Is it worth the cost of adjustable-tilt racks for PV?
arnoldk
| Posted in Energy Efficiency and Durability on
Currently we are looking at getting a 6kW PV system which will plan on installing on a outbuilding or a pergola. I want to know if it’s worth the cost and possible headache of have the PV on an adjustable tilt change it the angle four times a year; December, March, June and September?
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IMO it depends on your projected output. The gas operated single-axis passive tilt systems are much less expensive than motorized two-axis active tilt systems however the active systems squeeze a smidgen more power.
http://www.zomeworks.com/photovoltaic-tracking-racks/
http://www.solarpaneltilt.com/
https://www.solarpowerworldonline.com/2016/05/advantages-disadvantages-solar-tracker-system/
http://www.solar-tracking.com/
Thanks John for those links. It seems like for residential (I'm in Ottawa, Canada) use the cost and hassle doesn't seem to warrant installing solar tracker or adjustable tilt that I was considering. Most seem to suggest a fix system and simply add additional panel to account for the lost of solar production.
Would most here agree with this?
I've read various sources about benefits by facing PV panels south, and manually changing the tilt just a few times per year. Might be a difficult task with rooftop PV. For example: "Adjusting twice a year on the spring and fall equinoxes can increase production by about 5%—with quarterly adjustments, a little more can be gained. In the winter, especially, these few extra kilowatt-hours can be crucial to an off-grid home..."
https://www.homepower.com/articles/solar-electricity/design-installation/optimizing-pv-array-orientation-tilt
For the moment we will be grid-tied with net metering so every last kW isn't as crucial. Sounds like I'll simply find the most yearly optimal angle for the PV and make it fix.
I don't think it pays off in North TX (33° Latitude), which depends on your expectations and how long you plan to live in that house. It also depends whether you are off-grid or not and the type of tracker you buy (manual or motorized)
The cost of solar trackers for a 10kW system can be between $25-30K installed, almost or more than the price of the system by the time you get Fed and Local rebates. It pushes the ROI at 20-30 years.
Arnold, I'm in Ottawa as well. I've been wondering about increasing the angle of solar panels not only for increased winter production, but also using gravity to keep the panels clear of snow.
Here's a link to an interesting study done in Alberta, though Edmonton has many more thaw cycles per winter than Ottawa does:
https://solaralberta.ca/content/alberta-solar-performance-data
You could use PVWatts to model the different angles vs. a fixed angle. It is very accurate.
Arnold,
It seems to me that there are two questions here.
Question 1. Is the cost of a PV rack that automatically tracks the path of the sun justified?
A. In general, no. You're almost always better off to install your PV modules at a fixed angle, and to use the money that you would have spent for a tracking rack to pay for a few more PV modules.
Question 2: If I purchase or build a PV rack that can be adjusted manually four times a year, am I likely to perform the chore regularly?
A. The answer to this question is almost always no. You may adjust the racks as required during the first year of ownership, but by Year 3, the racks will be permanently set to a compromise position.
Thanks Lance for the article and it seem to line up with everything else I have read. For those off-grid it's worth adjusting the panels two or fours time a year to squeeze every last kW but for grid-tied it's not worth the initial cost or the headache for around 5% more production.
I'm surprised that clearing the snow off the panels didn't amount to a whole lot more production. If that's the case, I will likely only clear the panels after the large snow fall which would only be a hand full of times per winter in Ottawa.
I have to agree with you Martin that in most case people stop performing those type of task after the first year or two especially considering the return for the effort doesn't seem to be there, at least for grid-tied. I thinking find the best optimum year-round angle is what I will do and design the roof of the pergola or outbuilding accordingly.
I own a solar company, in my opinion, it depends. First of all, adjustable as in just the angle makes much more sense than say a Tracker. I would never do a tracker myself, as the cost of the tracker far outways the minimal improvement, I could throw on more panels for a fraction of the cost.
Now if you are looking for a 4 time a year adjustment, the answer is probably not. In most cases if you do the calculation based off of your location, you will maybe get an extra 5 percent. If it was roofmount, and anything but a flat roof, I wouldn't recommend it at all. If it is a flat roof install or ground array, then possible. It is work vs reward vs cost. I am putting in an adjustable as we speak for my new home construction. In the area I am in I don't have inspections, so manufacturing a top of the line home built rack with tilt is relatively cheap. If I was doing it in Utah, I probably wouldn't. The rack costs a lot more, and I would just take a fraction of that and put on more panels.
Basically does your ACA require engineered rack solutions and certification. IF so, do they have a certification / state letter for your area already ? Typically that alone puts them out of reach cost wise.
A company near me makes a new tracking system, motorized two axis. It uses a cable-based structure to reduce the weight and cost, and it's become pretty popular for installations around here. Friends who have installed them report that their favorite feature is the ability to orient it vertically during a snow storm so that snow accumulation is zero. The other reason for their popularity is that they have the convenience and flexibility of ground mount, but take up less space than a conventional ground mount system with the same annual energy production.
http://www.solaflect.com/solar-solutions/suspension-pv-tracker/
I went back and looked at my pv production for the last two winters. My best estimate is that snow cover reduces my annual production by about 3-4%. Since winter production is low anyway, snow isn't a big deal.
Half my panels are on an 8/12 pitch roof, half is 3/12. House is in Maine.
Adding a couple of panels might be cheaper than adjusting tilt or installing a tracker. I never try to remove snow.
Not enough information to answer. Generally yes, but simply run the numbers. Factors are: convenience, shading, area available vs need, cost of one system vs the other. Martin's answer simply reflects a lack of knowledge. Kevin's suggestion to use PVWatts (or other method) to analyze potential will give you the numbers that will let you compare gain against cost.
No affiliation, recommendation, or otherwise.
For those in Ontario, you may want to investigate this option:
https://www.solacity.com/product/fabrack-4-panel-adjustable-ground-mount/
http://www.fabracksolar.ca/
The page says they have been professionally engineered. A search of the PEO membership, however, shows that the owner of Fabrack Solar (currently at least) is not a member.
I agree with some of the posters that say skip the tracker and buy more modules. Modules are very cheap, you could probably up the power of your system significantly for the cost of the tracker. Hopefully you can face array as close to South as possible.
I’m going to say again, you can’t really know in less you have all the information. I’m going to say again, you can’t really know in less you have all the information.You need site information, including both how much space is available and what the sharing is like. And you need to run all the numbers, not just the number of panels and their cost but also the structure numbers. How much more it’s going to cost to add a few more panels Depends on not just crossed of the panels themselves, in some cases it might mean another set of peers. It’s not that hard to run the numbers.
Here's an update to my earlier comment.
Over a four year period, our array on the 3/12 roof has produced about 5% less power than the same size array on the 8/12 roof. Both are oriented in the same direction, about 10° west of south. We're at about 43° N latitude.
Snow stays on the shallower roof longer than on the steeper roof, so that might reduce the difference a bit. We have a total of 24 panels. I suspect adding one or two more panels would be cheaper and much less trouble, than adjusting the tilt.
Stephen, on a roof with room to add more, with all good exposure, I’d agree but would still run the numbers. A consideration: over the course of a year, your panels average closely, but in the summer your low pitch roof likely produces a lot more, taking advantage of the higher sun. In the winter the the snow decreases the productivity there. But the steep pitch takes better advantage of the lower winter sun and sheds the snow so I’d guess your productivity on that roof is much higher in the winter. So over a year they average out about the same. That said, I’d be curious to know what your numbers are for each set throughout the year, not the yearly totals.
Adding panels to a roof is less a big deal than adding panels on the ground, if you have adequate roof space.
Pierre: I don't have any specific numbers for winter/ summer production. But I've noticed that you are correct that summer production in the low slope roof is higher and winter production is higher on the steeper roof.
Probably most people are not going to design the roof pitch to maximize solar production, given the relatively small difference over the course of a year. But that's with Maine's net metering. Someplace that nets every month might create different incentives.
My peak production coincides with overall peak demand in New Endland, i.e. sunny summer afternoons. So the grid overall might benefit more from a low slope roof.
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An anecdote that may have no wider relevance, but the largest PV installation near me, sized to service a community of about one hundred homes, hasn't managed to adjust it's tilt racks for at least the past three years. Just haven't got round to it.
Though not perfect or complete, and noting every location is different, this article explains quite well the tilt arguments: https://www.solarpaneltilt.com/
Stephen, thanks for sharing those differences (probably similar to what is seen in the article).
Folks tend to suggest 4 adjustments per year to squeeze a bit more (if the adjustment is possible, why not). Do it when you change your oil. Not getting around to tilting is a different problem, but a 5-10% gain over the life of panels adds up to some cash and that much less GHG emissions.
We must remember the embodied cost of a few more panels and installation, beyond just the price of the panels alone. Another set of piers, more pipe, rail, fasteners, inverters, etc... and shipping, and manufacturing costs to the environment.
Pierre,
Maybe the answer to whether tilt racks make sense needs to be nuanced not only by running the numbers but by human behaviour. Solar enthusiasts can probably be relied on to adjust their displays fairly regularly, but as PV adoption increases I don't think it's something that should be anticipated when designing systems. Imagine a realtor telling prospective buyers the benefits of the PV system on the house they are thinking of purchasing, but then adding "Oh and you will need to go up own the roof four times a years and move the panels - especially if the buyers are elderly, perhaps a single mother, the house is two stories, etc.
That was one of the major problems with 1970s passive solar houses which relied on shades to modulate temperatures. People simply didn't open and close them the way the designers needed them to, and as a result the houses were uncomfortable and performed poorly. The same problems occur with almost all systems that rely on routine owner maintenance or input, like changing ventilation filters, seasonally turning off water to outside hose-bibs, etc. Human behaviour, outside the small set of motivated enthusiasts, can't be relied on.
The question that I’m answering or responding to is whether or not tilting is worth the cost. I’m not trying to address human behavior, though I’m assuming anyone asking the question wants to know the facts and wouldn’t ask if they had no intention of putting in the effort. They are what I would call an enthusiast simply because they ask and are contemplating.
That said, I would unlikely suggest it is ever worth tilting a roof based system because it seems to be too risky to ask anyone to go on a roof to tip panels. But if someone was so inclined I’d run the numbers.
If circumstances can suggest it is worth considering, run the numbers.
Stop looking for exceptions. There are always exceptions; never say never. All the concerns you raise are addressed today. If folks are too lazy to exert a little effort a few times a year, well those folks probably wouldn’t be asking. Otherwise, run all the numbers and decide. If it is too much work to run the numbers, well tilting is probably not for you either.
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