Question 1

Can you use it for usb charching

Accepted Answer

As supplied the 10W solar panel has no facility to directly charge either USB devices or simple batteries. In both cases there needs to be a secondary regulator  to limit the voltage  and power provided to charge your items.
In bright, direct sunlight the panel can provide around 21V with a light load, and around 17V with a loading of around two thirds of an ampere. But the power is dependent on the amount of sunlight actually  falling on the panel.
In essence, you will need a suitable charge regulator for the item that you would like to charge. Failure to use a suitable regulator would most likely damage, or even destroy the item.
NGS

Question 2

Is this a monocrystalline or polycrystalline panel

Accepted Answer

dear customer, this panel is monocrystalline  solar panel

Question 3

does panel have built in blocking diode?

Accepted Answer

No

Question 4

How many panels can you safely wire up in a series?

Accepted Answer

I cannot be  definitive about the answer, as it would depend on many conditions being met. 
Firstly the output voltage is around 21Volts with no load, and maximum supplied current, under full direct sunlight comes at an output voltage of around 17V, with a current loading of some 0.6A. So the units is not really suitable to directly charge a 12V lead-acid battery without an additional regulator. 
If you were to wire the panels directly in series, you would need to guarantee that any each panel is supplying the same power as any other one in the series, and that no panel was having current flowing back into it, under unbalanced-loading. These conditions, could prove rather more difficult tasks, especially if there was no protection circuit for each panel. 
Perhaps, a better solution might be to wire them in diode protected parallel into a battery charging system. From this setup, then use a boost charger circuit to generate the output voltage needed. 
This is a situation that you must explore, however, I am unaware of a definitive answer to your original question.

ASIN	B0140OO99O
Best Sellers Rank	76,495 in Business, Industry & Science ( See Top 100 in Business, Industry & Science ) 38 in Polycrystalline Solar Panels
Brand	ECO-WORTHY
Connector Type	USB
Customer Reviews	4.5 4.5 out of 5 stars (1,101)
Efficiency	High Efficiency
Global Trade Identification Number	00732659856522
Included Components	Solar Panel
Item Dimensions L x W x H	33L x 18W x 20H centimetres
Item Weight	850 Grams
Manufacturer	ECO-WORTHY
Manufacturer Warranty Description	5-year material and workmanship warranty.
Material	Silicon, glass
Maximum Power	10 Watts
Maximum Voltage	1440 Volts
Model Number	L02P10-N-1
Number of Items	1
Number of Packs	1
Part Number	L02P10-N-1
Special Features	High cell efficiency, excellent performance in harsh weather
UPC	732659856522
Unit Count	1.0 count

ECO-WORTHY 10Watts Solar Panel Module for 18 Volts Battery Charger for Camp and off-grid Ligthing Applications L02P10-N-1

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