Solar Panel Grid Tie does not look as good as I thought

Azel
Azel Registered Users Posts: 9
I hear quite a bit about going with a grid-tie system with ‘solar panels’ and it sounded good, but I failed to figured in that the sun only gives you about 5 hours of useable solar energy a day. I saw many videos on Youtube where people showed how their electric meters were running backwards (and it seemed so exciting), but what happens the other 19 hours of the day? 5 hours is only 21 % of 24 hours. The meter runs forward the other 19 hours. The grid-tie system only offsets 21% of your total electric bill.

I do think a grid-tie system might work well with ‘wind solar’ energy. Here in Texas, USA wind solar would not work at all during the summer months, but it would work very well, during the Fall and Spring (our windy months). I have not worked out the figures, but grid-tie with wind solar should work well four to six months out of the year. If I am correct (and I would have to take a whole years reading to check it), wind solar might cut ones electric bill by 50% over a year.

If one could afford two systems, solar panel and wind solar. I think that a ‘solar panel’ off-grid system with a battery bank would, allow one to power most small ‘low watt usage’ appliances 24 hours a day. And a gird-tie ‘wind solar’ system would help offset the power used by the ‘large watt usage’ appliances six months out of the year. It’s not a perfect system, but it should power everything except the large watt usage appliances during six months of the year.

What are your thoughts on the subject?

Comments

  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Solar Panel Grid Tie does not look as good as I thought
    Azel wrote: »
    I hear quite a bit about going with a grid-tie system with ‘solar panels’ and it sounded good, but I failed to figured in that the sun only gives you about 5 hours of useable solar energy a day. I saw many videos on Youtube where people showed how their electric meters were running backwards (and it seemed so exciting), but what happens the other 19 hours of the day? 5 hours is only 21 % of 24 hours. The meter runs forward the other 19 hours. The grid-tie system only offsets 21% of your total electric bill.

    I do think a grid-tie system might work well with ‘wind solar’ energy. Here in Texas, USA wind solar would not work at all during the summer months, but it would work very well, during the Fall and Spring (our windy months). I have not worked out the figures, but grid-tie with wind solar should work well four to six months out of the year. If I am correct (and I would have to take a whole years reading to check it), wind solar might cut ones electric bill by 50% over a year.

    If one could afford two systems, solar panel and wind solar. I think that a ‘solar panel’ off-grid system with a battery bank would, allow one to power most small ‘low watt usage’ appliances 24 hours a day. And a gird-tie ‘wind solar’ system would help offset the power used by the ‘large watt usage’ appliances six months out of the year. It’s not a perfect system, but it should power everything except the large watt usage appliances during six months of the year.

    What are your thoughts on the subject?

    I hardly know where to start, but here are a couple of things...

    How much a PV system will offset your electric bill depends on (among other things) how large the system is. It has nothing to do with what portion of a 24 hour day it is producing electricity. You can build a system which will totally offset your bill; in that case you would push energy onto the grid during the day and draw it back out at night.

    What in the heck is "wind solar"? With any wind system, you have to be very careful. Many folks have gotten burned by installing wind generators a) which are total junk, b) in locations where there is not enough of a wind resource to make even enough electricity for the equipment to pay for itself, or c) all of the above.
  • rollandelliott
    rollandelliott Solar Expert Posts: 834 ✭✭
    Re: Solar Panel Grid Tie does not look as good as I thought

    The grid-tie system only offsets 21% of your total electric bill.

    Really? then why is my bill around 60% less?

    Do you have thousands of $$$ to invest in a solar systme that will take 7 years or more to BREAK even on?
    Are you skillfull enough to install your own system for $2/watt or do you want to hire someone at $4 to $5 a watt?

    Does your utility company even offer net metering?
    Austin TX has some great solar rebate programs.

    For most people solar grid tie does not look good because they can't afford it and they dont' even know if they will be living in the same house 7 years from now, hence too long of a pay back period.

    so in general you are right grid tie solar is not for most, but your reasoning doesn't really make sense, as the time of energy harvest is not exactly proportional to amount of energy needed to power your home. In other words you can have a solar system that does not run 100% of the time, but still gives you 100% of your energy needs.
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Solar Panel Grid Tie does not look as good as I thought
    Azel wrote: »
    I hear quite a bit about going with a grid-tie system with ‘solar panels’ and it sounded good, but I failed to figured in that the sun only gives you about 5 hours of useable solar energy a day. I saw many videos on Youtube where people showed how their electric meters were running backwards (and it seemed so exciting), but what happens the other 19 hours of the day? 5 hours is only 21 % of 24 hours. The meter runs forward the other 19 hours. The grid-tie system only offsets 21% of your total electric bill.
    What are your thoughts on the subject?

    To extend your reasoning a little farther: At at typical signal-controlled intersection, each light is green only 45% of the time. Therefore only 45% of the traffic ever gets through. Where did the other 55% of the cars go?
    SMA SB 3000, old BP panels.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Solar Panel Grid Tie does not look as good as I thought

    Don't forget FITs and tax credits, that can futher reduce costs in the net.

    Back tot he OP, in essence, you sell to the grid when you have excess capacity (using less than you a generating) and buy back when you are short. Depending on how your utility meters (time if day, net metering, preferential rates of PV etc.) you can use more power than you produce and still have a near zero bill in some cases.

    Do some more reading, here and elsewhere, and do a proper analysis of your site to determine how much power you can actually produce.

    Tony
  • Azel
    Azel Registered Users Posts: 9
    Re: Solar Panel Grid Tie does not look as good as I thought

    Sorry, I did not make myself clear. My air conditioning is my biggest power watt user in the summer. I used a Kill-a-watt meter and tested all my home appliances power use. I added up the total kWh each used in a month. My air conditioner is about 2/3 of my total electric bill, because it runs 24/7 in the summer.

    My air conditioner draws about 700 watts when the compressor is running. It does cycle, but not much on these 100 degree plus days. Besides the kill-a-watt meter took this into account.

    I thought that if I put in a grid-tie solar panel system that produces 700 watts I would offset my air conditioner, but I didn’t figure in that this would only work for 5 hours a day. I don’t know if Abilene, Texas electric company has a buy back policy. But, if I understand you correctly, I would have to produce much more than 700 watts to sell electricity back to the grid. Probably around a 4000 watt solar panel system, or more if I figure in lost efficiency. And the local power company would have to buy that power, which I don’t know if they would. (Does anyone know who I would contact to find out.)

    But, yes I have read a few books, and I have used a kill-a-watt meter to add up the kWh each appliance uses over a month. My total kWh use each month is between 800 to 900 kWh (peak summer), and more than half of it is the air conditioner. So, I feel like I am half way there in understanding the power I am using and where it is going. It was a learning experience. I have a small freg, and my big box fans use as much as the freg, because I run them all day in the summer. But, no appliance comes even close the the air conditioner use of power. If it were not for it, my power bill would be half.

    Anyway, I have learned something. Thanks

    ps Sorry, about calling it wind solar, but the wind is produced by solar energy, right? grin
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Solar Panel Grid Tie does not look as good as I thought

    You might consider a proper energy audit. For example, changing from a conventional A/C unti to a ground source or hot water recovery heat pump system might be way more cost effective than you realize. Also, consider other energy saving options, like adding insulation, shade trees, awnings etc. The bottom line is, your cheapest energy dollar is the one you don't spend. (conservtion rules!). Also look seriously at the fridge. If it is more than a couple of years old, a new one is likey to be very much more efficient, and might pay off to replace. (you also mention that you have a " small fridge", amny small fridges are energy pigs, especially gi Ben thier size).

    Look at your electronics, your lighting etc, as there have been great advances in both in recent year. For example, I am now running LED lights exclusively, dropping power use to 1/3 what I had with CFls and 1/10 of conventional bulbs.

    As for your utility, simply. Pick up the phone and call them, and find out who you need to deal with about info for PV installations. Or better yet, call a couple of local solar contractors and have them give you an Assesment. They will know the net/net of your local situation.

    Remember, conservtion is way cheaper than PV. Do everything you can do to convert, then, and only then consider PV. (if money is the issue!)

    Good luck, nd keep in touch,

    Tony
  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    Re: Solar Panel Grid Tie does not look as good as I thought

    Conservation should always be your first watchword in a solar design, higher efficency AC unit, more insulation higher set points and air circulation all will contribute to a lower energy footprintand are more cost effective.

    THEN look at grid tie solar from the perspective of either reducing your utility cost or going all the way to net zero. If you have a TOU plan really that is what you want, see what your on peak consumption is replace that with grid tie is almost always the best ROI proposal. It is hard to beat off peak rate from the utility companies, like mine is $0.056 kWh. My on peak is $0.175 kWh, much better payback replacement with solar.
  • rollandelliott
    rollandelliott Solar Expert Posts: 834 ✭✭
    Re: Solar Panel Grid Tie does not look as good as I thought

    I guess the simplest solution is to use your air conditioner as little as possible. I live in an area that is 5 degrees F cooler than yours year round. I use my AC about 2 weeks max, and everyone I mention this too thinks I'm nuts.

    If you must have an air conditioner make sure your duct work is not in your attic, that will loose 15% off the bat, see the energy conservation forum for a recent thread on that. When your current air conditioner dies, buy an energy efficient one. Switching from a 15 year old one to a 21 SEER one might save you 30 to 50% on your bill. Add insulation ,etc.

    I'm going to add that NONE of these solutions is a short term one. They are long term investments that take typically 4 to 10 years to simply break even. People ask me all the time how they can save money, but as soon as they hear it's going to take a long time to get back they are uninterested.

    I guess it's the age of instant gratification. Just like the recently proposed new MPG standards for cars of 54.5MPG. All the media can fixate on is that cars will cost around $3,000 more to be this efficient. Never mind that over the lifetime of the car, the driver will save a boat load on gas.

    No wonder the USA's saving rate is one of the lowest among industrialized nations.
  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Solar Panel Grid Tie does not look as good as I thought
    If you must have an air conditioner make sure your duct work is not in your attic...
    For the vast majority of existing homes, moving the ductwork out of the attic isn't really an option.
  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Solar Panel Grid Tie does not look as good as I thought
    Azel wrote: »
    Sorry, I did not make myself clear. My air conditioning is my biggest power watt user in the summer. I used a Kill-a-watt meter and tested all my home appliances power use. I added up the total kWh each used in a month. My air conditioner is about 2/3 of my total electric bill, because it runs 24/7 in the summer.
    If your A/C must run continuously to keep your house comfortable in the summer, something is wrong. Either it is undersized for your house, or it is malfunctioning, or your system has very bad air leaks in the ducts, or your doors and windows are letting a lot of air exchange with the outside, or you are keeping your thermostat unreasonably low, or (which is likely) some combination of all those things. Before you even consider buying any sort of distributed energy producing equipment, you should make an investment in money, time, and/or effort to get that situation under control. IMO, of course.

    Here in Austin, if your house is more than 10 years old it must pass an energy audit before you can qualify for any financial incentives for installing solar.
  • rollandelliott
    rollandelliott Solar Expert Posts: 834 ✭✭
    Re: Solar Panel Grid Tie does not look as good as I thought
    ggunn wrote: »
    For the vast majority of existing homes, moving the ductwork out of the attic isn't really an option.

    I'm going to do it in around a month. I guess if you dont' have framing, drywall, insulation skills it is not economically feasible.

    However adding more insulation, burying the existing duct work and possibly making an insulated knee wall around the HVAC unit is doable and feasible for many homes.
  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Solar Panel Grid Tie does not look as good as I thought
    I'm going to do it in around a month. I guess if you dont' have framing, drywall, insulation skills it is not economically feasible.

    However adding more insulation, burying the existing duct work and possibly making an insulated knee wall around the HVAC unit is doable and feasible for many homes.
    How do you plan to do it? Will you move the ductwork to under the ceiling, or will you raise the ceiling to encompass the ductwork?
  • rollandelliott
    rollandelliott Solar Expert Posts: 834 ✭✭
    Re: Solar Panel Grid Tie does not look as good as I thought

    I'LL POST some photos when I get to it. i'll be lowering duct work into living space and replace the flex duct with a trunk and header system. stupid home has vaulted ceilings which look nice, until you get the utility bill!!! that is.
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Solar Panel Grid Tie does not look as good as I thought
    I'LL POST some photos when I get to it. i'll be lowering duct work into living space and replace the flex duct with a trunk and header system.

    Bulkheads or dropped ceiling?
    Just getting rid of the flex duct may allow you to run a lower fan speed setting in your HVAC, saving some power there too.
    One nice thing about a high ceiling is that it allows you to install a ceiling fan. I was a disbeliever in their usefulness until I actually got one. Now I swear by them.
    There are some *really* low power DC-motor fans (running off 120vAC) with very long blades if you are on a tight energy budget. But you need a lot of room to install them.
    SMA SB 3000, old BP panels.
  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    Re: Solar Panel Grid Tie does not look as good as I thought

    I too am a firm believer in ceiling fans, our are 10 footers and running a fan on low slow speed is just enough to keep the stratification down and air moving, we also have huge windows and use cellular shades on them in summer. Our house is very comfortable with 79F set points and when stressed we increase set points to 81F. I just checked and it is 106F outside and the AC units are working very nicely at 50% duty cycle. Still room to improve I am sure with more insulation and protection on the duct work, but it will have to wait till fall, as I will be damn to go into that attic now. :D

    Considering a retro-foam project on the exterior walls this fall as well, mulling over the quotes for possible ROI.
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Solar Panel Grid Tie does not look as good as I thought
    solar_dave wrote: »
    ...but it will have to wait till fall, as I will be damn to go into that attic now. :D

    Wear a harness and rope so somebody can drag your body back out, just as if it were a hazardous gas situation. :-)
    SMA SB 3000, old BP panels.
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Solar Panel Grid Tie does not look as good as I thought
    solar_dave wrote: »
    I just checked and it is 106F outside and the AC units are working very nicely at 50% duty cycle. Still room to improve I am sure with more insulation and protection on the duct work,

    If your situation is similar to mine, once the ducts are well insulated you may want to consider running the AC fan full time to avoid hot spots inside. Although with the ceiling fans that may not be as significant for comfort. Only an issue if the off times of the duty cycle are long.
    SMA SB 3000, old BP panels.
  • rollandelliott
    rollandelliott Solar Expert Posts: 834 ✭✭
    Re: Solar Panel Grid Tie does not look as good as I thought

    "Bulkheads or dropped ceiling? "

    It will be a combination of both. For those of you wondering a bulk head is just a drywalled off section to hide the ducting, some people call it furring or a chaseway as well.

    who ever designed the hvac system in this house was an idiot. Now I have the pleasure of fixing it. Sad thing is 99% of the homes in the entire 1 million population of my city are designed this way.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Solar Panel Grid Tie does not look as good as I thought

    Would not a cheaper alternative be to super insulate the attic, including a pile of loose fill over the ducts, so that you reduce "cool loss" from the ducts, and heat gain from the hot attic,, perhaps coupled with better attic ventilation?

    Tony
  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    Re: Solar Panel Grid Tie does not look as good as I thought
    icarus wrote: »
    Would not a cheaper alternative be to super insulate the attic, including a pile of loose fill over the ducts, so that you reduce "cool loss" from the ducts, and heat gain from the hot attic,, perhaps coupled with better attic ventilation?

    Tony

    When I did the solar contract I got them to throw in 3 solar powered attic fans. I do think it helped a bunch, at least it did no harm, I do know that the attic was much "cooler" relatively speaking after the combination of south facing panels and the fans.
  • rollandelliott
    rollandelliott Solar Expert Posts: 834 ✭✭
    Re: Solar Panel Grid Tie does not look as good as I thought

    for most people yes, but I have such a spider web of tubes, and I put down a plywood floor up there years ago, plus the main line is over the cathedral ceiling which is next to impossible to insulate at the peak up there.
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Solar Panel Grid Tie does not look as good as I thought
    f... but I have such a spider web of tubes....

    The Internet in your attic? :-)
    SMA SB 3000, old BP panels.
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: Solar Panel Grid Tie does not look as good as I thought
    solar_dave wrote: »
    ... Our house is very comfortable with 79F set points and when stressed we increase set points to 81F...

    Humidity makes a huge difference in comfort, I moved to Missouri where the air can be dry or humid and during dry periods 80 is fine, when it's humid it can be rough. Having lived in North Florida, where line drying is a contest to see if the clothes mildew...
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.