Aluminum Electrolytic Capacitor - current, power, efficiency
You will have two principal sources of energy loss.

1) ESR, Equivalent Series Resistance, which will dissipate power due to \$I^2R\$ losses when you are charging and discharging.

2) Leakage current, which will dissipate power any time the capacitor has a voltage on it.

The data sheet gives the ESR for 100Hz. This is a reasonable frequency to specify, as it's the ripple frequency for a simple full-wave rectifier + capacitor power supply. The ESR at low frequencies will be fairly constant, the figure they give will be a good estimate of the DC and low frequency value. If you want a better figure, you will have to measure it at the frequency of your choice.

Leakage current is a very different beast. It's very dependent on the charge history of the capacitor, the temperature, and the capacitor's age. Once the capacitor has been 'soaked' for a few hours, that is, charged to a higher voltage than you're going to use it, the leakage tends to settle down to a much lower figure than the worst case in the data sheet. You will need to measure it for your capacitors and temperature, by measuring the self-discharge rate. Do not leave a meter connected when you do this, connect it briefly, read, and disconnect. You might want to estimate how long you've connected the meter for, and deduct its effect from the loss of charge you observe.

Dielectric memory can change the voltage orders of magnitude faster than leakage current can, beware its confounding effect. Fun experiment - leave the capacitor charged for 10 minutes, discharge it quickly (a few seconds), connect a DMM and watch its output voltage rise over the next few minutes!