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  • EV Rate - Offsetting more than peak usage

    I was planning on getting a 5kW system (Mitsubishi with Enphase microinverters). I have a Rav4 EV in Walnut Creek. The installer did the measurements yesterday and because of the need to be 3 feet from trusses, he can only fit 15 panels taking it down to about 4kW. The car usage is 1000 of my 1300 kWH a month. He mentioned going with the Sunpower to generate more energy with the same number of panels. Does this make sense? I am paying 10 cents with the off peak rate with the car. My thought was generating at approximately 30 cents (peak and partial peak averaged) the extra panel kW he can fit would knock out my electric bill. The SP will cost about $4.75/W which is $1 more than the Mitsubishi ($3.75/W). Thoughts?

  • #2
    Hi Kumasdaddy and welcome to Solar Panel Talk

    It is a common thing to use larger capacity panels when roof space is an issue, eg 300watt panels rather than 250watt, so that seems ok. I am not familiar with pricing in your area but I am sure there are others here that are. My advise is to ask questions and read up as much as you can, and always look at the reviews of the companies you are getting quotes off, and I think it is also wise to get multiple quotes.

    My philosophy on micro inverters is only use them when you have to as they are a more expensive option than the traditional tried and proven string inverters. The thing with micro's is that no one, and I mean no one can tell you how they will be going in 10 years from now as they havnt been in use that long. So if you have shading issues or a weird roof shape that doesnt allow you to get the strings of panels in that you need for the string inverts then I would use micro inverters but only as its really the only option. Cheers

    Comment


    • #3
      Originally posted by kumasdaddy View Post
      I was planning on getting a 5kW system (Mitsubishi with Enphase microinverters). I have a Rav4 EV in Walnut Creek. The installer did the measurements yesterday and because of the need to be 3 feet from trusses, he can only fit 15 panels taking it down to about 4kW. The car usage is 1000 of my 1300 kWH a month. He mentioned going with the Sunpower to generate more energy with the same number of panels. Does this make sense? I am paying 10 cents with the off peak rate with the car. My thought was generating at approximately 30 cents (peak and partial peak averaged) the extra panel kW he can fit would knock out my electric bill. The SP will cost about $4.75/W which is $1 more than the Mitsubishi ($3.75/W). Thoughts?
      Which Mitsubishi panel ? Model # ?

      To be clear, the Sunpower panels may have an advantage in your case in that a 5 kW S.P. array will be (physically) smaller than a Mitsubishi 5 kW array in the approx. inverse ratio of the their "S.T.C." efficiency. (Get that # from the panel data sheets). This is approximately so because the vaunted Sunpower efficiency is an AREA efficiency, not a COST efficiency as you've found out. So, for example, if the Mitsubishi S.T.C. efficiency is, say 17%, and the S.P. S.T.C. eff. is 21.5%, The S.P 5 kW array will be about (17/21.5)~ = 79% as large (physically) as the S.P. Array. BTW, the array (electrical) sizes will probably not be exactly 4.0 kW or 5.0 kW, but they'll probably be "about" those sizes.

      The buck a Watt more for S.P. seems about right to the going rate in price diff. but in all fairness, that'll be down to about $.70/Watt more after fed, tax credit.

      I'd run PVWatts with a 4 kW Mitsubishi array (which I assume will fit) and a 5 kW S.P. array, and see what each will generate in a year and then subtract one from the other. Then, FOR EXAMPLE, if the diff. is, say, 1500 kWh/yr., to be somewhat conservative multiply that by your tier 3 rate (see your elec. bill) and that will be a (real approx.) SWAG at what a 5 kW S.P. array will save over a 4 kW Mitsubishi array in $$ per year. So, say, your tier 3 cost is $.32/kWh : (1,500 kWh/yr.) X ($.32/kWh) = ~ $480/yr. more savings with a 5 kW. S.P. vs. a 4 kW Mitsubishi.

      Now, 5 kW Sunpower : (5 kW) X ($4.75/W) = $23,750.
      4 kW Mitsubishi: (4 kW) X ($3.75/W) = $15,000.

      $23,750 - $15000 = $8,750 more for the S.P.

      $8,750 X .7 = $6,125 net after tax credit.

      The super dumbed down and not recommended way to look at it (but what many folks do and call it valid which is the only reason I bring it up at all) : $6,125/$480 = 12.8 yr. "payback" for the difference in price for what you get back (The bang for your buck factor). If you think you're going to move in say, 7 yrs, the smaller Mitsubishi might be worth considering to save $6,125, maybe not.

      Some other ways you may want to start looking at the choice(s) here for some perspective has 2 parts: How much more will a 5 kW S.P. system reduce my bill than a 4kW Mitsubishi system (that's the $480/yr. in my EXAMPLE). And then, is that amount of savings/year with SOME (at this time) unknown annual energy inflation worth ~$6,125 in terms of today's dollars ? Or, another way to look at it: How long will it take to get my $6,125 in current dollars back accounting for energy inflation, increased/decreased energy use, the PITA factor of maint./down time, etc, financing costs (if any), etc etc.? Or, what else could I do with $6,125 today that may generate more income than the added bill reduction generated by the 5 kW S.P. system over the 4 kW Mitsubishi system ? (in the EXAMPLE I used, without any adjustments 480/6,125 = ~7.8%. (Note = 1/12.8yr. "payback")). Or ????? other ways to look at alternatives.

      Some folks are of the opinion that the S.P. warranty is better. Read the warranty. It's good, but some think it not bulletproof, and overkill - sort of like paying more for more insurance - insurance poor in other words. Or, similar to extended product warranties that only serve to fill the pockets of fear mongers. Besides, if the product is so damn good, why is such a (claimed) superior warranty needed in the first place ? Another thought: Sunpower performance may degrade less /yr. and that may be worth something. I'd estimate that something to be about a 5% premium over 20 yrs., less for shorter periods, but not the 25+% in your case.

      Lastly on financials, keep in mind that CA rate reform will probably affect you in ways you may not be aware of at this time, making all assumptions about future rates, rates of change and rate structures more nebulous than they are already.
      Plug in "AB 327" to the net and spend about 45 min. reading. You will not be sorry.

      Then, there are the other non financial considerations which are probably in the end much more important than mere $$ and different for each person.

      Just a few things to ponder.

      BTW: What kind of mileage do you get in terms of miles/kWh on the RAV 4 ?

      Comment


      • #4
        Originally posted by solar pete View Post
        Hi Kumasdaddy and welcome to Solar Panel Talk

        It is a common thing to use larger capacity panels when roof space is an issue, eg 300watt panels rather than 250watt, so that seems ok. I am not familiar with pricing in your area but I am sure there are others here that are. My advise is to ask questions and read up as much as you can, and always look at the reviews of the companies you are getting quotes off, and I think it is also wise to get multiple quotes.

        My philosophy on micro inverters is only use them when you have to as they are a more expensive option than the traditional tried and proven string inverters. The thing with micro's is that no one, and I mean no one can tell you how they will be going in 10 years from now as they havnt been in use that long. So if you have shading issues or a weird roof shape that doesnt allow you to get the strings of panels in that you need for the string inverts then I would use micro inverters but only as its really the only option. Cheers
        Who told you that ?

        When available area for array placement is a small or expensive or available at a premium or other considerations, larger capacity panels, whatever that means, have nothing to do with it; AREA efficiency does - that is, you want the most S.T.C. Watts per square meter or square foot or square acre, hectare etc. Good area efficiency is usually not as cost effective as lower area efficiency, but may be the choice given the situation and preferences of the person paying the bill.

        Comment


        • #5
          Thanks guys. The Mitsubishi model is pv-mle265hd. The reason for the microinverters is that my roof is not straight. The panels will be located on three different surfaces. I did have someone quote Kyocera KD 200-60F with Solar Edge Optimizers for cheaper, but he had no reviews out there so I am wary.

          JPM thank you for the financials. I have reading a lot on the forum, but most is focusing on the financial parts of solar. I am choosing solar for the same reason that I leased the RAV4, it made financial sense. I was completely unaware of the AB 327. If I was not contemplating solar, I would definitely be in favor of flattening the rate tiers. However, it does affect my financials significantly. My math is based on the 20 cent spread between electricity produced during peak time and used in off peak. If the spread narrows, the payback is longer. Also, if I do not maintain my EV and my long commute into SF then my usage will cut down significantly. I am going to stick with the 4 KW system. I owe you one.

          As for the Rav4, I am averaging 3.1 miles/kW. I drive 60 miles round trip to work and tack on another 20 in the evening for around town stuff. Monthly it is about 2000 miles. Before I switched jobs, I put on less than 5000 miles a year.

          Comment


          • #6
            I'll choose SP 345W (only if good deal around....) or LG300W panel and shop as many installers as possible. Forget about Enphase micro inverter, try string or solaredge inverter.

            I understand South facing is the best, but if there are space in other roofs, perhaps add few more panels. My neighbor put most of the panels facing NE 75 deg, but he is happy. His Summer output is good and that's what he wants especially if you are looking for TOU-EV plan. Your POCO is SCE and here's update rates:

            Yes, you save $$$ switching to EV + solar. Without solar, you are not saving any $$$$.
            Attached Files

            Comment


            • #7
              +1 to J.P.M.'s post.

              Not that you need more to worry about, but at the same time you have the tier compression happening in the standard rates, there is also development occurring in TOU plans. The tier compression is occurring because of California's awesome legislative history. If you have some time to kill, this blog does an excellent job of explaining what led up to AB327 (part 2, and part 3). TOU development is occurring along with this, but for different reasons, one of which is dealing with solar adoption. SDG&E's testimony on TOU earlier this year is informative. There is a very real possibility that the definition of "peak" will be shifting to later in the day. You might want to look closely at your consumption and see how that might affect you.

              How the peak period is defined will matter a lot since the value proposition here has a 3X lever to that. You may have already factored it in, but any panels that are not southwest facing, or maybe even west facing with the peak shift, will be producing at a lower multiple. If you have the option to put Sunpowers in a westerly direction and other panels on less optimal faces, it *might* be a cost effective compromise. I'm not usually shy about clearly announcing assumptions and making calculations based on them, but here, the assumption sensitivity is so significant that I am not sure where to even start guessing.

              In your situation, I don't see much downside to waiting until TOU's future becomes clearer. You have plenty of time before the net metering deadline hits, and the federal rebate has time as well, unless you need a few years to spread it over.

              Either SolarEdge or the Enphase inverters would let you get creative with your panel placement without compromising your system efficiency. A great place to learn more about these types of systems is here . Check out his other posts if you want a deep dive into inverter and microinverter technology.
              CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

              Comment


              • #8
                Originally posted by kumasdaddy View Post
                Thanks guys. The Mitsubishi model is pv-mle265hd. The reason for the microinverters is that my roof is not straight. The panels will be located on three different surfaces. I did have someone quote Kyocera KD 200-60F with Solar Edge Optimizers for cheaper, but he had no reviews out there so I am wary.

                JPM thank you for the financials. I have reading a lot on the forum, but most is focusing on the financial parts of solar. I am choosing solar for the same reason that I leased the RAV4, it made financial sense. I was completely unaware of the AB 327. If I was not contemplating solar, I would definitely be in favor of flattening the rate tiers. However, it does affect my financials significantly. My math is based on the 20 cent spread between electricity produced during peak time and used in off peak. If the spread narrows, the payback is longer. Also, if I do not maintain my EV and my long commute into SF then my usage will cut down significantly. I am going to stick with the 4 KW system. I owe you one.

                As for the Rav4, I am averaging 3.1 miles/kW. I drive 60 miles round trip to work and tack on another 20 in the evening for around town stuff. Monthly it is about 2000 miles. Before I switched jobs, I put on less than 5000 miles a year.
                For my part, you're entirely welcome. Little more than (hopefully) informed opinion on my part. I would only stress another opinion: Question everything everyone says - even, or especially, me. Do your own research, ask question and form your own opinions. None of us is as smart as all of us.

                Thank you for the Rav4 mileage. I think I'll be waiting a few more years for an EV - that wait based mostly on range requirements and initial cost, but also a fuel cost/mile (for me only) better than, say, ($3.50/gal)/(50 MPG) = ~$.07/mile, which looks like the easier part to achieve than the range hurdle. Whoever solves the energy storage challenge will be the next Bill Gates.

                As for financials, and rereading your post and (finally) noticing the large proportion of your elec. usage that goes to replacing gasoline fuel cost, depending on the charging rate (in $$'s) you pay for the EV - at super off peak I'd assume - and what you think about future gasoline prices, the mental spoor I puked out last night may need another look.

                Thinking of fuel cost only, if you charge at night with a super off peak rate (?? $.05-$.07/kWh ?? -- >> ~ $.06/3.1miles/kWh = $.0198/mile), the Sunpower premium penalty may get larger as you replace super off cheap supplied power, at least for now, with the most expensive panels of the most expensive way to provide power, depending on a lot of assumptions about future gas costs, elec. rates, etc.

                On the flip side, if your off peak charging rate is closer to tier 1 rates ( ??~~ $.15-$.17/kWhr ?? -->> ~ $.16/3.1 = $.052/mile), the S.P. penalty, while probably still better than the ICE vehicle fuel cost, may change the cost effectiveness picture some and perhaps make the S.P. option, while not more cost effective, perhaps less cost ineffective.

                With the above in mind, panel orientation considerations MAY become less of a concern than they would otherwise be.

                There's probably as many or more ways to massage the #'s to back into a seemingly logical justification for any scenario as there are people's opinions.

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