But would not that blacked out panel suck current ? or because there is a hungry battery the current will flow there. I know that MPPT has diodes to prevent current from flowing back to panels during nights, but if the PS is in parallel to the solar panel on the same terminals MPPT cannot do much. And if the battery is full. Then the current has no where to go except the panel, correct? Would that damage the panel?
That is the whole object of putting the blacked out panel in parallel. It represents a stack of series connected forward biased diodes, one for each PV cell in panel, with any shunt leakage current from cells. It will not draw more then cell leakage current until it reaches about 30 vdc (for 60 cell panel) where forward biased series diodes start to conduct. Any ambient light will reduce the appearent cell leakage current from the panel terminals point of view. Slightly above the forward biased diode stack knee is Vmp where most of the current will go to the MPPT controller. Continue to raise voltage without MPPT controller connected and it will draw Isc (minus cell leakage resistance loading current). This is exactly the way the system acts in normal operation. Because the panel is blacked out the power supply current represents the illumination current that would normally be created by PV cells in sunlight.
The only thing missing is the extra panel heating from sunlight that would not have been converted to electricity in normal operation. Panel heating will only be a maximum of Isc * Voc which, because of PV cell efficiency, is only be about 18-20% of heating power it would get if exposed to sun without any load on panel.
Set power supply CV to Voc and CC to Isc. Without MPPT controller connected the panel will heat up by (Voc * Isc ) watts. This is okay as long as panel has some air flow over it and is not wrapped in blanket. It gets about five times that much heating power in full sun when panel is not connected to load. Even when MPPT controller is connected in normal operation only less than 20% of the sun heating power is reduced by electrical loading which is the electrical conversion efficiency of panel. Reducing CC current on power supply below Isc will represent reduced sun illumination current.
In normal operation with full sun in summer climate is not uncommon for panel to reach over 50 degs C. Think of the roof temp of a dark painted auto in mid day summer sun. I know Voc * Isc sounds like a lot of power to dissipate, and it is, but it causes much less panel heating then it would get exposed to full sun. There is a lot of surface area of panel to dissipate heat. Like I said, just don't wrap it in a blanket to prevent some dissipation. A light sheet will block out the light indoors and indoor light won't provide much illumination anyway. You just want to prevent small amount of illumination to make up for some of PV cell normal leakage current. A good suggestion is just place panel behind your workbench. It is shaded from most of room light, enough air flow, and out of the way. If you want you can put a fan blowing air on panel and a temp sensor on panel to make you feel better.
As to your comment about battery. If panel Voc is at least 10%-20% higher then battery voltage only panel leakage current will load battery. If you leave power supply at Voc and you back down CC to low levels, the panel's leakage current will eventually drop the voltage so the MPPT controller will shut down and disconnect. This exactly matches what happens with sun illumination in normal PV outside operation.