I wasn’t going to let our new roof space go to waste. We installed a new array of solar panels. These panels will be offsetting the heating load of the hangar. This winter (2020-2021) we heated it with a baseboard heater and two space heaters. I am working on getting an air to water heat pump.
Greg from South Pack Solar installed our system. We opted to go with him because he could do a custom designed rack mount that tilted the panels up steeper than the roof. We also picked micro inverters so we could more easily extend the array in the future if we want to.
Compare and contrast the house PV array
|Inverter peak power||7.6 kW||4 kW|
|System design||Solar Edge string inverter and DC load balancers||Enphase micro inverters|
|Number of panels||28||11|
|Orientation||Tilt 45, Azimuth 174||Tilt 45, Azimuth 185|
The house panels are up at 45 degrees because that is the roof angle. We chose the same 45 degree tilt for the hangar panels for two reasons
- Our electric load is already winter biased. The hangar heat will only make that worse. So we wanted to bias the solar gain towards winter.
- Our house panels have shed snow well, and thus produced power year round. We know people with lower angle panels that get snowed over for most of the winter.
On March 20th, a sunny day, our house produced 51.41 kWh. The new hangar array produced 28.9kWh. If you look at the graph of 15 minute average power below, you will see that the hangar array cuts out at 4kW. The limiting factor on the hangar array is the micro inverters. We loose a little bit of production mid day. The reason to accept this limitation is to reduce system installation cost. The inverters, string or micro, cost a lot. The rule of thumb Greg uses is to pick inverters whose capacity is 80% or greater of the panel capacity.
The other interesting thing in this graph are the cut outs and shoulders. The slower rise in the morning is presumably because the hangar faces a bit west whereas the house faces a bit east. The sharp drop in the afternoon is the shadow from the large pines across the road. I have always wondered why the house PV has a tail at the end of the day. The hangar shows the same pattern.
The only downside so far to the new panels, is that my Sense Energy Monitor has become a lot less useful. The Sense Monitor works with PV connected to the main panel, but it doesn’t handle PV on a sub panel. It now thinks the house is consuming negative power during the day. That scrambles it’s appliance detection algorithm and many of it’s stats. I had been relying on Sense to track the house PV production because the Solar Edge web page doesn’t compare production and consumption. The Enphase dashboard shows even less detail, and only exports data at daily resolution.