suitability of batteries for use in pumps/motors

[green_regards]

I have lots of queries over use of solar in various applications. I have read most of the posts before posting this, so if I have still repeated a question please feel free to direct me to the URL of the post.

Please note: Right now in my country, summer is fast approaching. The cities experience 3 hours of power cut daily and rural folks are the hardest hit, with powercut for 12 hrs (6.00 am to 6.00 pm). There is water in the borewells but no power to pump it to the sanding crop, so farmers are worst hit.
So, here are my queries:

Agriculture: Most of the farmers use 5 hp pumps to pump water to their fields. Some use 3 hp and some use 7.5 hp to 10hp. In this particular state, windmills wont work simply because of the location. So, people are looking at solar as an alternative to power their AC pumps.

There are two systems that have been proposed. One is an AC system, where a set of panels, VFD are used with the existing AC pump. Second is, a DC pump.

The desired panel wattage for a 5 hp motor is calculated as 5.5KW by a company that manufactures VFD’s. There is no data w.r.t Litres per day (LPD). Now, as I understand, the pressure and quantity of water that comes out depends on the path of the sun. During summer time, we have about 5 sun hours per day.so, between 11.00am to 2.00pm, we get water with good pressure. Also, I understand that it varies with the depth at which water is available.

As regards the price for powering one 5 hp AC motor through solar energy, cost about $9000 – $10000 and there are people who are willing to pay that amount to pump water out of the well to water their standing crops. But, I would like to quantify the water output in LPD. There are dealers/suppliers who claim a 1,00,000 LPD output with their systems. With 5 sun hours, will this be a realistic figure? Will the water output for a period of 2 hours(11.00 am to 1.00am, when the sun light is perpendicular to the solar panels) match that of the pump running on GRID over a two hour period?5.

I want to know if such a system can be used with a battery back up. I know it would be a huge battery bank, so let us consider the case of ½ hp motor. This system will be used to pump water from sump to an overhead tank.so will be operated for atleast 2 hours per day. However, the battery bank is for a specific application where in the water is supplied at 5.00am – 6.00am in the morning, when there is no sun. A tank cannot be constructed due to space constraints. The system without battery works out to $2000, so with the battery it may well double the price. But, will the battery(VRLA maintenance free) life be affected if we are to run pumps on it or for that matter any motor?.6.

Next application is for use in petrol stations. We generally use 3 Nos. of 1 hp pumps to pump out petrol / diesel and these outlets too are bearing the brunt of power cuts. With diesel also becoming costly, they are forced to look at solar. I think it is better to suggest them to first consider solar to power their lighting and computers and at a later time power the pumps. Since most outlets work 24X7, does a battery system work well atleast for one pump? The depth is just about 6 feet. Would it affect the life of the battery(VRLA Maintenance free) in any way? I guess we cannot suggest grid tied system since there is no power most of the time and operating diesel generators in idle state would also be expensive, although we have no data as to how much diesel is consumed by a generator when running on idle state, if used as a supplementary power.

I guess this is a very long list. Iam sorry to have posed many queries in one post, I felt they were interrelated. I have posted my queries here as I am sure I will get unbiased answers, as compared to the people I have spoken to, who are more of sales people than technical people.

Thanks is advance for any information provided.

Green Regards.

[Mike90250]

Wow. Starting planning now, is not likely to get a well designed system in place for THIS summer. The delay time to order parts from suppliers is likely to set you way back.

Pumping from wells, is always a factor of Lift and Volume.
Does the water level in the well change (get lower) as you pump - most wells fluctuate when pumped,
and so you have to size the system for the lowest depth you expect the water to decrease to.

AC or DC. What can you get parts for ? 3 phase AC is pretty cost effective,
brushless DC gets pretty pricey for the exotic controllers needed.

Pump Curves This gets tricky, if word gets out on how to read them, the vendors loose a lot of $$
they currently earn by overselling a 2 HP pump when a 3/4 HP will do the job. You have to match the
pump to the motor, to get the best efficiency, but you first match the pump to the Lift and Volume needed.

You may find "Staging" 3 smaller pumps, to be sequentially triggered as power becomes available as the sunlight varys, to be the best, as having enough panels to run a 3HP pump at 10am, would give you a
surplus of power at noon.

[inetdog]

Agriculture: Most of the farmers use 5 hp pumps to pump water to their fields. Some use 3 hp and some use 7.5 hp to 10hp. In this particular state, windmills wont work simply because of the location. So, people are looking at solar as an alternative to power their AC pumps.

Thanks is advance for any information provided.

Green Regards.

There is one part of this that I would like to discuss a bit, while leaving the rest for others:

Let us know what sort of time factors apply to the irrigation. Are these 5 HP pumps running 24 hours a day? 12 hours? 2 hours?
There will be a tradeoff when using solar power: The least expensive, most reliable, system will drive the pumps as much as possible when the sun is sending lots of energy to the panels, that is within a few hours either side of solar noon. This will reduce the need for expensive, short lived battery systems.
But in the case of spray irrigation, that it the worst time of day to do the pumping.

If you can, try to look at the irrigation process as two separate parts. One is pumping the water from shallow or deep wells to the surface. The second is distributing it to the crops. If you can do the two parts at different times, with water storage above ground or in a pond, you can make better use of the solar energy.

[green_regards]

Thanks Mike90250 and inetdog for your quick responses.

Pumping from wells, is always a factor of Lift and Volume.
Does the water level in the well change (get lower) as you pump - most wells fluctuate when pumped,
and so you have to size the system for the lowest depth you expect the water to decrease to.

Yes, the water level gets lower as we pump. By how much, that I guess varies and I probably should take this on case to case basis.

AC or DC. What can you get parts for ? 3 phase AC is pretty cost effective,
brushless DC gets pretty pricey for the exotic controllers needed.

Yes. I have seen the prices. Moreover, with regard to service after installation, 3 phase AC systems get a thumbs up. These vendors do have outlets in rural areas as well.

Pump Curves This gets tricky, if word gets out on how to read them, the vendors loose a lot of $$
they currently earn by overselling a 2 HP pump when a 3/4 HP will do the job. You have to match the
pump to the motor, to get the best efficiency, but you first match the pump to the Lift and Volume needed.

Yes, completely agree with you. I have seen petrol pump owners use 3hp motors to pump fuel from a sump that is not more than 6 feet. Iam wondering wouldn't 1 hp motor suffice?

You may find "Staging" 3 smaller pumps, to be sequentially triggered as power becomes available as the sunlight varys, to be the best, as having enough panels to run a 3HP pump at 10am, would give you a surplus of power at noon.

I guess this is a good idea. will explore the possibility of using the same.

[green_regards]

oops..i guess i answered the wrong way!!
My responses are within the quote itself...

will take care the next time..

[green_regards]

There is one part of this that I would like to discuss a bit, while leaving the rest for others:

Let us know what sort of time factors apply to the irrigation. Are these 5 HP pumps running 24 hours a day? 12 hours? 2 hours?
There will be a tradeoff when using solar power: The least expensive, most reliable, system will drive the pumps as much as possible when the sun is sending lots of energy to the panels, that is within a few hours either side of solar noon. This will reduce the need for expensive, short lived battery systems.
But in the case of spray irrigation, that it the worst time of day to do the pumping.

If you can, try to look at the irrigation process as two separate parts. One is pumping the water from shallow or deep wells to the surface. The second is distributing it to the crops. If you can do the two parts at different times, with water storage above ground or in a pond, you can make better use of the solar energy.

time factors: Iam told a 5hp pumps takes about 2-3 hrs to wet 1 acre of land. So, a farmer having 3 acres will pump it for 6 hours or more. But, unfortunately, in the case of grid, with power cuts, the farmer is always able to wet only the first acre or so...

[inetdog]

oops..i guess i answered the wrong way!!
My responses are within the quote itself...

will take care the next time..

A perfectly acceptable way to answer, especially if there are a lot of different questions. The only thing that is discouraged is quoting the whole post you are replying to (including pictures and other attachments) if you are only referring to a small part.
Just common sense stuff. Style does not matter a lot here.