Solar electric 6.5kw expanded to 12.3kw

[peakbagger]

I had some high winds today that cleaned off my shallow roof panels so I got some production back, they are shallow so the angle is bad in winter but on a cold day they still contribute when they aren't covered with snow. My pole mount panels angled for winter maxed out their inverter for a few hours due to cold clear skies and snow reflection and my oldest wall mount system was also humming along quite well today. Now all I need are some longer days.

As I have varying vintage systems installed to three NEC code revisions, not everything is optimally sized. I am really tempted to make an inverter swap so that my pole mount has more head room in winter. Inverter capacity means far less in the summer as the temperature derate usually limits peak production but obviously there are far more hours of daylight.

 

[jebatty]

Yesterday solar production beginning with Oct 28 passed the 1000 kwh mark. Oct 28-Jan 30 = 94 days, total solar was 1020 kwh, General service electric meter for same time period was 1008 kwh, so solar met 100% of general service electric use. Nov-Dec was at about 60-65% of predicted irradiance, and Jan is at about 80%, so on year to year average solar should do better than it has done this period. Next goal will be for solar to also meet 100% of dhw usage, which averages around 100 kwh/month.

 

[peakbagger]

Once you get over 1000 kW, you are generating Megawatt hours (far more impressive). I always have thought there should be club that awards a "first MW" award like the first dollar award that chamber of commerce's gve out. Good luck on getting to 10!

 

[jebatty]

I'm bending the rules a bit because this is a partial re-post of most of the same info in the thread $9 heating and electric bill combined. But it belongs here, so unless I get canned ....

I expected a longer payback than at the $4/watt install standard because I had to do a ground mount, underground wiring 280 feet to my house, etc., also I used micro-inverters rather than a DC string inverter, and my install cost came to $4.59/watt. All work was contracted, not done by myself. The cost is a real number. I get a 30% federal tax credit which reduces my cost to $22,400, or $3.21/watt.

Attached is a chart showing my payback at year 20, far less than the life expectancy of the panels. And most interesting, after 20 years the payback far exceeds a standard competitive investment. At year 30 the solar system is $16,000 ahead in present value dollar over a CD investment.

Here are the assumptions for the calculations based on historical 20 year averages:
Average 5-year CD interest rate the last 20 years = 3.75%
Average inflation (discount) rate the last 20 years = 3.5%
Federal tax rate, current, not expected to change = 25%
Annual panel derate/yr = 0.5%
Current kwh rate ($0.108 x 1.06875 sales tax) = $0.115
Average annual energy cost increase the last 20 years = 5%

 

[Former Farmer]

Are you or can you get time of use rates? With the solar producing during peak hours, this can really change things.

My utility pays back at the same rate that I am charged. For on-peak hours the rate is .2725 and for off-peak hours the rate is .0525. I have been averaging over $1100 per year payback from the utility for the last two years even though I use just about as much as I generate. I generate over 13MWh per year and consume 12MWh per year.

 

[jebatty]

I have general service rate at $0.108/kwh and dual fuel rate at $0.053, sales tax on these at 6.875%, plus $14.00/mo base charge. Utility buy-back is at $0.108 rate for all buy-back. During Jan I had general service meter usage of 281 kwh, direct solar usage was 103 kwh, and 318 kwh of utility buy-back. I also had 1750 kwh of dual fuel meter usage, about 100 kwh of which was dhw and the balance supplemental electric heat. The extra cold weather this season, and still continuing, is boosting supplemental electric heat quite a bit over that of recent years.

 

[DBoon]

Attached is a chart showing my payback at year 20, far less than the life expectancy of the panels. And most interesting, after 20 years the payback far exceeds a standard competitive investment.

Hi jebatty, nice spreadsheet. Another way to look at this is to calculate over the 30 year life of the solar PV installation what guaranteed rate of return would have to be earned to equal the investment return of the solar PV installation.

 

[jebatty]

I deluded myself into thinking that we could make it on 9000kwh/year estimated annual production. Our general usage + hot water will be about 350-400 kwh/month, which I think is quite low. We maybe can reduce usage somewhat more on our general service, but that won't be significant or make up what would be needed to cover supplemental heat. We used about 1675 kwh in each of Dec and Jan, and with the continuing very cold weather in February (-teens at night), Feb will be high also, then still some heat in Mar and probably a little in April. Total electric would be in the range of maybe 5-6000 kwh @ $0.06/kwh or $360/yr, subject to ongoing rate increases. Interestingly, that 6000 kwh translates to the btu energy in about 1-2 cords of aspen stove wood.

Have to consider a Plan B. Long have thought about adding some solar hot air. We have an area on the front of our house that faces SW, roughly 3' x 25', that could be fitted with a hot air collector to help warm the basement. Hot air should be the more simple and probably less expensive than hot water. Time to cost it out and see if it is in the range of reason. Plan B would involve minimal ongoing maintenance.

Or Plan C. Not as preferable, but also will consider an upgrade to our wood stove heat and a larger stove, probably a fireplace insert with blower (we have a large fireplace which we use little), that has capacity to move enough heat to the basement to maintain a 50F temperature. Time to cost this out also to see how it might work. Plan C means more effort in wood c/s/s, but the wood comes from our land and has no out-of-pocket cost.

 

[maple1]

Jim - what about a Plan C (1) - run some lines to your house & heat it & DHW with your boiler & storage? Or maybe you don't have a heat distribution system in your house?

 

[jebatty]

The Tarm is in my shop, about 250' from the house and across a township road. Quite expensive to run underground piping, plus no hydronic heat distribution system in house. Plus, wife loves the wood stove and the radiant heat it gives off. Great start to the day to sit in front of the stove with a cup of fresh brewed coffee.

 

[jebatty]

Did some simple math to calculate how much production loss was caused by some tree shading. I have morning shading from trees. Yesterday Feb 14 the sky remained clear dawn to dusk, although the satellite photo showed some haze. The sun zenith was 30*. My system logs output every 15 minutes. I simply added up the log points from first production to 12:30pm (approx solar noon) and then from 12:30 to last production: in simple terms the difference would be caused by shading. I assumed that insolation was the same in the morning as the afternoon, but of course it might not have been. The afternoon produced 3.4kwh more than the morning, so if no shading morning would have been 3.4kw higher. For yesterday that meant that production of 37.6kwh could have been 41kwh. Or stated differently production was 92% of maximum.

I did the same calculation for Jan 27, sun zenith 24.6*, production was 65% of maximum. Actual production 29.5kwh, could have been 45.4kwh.

Another interesting figure. My Jan 2014 production was 80% of predicted January, so the shading calculation likely means that if no shading my production would have exceeded estimated. Predicted Jan was 482kw, actual was 427kwh, could have been 561kwh, or 117% of predicted.

Of course other factors could impact these calculations. In general, fwiw, through observation it appears that the sky on a clear winter day is more clear in the PM than in the AM.

 

[jebatty]

Continuing with the math. The production records for Nov-Dec plus detail on the few days that appeared to be clear dawn to dusk indicate that a pretty good estimate for the impact of morning shading on daily production is 25% less than if no shading. Fortunately these also are the lowest production months. Based on estimated yearly production of 9000 kwh, the cumulative impact of the shading comes to about 4% reduction in estimated annual output -- not very much, but every kwh still counts.

By March 1 sun zenith will cross the 35* point and impact of shading should be very low to nothing until mid to late October.

With the snow we get each winter, and this winter has been more snow than some others, the ground mount has been a blessing. A floor broom with an extended handle makes short work of clearing the snow off the panels. I don't even want to think how I could clear panels if they had been roof mounted.

 

[peakbagger]

I did this post on another form which may be of interest

Thump goes the snow

My new array is mounted on a low pitch roof (for new england) 2nd floor roof about 35 degrees from horizontal. I have had snow cover on the panels on an off all winter but not significant. We have been having snow on and off for the last 10 days although luckily have been on the fringe of storms so I would estimate about 16" of snow cover compacted down 10" on the panels . Today we had a fast warm up and while on the phone with a client I heard and felt a rumble above me. Out of the corner of my eye I caught the snow sliding off the panels in one sheet ending with one big "Thump". The snow sort of arced off the roof and fell several feet away from the house which was fortunate as I have a set of wall mounted panels immediately below the roof array that are angled outwards. There was no trace of any snow landing on the lower edge of the wall mounted panels but it was close. I sure didnt engineer it that way but had hoped that if it did happen that that would be the result. My wall mounts are adjustable for angle but given this experience I think I might hold off a bit before cranking them out to their spring angle which would present more of a target. The rest of the roof is asphalt so snow never slides off, the only way it comes down is with a snow rake or melts.

I realize I could rig some snow hooks but I think I am just going to make sure I snowblow a path in front of the house away from the fall zone. Beats hurricanes and tornados but every climate has its solar challenges. (broken image removed)

Meanwhile the freshly uncovered panels are cranking out the watts until the next storm

The array on the roof is my "bonus "array intended for non snow season, my wall mount and pole mount arrays dont have the snow build up issues as they are at 30 degrees from vertical and shed snow quickly.

 

[jebatty]

On my system install cost, a 4% reduction in production results in one additional year to payback.

 

[jebatty]

Time to declare the array shading free. Sun zenith 33.84* at 12:33. Attached is yesterday's (Feb 23) production chart. Near perfect bell curve, very clear day, but some still some haze as shown by the satellite photo. The little blip in late morning is the last tall tree that fights the sun and the last gasp of shade. Also attached is the production log. Microinverters are rated at 6500 watts and 6760 maximum output power. From 11:30 - 13:45 the array was in the rated/maximum range.

 

[jebatty]

February was a great month. After 4 of the lowest production months, the system payback already is about equaling the one year return on a CD. Solar pays.

 

[jebatty]

Yesterday, Mar 8, my system reached the 2 megawatt production benchmark. Jan 29 was the 1 megawatt point. March so far has been electrifying, with 273 kwh in the first 8 days. Three of those days each had 47 kwh, the single day high point so far. Cold weather and clear skies mean lots of electricity.

The first 8 days of March exceeded in production the entire month of December.

 

[jebatty]

I just received my electric bill for the period of Feb 8 to Mar 8. The bill was -$41.00! I think I'm going to enjoy a solar electric system that meets all of my electricity needs and which results in the electric company paying me rather than the other way around.

 

[jebatty]

March was a very good month, exceeding estimated production by 117%, coincidentally the same as February. The first two days of April were good, but now we're headed for a couple days of snowy weather.

 

[jebatty]

... and the bill arrived for Mar 8 - Apr 8: bill was -$104.00, total accumulated credit is now $145.00.

 

[flyingcow]

Appreciate the updates.

 

[AK13]

I am curious how you are liking your Sunvia panels and how you decided to go with that brand. I just got a quote for 24 panel system and the cost to go with Sunvia is about a $1200 premium compared to the Canadian solar brand panels (after 30% tax credit).

 

[Vic99]

After a year and a half, no problems with the Suniva panels. My wife and I like the black color with very thin white lines.

First I looked at the tested rating for the panels here: (broken link removed) Essentially it compares panels watt rating with what they actually produced in the test. So for example if a panel is rated for 240 Watts and it tests at 211 Watts, that's 87.9% of output of what it was rated for during the test.

If you want to meet 100% of your electricity needs, try to size bigger than you need (see below). Look at the last two years of energy bills.

Higher number is better for obvious reason, but also UV light will degrade panels over time. I'm told a panel typically loses around 0.5 to 1.0% of its output Watts each year as the panel clouds up a bit. It eventually reaches a saturation point and does not cloud any more. Most manufacturers will "guarantee" a panel is producing at least 80% of it original rating after 25 years. Who knows if they will still be in business, etc. Thus a higher starting number is better.

I have enphase M215 microinverters which clip at 225 W, but realistically, I only reach that less than 1% of the time anyway.

I buy American where I can. I'm not a zealot about it, but it factors in strongly. Perhaps some of Suniva panels manufacturing is outside of U.S., but seems they make them in Georgia. Your quote looks like an extra 50 bucks a panel. For me that was not an issue when I look a break even point of around 7-8 years. State of MA gave me 1k, feds gave 30%, I'm in for 10 years of SRECs. I got a Chevy Volt the next year (another 7.5K rebate, thus paid only 24.5K for it new . . . I hardly buy any gas). Good long term investments that will probably pay me more than I could place elsewhere, not being in the investment field.

Canadian Solar are made in China.

I'd do it the same all over again, with maybe 3 more panels ( I got 25 rated for 255W). If you have any other questions post here or PM me. I'll talk your ear off, if you like.

 

[CaptSpiff]

After a year and a half, no problems with the Suniva panels. My wife and I like the black color with very thin white lines.

<snip>

I'd do it the same all over again, with maybe 3 more panels ( I got 25 rated for 255W). If you have any other questions post here or PM me. I'll talk your ear off, if you like.

Please don't go "private chat", unless what you're discussing is private. This is where I come to learn from others.

If i'm not learning from this group, I'll have to go back to "making it all up".

 

[CombatChris]

This thread has been super useful and inspiring to me also. Keep it all public, man! This is good information. I for sure am thinking about a setup like this for the future-homestead. With data like this, I'm sure it's a lot easier to get a loan to cover the installation cost.