Pumping water to roof

[solarguy]

Hello DIYers,

I currently spray, or rather stream, RO water on 54 roof-mounted solar panels with a conventional 2.5 gallon deck sprayer to remove accumulations of dust particulates, pollen, and bird-crap.
This is followed by a squeegee routine.
It requires about 10 gallons of water that I have to carry up the ladder and a lot of hand pumping topside.

Has anyone used a scuba tank to pressurize a ground-based water tank to lift water 20 feet and deliver 50 psi of water pressure on top ?

I wash just before sunrise before panel temperatures rise too far above the water temperature of my water supply that is stored outside to avoid shocking and possibly cracking the glass.
The noise of a compressor pump at that time of day would annoy my neighbors.
High water pressure greater than 50 psi is not as crucial as water volume, with 20 gallons as a target.
Hose length would need to be about 75 feet and the rise is about 20 feet.

I couldn't ask Archimedes to help, but did notice a thread here on pneumatic power tools that began to answer the question.

Anyone encounter this problem before, or have any thoughts ?

Solarguy

[dmoore19]

Don't know if this will help but a formula for figuring hydrostatic pressure is as follows

.052 X FW X Rise = psi hydrostatic pressure

.052= Constant
FW= Fluid weight ppg. Fresh water = 8.33 ppg
Rise= true vertical rise

so .052 X 8.33 X 20 = 8.6632 psi

I would think 50 psi would more than adequately move the water up 20'. There would be friction in the garden hose but it should be minimal over 75' depending of course on the flow rate. You can use 0.433 psi/ft for hydrostatic pressure for fresh water. I would think that as long as you had enough pressure to compensate for the rise you could lift the colloum of water.

I would think a small electric sump pump woud be more than adequate. You could put it on a timer and it could go off automatically whenever you wanted.

hope that helps.

[Peter_C]

How often are you washing the panels?

I would be really careful taking a squeegee to the panels since scratches could cause more harm than the water spots.

Take a look at Helio Tex for some ideas. Heliotex Solar Panel Home Security Fasteners Anti Theft The system works well, but does require somewhat clean water to begin with from a water softener if the water is hard. The soap solution helps dissipate the water spots.

Just curious how many watt panels you are using?

[rhwestfall]

following dmoore19 - you loose 1 psi for every 2.31 feet of rise + friction losses in the hose, so you want 3/4" vs. 1/2" hose.

Think similar to an electric pressure washer with a home made spray bar..... so a boat pump (see what west marine has) with the gpm you want (2.5 -5.5 maybe) rated at the head (likely 30'-50') you need....

[dmoore19]

This might help out.

Step 8: Calculate Pressure Losses

[solarguy]

How often are you washing the panels?

I would be really careful taking a squeegee to the panels since scratches could cause more harm than the water spots.

Take a look at Helio Tex for some ideas. Heliotex Solar Panel Home Security Fasteners Anti Theft The system works well, but does require somewhat clean water to begin with from a water softener if the water is hard. The soap solution helps dissipate the water spots.

Just curious how many watt panels you are using?

Thanks for the response.

I rinse as needed, when dust, pollen, etc. accumulate enough to visibly obscure the panels. So, about 9 times a year.
Oddly, the peak season for harvesting solar around Phoenix is between February and May, with a decline in available solar irradiation over the summer months.
Rainfall is scarce and when it occurs has not fully rinsed the array in 15 months of experience. Usually only enough rainfall to create water spots.

The array is rated at 11.5 kW and has produced nearly 25,000 kWh to date, or about 1,700 kWh per month.
Last calendar year produced an excess over our consumption, which the local utility purchased at wholesale rates at the annual settlement in December (net metering).
Monthly fixed charges, surcharges, other charges, and more charges are about $9.60 a month, which are now covered by the credit balance created December.

I am not overly aggressive with the squeegee; water does the heavy lifting and the squeegee removes the excess water.
The panel surfaces appear much the same as a glass stovetop. They have been formulated of tempered glass with high impact resistance to hailstones and other flying objects.
While durable enough for the larger items in the atmosphere, their 750 square feet of area is not immune to dust and receive their share of particulates.
Special coatings for the glass do exist but most only address water droplet formation and runoff, not dust accumulation.

Power monitoring indicates that the cleanings result in a 3% to 6% increase in production.
We have been producing around 70 kWh per day for the last week and anticipate a 3 kWh per day boost from today's cleaning, or an estimated 21 kWh for the next week.

Briefly,
the Solarguy

[Peter_C]

I am amazed to hear a 3-6% gain in efficiency by washing the panels, and here I figured it was marketing hype. We do not get as much dust as the desert. Then again the only dust storm I have ever seen was when I lived in Phoenix. We have set the Helio Tex system up on a couple of vineyard systems, since it is such a dusty area. You can't just clean a 15kw ground mount square (We also run 21 degrees of tilt here as the preferred, so a little better water run off then in AZ). With Enphase as our go to inverter, we see about an 8% increase over the EPBB's to begin with, so utilizing "Time Of Use" our clients often see credits build very quickly. Our local energy supplier will turn any excess credits into a gas bill savings too. Although that is not a good return on investment to be that oversized. Better to use a heatpump to burn up the excess power credits.

A module with a 50+ year life expectancy needs all the love it can get. FREE energy rocks! Now if we could just educate people to the point they realize it does work for them.

[solarguy]

I am amazed to hear a 3-6% gain in efficiency by washing the panels, and here I figured it was marketing hype. We do not get as much dust as the desert. Then again the only dust storm I have ever seen was when I lived in Phoenix. We have set the Helio Tex system up on a couple of vineyard systems, since it is such a dusty area. You can't just clean a 15kw ground mount square (We also run 21 degrees of tilt here as the preferred, so a little better water run off then in AZ). With Enphase as our go to inverter, we see about an 8% increase over the EPBB's to begin with, so utilizing "Time Of Use" our clients often see credits build very quickly. Our local energy supplier will turn any excess credits into a gas bill savings too. Although that is not a good return on investment to be that oversized. Better to use a heatpump to burn up the excess power credits.

A module with a 50+ year life expectancy needs all the love it can get. FREE energy rocks! Now if we could just educate people to the point they realize it does work for them.

Peter,

I'm curious about your source of water. What is the hardness and the composition of the total dissolved solids (TDS) in your water ?

After hearing the conventional mode of "hosing down" the panels, I wondered if the hard water of Phoenix would fall into that mode.
At the water meter, the hardness, measured in TDS, clocks in at 550 parts per million, or 550 ppm per liter of water. Certainly hard water.
The conventional water softener here raises that number to 605 ppm, replacing the original Mg+ and Ca+ ions with NaCl. Two liters of that and you meet the recommended RDA.
In contrast, the Reverse Osmosis (RO) system produces water at 5 ppm.

Everyone's usual acquaintance with "ppm" of TDS in the water supply is the accumulations one sees in sink aerators and shower heads.
Not the stuff you want anywhere near the business end of your solar panels.

A simple demonstration is to place a teaspoon of each water source, street water, softened water, and RO water, on 3 separate glass dinner plates. Allow to evaporate.
RO residue after evaporation is minimal, while street and softened water leave large amounts of residue.
Repeat the demonstration and you simply double the residue, ad infinitum.

Although a sqeegee will mechanically sweep the water containing the TDS away, it would be accumulating at the borders of the panel at the panel frame.
Using RO water removes the TDS portion out of that accumulation.
The follow-on squeegee routine also does not remove all drops of water and we have seen what a small volume of water does to the glass dinner plates.

I opted to use only RO water in the rinsing process, to minimize TDS from the water source.
Then the potential for residue is restricted to the particles already on the panels at cleaning.
My task is to loosen and move as much debris as possible with the force of water, followed by the mechanical sweep of the squeegee to remove water droplets.

My original question of moving (RO) water uphill with a scuba tank attempts to allow more water to be used.
The hand sprayer and carrying water up the ladder is too labor intensive, and I would like the process to be more water intensive.

I considered using a wetting agent, such is used in dishwashers to prevent water spotting.
That process assumes that treated water droplets will slide off a surface, taking the TDS in the water with them. My array is on a mild 16° slope.
The wetting agent sounded plausible, but starting with high TDS water was not appealing.
RO water with a wetting agent seemed a better combination.
However, the effects of wetting agent on seals, adhesives, or any other parts of the panel that it may come into contact is not known.
In the interest of simplicity, wetting agent was removed from consideration.

So, how hard is your water, what is in it, and with your high angle of tilt have you tried or considered a wetting agent ?

The automated sprinkler system you suggested was actually considered early on, but never with "tap" water.
Panel temperatures last summer peaked at about 165° and I'm not sure what the temperature of a spray of water might be.
The effect of applying that temperature differential could be surprising.

Thanks again,
Solarguy

[Peter_C]

I only know our PH locally for city water, which doesn't do much for water hardness. We don't drink city water straight, but after run thru an RO happily drink it. City water is not very hard, but those using well water have to soften it for household uses. Just looked it up, our city water average is 93 PPM. Not bad at all.

The Helio Tex system uses an agent to prevent water spots, but more importantly it is an environmentally friendly soap solution (Maybe you could buy a gallon and try it?). After all we don't want to be polluting our water ways. Since we have been setting up the washing systems on well water systems, we make sure there is a water softener on it. They are put on a timer to run when the sun is not shining on the panels, so temperature is a non issue.

Most solar systems here in California are roof mounted and never get cleaned. The rain washes them off. I will have to do some research on a couple different systems for performance gains after washing them. Would be interesting to wash just half an array and see the difference panel to panel (Enphase!). Although all day yesterday and all last night everyone's array around here got a good cleaning.

If it were me I would just buy a pump to move the water from a small barrel up to the roof. Most every pump lists the distance vertically it will lift the water. If you are washing them as much as you say, I would install a sprinkler system for convenience, that way it would get washed more with less effort and more safety. Plus less damage to the roof and gutters.

[350xfire]

You may be able to take some type of storage tank, add a tube from the faucet going to the bottom of the tank and use a tank to pressure up the airspace within the tank to push the water out of the bottom into the roof... This would be better done with an air compressor thought....

Even better- a sump pump in the tank... or two in prallel if the distance is too long for 1 to get it up there. There is also a centrifgal pump option if you have enough water pressure and flow behind it.