In the first and second posts of this series, I laid out my general reasoning and plan for incorporating solar power into my new home and covered the basics of solar power systems and integrated batteries. This post will go into more detail about the choices we’ve made regarding our solar installation. Details about our battery system choices will be in the next post of the series.
Let’s recap the original goals for our solar+battery system:
- Have enough solar capacity to reach annual “net zero” on my electric bill
- Have enough battery capacity to provide a safety buffer in the dead of winter
- We want to be able to run the heat pump plus a handful of critical circuits
- Have the ability to integrate V2G/V2H from an electric vehicle in the future
It turns out that meeting all three of these goals is, as I suspected, not feasible right now. As we looked at different options, we saw that each had its own set of drawbacks. We had to decide what was most important and evaluate the options against our prioritized criteria. We ended up loosely ranking each solution along the following dimensions, in order of priority:
- Cost
- Performance against our power needs, especially during low solar generation periods
- Simplicity of operation
- Implementation complexity and physical footprint
- Upgradeability and openness of the platform
We short-listed four possible options - one option that is solar-only, and three options that include backup batteries. The three battery-based systems use components from EcoFlow, Enphase, and Tesla Energy, respectively. I’ll describe the potential battery solutions in more detail in my next post, but let’s talk about the solar portion first.
Even though we don’t have much historical electricity consumption data to work with, the two months we’ve been here have provided some insight into our electricity usage. JeffPUD has a nice consumption view on their billing site which updates daily. They allow you to adjust the date range of the view, and give you the option of seeing either monthly or daily kWh consumption:
Given our estimated consumption rate of ~10MWh/yr, we determined that to meet our net-zero solar generation goal we would need to install at least twenty-four 420W panels on the south-facing portion of our roof. The estimation tool at PVwatts tells us that a 10.08kW solar array at our latitude should produce just under 11MWh/yr. That would give us a small buffer for future usage growth assuming no addition of an EV into the mix. In addition to a good south-facing roof section, we also have a good east-facing roof section with room for 4-6 panels. This roof section is never shaded by trees or other obstructions and will start producing energy earlier in the day than the south-facing section. Putting this all together, we decided to target a total solar installation of 30 panels, with 24 facing south and 6 facing east. We plan to use 430W panels, so our total generation capacity will be 12.9kW, or an estimated 14MWh/yr per PVWatts.
But wait! I just said we only need 10MWh/yr to meet net zero! Why such a big solar array? Well, there are two reasons. First, we do intend to get an EV soon. Charging an EV with a ~75kWh battery from 20% to 80% once per week adds ~2.2MWh of consumption per year. Second, if we have a grid outage in the winter months we’re going to want the longest possible window of solar generation time to charge the batteries. Having panels on the east-facing roof section effectively lengthens our power generation window, which may prove very helpful (as you’ll see in more detail in my next post). So 30 panels it is.
The other decision for the solar panels was which manufacturer’s panels to use. That was a pretty easy decision. Every installer in our area uses Silfab Solar or REC panels. Silfab manufactures panels in North America (plants in Washington, South Carolina, and Ontario), while REC panels are manufactured in Singapore. Both panel lines have similar performance, warranty, and cost. All else being generally equal we’d prefer to support a company that has invested in manufacturing in the US. We’ll go with Silfab Prime NTC SIL-430 QD 430W panels.
Now for the harder decision. Which battery system should we choose? Or should we integrate batteries at all? My wife and I spent quite a lot of time going back and forth on this question. In my next post, I’ll explain why it was such a tough call. Stay tuned!
Other posts in this series:
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