Author Topic: Solar window blinds  (Read 2149 times)

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Offline IanMacdonald

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Solar window blinds
« on: August 26, 2017, 04:59:09 pm »
https://www.indiegogo.com/projects/solargaps-energy-generating-smart-solar-blinds

The principle is not at all unreasonable, and I've on occasion slung a 20W panel behind a window to charge a battery. As such, it works.

"Once installed over a window (inside or outside), the smart blinds with built-in solar panels can generate up to 100W of energy per 10 sq. ft. (? 1 m2) "

OK, that sounds about ballpark, a square metre of PV gives about 150W max if at optimum angle, and since this probably won't be optimally angled, 100W is a reasonable assumption.  However, they then say:

"For example, a three-room apartment with four windows of 2 sq.m. (about 20 sq. ft.) each facing south may be able to produce on average 7 kWh a day / 210 kWh a month assuming average daylight of 8.5 hours a day."  ???

The mention of South-facing windows suggests a Northern latitude, since South-facing windows wouldn't get much sun if on the equator.  However, Northern latitudes don't get anything like 8.5 hours of strong sun per day, averaged over the year. Neither would the equivalent Southern latitude.

The typical yield in Northern Europe is about 2kWh per kW of installed capacity, per day, averaged over the year. So, a realistic claim for 8 sqm of panel at 100W per sqm (their figure) would be 2x800W, or about 1.6kWh per day on average.  In equatorial regions you are going to hit the problem of the vertically-placed panels being poorly aligned to the sun. Tilting panel sections can only compensate for this up to a point, since you end up with sections shadowing each other. I'd take a guess that you might double the European figure in a few really sunny places, but that's still way short of the claim. 

Thus, that 7kWh figure does seem like a serious overstatement of its capability. Anyone care to check my math?

Oh, and: "ENERGY REDUCING - In addition to generating solar energy, the window blinds also save energy by shading your home interior and reducing air condition cost by up to 80%. " Seems unlikely. Black solar panels placed in a sunny window become, in effect, a solar room heater. If you want to keep the heat out, you need white or reflective blinds.

Obvious issue here is that buyers will be expecting a return on their investment, which by all accounts is not far short of the cost of a rooftop install.
« Last Edit: August 26, 2017, 05:14:54 pm by IanMacdonald »
 

Offline Refrigerator

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Re: Solar window blinds
« Reply #1 on: August 31, 2017, 08:31:08 pm »
Looks like a fun gadget, maybe a little battery in the base unit could help store the energy it produces.
I guess this could produce about enough energy to charge a couple phones on a pretty sunny day.
Since i didn't bother reading through the KS campaign (who does) i assume it comes down when the sun starts shining, which seems quite handy and would probably give you that futuristic vibe in your room.
Let's hope this has some software to keep it from constantly going up and down on a mildly cloudy day.
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Offline fievels

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Re: Solar window blinds
« Reply #2 on: September 01, 2017, 04:39:27 am »
so... it just plugs right into the wall??  :scared:  what happens when there is a power outage and your house feeds back onto the grid?   Does the inverter stop working during a power outage??  If so, the video showing the house enjoying power during an outage is incorrect.

 The step-down transformer near your home becomes a step-up transformer when electricity is going the opposite direction.  And, the more homes doing this.. the more dangerous it's going to be to the guy working on the line to repair your outage.

Is there something i'm missing?  ...because, they need to tell people that, or...  I mean, how else will we know who to charge with the 2nd degree murder penalty? 


edit: clarity
« Last Edit: September 01, 2017, 05:36:26 am by fievels »
 

Offline fievels

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Re: Solar window blinds
« Reply #3 on: September 01, 2017, 02:27:25 pm »
also, the thing about over-lapping panels is that they cause self-shading.   ..it says it will charge your phone.  It doesn't say how fast it will charge your phone.
« Last Edit: September 01, 2017, 02:59:50 pm by fievels »
 

Offline David Hess

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Re: Solar window blinds
« Reply #4 on: September 01, 2017, 06:15:24 pm »
so... it just plugs right into the wall??  :scared:  what happens when there is a power outage and your house feeds back onto the grid?   Does the inverter stop working during a power outage??  If so, the video showing the house enjoying power during an outage is incorrect.

Grid tie inverters are deliberately designed to shut down if AC power is lost.
 

Offline RGB255_0_0

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Re: Solar window blinds
« Reply #5 on: September 01, 2017, 08:17:26 pm »
so... it just plugs right into the wall??  :scared:  what happens when there is a power outage and your house feeds back onto the grid?   Does the inverter stop working during a power outage??  If so, the video showing the house enjoying power during an outage is incorrect.

Grid tie inverters are deliberately designed to shut down if AC power is lost.
That's what he's asking. Are there any smarts in the device to shut the output if there is no mains detected. The campaign states:

DIY PLUG & PLAY - With apartment renters in mind, the interior wall brackets are designed as a non-permanent, plug & play solution with additional installation options for homeowners to maximize energy production.

and then

Sell To Grid - With a two-way meter from your utility company, you can sell your surplus energy by supplying it to the power grid during the day when the demand and price is higher.

Many renters are unlikely to get permission to install a new meter and any costs would be paid by the tenant. Makes it uneconomical for the 6-12 month lease holder.

Nonetheless, I actually like this as a product and would be interested in its efficacy. The prices are outrageous though!
Your toaster just set fire to an African child over TCP.
 

Offline David Hess

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Re: Solar window blinds
« Reply #6 on: September 01, 2017, 10:57:53 pm »
so... it just plugs right into the wall??  :scared:  what happens when there is a power outage and your house feeds back onto the grid?   Does the inverter stop working during a power outage??  If so, the video showing the house enjoying power during an outage is incorrect.

Grid tie inverters are deliberately designed to shut down if AC power is lost.

That's what he's asking. Are there any smarts in the device to shut the output if there is no mains detected.

If it is designed for a direct connection to the AC grid, then it will almost certainly shut off if AC power is removed.  It would take a special effort to design a grid tie inverter which does not and offhand I do not know of any with only one AC connection which will not shut off when grid AC power is lost.  The others use separate AC connections for the grid and a backed up inverter output which will attempt to continue operating without the grid.

There are regulatory standards for the conditions under which a grid tie inverter must disconnect and that hopefully they will follow.  Given how grid tie inverters work, it is not difficult.  Keeping them connected is the problem although not a difficult one since they follow the very low impedance signal from the power line and this is what makes them effectively disconnect automatically.
 
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Online blueskull

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Re: Solar window blinds
« Reply #7 on: September 02, 2017, 01:04:20 am »
So, their $1125 offer provides 2.3m2 of area, probably max 2m2 of active area, that translates to 2kW of insolation power.
Assuming they are using a very good solar panel, say, 22% SunPower, then one panel converts 440W of peak power.
If average power of 300W for 8 hours, then the system dumps 2.4kWh per day, that's ~$0.2 per day.
In other words, the system needs to be run for 5000+ days to recover the cost, but I can't see it lasts that long.
In fact, if factoring in depreciation, it may never recover its cost.
 

Offline fievels

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Re: Solar window blinds
« Reply #8 on: September 02, 2017, 04:21:04 am »
so... it just plugs right into the wall??  :scared:  what happens when there is a power outage and your house feeds back onto the grid?   Does the inverter stop working during a power outage??  If so, the video showing the house enjoying power during an outage is incorrect.

Grid tie inverters are deliberately designed to shut down if AC power is lost.

That's what he's asking. Are there any smarts in the device to shut the output if there is no mains detected.

If it is designed for a direct connection to the AC grid, then it will almost certainly shut off if AC power is removed.  It would take a special effort to design a grid tie inverter which does not and offhand I do not know of any with only one AC connection which will not shut off when grid AC power is lost.  The others use separate AC connections for the grid and a backed up inverter output which will attempt to continue operating without the grid.

There are regulatory standards for the conditions under which a grid tie inverter must disconnect and that hopefully they will follow.  Given how grid tie inverters work, it is not difficult.  Keeping them connected is the problem although not a difficult one since they follow the very low impedance signal from the power line and this is what makes them effectively disconnect automatically.

Okay, I get it.  Power goes down.. Inverter shuts off and DC is allowed to bipass the inverter.  And, you can run your DC appliances.  So, your fridge is down.. but you still got wifi.  works for me.

I kind of like the idea of switching our homes to run off DC.  Power electronics has progressed to the point that we don't really need transformers anymore.  Most of our household devices runs off of DC.
 

Online NorthGuy

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Re: Solar window blinds
« Reply #9 on: September 02, 2017, 03:05:55 pm »
Thus, that 7kWh figure does seem like a serious overstatement of its capability. Anyone care to check my math?

My panels are roughly 360 sf and carefully positioned to the South. At the sunniest day in the middle of the summer (and we have long days here) they probably can produce 30 kWh, which is roughly 80 Wh/sf. If installed vertically, this might be 50 Wh/sf, much worse if you go closer to equator because the Sun is higher over the horizon. Also, just a little bit of a shadow from eves or trees will kill it completely - you'll be lucky to get 10% of full sun exposure.
 

Offline David Hess

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Re: Solar window blinds
« Reply #10 on: September 02, 2017, 04:36:05 pm »
I kind of like the idea of switching our homes to run off DC.  Power electronics has progressed to the point that we don't really need transformers anymore.  Most of our household devices runs off of DC.

DC has a myriad of problems compared to AC.  Unlike DC arcs, at high power AC arcs are self extinguishing so special connectors, switches, fuses, and circuit breakers need to be used for high power DC.  DC motors are more complex than AC motors.  DC impedance conversion is more complex than AC impedance conversion which only requires transformers.  Complexity yields lower reliability.

Big household loads like motors and heating all work fine on AC.  Only a minority of applications can take advantage of variable speed motors for a worthwhile increase in efficiency and the cost of AC to DC conversion only applies to them.  Use only DC and instead you are paying the cost of DC to AC conversion on every motor.
 


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