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Tesla Motors, Inc. Message Board

  • temagami67 temagami67 Mar 25, 2013 1:51 PM Flag

    Solar Panels and Charging Efficiency

    NoMore, the solar panel calculation truly is as simple as what I showed. Yes, there’s about an 85% inverter efficiency that needs to be factored in, but I don’t think Tesla is the least bit concerned about solar efficiency. If they were, they would angle the solar panels at the sun. So it’s purely a marketing tool.

    If Tesla really wanted to solar-power the SC’s and not just give it lip service, they could do it easily. First of all, it doesn’t matter where the panels are located. You can put energy onto the grid and take it off of the grid wherever you want. So all they need to do is install enough PV panels on the Freemont plant to cover all of the SC needs. And it’s a lot more cost efficient to have one large array than to manage and maintain a number of small ones. So how big does the array need to be? If there are 32 SC bays in existence averaging 4 hours/day at 90kW, that’s about 8 MWh/day. Keeping the math simple, I’ll use 4 equivalent sunlight hours for Freemont, so we need 2MW of solar panels. At 13W/sqft, that’s 150,000 sq ft. Then they simply need to add incrementally more as more SC bays are added. I would think they could get a very attractive lease deal from Solar City, which would minimize the upfront cost.

    Another efficiency to keep in mind is charging efficiency. Tesla owners are reporting 80-85% charging efficiency. It means that to add 50 kWh to your battery, you need to use 60 kWh of energy. Not a big deal, really. Your energy cost is still about ¼ that of gasoline.

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    • The SC solar panels are symbolic gesture. Any green minded average owner or potential owner looking at the SC station with the solar panel will be impressed. The average bloke/sheila go no clue how makes all those calculations. Plus they do not know the the usage, either. Really, how many folks balance their check and reconcile their check books, credit cards?

      I think it is a waste of capital. Tesla can not afford the extra $50k-100k they spend on the panels/SC. Better off adding more SC sites. I suspect most sites will have have solar panels.

      They are better off focusing their efforts in purchasing hydropower cheap and have it delivered, where possible. Or even wind power. Easier said than done.

      • 2 Replies to ajitmd2000
      • To put an example to the SCTY business model.

        If I pay $200 a month now, and I install solar panels, the plan would be my bill gets reduced by $100 a month and my monthly lease rate is $50, thereby instead of paying $200 a month, I install solar panels and now I'm only paying $150 a month. (All numbers made up, just used to give a simple example of how the SCTY plans are supposed to work). I hold no position in SCTY, only TSLA. I may go long on SCTY sometime in the future, but no immediate plans.

      • "Tesla can not afford the extra $50k-100k they spend on the panels/SC. Better off adding more SC sites. I suspect most sites will have have solar panels. "

        The whole point of SCTY is you pay less monthly costs overall because there is no upfront costs to install and the lease/finance rate on your monthly bill is supposed to be less then the energy the solar cells produce. Add this to the fact that Tesla is probably getting a much better deal then your average consumer, in part due to bulk buys and ease of installation, and in part because of the business relationship itself, and the solar cells make even more sense.

    • OK, TG I think we are on the same page (but I can never be sure with your sense of irony.) So if one considers the energy conversion efficiency loss, the charging efficiency loss, the house loads, etc., SCs powered by solar panels with associated batteries and switchgear don't make economic sense and are unlikely (in Musk's words) to pay for themselves in a few years. Solarcity doesn't seem to be much more than a financing broker (with panel installers) that would likely have to lay the capital costs of the leased installations off to some kind of investment partnership. A nationwide network of proprietary chargers without a supporting revenue stream would seem to be a risky bet on the long term viability of the lessee.

      • 3 Replies to n0m0renancy
      • Batteries are a non-starter for a solar solution for SC. grid-tied is the only way to do it. Charging batteries which then charge batteries especially at high dump rates is not good engineering. Runs very well on a whiteboard, though :)

        SCs are a grid type power application. The flow rate is high and a set of solar panels above them will never power the SCs. You need a big thick grid-based line carrying high voltage and amperage to supply the power. The solar panel roof is decoration at best when it comes to what power it really will supply back to the grid when cars aren't charging. I'd rather see them go green by planting a few well-placed maple trees to allow for shade.

        Sentiment: Buy

      • the solar panels will pay for themselves after x number of years, I believe was his point. Not that the solar cells would pay for the entire supercharger. Isn't that the very nature of solar cells, eventually they pay for themselves?

      • In all seriousness, Tesla’s claim that the solar panels generate excess power is deliberately misleading and it’s disappointing that they undermine their integrity that way. If you assume that a charging bay is used for 4 hours a day, it would require 8000 sq ft of solar panel area per bay. This can be verified using any number of online solar calculators. Why don’t they simply tell the truth and just say that it doesn’t provide all of the power, but every little bit helps? Why lie? After all, it’s not a scam, is it?

        As for the comment about Solarcity, well you’ve got me there. That was purely for amusement.

    • The only reason to have solar at a SC site is for sun shade for the cars under them. The size is far smaller than what a charging event will draw in terms of KW. You need a huge array to do 90KW+ charge rates. If three cars are plugged in, you need something as big as the gas station's entire parking area. The SC solar panels will be grid-tied and feed in their "miniscule" 10-20KW peak rate and the draw from the grid by the cars will dwarf what the panels put back into the grid.

      What the panels may do is offer a nice place to put marketing fliers for SCTY-based installers. That's why you do the panels at charging stations. The public will catch on that the cars are not charging from the sun - especially if they are charging at night. SCs will be 24x7.

      Sentiment: Buy

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