ERCOT has PV/solar available

I don't know if pyiso is still maintained, but ERCOT now has solar data available, you can get it in addition to wind, i.e.:
```
    # get other values
    load_val = df.loc['Actual System Demand'][1]
    wind_val = df.loc['Total Wind Output'][1]
    solar_val = df.loc['Total PVGR Output'][1]
```

etc

-Eric