Grid tied system sorting through the options
Comments
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Re: Grid tied system sorting through the options
You are likely just suspicious enough. The .77 default derate factor used by PVWatts is supposed to be an "average" or "typical" derate factor for a normal system. Manufacturers and vendors may well have detailed rationale for why their specific system is better, but when every one of them claims to be above average, you can bet that there's something going on besides all these vendors paying homage to Garrison Keillor's Lake Woebegon.So how do you choose the right? derate. It sounds like a bit of sales trick to increase the power output by boosting the derate factor Or am I being too suspicious?
Detailed help on the derate factor used by PVWatts can be found here: http://rredc.nrel.gov/solar/calculators/PVWATTS/version1/system.html#derate . You'll see that there are 11 factors included here which range far beyond simple panel and inverter specs. Enphase has a detailed explanation of why their derate factor should be .819...some of this difference (like less issues with panel output mismatches) may be reasonable, but some of it (like better system availability and less voltage loss with longer AC wiring runs) sure sounds like just marketing. -
Re: Grid tied system sorting through the options InvertersNext question Choosing panels
For grid tied fixed or grid tied tracking Sanyo seems to look awfully good Good in the heat, great efficiency per square foot. They seem to come in at a 18-20% premium $ Is it worth it? Will they generate 20% more per year? Will they degrade more slowly? Are they burned into start so initial degrading is low?
A buddy did a comparison using PTC numbers of Sanyo 220 +10% and Conergy 235 +- 3% Both have a low end PTC of about 204 and 207 So with Conergy being 30% cheaper it looks easy to choose. Does it really come down to which company will stand behind its warranty and speed of getting replacements. Is there something I am missing about the performance of lower cost panels? I see that around here there are so many different panels.
Walt, you've got the right idea here. 10kW PTC of more efficient Sanyo panels will generate the exact same amount of energy per year as 10kW PTC of less expensive and less efficient panels from any other reputable manufacturer. The only difference is that the Sanyo panels will require a little less space. If you have the room for either, the extra cost of the high-efficiency panels will generally far outweigh the small savings for slightly smaller mounts.
Your key metric here is $ per installed PTC watts. Add the price of the panels + mounts and divide by the array size in PTC watts. The lowest price for UL/CSA approved panels from a reputable manufacturer wins (although you may want to stay away from some of the really low-end thin-film stuff if you want panels that will last for 20+ years). Keep in mind that you can likely see some pretty big savings if you purchase your panels from a large online US vendor, have them shipped to a freight depot near you on the US side of the border, and bring the panels across the border yourself (paying the HST to Canada Customs at the border). Panel pricing in the $1.85 to $2.25 per "STC" watt for good quality name brand panels is pretty easy to find right now. -
Re: Grid tied system sorting through the options InvertersYour key metric here is $ per installed PTC watts. Add the price of the panels + mounts and divide by the array size in PTC watts. The lowest price for UL/CSA approved panels from a reputable manufacturer wins (although you may want to stay away from some of the really low-end thin-film stuff if you want panels that will last for 20+ years). Keep in mind that you can likely see some pretty big savings if you purchase your panels from a large online US vendor, have them shipped to a freight depot near you on the US side of the border, and bring the panels across the border yourself (paying the HST to Canada Customs at the border). Panel pricing in the $1.85 to $2.25 per "STC" watt for good quality name brand panels is pretty easy to find right now.
One last piece in the panel selection What should I look for in warranty? Are there traps It looks like most are 5 years manufacturing then 10 years 10% degradation and 20 years 20% degradation. I am struck by the fact that no one really knows because we have not being do this that long and techniques and material have changed over time.
I appreciate that this is being supported by volunteers and DIYers who are mostly off grid or net metering.
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Re: Grid tied system sorting through the options InvertersOne last piece in the panel selection What should I look for in warranty? Are there traps It looks like most are 5 years manufacturing then 10 years 10% degradation and 20 years 20% degradation. I am struck by the fact that no one really knows because we have not being do this that long and techniques and material have changed over time.
I appreciate that this is being supported by volunteers and DIYers who are mostly off grid or net metering.
It seems to me, that the first thing to consider concerning the warranty is; Will the company still be around in 10 or 20 years time to honor it?
As you say, this is all fairly new, and long warranties aren't all that common, so I think you have to really look closely at the companies involved.
Sharp is almost a 100 year old company. Kyocera and Sanyo were founded in the 50's. Sanyo now belongs to Panasonic (which used to be Matsushita and is also coming up on 100 years in business) so all Sanyo branded products will end up with the Panasonic name.
Siemens was founded in 1847 and still going strong. BP has taken some knocks lately, but is still going strong. Evergreen seem to be on the ropes, but not out yet, though compared to some of the other players, they aren't that big.
It's nice that Canada is helping out domestic businesses in the renewable energy sector and trying to keep the money in the family - but will those companies that are being pushed today still be around down the road? Like anything else, it's a matter of doing your homework and taking your best guess. -
Re: Grid tied system sorting through the options InvertersI started looking into STC and PTC Ratings Thanks for the lead. What I understand now is that 220 is probably not 220 Ouch. At one site I also got info on temperature coefficient, and % Tolerances.
Next question Choosing panels
For grid tied fixed or grid tied tracking Sanyo seems to look awfully good Good in the heat, great efficiency per square foot. They seem to come in at a 18-20% premium $ Is it worth it? Will they generate 20% more per year? Will they degrade more slowly? Are they burned into start so initial degrading is low?
A buddy did a comparison using PTC numbers of Sanyo 220 +10% and Conergy 235 +- 3% Both have a low end PTC of about 204 and 207 So with Conergy being 30% cheaper it looks easy to choose. Does it really come down to which company will stand behind its warranty and speed of getting replacements. Is there something I am missing about the performance of lower cost panels? I see that around here there are so many different panels.
I actually real world tested some panels (actually still am) to gain a reference point of how much more "gain" some of these higher effieciency panels are worth for my own sanity. At first was kind of skeptical, but after testing some of them - the numbers are pretty amazing. Now, it just means the numbers are tighter, though not necessarily in their favor. So, its not as bad as some make you believe, but certainly not better $$$/Watt either.
So, for instance several manufacturer 220/230 watt panels (Sharp, Rec, etc) - the 220 panel will output approximately 196ish (these are the larger 66x39 REC panels). This is in Mid-Atlantic with outside temps around 55-60. The smaller footprint Sanyo HIT 215 panel will output 208 under same side by side conditions. Whereas the Suntech STP180 will output 167 and is the same foot print as the 215 Sanyo.
I've seen as high as 211 on the Sanyo 215 panels and they do seem to get up to "power" a bit faster than the REC and SunTech panels (probably due to their supposed better side reflectivity). The Sanyo's would be at 57W before the REC panels were pushing 10W. Suntech was just a bit further along at 14w. Sanyo's would get to 190+ (85% of their rating) about 30 minutes faster than the REC and Suntech panels would get to comparative 85%. Not a huge difference, but noticeable. I do not have hotter climate data as its now November.
These were all run on Enphase 210's (vs the 190's) to get rid of the 199 bottleneck on the m190's. Now, the numbers -
If you have space - it still makes better financial sense to get the 230W panels over the more expensive Sanyo (and by extension Sunpower). The additional cost in racking is probably 5% to achieve the same power. If you have limited space - then it becomes a much more interesting equation. As you have to factor in how you are going to achieve the power you need vs the cost of additional racking and limited space. The numbers start to get much closer on a microinverter type of system because you are factoring in the cost of additional watts per panel+microinverter combo vs just the module itself.
Anyhow, the calculations only get interesting when you are on limited space and need to hit a particular kw level. Although one key factor that people need to realize is that if you use microinverters, you absolutely have to maximize the microinverter capacity. You cannot use any of these 180 Sharp/Suntech/BP/etc panels as the numbers really start to go against you. IF you plan on using microinverters - you really need to get as close to the 190 (actually 199) of the M190, or slightly higher on the M210. Otherwise the cost of the microinverter comes back to eat at your cost/$$ calculations and the more efficient panels can come very close or better. -
Re: Grid tied system sorting through the options
It looks like we are going to overglass, that is the panel PTC will be 11-12KW but we can only send a maximum of 10KW to the grid. It may be wishful thinking, but it seems there may be times when we overproduce and the inverters (2x5KW) will have to dump the excess by dissipating heat. So we have been thinking about net metering. Lets run the air con and computers with the excess electricity. We could direct the DC excess to a seperate inverter and then to net metering.On very good days, you can 85% (I get this a few times a year on my system in the SF Bay area--on the warmer side of the coastal hills. I always get at least ~72% peak... (this is just random checks during the day--I don't have my array logging data).
Take your pick... In real life, you are not going to be able to measure much better than 10% accuracy based on temperature/clouds/humidity/dust/etc. in the air.
Can this be done? How? Are`there other threads to read on this?
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Re: Grid tied system sorting through the options
The inverter will not dump the excess as heat - it will simply limit current as necessary instead. Otherwise it would potentially have to dump a significant amount of extra heat. 2000W is a LOT of heat to dissipate in small area...It looks like we are going to overglass, that is the panel PTC will be 11-12KW but we can only send a maximum of 10KW to the grid. It may be wishful thinking, but it seems there may be times when we overproduce and the inverters (2x5KW) will have to dump the excess by dissipating heat. -
Re: Grid tied system sorting through the optionsIt may be wishful thinking, but it seems there may be times when we overproduce and the inverters (2x5KW) will have to dump the excess by dissipating heat.
Electricity doesn't actually exist until it is used. Generators don't make electricity, they make "potential". How much of that potential gets realized is purely dependent on how much load there is to draw from the pool of potential.
In other words - PV doesn't push, the inverter sucks.
You can have a 10kw solar system, but if the only load you have hooked up is a 50w light bulb, then 50w is all the electricity that will be created, even though there is enough potential available to supply 10kw of loads.
Small wind generators dump excess potential into a dump load in order to act as a brake against overspeed. Big wind generators don't have to do that since they can feather the props. -
Re: Grid tied system sorting through the optionsIt looks like we are going to overglass, that is the panel PTC will be 11-12KW but we can only send a maximum of 10KW to the grid. It may be wishful thinking, but it seems there may be times when we overproduce and the inverters (2x5KW) will have to dump the excess by dissipating heat. So we have been thinking about net metering. Lets run the air con and computers with the excess electricity. We could direct the DC excess to a seperate inverter and then to net metering.
Can this be done? How? Are`there other threads to read on this?
I think you may want to call or e-mail the OPA microFIT folks to ask for a little guidance on this idea. Even if there was a way for this to be technically possible with some pretty fancy DC switching within your PV strings, somehow I guess that OPA would not be happy with someone skirting their rules on multiple systems of the same renewable energy source greater than 10kW on the same property. Do not risk your microFIT eligibility on trying to pursue this last little bit of efficiency without getting OPA's blessing. I'd also guess that even if OPA was fine with the idea, it would be difficult to come up with a workable, cost effective way of capturing that last little bit of power to a separate inverter, and even more difficult to get an ESA inspector to approve the franken-install of switches and wiring and combiner boxes you would have to build.
That being said, there appears to be one way that you could possibly generate 10.3kW of AC during peak production hours and still comply with the program rules. If your inverters have a manufacturer's "nameplate" rating of 10kw or less, and they actually sometimes output a little more than 10kw, that appears to be OK under the microFIT rules. (Meaning that 52 Enphase M190s nominally rated for 190 watts each can output 10.3kW at their known 199w limit and still qualify for microFIT). But please don't just take my word for any of this - call or e-mail OPA with a carefully worded question to confirm this scenario. -
Re: Grid tied system sorting through the options
Northwalt,
Don't forget that net-metering and microFIT together can't exceed 10kw at the connection point. My domestic solar/wind could not be net metered when my microFIT of 10kw was factored in without reducing the microFIT output. But who would turn down 80cents per kwhr for net metering?
It doesn't make a lot of sense, but that's the regulation...only 10kw per connection point. I guess this stops people from putting 2 or 3 microFIT projects on the same piece of property and transformer. And...the properties must not just be a different civic address, they have to be on separate municipal tax roll number!
I've found that there's not too many hours where you are clipping the Enphase output...maybe from 11am-2pm, and the amount is unknown (I suspect very few kwhrs, and that's the inverter's clipping at 199 watts) You just aren't going to find that power anywhere, to use, the limit is from the inverter operation.
I'm at 12kw pv and 52 Enphase 190's for a connection of 9.98kw. Actual peak output sustained is 10.3kw...shhh, don't tell Hydro One or the OPA:p
Ralph -
Re: Grid tied system sorting through the options
Ralph and John thanks for the responses. and the clarity. Your secrets are forgotten. ;-) Maybe some day we will be able to do this kind of thing, but I understand the limits imposed by the rules and by the technology.
Another question about site selection.
On this property to get away from the trees requires at least 350 feet to the first tracker from the meter. I have been looking a wire guages and line losses. 4/0Copper @ 350 looses about 3% . is this acceptable. How far can I push this? If I go 400 (copper is 3.36 % loss) feet I have an even better site - no shade and 3.36% loss of total production which seems small for guaranteed no shade. a (yes miro's would have been better here
)
Alunminum at double the % loss seems to be a bargain but I am wondering if it is generally acceptable to ship so much less than 240 Volts. I am thinking outloud here and will call Hyro the electrical untility to see what their policy is. I'll get todays copper 4/0 price too.
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Re: Grid tied system sorting through the options
As the current king of long wire runs (950' underground in condouit) I used #6 alunimun wire for a 240VAC split phase N.A. install.. For my 50watt water treatment ozonater, I loose about 4% in the long 950' run. the tap off at 300' for the pump is still ok.Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A
solar: http://tinyurl.com/LMR-Solar
gen: http://tinyurl.com/LMR-Lister , -
Re: Grid tied system sorting through the optionsRalph and John thanks for the responses. and the clarity. Your secrets are forgotten. ;-) Maybe some day we will be able to do this kind of thing, but I understand the limits imposed by the rules and by the technology.
Another question about site selection.
On this property to get away from the trees requires at least 350 feet to the first tracker from the meter. I have been looking a wire guages and line losses. 4/0Copper @ 350 looses about 3% . is this acceptable. How far can I push this? If I go 400 (copper is 3.36 % loss) feet I have an even better site - no shade and 3.36% loss of total production which seems small for guaranteed no shade. a (yes miro's would have been better here)
Alunminum at double the % loss seems to be a bargain but I am wondering if it is generally acceptable to ship so much less than 240 Volts. I am thinking outloud here and will call Hyro the electrical untility to see what their policy is. I'll get todays copper 4/0 price too.
I'm likely missing something here, but what if you put your two 5kW inverters right beside the meter, and run 350-400 ft of 600V DC AWG-10 direct-burial PV cables from the arrays to the inverters? Lower amps, higher volts, less expensive wire, and lower line losses? Obviously this would mean using traditional inverters instead of micro-inverters. Am I forgetting to take something else into account? -
Re: Grid tied system sorting through the options
I also like the inverter near the meter instead of long runs--Especially if you have high line voltage. The extra run with voltage drop (voltage rise due to cable resistance) can make the inverter fault from too high of voltage.
-BillNear San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset -
Re: Grid tied system sorting through the options
This is an interesting thread Northwalt. I am in sw Ontario and was also contemplating a tracker or fixed mount. I decided to go with a 10.8kw fixed mount as I do like the zero maintenance. I have talked to tracker manufacturers about wind damage. The two I talked to both had a few that had the main pivot point snap. With my incredible luck, I'm sure this would happen to me at year 11... one year after the warranty runs out. The cost is less than a tracker, but I decided to use a Canadian solar cell manufacturer who's panels are currently made in Europe. The system cost is quite a bit more than purchasing made-in-china panels, but I think that at the end of the 20 year opa contract, the cost will be justified. I am a wholesaler in a completely different line of business who recently went through a large warranty issue with a manufacturer in China. All I have to say is if you need warranty on a made-in-china panel after 10 years...good luck. This is of course my opinion, but it comes from my experience. -
Re: Grid tied system sorting through the optionsI'm likely missing something here, but what if you put your two 5kW inverters right beside the meter, and run 350-400 ft of 600V DC AWG-10 direct-burial PV cables from the arrays to the inverters? Lower amps, higher volts, less expensive wire, and lower line losses? Obviously this would mean using traditional inverters instead of micro-inverters. Am I forgetting to take something else into account?
John I think you and Bill are saying the same thing. It is very different than what I have been hearing from electricians. This is what I understand. Send the the DC power down the 350 feet to the inverters which are then located by the meter and transformer. This means reduced wire size and lower line loss so lower costs of install and higher returns. Have I got it?
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Re: Grid tied system sorting through the options
Yep, and less problems if your area has high line voltage (my area runs around 250 VAC). If you have high line voltage at the curb, and a long AC line run to the the inverter, a 3% voltage rise of ~7.5 volts pushes me very close to the inverter safety shutdown of ~260-264 VAC.
If the AC lines between the curb and the GT inverter are kept short, then that is another ~7.5 volts of "headroom" for your system (and less headaches with 5 minute GT inverter shutdowns with power line surges).
-BillNear San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset -
Re: Grid tied system sorting through the options
Thanks for the prompt response.
I was looking around the site and found a similar thread in the grid tied forum. There one writer suggested what the electrician said to me that 4 AWG wire running 400 feet from the inverters, at the arrays, AC to the meter and transformer.
Please help me understand how this works. How is it that a DC run of 400ft from the arrays to the inverter, meter, and then transformer would have less line loss and use a smaller (10AWG) wire.
It sounds great. As a newbie I need to be able to explain it to the electrician who probably is used to working with almost exclusively with AC. One friend who I talked with about this said that this is is an old debate between Tesla (DC) and Edison (AC) that Edison won in North America.
Thanks
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Re: Grid tied system sorting through the optionsThis is an interesting thread Northwalt. I am in sw Ontario and was also contemplating a tracker or fixed mount. I decided to go with a 10.8kw fixed mount as I do like the zero maintenance. I have talked to tracker manufacturers about wind damage. The two I talked to both had a few that had the main pivot point snap. With my incredible luck, I'm sure this would happen to me at year 11... one year after the warranty runs out. The cost is less than a tracker, but I decided to use a Canadian solar cell manufacturer who's panels are currently made in Europe. The system cost is quite a bit more than purchasing made-in-china panels, but I think that at the end of the 20 year opa contract, the cost will be justified. I am a wholesaler in a completely different line of business who recently went through a large warranty issue with a manufacturer in China. All I have to say is if you need warranty on a made-in-china panel after 10 years...good luck. This is of course my opinion, but it comes from my experience.
We got a warranty on the trackers by way of a $150/year maintenance contract. Trust that the contractor who is very large and well known is reliable and the tracker is meant to be one of the best. The panels were offered to us with a warranty guaranteed by Chubb insurance included in the cost.
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Re: Grid tied system sorting through the options
Lets say you have 10kW of solar panels with a Vmp-array of 350 VDC vs 240 VAC. And we design for a maximum of 3% voltage drop.- 10,000 Watts / 350 VDC = 29 amps
- 350 VDC * 3% = 10.5 volt drop maximum
- 10,000 watts / 240 VAC = 42 amps
- 240 VAC * 3% = 7.2 volt drop maximum
- 350 VDC system -> 4 AWG copper with 6.9 volt drop
- 350 VDC system -> 4 AWG aluminum with 10 volt drop
- 240 VAC system -> 2 AWG copper with 6.3 volt drop
- 240 VAC system -> 1/0 AWG aluminum with 7.2 volt drop
Also, the exact DC run depends on the inverter you are are using... Depending on exact panel Vmp and your min/max temperature range (Voc-cold for maximum array voltage; Vmp-hot for minimum array voltage) will affect the above calculations. Note that a Vmp-array of 357 VDC @ -10F will give you a Voc-cold=518 VDC...
For a 600 VDC maximum input inverter, Vmp-nom=393vdc will give you a Voc-cold=569 volts.
But not all GT inverters will accept 600 VDC Voc-cold arrays... So your exact setup will vary. But even if you end up with Vmp~VAC (same size wire in both cases)--I would still prefer to run DC array voltage over the 400 feet vs AC because of the possible issues with voltage "rise" and possible High Line voltage from the utility unless you are pretty sure that your high line is less than ~250 VDC during the day.
-BillNear San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset -
Re: Grid tied system sorting through the options
Lots to chew on there. I need to step back a bit.
I checked the panel specs and found Vmpp of 27 and Voc 33 at normal operating temp. So with 2 arrays of 25 panels each are we at 25x27 Vmpp and 25 X 33Voc for each array? So 675 Vmp and 825voc. These seem to be way out of line with your examples.
Sorry for the really basic question. It is: how do I use the panel specs to arrive at the array voltages. I understand that higher voltages are the key to transmission down the longer run. More pressure more volts.
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Re: Grid tied system sorting through the options
You have to play the inverter you think you want to use against the solar panels you think you want to use.
You will mix series parallel combination of solar panels to meet the temperature range of your location and the specifications of the inverter.
Tell us what panels, how many panels, and what brand and model of inverter you would like to use and we show you how they play together.
-BillNear San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset -
Re: Grid tied system sorting through the options
50 X Grape 240's with 2 x Power One PVI 5000 inverters The cable run will be 350-450 feet. 2 arrays of 25 panels each on 2 Deger trackers
One thing I think I figured out is For DC transmission that each string would have a cable going to the inverters that means 2 strings for each array or 4 cables going from the arrays to the inverters at the pole.
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Re: Grid tied system sorting through the options
The string sizes for the Power One inverters are 12&13 panels. The temperature range is -22F (-30C) to +105F(+40C)
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