Preprepared Roofs and Backfeeding Questions

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  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Preprepared Roofs and Backfeeding Questions

    Yes, conservation does avoid sharing in grid costs -- if that conservation does not reduce peak demand too (i.e., use very little electrical power, but power up the microwave/electric oven/electric grill at dinner time (just about the peak grid load for summer)...

    That is why commercial power customers are shocked to find that solar GT systems do not save them very much money, or as the San Diego Schools found out--actually increased their power costs (after spending $4,000,000 on their systems--they had to stop installing more -- or go broke).

    I may not like reservation charges (pricing based on average 15 minute peak out of an entire year)--but they are based on the costs required to service the peak load required by the customer (somebody here said that their place--maybe a school/college--was a core customer for a major power distribution line. If they continued to reduce their power usage, they were going to see their rates go up because of the stranded capacity).

    What I don't like about Smart Meters and Demand pricing--is this is exactly the model that California PUC did with "deregulation" and the whole "Eron" / Los Angeles Department of Water and Power arbitration scheme that crashed and burned around 2000/2001.

    Basically, the utilities were forced to purchase power on the spot market with contracts no longer than 24 hours out... When capacity was high and economic need of power was low--it worked. The utilities got cheap power. And no additional power plants were built because there was no long term contracts that anyone could take loans out on to finance new power plants based on firm contracts with power costs.

    However, when demand went up--there were no power plants in the pipeline. And the utilities were forced to purchase power at any price--and generators where able to game the system to drive pricing higher by taking plants off-line (I am not clear if this actually happened or was an urban legend).

    And, the utilities where forced by the state to pay those high rates, but consumers/commercial customers were protected by having long term fixed price contracts (enforced by the PUC bureaucracy and difficult to change state laws).

    In California--the Smart Metering program is setting the consumer up for something like $0.11 per kWH--and with 23 hour notice--they will jack the power to $0.60-$0.75 per kWH some 15-20 "random" summer afternoons between 2pm and 8pm (don't remember the exact program details).

    This sounds like the basics that killed us last time... Put the customers in the spot market with no ability to set long term contracts for predictable power costs... Again, one of the major reasons I installed my GT solar.

    For California, you can go to www.caiso.com (approximately 85% of all electric power consumed in California) and see that today's peak is at 21:00 (9pm local time)... Long past where solar power is of any help to the power grid.

    PV Power does not follow the energy demand curve very well at all unless you are expecting blackouts after 3-4 pm...

    With AMI--we have now spent $40 Billion and not increased generation power or grid capacity by 1 cent. And, we have made the power infrastructure much less secure (RF modems subject to interference and hacking)... In fact, I have been getting "free natural gas" at home for a while because they could not get the meter reading software to work... (I am expecting a bill to catch me back up).

    All we have done is not put the consumer smack dab in the spot market... How would you like to pay rent based on the spot market--apartments are cheap during the day--everyone is at work--but dear at 6pm-7am--so we will jack the rent up during this time (on an hour by hour basis).

    Or, how about forcing your bank to float your fix rate 30 year mortgage and prohibit you from negotiating a fixed interest rate loan by state law... That is going to get exciting. I own my own home--so I must be paying my fair share. The Feds a few years ago where looking at creating the concept of taxing "imputed" income... The fact that I own my own home means that I am getting the benefit of not paying interest to somebody else--so I have to pay "income taxes" on the interest I would have gotten if I had the money in interest bearing account (or on the money I have "saved" by not having a mortgage).

    I am real leery of these government programs that try to "help me". Almost none of them even come close to accomplishing any of their stated goals.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Ricky
    Ricky Registered Users Posts: 20
    Re: Preprepared Roofs and Backfeeding Questions

    "PV Power does not follow the energy demand curve very well at all unless you are expecting blackouts after 3-4 pm..."

    PV is not available when the sun is down. Got it... The point I'm trying to make is simple: In California PV delivers electricity when the price of electricity is more expensive. This gives PV an inherent advantage in dynamic pricing scenarios. You can argue against dynamic pricing (AKA Real time pricing) all you want but the wheels are in motion. Dynamic pricing has nothing to do with the California Electricity Crisis. Many have argued that a healthy dynamic pricing system would have reduced the economic losses associated with the crisis because the demand response would have been stronger than it was.

    I've got a few more questions that should finish off the PV prepared roof idea. What are the easiest residential roof types to install systems on? What conditions of the roof (not the area around the roof) facilitate installation and help produce the best quality end product?

    Has anyone installed micro-inverter equipped AC panels? What is the general sentiment concerning this type of panel?
  • Ricky
    Ricky Registered Users Posts: 20
    Re: Preprepared Roofs and Backfeeding Questions

    Here's the Andalay report again. Does the cost comparison breakdown on page four look valid?

    http://andalaysolar.com/Library/data/A%20Solar%20Power%20Shift%20-%20Andalay%20AC%20-%20Revolutionizing%20Rooftop%20Solar%20Installation.pdf
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Preprepared Roofs and Backfeeding Questions

    i do not believe there will be a savings in going this route. you still have pvs that need mounted. you won't have a single gt inverter inside, but you still have many smaller and more costly inverters on a per watt basis that still need combined and fused and connected to the home's utility panel along with ground requirements. given an inverter up on the pv may fail sooner than the pv, this is another costly sore spot as you would need to replace both after you painstakingly go through them all to determine which went bad if you even notice the output isn't right.
    they left out needed stuff in their analogy of costs.
  • Ricky
    Ricky Registered Users Posts: 20
    Re: Preprepared Roofs and Backfeeding Questions

    Here's an interesting blurb on AC photovoltaic modules.

    http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=656653

    DEVELOPMENT OF THE CONCEPT
    The current development of the AC module comes mainly from two inadequacies of central inverter systems: at the time, central (4 kW) inverters for residential utility-interactive PV systems were produced in low quantity, and hence they were expensive and unreliable. Second, the complexity of dc string combining added to hardware, design and installation costs. The AC module at first appeared to be a poor economic solution as a “brain” would be needed for each module - rather than having one for the whole array. Recent reductions in microprocessor cost have resulted in “brain” costs for our units of about $30, with a projected mass produced cost of under $5.

    ADVANTAGES OF THE AC MODULE
    The advantages of the AC PV module are:
    -AC Module systems improve system reliability because of distributed hardware (i.e. redundancy), testability (via communications links) and simplicity (no high voltage DC components or wiring)
    -The minimum system size of one AC module provides a low barrier to market entry.
    -The minimum array increment of one AC module and the elimination of balance-of-system equipment allows for maximum flexibility in initial sizing and simple future array expansion-There are no constraints on module / array orientation, shading or solar exposure - each module has its own dedicated maximum-power-point tracker.
    -Module and string mismatch losses from long series strings are eliminated.
    -No special string combiners, DC wiring or DC groundfault protection are needed.
    -A dramatic reduction in manufacturing costs is possible through mass production of the inverters.
    -System design and installation costs are reduced via product standardization
    -AC modules are inherently safer than conventional, high-voltage DC photovoltaic systems

    There are of course some disadvantages. The main one is that for systems over about 50 kW total, a central inverter can be made very cheaply - it is likely that large systems “behind the utility fence” will not be AC module devices.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Preprepared Roofs and Backfeeding Questions

    my comments in bold
    Ricky wrote: »
    Here's an interesting blurb on AC photovoltaic modules.

    http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=656653

    DEVELOPMENT OF THE CONCEPT
    The current development of the AC module comes mainly from two inadequacies of central inverter systems: at the time, central (4 kW) inverters for residential utility-interactive PV systems were produced in low quantity, and hence they were expensive and unreliable. Second, the complexity of dc string combining added to hardware, design and installation costs. The AC module at first appeared to be a poor economic solution as a “brain” would be needed for each module - rather than having one for the whole array. Recent reductions in microprocessor cost have resulted in “brain” costs for our units of about $30, with a projected mass produced cost of under $5.

    ADVANTAGES OF THE AC MODULE
    The advantages of the AC PV module are:
    -AC Module systems improve system reliability because of distributed hardware (i.e. redundancy), testability (via communications links) and simplicity (no high voltage DC components or wiring)

    so are they saying you won't need any conduit or combiners or disconnects? pure bull and it is just as difficult or moreso difficult in determining a faulty module or add the extra costs for communications links for the ac modules.

    -The minimum system size of one AC module provides a low barrier to market entry.

    yes, this can create a low end gt system so i agree.

    -The minimum array increment of one AC module and the elimination of balance-of-system equipment allows for maximum flexibility in initial sizing and simple future array expansion-There are no constraints on module / array orientation, shading or solar exposure - each module has its own dedicated maximum-power-point tracker.

    yes, this allows adding one module at a time, but each module has an inverter adding high costs per watt for each module added. note here that the beginning statement with the - in bold is the op's and not mine.

    -Module and string mismatch losses from long series strings are eliminated.

    this is not a problem when the dc is made from identical pvs and it is wired right, but would be correct that you cannot vary the numbers of modules in each string either.

    -No special string combiners, DC wiring or DC groundfault protection are needed.

    wrong as individual ac modules each need combined and wiring to be made thicker than dc as dc operates at higher voltage potentials for conversion and thus the ac has more current and more vdrop losses than the dc with wattages being the same. ac groundfault protection would be a good idea seeing the stuff is outside and subjected to the same hazard possibilities as the dc counterparts.

    -A dramatic reduction in manufacturing costs is possible through mass production of the inverters.

    mass production needed because more would be used for the same number of watts in a system and won't be lower $ per watt than a single larger gt inverter.


    -System design and installation costs are reduced via product standardization

    redundant statement as this applies to all methods.

    -AC modules are inherently safer than conventional, high-voltage DC photovoltaic systems

    this is no different than saying 120vac is safer than 240vac. both can kill and start fires when something goes wrong.

    There are of course some disadvantages. The main one is that for systems over about 50 kW total, a central inverter can be made very cheaply - it is likely that large systems “behind the utility fence” will not be AC module devices.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Preprepared Roofs and Backfeeding Questions
    Ricky wrote: »
    There are of course some disadvantages. The main one is that for systems over about 50 kW total, a central inverter can be made very cheaply - it is likely that large systems “behind the utility fence” will not be AC module devices.

    Over 50 kW to be cheaper? Over 1 kW are cheaper than micro-inverters. Just compare the per Watt costs (inverter only) on prices from NAWS:
    Enphase = $1.26 per Watt
    Xantrex 2.8 = $0.72 per Watt

    The "support" equipment - panels, wiring - is pretty much a wash.
  • Ricky
    Ricky Registered Users Posts: 20
    Re: Preprepared Roofs and Backfeeding Questions

    The Battle of the Currents all over again. Thanks for the responses. Cya.
  • Ricky
    Ricky Registered Users Posts: 20
    Re: Preprepared Roofs and Backfeeding Questions

    niel

    -A dramatic reduction in manufacturing costs is possible through mass production of the inverters.

    mass production needed because more would be used for the same number of watts in a system and won't be lower $ per watt than a single larger gt inverter.

    I've always thought standardization would be the microinverters primary technical advantage. If you look at Enphases' microinverter compatibility list you'll see that one MI is compatible with nearly two hundred different modules. Central inverters will never be able to standardize at the system level in a similar way. This should allow microinverters to move down the learning curve more quickly than central inverters. I'm a big believer in the learning effect. Mass production is the key to lowering costs. This whole industry is still just getting started.

    -Another one of the bigger advantages of microinverters is that they can be incorporated at the factory. At the technical level this allows module makers to optimize the module and inverter as one device. From a profit perspective this gives module makers a means to capture another part of the PV value chain.

    -Another potential advantage of microinverters is that they open the door to larger wafers/cells. In the semiconductor industry larger wafers have translated into lower processing costs. For example, 300 mm wafer fabs have been estimated to cut costs by 30% vs 200 mm fabs. The problem at the DC module level of using larger cells would be either oversized modules for the same voltage or low voltage for the same size module - AC modules offer you a way around this. With wafer processing costs trending towards $.25/Watt this might be a dead end proposition but I find it interesting.

    -As far as safety goes the guys in my utility think AC is safer. The primary reason I I've been given is that you can let go of AC because the waveform zeros. I tried to argue the whole Edison vs. Westinghouse thing but nobody would have it. Personally I've always treated AC and DC wiring with the same respect but my experience is limited to switching operations.


    Cariboocoot

    Enphase inverters are selling on ebay for about $1/watt but even then the cost differential is way too high. Problem is, simply comparing your $/watt is instructive but you need more information. In the end it comes down to your levelized cost of electricity.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Preprepared Roofs and Backfeeding Questions

    my comments in bold italics.

    niel

    -A dramatic reduction in manufacturing costs is possible through mass production of the inverters.

    mass production needed because more would be used for the same number of watts in a system and won't be lower $ per watt than a single larger gt inverter.

    i stand by my statement as all that is basically needed for a single inverter to handle more power is parts rated to handle more current along with more fets. too much duplication of parts is needed for separate smaller inverters no matter how many they sell. this is not necessarily a case of smaller inverter equal a smaller number of parts over a larger inverter.

    I've always thought standardization would be the microinverters primary technical advantage. If you look at Enphases' microinverter compatibility list you'll see that one MI is compatible with nearly two hundred different modules. Central inverters will never be able to standardize at the system level in a similar way. This should allow microinverters to move down the learning curve more quickly than central inverters. I'm a big believer in the learning effect. Mass production is the key to lowering costs. This whole industry is still just getting started.

    the connection standards are the same for 1 or many large inverters as would be for one or many small ones. it is all to be connected to the grid and one does not have to match one inverter to another inverter as they have to all go to and be matched to the grid. large inverters can be mass produced too you know.

    -Another one of the bigger advantages of microinverters is that they can be incorporated at the factory. At the technical level this allows module makers to optimize the module and inverter as one device. From a profit perspective this gives module makers a means to capture another part of the PV value chain.

    these aren't any more optimized as it is mppt and it adjusts as it goes so this sounds more like salesman sound bites. so the company makes the connection to the module's inverter as they still have to be tied together to go to the grid and are subjected to the same wiring constraints. you replaced dc lines with ac lines, big deal. at least with dc the pv strings can and usually are in series so it won't be a pair of wires to be combined for every module as is the case for many microinverters so the dc will save in wire and voltage drops being better as higher voltages are used in the dc systems.

    -Another potential advantage of microinverters is that they open the door to larger wafers/cells. In the semiconductor industry larger wafers have translated into lower processing costs. For example, 300 mm wafer fabs have been estimated to cut costs by 30% vs 200 mm fabs. The problem at the DC module level of using larger cells would be either oversized modules for the same voltage or low voltage for the same size module - AC modules offer you a way around this. With wafer processing costs trending towards $.25/Watt this might be a dead end proposition but I find it interesting.

    the cell thickness has no bearing on the type inverter being used so what are you talking about? again it sounds like salesman sound bites.

    -As far as safety goes the guys in my utility think AC is safer. The primary reason I I've been given is that you can let go of AC because the waveform zeros. I tried to argue the whole Edison vs. Westinghouse thing but nobody would have it. Personally I've always treated AC and DC wiring with the same respect but my experience is limited to switching operations.

    gee, that makes a big difference? both are lethal is what i was trying to say.

    note: you will notice it shows that i edited your post. i did not edit your content, but accidentally entered into your post as i should've hit quote and not edit. i wound up doing a copy and paste rather than quote so it doesn't look as i wanted.:cry:
  • Ricky
    Ricky Registered Users Posts: 20
    Re: Preprepared Roofs and Backfeeding Questions

    200 mm vs 300 mm refers to the diameter of the wafer/cell. From a processing standpoint larger diameters save you money during wafer/cell production - this is an established fact in the semiconductor industry. The problem with larger cells is that you get a drop in voltage if you keep the module size constant. You can make larger modules but the problem here is that module size is relatively optimized where it is so increasing the size would actually add cost. AC has the potential to solve these problems because you can step up the voltage. I'm not saying the industry is going to move to microinverters because they're determined to use larger wafers. On the other hand if microinverters did become ubiquitous I think you would see the industry take another look at larger wafers. Does that make sense?

    I'm surprised you guys don't have anything positive to say about AC modules. I've heard rave reviews from other installers who have worked with this technology. In particular the time savings during installation have been lauded. I've also heard from engineers who have run into serious reliability issues with microinverters. There's certainly a balance of good and bad.

    Being able to let go of a live wire makes a big difference niel.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Preprepared Roofs and Backfeeding Questions

    ac modules, as you term them, have there place, but it is not the answer to everybody's problems. there have been other discussions on these inverters and feel they are fine small scale, but i'll stick to the larger inverters for larger jobs.
    btw, i'd like to see that you put your hands into a 240vac circuit and let go. when can i see the video on it?
  • System2
    System2 Posts: 6,290 admin
    Re: Preprepared Roofs and Backfeeding Questions

    Just a little aside, having seen both side of the terminology fence, the guys at the utility have a completely different language (and viewpoint) than the average electrician. It goes as deep as demand vs connected load. If the OP is a utility guy, he won't be familiar with the "past the meter" terminology, just like many electricians don't get why we get all concerned about ferroresonance and switching procedures.
  • russ
    russ Solar Expert Posts: 593 ✭✭
    Re: Preprepared Roofs and Backfeeding Questions

    İt's tough to be in love with something others don't think is so sweet!

    The microinverters seem to be getting a real PR push!
  • CaptTurbo
    CaptTurbo Solar Expert Posts: 66 ✭✭✭✭
    Re: Preprepared Roofs and Backfeeding Questions

    It's cool that old threads get brought back to life. Not much of this subject pertains to me at this point after having purchased a GT inverter based system but I really enjoyed reading the "back and forth" and hopefully learned a little.

    If any of it does apply to me it's the part about preparing the roof. I decided to roof-over my 30 year textured asphault shingle roof which was in the 14th year of her life and in very good condition.. It seemed to me that removal and replacement costs of the array made this a good decision.

    The new roof of choice was a 5-V Metal roof in the color of Solar White. The color was chosen for the reason of providing a cooler bed for the PV array and that it qualifies for a Federal tax crediit.
  • Ricky
    Ricky Registered Users Posts: 20
    Re: Preprepared Roofs and Backfeeding Questions

    Speaking of brought back to life here's an update on the preprepared roof situation. They're calling it "solar ready" these days and I have to admit that rolls of the tongue mawch betta. I reread this thread and was amazed by the push back from you guys. Now that component costs are a third of what they were back in 2009 the savings on installation are taking on more importance. The CEC's solar ready rules are straight-forward and inexpensive from what I can tell. What's not to love? Don't tell me - I don't care.

    http://www.solarindustrymag.com/e107_plugins/content/content.php?content.10446