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After 3 years of suggesting , answering questions, homework, etc ... Where I work finally had their commercial Photovoltaic power system on the buildings roof go live a short time ago.

:D

  • Utility limited to a max of 495kw AC output at any one time.
  • (Pending weather) year 1 energy output estimate of ~619MWH AC.
  • Power warranty (pending Weather) minimum of ~543MWH AC output for the 25th year.
  • ~20.3% (yr1) Sunlight to DC efficient SunPower Panels ( 1,596 Panels )
  • ~96.9% (yr1) DC to AC efficiency Sunny Central Inverter ( 1 Inverter )
  • Estimated to pay for itself in about ~7 years.
  • After it pays for itself (~7years) 25 year warranty has another 18 more years of production.
  • System coincided with a new roof on the entire facility (new roof also has a 25 yr warranty).
  • Ballasted non-penetrating panel racking system
Good Stuff
:D
 

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Wow, and thats pretty far nawrth, Rhode Island, right? :)

I need to check my little array. I won 2 gtis on ebay that have a lower cut off voltage vs the ones I have, same efficiency. I had hope they would make more usable power in low light.

Last month my power bill went up 50 bucks. Im assuming part is more heating and other half is less sun. Maybe a 60/40 or 75/25?
 

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Discussion Starter #3 (Edited)
Wow, and thats pretty far nawrth, Rhode Island, right? :)

I need to check my little array. I won 2 gtis on ebay that have a lower cut off voltage vs the ones I have, same efficiency. I had hope they would make more usable power in low light.

Last month my power bill went up 50 bucks. Im assuming part is more heating and other half is less sun. Maybe a 60/40 or 75/25?
If you wanted to precise fraction you could see where your average temperature and sun have changed... but winter is a double hit ... just like you said ( less sun and colder ).

- - - - - - -

Yup, RI.

And it is not a max / best possible array.
Instead it's a compromise cost vs benefit as part of many interconnected parts.

If they had maxed it out ... it would have been as much as a 2,136 panels and combined with a slightly better SunPower X21-345 would have bumped it up to 21.5% PV efficiency for a total roof max of about ~737kw ... combined with ideal tilt and tracking the ~600MWH per year could have been at most as high as ~4.2GWH ( as much as ~7x what is there) but like most things in life ... it becomes a question of cost vs benefit... for here the best cost vs benefit was for the system they put in.

But even with not ideal ... a ~7 year estimated pay back is pretty good for a system with 25 year warranty ... and longer than that potential service life... and ~600 MWH per year is a significant amount of electrical energy.
 

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Is the break even point calculated or guestimated? I know many states out west the utility is tiered. So up to 500 thousand watts maybe 13 cents a kiiowatt, then once you go over its more and goes up several tiers til almost 50 cents a kilowatt.

We may pay 10 cents a kilo, but we are also charged a "service Fee" and its pro rated based on the kilos used and ironically its the same prce with a min 20 dollar charge.

This year Id like to try something with steam, a steam engine and an alternator with a gti. Im sure it wont break even like solar will in general, but it would be a neat hobby to have a solar powered generator. :D
 

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I'd guess that with a 1600 panel installation, they probably did some significant calculations and probably weren't spending much time saying "well.... it'll probably pay for itself."
 

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Just wondering as many give the similar estimate. I spent several months testing live with a panel off and on, then the whole array.I did however poorly underestimate the winter output and the month of December is the worse.
 

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Discussion Starter #7
Is the break even point calculated or guestimated?
It's a bit of both.

It is calculated. But it makes certain assumptions ( guesses ) about the future weather conditions and such. Although those future weather predictions are based on past historical trends, and they are a bit on the overly conservative side, the future is always a bit of a guess.

I know some of the financials , but not all of them.
The final financial deal was done behind closed doors between the owner of our company and the owner of the solar installations company.

I know historically ( sense 2009 ) the company had paid on average around ~$0.155 per kwh for grid electric.... highs up to $0.18 and lows down to $0.14 ... the $/kwh rate charged per month varies month to month.

I know the RI Utility company would not let them go over 495kw of AC output. The SunnyCentral inverter had to be programmed to never ( even under ideal conditions ) allow more than 495kw AC to be output from the system. At one point in the system options 698kw system was proposed ( Utility grid flat out rejected that proposal ).

I know they had tried for over a year to get into the RI Utility Grid's system for getting paid a 'green' rate for the kwh the Solar system produced. Those that get that can get up to like $0.28 per kwh they produce , while only buying what they need for regular ~$0.14 per kwh rates. That would have accelerated the whole thing allot. But the utility company kept fighting them, backing out of contracts, violating RI state policy etc ... and unfortunately... in RI if the Utility wants to get out of something the whole State Legislature passed all they has to do is get the majority of those sitting on the oversight comity to agree. Which is crap, but oh well.

Anyway.... so after a lot of fighting with the utility grid they just chose a straight net metering agreement which had less options for the utility grid to fight them on ... but it means it's a 1 for 1 even trade ... no additional 'green' power benefit from the utility company.

Sense they weren't getting additional $ from the utility company the company is able to sell renewable energy credits to other companies who want to ... at least on paper ... reduce their carbon foot print ... even if they aren't actually reducing their carbon foot print.... of course the prices for renewable energy credits vary also... they make an estimate (based on historical trends) used in their calculations , but prices change... future is not set and known... I've seen renewable energy credits vary from as low as $3/MWH to as much as $680/MWH.... AFAIK RECs are only sold in 1MWH units. although it is yearly production.... so a home system that produced 1MWH over a year could sell them as well ... in addition to having a lower electric bill.

A conservative estimate would put the average yearly output over the 25 year warranty period as ~572MWH at just $0.15 per kwh ... that's over $2.1 Million in direct conservative electrical savings ... as electrical rates increase over the next 25 years this savings increases with them ... then on top of that there is also a tax right off for depreciation which is additional $ back you would have otherwise had to pay for taxes if you didn't have such a system to depreciate ... then there is the other $ back for the selling of the renewable energy credits.

Even without the additional 'green' selling of the kwh themselves to the grid ... it isn't too hard at all for the system to pay for itself.

I know initially early on around ~2 years ago the first installer numbers were around ~$2.80 per watt ... I know it was reduced to less than that in the end ... but I do not know by exactly how much to exactly what finial price.

December will be the lowest expected output month ... historically the lowest solar input for this location ... the 495 kw system might only do around ~30MWH for an average December ... of course that will fluctuate ... with some years doing better than average and other doing less.... and July will be the highest output.... +/- normal weather fluctuations.

This year Id like to try something with steam, a steam engine and an alternator with a gti. Im sure it wont break even like solar will in general, but it would be a neat hobby to have a solar powered generator. :D
definitely neat ... and I wouldn't rule out the potential to break even... it will of course depend completely on the details of costs, design, etc .... but solar heat collectors convert much higher % of the solar light energy to heat than PV convert the light energy to electricity... some solar to heat systems are over 80% light to heat efficient.

So First I would use the heat as heat for hot air and hot water... that's the biggest bang for the buck.

Then second if you have surplus solar heat collected ... If you're careful you could reasonably get up to ~30% stream ( heat engine ) efficiency from heat to mechanical shaft power ... a good generator can do over 90% from that mechanical to electrical ... and you are reasonably in the range of around ~21% sun light to electrical output.... so from an energy efficiency point of view ... it might be competitive.... just a question on what it will cost you ... and what kind of performance you can get for that $ investment.
 

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Yeah, preheating water for heating like under floor loops or hot water for use in cooking, cleaning, etc would be the biggest benefit. My mother just ask I do not fool with the roof , plumbing or electrical. That kind of limits me to stuff thats ce, ul approved or a self contained system. :D
 

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Discussion Starter #9
Yeah, preheating water for heating like under floor loops or hot water for use in cooking, cleaning, etc would be the biggest benefit. My mother just ask I do not fool with the roof , plumbing or electrical. That kind of limits me to stuff thats ce, ul approved or a self contained system. :D
I guess that leaves the windows ... the exterior of outside walls ... and the ground / yard as potential installation locations.
 

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Ive wanted to make a solar window heater. Its like a window ac unit, but it uses solar for powering the fan and heating a box or intercooler like.
 

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Discussion Starter #11
Ive wanted to make a solar window heater. Its like a window ac unit, but it uses solar for powering the fan and heating a box or intercooler like.
1,000 Watts per square Meter ... even at just ~80% efficiency , that's still 800 Watts of heating power per square meter.
 
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