Plugging into the Sun in Arcata
You’re walking past a school, and you see a blue square on top of a pole…what is this strange sight? Did a piece of a satellite get installed as a science art project on the school campus? A passing student tells you it makes solar power…but how? How does a pole plug into the sun?
Here’s a glimpse into the physical process of how a pole mounted photovoltaic system is plugged into the sun. Thanks very much to Ben Scurfield of Scurfield Solar for providing this account of a solar installation. In future posts we’ll talk about electricity, and how a solar electric system actually makes power.
A Site within Sight
Sites are selected based on: proximity to educational centers or other “green/environmental” areas of the school campus; solar access (our energy seed needs good sunlight much like a plant that wants full sun); and ease of “plugging in to the sun” (this includes tying in to the local school electrical system and the PG&E meter). Plugging in isn’t always as easy as it looks… It doesn’t happen over night, but after a series of site visits with all the decision makers at the school and our design team, site specific design documents are finalized, and the actual installation process takes about a week.
The first part of the job is to dig the hole. Before anyone digs a hole – on a school or even in their own home – they can check with Underground Service Alert (USA) - http://www.pge.com/safety/call_before_you_dig/. The school maintenance and custodial staff often has this information as well. It’s very important that we make sure that the hole and trenches aren’t going to collide into any gas lines, electrical, sewer, water or underground tanks.
At Sunny Brae Elementary, Scurfield Solar dug and plugged the school into the sun. We think every solar installer is like an art installation artist - they listen to the school, the design team, and then it’s their job to work within code and guidelines to plug the art into the school building (powered by the sun). Here’s how it happened in Arcata.
Cool Tools
They rented a Bobcat excavator for the hole drilling. They also rented a giant drill bit (called an auger) attachment for the Bobcat. Half the fun of this process is all the great equipment! Some say beauty is in the eye of the beholder, but…we think an auger is a pretty cool looking tool…and very useful.
This made the job much quicker and cleaner than trying to use a backhoe…let alone a bunch of shovels! This saves the backs of our solar installers so they can be ready for future installations. The next job was to dig the trench for the conduit. This job was made easy by the use of a walk behind trencher. This machine saved Ben’s already sore back and provided a uniform depth and width trench. The pole utilized for the installation was picked up at a local plumbing supply store, put on Scurfield Solar’s trailer, and taken to the machine shop to have cut to the right size. The pipe was then delivered to the site where it was put in the hole and leveled. Scurfield Solar used the bobcat bucket and some tow straps to pick up the pipe and deposit it in the hole. Before they did this, they drilled two holes in the bottom of the pipe and inserted two pieces of rebar. Next a wooden form was made to hold the pole plumb and electrical conduit was laid in the trench and up the pole. It was then time for the concrete. A concrete truck came and dumped a small bed of rocks for drainage and concrete in the hole. After a few days, the form was ready to come off.
The trench for the conduit was also filled. Next came the really challenging part. They started by laying the racking pieces out on the ground to make sure everything was square before they put them up on the pole. These are like the branches of our solar tree.
The next job was to install the inverter. It was mounted on the pole using some big clamps that grabbed the pole. There was also a disconnect switch and a electrical meter on the pole. The wire was run from the inverter and back to the electrical panel on the side of the building. The finishing touches on the system were the data monitoring system. The PV system actually talks through the internet through a series of translators (well, we think it’s easier to conceive of them as translators anyway). The data is sent to a database where it is organized in a common format, and then visualized. The hardware is pretty straightforward – each pole has a box on the pole for the wires of various data sensors to come into. This consisted of an ambient temperature probe, a solar panel temperature probe and a pyronometer. Wire was run from this box to another box in the building. This box was hooked to the computer and with a little magic, the data is sent for all to view.
