Preprepared Roofs and Backfeeding Questions

Has anyone heard of preprepared PV roofs?

i.e. Are there any steps that could be taken during new construction or reroofing that would preprepare the roof for a PV system down the road? Would it be feasible to preinstall mounting points? Are there preferable vapour barriers?

Does anyone know how AC panels protect against backfeeding?
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Comments

  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Preprepared Roofs and Backfeeding Questions

    my comments in bold.
    Ricky wrote: »
    Has anyone heard of preprepared PV roofs?

    i.e. Are there any steps that could be taken during new construction or reroofing that would preprepare the roof for a PV system down the road? Would it be feasible to preinstall mounting points? Are there preferable vapour barriers?

    i suppose one could reinforce a roof for the extra stress the winds can place upon pvs, but i think most are strong enough in most circumstances normally and yes the posts can be placed if you would like. the vapor barriers are to do with normal insulating techniques and i am not aware of any one in particular.

    Does anyone know how AC panels protect against backfeeding?

    there is no such thing as an ac panel as they all produce dc and can you define what it is you mean by backfeeding?
  • Ricky
    Ricky Registered Users Posts: 20
    Re: Preprepared Roofs and Backfeeding Questions

    I'm looking for a definitive answer from an experienced installer. Is there an experienced installer on this board?

    Any panel with its own micro-inverter is an AC panel. Andalay panels are probably the best known so far but there are several manufacturers.

    Backfeeding is the movement of electricity from the PV system on your house back into the powerlines. Backfeeding is a safety concern for power line technicians working on the lines.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Preprepared Roofs and Backfeeding Questions
    Ricky wrote: »
    I'm looking for a definitive answer from an experienced installer. Is there an experienced installer on this board?

    Quite a few of them, actually.
    Any panel with its own micro-inverter is an AC panel. Andalay panels are probably the best known so far but there are several manufacturers.

    Niel's response is correct: all solar panels are DC. It's just that your question wasn't completely clear. The inverter fed by the panels may or may not be grid-tied. This forum deals with many different types of solar power systems so it's really important to be as specific as possible when asking a question. I don't mean to insult you or your post, but you'd be amazed at some of the questions that get asked!
    Backfeeding is the movement of electricity from the PV system on your house back into the powerlines. Backfeeding is a safety concern for power line technicians working on the lines.

    This has been the subject of much discussion and no doubt will continue to be. Basically, grid-tied inverters are meant to back-feed the grid. This normally isn't a problem unless, as you say, someone is working on the grid. That's why installs are supposed to be done with the knowledge and co-operation of the local utility. Then, in theory, they know what houses may present this hazard and can disconnect them from the grid before doing any repairs. This can either by by having the homeowner shut off the inverter's connection, or by pulling the meter. As far as I know, there is no fully-automatic way to achieve this protection, albeit most GT inverters do not produce if they don't detect the grid. Even so, there's always the possibility of some charge potential.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Preprepared Roofs and Backfeeding Questions

    And to be clear--GT inverters in current production are designed and tested to meet specifications such that if the voltage or frequency (or power line quality) is out of specification--the inverters are designed to shut down in a few cycles (5060 cycles per second). Plus, as the inverters operate as a "slave" to the grid--they are not even capable of operating without a "master" (such as the utility power) waveform to follow (as always--exceptions to the rule, there are types of inverters that can do both GT and Off Grid power--so they have several modes they can operate in).

    There is another from of "back feeding" that the specifications talk about... This is the AC mains "back feeding" the DC solar panels... Most (all) GT inverters are designed that they cannot back-feed the panels at all (or meet the requirements in some other way).

    The utility and code requirements are to help ensure that the correct equipment is installed and safely wired.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Preprepared Roofs and Backfeeding Questions

    as to your term of backfeeding now that you clarified that to mean disconnecting a gt system during times of outage that concerns the safety of people and equipment, all inverters that connect to the grid (gt) are required to be what is known as anti-islanding. since you disqualify my answer being i don't install for a living then don't take my word for it and look it up yourself.

    edited to bold it and correct my bad spelling on known as i left off the n.:blush:
  • Ricky
    Ricky Registered Users Posts: 20
    Re: Preprepared Roofs and Backfeeding Questions

    Good to know there are several experienced installers. I'm not an installer, I work in grid management.

    Solar panels are DC... Agreed. The term AC PV or AC panel refers to solar panels that have an integrated microinverter. I don't feel insulted and I hope I'm not insulting anyone but the term is relatively standard and it's been around for over 15 years.

    I understand the basic issue with backfeeding. What I'm having a hard time understanding is how a micro-inverter equipped AC panel could somehow prevent backfeeding when a standard central inverter setup doesn't. It must be, as you say, a matter of sensing grid voltage and disconnecting on a loss of voltage. Thing is, I'm not satisfied with guessing. I'll have to write directly to a AC PV manufacturer who is claiming safety from backfeeding. Will post response if I get one.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Preprepared Roofs and Backfeeding Questions

    Here is a quote from Enphase's (Andalay uses Enphase microinverters) website which may have relevance for you too:

    "Do I need an A/C disconnect on my roof for each Enphase branch-circuit?
    This varies by Authority Having Jurisdiction (AHJ)."


    As you can tell, the actual installation of any Grid-tie system is subject to local authority, so there is no one answer as to how it should be installed.

    Regarding the anti-islanding issue (could not remember the term before! Thanks again, Niel) you would indeed be wise to check with the particular manufacturer about this aspect. It's not the sort of thing they advertise, because it isn't seen as a "selling feature".

    Like I said, i doubt there's any of them that don't have this feature - even the microinverters. But you never know; there's some pretty awful junk out there sold cheaply over web sites and such.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Preprepared Roofs and Backfeeding Questions

    "Regarding the anti-islanding issue (could not remember the term before! Thanks again, Bill)"

    talk about getting discredited and dissed,:cry: i seem to be getting bent over here first by the op and now you say bill told you the term.:confused: i guess you "installers" can carry on.:roll:
    wow bill, i guess i'm more invisible than you are in invisible mode.:p
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Preprepared Roofs and Backfeeding Questions

    I sorted through Enphase's website some more and found your answer for you:

    "Do the Enphase Microinverters automatically disconnect when the grid shuts down (e.g. for power company repairs)?
    Yes. Enphase Microinverters are CSA-listed to the UL 1741 standard for utility-interactive applications. If the utility voltage source is out of voltage or frequency spec, or if the utility is disconnected, the inverter will not feed current or voltage to the grid side terminals. This functionality is implemented with any grid-tied inverter, so it will not "island" and potentially hurt line workers."


    Does that help?
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Preprepared Roofs and Backfeeding Questions
    niel wrote: »
    "Regarding the anti-islanding issue (could not remember the term before! Thanks again, Bill)"

    talk about getting discredited and dissed,:cry: i seem to be getting bent over here first by the op and now you say bill told you the term.:confused: i guess you "installers" can carry on.:roll:
    wow bill, i guess i'm more invisible than you are in invisible mode.:p

    You both know I always get you two confused! I think its because of the masks you wear. :p

    There: I went back and fixed it for you.

    Shall I mention this thread's in the wrong area?
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Preprepared Roofs and Backfeeding Questions

    no problem rudolph.:p i know you didn't mean it.

    boy, am i doing a royal lmao:D
  • Ricky
    Ricky Registered Users Posts: 20
    Re: Preprepared Roofs and Backfeeding Questions

    I see the confusion now. Backfeeding (as defined by grid operators) nearly always means feeding power into a system that is supposed to be isolated. It can be used more generically to describe feeding power opposite the normal flow but this is the exceptional case. I suppose to you guys, backfeeding means using a gt inverter to feed the grid? Is this correct? Using this word in both ways is problematic.

    So anyways, I recently read this spec sheet from Andalay.

    http://www.andalaysolar.com/Library/data/A%20Solar%20Power%20Shift%20-%20Andalay%20AC%20-%20Revolutionizing%20Rooftop%20Solar%20Installation.pdf

    On page 6 there's a blurb that mentions how these microinverter equipped panels disconnect from the grid on a loss of power. The section is called "Enhanced Safety" and I understood this to mean this feature wasn't a normal feature. What I'm hearing here is that ALL gt systems are designed to prevent backfeeding during a blackout. That makes perfect sense.

    As to the preprepared roofs, the basic idea I'm trying to explain is that you prepare your roof for a PV system to be installed at some point in the future. The idea is akin to building a dam with only 3 turbine units but providing space for an additional unit or two down the road (not uncommon by the way). This sort of planning costs you a little extra at the beginning but you save a pile of money down the road. Hopefully that makes sense now. Are there any obvious features (aside from pitch and orientation) that would make a roof PV ready and not cost you a bundle?
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Preprepared Roofs and Backfeeding Questions

    Unless the roof is woefully under-structured or in an extremely high wind area, there really isn't much difficulty in putting panels on. The slope and orientation are the big factors, as you already know.

    There is quite a bit of debate about the best way to run wires from the array into the house. Some people want to go through roof or ridge vents, which I personally don't like to do. Nothing like conduit over the edge and having the point of penetration sheltered out of the weather. You could pre-install conduit, but what size? Spend too much money on putting in the largest possible and then not use the full capacity, or put in something that ultimately turns out to be too small? Tricky to pick before knowing what you're going to be using in terms of wire.

    I should note that the roofing material makes a difference too. Easy to go through asphalt/fibreglass shingles with lag bolts. Not so easy with metal. Practically impossible with tile. Most of the time this issue doesn't come up.

    Basically, the roof has to be structurally adequate to take the additional weight and "sail load" of the panels, and you need to be able to run the wires.
  • Ricky
    Ricky Registered Users Posts: 20
    Re: Preprepared Roofs and Backfeeding Questions

    Here are some what ifs for you. Shoot them down at will.

    1. Could you pre-installed standardized anchoring points? The idea would be that you lift up the shingle and there's already a sealed connection point for your racking? I would think roofers could do this.

    2. You don't need to pull wires necessarily but you could still run conduit. I'm thinking in terms of thumbrules. Run conduit in such and such obvious situations. Do you think there are any obvious situations that would save you money on a subsequent PV installation.

    3. Any potential for rerouting ventillation penetrations. This one is more of a design issue but I suppose there's some potential for rerouting during a reroof. I'm just asking.

    I'm looking for simple cost effective features that you'd incorporate at the time of construction or during a reroof. These are the only ones I can think of. This idea is basically about minimizing labor to save money. If there is any merit to the idea you could pitch it to the Energystar people and have them incorporate it in their standards.
  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Preprepared Roofs and Backfeeding Questions
    Ricky wrote: »
    Here are some what ifs for you. Shoot them down at will.

    1. Could you pre-installed standardized anchoring points? The idea would be that you lift up the shingle and there's already a sealed connection point for your racking? I would think roofers could do this.

    Well, the first problem is that whole "standardized anchoring points" thing...they aren't really standardized. There are loads of different mounting systems. Murphy's Law says that if you install mounting points for System A, then the homeowner will opt to purchase System B.

    And about pulling up that shingle...well maybe the house started with asphalt shingles, and the homeowner decided he likes Spanish tile better. Now what do you pull up?

    And how do you even find the anchor points a couple of years after no one knows what happened to the plan that shows where they are?

    2. You don't need to pull wires necessarily but you could still run conduit. I'm thinking in terms of thumbrules. Run conduit in such and such obvious situations. Do you think there are any obvious situations that would save you money on a subsequent PV installation.

    Installing for something that might/will be there later is called, "future". Sure, you could run conduit for future PV - what size conduit? Depends on what size wire. Okay, what size wire? Depends on what size PV array. Okay, what size PV array?

    Dunno...

    3. Any potential for rerouting ventillation penetrations. This one is more of a design issue but I suppose there's some potential for rerouting during a reroof. I'm just asking.

    I'm looking for simple cost effective features that you'd incorporate at the time of construction or during a reroof. These are the only ones I can think of. This idea is basically about minimizing labor to save money. If there is any merit to the idea you could pitch it to the Energystar people and have them incorporate it in their standards.


    I think all this is best handled at install time. There are just too many unknown variables to make it a requirement to install for "future" when there is no way to know what, or even if, that future will require.

    One problem seen here on the forums several times is undersized service entrance panels. Say the house has a 200a main panel - the max backfeed breaker that can be put into that panel from the solar is 40a - and if the solar array puts out more than that...

    I think the best that can be hoped for is to require larger main panels in case of a "future" PV backfeed installation.
  • Ricky
    Ricky Registered Users Posts: 20
    Re: Preprepared Roofs and Backfeeding Questions

    I appreciate the response but I need some clarification. Are you saying that anchor point spacing (what's the correct term? Mounting point?) isn't standardized? What is the typical spacing and what's the range of spacing? I don't quite understand how we can standardize stud, joist and truss spacing at 16 inches but can't standardize panel mount spacing? This is problematic. What's the worst case loading requirement? Every 64 inches?

    Routing the roof penetrations to the north side of a roof or grouping them where feasible would be done in the design phase. This seems like a non-issue.

    "Installing for something that might/will be there later is called, "future". Sure, you could run conduit for future PV - what size conduit? Depends on what size wire. Okay, what size wire? Depends on what size PV array. Okay, what size PV array?"

    How big is the hypothetical PV system predicted to be? I imagine you'd use an excel spreadsheet to calculate this. You'd type in the area's insolation, hdd, cdd, the baseline territory, the home's square footage, check pool or no pool, check gas or all electric and press enter. The spreadsheet would kick out a number and you'd build to that standard spec. If you guys think this idea is ridiculous take a look at San Luis Obispo. They are straight up mandating the installation of PV on a percentage of new homes. That's overkill as far as I'm concerned. Why not mandate building homes that are "PV Prepared" thereby lubricating the future choice to go PV? Make any sense?

    "And how do you even find the anchor points a couple of years after no one knows what happened to the plan that shows where they are?"

    A metal detector perhaps but I was thinking the shingles/tiles would be marked in some subtle way. You'd only need to identify one point and the standard itself should lead you to other points. i.e. It would be an evenly spaced grid.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Preprepared Roofs and Backfeeding Questions

    One issue is that home energy use can have quite a wide range--depending on who lives in the home and their lifestyles...

    In our home--the people before used several hundred dollars per month of electric and gas power... We used roughly $40-$50 per month (summer months/no A/C, before Solar Grid Tied system was installed). Same home, similar appliances, 3 kids vs 2 kids, etc...

    The array I have on my home offsets a bit more than 100% of my electric usage (and pretty much fills my south facing roof area). There is no way that we could fit 5x more solar panels on our home to power the family that lived here before us to offset there energy usage.

    Installing Solar PV on homes is a political solution--not a real energy policy (in my humble opinion). After all of the years that California has done this--we have about 1% of the electric grid from solar PV system. One person commented in another forum that 80% of the installations are residential--but about 80% of the energy generated is from commercial (sounds true--but I do not have any data to prove this).

    The current policies of forcing the utilities to sell power at retail and buy solar power at retail (or even higher for wind power) only makes sense when there is such little power being generated. The true costs of the polices are buried in round-off error.

    If the current solar program ever got 10-20%+ of the total power generated--the net metering program would either collapse or electric rates would have to increase dramatically to offset the lost revenues to the utilities and the wide changes in power consumption between daytime and evening usage (lots more expensive peaker plants using natural gas, lots less use of cheap base power plants like coal and nuclear).

    -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

    I don't understand the details Bill. How much electricity did you use before installing the system? Did you chage anything about the house in addition to installing the PV system? How large (in KW) is the PV system?

    "Installing Solar PV on homes is a political solution--not a real energy policy (in my humble opinion). "

    I realize PV isn't currently cost effective but things are getting interesting. Judge the current trends to your fancy.

    "Installing Solar PV on homes is a political solution--not a real energy policy (in my humble opinion). After all of the years that California has done this--we have about 1% of the electric grid from solar PV system. One person commented in another forum that 80% of the installations are residential--but about 80% of the energy generated is from commercial (sounds true--but I do not have any data to prove this)."

    The CSI database breaks down the information you're looking for. Commercial systems get additional tax breaks so they've been the first adopters. California has been funding PV a long time but things are only now getting started. I think the growing market in California is going to drive some intense competition between the installers in the near term. This line of thought is generating my ideas about standardization and PV Prepared (TM) roofs.

    "If the current solar program ever got 10-20%+ of the total power generated..."

    My basic belief is that PV will generate 10-20%+ of California's electricity if the price comes down far enough.
  • Ricky
    Ricky Registered Users Posts: 20
    Re: Preprepared Roofs and Backfeeding Questions

    Hmmm... just saw the tag line at the bottom of your post. So you're generating about 250 kWh in the winter months and 450 kWh in the summer? Something like 4300 for the year? Is PVwatts close?

    You seem like a statistically unlikely customer to me.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Preprepared Roofs and Backfeeding Questions

    My system generates around 4,850 kWhrs per year (400 kWhr per month average solar generation)--and we (2 adults/2 kids) use around 250 kWhrs per month (12 month average)... I have Time of Use metering--so, I currently come out with around $300 or so of "excess energy generation" -- which with net metering, becomes worth zero at the end of the 1 year term.

    I purchased the system because I saw what California had been doing with the costs of power (and the blackouts around 2000) because of the "deregulation" of power (not deregulation at all--just very poorly thought out and implemented change of regulations that nearly bankrupted our utilities).

    We worked at conservation--the usual stuff--insulated a 70 year old home, double pane vinyl windows, new doors, weather stripping, new furnace, energy star appliances, CFL lights (wife still hates the color--but likes the low bills, no A/C, etc.).

    Installed more panels than we needed with the plan of installing A/C eventually. But it turned out that insulation/low-E glass and reducing the use of power in the home would keep our internal temperatures pretty reasonable in all but the very hottest weather.

    And--still run around after the kids to turn off lights and computers/printers/copiers/home stereo/TV when not in use (use laptops mostly--much less power draw than desktops).

    And lastly--kind of thought that electric (or hybrid electric) cars where going to be here sooner rather than later (again--because of the state laws). Been using electric heaters in a couple rooms (rather than central heat) somewhat during the winter because, currently, we have so much "extra" power.

    We probably used to use $30-$60 per month of electricity (maybe 300-600 kWhrs per month--before kids)--that was years ago with older fridge and when "I did not care as much" a decade or two ago. We currently use around 180-300 kWhrs per month and have a $5.42 per month electric bill (basically minimum charge with our utility).

    Because of the policies from the Carter years--we still have tiered residential rates where the more you use, the higher rates you pay... Almost the equivalent of going to the local quickie mart and buying a gallon of milk for $1.00 and going to Costco (mega-mart) and paying $7.00 per gallon for 10 gallons of milk.

    My minimum charges are around $0.09 per kWhr (off peak), and my maximum rate is near $0.60 per kWhr (summer peak)--although, I don't "pay" any more than $0.30 per kWhr because my bill is less than 300 kWhrs per month. The $0.60 per kWhr is for usage over ~1,000 kWhrs per month. The new "Smart Meter" summer peak rates are $0.75 per kWhr for commercial accounts.

    One of the reasons I am so concerned about the current Net Metering plan (I buy power at $0.09 per kWhr at night, and get paid $0.30 per kWhr for summer afternoons)--is that, roughly, 1/2 the bill is related to energy charges (cost of generating the power). And the other 1/2 is distribution (and a smaller portion is long distance transmission charges).

    If I consume 250 kWhrs per month, and generate 400 kWhrs per month--that is ~650 kWhrs per month I am "moving" across the utility's power lines (basically I shift all of my loads to off-peak use, and nearly full generation goes to the utility during the peak time)... At current rates (around $0.20 per kWhr for flat rate residential at that tier), that would be ~$65 worth of local distribution costs--and I am paying $5.42 instead...

    Basically, I am getting a subsidy of $60 per month from the other rate payers (plus the 1/3 rebates/credits I got from the "state and feds" to pay for my install).

    And, if I was just paying the $0.12 per kWhr instead (residential flat rate) at 250 kWhrs per month--my bill would be $30 per month...

    So--if "everyone" did solar--where would the peak power go during the daytime (my system, ~2kWatts generated for almost 7 hours per day, and I consume an average of 0.49kWatts off-peak. (note that my average generation power is higher than my average consumption power--the power lines need to be sized for the larger generation currents that solar PV generates during the day--and there has to be a "matched" load somewhere to use that power--there is hardly any power storage/shifting in the network today).

    Granted--I am "forgiving" $300+ per year in unused power credits--but if I consume more power to burn up the credits (electric power, more electric heat/cooking/etc.)--the subsidies only get worse.

    If every home in the state where to do what I am doing right now (solar grid tied; not that could even be practical)--somebody (commercial, industrial, residential minimum charges) would have to pay more to keep the utilities network running as Net Metering is not economically feasible on a large scale--it would drive the utilities back into bankruptcy...

    Here is an old thread that I started that showed a school district actually ended up spending more for their power after installing solar because commercial billing is different... There is the energy generation charges, but there is also the other 1/2 of the typical bill which is the "reservation charges"--based on the peak 15 minute period in the last year... And with solar does not reduce that peak (if occurs during dark/cloudy weather)--or could make it worse because it is the peak of solar generation (solar generates 7 hours per day, but there are 24 hour per day loads--so to net to "zero" energy usage--solar peak power has to be higher/longer than average peak power from the loads spread out over 24 hours).

    In the end, I installed solar GT because--1. I did not trust the state public utility commission to not further mess-up our power charges (newest "smart meter" plans have $0.60 per kWhr for summer afternoon peak charge for roughly 15-20 days per year when A/C loads near generation/transmission capacity); 2. because I believed that older systems would be grand-fathered in with better rates/terms than newer systems (and so far--that has been true); and 3. that electric vehicles where going to be cost effective because of high fuel/road taxes and the absence of road taxes on electric vehicles (true so far).

    In the end, I did it because government "free money" and policies/incentives made the solar PV GT system worthwhile to me as an "investment" to hedge against future energy price increases. However, I am under no illusion that this "fixes" any of our long term financial or energy issues.

    -Bill

    By the way, what do you mean by "statically unlikely customer"?

    Size of system, amount of power I use, reasons for installing solar (not to reduce green house emissions), or what?
    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

    "If I consume 250 kWhrs per month, and generate 400 kWhrs per month--that is ~650 kWhrs per month I am "moving" across the utility's power lines (basically I shift all of my loads to off-peak use, and nearly full generation goes to the utility during the peak time)... At current rates (around $0.20 per kWhr for flat rate residential at that tier), that would be ~$65 worth of local distribution costs--and I am paying $5.42 instead..."

    If you are generating from within the network your electrons don't need to travel very far before they are used. Are you getting free access to the powerlines? I don't think so, it's more like an exchange. You have to think about losses and wholesale electricity pricing.

    Those electrons that you ship over to your neighbour during the day offset electrons that would otherwise come from much farther away. This essentially bypasses the utility's need to cover losses for those kWh. That saves them something like 6% off the top. What's more, your neighbor still gets charged for the losses as part of their applicable rate structure.

    But wait, later on you use electricity at night. Doesn't everything balances out in the reverse exchange? No... #1 Congestion is lower at night so losses should typically be lower. That might seem marginal but when you multiply it over a system it's millions of dollars. #2. Wholesale electricity rates are lower at night. It would take a truly thick headed utility to overlook the oppourtunity to trade day electricity for night electricity. British Columbia pretty much bases their energy policy on the spread between daytime and nighttime electricity rates.

    As to statistically likely vs unlikely customers: In general there's a strong correlation between energy use and affluence. This is fortuitous because it means that the very people using the most electricity are more likely to be able to afford the PV system which would in turn makes the most difference in their energy bills. You could call this customer group "targets" or "statistically likely customers" or whatever... Maybe I used a confusing term. Your home uses less than half the Californian average (3000 vs. 7000 kWh) so that's why I called you an unlikely PV customer.
  • Ricky
    Ricky Registered Users Posts: 20
    Re: Preprepared Roofs and Backfeeding Questions

    And Bill... Word on the street is that we're all likely to move to time of use rates in the near term as part of the smart meter roll out. I've heard this from vetran operators up to utility execs.

    You'd hope that having all the customers in one boat would simplify things? Not sure but it seems like the most equitable way to run things and I figure if everybody is on TOU rates the utility won't be able to jerk around PV owners by placing them in a separate category. The other positive is that "rational" TOU rates (i.e. not rigged rates) are statistically beneficial to PV system owners.

    P.S. I need more feedback on the PV Prepared (TM) roof concept.
  • peakbagger
    peakbagger Solar Expert Posts: 341 ✭✭✭
    Re: Preprepared Roofs and Backfeeding Questions

    In a static industry, the concept of a preprepared roof is probably viable but given that the PV industry is evolving on a monthly basis with rather significant changes to the the code on a yearly basis, prepreparing a roof is more of a marketing term than a defined standard. What was the best panel and inverter combination a year ago is probably not the best today and what was the best 5 years ago is probably out of production. Sure the solar industry could get together at some point and develop the equivalent of a ANSI standard specifying standard dimensions and mounting points, but to date, there really isnt anything in it for them to take on this effort and a lot of disadvantages to future designs for implemening a standard.

    Arguably, if the buider elects to run a capped oversized metalic conduit from an area adjacent to the service panel to an area under the roof that will be accessable post construction, that could be defiined as "preprepared". Very rarely discussed is that adding PV's adds some loads to roof, therefore, having some extra margin on the roof load could be argued is "preprepared. This is actually of more concern with SHW panels as they have a higher load.

    The inherent marketing value of "preprepared" is probably negligable to the average buyer so the only driver would be for a AHJ to require it. Of course generally for an AHJ to require something, there needs to be some sort of background and basis for the decision in case of a challenge, so its a catch 22.

    On a practical basis, my recomendation to people who are serious about installing roof mounted PV's is to seriously consider installing an EPDM underlayment under shingled roofs on the southerly exposure. This underlayment is inherently seal sealing, and is fairly easy to patch in new penetrations. As for standing seam roofs, getting a couple of capped roof penetrations in place when the roof is installed has some value as cutting them in after the fact is an exercise in fustration and an frequent future leak point.
  • Ricky
    Ricky Registered Users Posts: 20
    Re: Preprepared Roofs and Backfeeding Questions

    Thanks peakbagger. That is helpful information. Is mounting point the correct term or anchoring point or is there another term? The basic reason I'm thinking mounting points could be standardized before a static industry took form is that your racking system could potentially be built to accommodate legacy mounting points. Does that logic hold water?

    It's only my gut feeling but I think the need to standardize PV installation codes is going to become apparent sooner than expected. I agree the industry is experiencing constant change but I can't shake the feeling that a few simple modifications could potentially save a bundle. Who would mandate these standards? Good question. At the state level you'd think California would lay out the law. The law would be roof pitch needs to me this to this, roof penetrations need to be over here vs over there, conduit goes there, put EPDM over there etc. Do they have the power? I have no clue. I'm merely brain storming at this point.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Preprepared Roofs and Backfeeding Questions

    Maybe we better explain about how arrays are mounted to the roof.

    The panels are held by a mount made of several pieces of aluminium channel and bracket. The parts that contacts the roof are 'L' shaped, and the "mounting points" are holes spaced along the length. The standard procedure for mounting to a asphalt/fibreglass shingled roof is to drill pilot holes and run lag bolts into the sheathing below. (Lag bolts are "screws on steroids" with bolt heads.) There's not much chance of getting things to line up with the rafters, so short bolts are used; no through penetration. This works and doesn't leak; there's enough sealant provided by the tar in the shingles and the compression from tightening the bolts. The only time it would be a worry is if the shingles are already old and crumbling. Build a new house and put 50 year shingles on it and chances are you'll be changing the PV's out for something more modern and efficient before the roof starts to leak anyway.

    Weight-wise, you're looking at less than 40 lbs. per panel. A good roof structure is easily capable of supporting this additional load, as it is spread out over a large area (although concentrated at the mounting). Most of the weight goes straight down (gravity works that way) and for most roof pitches there would be little inclination to slide off even without the bolts, therefor in the best practices of engineering the bolts are called on to do very little in the way of resisting gravity.

    In some areas the climate may be extreme and call for additional measures. Worst-case scenario would be a place like the Canadian Maritimes where it can be boiling hot in Summer, super cold in Winter, with snow, hail, and high winds all trying to tear the panels off the roof. In such places extra care must be taken to ensure that the mounts, mounting, and roof itself can stand up to the extremes. You need an engineer to be sure.

    Lastly there is the case of the El Cheapo Fly-By-Night Roofing Company. If they built it with 2x4 rafters every 2' on center and sheathed it with 3/8 OSB then shingled with the cheapest thing they can find (no paper underneath either) you've got a problem in any case, solar panels not withstanding. Some companies feel its better to spend the money on bribing inspectors than actually doing the job right.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Preprepared Roofs and Backfeeding Questions

    If I was gong to "prep" a home for solar power on the roof... I would adjust planning codes and create solar access rights such that:
    1. A large percentage of the roof face south (or flat roof with access to shade free sun)
    2. Roof Angle set to optimum pitch for solar collection (if pitched roof)
    3. No obstructions (vent pipes, chimneys, etc.) to east, south, west
    4. No power lines/street lights/etc. to east, south, west
    5. No tall landscaping to east, south, west
    6. South Roofs should have access to sun from at least 9am-3pm to ESW.
    Huge numbers of homes do not have access rights to sun (trees, neighboring buildings, etc.). City Planning want complex roof lines to reduce "visual bulk" of homes/buildings (especially in scenic areas), etc...

    Other than running an empty conduit from an appropriately sized main service to the roof--most of the costs of an install are parts--not labor, so reducing installation labor costs are not huge part of the bill (certainly solar panels have come way down in price in the last few years, so labor cost is becoming more of an issue).

    But the lack of sun and south facing roof face with access to shadow free sun is something that no amount of money can resolve--and stopping even those that can afford the installation to give up).

    However, this does not come without costs... Here in California, we do have solar access rights (to a degree) and I could force my neighbors to pay thousands of dollars to trim/cut down their mature/large trees to save me 10% of $30 per month in power costs (there is a nice Redwood that I am watching at in one yard, and a live oak in another)...

    Regarding distribution--most of the utility's costs and losses (network vs transmission) are in local distribution... The physical plant costs to supply an average of 0.5 kWatts to a residence that practices conservation are about the same as to supply a drop to somebody who averages 2kWatts of power consumption... (everyone gets a 100-200 amp service and has the same access to peak power--i.e., I can use my power microwave, electric oven, power tools, and electric heaters, etc. just like the person next door). But the residence who conserves, does not pay for the network capacity to supply those peak loads (unlike commercial which pays reservation charges).

    And that leads back to the intent to make it economically feasible for a large percentage of homes to install solar PV...

    Years ago, there was a large subdivision that was being planned that would have installed solar PV on every home... The utility flat out refused to service the new development if it went forward as planned (I cannot find the article, and I do not know what the eventual outcome was).

    Just from the utility ledger point of view... If the average new home (affluent with lots of electrical goodies like A/C, dual electric ovens, lots of accent lighting, etc.) and consumes the national average of 10,000 kWhrs per year--In California, that is near a $200 per month electrical bill per home... If that subdivision was designed to have Solar PV GT systems to exactly equal the homes net electrical consumption--then every home would have a $5.42 per month electric bill... But with infrastructure costs that would be would have supported a $200 per month bill, of which near 50% was allocated to infrastructure payments...

    Where would the ~$100 per month money/revenue stream come from to pay for the infrastructure? If it comes from the residences of the subdivision, they would still have to pay at least $100 per month for reservation charges--which make solar even more expensive (at best, you could only cut your power bill by 1/2). Very roughly, the homes are paying only 1/20th of their share of costs for the local grid.

    Or would you increase the charges to people who don't have solar? -- Well, that hits the "poor" that don't have solar and those people that can't install solar because of other issues (shading, no south roof, etc.). That is not fair. Charge the Commercial/Industrial customers and have them subsidize the Solar powered homes? That increases the cost of business in California and forces wages down and jobs out of state/country (which is already happening) and increases the price of products and services of the firms that are left behind... Which is just cost shifting.

    Regarding Smart Metering and moving everyone to Time Of Use billing--Other than possibly reducing costs (no more meter readers)--Smart Meters are the result of government policies/subsidies that have Meter Companies (and related services) chasing after billions of dollars of government cash...

    Another thread I created is Grid of the Future: Smart Meters where we discussed some of these issues (and possible hacking opportunities / network insecurity provided by a "smart grid").

    If the utility was so concerned about cutting costs of meter reading--they could have saved 1/2 to 2/3rd's the costs of meter reading by simply going to a 2 or 3 month meter reading schedule vs the current 1 month schedule. And, if they wanted, use predictive technologies to estimate the unread months billing... A lot cheaper (and no hacking opportunities/security holes) than a smart meter.

    As to whether or not I am a statical outlier--There are probably two groups of Solar GT owners... Those that are wealthy and have the money to install a system (energy costs are probably not a concern anyway) and those that care about the environment/conservation/etc. and watch their energy use fairly closely (and have already implemented personal conservation measures before even installing their PV array).

    While I am not a supporter of "Global Warming"--I am a conservationist/"fiscalist" engineer--I try to leave things a little better than I found them...

    However, I find much of government actions to be beset by the "law of unintended consequences" which frequently create the exact effect that they were intended to prevent int he first place (i.e., green polices to create green jobs which create few green jobs and end up killing lots of other jobs in the process while causing un-green damage--such as wind turbines killing birds, dams and turbines killing native fish, salt water intrusion, change in silting patterns, loss of sand to beaches causing shoreline erosion, etc.).

    And while one arm of government is subsidizing solar installations (via tax money and by hidden required charges by utilities)--another part is enforcing planning codes (roof lines, community look and feel, landscaping, aerial utility right-of-ways, neighbor additions, HOA covenants, etc.) that make installing solar PV and Thermal almost impossible.

    Nothing is "free":

    FirstEnergy to give away 3.75 million low-energy light bulbs:
    FirstEnergy Corp. is getting ready to leave two high-efficiency light bulbs on your doorstep. But they're not a gift.

    The utility will charge average users 60 cents a month extra on their electric bills for the next three years -- $21.60 all together. That covers the cost of the bulbs ($3.50 each), their delivery and the delivery of the power consumers would have used if they didn't have them.

    The good news: These compact fluorescent bulbs will reduce your electricity use. If you replace two 100-watt incandescent bulbs with these 23-watt, warm-white CFLs, you'll save $60 by the time they burn out in five to seven years, according to FirstEnergy.
    And you'll pay for the bulbs whether you use them or not, so it makes sense to use them.

    FirstEnergy is distributing the 3.75 million bulbs to comply in part with an energy law enacted in Ohio last year. The law requires utilities to cut their customers' energy use by 22 percent by 2025. The law also mandates that utilities use solar, wind turbines and other renewable energy sources. The Public Utilities Commission of Ohio approved the light bulb distribution and the extra charge on your bill.
    Two CFL's for $21.60??? I can buy CFL bulbs for $1 each all day long... So, instead of 20 CFL bulbs for the whole home--the people only get two for the same amount of money. Sounds really nice.

    And, at least from the article (may have been poorly written); "...covers the cost of...delivery of the power consumers would have used if they didn't have them..." It looks like the utility is getting paid by the customers (tax/fee required by law) for not delivering the power the CFL program is saving... :roll:

    I am sure the people in Ohio are happy the government is watching out for them.

    Not claiming that I have all of the answers--but from an engineering and financial point of view--the picture is pretty muddy for solar RE at the residential level. Instead, it would probably be better to set aside a clear field someplace (in town, or down in So Cal deserts) of xxx square feet per home/business/etc. and install the Solar RE system there (with professional maintenance) vs installing on home roofs just from a cost/efficiency/practicality point of view.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Preprepared Roofs and Backfeeding Questions

    Ah, the ol' "charge 'em for not buying your product" trick!

    Even up here CFL's aren't that expensive!

    I'll say this for BC Hydro: their "green" incentives aren't a scam. They've given rebates and trade-ins on CFL's and LED Christmas lights - buy them wherever you want at whatever price; same rebate. They give you money for scrapping your old 'frige, and currently have incentives on for EnergyStar TV's and appliances.

    And this from a company that charges seven cents for electric to begin with.

    Sounds like some US Utilities need a little consumer pressure on them.
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Preprepared Roofs and Backfeeding Questions

    I've got a good shot of my roof here:
    http://www.mike-burgess.org/images/FinalRoof_c.jpg
    that shows the mounting posts (installed first, then shingles, and regular plumping vent jacks over them to make it all weathertight) and you can see the rails on the posts.
    Between the 2 arrays, you can see 1 rail that connects between, the DC cables are tucked up inside the internal channel of the rail. other photos at
    http://www.mike-burgess.org/PVinfo_1.html
    Getting the PV installers to work / schedule with the roofers was a struggle, but got it ironed out in the end.

    Of course, now there is the "Fire Department Access Debacle" trying to kill rooftop PV.
    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 ,

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

    Sort of reminds me of when I was doing the major remodel of my home... I not only looked at energy (and knowing what I know now--I would have done more/been more careful)--I also looked at fire sprinklers...

    Why not--It is a small two story older home and I was going to have the walls open (and much of the ceilings) be cause I was installing insulation...

    Well, looking around. I found that the dollar damage from fires/smoke was almost exactly the same as the water damage from sprinklers (putting out the fires and accidental activations/leaks/etc.).

    So, now I am left looking at just the life saving of sprinklers--a good thing. But, to install a sprinkler system I would have to have it permitted and approved.... Well these are not just low flow shower heads for residential use around here... These (seem to be) full flow commercial systems (or at least similar to commercial) and I would need something like a 1.25" or 1.50" water meter. I already have a 1" meter and pay some $20+ for the privilege (came with the home in 1930's). And the standard size is 5/8" around here (which would be fine with me).

    In the end, the cost per month for the "right size" meter (and line from the water main) charges would be more than my fire insurance is today...

    Our city is requiring "major remodels" and new home construction to have fire sprinklers... But our water connection fees are so high (based on the assumption that if you have a large meter, that you will use lots of water, and are willing to pay through the nose for the privilege) that the the powers that be have discussed an alternative billing scheme where you could have access to high volume water flow for that once in a life time need, without the burdens of paying for the infrastructure like you are going to use that large flow every day of the year.

    -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

    "Where would the ~$100 per month money/revenue stream come from to pay for the infrastructure? If it comes from the residences of the subdivision, they would still have to pay at least $100 per month for reservation charges--which make solar even more expensive (at best, you could only cut your power bill by 1/2). Very roughly, the homes are paying only 1/20th of their share of costs for the local grid."

    I see what you're getting at but by this logic the customer that practices conservation is avoiding their share of local grid costs. This logic doesn't make sense to me. To reach an equitable solution to electricity pricing you need to have accurate prices that reflect costs. To get these price signals you need dynamic metering (smart meters). Up to this point we simply haven't had a cost effective metering technology but this situation is quickly changing.

    Here's a study that examines the situation:

    http://www.hks.harvard.edu/hepg/Papers/2009/The%20Power%20of%20Experimentation%20_01-11-09_.pdf

    "The cost of upgrading all residential meters in the US would be staggering. Using the California cost estimates as a proxy, the nationwide cost would be around $40 billion. Is it worthwhile to pursue AMI (Advanced Metering Infrastructure)? Yes, if two conditions are met. First, AMI is accompanied by dynamic pricing. This represents a major change in the pricing paradigm and is the subject of much deliberation by state commissions. Second, if customers respond to dynamic pricing sufficiently to offset the net investment in AMI (i.e., that amount which is not offset by savings in distribution system costs). That, of course, is an empirical issue and is the focus on this paper."

    PV generation follows the load profile relatively well so this electricity has a higher value within dynamic pricing scenarios. Point of use PV generation also reduces distribution losses so there's an additional value associated with this type of generation. Everyone benefits from reducing losses and capacity payments.