s but too low for a 14s if using Li-ion cells. Changing this requires recompiling the source and programming with a special tool, neither of which are available.
I’m currently working on a system like this with a 13s battery; I plan to make some sort of voltage-cutoff circuit to avoid overcharging the battery.
Use a battery-input inverter. I haven’t tried this but it should work. By simply using a large capacitor to take the place of the battery, any inverter that runs off a battery should operate, provided that the inverter doesn’t demand more power than the modules produce.
That's about it. If you have questions, I'm active on this forum. I really think the TenK system is pretty cool, but the lack of compatibility with standar solar components makes them troublesome.
There is a weird breed of solar panel made by an defunct Minnesota company called Ten K Solar. They operate very differently from the standard solar panel. Every now and then I see a post on the internet asking about these, so I'd like to share what I know about them.
I know this is probably going to help nobody on a battery forum, but some people might get here on a google search or whatever and I wanted to get this information out somewhere.
If you're from the North-Central US and you just got your hands on a second-hand, weird-looking solar panel, then you've come to the right place. For everyone else, this write-up is entirely useless but might be an amusing anecdote.
Ten K Solar (AKA tenksolar or just TenK) was a solar company founded in 2008 in Minnesota, USA. Leveraging some “interesting” design choices, they grew out of the start-up phase thanks to some state incentives in place at the time. I joined the company in 2015, and left just before they shut down in 2017. (Many reports claim that Tenk went out of business due to the unreliability of the inverters. While there were definitely inverter troubles, the real issue was simply the difficulty in maintaining cost-competitiveness.)
Since I left before the shutdown happened, I don’t know what happened to all the company’s assets when they stopped operation. Specifically, the company owned a lot of unique IP which may be lost forever for all I know. I didn’t have the forethought to secretly take a copy of the source with me so the following is based on what I remember.
The short version of TenK’s design is “put it all in parallel”. Specifically regarding the latest 500W “Apex” modules:
Cells: half cells in a 25s8p configuration. The parallel cells are from bottom to top and series from left to right; this way if the bottom row is shaded (as they often are in order to get panels close together), it doesn’t interrupt the string.
Internal electronics: The plastic housing contains a MPPT boost converter to go from the ~15V cell voltage up to ~56V. The converter itself is an 6-unit interleaved boost converter (6 converters in parallel).
String connections: Around 10-15 or so modules are wired in parallel. The limiting factor is the amount of current that the wire can handle. #2 aluminum wire was the most common.
Inverters: The string of modules were wired to 10-12x ~700W micro-inverters wired in (you guessed it) parallel. The inverters were off-the-shelf units modified by the OEM to run in constant voltage mode (instead of MPPT).
Because of the integrated electronics, the TenK modules can’t be used in normal solar systems. In order to even get the module to produce power, it needs to be presented with a valid load. A load can be either:
A voltage source, such as a battery, or another module that has already started up. I forget the exact voltage requirements but I think anything between 20-55V would be acceptable.
A large (1000 uF+) capacitor, such as would be present on the input stage of a microinverter. There's a precharge step so the anything connected to the cap will need to wait a couple seconds before drawing power
So options for using these panels:
Find a Modified micro-inverter. This might be hard since they're not made anymore and they weren't perfect even when they were. LeadSolar and APS built them. Some of the companies that own the arrays do get inverters as replacements and I have a contact at one of them, so it may be possible to get some at full price.
Use a Standard Microinverter. You’d need something with a 60V input voltage. The interaction between the inverter MPPT and the panel electronic’s output tends to be unstable. It may be possible to improve it with some filtering between the two devices but we never experimented with this.
Use a battery. One of the less-frequently-used but fully-supported use of the panels is to directly charge a battery. The panel electronics double as a charge controller; you can simply hook up the panels directly to the battery to be charged.
One caveat: the end voltage is programmed by default to around 56V, which is too high for a 13s but too low for a 14s if using Li-ion cells. Changing this requires recompiling the source and programming with a special tool, neither of which are available.
I’m currently working on a system like this with a 13s battery; I plan to make some sort of voltage-cutoff circuit to avoid overcharging the battery.
Use a battery-input inverter. I haven’t tried this but it should work. By simply using a large capacitor to take the place of the battery, any inverter that runs off a battery should operate, provided that the inverter doesn’t demand more power than the modules produce.
That's about it. If you have questions, I'm active on this forum. I really think the TenK system is pretty cool, but the lack of compatibility with standar solar components makes them troublesome.
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