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  • OT Solar planning help needed please!

    Thinking of going solar as I can buy new US made panels for 80 cents a watt ready to install & 1/2 that if I assemble. I have an electric 50 gal water heater I'd change to LP. My average elect use is 1000kw-1200kw per month. Can anyone give me an idea how many 260watt panels I'll need. We have a very high south facing roof thats seems steep enough to work well. I'll light the shop with solar & put in a 3 phase 15kw generator. Thanks!
    "Let me recommend the best medicine in the
    world: a long journey, at a mild season, through a pleasant
    country, in easy stages."
    ~ James Madison

  • #2
    Tell us more... assuming you are going to charge batteries, what's the peak power that you want from the battery or panel array? Averages don't mean squat unless you store that all away somewhere and use it for the peaks. And you generally use AC not DC, so honking inverter needed (sized for the peaks).

    If no batteries, just dump the power into your hot water tank or heating system!
    Last edited by lakeside53; 12-20-2012, 02:20 AM.

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    • #3
      "My average elect use is 1000kw-1200kw per month."

      WHAT? Are you talking about kilowatt hours?
      At 1000 KWH per month you would need 1,000,000/30 days/24hours= 1.388 kwh per hour. But since you have about 8 hours per day of daylight you need 412.66 kw production for those hours in brilliant sunlight. Oh wait you're in Michigan. Better 4 hours on a good day. so you need 32.05 panels for a 30 day month. At .80 per watt you need to ante up $33012.80 to start. That is until the next hailstorm which in Michigan is what, 2,3 years? So $10,000 or so per year in panels while that generator eats your ass alive for the 3 phase. Spit out that Koolaid .

      remember, TANSTAAFL
      with fond memories of Robert HeinLein

      Comment


      • #4
        Please share more info, the closest I've found is just under $2/watt.

        Your optimal roof angle is based off of your latitude and you can use your current roof angle to estimate average annual efficiency due to the angle. Next factor in panel efficiency, panel area, and your area's solar irradiance number.

        If average solar irradiance at your location is 3kWh/day per square meter then your roof angle is ideal, you are looking at 70-74% efficiency (or 2.1kWh) times whatever the panel efficiency might be. Panel efficiencies run 7-20% depending on type. At 7% on the ideal roof angle, you'd get about 147Wh/day per square meter. You'd need about 272 square meters (2,928 square feet) to manage 40kWh/day on a 1200kWh/month cycle. The numbers change with irradiance, panel efficiency, and angle. There can be reasonable benefit to different summer/winter angles, but that can bring its own challenges. If irradiance is 4kWh per square meter per day, your panels are 20% efficient, and you use a summer/winter angle, then 67 square meters (721 square feet) should get you 40kWh/day.

        My numbers are just rough and don't account for gaps, borders, or spacing either.

        Comment


        • #5
          There are multiple online calculators to help with this. Try this map-based one:

          http://www.nrel.gov/rredc/pvwatts/grid.html

          In general, grid-tied systems are the best as you don't need to maintain a huge bank of batteries. Of course, it helps immensely if your state has net-metering so that your PV array can spin your meter backwards! IF you do have net metering, also consider getting TOUR (time of use rates), i.e., peak/off-peak pricing - this really helps defray the cost of installing a PV system as most peak-rate times coincide with daylight hours.

          Brian
          Taxachusetts

          Comment


          • #6
            Originally posted by flylo View Post
            Thinking of going solarThanks!
            My advice is "Stop thinking so much". :-) In any location but the "sunny southwest" , fergettit for any but incidental (like pre-heating water) use.
            ...lew...

            Comment


            • #7
              Originally posted by tdmidget View Post
              "My average elect use is 1000kw-1200kw per month."

              WHAT? Are you talking about kilowatt hours?
              At 1000 KWH per month you would need 1,000,000/30 days/24hours= 1.388 kwh per hour. But since you have about 8 hours per day of daylight you need 412.66 kw production for those hours in brilliant sunlight. Oh wait you're in Michigan. Better 4 hours on a good day. so you need 32.05 panels for a 30 day month. At .80 per watt you need to ante up $33012.80 to start. That is until the next hailstorm which in Michigan is what, 2,3 years? So $10,000 or so per year in panels while that generator eats your ass alive for the 3 phase. Spit out that Koolaid .

              remember, TANSTAAFL
              with fond memories of Robert HeinLein
              A little OVERDOSE of "realism"............. that isn't entirely realistic.

              Solar beats heck out of wind power...... in small systems

              in reverse order....

              1) 3 phase..... Outback brand inverters will chain to make 3 phase.... problem solved, no generator. Maybe other brands will also.

              2) I have had panels up for about 20 years. No hailstorm has damaged them yet, and we have had a number of them, with golf ball or larger hail. What destroyed the original set was a tree on the north side of them falling and squashing them, a couple years ago.

              3) If you get the right type of panels, like my original set, they produce well (half power) on an overcast but not dark day... so there is more input than you think. Old panels were single crystal.... a new multicrystalline panel I have produces well in sun but drops to nothing every time a cloud of gnats flies over it... can't tolerate ANY less than full sun... you gets what you pays for.

              4) Yes, absolutely you have to be realistic about the total sunshine input. Some places are simply not candidates, but it also is not true that Michigan is impossible.... You will very substantially improve your numbers by adjusting angle seasonally, and also by sun tracking. Also "improves" your costs......if larger is better...

              5) net metering and grid tie.... THIS has been a bunch of BS...... Who wants a setup that MUST BE OFF if the grid goes down? Up to recently, all grid tie systems HAD TO shut down and produce nothing if the grid was down.... STUPID.... you have no power, so you WANT to use solar, but the anti-islanding rules meant that a UL recognized inverter COULD NOT OPERATE without the grid, so when power is out, it sits like a brick, doing nothing but costing you money.

              This is starting to change. Some systems are being allowed that can be used with a cutover switch similar to a generator.
              1601

              Keep eye on ball.
              Hashim Khan

              Comment


              • #8
                Solar is great if you don't use much electricity. Machine tools? With lead acid batteries? Better take a pot of strong coffee and read up on battery life and discharge rates, talked me out of it, completely.
                We all should look at energy use. But buck for buck you will likely get your greatest return on conservation. Read up on German Passive houses.

                This is the best I have found with full documentation of results of various projects.
                http://www.nofossil.org/
                more
                http://www.builditsolar.com/Projects/Projects.htm
                http://www.passivehouse.us/passiveHouse/PHIUSHome.html
                hot air solar panel research by an engineer
                http://www.youtube.com/watch?v=gBLQ2ZUeP7w

                "Put on a sweater" - Former president Jimmy Carter who had a degree in engineering, and installed solar panels on the white house. A white house solar panel is now in a Chinese Museum. They were removed by former president Ronald Reagan who was a Hollywood actor.

                Sounds like JT has real life experience, I don't, I would ask him about batteries.
                Last edited by Abner; 12-20-2012, 10:37 AM.

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                • #9
                  Start reading Home Power magazine to get a dose of "real world" solar systems. A lot of the articles feature people living totally off grid, but they don't always live a "power rich" lifestyle. If you are installing this system yourself, it still has to meet all national, state and local electric code. As said above, don't expect full output from your panels, except maybe at noon on an absolutely clear summer day. The life of the panels is very finite, even the newer panel degrade with time. In 20 years the output of todays panels will have degraded to the point where their are nearly useless. Panels have dropped in price where watts per dollar seems cheap, but the cabling, control and monitoring equipment, inverters and suitable batteries are still the major cost of the installation.
                  Last edited by Rosco-P; 12-20-2012, 11:18 AM.

                  Comment


                  • #10
                    Grid tie or stand alone system? Two different animals. Rebates for one nothing for the other.

                    I live at the southern end of the Sierras,I get more sun than you so take me with a grain of salt.I use more energy for cooling than heating.
                    I self installed a 7kw grid tie twelve years ago. ( thirty two 180 watt panels) Best thing I ever did. The bill went from 200/250$ a month to 400/500 a year.
                    I pay yearly because output is really seasonal.

                    What I learned:
                    Buy as big of an inverter as you can afford,it's the heart of the system and the biggest single expense.Then later on you can add more panels if the system is too small. Max out a small inverter and you have to buy a bigger one if you want to expand.

                    I went by the book to determine the tilt of the panels. ( average between summer and winter). I should have made them flatter.Summer is the real production time.Winter is spotty.
                    Then again, a friend in Montana tips his more to the vertical in the winter to catch reflected light from the snow.

                    My inverter has remote computer connection terminals.I wish I had run computer wiring in the conduit when I laid it. Sure would be nice to click a button and monitor them.

                    If there are trees to the south of the panels,sooner or later they will get tall enough to shade the panel.
                    Lucky for me,I have an understanding neighbor that lets me trim his trees.

                    Solar trackers? I dunno,I think I would spend that money on some more panels. The radiation isn't enough until around 9/10 o'clock. Early morning and evening its traveling through too much atmosphere.

                    Seasonal tilt?Absolutely .Too bad I didn't think about that when I built mine.

                    How much wind do you have? The smaller eggbeaters have really improved.

                    p.s. I love my tankless water heater,I can take a shower for days.
                    Last edited by 1-800miner; 12-20-2012, 11:52 AM.

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                    • #11
                      I have 2 new 12,000 watt inverters plus 3 used 2000 watts, I've always gotten 10 years + on lead acid batteries but I take good care of them.
                      2ManyHobbies I PMed you the info on the supplier. I'll do my homework & decide, Thanks All!
                      "Let me recommend the best medicine in the
                      world: a long journey, at a mild season, through a pleasant
                      country, in easy stages."
                      ~ James Madison

                      Comment


                      • #12
                        I wanted to do a Grid-Tie system, however, my Electric Company here in Portland Oregon, will not approve any system that is not installed by
                        qualified "Good Buddy" Contractors and Electricians that use qualified equipment.
                        I know the Safety concerns with back-feeding power during an outage, but, the cutout circuits are not all that complicated.
                        I becomes so expensive, that any dollar incentives available are only a drop in the bucket and the cost is prohibitive.
                        They also reserve the rite to come on your property, unannounced, for regular inspections.
                        I understand that individuals can do the installs with the proper paperwork and approvals.
                        I have not been able to find any one person that was able to get through the Red Tape.
                        Tom M.

                        Comment


                        • #13
                          Go to the Florida Solar Energy Center's website. It's located at Kennedy Space Center and run by the US government and the State or Florida and the University of Central Florida. They test EVERYTHING! You can get a lot of advice and factual information there instead of the manufacturer's and retailer's BullSh1T. If you're buying this through a retailer that's gong to install it for you, you'll probably find that everything that they tell is wrong or else a flat out lie! Most are absolutely clueless about what they're doing.

                          FWIW Florida had a rebate program up until a few years ago and the retailers were selling systems that were entitled to get the rebate but the state was two years behind in paying (the rebates had to be reauthorized every year) however the retailers SWORE that the buyers would get their rebates. NOT!

                          The lazy, sorry, stupid retailers here were installing the collectors flat on people's roofs no matter which way they faced and no matter which way they pointed. Solar collectors WILL NOT work that way.

                          My advice, go take a solar energy class at a nearby college. I did and after I knew something about SE I found a company that had a GOOD system and I bought it and it's been up for over 25 years now with very few problems.

                          Don't trust anything a retailer tells you!
                          Go verify it on one of the reputable websites. Florida runs one, so does California, and I think both Texas and Arizona.

                          Comment


                          • #14
                            Originally posted by mayfieldtm View Post
                            I wanted to do a Grid-Tie system, however, my Electric Company here in Portland Oregon, will not approve any system that is not installed by
                            qualified "Good Buddy" Contractors and Electricians that use qualified equipment.
                            I know the Safety concerns with back-feeding power during an outage, but, the cutout circuits are not all that complicated.
                            I becomes so expensive, that any dollar incentives available are only a drop in the bucket and the cost is prohibitive.
                            They also reserve the rite to come on your property, unannounced, for regular inspections.
                            I understand that individuals can do the installs with the proper paperwork and approvals.
                            I have not been able to find any one person that was able to get through the Red Tape.
                            Tom M.
                            Oh, oh that sounds like the same arrangement that they had here in Florida! I called EVERY registered installer and talked to them and NONE of them knew anything about electricity or about solar energy systems. They were just throwing systems on people's roofs with no regard to where they pointed or if they were shaded or anything else. I TRIED to get a couple of them to install a system on a free standing frame that I could properly orientate but none of them would do anything other that a roof mount. (I also didn't want the eventual roof leaks!) I took the contractor's test and aced it with 100% score but there's not even a way to get the contractor's license any more. It seems that there was a good old boy network of power companies, retailers and State of Florida office that set up this system and only allowed in their buddies and then closed it to everyone else, including licensed electricians and contractors.

                            yeah it sounds like the same SCAM is going on where you live. IIRC they promise a 40% federal rebate and a certain amount ($2.40?) per KWH rebate from the state. If that's it, STAY AWAY from it! If you really want solar power do your homework and learn what you need and then buy and install it properly. The crap these folks are selling will work POORLY at best and won't last long. Go look at the specs for the inverters and panels that they're using. They're made in China and only good for ten years. (Some do have German names like Siemans but they're still MADE in China!)

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                            • #15
                              Flippin 'eck, "everything is made in China" these days and even the sun shines on China before it shines of the US, about 13 hours.

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