Help with controller selection.

If I'm understanding the issue correctly, the basic problem is not enough sun.

You now have two types of storage; the livestock water trough, and the batteries. Of these, the trough will be the most efficient, taking less sun per gallon of water. As a result, adding the batteries actually makes the not enough sun problem worse.

There are 24v controllers that can charge your batteries and supply extra current for pumping, but the power to both has to be available.

Making a few assumptions / wild guesses:
- 2x100 amp hour 12v batteries
- 1x250w solar panel
- pump averages 8a@24vdc for 5hrs = 40ah(960wh)/day.

This time of year, the panel might put out 150w for 2-3 full sun equivalent hours per day, depending a lot on tilt, wire losses, climate, etc. That provides maybe 50% of the load to get/keep the troughs full.

Adding batteries into the mix to supply the other half is 480wh/24v nominal or 20ah (~20% of our 100ah@24v bank), but charging batteries isn't 100% efficient. Depending on battery type, condition, and charging regime, we might need ~20% more to account for this, so ~600wh.

So our power requirement is now 600 + 480 = 1080wh/day. One panel is giving us 300-450wh/day, so the bottom line is we need a couple more panels to be able to fill the trough and charge the batteries with the sun available at this time of year, or run the generator, or some combination of both.

These are all made-up, but plausible numbers. You could get more accurate average solar data for your location at pvwatts.nrel.gov and use actual specs for you pump, batteries, and panel to get more than the wild guess I've made.

This time of year at higher latitudes is tough for solar. As well as short days and low sun angle, many areas also tend to be cloudier around now. This means some combination of more panel and more generator run time. Often it comes down to enough solar to cover all but the worst 2-3 months of the year (now in the northern hemisphere), and planning to run the genny to make up the deficit in the worst months.

In terms of storage, it will be more efficient, and maybe cheaper in the long run, to add water storage rather than battery storage. Depending on your pump capacity, with more panel you may be able to fill a bigger storage tank as well as the trough, so instead of running off batteries on cloudy days, you draw down the tank. May not be practical if freezing is a concern though.

Depending on the pump specs, something like a Midnite Solar "Brat" ($89 from our hosts) might work. I think the load control is max 10adc though.