Thoughts on TekK solar panels?

[pleppik]

I'm planning a new solar installation this spring, and my installer has suggested a system built around modules from TenK Solar.

I've been reading some of the company's marketing literature, and the TenK modules seem to be a very different architecture than is usual in the solar world today. They do the MPP tracking in the module itself, and the company claims they get something close to optimal output even when part of a module is shaded.

They also output DC from multiple modules to a low voltage (60V) DC bus, with multiple inverters attached to the DC bus. But since there's not a 1:1 relationship between inverters and modules as you would have for microinverters, they claim they can do some magic to bring inverters on- and off-line to reduce the duty cycle for each inverter and reduce their chance of failure.

For our home, our installer is quoting us a system with TenK modules for about a 10% per watt premium over a more traditional microinverter-based installation.

The claim that TenK makes is that their modules will give us a higher yield per watt than a traditional architecture (we have some partial shading issues)--our contractor says he can't quantify this but it sounds plausible. TenK also claims that their architecture will be more fault-tolerant if an inverter fails, since other inverters will be able to take over, and also that the reduced duty cycle on the inverters will prolong their lives.

Has anyone had any experience with the TenK system? Is this a product worth a (modest) premium?

[russ]

Has anyone had any experience with the TenK system? Is this a product worth a (modest) premium?

The real question - Is it worth taking any risk on? I say no. A lot of their sales pitch is blather and part doesn' make sense.

Look for another installer. This guy has problems.

[pleppik]

Look for another installer. This guy has problems.

I'm disappointed with this response. I was hoping for someone with some real insight and/or experience around this product to offer some actual thoughts in response to the question.

I also find the attitude rather surprising--that I should fire my installer because he offered me an unconventional option which I found interesting enough to research further. For what it's worth, the other three options he provided are all very conventional.

So, back to the original question: Does anyone here have any experience with TenK modules? Is this a product which may be worth a modest premium?

If nobody is familiar with this, that's fine.

[russ]

I'm disappointed with this response.

Be as disappointed as you like - makes no difference.

From an industrial background, no one wants to be first to try a new product - customers are often burned. Even the microinverters/optimizers on the market with name and a few years are short on proof of what will happen.

[pleppik]

Be as disappointed as you like - makes no difference.

From an industrial background, no one wants to be first to try a new product - customers are often burned. Even the microinverters/optimizers on the market with name and a few years are short on proof of what will happen.

Russ:

I agree that "no one wants to be first to try a new product," but it's also true that by definition someone has to be first. Whether or not to go with a novel approach should be a calculated risk, which means gaining an understanding of both the risk and the potential benefit. I don't believe that the maximally risk-averse approach is always (or even usually) the right way to go. Otherwise, we'd never get out of bed.

So all that said...TenK is a new-ish company and they are taking a different approach, and that's why I'm hoping to find someone with actual knowledge and experience to help me in my decision making. If you have any data or experience with this company you can share, I would love to hear it and it would be extremely helpful. If you do not, you can consider me appropriately warned about the general risk of going with a relatively young company and a novel approach. After all, it's exactly those risks that made me come here in the first place.

[russ]

Trying a new vendor with a new product at a 10% premium does not come under any classification except one. If they offer a deep discount then maybe. Any claims by TenK about greater output are total baloney until they are backed up by third party testing - and that has to be a recognized third party - Not Joe's Bar & Grill + Third Party Testing.

[Naptown]

Russ:

I agree that "no one wants to be first to try a new product," but it's also true that by definition someone has to be first. Whether or not to go with a novel approach should be a calculated risk, which means gaining an understanding of both the risk and the potential benefit. I don't believe that the maximally risk-averse approach is always (or even usually) the right way to go. Otherwise, we'd never get out of bed.

So all that said...TenK is a new-ish company and they are taking a different approach, and that's why I'm hoping to find someone with actual knowledge and experience to help me in my decision making. If you have any data or experience with this company you can share, I would love to hear it and it would be extremely helpful. If you do not, you can consider me appropriately warned about the general risk of going with a relatively young company and a novel approach. After all, it's exactly those risks that made me come here in the first place.

So it is a brand new product with a limited distribution. The only projects were within 10 miles of their factory.
This is so new that most likely they are the only two installs they have or close to it. So no one really knows about them.

[pleppik]

Maybe a little more background would help explain why I'm researching this.

I live in the Minneapolis area, which isn't as good as Arizona for solar, but it's not horrible either. I've been tracking solar prices for over five years, all the while our power company has been raising rates at twice the rate of inflation. Last fall we decided that solar was close enough to grid parity that it was time to pull the trigger. We looked at a bunch of different installers, interviewed several, had multiple site assessments done, and got a lot of different proposals. We selected our installer because, in addition to being experienced and well-regarded by his competitors, he gave us realistic performance estimates for our challenging location (we have two roofs, facing SW and SE, and some partial shading issues) and was willing to show us exactly how this was going to cost us in productivity. So I'm comfortable that our installer isn't trying to sugarcoat our performance, and he's also not tied to a particular vendor or approach.

Minnesota recently passed a very generous "Made in Minnesota" solar credit for buying modules made by a Minnesota-based manufacturer. I wasn't a supporter of this when it was proposed (I don't think it's an efficient way to encourage the development of a local solar industry, and just encourages companies to overprice their products), but I'm not too proud to accept the money if it's on the table. However, last fall there was only one Minnesota-based module company selling into the residential market, and their modules were crazy expensive--to the point where even with the generous credit it was too expensive. So the initial design was with SolarWorld panels and Enphase microinverters (to get better yield with our partial shading).

Since then, however, TenK started selling its modules into the residential market--until now they only sold into the commercial and utility markets. TenK is also a Minnesota-based company, and so this product also qualifies for the state credit. The system engineered with TenK modules is about 10% more expensive per watt than the SolarWorld system, but since the TenK system can get the state credits it would wind up being considerably less expensive (between the federal and state credits alone, we will get back about 85% of the cost of the system). Based only on that, the TenK seems like an obvious choice.

But TenK is a new-ish manufacturer. Their architecture is very different from other companies', and this offers both risks and potential benefits. They have been selling a system which combines their special module design with north-facing reflectors on a flat roof. The reflectors help capture light which normally would fall in the gaps between rows of panels, and they have published data from a dozen test sites around the country (including NREL) over two years showing that they get about 30% more production per installed watt than a conventional design. The claim is that part of the improvement is in the reflectors, and part of it is their module design which allows them to get more power out of a module which isn't uniformly illuminated.

In our installation, we don't have the option of using the reflectors as it's on a sloped roof, but we're hoping that this design might give us a little more yield because--in theory--it should deal with partial shading more efficiently than a standard module.

I was hoping that someone here might have some more specific input to offer. I understand and share your apprehension about making a major investment in a system from a new company exploring a new approach. Given that, are there specific things I'm not appreciating here? For example, is there a reason not to put the MPPT in the module itself? Are there inherent problems with a low-voltage DC bus instead of a string inverter? Have these things been tried and abandoned for some reason?

[Naptown]

Maybe a little more background would help explain why I'm researching this.

I live in the Minneapolis area, which isn't as good as Arizona for solar, but it's not horrible either. I've been tracking solar prices for over five years, all the while our power company has been raising rates at twice the rate of inflation. Last fall we decided that solar was close enough to grid parity that it was time to pull the trigger. We looked at a bunch of different installers, interviewed several, had multiple site assessments done, and got a lot of different proposals. We selected our installer because, in addition to being experienced and well-regarded by his competitors, he gave us realistic performance estimates for our challenging location (we have two roofs, facing SW and SE, and some partial shading issues) and was willing to show us exactly how this was going to cost us in productivity. So I'm comfortable that our installer isn't trying to sugarcoat our performance, and he's also not tied to a particular vendor or approach.

Minnesota recently passed a very generous "Made in Minnesota" solar credit for buying modules made by a Minnesota-based manufacturer. I wasn't a supporter of this when it was proposed (I don't think it's an efficient way to encourage the development of a local solar industry, and just encourages companies to overprice their products), but I'm not too proud to accept the money if it's on the table. However, last fall there was only one Minnesota-based module company selling into the residential market, and their modules were crazy expensive--to the point where even with the generous credit it was too expensive. So the initial design was with SolarWorld panels and Enphase microinverters (to get better yield with our partial shading).

Since then, however, TenK started selling its modules into the residential market--until now they only sold into the commercial and utility markets. TenK is also a Minnesota-based company, and so this product also qualifies for the state credit. The system engineered with TenK modules is about 10% more expensive per watt than the SolarWorld system, but since the TenK system can get the state credits it would wind up being considerably less expensive (between the federal and state credits alone, we will get back about 85% of the cost of the system). Based only on that, the TenK seems like an obvious choice.

But TenK is a new-ish manufacturer. Their architecture is very different from other companies', and this offers both risks and potential benefits. They have been selling a system which combines their special module design with north-facing reflectors on a flat roof. The reflectors help capture light which normally would fall in the gaps between rows of panels, and they have published data from a dozen test sites around the country (including NREL) over two years showing that they get about 30% more production per installed watt than a conventional design. The claim is that part of the improvement is in the reflectors, and part of it is their module design which allows them to get more power out of a module which isn't uniformly illuminated.

In our installation, we don't have the option of using the reflectors as it's on a sloped roof, but we're hoping that this design might give us a little more yield because--in theory--it should deal with partial shading more efficiently than a standard module.

I was hoping that someone here might have some more specific input to offer. I understand and share your apprehension about making a major investment in a system from a new company exploring a new approach. Given that, are there specific things I'm not appreciating here? For example, is there a reason not to put the MPPT in the module itself? Are there inherent problems with a low-voltage DC bus instead of a string inverter? Have these things been tried and abandoned for some reason?

One issue I saw on the commercial roof was inter row spacing. The modules will shade the ones behind them even with the mirrors on the back slope at some point in the year particularly in Minnesota as shown in their website. Perhaps a bit more summer production but you will not have that extra bit provided by the mirrors.
Caveat emptor this is too new to make an informed judgement

[pleppik]

Through a friend-of-a-friend (and not through either my installer or the manufacturer), I've gotten connected with the guy who oversees and runs one of TenK's reference installations. This site has been in place through two Minnesota winters, and was put in place about six months or so after TenK first started shipping.

Any suggestions for questions I should ask?

So far, I've asked:

• Is the published performance data accurate? (yes)
• Can he confirm the claims about the inverter duty cycle? (no data)
• Have there been any problems? (yes--the first winter, a handful of comm boards failed and were replaced by the manufacturer. This is out of 200 modules. No other problems as yet)
• Overall impression of the company and product? (very positive)

He's also offered to give me a tour once things defrost a little up here. I'd love to hear ideas for things I should look for or questions to ask.

[bcroe]

Through a friend-of-a-friend (and not through either my installer or the manufacturer), I've gotten connected with the guy who oversees and runs one of TenK's reference installations. This site has been in place through two Minnesota winters, and was put in place about six months or so after TenK first started shipping. Any suggestions for questions I should ask?

I don't know anything about the company. Certainly individual converters will deal with shade better
than a string system. So do micros. But if you first convert to 60 VDC, then to 240 VAC, HOW can the
process be as efficient as a micro converting DIRECTLY to 240 VAC? And that is a lot of converters &
inverters to buy.

With all the money I have in copper wire at 240 to 400 V, I am trying to understand why they picked 60 V.
If you are collecting power at 60 VDC, you will need 16 times as much copper to hold wire losses to that
of a 240 VAC micro system. Or 4 times to match a 120 VAC micro system. The only reason I can see to
go this way, is to address safety issues now coming up regarding high outages.

The mirrors are interesting; reflection from snow makes power. But panels tend to absorb a lot more sun
than a mirror, helping clear snow. Mirrors need to be completely cleaned. I think I'd rather clear snow off
more panels, than mirrors. Mirrors will need expensive supports too, are they worth it? What material,
how do they like hail? Bruce Roe

[pleppik]

I don't know anything about the company. Certainly individual converters will deal with shade better
than a string system. So do micros. But if you first convert to 60 VDC, then to 240 VAC, HOW can the
process be as efficient as a micro converting DIRECTLY to 240 VAC? And that is a lot of converters &
inverters to buy.

Their claim is that by doing the MPP tracking inside the module, they can be much more efficient about harvesting every last joule of energy. The claim is that they are effectively doing MPPT down to the individual cell level.

So presumably the gains by doing this are greater than the losses from the extra DC-DC conversion. In this respect, it would be no different than having a DC optimizer, but more fine-grained.

I'm just channeling what I understand their claims to be--I'm not enough of an expert to verify any of this of course.

With all the money I have in copper wire at 240 to 400 V, I am trying to understand why they picked 60 V.
If you are collecting power at 60 VDC, you will need 16 times as much copper to hold wire losses to that
of a 240 VAC micro system. Or 4 times to match a 120 VAC micro system. The only reason I can see to
go this way, is to address safety issues now coming up regarding high outages.

According to their literature, they picked 60V because it's considered low voltage and avoids a lot of safety equipment required for higher voltages.

As for the wire losses, this is something I actually know something about. They're using a power bus with multiple microinverters, not a single long cable to a central inverter. Imagine a pair of fairly beefy wires, and along the length of the wire you attach both the modules and the inverters, interspersed among each other.

So even though the system as a whole might be carrying a lot of power, each point along the power bus carries only a modest amount of power, and the distance between power source and sink is fairly short. So the DC current loss should be quite low.

The mirrors are interesting; reflection from snow makes power. But panels tend to absorb a lot more sun
than a mirror, helping clear snow. Mirrors need to be completely cleaned. I think I'd rather clear snow off
more panels, than mirrors. Mirrors will need expensive supports too, are they worth it? What material,
how do they like hail? Bruce Roe

Not actually mirrors--they're plastic panels coated with some sort of reflective material. I think it's entirely plausible that they're fairly light weight and darn near indestructible.

The rationale is that plastic panels are a whole lot cheaper than the extra solar modules needed to give the same increase in total output.

I'm not sure about clearing snow from the panels. That's a good question to ask.

[bcroe]

their claim is that by doing the mpp tracking inside the module, they can be much more efficient about harvesting every last joule of energy. The claim is that they are effectively doing mppt down to the individual cell level.

So presumably the gains by doing this are greater than the losses from the extra dc-dc conversion. In this
respect, it would be no different than having a dc optimizer, but more fine-grained.

I don't believe doing mpp at the cell level is either practical or useful. Or that the "gains" are greater.

According to their literature, they picked 60v because it's considered low voltage
and avoids a lot of safety equipment required for higher voltages.

I can relate to that, maybe they are trying to prepare for future regulations.

As for the wire losses, this is something i actually know something about. They're using a power bus with multiple microinverters, not a single long cable to a central inverter. Imagine a pair of fairly beefy wires, and along the length of the wire you attach both the modules and the inverters, interspersed among each other.

So you have a number of small systems internally connected at 60 VDC, and the burden of power and distance
is put on the AC "bus". The AC must still be singly brought to a feed point properly current protected. I don't
believe having a single long 60 VDC bus incapable of all generated current is a safe & workable design without
elaborate "protection" disconnect stations. Here that would be 250 A.

So even though the system as a whole might be carrying a lot of power, each point along
the power bus carries only a modest amount of power, and the distance between power source and sink is fairly
short. So the dc current loss should be quite low.

See above.

not actually mirrors--they're plastic panels coated with some sort of reflective material. I think it's entirely plausible that they're fairly light weight and darn near indestructible.

The rationale is that plastic panels are a whole lot cheaper than the extra solar modules needed to give the same increase in total output.

I'm not sure about clearing snow from the panels. That's a good question to ask.

OK. Bruce Roe

[russ]

Maybe a little more background would help explain why I'm researching this. Would have been nice to start with

Since then, however, TenK started selling its modules into the residential market-we will get back about 85% of the cost of the system). Based only on that, the TenK seems like an obvious choice.The real reason and not a bad one

But TenK is a new-ish manufacturer. over two years showing that they get about 30% more production per installed watt than a conventional design.

I doubt their 30% number - depending on how testing is set up you can often prove most anything either way - It seems you have made your decision but want others available to blame it on.

First Solar is in trouble again - no one has ever heard of TenK in the market and several read most articles about industrial as well as residential manufacturers.

[pleppik]

I doubt their 30% number - depending on how testing is set up you can often prove most anything either way - It seems you have made your decision but want others available to blame it on.

First Solar is in trouble again - no one has ever heard of TenK in the market and several read most articles about industrial as well as residential manufacturers.

Well, having a special incentive which pays so much of the system does go a long way towards helping make a decision. That doesn't mean I shouldn't do my due diligence. Heck, if they offered to give it to me for free I would probably still be here asking the same questions.

I'm curious why you would be so skeptical of their claim that they can yield 30% more power by reflecting more light onto the modules. That hardly seems like snake-oil on the face of it, and I usually have a reasonably well-tuned BS detector. I'm not saying you're wrong, I really want to understand--they're making what seems to me to be a fairly reasonable (maybe even kind of boring) claim, they published data from NREL and others which backs up the claim, I even talked to the guy who runs one of the sites where they got the data from. What am I missing?

I'm not sure how First Solar is relevant here. First Solar predicated its business on the assumption that silicon would always be expensive, and when the price of solar-grade silicon wafers collapsed a couple years ago they were doomed.