Solar pond filter

We had a question about which solar filter from Sandra in California.

Sandra asks (March 2011)

The pond

Small pond, how small is small? In order to work out the size of the required pond filter the pond volume must be known, then a suitable size pump and UV can also be chosen.

Lets assume the pond  is 4 x 5 x 3 feet = 374 UK gallons

The requirements

In order to keep the water clear etc the entire pond volume must go through the filter once every four hours which means it must be able to pump around 100 gallons  / hour. In order to achieve this a suitable mains pump will use 35 watts (We googled and found a suitable pump)

Next a UV will be required, as its a small pond lets say a 9 watt lamp unit. Lets say the electronics use 3 watts giving a total of 12 watts required.

The problems

The above is all mains operated equipment, the requirement is for solar. As far as I am aware there is no 12v pond UV available*

Then you need a 12v pump that can pump at least 100 gallons / hour to the required filter height. I am not aware of a such a pump*

 This solar project is not looking very good, there must be a way?

There is. If you use mains equipment, feed it via an inverter (it changes 12v dc into mains) you can then run it by solar. Simple?

Actually no its not. A pond filter and UV have to run 24 /7 so that means a "battery pack"  is required. (as Sandra asked)

You can not just add a "battery pack" and expect it to work, I shall explain.

To calculate the battery size you need to know the power consumption.

35 watts (pump) + 12 watts (UV) =37 watts

The inverter will also use power lets say 13 watts (makes life easier)

So in total we are looking for 50 watts.

50 watts at 12v is around 4 amps (Batteries are configured in amps)

So we need a 4 amp battery?

Well no, we want the pump to run all night, 4 amps will run just for 1 hour

Lets say (as its for California) 12 Hours / day of no useful sunshine.

So we need a battery that can deliver 4 amps for 12 hours. 4 x 12 = 48 Amp hour battery.

Lets have the next size up to be sure that's 65 Amp hour

Now we need a solar panel to make it all work.

We are going to need to be able to supply 50 watts for the equipment, and another 25 watts (at least) to charge the battery

Approximate (UK sterling) costs (All prices from makers websites)

Pump £99

UV £45

Pond filter £25

Inverter £40

Not too bad? Are you ready?

65 amp hour, deep cycle battery £190

and the best bit.

75 watt solar panel

£716, here is the proof, and you do get what you pay for.

Not included or even mentioned, is the charging regulator, a storage facility, and other small items. Also its worth noting, this assumes the sun does shine brightly for 12 hours  / day, any less and the panel will not be able to supply the 75 watts required.

So its going to cost you at least  £1,115.00 for a solar operated filter for a (small) pond. Are you still going to do it? (Bigger pond will cost more)

Sandra, so now you know why you will not find a UV and bio filter and pump that is solar, and more to the point, why no one has done it.

You may also like to see our solar pumps page

Although its priced in UK pounds, the project is in America so that's even more dollars, and also they do get a lot of sunshine in California, we here in the UK don't.

*Unless you want to tell us different