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Published on November 13th, 2015 | by Kyle Field

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EVs & PVs — Driving on Sunshine!

November 13th, 2015 by  

This is an overview for how to assess a solar installation for a residential property and pair the system with an EV or two to generate your own power and drive on sunshine. This is not an attempt to document every scenario, but rather to share the overall direction and flow from which you can, with your newfound knowledge, move forward with an installation of your own. Let’s get started!

When we first put solar panels on the roof of our 2-story home here in sunny Southern California, I understood the concept but had some questions about how it all actually worked. It was quite the learning process, and since then, I have continued to add panels to the roof to offset our base usage while also adding more load to our system with the addition of 2 EVs in the last 12 months. With all this, we are now living the dream and effectively “driving on sunshine.” As there were so many learnings with both systems, this article will help frame both pieces of the puzzle in order to help others understand some of the nuances and how they work together.

The Roof today with our 17 solar panels

The first step towards getting solar panels up on your roof is sizing the system. This is one of the first steps a solar installer will typically do for your site, but you can also go through it yourself to understand the details or for a DIY installation. Many factors dictate system size but the two big ones are the usage you want to offset with new solar generation and the solar potential of the installation location.

Calculating your estimated usage is very straightforward, as your utility has a vested interest in tracking usage accurately so it can bill you for it. πŸ™‚ Look up the last 12 months of bills and capture the monthly usage in kWhs for each month. The resulting total is your starting point for annual usage. Next, take into account any big project that could impact your usage in the next few years — adding an EV (I’ll review estimating EV usage below), removing a hot tub, installing LED lighting, etc., and either add or subtract those from the annual usage total. Finally, determine what % of that usage you would like to offset. Most installers will use 90% of the production, as any excess is typically not a good investment for the homeowner. My personal goal is to continually generate at least 105% of my total usage.

To understand the solar potential of your location, use an online solar production potential calculator like PVWatts. You enter the key details of your system — some which take more work than others, like installation address, system size (from your work in the previous step), tilt, module type, etc., and the system spits out a nice annual chart of estimated production by month, including the value of the energy produced.

PVWatts Estimated Production

One of the first question folks normally ask about residential solar is “but, what about the batteries?” In most residential installations, the PV solar system will be connected to the grid, meaning that any excess energy produced will be sent to the grid. In a net metering arrangement, the utility will track how much the PV generation sends to the grid and keep a tally sheet, “netting out” usage vs generation at the end of the year. Why annually? This allows systems that generate more in the summer and less in the winter to level out over the year instead of the utility paying the customer in the summer and vice versa in the winter. This could be a whole separate article but I’ll leave it at that for now. πŸ™‚

Now that we have our system sized up, let’s go get some bids from installers! I’m not going to go into full detail on how systems are priced out, but there are primarily 3 options:

  • Buy this system outright with cash. The system is yours and all generation is “free” after the initial purchase.
  • Sign up for a Power Purchase Agreement (PPA). The installer will front the money for the system and you agree to buy power from them for a predefined term of 20, 25, or 30 years. Terms such as annual % price increases, duration, upfront cost, and savings vary. Do yourself a favor and read the fine print… that’s a long period of time to be locked into bad terms. πŸ™‚
  • Financing. Finance the system through the installer. These contracts are getting sticky so definitely another one to watch out for. It may be better to finance through an unrelated bank to pay for the system vs finance through an installer. A great article on Solar Love flagged some key details on a new SolarCity financing scheme that seemed less than consumer friendly.

My Solar System's Production Summary

Before you lock in and sign papers, dig into the return on investment that the solar salespeople (yes, they are trying to sell you the system, even if it’s a zero-down deal) pitch to you. A few tips — look for price increases in the retail electricity they are comparing to. For instance, in my area, Tier 1 rates were $0.12/kWh when I signed up and they projected 5% increases every year. To validate that, I went in and flattened the price of electricity for a “worst case scenario” payback. Since 2011, however, we did offset the small amount of Tier 2 power we had been paying for ($0.19/kWh) and our Tier 1 pricing has gone up quite a bit and is now $0.15/kWh which is inline with the solar company’s projections.

I have also built an Excel sheet (as I’m prone to doing) to track our solar production, home usage, efficiency savings (improvements in total usage vs base), payback, etc. There’s a notable blip in Jul ’13 when we went from 5 to 12 panels, with each calendar year change as we “net out” and either add or subtract the annual bill or credit into the equation and add in any pricing changes in the “SCE $/kWh” column. I dropped a copy into my Dropbox public folder if anyone wants to find all my errors/reapply/make it your own (link).

solar_savings_thing

What a whirlwind of data. Now that your head is spinning with numbers, take a break, grab some coffee, and come back in 5.

We’ve determined what your usage is for the year, adjusted for all the great efficiency improvements you’re going to make with your tax returns (right?), sized the system based on your specific location, and worked through the financial side of the system. What now? Let’s throw an EV into the mix! Put some miles on those solar panels! But seriously, how do you figure out how much power you’ll need to get back and forth to work? Come with me, friend…

When buying an EV, you enter a new world of numbers and metrics. Nobody will tell you the most important factor in calculating your energy usage, but it’s simple — miles per kwh. Basically, how far you can drive on one unit of electricity. Boiling it down to the basics, your EV has a certain battery size — say 24 kWh — and gets a certain range — like 84 miles. Roll those two together and you get the manufacturer’s estimated miles/kWh rating. In this case, that’s 84/24 or 3.5 mi/kWh for my 2014 Nissan Leaf. I must have a light foot because I have averaged 4.1–4.3 mi/kWh since we’ve had it… which also means I get more miles out of a charge, which is nice.

Now that we know how efficient your EV (or EV-to-be) is, just roll that into the number of miles you drive per year or plan to drive in the years ahead to get your EV’s annual kWh usage. You can run this through the same usage-to-system-size calculation to determine what size PV system you need to power your car. In my case, I used the actual production averages from my panels to calculate this at a “high” miles per year number (12,000) and a “low” miles per year number (8,000) to understand what those thresholds looked like, then sized accordingly.

Our Leaf Charging in a Santa Monica, CA Parking Structure FREE!

Tracking solar generation allows us to understand our system payback vs retail pricing, aka “what you would have paid for the power” — or the cost of the solar system per month. Keeping a running total of the savings allows you to estimate payback time for the system, at which point the system is effectively producing free power. Tossing an EV into the mix, I track EV savings as :

[miles driven / mpg of the car we replaced * price of gas for the month (actuals)]

minus

[miles driven / (mi/kwh of the car) * retail cost of electricity/kWh]

Or… in simple terms, the amount of money we would have spent on gas minus the money we would have spent on electricity = savings from the EV vs a gasmobile.

Solar-powered charging at home is the most cost-effective, environmentally friendly form of vehicle-based transport that fits our lives (today). After we added the first EV in late 2014, we decided to go all-in and added a second EV just a few months ago. We are currently saving money on our electricity bill with the 17 solar panels we have up on the roof, with another 10 panels that we’ve already purchased that are currently waiting for a home electrical panel before we can add those to get back to a state where we are producing more power than we use. The second EV put us back “into the red” but also gets us off gas, which is a bigger win in my book. πŸ™‚





Check out our new 93-page EV report, based on over 2,000 surveys collected from EV drivers in 49 of 50 US states, 26 European countries, and 9 Canadian provinces.

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About the Author

I'm a tech geek passionately in search of actionable ways to reduce the negative impact my life has on the planet, save money and reduce stress. Live intentionally, make conscious decisions, love more, act responsibly, play. The more you know, the less you need. TSLA investor. Tesla referral link: http://ts.la/kyle623



  • Kraylin

    Thank you Kyle for the great article! I love spreadsheets and appreciate the time it would have taken you to produce it all.

    • Kyle Field

      It’s my pleasure! No really, I love spreadsheets, data and being able to see how much I’m saving/spending/earning etc with these fantastic solutions. It’s one of the things I like the most about my enphase microinverters…they give me all the data πŸ™‚

  • Dragon

    Great article. Did you have any problem with not being able to put panels within 3 feet of the roof edge due to recent CA fire regulations? Or is your roof big enough that that didn’t matter?

    • Kyle Field

      The west side was large enough to fit the current 17 panels with the 3′ off of the roof spine. The next 10 will go on the east side…any maybe a few more if I end up going the route you’re looking into with water heating, heat pumps, water heating etc. I also have an east facing garage roof that won’t get as much sun but is a better option than not having the space.

      …unless I get creative and opt for some of those sexy glass-laminate PV panels as shade for a deck…hmm….

      • dRanger

        “… water heater…” If you are thinking that way, I suggest considering a GE Geospring heat pump water heater. It has a COP of 2.7 so 270% better than straight electric. I’ve never had the old-style roof panel solar water heater but I have heard horror stories about maintenance with them from people who installed them professionally. I replaced my propane water heater when it sprung a leak and my decision to go with solar and the Geospring had a 20% annual ROI. If your existing water heat works or uses natural gas, the ROI will be significantly lower, but it was a no-brainer for me. Originally, the controls for the unit were made in China in 2012 and there are a lot of horror stories about that. GE brought the controls back to the U.S. in 2013 and the problems seemed to disappear. I’ve had mine for 18 months and it has been flawless.

        • Kyle Field

          The studies I’ve read (I think the last one was on here) indicate that solar PV is a better choice because of the issues you mentioned and non-value add complexity of adding a fully new system to the mix vs just expanding a PV system and adding another appliance. I’m not sold on electric water heating but it’s not totally off the table. Heating with electricity just plain takes a ton of juice…which is why I’m a bit nervous about our hot tub jacuzzi thing…

          • dRanger

            I appreciate your point about a straight electric water heater, but a heat pump water heater is over 250% more efficient than an electric heater which are almost 100% efficient. Natural gas is around 70% efficient IIRC. Getting better than 100% efficiency is what heat pump magic is all about.

          • dRanger

            BTW I am not a shill for GE. In fact my luck with their appliances has been so bad, I swore to never buy another one. Their water heater seems to be an exception so far.

          • Kyle Field

            That unit does look impressive – thanks for sharing it. Estimated usage of 1830 – 1856 kwh/year so it would require 4.4 panels to offset…or 2 more than the 10 I’m adding (back to the ebb and flow for me πŸ™‚ ). We currently have a tankless natural gas heater so I’m not expecting any savings but it’s nice that it only sips on power. Looks like they are ~$1400 – also not too bad. The only bummer for me is that I just tore out our water heater stand as we are currently tankless but that’s something I can work around.

            https://www.youtube.com/watch?v=vKCsvRxpj2g

          • dRanger

            Climate change is very important to me but so is practicality and return on investment. I was switching from propane so the decision was a whole lot easier. Frankly, I am a bit envious of your tankless water heater.

          • TedKidd

            Don’t be. They can be real headaches. Need a lot of service, particularly if you have any water quality issues. They should be descaled every year or two, which typically more than erases any $ savings from efficiency.

            We ended up installing them all with their own filters to help prolong time between breakdowns.

            I like having a tank so much that I got an indirect tank, and no longer use the tankless portion of my Navien combi boiler.

  • Michael Torres

    Is SCE KwH/M what you use on average? Wow, I’m in Texas and I use nowhere near as little as that. Average in Texas 15000 KwH per year.

    • Otis11

      In Texas we need more climate control…

      • Dragon

        I thought everyone in Texas was more manly? Real men don’t need AC or heating!

        • dRanger

          I heard the men in Texas don’t even wear shoes…or maybe that was Arkansas. ( just kidding – we Californians love Texans and I’m sure the feeling is mutual)

          • Otis11

            Hahaha… =-P

            We typically get along with most. (Funny you mention that though… I bounce between various Texas and California cities quite regularly. Some years more time in texas, some, more time in CA. Interesting differences… anyway, another time…)

        • Otis11

          Tell that to a wife/mother/girlfriend… see how that goes.

          (Honestly, I do use the ac a fair amount too, but i’m perfectly happy without a heater. With a decently insulated house and the fairly mild winters, it typically stays low 50s inside all winter, which I find brisk – but acceptable. 100+ with humidity, not gonna happen.)

    • It is possible to retrofit most standard California houses (about 2000 sq ft) which are smaller than Texas houses with insulation, latest heat pump technology and efficient appliances to run on about 8000 kWh per year for a family of 4. I am asserting this after going through at least 10 case studies in the Bay area. The houses were nothing fancy. Just needed good insulation in attic, walls and crawl space, double pane windows, 20 SEER or better heat pumps, LED lights, and energy star appliances. One particular factor of importance under such a reduced energy consumption pattern is phantom loads which become a larger percentage of the usage. Add the annual mileage of the EVs and divide by 3.5 to get total kWh for the year approximately.

    • Kraylin

      Home size, family size, and now EV’s change your usage drastically. You would need far more information to determine if your usage is as “high” as you think it is.

      My wife and I have no children, we are able to keep our usage quite low in a moderate sized house.

    • Kyle Field

      Our home uses 7.6kwh/day, my wife’s EV uses ~7.8kwh/day and mine uses ~5kwh/day. Looks like 20.4kwh/day but most of that is the cars. Avg for a US home is 11kwh/day I believe.

    • Kyle Field

      The Total Usage Column (with the border around it) is our total. SCE kwh/M is the amount pulled from the grid.

      Our home uses 7.6kwh/day, my wife’s EV uses ~7.8kwh/day and mine uses ~5kwh/day. Looks like 20.4kwh/day but most of that is the cars.

  • dRanger

    Good article Kyle. I would like to raise two issues that you didn’t mention – Time of Use rates and net metering. These are critical to sizing your system. I am most familiar with PG&E but I think your rates are similar. PG&E has an EV rate which is about 10 cents for off-peak (midnite to 8), 20 cents near peak (8am-2pm) and 42 cents peak (2pm-9pm). There are no tiers. Although the 42 cents might seem scary at first, it’s actually great because net metering means the utility is paying YOU that much for your excess solar power. The 10 cent off peak rate is perfect for charging your EV and net metering means you can get 4kWh for each peak kWH you pushed onto the grid.

    • dRanger

      BTW I was glad to see your comments about evaluating things like LED lighting before settling on a PV size. So which is cheaper – incandescent lighting powered by PV or LEDs at 90% less PV? Remember that incadescents are only about 1% efficient so 99% of the wasted heat must also be removed by your air conditioner. Which is cheaper – PV to power your air conditioner or extra insulation in the attic, which will also help your heating bill? I found that by going to 20″ of attic insulation and replacing defective ducts, I was able to downsize my new geothermal HVAC system from 4 tons to 3 tons. One small problem is that when you plan these kinds of things, the solar salesman will look you in the eye and say “OK, so what size PV system do you want?” You will need to have a hard number ready to go.

    • Wow, I didn’t realize you get paid the peak rate when sending electricity into the grid at peak times. I’m pretty positive that’s not very common. Well, a lot of utilities don’t have TOU pricing at all.

      • dRanger

        According to Wikipedia, 43 states have implemented some form of net metering, but there’s quite a bit of variation among the states. Interestingly, US law requires some form of net metering anywhere it is requested. There’s also a lot of variation on what happens to excess credits. One thing that doesn’t seem to vary much is that investor-owned utilities hate it.

        • Yes, but the rates are also different, and I don’t think I had ever heard of people getting paid peak demand rates.

          • dRanger

            Going to Wikipedia again, 26 states net meter at the going retail rate. A few only match the wholesale rate and Hawaii doesn’t compensate at all. Supportive folks.

          • But I think “going retail rate” is the average rate, no? Not peak rate? (I know, I’m being lazy, but it’s 3am here πŸ˜€ )

          • GCO

            kWβ‹…h are credited at the (retail) rate in effect at the time the energy is pushed to the grid.

          • How much do you make selling electricity to your neighbor who has been disconnected for not paying his bill?

          • GCO

            Huh? I’d give the guy electricity for free if needed. I already do so for PEV drivers, my address is listed as public charging station and anyone is welcome to plug in on my driveway.

            I’ve also donated all the surplus my PV system has produced so far to my utility’s customer assistance program. Better to see those excess kWβ‹…h reduce other people’s bills at full retail cost, instead of getting paid to me at wholesale, a couple cents a pop.

          • Kyle Field

            Heck yeah. This is what I’m working on for our second EV charger…when we eventually get the thing wired up. Great stuff!

          • dRanger

            “I know, I’m being lazy…” Zach, I am totally sympathetic, but you made me look. I found a website that contains a database with every utility rate in the nation – over eight thousand of them. If you’ve ever tried to take apart a utility rate, you know that analyzing all those rates would qualify as one of the circles of hell. I’m going to download the whole file and see if I can find a shortcut. My previous reading on this topic suggested to me that the key feature of net metering in the US was that the utility paid you what they would charge you at any given moment. I know that SoCal Edision and PG&E work this way; I’ll see what I can dig out.

          • Kraylin

            Above i mentioned our solar incentive program in Ontario Canada in a reply to Zach, would you please have a look at it and share your thoughts?

          • dRanger

            I found your comment. It seems Ontario has a FIT (feed-in tariff) instead of net metering. My sense is that you have a very good rate. My 7.3 kW system cost $30,000 before Federal tax credit, so I think your cost was reasonable.

      • GCO

        Especially with a PEV charging mostly at night, TOU + net metering is an awesome deal, effectively multiplying the PV production by whatever the day/night pricing difference is.

        PG&E offers this combination (along with other goodies like an option to have the PEV metered separately), and with their rates, I don’t understand why every single one of their customers hasn’t gone solar already.

        • Dragon

          Because OBAMA!

        • dRanger

          “I don’t understand why every single one of their customers hasn’t gone solar already”. Completely agree. It’s probably because very few people understand their electric bills, much less TOU, net metering and how solar works. My pet peave is looking at the time to payback. I think that is a totally misguided way to look at the situation. Thinking of the payback period followed by free electricity is like asking for the payback on a mutual fund. Solar is much more like a tax-free investment with a very low risk and a very attractive annual return on investment (approaching 18% in PG&E territory.) It’s only real negative is liquidity and that could be offset by a home equity loan if necessary. The federal 30% tax credit is a major attraction, as your house will actually be appraised at the full solar value, not after the tax credit. The PV can do a lot of depreciating before you even hit your actual purchase price. One good thing with PG&E is that the second meter is no longer really needed. It’s only advantage was to prevent electricity for your EV from pushing you up in the usage tiers, and their new EV rate does away with the tiers. That meter installation was expensive.

      • Kraylin

        Here in Ontario Canada we get paid a great price for any electricity produced from PV. Currently we get 38.4c/kwh set to be reduced to 29.4c/kwh January 1st. Our ToU rates currently range from a high of 17.5c to as low as 8.3c. So you get the fixed generation payment and can still keep your usage costs low by shifting energy intensive tasks to off peak hours.

        That all being said… our prices for PV system installations seem to take into account the economics of this government assisted program more so then the actual cost of the system. Should a 10kw residential rooftop system really cost $35,000?

        • vensonata

          At $3.50 watt Canadian that is US $2.75 watt. A steal in north america. The 38cent kw feed in is off the charts generous in North America.. nowhere else even gives you half of that…except Germany, and they don’t anymore.

      • Kyle Field

        We get paid $.05/kwh here. It’s counted 1 for 1…on a kwh basis so not the same. Also, I don’t want to rely on net metering being around so just shoot to offset full kwh usage…and we can always add batteries later to keep our production in house if needed.

    • Dragon

      It certainly benefits the planet to generate more power than you use even if PG&E doesn’t pay you for it, so don’t say generating more power is “for nothing”.

      I’m in the Southern California Edison area and they actually do pay you for excess power generated, but they won’t let you connect a system to their net metering program that generates more than 120% of your historic usage. This is very annoying because I want to convert all our gas appliances to electric and get an EV but since I can’t show historical usage, I either have to get some sort of complicated exemption (which then makes solar installers want to ignore me and move on to an easier customer) or I have to expand the system later after I’ve had the EV for a year and maybe go full electric, and that increases the installation cost.

      • dRanger

        “…they actually do pay you for excess power…” Be very careful about that assumption, because it depends on the definition of “excess”. PG&E pays for excess power too, but they define excess as greater than what you consume, not greater than the net metering credits you generate – a big difference. As to whether the excess is “for nothing”, if you have any concern at all for return on investment, excess generation is a donation. If you wish to use your personal capital to provide free electricity to an investor-owned for-profit corporation, then by all means please proceed. I think there are more effective ways for the planet to benefit from my money, but that’s just me.

        • Dragon

          I’m not sure what net metering credits are in the PG&E framework. With Socal Edison they simply track how much power you use minus how much power you generate and once a year, you pay the difference (or they pay you if you generate more than you use). From https://www.sce.com/wps/portal/home/residential/generating-your-own-power/net-energy-metering/!ut/p/b1/hc_NCoJAFAXgZ2nRMufoQFm7Ec3GQimjbDahYZNgTpglvX0Wbfq_u3P5DtxLBImIKOJzJuMqU0Wc37LornXTZSMegpsWdcAtBD6bMYxtowGrBuDLMPzrL4l4Ju5Qt8G9hR5OYCP06RuY9YwbcCaBpRswjQfou3BGXtCA-ZSC0yn8kDEKdB_gx5EeETJXyf3hFSsSakoiynSblmmpncpmvauqw3HQRht1XWtSKZmn2kbtPxV26liR6MUd9hEy3hHJpW5dAb9-hlw!/dl4/d5/L2dBISEvZ0FBIS9nQSEh/?from=nem#accordionGrp1-1-hash/accordionGrp1-2-hash

          As a Residential/Small Commercial NEM customer, you will continue to receive monthly bills, but only for non-energy related charges such as taxes and fees. On an annual basis, you will be billed for electricity based on your net use for the previous year – for example, the amount of electricity you used minus the amount you generated.

          They also have an online application now but the NEM program is going to close in July 2017 or earlier if they reach 5% of customers on NEM earlier. Bah.

          • dRanger

            If you dig deep enough into that link you posted (read the FAQ section) you will see that the net metering credits for TOU rates work just like I described for PG&E. They track simple usage if you don’t have a TOU rate because the rate is always the same. Under TOU, they credit you for higher peak rates. It’s not surprising that they are the same as PG&E because both companies are regulated by the California PUC. I did notice that the explanation seems to be pretty well buried, almost like they really didn’t want to advertise it. Maybe I’m just being cynical.

          • Kyle Field

            This creates two worlds…the “under the total net metered / TOU credit amount” and the “produced more than the actual kwhs used” world. Last year, I was in the “produced more than the actual kwhs used” world and was credited at $.05/kwh in cash ($129US). Not profitable but better than nothing.

          • dRanger

            Yeah – that’s the situation exactly. Do you mind if I ask how that situation arose? Was your system sized by a solar provider or did you size it yourself? What would you do differently, if anything?

          • Kyle Field

            Hah. This was on purpose. I build up the system, then add load (convert something fossil fuel based to electricity) then add more panels. ebb…flow…ad naseum. First, we cut usage, added panels, added an electric washing machine (gift from friends who no longer needed it), added more panels, added EV1, more panels, eV2…I really enjoyed the approach. I had an installer put in the first 5 panels, worked directly with one of their guys to put up the next 7 then added the final 5 all by myself (and of course, these were the hardest by design and right on the edge of our 2 story roof). I’m planning to do the last 10 by myself as well as it’s rather straight forward. Depending on where we net out from an energy usage/production standpoint (I suppose I just need to run the numbers…please hold…ok, there we are)…I should have ~2.5 panels worth of production – or 1000 kwh surplus assuming 12k mi/yr per EV. That puts me back in the black…but we are also adding a hot tub to the mix around that timing. Anyhow…we’ll continue with the cycle…more usage, more panels…until we max out on roof space, ideas or money. I’m seriously considering building a patio shade out of those glass-laminate panels…they are beautiful!

      • Kyle Field

        …or just add on the necessary panels after the system is permitted as you need them (without bothering to permit the new panels). That will keep your monthly/annual true-up surplus level while still allowing you to offset your usage. …just sayin’

  • sjc_1

    In southern California a large array could power the house and car. Put a battery bank in the garage, use LED lights and big screen, an efficient refrigerator and heat pump…good bye utilities.

    • TedKidd

      Unfortunately that’s romance disconnected from reality. Just like the grid suffers from capacity and tou issues, so do individual homes.

      The most economic way tends to capture the most societal benefits as well – and that means staying connected.

      Here’s a great example of how things work, or don’t, if you were to only rely on your own production. http://www.teslamotorsclub.com/showthread.php/34531-Plan-Off-grid-solar-with-a-Model-S-battery-pack-at-the-heart

      It’s very expensive and sometimes the weather’s unwillingness to cooperate will STILL leave you in the dark with warm beer.

      • sjc_1

        A large enough array and battery bank can be managed.

        • Dragon

          We DO sometimes have multiple cloudy, dark days, even in socal. Covering multiple days of little sunshine is prohibitively expensive with batteries. Better to stay grid connected and use power from wind farms on stormy days.

        • TedKidd

          It’s not whether they can be managed, it’s whether they can be purchased.

          You can sniff unicorn farts all you want during design, but if you design a project that has no basis in logical reality the likelihood of it being actually implemented quickly drops towards zero when you ask someone to start writing checks.

          For mass adoption of these technologies they need to be implemented such that their incremental cost relative to alternatives is negative or at most zero when you do present value analysis. (If this needs further explanation please let me know.)

          • dRanger

            When I did this analysis two years ago here in Northern California PG&E territory, the solar provider estimated an annual ROI of 13% tax free. My own analysis came in at 14.5% and mine turned out to be more accurate. Since that time, the utility rates have gone up 15%. These are NOT unicorn farts – these are hard dollars I earn every single month by NOT sending the utility my after-tax $300. No magic and no hand-waving. You can plug in any reasonable discount rate you want into your net present value calculator and this comes out a big winner, especially considering the low risk of the investment.

          • GCO

            You’re preaching to the choir regarding grid-tied solar.

            @sjc_1:disqus was talking about going off-grid.

          • dRanger

            Apologies – reading comprehension issues. Unless there are dramatic rate changes, I will not be leaving the grid for financial reasons either.

          • sjc_1

            You assumed I was talking about going off grid, I was not.

          • GCO

            Sorry then. @TedKidd:disqus got the same impression.
            What were you suggesting in your initial comment, the one ending with “good bye utilities”?

          • TedKidd

            …and, when you replied to my comment that going off grid was very expensive with:

            “A large enough array and battery bank can be managed.”?

      • Kyle Field

        Warm beer? gasp! But seriously, I’m doing this in…sunny southern California :). I know we still need batteries to make full use of it and protect for grid downtime (no more #warmbeer…mainly because I don’t really drink) but it still offsets most of our usage…and is on track to offset all of it.

        • TedKidd

          You going to attempt to disconnect?

          • Kyle Field

            Nah. Just trying to keep the right levers installed to keep the utility out of my pocketbook. Net metering will not last forever and batteries are the stop gap for whatever follows…good or bad. Being in California, I don’t expect it will be that bad but always better to err on the side of caution and plan ahead with eyes wide open.

          • TedKidd

            Absolutely.

            There is a BIG difference between having 5-10 kwh of batteries for capitalizing on grid services and providing a little backup for outages and having the production and storage needed to be off grid.

            Jason Hughes is a real world example of how 60kw of solar, and over 170 kwh of storage can neither store all his production at peak summer, nor produce enough to meet his needs if he has a rainy week in late fall.

            What looks like it would be WAY more than enough to match needs from an annual lense starts to get really wonky when it’s brought to daily or weekly.

  • Frank

    Couldn’t I intest you in some so fracky shale oil, some tar sands goo, or some Saudi sour crude? πŸ˜‰

    • Kyle Field

      Frack that, mate. ;P

  • FireEcologist

    Nice article! We are headed the same way, going to add panels to cover new plug-in’s electric usage. We are in a net-0 all-PV electric, passive-solar home with just wood heat (only 1 cord/yr. needed), will be extremely cool to be able to cover the local driving too via PV. Everyone pondering this should know that PV costs/watt are declining pretty rapidly, have seen this go from $5/watt 3 years ago to $3.75/watt right now locally. Timing could be important, since the federal tax credits for EVs could be challenged at the end of 2016. Also, be sure when you get your inverter that you get a large enough one to allow future expansion–we estimate going from 16 kwh/day production for the house to 26 kwh/day production need with the EVs, and we did not plan for this at the outset, so will have to upgrade the inverter. If you are looking at plug-ins be sure to pay attention to that key figure pointed out in this article, miles per kwh of battery use, as the plug-ins do vary on this…

    • TedKidd

      IIRC, you really want your inverter to match your current system or your setup may not be able to excite the inverter without full sun. Then you miss out on power generation opportunity in the mornings, evenings, and on cloudy days.

      • GCO

        I disagree. Inverters ramp their output up or down depending on what they can get from the PV modules, and I see absolutely nothing wrong going with one that could accommodate future expansion plans. In fact, I think it’s a good idea and second @EmissionsConcerns:disqus’s recommendation.

        FWIW, I have a 6 kW inverter, which happily outputs anything from a few watts to 6000 (AC), apparently wringing every possible electron from the PV modules it’s hooked up to regardless of conditions.

        I don’t see how a smaller-capacity model could do better. Quite the opposite in fact, as it’d clip more often (yes, PV modules produce more than their rating every once in a while, like when they’re cold).

        • dRanger

          And I must respectfully disagree with you. It’s true that any inverter will ramp, but they use SCRs to do their magic, and the larger the SCR, the more current they must pass in order to fire during a cycle. In other words, lower power inverters are more sensitive to low light situations, come on sooner and stay on longer. My solar provider warned me about this specific issue, as their testing had confirmed it. They always undersized the inverter to use some of its safety margin because of this issue. They said they had often seen this mistake made by do-it -yourself systems that couldn’t produce rated power.

          • GCO

            “Their testing”? I’d love to see that. And the only DIY mistakes I could foresee would measurably affect output would be too-short, out-of-spec string lengths, mixing up modules types or orientation without using optimizers, things like that, not inverter sizing (unless grossly oversized like 5Γ— or more).

            Meanwhile, here’s some actual testing and efficiency curves from the California Energy Commission (CEC) => http://www.gosolarcalifornia.org/equipment/inverter_tests/summaries/

            This should make two things quickly apparent:
            – The sweet spot for most inverters is around 50% output.
            – All curves are pretty flat to start with anyway.

            So while it probably won’t make a measurable difference, trying to scavenge a few Wβ‹…h by installing an inverter able to work down to e.g. 5W instead of 10W, while taking a 1~2% efficiency hit from running it more often near 100% output, is likely counterproductive, and certainly pointless.

          • TedKidd

            An installer friend, after nudging him for years, had an intern put together performance spreadsheet on his projects.

            His string inverter projects typically overproduced to projections. He sized his inverters aggressively and suspected this excess production to early activation and late deactivation, and better production under clouds and snow.

            His micro-inverter systems tended to slightly underproduce to projections.

            He was grateful I persisted as the data was very enlightening.

          • dRanger

            Thanks for the real-world data. So that’s two installers reporting similar results, if I have interpreted “sized his inverters aggressively” correctly.

          • TedKidd

            It gets cold and clear here, and he often installs Sun power (high efficiency/output). I don’t think he’s blown up an inverter, but I think he walks tight to the line.

  • sault

    Not just fuel, gas cars need oil changes, air filter replacements, brake pad replacement, and a whole host of other maintenance items that EVs don’t have, or require much less of. And each of these maintenance items has a $ / mile cost associated with them. For example, even a $60 oil change every 5,000 miles costs 1.2 cents per mile. Every maintenance item, from timing belt changes to transmission overhauls / replacement have a similar cost and they add up. After all these costs, battery replacement every 5 – 10 years is a small cost to pay.

    • Kyle Field

      I agree and that’s why I threw in the disclaimer πŸ™‚ This article was already a bit of a novel so I had to keep it tight else risk going full bore encyclopedia πŸ™‚

  • Martin

    Nice breakdown and charts. πŸ™‚
    Now if more people are doing this and not just for electricity use but for their total energy use and the governments help along we will be a huge step towards going carbon neutral for the whole planet! πŸ™‚

    • Kyle Field

      Thanks! It has to start somewhere…and now all of you know about it! buwahahah…hahahaha! hahah…uh, now it’s just awkward. But anyways, yeah πŸ™‚

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