Since October we’ve been installing solar panels, an inverter, and battery here at the institute. Last week we got permission from our energy utility to operate our system. It took longer than expected, but we’re up and running.
You can read about our site evaluation, system design, components, system layout, and part of the installation process in previous blog posts. I still need to write up the wiring of the system.
The most exciting part of the system is the constant monitoring of our energy use and production through the dashboard platform of SolarEdge (our inverter manufacturer). This saves me from having to rig up something like I had to for our DIY solar hot water system in the previous post.
This is a typical partly sunny day. The red graph shows the energy we’re using throughout the day. The low constant power through the night is an electric heater in the bedroom. The spike around 8:00 a.m. is the heating of water for tea and oatmeal as well as the water heater kicking in after a morning shower. Energy use drops through the day and picks up again in the evening.
The green and blue lines show our solar production and consumption, respectively. If we didn’t have a battery, the extra power (where the green spike is greater than our red consumption), the power would be fed back to the power grid. But because we have a battery, that energy is stored on site. As the sun dips, the power is fed back into the house instead of drawing from the grid.
On this day, we created and consumed a quarter of our energy. This is at the least-sunny and most energy-intensive time of the year. By the summer, we’ll be using less than half of this power and producing two times the amount of energy per day, plus the number of sunny days goes from 12 on average in December to 19 in July. The system is designed to generate 100 percent of our net energy (extra in the summer to make up for winter deficits).
We can also monitor production in real time. The top of the display shows our current solar production, energy consumption, and battery energy storage. Arrows show the flower of power from the panels, battery, and grid to and from one another. The numbers show how much kW of power is moving. For comparison, 1.500 kW would run fifteen 100-W lightbulbs, a microwave, or a hot water kettle. On your energy bill, a kWh is one hour of 1.000 kW energy use. We currently pay 11.7¢/kWh of energy. Our utility only pays 2.9–3.3¢/kWh depending on conditions. Luckily, we have “net metering,” which means our utility just subtracts what we generate from what we use and either pays or charges us the difference.
Another nice component of the monitoring platform is that we can break down which panels are producing what amount of energy. We have minor shading issues between the top and center rows and the center row may get moved down a few inches to alleviate it, but we’ll mark where the shadows fall on the winter solstice. The lower row is producing less than the upper rows right now, but as the sun rises over the summer, it will be less shaded than the upper row. We’ll operate the system for a year before making any changes, and only then when we have significant power differences between panels.
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