If you buy solar credits from KC to use in Seattle, you've increased the solar generation in KC without affecting demand in KC. This will idle one plant's wort

If you buy solar credits from KC to use in Seattle, you've increased the solar generation in KC without affecting demand in KC. This will idle one plant's worth of fossil generation in KC. In Seattle, you're buying one plant's worth of additional power. In Seattle excess demand is generally met by buying Hydro from BC, but let's assume worst case and it spins up previously-idle fossil. So in KC you're +1 solar, -1 fossil. In Seattle you're +1 fossil. Net: +1 solar.