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Old 08-22-2017, 02:33 PM   #1
NH.Solar
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Default The effect of the Eclipse on Solar PV production

For all the "geeks" out there..
This was from an 8,400 kW roof mounted array in Sandwich. Note the perfectly linear way in which the power fell off and rose again during the eclipse. The dips around noon are simply the effect of passing clouds.
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Old 08-22-2017, 03:48 PM   #2
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Very interesting.. Why was an 8.4kw array only producing under 5kw during the prime hours yesterday. Seems like yesterday (minus the eclipse), was a pretty much perfect solar day.
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Old 08-22-2017, 05:47 PM   #3
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Quote:
Originally Posted by jazzman View Post
Very interesting.. Why was an 8.4kw array only producing under 5kw during the prime hours yesterday. Seems like yesterday (minus the eclipse), was a pretty much perfect solar day.
Well jazz just a guess. If we were selling solar panels we might quote the output at high noon on June 21st with zero cloud cover. But I am not a marketing guy.

Back to the graph it looks like the dip is more than the 60% eclipse coverage would account for.
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Old 08-22-2017, 07:58 PM   #4
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We were in the Roberts Cove area from 1215 to just before 4pm. For most of that time, it was partly cloudy to mostly cloudy. About 315, it cleared right out, just as the eclipse was finishing up.

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Old 08-23-2017, 10:31 AM   #5
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Good eye Jazzman ...and you bring up a common point of confusion about how electricity is measured. Kilowatts (kW) and kilowatt hours (kWh) are two entirely separate entities. Kilowatts is a measure of momentary power production whereas kilowatt hours is a measure of power over time. Kilowatt hours is a quantifiable and can be presented as a billable unit of power consumption.
The solar array is measured in kilowatts and in this case those panels would have the capability of producing a peak of 8.4 kilowatts DC at any given moment. The power goes from the panels down to an inverter which then converts that DC power into the 240 volt AC power used in most homes and feeds it into the main panel. It can then be consumed directly in the home. Any excess not used by the home is exported back into the grid and creates credits on the client's utility bill. When you pay your utility bill you are paying for kilowatt hours (kWh), not kilowatts.
Another way of understanding the difference is to look at a common appliance, let's consider a 1500 watt rated well pump. The pump has the capability of drawing 1500 watts at any given moment and if you ran it continuously for an hour it would use up 1,500 watt hours. Because the utility companies bill in kilowatt hour units and you would be billed for 1.5 kWh.
Clear as mud ...maybe this webpage will help; https://www.nh.solar/how-solar-works.html
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Old 08-23-2017, 11:10 AM   #6
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Peter--I really enjoy your posts, but I don't think you quite answered jazzman's question. I'm still learning on solar, so please correct me if I'm wrong. Here's my take:

jazzman is correct that on a runrate basis, the panels did not approach their capacity in the chart. They delivered 32.31 kWh for the whole day, with their best hour being less than 5kWh.

The reason for the gap between 5 and 8.4 is some combination of being in NH where the sun is less intense, the angle of the panels relative to the sun at any given moment, and cloud cover.

But most importantly--to Slickcraft's good question--we should not care if panels are less efficient in NH than, say, Arizona. We should just focus on the cost of whatever number of panels we decide to buy (after incentives), the amount of electricity they produce on our home, and impact on our electric bill after net metering. In other words--I shouldn't care if my 8.4 kWh panels are never going to hit 8.4kWh, I should only care that my panels are going to pay for themselves soon enough that they are economical.

Please advise. Thanks
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Old 08-23-2017, 11:51 AM   #7
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I'd very much like to buy into the solar power argument, but the industry seems full of snake oil salesmen. It's very hard to get any real info from the internet with out exposing your contact info to who knows how many less than totally honest companies who seem more driven by the financing end of solar rather than the technical end.

So looking at the example here, we had a 8.4kw array that generated 32kwh of electricity on what was a pretty sunny day overall.

The whole buyback rate thing in NH looks pretty complicated, but lets say you can run your meter backwards to the tune of 15 cents per kwh. So on this really sunny summer day we generated $4.80 of electricity. I'd guess that we'd be 50% efficient on that rate over the course of a full year given the short days in winter and the general cloud rate, so we're generating maybe $900 in power over a year.

If that 8.4kw array cost us $3/kw to install (looking at average rates on the internet, but I bet NH is more because of the very high cost of labor up here), we've put out 25k to purchase the array. It seems like the payback period is going to be pretty long. I also assume that you don't want to place panels on anything less than a fairly new roof too, so there could be even more expense if you have a 20 year old roof.

I also wonder what the recoup rate on solar panels is if you sell your house (extremely likely before you ever hit the payback point).

Like I said, I really want to see solar work, but it's hard to cut through all the numbers. Given the number of huge arrays I see in VT, the numbers must work somehow
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Old 08-23-2017, 07:57 PM   #8
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PeterG, your post is actually probably a better explanation than mine. It is late August, at a 42 degree latitude, and the client's roof has an azimuth of 222 degrees which is 28 degrees west of perfect. Still, the system produced 32.3 kWh on a day with both some passing clouds and a partial solar eclipse.
When designing a system for a client the best practice is to size the system to produce 100% of a clients annual kWh consumption. In the long bright days of summer the excess energy produced by the solar system will "spin the meter backwards" generating credits on the customers account, and during the short dark days of winter when there is a shortfall of solar energy those credits will be consumed. In a perfect situation the last of the banked credits will be used up in the spring just as the solar array is beginning to produce break even power again. This is known as a net zero situation.
The payback period for this NHEC customer was 6.5 years, ie the same amount of money that they will have paid in 6.5 years to the Co-op will have paid the for net cost of the solar system. They haven't paid any extra, they have just switched the funds from going toward the expense of a utility bill toward the cost of purchasing the asset of the solar system. There are variables here such as discounted net metering, the fact that an ongoing utility bill is paid with after tax dollars and can't really be compared directly with a once and done payment, and the near certainty of rising utility rates. It is fair to assume that the ROI would in fact be even shorter than is presented.
At the end of 6.5 years this paid off array will be generating the power for this home at zero cost ...and it will continue to do so for the next 30+ years with very little maintenance. Solar modules generally carry a 25 year warranty and the other major component, the inverter carries a 10 or 12 year warranty. I feel it would be prudent to assume that at some point during the generally expected forty year life cycle of a pv solar system, an inverter might have to be replaced. Cost? $1,500 or so ...about what the home had previously been paying to the Co-op annually to buy power. So let's add one additional year to the 6.5 year payback to cover the maybe cost of replacing an inverter somewhere around year 20 and to keep it simple round up to 8 years. That will mean that for 32 years the system will be producing free power, and if we use the $1,500 annual billing cost the customer was paying to the Co-op before installing the solar system, this system will save the client $48,000. Sure there will be multiple other factors (panel degradation at 1%/year, utility rate increases, tax benefits) but they are pretty much a wash.
The solar installation industry grew 17x last year in New Hampshire, and the bulk of that growth was in installations that customers purchased and own. I will admit that the leased systems so common in other States are not a particularly good ROI investment an could be a problem when a home is sold, but the leasing industry has just not caught on very strongly here.
Most solar leads in my experience have come from referrals, not a huge advertising budget. Want to know the best salesman for a solar system? talk to someone who owns one. And leads are converted to sales with honest and open spreadsheets, not "snake oil" salesmanship. I generally give my prospect multiple options, excels for each option, and take all the time they need to explain how each number is derived. If I have done my job well, the customer will fully understand all of the costs and benefits and can freely make a decision based on their own wants and needs. It's a very honest and rewarding way to make a living, and I feel the I'm leaving a legacy of good for the client and the planet with each and every sale.
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Old 08-24-2017, 07:22 AM   #9
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I know I am knit picking but this confuses me.

the fact that an ongoing utility bill is paid with after tax dollars and can't really be compared directly with a once and done payment,

Huh? That once and done payment was paid with after tax dollars wasnt it? Unless your telling me that my upfront cost was all tax deductable then I get it.
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Old 08-24-2017, 08:51 AM   #10
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Peter NH Solar--thanks for filling in the blanks.

The financials you describe look great, and they are consistent with my next door neighbor's experience. This is both better than the stock market, and less risky, just for example.

I would love to add solar, but my Mass house is not situated properly, and my lake house does not use enough electricity.

Good luck!
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Old 08-24-2017, 09:37 AM   #11
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I have a question, because I am curious and skeptical as well.

Who controls the buy back price and rate, and am I correct in saying there is a cap?
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Old 08-24-2017, 10:43 AM   #12
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Siksukr, Let me fill in some detail and then hopefully the "one and done" statement will make more sense. If you see a flaw in my thinking please let me know why with details. This argument was pointed out to me recently by a very knowledgeable customer and I'm always anxious to learn more!
An 8400 watt array roof mounted on a roof with a good clear southern exposure will produce about 10-10,500 kWh per year. A perfectly oriented roof or ground mount will produce about 11,000. This can be verified here at the Federal government's official research lab. To come up with a figure for the amount of cash the solar array will save annually just multiply the kWh by the utility rate. Let's use the lower 10,000 kWh figure to be conservative, the annual savings for a Eversource customer would be $1,800 , and the savings for a Co-op customer would be $1,400
Our pricing for a straight ahead roof array is currently $2.35/dc watt, so an 8,400 watt (the total of the panel ratings) array would have an gross upfront cost of just under $20,000.
To get that $20,000 dollar funding let's make another assumption and say that the client is in a 25% net tax bracket and needs to generate $26,700 in pretax income to come up with $20,000 in cash funds ($20,000/.75). The simple one and done figure is $27,700 in pretax income needed to cover the upfront cost of the solar array installation.
The customer will be able to claim a 30% tax credit on their next tax return and all the formulas I'm familiar with deduct this from the gross after tax cost making the system a net cost of $14,000. I have only average accounting knowledge and am not sure where the credit should be entered into the after and pretax figuring above, should it be the $27,700 pretax income -6,000? or should it be the $20,000 gross -6,000/.75?? There is a huge difference. To keep it simple and be conservative let's stick with the $27,700 as the amount needed in pretax income to install the solar array.
A solar array is assumed to have a useful lifespan in excess of 40 years, but to again be conservative let's use 25 years because that is the warranty of most solar modules (aka panels) In 25 years of paying utility bills you will have sent $45,000 25 years x $1,800) in after tax dollars to Eversource to pay your monthly bills ($35,000 Co-op) ...and that is assuming that the utility rate never goes up. To generate the pretax income needed to pay those Eversource bills for 25 years you would have need to generate $60,000 in pretax income. Conservatively the solar system will save the client $32,300 in pretax income over 25 years. Would you agree??
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Old 08-24-2017, 11:01 AM   #13
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AC2717,
The NH PUC controls the export rate for the public utilities (Eversource, Unitil, & Liberty). The NHEC is member owned and is not subject to the PUC rulings.
The Co-op current credits the excess solar energy exports at about 75 cents on the dollar, retaining 25 cents to cover the logistical costs of their facilities, power lines, and personnel.
The public utilities currently net meter at a dollar for dollar rate, but this will be changing September 1st. As of that date they will be instituting a discounted net metering schedule similar to the NHEC's.
Anyone that is already has a renewable energy interconnect agreement in place on file with their utility will be grandfathered at the 1 for 1 rate until year 2040. This is a significant financial advantage and there is still a week in which to lock into it. An installation does not need to be in place, but the system details much be figured and a contract drawn up so the solar installer can file the interconnect agreement. As you can imagine, I'll be working right through the weekend... We are out about 6 weeks in our installation schedule, so there will still be time for the last minute Charlies to think things through thoroughly and cancel their contract if need be. That being said, I've yet to have anyone do that
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Old 08-24-2017, 12:17 PM   #14
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For the reasons outlined above, it made sense for me to buy and install solar on my Massachusetts home. For me, the payback is even faster because I also generate solar credits for 10 years; these solar credits have a cash value (fluctuates with the market) but conservatively will generate $1500 per year - for 10 years. So far the credits have sold for more.

I know many people who leased a system and while they had no upfront costs - and generally were paid by the installers - they do not have any of the benefits (tax deductions of SRECs) - that come with ownership. Too me, it doesn't seem like as good a deal.

I admit, I initially thought I was talking to a snake oil salesman as it seemed too good to be true. It wasn't. I pay zero in electric costs and was able to finance the whole system at such favorable rates that the cost of my loan is less than what I used to pay for electricity. If I was really smart I would apply my SREC checks to the loan and pay it off that much faster... My house is not for sale, but from all I have learned the solar array increases its value.

The NH house is not a candidate for solar (too many trees and not enough in electric costs).
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Old 08-24-2017, 01:56 PM   #15
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Wink You're too hard on yourself

Peter, you're close on the savings, but too hard on yourself in these calculations.

A finance professional would call the upfront investment $14,000. The taxes paid on the $20,000 are a "sunk cost"--you already paid them and can't get the money back, no matter what you do about electricity. Best to think of it this way:

I'm sitting at home typing on Winnipesaukee Forum. On the coffee table in front of me is $20,000 (yay!). I can spend it on my monthly electric bills, solar panels, or beer. If I spend it today on solar panels, the IRS will give me a tax credit (refund) of $6,000, which I will then place back on my coffee table. So I'm only out of pocket $14,000 for the panels now on my roof. Now I'm going to save $1,800 a year on my electric bill, placing the extra cash on my coffee table each month (or buying more beer). This is a 7.8 year payback period, getting 3X your investment back over 25 years.

Even better--the return on this investment in percentage terms is 12%, tax-free! (We do not pay taxes on money we save.) This is the financial equivalent of over 15% per year in the stock market for 25 years in a row--it's huge!
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