Low Technology Institute

We’ve been chronicling our addition of solar panels in Part I and another post evaluating our solar resources. In this entry, we’ll go through the different components of the system and how we chose them. We have received no compensation from any of the companies mentioned.

The Panels

Many types of panels are out there with a confusing soup of names, including crystalline silicon, monocrystalline, polycrystalline, thin-film, PERC. After reading ourselves to information overload, I stumbled upon some advice (and forgive me, I’ve lost the link to the source) that the important thing is getting panels with a good 20-year warranty, as the difference in performance is a few percentage points and may not be worth the cost.

We looked at panels from Mission Solar, Canadian Solar, and Jinko Solar. In the end, we chose Jinko because of their size. In running a variety of simulations on our roof, it was clear that we didn’t have space for four rows of medium panels because they would be too close to one another and crowding causes shading and loss of power. We had plenty of space for three rows, so we decided to maximize our panel area with the tallest panels we could find.

We also added “power optimizers” to each panel. Without these, the whole system could function like old christmas lights: one panel is shaded (like a lightbulb being out) and the whole string goes dead. With the optimizers, any shaded panel is looped out and the rest can function normally.

The panels are Jinko Solar “Eagle 72” (JKM395M-72HL-V). They measure about 2 × 1 m (79.1 × 39.5 in), so they are big. Because of their size, they bring in a large amount of energy: 395 watts. We bought a total of 16 panels, for a complete system generation capacity of 6.32 kW. Each one costs $275, so we’re paying $0.70 per watt. The average cost of a complete solar system in 2019 in the US is $2.98. We’ll keep a running total to see how we do.

The Rack

The rack has to withstand high winds, the weight of panels and snow, and other environmental factors. Most racks are made of high-quality aluminum (which doesn’t degrade like steel). They consist of feet that screw to the roof, legs that support the rack, and horizontal bars that support the upper and lower parts of the panels.

Because we live in the tame Midwest — that is, no earthquakes, hurricanes, or other extreme activity — we could go with a middle-strength rack system. We bought IronRidge rack, which has since merged with EcoFasten and QuickMount PV to form Esdec.

We used their design tool (discussed in Part I) to create a system using XR100 railing. The system was designed to hold up to 30 psi snow load. The rack holds the panels on with bolts — called universal fastening objects, or UFOs — sandwiched between adjacent panels. Each panel is grounded to the rack, which is then grounded to, well, the ground to help protect from lightning strikes and electrocutions due to short circuits.

With the feet, legs, rail, end caps, wire clamps, UFOs, and other associated items, the rack cost was about $3,015, bringing us to $7,451 total, or $1.18 per watt.

The Inverter

We live in the country and if we get a power outage in the winter, it can mean we’re without heat other than our wood stove. Our septic system and water also run on electricity, so a prolonged power outage can cause problems. Additionally, as detractors from solar constantly complain: the sun doesn’t shine all the time. So we decided to invest in a battery backup. This informed our choice of inverter.

Most systems are grid-tie systems, meaning generated watts get fed back down the electrical line connected to your house. You might use some of the power, but so will your neighbors. The utility pays for generated watts. In many cases, as with ours, the utility uses “net metering” meaning it subtracts the watts fed into the system from the watts used by the household and any surplus is payed back as a credit (and any deficit is just paid for like a typical electrical bill). This allows the grid to function essentially like a battery. Since most energy is used during the day, this actually works out well for the utility and panel owners.

We upgraded from the grid-tie inverters to a SolarEdge 7.6 KW StorEdge inverter (SE7600A). This inverter takes DC energy from the solar panel and inverts it to AC power for the house. If all the domestic energy needs are met with solar power, it shunts the extra energy to the battery for later use. If the battery is full, then any extra electricity is fed back to the grid and we’re paid for the excess. If the power fails, the inverter routes power from the battery and panels to our backup loads. At night, the inverter draws from the battery to power our house before drawing from the grid.

The inverter cost $2,375, an upgrade from the grid-tie version, which is $1,875. If we were doing a typical grid tie, this would be the end of our shopping list. With the grid-tie-only inverter, our total would be $1.48 per watt. With the upgraded inverter, though, it brings our total to $1.55 per watt.

The Battery

Three types of batteries are generally available for solar: flooded lead-acid, sealed lead-acid, and lithium-ion (I also saw a salt-water battery mentioned, but couldn’t find details, so will have to follow up on that later). Generally, the cheaper the battery, the shorter the life, weaker the performance, and more the maintenance. Flooded lead-acid require monthly maintenance checks and should be charged and discharged daily for optimum performance. Oh, and they off-gas hydrogen. But they’re cheap. Sealed lead-acid batteries are deep-cycle marine batteries similar to car batteries. They’re more self-contained and safe, but slightly more expensive. Both lead-acid batteries have a about a five-year life. Lithium-ion batteries are by far the best performance (deepest discharge, longest life, no maintenance) but are more expensive and come from a worrisome supply chain. These are used in electric cars, laptops, and cell phones.

For this first go-around with a battery, we’ve decided to go with the lithium ion, which should last 10 years (that’s the warranty, at least). The LG Chem RESU10H supplies almost 10 kWh of power (most houses use between 20 and 30 kWh in a day), which will power our water pump, septic, refrigerator, and other basics for at least a day or two. To receive this battery, I had to become a certified installer, which took an afternoon where I watched a webinar, read up on the battery installation, and passed an exam.

Even with the $5,880 price tag, this only brings us to $15,706, or $2.49 per watt! We also had to add on an autotransformer and monitor to the system, bringing the grand total for materials up to $16,245, or $2.57 per watt. This is significantly under the average because we’re doing most of the labor ourselves.

Providers

We bought most of the system from Wholesale Solar: panel, rack, inverter, etc. The battery came from Solaris along with the autotransformer and monitor. Both had good customer service. Wholesale Solar is more geared to DIY installations, with kits and guides available on the site. Solaris is more of a traditional supplier and may have a slightly larger selection. Everything shipped freight.