Need Help With Senior Design

solarpanelcleaner · November 2011

Hello,

For our design project we are working with a client in Wisconsin to help them remove snow from their roof-mounted solar panels in the winter. We are designing a system to spray water a vertical distance of 40-50 ft.

- Flow rate coming from the hose in the house measured at 4.9 gal/min

- The pressure is being pumped to the house from a series wells at 60 psi

We want to increase this flow rate to 10 gal/min to help melt the snow off the panels more effectively. Our idea was to use a 100 gallon storage tank, we would fill this with the garden hose, and have water leave the tank to get our desired flow rate.

From the tank the hose would approximately be 50 ft. in length, and at the end of the hose we were planning to use nozzle designed to give us a solid stream.

If from the tank the water leaves at 10 gal/min, using the inner diameter of the hose (0.62992 in.) we calculated the velocity of the water to be 3.1375 m/s. Will this velocity stay constant until the end of the hose and be the Vin for the nozzle?

Then if we had a nozzle diameter of 0.2 in, using AinVin=AoutVout we calculated the water leaving the nozzle to be at a velocity of 31.09 m/s. Using the trajectory equations R= Vi^2*sin(2 θ)/g and h=Vi^2*sin^2(θ)/2g we found our stream would travel R=92.58 m and h=62.55 m

Could we put a valve at the bottom of the tank, and get that flow rate and velocity to shoot the water that distance, or will we have a problem with pressure with this system?

If we use a pump to pump out the water at 10 gal/min would the water still be able to shoot that far, or would we have to model our system similarly to a pressure washer and have a pump attached closer to where we would be spraying the water from?

Cariboocoot · November 2011

Re: Need Help With Senior Design

You want to spray water on panels in sub-freezing weather to clear snow off them?

Normally panels are tilted more vertically in Winter to keep snow from adhering, or if the latitude does not permit this the snow should be removed mechanically.

I don't see the advantage in replacing snow with ice.

mike95490 · November 2011

Re: Need Help With Senior Design

Cariboocoot wrote: »

.......I don't see the advantage in replacing snow with ice.

Or shocking frozen panels with "warm" unfrozen water....

solarpanelcleaner · November 2011

Re: Need Help With Senior Design

The home we're working on had 54 PV panels with a 34 pitch. The pitch cannot change, and in previous winters, they would go days with snow covering the panels.

The panels are made by Kyrocera and are very durable. The solar panel installers actually suggested water to our client and they've used water in the past and there were no problems.

The only problem is not enough water. Let's say there was 5inches of snow on the total square footage of the panels (their entire roof facing the south is entirely covered by solar panels; over 700sqf of panels), that is over 1600lbs of snow.

The water won't be warm. it is water from the garden hose which is normally at 40-50degress, which is relatively cold. The panels are durable enough that temperature shock is not a problem. The home is well insulated too, so the use of water won't be a problem.

rollandelliott · November 2011

Re: Need Help With Senior Design

why not just put piping at the very top of each solar panel and use a slower flow rate? once the bottom snow is wet it should just slide off. I guess it depands on how many rows they have? a photo would help.

Or better yet buy a $100 ladder and build some steps on the roof so they can easily clean them by just walking up there.

icarus · November 2011

Re: Need Help With Senior Design

Welcome to the forum,
Please realize that your system is likely to cause more trouble than good. It is likely to cause more , not less panel obstruction.

As an alternative project, consider a semi conductor heat tape, t-stat controlled, with a timer and a photo cell. During daylight hours, if the photo cell goes dark, being covered with snow, and the t-stat says it it below freezing, the heat tape heats. A simple regimen of tape around the lower edges and perhaps the sides will quickly heat enough for the snow to slide off.

Here is a link to a heat tape company that I use,, there are lots of others for a prototype/beta system.

Tony

ggunn · November 2011

Re: Need Help With Senior Design

It's a school senior project. It doesn't have to be practical or even a good idea, it just has to work.

Vic · November 2011

Re: Need Help With Senior Design

Rumor has it that "Snow Melt" is on the list of features for the Midnite Classic CC. Dunno how it would work, or when it might be implemented. Vic

Cariboocoot · November 2011

Re: Need Help With Senior Design

Vic wrote: »

Rumor has it that "Snow Melt" is on the list of features for the Midnite Classic CC. Dunno how it would work, or when it might be implemented. Vic

Connect PV to batteries; send a small amount of current through the panels to warm them up.
Snow melts, panels start producing; changes the current flow - switch off snow-melt mode.
The tricky bit is controlling the current because of the many differences in array configuration.

They're probably trying to come up with a way for the controller to automatically "learn" the array based on its output and adjust the melt mode accordingly.

jagec · November 2011

Re: Need Help With Senior Design

solarpanelcleaner wrote: »

The panels are made by Kyrocera and are very durable. The solar panel installers actually suggested water to our client and they've used water in the past and there were no problems.

The panels are durable enough that temperature shock is not a problem. The home is well insulated too, so the use of water won't be a problem.

I was under the impression that humidity/freeze cycling was one of the major failure conditions in accelerated lifecycle testing of solar panels.

Vic · November 2011

Re: Need Help With Senior Design

Marc,

Was trying to say that I do not know how WELL it would work, not that I did not know the mechanism.

To me, seems to be a bit risky, as this function could come up should there be some warranty issues on panels that have been subjected to this process.

Whatta I know (?). Vic

Cariboocoot · November 2011

Re: Need Help With Senior Design

jagec wrote: »

I was under the impression that humidity/freeze cycling was one of the major failure conditions in accelerated lifecycle testing of solar panels.

It is.

And weather is not consistent. You can have snow at 0C or snow at -17C, et cetera. Will the water temp always be 10C? The difference in temperatures is what causes the thermal shock; the greater the difference the greater the shock. No, it won't cause the panels to explode like dropping from 80C to -40C would, but repeated thermal stress takes its toll.

Other weather factors will effect the efficiency of this water-spray method, including relative humidity and wind. My brother used to run a ski resort. The snow-makers had quite a few adjustments for changing the type of snow according to the prevalent weather conditions. You can make snow above freezing if the settings are right. I realize this is not the intent of the OP's experiment, but it could be an unexpected side-effect.

On the whole, Rolland's suggestion of placing piping at the panels is far more practical than trying to spray water 60' in the air to knock snow off panels in freezing weather. Ask a fireman how much fun that sort of thing is.

Cariboocoot · November 2011

Re: Need Help With Senior Design

Vic wrote: »

Marc,

Was trying to say that I do not know how WELL it would work, not that I did not know the mechanism.

To me, seems to be a bit risky, as this function could come up should there be some warranty issues on panels that have been subjected to this process.

Whatta I know (?). Vic

Yes; lawyers always look for ways out of warranty claims. :roll:
From an engineering standpoint, as long as the panels were not subjected to greater than their Isc rating they'd be fine.

But what do we know?

ggunn · November 2011

Re: Need Help With Senior Design

I think all you guys are missing the point. It's a school senior project. It just needs to work for the OP to get his grade. It doesn't need to be a good idea.

Dill · November 2011

Re: Need Help With Senior Design

I guess..I would worry about accelerating the build up of ice dams on the roof as well. Ice is heavy. Not to mention keeping a garden hose from freezing up in Wisconsin in winter without bringing it inside is impossible.

solarpanelcleaner · November 2011

Re: Need Help With Senior Design

This system will only be used every once in a while, mainly after a large winter storm. It won't be used on a regular basis in the winter. Most likely 2-3 times a month, depending on the weather.

We're on a time crunch, so using water is the only option we have to pursue. The client also wants nothing attached to the home, thus why we decided to use water.

It's more of a water cannon that will sit on a tripod and shoot water up.
It can be used during the summer too to clean the panels.

We're just having trouble figuring out what pump is necessary to bring enough water up 30-40 feet.

Cariboocoot · November 2011

Re: Need Help With Senior Design

solarpanelcleaner wrote: »

The client also wants nothing attached to the home, thus why we decided to use water.

This is what worries me. This does not sound like an academic exercise but a practical application, and it isn't practical.

The use of the term "water cannon" is entirely accurate.
To lift water in a pipe 50 feet is easy (relatively). To push it through air the same distance requires a lot of pressure. Enough so that if it were effective at blasting snow off the panels at such a distance it would be dangerous to anything close to the outlet. If a person should happen to be in front of that when the water lets loose they could be killed.

It would be a weapon.

rollandelliott · November 2011

Re: Need Help With Senior Design

"We're on a time crunch, so using water is the only option we have to pursue. The client also wants nothing attached to the home, thus why we decided to use water."

tell your client that their stipulations are impossible for a good system. If i were a teacher grading this there is no way I would give you a good grade if I knew you dismissed all the practical ones given so far.

solarpanelcleaner · November 2011

Re: Need Help With Senior Design

"And weather is not consistent. You can have snow at 0C or snow at -17C, et cetera. Will the water temp always be 10C? The difference in temperatures is what causes the thermal shock; the greater the difference the greater the shock. No, it won't cause the panels to explode like dropping from 80C to -40C would, but repeated thermal stress takes its toll.
Other weather factors will effect the efficiency of this water-spray method, including relative humidity and wind. "

We understand shooting water up onto the solar panels in the winter is not ideal. Our clients are getting old and wouldn't be able to manage raking the snow off of the panels or any physical solution to the problem. Not to mention the base of the roof the panels are mounted on is 30 ft. vertical. Also, when we were brainstorming with the client proposing our multitude of ideas, the client wanted nothing attached to the solar panels or to the house. Under warranty we can't attach anything to the panels as is, but we can spray them with water.

One of our favorite alternates was to have a standing vertical pipe go through the house vertically sitting along the chimney, and discharge water onto the panels.... like I said we can't do anything to the house. We are stuck with figuring out a way to shoot water on to the panels, it is what the client wants. This would have been nice to plan pre-construction of the house, maybe some type of irragation system to distribute water onto the panels.. hindsight is 20/20.

We have many issues that are difficult to account for,
- the separation of the stream as we shoot the water stream at further distances
- the temperature loss of the water leaving the hose.. we are assuming it leaves the hose at 10 C and hits the roof at 10 C, which will not be the case but we are using a factor of safety to account for this.
- The Solar Panels are UL-1703 listed, have passed safety inspections under code UL-1703, under those codes they are tested to successfully operate within the range of -40 C° to 90 C° However this was tested over a 40 minute period, so we don't know how well they handle immediate temperature shocks, but the manufacturers believe water at this temperature will not damage the panels.

For calculating the energy needed to melt the snow we assumed the water will hit the panels at 10 C and the snow will be at -10 C. This gave us an idea of how much water we needed to melt the snow. Which is a lot of water.

The Idea was to use a 100 gallon tank to allow us to increase the flowrate from 4.9 gal/min to 10 gal/min... The thought is the larger amounts of water we could shoot up there and be more effective at melting the snow. The higher mass of water the less chance the water would have chilling to 0C and becoming just another layer of ice on top of the snow. We are having difficulty designing this system with a 100 gallon tank, So are other option would just be to use a pump to increase the pressure and shoot the current flowrate of 4.9 gal/minute onto the panels.

If we had a 100 gallon tank do you think a pump would be able to pump that water out and still have enough pressure to deliver the water approx. 50 ft. (hypotenuse) ? Or, would having a pump towards the end of the hose at the nozzle be the ideal situation for shooting the water this distance?

Do you agree with the thought that we need to increase the flowrate with a 100 gallon tank, or do you think that we should just stick with the current flow rate and pressure coming from the house?

solarpanelcleaner · November 2011

Re: Need Help With Senior Design

Btw, thanks for all the feedback so far!

icarus · November 2011

Re: Need Help With Senior Design

Once again, if it were me, I would avoid water, and consider heat!

Just keeping the plumbing from freezing presents a significant issue all by it self.

Tony

BB. · November 2011

Re: Need Help With Senior Design

I would Google for a Fire Fighter's Math or similar type site (pump/equipment mfg) and look for their rules of thumb for pumping water.

www.firefightermath.org/index.php?option=com_content&view=article&id=31&Itemid=45

We are not hydaulic engineers here (at least not many of us are--there are a couple fire fighters though)--So the answers you will mostly get are based on Water, Freezing Weather, Snow, Solar Panels, and Structure Issues.

The problem is made worse by looking at the numbers... Water cooling from 10C to 0C does not have much latent heat vs that contained by an equal weight of ice to water sublimation. If you where going to melt a 100 lbs of ice, with this method, you probably would need something near a 1,000 lbs of 10C water.

I think we have a few threads on people experimenting on removing/keeping snow off panels... RainX, waxes, etc.? You can try Google with the "site:wind-sun.com" tag to limit searches to this website.

Try typing this into Google:

rainx snow panel site:wind-sun.com

I cannot help much more--Snow is what I get from my defrosting my freezer a couple times a year (I move it outside a spray with 120F hot water--It still takes an amazing amount to melt all of the ice with a hose).

I would also look at aircraft deicing procedures and chemicals too. They do not spray just warm water, but some form of (chemically safe) anti-freeze too.

www.icao.int/anb/FLS/flsicing.html

Adding an environmentally safe anti-freeze you your 100 gallon tank may be a big help too.

But adding a bunch of water to a roof and creating slush sure sounds like it is more problem than a solution.

You might also look at the "lost energy" because of snow on panels... Depending on weather and other factors, it is possible that an efficient generator to keep the battery charged during winter may be a better/lost costly solution (overall) than "clearing" panels when there is little sunlight and solar power available.

-Bill

TheBackRoads · November 2011

Re: Need Help With Senior Design

Ever considered a roof rake for the snow with some pipe wrap on the leading edge? Works for a lot of us that get snow and dont have the proper tilt....

I bought one like that from Fleet Farm for 30 bucks. you can use extensions as well to reach higher if needed.

Jeff

rollandelliott · November 2011

Re: Need Help With Senior Design

just walk away from the client you will most likely spend more time and money than you will ever make on this project. I would not even consider doing a project with so many unknow outcomes, potential water damage and leaking due to high pressure.

electrical heat tape is the easiest solution, though not that effcient. good luck.

RCinFLA · November 2011

Re: Need Help With Senior Design

Vic wrote: »

Rumor has it that "Snow Melt" is on the list of features for the Midnite Classic CC. Dunno how it would work, or when it might be implemented. Vic

You can push some power into the panels to 'defrost' them. Without boosting the voltage it will depend on how much leakage the cells in the panel have.

You can also raise the voltage near Voc. This will cause all the cell's inherent diodes to conduct. An MPPT, buck switching, battery charge controller could, in theory, operate as a boost switching supply in reverse direction to take battery voltage up to panel near Voc voltage. When they are cold this could be significantly higher Voc then normal.

It probably only will take about 50 watts per 200 watt sized panel to warm them up enough to cause the snow/ice to slide off.

You will also burn some battery power doing it. Probably want to make sure it is not overcast before spending the battery power, weighing what you might gain over what you will loose in battery charge.

Spraying them with water, warm or not, is just a bad idea. Have you every activated your windshield washer on a cold snowy morning?

mike95490 · November 2011

Re: Need Help With Senior Design

With 60 PSI of water pressure, and a sidewalk sweeper nozzle ( $0.99 @ the 99 cent store) I can just barely reach the top row of panels, that are 20' away, and 20' high, see last row of photos here:
https://www.facebook.com/media/set/?set=a.161025670637561.41240.120212794718849&type=1&l=9f8cb32526

ggunn · November 2011

Re: Need Help With Senior Design

solarpanelcleaner wrote: »

"And weather is not consistent. You can have snow at 0C or snow at -17C, et cetera. Will the water temp always be 10C? The difference in temperatures is what causes the thermal shock; the greater the difference the greater the shock. No, it won't cause the panels to explode like dropping from 80C to -40C would, but repeated thermal stress takes its toll.
Other weather factors will effect the efficiency of this water-spray method, including relative humidity and wind. "

We understand shooting water up onto the solar panels in the winter is not ideal. Our clients are getting old and wouldn't be able to manage raking the snow off of the panels or any physical solution to the problem. Not to mention the base of the roof the panels are mounted on is 30 ft. vertical. Also, when we were brainstorming with the client proposing our multitude of ideas, the client wanted nothing attached to the solar panels or to the house. Under warranty we can't attach anything to the panels as is, but we can spray them with water.

One of our favorite alternates was to have a standing vertical pipe go through the house vertically sitting along the chimney, and discharge water onto the panels.... like I said we can't do anything to the house. We are stuck with figuring out a way to shoot water on to the panels, it is what the client wants. This would have been nice to plan pre-construction of the house, maybe some type of irragation system to distribute water onto the panels.. hindsight is 20/20.

We have many issues that are difficult to account for,
- the separation of the stream as we shoot the water stream at further distances
- the temperature loss of the water leaving the hose.. we are assuming it leaves the hose at 10 C and hits the roof at 10 C, which will not be the case but we are using a factor of safety to account for this.
- The Solar Panels are UL-1703 listed, have passed safety inspections under code UL-1703, under those codes they are tested to successfully operate within the range of -40 C° to 90 C° However this was tested over a 40 minute period, so we don't know how well they handle immediate temperature shocks, but the manufacturers believe water at this temperature will not damage the panels.

For calculating the energy needed to melt the snow we assumed the water will hit the panels at 10 C and the snow will be at -10 C. This gave us an idea of how much water we needed to melt the snow. Which is a lot of water.

The Idea was to use a 100 gallon tank to allow us to increase the flowrate from 4.9 gal/min to 10 gal/min... The thought is the larger amounts of water we could shoot up there and be more effective at melting the snow. The higher mass of water the less chance the water would have chilling to 0C and becoming just another layer of ice on top of the snow. We are having difficulty designing this system with a 100 gallon tank, So are other option would just be to use a pump to increase the pressure and shoot the current flowrate of 4.9 gal/minute onto the panels.

If we had a 100 gallon tank do you think a pump would be able to pump that water out and still have enough pressure to deliver the water approx. 50 ft. (hypotenuse) ? Or, would having a pump towards the end of the hose at the nozzle be the ideal situation for shooting the water this distance?

Do you agree with the thought that we need to increase the flowrate with a 100 gallon tank, or do you think that we should just stick with the current flow rate and pressure coming from the house?

Unfortunately, sometimes after exercising due diligence you have to tell the client that what he is proposing just isn't a good idea. Either it's prohibitively expensive, hazardous to equipment or people (or both), not doable in the real world (I cannae rewrite the laws of physics, Cap'n!), or all the above. You might not be there yet, but it seems to me that you are approaching that point.

solarpanelcleaner · November 2011

Re: Need Help With Senior Design

Thank you everyone for all your responses. We will take them into consideration. You guys have helped us a lot.

Need Help With Senior Design

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