DIY Solar power?

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Bill Clemmons

Bill
Corporate Member
Certainly looks interesting. Wonder how much power each panel can provide? Enough to run a few appliances, or run a whole house? Might be worth looking into when they come out next year.

Thanks for sharing.

Bill
 

ehpoole

Administrator
Ethan
If I had to guess, an amorphous panel the size of the awning pictured woud likely be no more than 100 watts. In most parts of the country you'll average 5-6 hours of optimal energy generation, so on the order to 0.5 to 0.6KWH/day, though there is no reason you could not add additional units to up that total.

I would love to go off-grid, but with my servers, A/C (which, thanks to the servers, even has to run during winter months when it is 15F outside!), I would need a minimum 120KW of daily generating capacity to meet our 70-100KWH of daily usage. I would also need 200-300 KWH of storage capacity and 40-60KW of inverter capacity. Hopefully this becomes an affordable goal one of these days when new solar cell designs bring the price to $0.10/watt to $0.15/watt.

At least I can dream!
 

NCGrimbo

NCGrimbo
Corporate Member
I'd be wary of the claims this guy is making. When asked how long it would take for the panels to pay for themselves, he says four years or less. But in the next paragraph he says the $600 panel saves about $50 a year. Do the math and it means the $600 panel will take 12 years to pay for itself, not 4 or less. And looking at his company's website, this panel is their 200W panel. I wonder if it would really save $50 a year.

I'm not an EE, but I would think you would have to add some sort of protection between the home and the power grid if you are feeding power from the panel directly into your home's electrical system. I may be wrong in this, though.

I've looked into getting solar panels, and if I lived in Chapel Hill, the loan program they have there would make it worthwhile. But the article is correct in saying that you need over $20,000 to get a good solar system up and running. And by good, I mean one that has a chance of reducing power usage by 50% or more.

I'm not convinced that his solution would be worth doing over spending the money to get a full system installed. I think he's just targeting people that want to be able to say "I'm green. I have solar power" but don't want to sink the money into a full system.
 

thrytis

New User
Eric
My guess is their payback time takes into account the federal and state rebates, which the article is estimating the cost post rebate of under $200.

It sounds like the way they avoid having protection between the home and the power grid is the panels require the power grid to be delivering power to the panel for it to work. If the power goes down, your solar panels are useless.
 

Gotcha6

Dennis
Corporate Member
Regardless of the panel size & output it would have to include some type of frequency converter to get the DC power of the panel to alternating current. It would also require a phase synchronization system to apply the power to the circuit at the appropriate time in the power cycle. I'm assuming it does all this by capacitors & reading the frequency pulses from the grid/receptacle. I'm not an EE either, but it sounds a little more complex on the manufacturer's end than plug 'n play for the average homeowner.
Like most new things, I'd like to see a track record before I jump on the bandwagon. I bought one of the first Vegas. :gar-Cr
 

ehpoole

Administrator
Ethan
Although I haven't studied the grid-tie inverters terribly much (and micro-inverters even less so), the simplest approach to ensure power isn't injected into the grid during outtages (backfeeding the grid and creating an electrocution risk for line crews and neighbors) is to simply skip a half-to-full-cycle every few seconds to sample the utility power and verify that the grid is still live. If no grid voltage is detected during this 1/120 to 1/60 second interval, then the inverter would simply shutdown until such time as grid voltage is once again detected (for some pre-defined minimum period).

As for phase syncrhonization, that is a very trivial task for an inverter, you merely need a timing lock (PLL or otherwise, 60hz isn't a difficult frequency for a modern crystal-locked microcontroller to maintain with regular resync intervals) synchronized to the utility's grid, which you can easily resync with at the zero crossover during your already necessary half-cycle pause to verify a live grid.

Any higher-end online UPS (such as those backing up my servers) will do this already since they regularly have to take up precisely where the utility leaves off during power interruptions and transients. Cheaper UPS's, however, don't bother with synchronization since they don't activate until some number of milliseconds after power is lost -- they just allow the end-device's power supply deal with the distortions and harmonics momentarily created by the transfer event.

I'm sure there are others who can think up more novel ways to sense utility power loss, but the above is by far the simplest (and likely cheapest) way to do so since there is no penalty for a micro-inverter to skip a half-to-full AC cycle every few seconds.

I'm not an EE either -- would have been if health hadn't force me to withdraw from college 3 times. I am, however, a very avid electronics enthusiast (and have been since age 8). Though, woodworking has been monopolizing my time lately.

As for claiming the awning is a 200-watt panel -- only if you build your house in the middle of a laboratory! Aside from the curvature of the awning (which is only optimal at noon local time), I don't know of to many homes with suitable locations for awnings which have been optimally desined for maximum solar capture! You might conceivably get 200-watts if the awning is optimally placed over a door/window on an unobstructed southern wall finished with highly-polished stainless steel for an exterior siding.
 
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