IBM - Welcome to the Thunder Dome II

I've been meaning to discuss and size up the IBM hybrid attempt. I saw their cell/module cooling device for large high concentration dishes awhile back. take a look:

 

Illustration from a Whitepaper on the IBM Sunflower (hybrid CPVT)

What do you see? you see water inlets and outlets for a mission critical back side cooling array. That is the left/bottom side plumbing bits. We cannot see the very smart way they put a high flow highly conductive network for flowing very close to the back of the cells (the 9 dark squares) For size you can see the thermocouple plugs (grey with two different sized and colored blades) they are about a half inch wide (just checked, .66 inches or 17 mm which means those cells are 10mm/10mm.


This needs to be really heat hardy as the cells are supposed to be exposed to some 2000 suns. The paper (or some-other source, they are starting to run-together, sorry) says they are backside conductor cells. Those black faces, unlined by traditional front-side conductors, are confirmation of that.

The two thermocouples are there to monitor the coolant temperature before and after to regulate the flow of coolant. This of course means they have the traditional tradeoff issues that I am trying to avoid with frequency splitting. If the temp goes up the voltage goes down and the electric yield drops. So they are stuck with a lot of very warm water as a product. The good news is they have a vision of this as a very large device and some ideas about what to do with the warm water. More on that in the next post.

I saw some confused notions about using this for boiling water for desalination. The description in that story is pretty vague and has a real units of measure problem. Maybe a deadline pressure meets domain knowledge weakness caused it. Anyhow, further looking shows they have a reverse osmosis scheme (in separate equipment) that uses pressure rather than brute force boiling (which is why reverse osmosis and the related technologies are being explored in general: less energy intensive.) The cooling circuit needs to be closed to keep the high purity and reliability going behind the cells.

We'll look at the collector's reflector array next time.

You get more of what you measure...

I had not noticed SolarThermalWorld until today. Looks like PVT is in a ghetto there too. Still some good coverage of PVT with a thermal emphasis. Fair enough. This story got my attention and maybe it should get yours.

Story here 

here is what jumped out for me:

• So far, PVT collectors have not been included in the standard. But there is already a so-called extended scope, which means that they may be included later in a second part of the standard.
• Fluid-based collectors will see some changes in their testing procedures compared to EN 12975-2. The new standard regards the collector gross area as the relevant reference for all area-specific data, e.g., the yield per area. Until now, the reference used in Germany has been the aperture area, which has presented some difficulties in comparing collector data on an international basis.

PVT with its interaction between the energy streams is going to be tough to pin down. My design has low interaction between the "sides" which is great for me but all of the hybrids are going to need to represent the various modes of operation and the variety of operating temperatures is vexing.

Hawaii - way out font. In a bad way.

Greentech media has a pretty good intro to the current state of things in the USA's most built out PV market: Hawaii.

story here

Among the things that stand out are

1) Many circuits on Oahu that are 120% of Daytime Minimum Load.  Too much of a good thing?
2) Discussion of the end of Net Metering. (duh!)

Some more up to date comparisons...

I'm off to work on Rev 2 of the design but it seems appropriate to layout why it is worth the bother.

Here are some comparisons to two good examples to give context :

Kyocera 325W Polycrystalline Solar Panel KD325GX-LPB
and (the awesome)
SunPower SPR-X20-445-COM (445 watts!)

Fortunately they are both 2.19 square meters each so watts per square meter STC can be derived but a better gauge is PTC (avail here) which mostly accommodates the Temperature Coefficient in a more real world manner:

Kyocera's goes down to 290.4 for the panel and so 132.6 per square meter
Sunpower goes down to 412.7 for the panel and so 188.45 per square meter
vs
Hybrid V1 is 23 watts per tube and 128 per square meter

We could imagine those panels reformed as magic edge-less strips as long and wide as our tubes and get
23.9 watts per strip from the Kyocera
33.9 watts per strip from the Sunpower
vs
23.0 watts from our tube (setting aside the thermal for the moment) 

How to layout the hybrid value? Here is an attempt at a tote board, normalized to per square meter



Top scored cells BOLD

OR if you'd rather:
1 panel of 2.19 square meters (1.66m X 1.32 m = 2.19 m^2) ≈ 12 Hybrid Rev 1 tubes ( .18 m square each X 12 tubes  = 2.16m^2 of area)

More on Hybrid version 1:
The Hybrid collector's first design iteration was analyzed in part by BRO (http://www.bro.com/) This design revealed some shortcomings that I've attacked in the version two but the analysis of version 1 can serve as a "floor" for evaluation. The figures were good enough to keep going on... Some of the shortcomings of the rev one design and their easy resolution I'll cover later. But for now Rev 1 is the best understood as far as throughput. I think 20% of the losses in Version 1 can be clawed back but all of this post is about Version 1.

For a square meter of tubular collector 320 watts of visible light hit the PV cells in clear light. That light arrives on 10X10mm cells at 46,700 W/m^2 (46.7 Suns.) The 320 watts would hit 98 10mmX10mm concentrator cells in that design. and the cells should be able to operate at @66C or below. They could be expected to run at 40% (due to the rich diet and the high concentration/low temp.) that 320W*.40= 128w =12.8% efficient (started vs the 1000 Wm^2 total light) on the PV side in realistic atmospheric conditions. There are troubles with that 12.8% number but they cut both ways. The fraction of incident light captured in the heat components is about the same (340W) but the conversion is much more efficient ~80% at 160C output temp. So 340W*.80=272 or 27% on the thermal side for a net 39.8%

Some of the columns need explication:
Relative Performance on a Heat Load:
Cogenera (in a white paper) sees the _heat value_ as 25% of electric value in a Watt to Watt comparison when that heat is delivered at Domestic Hot Water Temps. Sounds fair. So 128+(272*.25)=196. I weighted them all at the Sunpower as 1 (the conversion losses in electric resistance heat being very low, these correspond to the Gross Efficiency number.)

Cooling Power in Watts:
Cogenra shows the way again in a paper "Cooling with Cogen" they find the value of high temp heat used in chilling service to be higher than plain old thermal DHW service due to the COP (coefficient of power) in double effect chillers. Thus we get the "Cooling power in Watts" comparison. In most cases I imagine those "Cooling Watts" would be Watts not used ("negawatts" generated at peak rates) and potentially freeing up watts from the electrical side to sell at those peak rates or to otherwise address demand charge problems. All subject to the particular installation conditions and metering contracts of course.

String vs Micro-inverters... I found a pretty good comparison.

Aussie Made Solar has a pretty good pro/con size-up of the micro-inverters (usually one per panel) and traditional string inverters (just one for the whole shebang.)

The biggest difference to me is the lifespan. The micro-inverters should last as long as the panels (25 years) while the string inverters are considered a success if they last 20% of that. But that is just one of the issues - they do a good job of thinking out several issues including the crew size.  Take a look and let me know what you think.

Oh, uparmoring the conduits for the highvoltage DC runs is also an expense that does not jump out until, well... it jumps out.

Securitizing Solar Backed Assets. Nice to see the rates are so reasonable

SolarCity announced some good news on their efforts to rap up parts of their business, sell them off as Securities and roll the money forward.

Street Insider has the story. They frame it as good news for SunPower and I suppose it is. Beating the rate you expected by 2% over a 13 year period is a pretty strong indication that your credit is good. So Congrats to SolarCity. I'm going to let them off the hook on predicting because it is a new market and until a match is found, it is just guess-work...

I'm foggy on how those instruments wrap up at the end. Who owns what. The security holders have their money back with the interest. I guess the contract for Power Purchase is still in play so the income still flows to SolarCity and there is no more debt to service... Maybe they can do it again?

Meyer Berger - Welcome to the Thunder Dome!

check 'em out:

A new flat panel hybrid from the Swiss company Meyer Berger.

One of the selling points is that they are made in Thune (Switzerland.)  In one of the press releases they are promoting its use as a geothermal probe recharge method. Smart. That would mean lower temps which means more electric production but the pumping cost are non trivial: 50 to 100 liters per hour (per panel) to keep it down to 80c. Obviously lower temps would require more pumping. The fittings are 10 mm diameter.

They reference vacuum technology but I do not see where it is folded into the design looking at the PDF cited above. It is patented but the patent may not be held by them? I could not find it.

Some more digging is in order I suppose.