shah269 0 #1 January 3, 2012 Ok guys some kids have asked me for something that's causing my brain to explode! While mentoring some student groups one of the kids had kind of a smart idea....that they raise money to buy solar cells for their school and in NJ every time a solar cell pumps out 1,000kWh or energy it produces a certificate that can be sold for about $400. The idea is that the kids buy solar cells to reduce the schools energy consumption and then sell off the certificates to fund "stuff". Not sure of the legalities of all this but the kids asked me a mechanical engineer how many solar cells they needed? Aaahhh.....ok now my brain is hurting? How the hell do you figure this out for a school in NJ? How many solar cells units do you need so that they produce 1,000kWh of energy per month? On an average month? And how much does a solar cell unit go for? All I can find when I google is things like max power. Which seems to be around the low 200 W. I could really use some help here...my brain is hurting and I'm about to give up and tell the kids it's not worth it.Life through good thoughts, good words, and good deeds is necessary to ensure happiness and to keep chaos at bay. The only thing that falls from the sky is birdshit and fools! Quote Share this post Link to post Share on other sites
Remster 30 #2 January 3, 2012 There are plenty of calculators online. http://www.mrsolar.com/page/MSOS/CTGY/ce http://www.solar-electric.com/linecard.htmlRemster Quote Share this post Link to post Share on other sites
PhreeZone 20 #3 January 3, 2012 You are a Zone 5 location: http://www.wholesalesolar.com/Information-SolarFolder/SunHoursUSMap.html That puts you on average at 4.2 solar hours per day. Take 1000 KWH divided by 30 to figure out how many KW's per day you need to generate. = 33.3 KWH per day Divide the KWH's needed per day by the solar hours per day 33.3 / 4.2 = 7.9285 KW per hour. This is the number you need to put in panels to generate that wattage under 100% ideal situations. Most systems are pretty inefficient so figure a 20-25% loss of power over the system and you are now looking at 7.9285 / .75 = 10.571 KW's needed to be installed. If you are doing flat and not motion tracking you will need more also. Price per watt on panels with out any tax credits or rebates range from $1.50 to upwards of $3.00 per watt. Rough cost is going to be 10571 watts * 1.50 = $15,856 plus install, shipping, certification, etc... I also assume you want a Grid tie so that you can draw power from the grid on cloudy days or pump power back to the grid on really sunny days. That is going to be a lot of money for a system that large. Here is a system that would be large enough to meet your requirements all for a low price of $26k... http://www.wholesalesolar.com/system/solaredge-50-astronergy-panel-gridtie-system.htmlYesterday is history And tomorrow is a mystery Parachutemanuals.com Quote Share this post Link to post Share on other sites
Andrewwhyte 1 #4 January 3, 2012 So the first link has a cool colour coded map of the US with the expected kwh/m3 values. How come Maine, Michigan and Puget sound are purple. The index doesn't even list purple. Quote Share this post Link to post Share on other sites
billvon 3,118 #5 January 3, 2012 >Price per watt on panels with out any tax credits or rebates range from $1.50 to >upwards of $3.00 per watt. If you don't care about rebates and warranties you can get Chinese panels for about $0.95/watt. Quote Share this post Link to post Share on other sites
Remster 30 #6 January 3, 2012 Quote So the first link has a cool colour coded map of the US with the expected kwh/m3 values. How come Maine, Michigan and Puget sound are purple. The index doesn't even list purple. Good thing they dont show Alberta! lolRemster Quote Share this post Link to post Share on other sites
quade 4 #7 January 3, 2012 Quote>Price per watt on panels with out any tax credits or rebates range from $1.50 to >upwards of $3.00 per watt. If you don't care about rebates and warranties you can get Chinese panels for about $0.95/watt. I don't want to go off on a rant here, but buy American.quade - The World's Most Boring Skydiver Quote Share this post Link to post Share on other sites
shah269 0 #8 January 3, 2012 so according to this, http://www.mrsolar.com/page/MSOS/CTGY/ce At NJ being 3.5 kWh/m^2 ..... hu...you know what's important...UNITS! WHERE THE HELL ARE THE UNITS? Hi what is this? 196 Output (AC kWh)? Is that per cell? OK so you get what 3.5 peak power hours of sun per day? In NJ? HU? How the hell is that! So it's 196(kWh)*3.5(h) = 591.5kWh/Day/WHAT! Cell? Is my math way off? Or should all numbers be designated with units as to what they are. Be it kW or kW/Unit? So say they buy the 1.84kW Online Solar Grid Tie System for $5k.....what does this mean? Kids when your professors scream at you for not including units when you do your work they are not joking...without units numbers are meaningless! ----------------------------------------------------------- PhreeZone Thank you that was great math! You rock! I'll use it to speak with the students! Thank you!Life through good thoughts, good words, and good deeds is necessary to ensure happiness and to keep chaos at bay. The only thing that falls from the sky is birdshit and fools! Quote Share this post Link to post Share on other sites
Remster 30 #9 January 3, 2012 What f'ing engineering school did you graduate from?Remster Quote Share this post Link to post Share on other sites
billvon 3,118 #10 January 3, 2012 >At NJ being 3.5 kWh/m^2 >hu...you know what's important...UNITS! WHERE THE HELL ARE THE UNITS? Right there. 3.5 kilowatt hours per day per meter squared total insolation. >196 Output (AC kWh)? Is that per cell? A Trina 230 outputs approximately 196 kWh per month in that location. >OK so you get what 3.5 peak power hours of sun per day? In NJ? HU? How the hell is >that! Because you have things like nighttime, winter and clouds out there in NJ. Over the course of a year you get an average of 3.5 hours of direct (i.e. noontime equivalent) sun. >So it's 196(kWh)*3.5(h) = 591.5kWh/Day/WHAT! Cell? You're starting to mix units there. Can't multiply a per-month number by hours. That makes no sense. >So say they buy the 1.84kW Online Solar Grid Tie System >for $5k.....what does this mean? That's pretty straightforward. 8 x 230 watt panels = 1.84kW total DC power out of the array (in full sun) >Kids when your professors scream at you for not including units when you do your >work they are not joking...without units numbers are meaningless! Yep. But all the units are there. Quote Share this post Link to post Share on other sites
shah269 0 #11 January 3, 2012 I'm saying it should be easier. Insert how much power you want on one end. where you live click enter stand back go get beer and out pops the answer. This is no way to sell to the average person. Just my thoughts. Ok so let's use the low number of $1.5 $/Watt costing $15,873 to procure a 1,000kWh system. So of those 4.2 hours of they day does it then produce 4,2000kWh? Never knew how much power schools consume!Life through good thoughts, good words, and good deeds is necessary to ensure happiness and to keep chaos at bay. The only thing that falls from the sky is birdshit and fools! Quote Share this post Link to post Share on other sites
PhreeZone 20 #12 January 3, 2012 QuoteOK so you get what 3.5 peak power hours of sun per day? In NJ? HU? How the hell is that! The strength of the sun power is what is being measured, sure the sun might be up for 9 hours during the winter but how much of that is behind clouds? Morning and evening sun is at an angle that does not allow for that great of absorption so you lose power there and all the other factors. This is no different than why does a 60 watt light bulb light up a bathroom but the same bulb in an arena would not be seen across the building let alone light up the room. Its all energy right? Most panels put out Watts, not Kilowatts.... most panels at 2 feet by 4.5 feet will put out at most around 250-300 watts. At 9 Square feet per panel you also need to figure out how much area is needed. Say 250 watts / 9 = 27.77 watts per SQ foot. 10571 watts / 27.77 = 380.57 SQ feet at a min needed and with the excess room and things like that figure 425+ needed. That's not huge but it needs to be on a south facing roof, not a flat roof. If its flat then you need to have racks built to have the panels face south.Yesterday is history And tomorrow is a mystery Parachutemanuals.com Quote Share this post Link to post Share on other sites
shah269 0 #13 January 3, 2012 hey check this out! http://www.pvsyst.com/Life through good thoughts, good words, and good deeds is necessary to ensure happiness and to keep chaos at bay. The only thing that falls from the sky is birdshit and fools! Quote Share this post Link to post Share on other sites
skydiver30960 0 #14 January 3, 2012 Some VERY basic calculations looking at grid-tie systems on that wholesalesolar.com website suggest about a 12-15 year return on investment. Does that sound about right for a ballpark estimate? Just curious as I live in Arizona and thought solar would be a no-brainer around here but don't see nearly as much of is as I thought I'd see before moving here. Elvisio "Thanks!" Rodriguez Quote Share this post Link to post Share on other sites
spikes2020 0 #15 January 3, 2012 Quote I don't want to go off on a rant here, but buy American. America~ Fuck Yeah! there are companies that will put solar cells on your roof and what money you save goes to pay for the instalation until its paid off then you get all the savings... Most of the time it takes 5 to 10 years to pay off the systems just fyi~ if you have free labor then maybe 3-6 years to pay for them selfs....Cheers Jon W Quote Share this post Link to post Share on other sites
jakee 1,595 #16 January 3, 2012 Quote Kids when your professors scream at you for not including units when you do your work they are not joking...without units numbers are meaningless! I dunno, things like strain, Reynolds numbers and drag coefficients can come in handy every now and again. (And yeah, where did you graduate from? Was it the Pointy Haired Boss School of Engineering?)Do you want to have an ideagasm? Quote Share this post Link to post Share on other sites
PhreeZone 20 #18 January 3, 2012 The Pointy Haired Boss School of Engineering is a pretty high standard for admission into in this situation... The math on this is easy, I just confirmed it by asking a JR high schooler via facebook to solve the same issue and gave him a few pieces of data and he came back with the correct answers. I might take some time and write this up as an SAT style question to see how many of the DZ kids on Facebook can get this right since I am guessing it is around a 6th grade word problem. BTW, the rate of return of $15k to get $400 in credit is about .015% rate of return. The time to pay off a system like this in NJ is around 8-12 years from the energy savings. My home usage averaged over a year is 1016 KWH per month. Cost per KWH is $.0954356 here so my average bills are $96.96 and a solar system would break even around 163 months or 13 years and 6 months at current electric costs. with the projected rate of growth of electricity costs pay off in reality would be around 10-11 years.Yesterday is history And tomorrow is a mystery Parachutemanuals.com Quote Share this post Link to post Share on other sites
billvon 3,118 #19 January 3, 2012 >Insert how much power you want on one end. >where you live >click enter stand back go get beer and out pops the answer. Well, you actually have to design the system, so that's a little unreasonable. It's like saying "how hard can it be to design a bridge? Just enter the length, the number of cars it has to carry and click enter." But here are the basics if you want to: 1) Decide what panel you want to use. This will have an STC DC rating in watts. Call this Ppanel. (Units are watts.) 2) Decide how many panels you want to use. Call this Npanels. (Dimensionless) 3) Decide how much equivalent direct sun you get a day. To do this: 3a) Figure out where the system will go. 3b) Figure out what mount you want to use. Fixed, south azimuth, latitude tilt? One axis tracking? Two axis tracking? 3c) Go to http://rredc.nrel.gov/solar/old_data/nsrdb/1961-1990/redbook/atlas/ and enter all that info. 3d) Look at the map and figure out your average daily solar radiation. Call this Psolar. It will be in kWhr/m^2/day. 1 kWhr/m^2 is one "standard sun" under standard test conditions (STC.) Thus these units cancel to days when applied to panels calibrated for STC. 4) Figure out how efficient your inverter will be. Call this Effinv. Dimensionless. 5) Figure out your averaging period, Tavg. For most people this will be a month because they get one power bill a month. Units here are days. The formula is then: Ppanel * Npanels * Psolar * Effinv * Tavg (all multiplication, easy.) The resulting number will be in watt-hours per Tavg time, usually a month. Divide by 1000 for kilowatt-hours a month. Quote Share this post Link to post Share on other sites
JackC1 0 #20 January 4, 2012 QuoteWhat f'ing engineering school did you graduate from? eBay. Quote Share this post Link to post Share on other sites
normiss 897 #21 January 4, 2012 That's a tad better than Phoenix! Quote Share this post Link to post Share on other sites
shah269 0 #22 January 4, 2012 Quote BTW, the rate of return of $15k to get $400 in credit is about .015% rate of return. The time to pay off a system like this in NJ is around 8-12 years from the energy savings. My home usage averaged over a year is 1016 KWH per month. Cost per KWH is $.0954356 here so my average bills are $96.96 and a solar system would break even around 163 months or 13 years and 6 months at current electric costs. with the projected rate of growth of electricity costs pay off in reality would be around 10-11 years. Amazing isn't it? Not much savings and lots of years to get it paid back in full! The students wanted to raise money to buy a system and then cash the SREC's to fund their various after school activities. Not a bad idea. Not huge money but not a bad idea. In NJ average SREC value is about $300 Not much for you and me but for kids....yeah it's enough.Life through good thoughts, good words, and good deeds is necessary to ensure happiness and to keep chaos at bay. The only thing that falls from the sky is birdshit and fools! Quote Share this post Link to post Share on other sites
shah269 0 #23 January 4, 2012 QuoteYou should have them build some of the panels themselves. That would be a cool school science project. They are! Some from scratch and others they are just building. Ever see solar sprint challenge? The kids are building little solar powered race cars. Very good kids, very smart, I was just trying to see if it was possible and viable for them to install a solar rack on their school roof to make some spending money from the subsequent SREC's they would generate.Life through good thoughts, good words, and good deeds is necessary to ensure happiness and to keep chaos at bay. The only thing that falls from the sky is birdshit and fools! Quote Share this post Link to post Share on other sites
billvon 3,118 #24 January 4, 2012 >Some VERY basic calculations looking at grid-tie systems on that wholesalesolar.com >website suggest about a 12-15 year return on investment. That's about right. "Value of money" estimates will tend to increase that; rising power prices will tend to decrease it. If you have more land a tracking mount will decrease payback time. Quote Share this post Link to post Share on other sites
skydiver30960 0 #25 January 4, 2012 Tracking mount, huh? Interesting. (Just thinking about how my wife would SHOOT me to find such a contraption in the backyard)... that alone should be reason enough for the extra initial investment! We close on the new home Jan 30, and I already have enough projects and honey-dos lined up to last me the first year or two of occupancy. But some day... Elvisio "can we do an electric 8-way off of solar panels?" Rodriguez Quote Share this post Link to post Share on other sites
