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  • Looking for a large commercial solar system, not sure where to start.

    I apologize in advance if my incompetence on this subject becomes clear. I just recently began looking into solar systems, and I am far from fully understanding the concept.

    My (middle school) class recently began working on a project. We have plans to create a presentation that would convince the school board, and eventually the superintendent, to allow our school to "go solar." (Keep in mind we are actually trying to accomplish this, so any answers must be reasonable in terms of cost, warranties etc. ) We have created a spreadsheet showing how much power our school consumes per month, and how much DC energy we would need to produce to satisfy our school's consumption.

    jan feb mar apr may jun jul aug sep oct nov dec Anual
    kW usage 77,839 69,917 105,119 92,112 105,119 116,473 76,967 106,193 143,020 108289 78282 65378 1,144,708
    DC Production required 97298.75 87396.25 131398.75 115140 131398.75 145591.25 96208.75 132741.25 178775 135361.25 97852.5 81722.5 1430885

    When I try to calculate the amount of hourly kW production required in September, using the formula "Monthly production/30/5" Where 30 is the days and 5 is the hours, I get about 1200 kWh for that month, which is a way higher kWh amount than any system I have found so far has offered. Could someone help me find a cost efficient (I don't think anything above 1 mil dollars would help persuade them) system that would produce enough kWh for our school? If we are headed in the complete wrong direction with this project, or we are obviously missing a key factor that must be considered, I would appreciate it if someone would help clear up these misconceptions.

    PS: If anything in this question came across as vague or unclear, let me know and I will do my best to elaborate.

  • #2
    I would suggest an energy audit to see where you can improve efficiency thus allowing a smaller need for power production. Being a school you probably have substantial lighting requirements. Changing to all led lighting can make a big difference depending on what your lighting type is now.
    2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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    • #3
      I would suggest you approach this differently. Start by learning more about what the kWh usage translate to in dollars... what rate plan are you on? how much do you spend per month?

      Generally, I'd agree with littleharbor that a series of projects designed to improve energy efficiency may yield a better financial return than solar, and might be easier for the school board to approve if presented in smaller chunks of expenses over a period of time.

      If you are committed to pursuing solar, know that the DC to AC conversion efficiency for grid tie systems is generally much higher than the 80% you've assumed. You might want to seek a bid from a solar installer to get a rough idea of the costs and expected production of a system appropriate for your school, as it will be sensitive to the orientation of the array, among other things.

      To give you a rough idea of costs, here in San Diego, with south facing panels mounted at a low angle (<10 deg) and otherwise unobstructed, I have projected for my employer that a commercial 300 kW carport system costing $900k (pre incentive) would produce about 518000 kWh, reducing our electric bill by about $70k annually under our current rates (we currently use about 1.8 GWh annually, somewhat more than you but comparable).

      If $1M is your budget, and your system was similar to mine, that would offset about 45% of your annual consumption, but the actual dollar savings might be different depending on your rate plan.

      Another aspect to consider is how your usage varies throughout the day. For us, our load is level enough that the 300 kW PV system would never produce enough to exceed our consumption (even on weekends!), so "net metering" is not a concern and all generated energy will be immediately consumed. As your system size exceeds your power usage, you have to look more closely at how your power company handles that.
      Last edited by sensij; 03-10-2017, 01:51 AM. Reason: fixed errors.
      CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

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      • #4
        I will tell you that I worked on a project for a High School out in Nevada that had installed a 1 Mega Watt solar pv system. While it might have been a little oversized for a normal daily power usage the extra power it generated was sold to their electric utility and covered the days it did not produce due to cloudy weather as well as for early morning or late afternoon when the school was in use but the sun was not shining enough to generate useful power. At the time they installed that system the cost was around $4/watt before any rebates.

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        • #5
          Agreeing with Littleharbor, I'd suggest an energy audit as a start after or as an adjunct to much more focus on how energy is used, and then how to use less of it. I appreciate that yours is primarily a teaching task, and also that solar PV is sexy and has mass appeal at this time. But the meat and potatoes of a more sane existence and probably a better long term bet starts with using less energy, not simply getting more of it in what amounts to popular but usually - in spite of current headlines and pitches from those with $$ to make from solar and energy ignorance - less than cost effective ways like PV.

          Not my school/job and absolutely NOMB, but pushing PV, subtly or otherwise on young students at the expense of or before prior emphasis on the benefits of sane use reduction and conservation measures (Note: The two are similar but not the same) is showing students how to drink the koolaid before the healthier choices. Keep the cart before the horse, etc. The rest of the world can brainwash them into thinking solar can da anything/everything and save the world. Give them some ammo to help develop critical thinking skills and maybe make saner choices.

          If one goal is to produce cost effective choices to your school board, I bet the powers that be will take a better if only longer view of your students efforts if PV is among the list of things suggested for energy reduction, rather than an emphasis on PV as an end in itself. Put yourself in their shoes and consider that saving $$ is probably a goal closer to the forefront of the board's mind, rather than throwing expensive PV at electric bills. I bet it'll also make it easier for them to sell any of your student's ideas to the community.

          Also, maybe some efforts to a tie in using a simple explanation of the concept of the time value of money might be a valid precursor for your students intro into the world of long term thinking about the cost, or savings possible by effective energy use. FWIW, I believe I learned about compound interest in the 5th or 6th grade.

          A respectful suggestion: Download a free but slightly outdated version of "Solar Power Your Home for Dummies", or a newer, hardcopy at bookstores etc, for ~ $25 or so. Knowledge is power. Read the book and get some of the first. Then transfer the second to your students.

          Take what you want of the above. Scrap the rest.
          Last edited by J.P.M.; 03-09-2017, 07:33 PM. Reason: Corrected last word to Scrap. Apologies.

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          • #6
            Take what you want of the above. crap the rest.


            Small typo, still kinda the same meaning.


            2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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            • #7
              Originally posted by littleharbor View Post
              Take what you want of the above. crap the rest.


              Small typo, still kinda the same meaning.

              Sorry about that.

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              • #8
                Howdy RandomPerson, you have received some very good advise in the above posts. I would just add it's all about the ROI, where is your school? You will need to get a copy of the last years electricity bills as you absolutely have to understand the way you are currently billed for electricity, other wise you have no chance of working out the ROI, the other thing I would do before I went to far is contact your local POCO (power company) and city as to the local rules and regulations around solar, sometimes there are size restrictions on PV systems and sometime's on very large systems they wont let you put power back to the grid and or wont pay for power you put back to the grid, you need to think about that as I am assuming no one is at the school on Saturdays and Sundays and holidays so you will probably end up with a bunch of excess generation on those days, whats is going to happen to that??

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                • #9
                  Making a few estimates: 1,144,708kWh per year x 90% = 1.03mWh per year / ~1400kWh/kW (typical yearly yield ratio) = 736kW system size x ~$3/watt (depending on your local cost of living) = $2.2million. The bad news is your school is probably not eligible for the tax credits. The good news is that this is a big enough project that many solar finance outfits will gladly take you on. You should be able to put together a cash-flow positive deal.
                  Last edited by solar pete; 03-10-2017, 08:49 PM.
                  BSEE, R11, NABCEP, >1200kW installed

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                  • #10
                    Thank you for the replies. We are in Dallas Texas.

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                    • #11
                      I work for a major Solar EPC (engineering, procurement, construction) based in California. ....... This process is painless and fast, and at minimum would provide you and your class some strong value points to present to the school board.


                      Mode Note. We do not condone advertising on this Forum to obtain work for your company. Savant123 has been given a few days off to think about that. Another attempt will get them a permanent vacation.
                      Last edited by SunEagle; 03-23-2017, 02:33 PM. Reason: Added Note.

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                      • #12
                        Originally posted by _RandomPerson_ View Post
                        Thank you for the replies. We are in Dallas Texas.
                        I am afraid that being in Dallas probably means you don't have a good chance of convincing the school board.

                        What you need is:
                        1> billing information including the rate plan that you are using
                        2> what rate plan would you use if went solar
                        3> What kind of credit would you get for power produced and sent to the grid
                        (You == the school)


                        In other states you might have net metering where you'd be able to get credit for each kwh sent to the grid and take out an equal number of kwh at night (or the next day or a month later)
                        And in those cases you effectively size the installation to produce as much kwh as you consume, and it comes out good.

                        In your location you may be better off (financially) to have a small array that effectively cancels the consumption during some hours/days, but doesn't have much time where power is sent to the grid.

                        Or there may not really be any case that makes sense financially right now. (quite possible in TX with cheap power and probably no net-metering)

                        A small array shaving off the peak usage is not usually what people mean when they say "go solar"...

                        It's much easier to show and convince a school board with "It will cost $30k the first year for a 11kW install - but it saves $5k each year. Since School Bonds are only 3% interest rate it could pay for itself in well under 7 years, even including the interest for the money borrowed."

                        Doubtful you'll actually have those numbers - but that kind of numbers would be pretty convincing to a school board. Most school boards when it comes to things like this will look at the finances. And $30k in capital expense/bonds, resulting in $5k lower costs in the operating budget is probably going to be a easy sell. In many school districts it is easier to get approval for a bond for capital improvements than it is to get an increase for yearly operating budget.

                        BTW - I'd point out that this can also be an education for the middle-schoolers in politics. *IF* you have a convincing case (which is doubtful, but you might) then you need to consider what the best way is to get support from the board - is it better to spend some time one-on-one with a board member or two, so they can help champion your cause because they understand it? And they can potentially help you refine your presentation. Or better to do this at a board meeting with all present? And when is a good time to do this that it won't get less attention because there's some other thing going on (ex. contract negotiations or other issues).
                        Last edited by foo1bar; 03-23-2017, 08:31 PM.

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