The simple way would be to have several cells and put them in series. Then no electronics needed to power the valve. Charging would be a bit more complex, but not demanding so much current.

 

I'm with Max on this one - a latching valve would be more useful for a DC operation. My early "Drip Irrigation" projects used a 9V battery powered valve with hose bib hookups. A 9V pulse to turn the valve on then another 9V pulse to turn it off. I've even seen them operating on 2 or 4 AA batteries, and they can easily last the entire season, depending on how much use they get.

However, there is one concern I have that hasn't been broached yet - - - what are you controlling? Water? Natural Gas? Propane? If using it to control gas then you DON'T want a latching valve. My experience has been that when the batteries get low they CAN turn the valve on then fail to close it.

I recently replaced my 24VAC valves with new ones because the old ones were leaking. It's my hope to build an air powered rocket launcher for the grandchildren. A charged tank and a momentary blast of air to launch a rocket skyward. No pyrotechnics involved, just air power. I plan on using the 24 volt valves because 12 volts WILL open them. And since it's a brief opening, long enough to puff a rocket skyward, I could even use capacitors to charge to a higher voltage just in case the valve needs a little bigger charge. Thus making the need for a smaller battery.

Details are important in getting good answers. So far we know you have a 24VAC valve you want to operate with DC. A lower DC voltage should be able to open the valves, as I have tested 12VDC on my own 24VAC valves, and yes, they open. However, I have not tested for current draw.

Something to keep in mind with a a boost converter: 4V @ 3.5A ( 14 watts ) boosted (as Mr. Bill mentioned) will convert to (in your case) 24V @ 583mA (assuming 100% efficiency with the converter). Assuming 80% efficiency with the converter, you're looking at about 467mA (and that's "Per Hour"). How long do you want your valve to be open? That's another question that hasn't been addressed yet. You said you want to operate your thing during the daytime, charged with a solar panel. There are yet details we need to give you a "GO" - "NO-GO" answer; and how to achieve your goal.

Like I mentioned, I (still) have some valves that are latching somewhere laying around in my gardening cabinet. They are 3/4" hose bib connections. If you're controlling water then these will do just fine. And if you get an entire drip irrigation controller and valve system then you have the whole thing Kit-N-Kaboodle. No need for electronics. You can program the day(s) to come on, time of day to come on and duration of ON time. The whole thing in one package - battery powered. All you'd need to do is figure out how to put rechargeable batteries in it and charge it with solar power.

 

@ Tony:I have built and used a compressed air launcher, in fact, quite a few of them, over the years. The distance is determined, to a large extent, by the length of the launch tube, the longer the better. And the performance with the best solenoid valve is not even close to the performance of an adequately sized ball valve. That is because of the difference in pressure drop at high flows.
Of course, for safety it iis mandatory to use an adequately rated pressure tank. I use either a carbon dioxide fire extinguisher tank or one of the disposable high pressure dry nitrogen tanks that are sometimes available. A one-inch port ball valve feeding a 2 inch diameter barrel has sent a paper-cone rocket as high as others were able to go using the commercially sold "Estes" brand rockets, And that was with only 100PSI in the tank, rated 3AA1800 (1800 psi).

 

We're getting a little off topic here - but 80PSI through a 1" solenoid valve into a half inch tube with a suitable sized rocket body. The tank is a fiberglass spun woven tank out of a water softener; rated for 250PSI at some given higher temperature; I'd have to go drag it out to see what it's exact rating is. No, I haven't built it yet; not a priority on my list. Still, all it needs to do is shoot a cardboard rocket a few dozen feet into the air to excite the kids. No need for parachute recovery, and if the kids break the rocket - no big deal. Just take another slip of paper and roll it around the half inch pipe and make some kind of nose cone and the kids are flying again. Doesn't even need fins if it's balanced properly. A little wad of paper in the nose to give it the weight needed to move the center of pressure ahead of the center of gravity. Experimentation is the key.

And now - back to this thread. Controlling a 24VAC solenoid from a LIPO battery.

 

A string of 5 batteries would work But a boost regulator would be the best choice.

 

@Tonyr1084 Tony, we ( wasn't involved), had a research project that never went to completion, but it was a huge air cylinder mounted horizontally and maybe a 10"diameter Stainless lines going straight up. These would be filled with smaller tubes that needed to be "cleaned". We never had a "dirty tube" and never likely to have one and we never pulled the trigger. It was impressive. It was a proof of concept plan. My understanding was it was carted away and re-assembled.

 

And I am still thinking that some sort of boost regulator/driver for the valve that can deliver 20 volts at 200mA is required. That would be 2 watts, and for an hour that would be two watt hours. The selected battery has 3500mA hours capacity claimed=3.5 Amp hours. At 4 volts that will be 14 watt hours. Unless my math has an error.
so if the math is right and the efficiency is not really bad, it may drive the valve open for ten hours on one charge. So the required boost regulator switcher needds to provide a 5x voltage multiplication. That is reasonable.