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Here you will find some useful tips for self installers:-

1/ What can I do to manage my 12 volt system during an unexpected power cut?

If you live in an area where power cuts are possible then it is a useful idea to fit a "UPS" device - an Uninterruptible Power Supply. This can be as simple as a £1 electronic relay and requires only limited skills to make up.

This is a small switching device that will ensure your system switches to an alternative power source such as a battery if the main power is cut off. You can see an explanatory video below.


The benefit of this valuable fail-safe feature is that your system will click over automatically to backup power in the event of your primary power source going down, tripping back over as soon as power is restored.

You can make your own for just £1 or £2 and an old car battery will run a solarproject pump and controller for several days, avoiding overheated systems and loss of free hot water during the outage.

A relay comprises two terminals that actuate the switch and other terminals that are either joined or broken according to actuation. The trick is to use the principal power supply to open the relay and connect the power.

Connect the battery backup to the terminals that are joined when the relay is not actuated. That way, when power is lost, the relay closes and connects the backup source.

UPS Wiring plan



You will notice from the rough sketch below that the two supplies share the 0 volts line (i.e. the Negative)









Examples of relaysRelays come in all voltages, you will need a 12Volt DC relay. Look for one that has 5 or more pins to provide both power-on and power off connections. Minimum current capability of around 3 Amps at 12V will manage even most multi-pump systems.

This technique is only appropriate for low voltage DC systems. Do not attempt this using direct Mains power voltages.

Some more thoughts: This same method could be used to install a secondary power adaptor, to manage in the event of the first failing. Or it could be used to provide battery power to a PV generated system during dull periods

2/ Some notes on using PV Panels as a power source

PV Panel

PhotoVoltaic power is free, once you have bought the PV panel, so PVs offer an attractive power source to the self installer. They can be used to drive our 12V pumps in suitable weather conditions, though their use is not quite as straightforward as their vendors would have us believe.

Some considerations -

1/ PVs are rated for Voltage and Watts. This rating is somewhat misleading as a 12Volt 20Watt panel will routinely produce up to 18Volts and is unlikely to deliver much above 15 Watts in anything short of Sahara strength sunlight.

2/ An 18Volt supply can damage any pump designed to work on 12V. For this reason it is advisable to limit the voltage output with some form of regulator to ensure you do not overload a 12V appliance.

3/ Feeding the PV power into a large car battery will damp down the voltage peaks. It is possible to match a small PV to a large car battery ( say 15W PV to a 50Ahr battery) without using a charge regulator as the sheer capacity of the battery will reduce the PV output voltage, but larger panels will overpower a battery and a regulator is necessary.

4/ Car dismantlers (scrap yards) are usually keen to sell perfectly serviceable car batteries for £5 to £10.

5/ Connecting your panel directly to a pump leaves the pump at risk of being fed a voltage that it cannot handle and damage can result, so see the low cost solution below if you are not planning on fitting a battery.

Which Panel? - Matching PV solar panels to pumps

We are often asked what size PV panel should be used to power our popular 12Volt pumps. It isn't a simple answer but here's some information to help you understand the issues and decide:

Firstly, some questions......

1/ What is the wattage of the pump you plan to use?

2/ How many hours a day do you want the pump to run?

3/ How sunny is your location?

Our experience is that at their peak PV panels only seem to produce about 2/3rds of their rated capacity, and much less than this in hazy or cloudy conditions.

They work well when the sun is shining directly on them but performance is reduced while the sun is at an oblique angle in the morning and evening.

So if you have a 12Volt, 20 watt PV panel in good sun then you might expect to harvest a maximum 100 Watt Hours a day.

Meanwhile, to run constantly, even an 8 watt pump will need 8watts X 24 hrs = 192 Watt Hours, so this panel will not be able to keep up with demand if the pump is to run 24/7.

Also, you would need to feed the power in to a battery to store the excess power for the dull periods of the day.

So, assuming that you have a PV charging a battery which in turn powers your pump, then a formula along these lines may give an indication of the appropriate size of PV:

Pump watts x No. Hrs daily use = Power Need

(Power Need x 1.5 ) divided by 6 daily sunshine hrs = Wattage required of PV panel

Using the example above, a panel of 48Watts or less will struggle to maintain battery charge, even in ideal sunny conditions. Something around 60 watts might be more suitable

and this will need a charge controller to avoid overcharging the battery.

If you need the pump to run for a total of 6 hours per day then a 15 watt panel or more will be needed.


I'd still like to power my pump directly from my PV panel - How can I make sure I don't damage the pump?

Look on eBay for a little regulator chip called a 7812 which costs under £1 and will limit the voltage output to ensure no more than 12V is passed to the pump, even if the PV is producing 20Volts or more. Fitting one of these in the supply wiring will protect the pump from being fried.

7812 Voltage Regulator Chip


These chips can get warm if they are having to reduce voltage from a higher input so using a metal heat sink is advisable . Each chip can handle about 1 amp and can be used in parallel to manage higher loads. The PV positive connects to pin 1, negative to pin 2, with the regulated output leaving the chip from pins 2 and 3. (neg and pos respectively )

UPDATE: eBay has a wide range of very cheap DC to DC converters, for as little as £2 delivered from China. Look for one with a variable input and 12V output . See photo as example only- Example DC to DC converter



3/ Purging air from difficult solar circuits.

Sometimes it proves difficult to remove all the air from a new solar circuit. This can be detected as a lack of circulation and the pump can be heard to 'hunt' as it attempts to bite on the aerated water.

The usual advice is to bleed the circuit at the highest point by slackening the joints until non-aerated water is seen to leak out. An auto air vent is very useful to catch the bubbles as they pass but this may not work effectively until an initial flow is established.

It is a feature of all centrifugal pumps that they work best with all air excluded and they can struggle to provide a proper flow if they are having to push a water/air mix. It can be helpful to conect a garden hose to a point in the circuit to push persistent air through, draining into a bucket until the flow looks clear of air. Slackening the connector of the pump outlet will clear any air that is stuck in the pump chamber, thus allowing the pump to create a flow.

I have found that it can help to fit a home made temporary device to the catch air as it passes, ideally before it reaches the pump. This can be made in a few minutes using a jam jar and some soft flexible pipe(see photo). The pipes are sealed with epoxy or silicone to avoid leaks.

AirTrapThe flow into the jam jar is through the shorter pipe, which should be just below the water level in the jar. Air bubbles in the water flow will rise to the top. The flow out, to the pump, is from the bottom of the jar and so will not include the bubbles.

The jar lid is held closed and you will see the water level drop as air is trapped by the device. Loosening the lid will allow the fluid level to rise again.

This method is particularly useful as it gives visual confirmation that you have a flow and gives a clear view of the amount of aeration in the fluid. The system can remain connected until no more air is visible in the flow.

And it is free!

4/ Do I have to buy a new tank to allow Indirect Heating?

No! Even if your tank does not have a solar coil fitted it is still suitable for use with a solar hot water panel.

Option 1 - is to connect it to heat water Directly - click here for details

Option 2 - is to use a retrofit coil which replaces the immersion element. (approx £70 from eBay or make your own)Retrofit coil

Option 3   - We have experimented successfully with a £35 Plate Heat Exchanger mounted externally alongside a vented Hot Heat Exchanger LayoutTank.

Plate exchanger

The pumped solar circuit feeds one side of the unit and passes heat in a separate flow to the main tank.

By locating the unit vertically, low down by the base of the main tank, a thermal flow is created which pushes the heated water into the top of the tank, replacing this from the cold base in a circular action.

The speed of the thermal flow is determined by the heat available from the solar circuit and no additional pumping is necessary.

Key points for the installation are:

a/ Fit the heat exchanger as low as possible to allow the maximum height above it for the thermal flow to establish.

b/ Use larger bore pipe (15mm) for the thermal flow side, to minimise friction and optimise flow.

c/ A 10 plate model seems to be enough to shift the heat, though it might be worth the extra few pounds to buy the 20 plate version

d/ Mount the exchanger vertically to encourage a flow to establish.

e/ It may be necessary to slow the thermal convection flow if the water entering the top of the tank is colder than desired. If so, try placing a service valve in the pipe work to allow adjustment.


5/ My SP20/20 pump seems to have stopped working -

What can I do? (Click here for video guide to Fault Finding )

go to HOMEPAGE or here to go to SOLAR FAQ page Q&A or here for INSTALLATION GUIDE