The Solar Power Expert Blog

Upgrading a Solar Pond Pump Kit

by Chris - April 20th, 2011.
Filed under: Projects. Tagged as: , , .

A reader of my solar pond pump kit page ask a detailed question in the comments as to how to modify her solar pond pump so that it would work better. I think there are a lot of people like her in the situation of being underwhelmed by the performance of their solar pond pump kit, so I thought I would elaborate on how to go about upgrading such a system. Here is a paraphrased summary of the information she gave:

I bought a ready-made kit (DC pump, solar panel, battery) to make a very small fountain, and I’m suspecting the panel is not large enough to properly charge the battery *and* run the fountain during the day. To complicate matters, I also added to the length of cable running from the panel and the battery (so I could put the panel on the roof instead of on a stake pushed into the ground). I suspect the panel has a diode to control the charge, since there is no separate charge controller.

My questions are: Does increasing the cable length decrease the charge actually getting to the battery? And, the original panel is rated at 8 watts, would 25 watt panel as a replacement work, or will that fry the battery?

I'm not sure I have the information needed to make the decision, can you help me with that? Below I'll list all the info available to me about this kit:

DC Pump:
131 gallons per hour / 780 litters per hour Voltage range: 6-9V DC (couldn't discern ampere info)

Solar Panel:
Rated power output: 8w
Nominal voltage output: 18-20 volts
Nominal current output: 444mA

12v 2.6Ah/20hr
Voltage Regulation:
--standby: 13.4-13.8v
--cyclic: 14.6-14.8v
Initial Current: .78A max

The cable between the panel and battery was originally 5m/16.4ft, I added 15ft to it, for a total of 31.4ft.

To cut to the chase, I’ll go ahead and just say that I recommend integrating a charge controller and upgrading both the batteries and the solar panel with these products:

The Current Solar Pond Pump
Based on your description, I’m going to assume that your batteries are lead acid, and the system looks something like this:

Existing Solar Pond Pump System

Existing Solar Pond Pump System

This is a pretty common setup among solar pond kits. However, there is one large problem with this setup: there is no way to protect the battery from over-discharging. What happens is this: as the sun goes down the battery discharges into the pump until the voltage decreases low enough for the pump to stop working (around 3 volts). Whenever a 12 volt lead acid battery goes below 10.5 volts, it is considered ‘deeply discharged’ which damages the battery. For this reason, the battery probably won’t last much longer than a year.

If your setup has a relay or some means of low voltage disconnection, then you can ignore this warning. If your system does not have this protection, it will still work, but when it stops working after six months to a year, you can be guaranteed that the battery is being killed by a poor design.

Install a Charge Controller

For this reason the first improvement you should make to your system is to get an inexpensive charge controller that has discharge protection, such as this HQRP Solar 10A Charge Controller:

This will regulate power both into and out of the battery. You can also remove the protection diode (if you can find it) from the solar panel if you switch to a charge controller. This will save you some significant energy.

Upgrade the Battery

The second improvement that you can make, which is also low cost, would be to increase your battery capacity – especially if you’ve been running the existing system for a while. If it appears the solar panel is incapable of charging the battery, it is probably because the battery is damaged.

Luckily, small lead acid batteries aren’t too expensive. I recommend using an maintenance free AGM battery such as this one:

Upgrade the Solar Panel

Only after you make the first two upgrades would I recommend you to get an additional solar panel. You really have two options here:

  1. If you decide to not use a charge controller, then you should not add more than a 5 watt solar panel. Read my article on How To Build A Simple Solar System so that you understand that you do not want to trickle charge your batteries beyond 1.5% of their 20-hour amp-hour rated capacity. Your best bet would be to get a 5 watt solar panel that is designed to work with a 12 volt system such as this Sunforce 5-Watt Solar Battery Trickle Charger:

  2. If you do use a charge controller, then you can be free to get the best deal ($ per watt) on a solar panel. 25 watts is probably overkill. You probably don’t need more than 15 watts.

    At $5 per watt, this 20W Watt Solar Panel is a pretty good deal:

Integrating the Solar Pond Pump System

The good news is that you can add the batteries and solar panels in parallel to the solar pond pump system. This allows you to add more as you need them. However, be sure to watch out for these two tripping points:

  1. The batteries need to be of the same type and voltage in order to add them in parallel. E.g. only add a 12 volt lead-acid battery in parallel if the existing battery is lead acid and 12 volts.

  2. The same holds true for solar panel voltage. Only add solar panels that operate in the same voltage range (12 volts in this case). The wattage can be different, but the voltage needs to be the same. Also, when adding solar panels in parallel, they should each have their own diode – even if you’re using a charge controller. This prevents a more powerful solar panel from discharging into a weaker one.

If you were to add in all the upgrades I suggest, you system would something like this:

Ideal Solar Pond Pump System

Ideal Solar Pond Pump System

You can see the solar panels in parallel and the batteries in parallel. The whole system runs through the charge controller, which has both over-charge and over-discharge protection. By adding more battery and solar power to the system, you’ll eventually be able to get your pump to run 24 hours continuously if you desire. This system will also maximize the battery life.

You don’t need to upgrade the system all at once. You could start by getting a charge controller and new battery. See if this makes an acceptable improvement in the system. If the system still isn’t running to your satisfaction after that, add a solar panel to increase the power of the system. If you need a recommendation for a diode, I like to use these Schottky diodes.

A final tip: Put your batteries in a wood or plastic box and bury the box. This will help prevent your batteries from freezing during the winter. It’s incredibly damaging to batteries when the electrolyte freezes.

2 Responses to Upgrading a Solar Pond Pump Kit

  1. Hey Chris, thanks so much for this post! I was out of the country for a bit, so I’m just now catching up.

    I need to sit down with this tomorrow and read in detail… but one thing is different from my set up, your diagram… Mine is all in one line, not a “T” like you have… it goes Solar Panel (and I assume diode) into Battery, then another cable comes out of the Battery and goes to the Pump.

    But I’m guessing that isn’t going to make much difference.

    Thanks again!

  2. You are correct. It won’t matter. The circuit is the same. The battery, solar panel, and pump are all connected in parallel.

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