Thursday, April 3, 2014

Project details

(Japanese article is here.)

Here are some details about our solar sharing project.

Our contractor

Our solar sharing plant will be built by Ceratech Tsukuba, a company with 12-year experience in roof- and ground-mounted solar systems.


Ceratech Tsukuba is our main contractor, but we also have a consultant: Ken Matsuoka from Solar Culture, who is designing tilt-adjustment mechanism for our plant. Thanks to this mechanism, we'll be able to change the tilt-angle of the panels, which is a useful feature for many reasons. It will not only allow us boost electricity generation, but if necessary, we can also change the tilt so that more sunlight reach the ground (in case hens complain it's too shady), or put panels to horizontal (zero angle) position to reduce wind resistance during typhoon, and other.

The plant

In the current design (which might slightly change), generation capacity will be 42 kilowatts, or about 350 solar panels with output 120 watts/panel.

Solar panels used in solar sharing are inevitably smaller than those commonly used in roof or ground installations. In solar sharing, panels are attached to pipes 3 meters above the ground. They need to be lighter and more compact mainly for two reasons:

1. to make the whole structure safe (e.g. smaller size means smaller wind load)

2. to distribute the light and shade areas evenly, because the ground is supposed to be used for farming.

But our 120 watt panels are in fact larger than those I saw in other solar sharing project. Up until last month, we thought we would be using 100 watt panels. With 100 watt panels, it's very easy to count the plant's generation capacity, or the other way, it's easy to calculate how many panels you need for a certain output.

For example, how many 100 watt panels do you need for a 42 kilowatt plant?

Answer - super easy: 420 panels. (= 42 x 1000 / 100)

But: How many 120 watt panels do you need for a 42 kilowatt plant?

Answer: ........ (open calculator on your PC)......... 350 panels. (= 42 x 1000 / 120)

With 120 watts you need to make some mental effort.

Our panels are made of 6-inch monocrystalline cells, with 27 cells (3 x 9) per panel.

There are two basic cell sizes: 5-inch and 6-inch. Why are there two types? Which is more common? Is there any other difference besides size? Good questions. I'm sure Google knows the answers.

Shading rate in the current plan is 33 %, meaning that one third of sunlight hits the panels and two thirds reach the ground. Imagine being in a park with trees - it's sunny and warm, but not dazzling and hot. But! Just in case our hens like it dazzling and hot, we'll keep part of the 1100 m2 plot completely without panels, so they can choose.