We are currently needing to purchase a solar tester per customers request. do you know of any others line the Seaward Solar tester?
The Solmetric PV Analyzer is a favorite. Unless you are doing residential only, get the 1000V version.
I also like the people at Solmetric, except for the fact when Vivint bought the company they took the SunEye off the market.
The HT is very good:
Here is another one, the TRI-KA
Some of the things you want to look for is IV curve testing, voltage range (2017 NEC will go up to 1500V for ground mounts), insulation testing (megger testing), and of course voltage, power and current. Accessories include, irradiance sensor(s), PV cell temperature testers and networking with wifi or bluetooth.
The cheapest most time consuming method:
We used to plot an IV curve with a variable resistor, an ammeter and a volt meter. We did it with classes it the college and the students made some good looking curves.