Pumping water

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dougal

Joined: 15 Jan 2005
Posts: 7184
Location: South Kent

Posted: Mon Oct 31, 05 11:20 am Post subject:

dougal wrote:

Mr Solar wrote:

I sugested using solar power direct with a DC pump of this type ...

Is that all one needs to do? Hook the DC pump up to the output from the PV array?

I'd guess that we are talking about a centrifugal pump, ...

My suspicion is that some sort of basic control circuitry might be needed with a high pressure (positive displacement?) pump, so that it was only switched on when there was enough power to drive it...

I read the reply as implying, yet not confirming, that this is a centrifugal pump. A "ball cock" sounds like a valve, rather than a 'float switch' which would disconnect the pump electric power supply. One doesn't run a positive displacement pump against a closed valve...

I also note that the only control circuitry mentioned is a "time switch". Nothing about preventing the pump trying to operate when there is inadequate solar power.

Such pumps would have a limited (supply power dependant) delivery pressure. And as such, as you noted, Tahir's application would need multiple pumpsets of that type.

dougal

Joined: 15 Jan 2005
Posts: 7184
Location: South Kent

Posted: Mon Oct 31, 05 11:21 am Post subject:

Mr Solar wrote:

... a higher voltage than 12 volts, hence connecting 2 x 55 watt PV panels together to create a closed circuit of 24 volts...

The number of PV panels used is always down to need and budget.
Conect 10 x 100 PV panels together, same single pump, you still have the same voltage output.

These conflicting comments are unnecessarily confusing.

If you connect the panels in series you add their output voltage (strictly "emf") together.
If you connect the panels in parallel you add their current generating capacities.

The amount of current available from a panel system depends on the sunlight available.
However, if your load's current demand is more than the cell can provide with the light available, the available voltage will fall (something has to give), and your thing won't work.

So, one has to design such that there is enough current generation capability for operation down to a threshold low light level.
Which means that the system inevitably has overcapacity in strong light conditions.

dougal

Joined: 15 Jan 2005
Posts: 7184
Location: South Kent

Posted: Mon Oct 31, 05 11:29 am Post subject:

tahir wrote:

HOw big are 10 x 100v panels going to be?

Each individual cell actually produces about 0.4 volts.

Many cells are stacked up by the manufacturers, (people like BP Solar), to make robust packaged units. The particular size, shape and capabilities of these assemblies depends on the make and model.

So 100 of them would be... 50x bigger than two!
How big the individual particular panels mentioned might be, would seem more relevant!

I believe the relevance of the "100 panels" comment was that if the pump would operate in good light with one (series-connected) pair of panels, then adding another 49 pairs in parallel with the first pair, would allow the pump to operate in much much much worse light conditions.

tahir

Joined: 28 Oct 2004
Posts: 45669
Location: Essex

Posted: Mon Oct 31, 05 11:32 am Post subject:
But isn't this going to be hugely expensive? PVs aren't exactly cheap.

dougal

Joined: 15 Jan 2005
Posts: 7184
Location: South Kent

Posted: Mon Oct 31, 05 11:48 am Post subject:

tahir wrote:

But isn't this going to be hugely expensive? PVs aren't exactly cheap.

I don't think anyone seriously suggested anything to do with 100 panels.

Mr Solar has pointed out that a single pump, exactly as he installed for a water feature, does not have enough output pressure for your application, Tahir.
He has suggested that it might be appropriate for a rather different use.
His suggestion was that you might therefore consider having multiple sets of pump and panels (and maybe holding tanks) spread along your long delivery pipe...

I think it would be interesting to explore using an appropriate pump, and have queried the control requirements.

tahir

Joined: 28 Oct 2004
Posts: 45669
Location: Essex

Posted: Mon Oct 31, 05 11:50 am Post subject:
Ta dougal, not thinking very well at the mo (bunged up head)

Mr Solar

Joined: 23 Oct 2005
Posts: 10

Posted: Wed Nov 02, 05 9:04 am Post subject:
For every 100 watts of PV panels you need 1m2 of space, so 10 x 100 watts is 10m2. Efficency of 12% compared to solar hot water vacuum tubes at 75% which uses 3m2 of space to deliver 1.2kW in best sunlight conditions.

tahir

Joined: 28 Oct 2004
Posts: 45669
Location: Essex

Posted: Wed Nov 02, 05 4:08 pm Post subject:
That's quite a large area isn't it?

Mr Solar

Joined: 23 Oct 2005
Posts: 10

Posted: Thu Nov 03, 05 7:51 am Post subject:
Thats becouse of the low efficency of the ouput of PV that the area is large. If you go to thin film PV technology its even bigger to get the same as the efficency of that technology is 7%, the lower the efficency the greater the area, thats why solar thermal at 76% is much more cost effective in terms of money and what you get out even on overcast and rainy days.

dougal

Joined: 15 Jan 2005
Posts: 7184
Location: South Kent

Posted: Thu Nov 03, 05 11:11 am Post subject:

One risks comparing Apples and Oranges.

Solar Thermal (heat collecting) and PV (electricity generation) are different animals.
So different that they should rarely be considered together - and *never* as alternatives, one to the other.
(OK there are such things as heat driven irrigation pumps - but that technology is more applicable to Africa than Essex.)

Solar PV can provide a simply-deployed source of (fairly small quantities of) electrical power. And electricity is the most versatile form of applicable energy. But it comes at a premium cost. Energy from solar pv would be a frightfully expensive means of heating.
Equally, generating electricity from solar thermal is so perverse that it has no real application either.

To *compare* "efficiency" in terms of energy per unit area of the collector is irrelevant in the real world.
The economic efficiency, how many watts per � cost, is something any buyer should be interested in.
More obscure, but worthy of consideration, is the resource efficiency - what resource investment goes into the manufacture of each watt of output capacity. Its a tough job to get those figures.

So, in short, you're worrying about the wrong thing in terms of panel area, Tahir.
Think of what *cost* the panels might be, but don't bother about whether or not there's enough room in the field!

Mr Solar

Joined: 23 Oct 2005
Posts: 10

Posted: Sat Nov 05, 05 4:56 pm Post subject:

I expect if I carried out a survey across all those who subscribe to this web site with the question 'How many of you have invested in any form of renewable energy' I expect the the reply will be around 0.1%, hence the main reason this government will in the end go for Nuclear, more wind farms and more imported gas as the answer to this countries needs. To date over �6 billion has been invested by interested parties to secure supplies of gas for the UK market as far as Malaysia, but at what cost to get it here?

Six year ago a person asked me what the price of a solar hot water system was, I replied around �3,000 installed.

At that time gas was so cheap you could hardly meter it, so the so called pay back based on gas units consumed was around 25-50 years.

Reply back from this person, the price of solar hot water has to come down !, to what level I replied, answer, under �1,000 pounds installed to reduce hot water costs by 70%, with the goverment paying half.

Excluding the 2-3 qualified heating engineers we use, who today charge around 200.00 a day each, does not leave much for the 16 odd componants assoiated with the system, so I said come back in 5 years.

That person called me back 6 months ago, requesting the same information.

I replied, in that 5 years I have reduced my gas bill by �570.00 pounds, How much has the gas utility given you back for using their fuel? Prices of our solar hot water system did reduce in cost a year ago to �2,500 installed with improved technology, however sadly the price of energy has risen, as has materials, as has shipping, as has labour etc etc , so the price is now �3,200 pounds, unless you DIY and save the �800.00 of labour?

My final reply was, while 99% of the population continue to purchase energy/power as an onging loan through out your life, the utilities will keep raising its prices to what ever the world market dictates and nothing anyone can do about it, except enhance the heat and power of the sun, where the energy is both tax free and has a fixed zero cost for life.

To that person I spoke to 6 years ago, I told him its better that the people of this country continue as they have for the past 100 years burning what we have left, then when we have an energy/power crises, as was the case in 1973 then act.

The good news is for our company, sales to the USA have trippled as they have already reconsied a wake up call as gas prices rose 70% this year and rising.
Next year when the low carbon buildings directive hits every developer and house builder, very few companies like ours will be servicing the home owner, instead looking to service the house builder who with a government and EU stick, at their cost have to reduce carbon emmisions by a further 18%, was 25%, watered down under pressure from home builders, to your cost.

Once the new build market starts to use solar thermal as a way to reduce 1/2 ton of Co2 per year per house and gain the A rating certificate, this the industry hopes will start to effect the existing home market when in 2007, every home owner has to have a survey on the house before it can be offered for sale.

Some interesting times ahead for all of us whos head is stuck firmly in the sand.
The bright side to those buying these new homes, is the gas/oil boiler has now gone, as has steel radiators and servicing.

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