In this form, the card feels very much like a Solar Shield / Solar Buckler but with damage reduction of 2 instead of 1. If we count the different means of generating light qua(n)ta for the controller of this shield as comparable but differently situational, then we can focus on the damage reduction.
For the unupgraded Solar Panel card, the only comparison is Titanium Shield, which is a thematic choice of earth having the largest straightforward damage reduction at the cost of any other benefit. As such, I'd think any other unupgraded shield with straightforward damage reduction of 2 that may exist would need to have some sort of counterbalance, and I'm not sure costing 5
as opposed to 4
achieves that counterbalance, particularly given the quanta generation potential of the shield. At only 1 damage reduction, this concern fades, and the situational quanta generation makes it a more defensible alternative to Solar Shield.
For the upgraded Solar Buckler card, we have as comparisons Tower Shield (5
), Jade Shield (7
), and Permafrost Shield (
) with respect to the straightforward damage reduction of 2. Now, certainly, Jade Shield and Permafrost Shield each have additional protection benefits beyond their straightforward damage reduction, but Tower Shield does not. Valuing the quanta generation potential of Solar Cell similarly to that of Solar Buckler, a cost of 6 for Solar Cell seems more appropriate.
One concern in your notes is how the shield absorbs quanta in the situations where an opponent cancels the use of a spell. If a player clicks Improved Steal and then decides not to select a target and instead to cancel the spell and play a different card, would his opponent with an active Solar Panel / Solar Cell generate 6 light quanta?
