Golanido......It would be more practical to have the Signal Generator Drive a Mosfet that also has a 24 volt DC supply.
This would Not be an Off the Shelf Product, But Much Cheaper than one like that.
You Don't say Where you Live, But it would be possible for me to Make you this.
I doubt your Solar panel has Enough Output Current.
When you Step up the Voltage, The Output Current Goes LOWER.
And When you apply a Load that Draws More Current than is Available, Than the Voltage will DROP Even LOWER.
However I Don't think that will Solve your Problem.
What are the Specifications on it?
It Appears to Reduce the output Downward.
You need one that Boosts the Voltage.
Possibly like This one...
These batteries usually have more than 2 Terminals on them, some of the terminals are for protection against Over Charging and Over Heating. PREVENTS FIRE or EXPLOSION.
So they should be charged with a Proper Charger designed for them.
Lead Acid batteries are 2 Volts per Cell.
ni-cad, ni-mh are just 1.2 Volts per cell, so 5 of them will be needed.
But you will also need a Different Charger, Preferably Current Limited.
I could supply you with one of those ROX-3, 30 Meg Resistors and a 1/4 Watt 3.0 K Resistor.
Both are Rated at 5 % Tolerance.
By my calculations: With 10 KV in it will be Close to 1 Volt across the 3.0 K, Assuming a High Impedance Volt Meter.
No Charge for the Resistors, Just $8.00 USD for the...
Definitely Not something I would recommend and resistance is Not Constant with Voltage Changes.
These High Voltage Resistors are usually Custom made to Specific Values and Normally NOT Sold in Single lot.
So first you need to determine the Voltage rating and the resistance Value you want...
This is the Largest HV Resistor I have, 38 Gig-Ohm, 1% Tol with a 10,000:1 division ratio and rated at 100KV. It is Custom made in 4 Sections that Screw together. You Never Touch this with your Fingers as that will contaminate the surface. If I remember Correctly, it cost about $80.00.