Wednesday, July 25, 2007

Solar Step 3: Cabling & Inverter

Today the solar system setup was completed.

The rails holding the solar panels got cut so they don't protude far out on the sides. If you look closely you can see the cable piping on the roof between the panels on the top row. The panels are connected to a Xantrex GT3.3 inverter.

The silver pipe on the right carries the cabling from the roof to the inverter. The inverter converts the generated DC power to 240V AC, which is then fed to the main electrical panel on the left. There is a disconnect switch in the inverter that takes the inverter offline from the panels if needed. Fuses in the panel connect the inverter to the power grid (right above to the big yellow "solar backfeed" sticker).

We are generating power. While the system is rated at 3.9kW DC (22 * 180W/panel), due to inefficiencies of the panels and inverter, as well cable resistance, we can expect ~3kW AC peak production on very sunny days. The picture was taken late in the early evening with the sun already pretty low. The system still generated over 900W which was enough to spin the electric meter wheel backwards.

The city building inspectors will come by in the next few days to review the work. Afterwards, PG&E will replace the old electric meter with a TOU meter (TOU="time of use") and switch us to tariff E7. With TOU, electricity used during high demand times is more expensive than during low demand times, e.g. day vs. night. However, we also get compensated at the higher daily rate when we feed power back into the grid. Conveniently, the sun shines the brightest during high-demand times ...

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