The Basic Things you Should Know
the Quail Manor uses the sun to generate electricity using photovoltaic panels on the garage roof. When we (Geo Innovation) designed the system we had not a clue as to actually how we would use the Manor and when. And there was no usage history to plan from. So we (Geo Innovation) guessed. This stuff ain't cheap. So the guessing got some attention.
To keep things interesting. The photovoltaic panels on the roof make Direct Current (DC). The Electric Company sends out Alternating Current (AC) so stuff in your house that plugs in is pretty emphatic that it wants AC. Interestingly though, all the smart electronics with chips in them turns it back (rectifies it) into DC. So round and round we go.
In the dawn of the electric era there was a big fight over DC vs AC. DC came first. Then AC kicked it's ass. Surprising amount of politics involved, but net net was DC can't be transmitted very far - AC can. Function of someone (a smart engineer someone) coming up with efficient transformers so the electric company became able to turn efficient very high voltages (around 115 kVAC) that are efficient for long distance transmission down to lowish household line voltage (around 120 VAC). In their infinite wisdom, to avoid having generating stations in every neighborhood, the world went AC. Money was lost (the folks selling DC generating stations). Money was made (the folks making transformers). Over time, the resulting AC transmission grid has gotten old and these new fangled technologies now allow pretty straightforward local electric generation that wants to play on the old grid. Change is a coming. Lot of tension about rates and taxes for local generators since they don't use as much off the grid as they did and everybody still wants to wet their beak. But that is a story for another day.
So. To use the electricity being generated on the roof, we gotta make our DC into AC. To do that you use an inverter.
There are a couple of ways to go when acquiring and paying for solar systems. You own the system and sell excess electricity to the utility. Called Netting. Or, someone else owns the system. It sits on your roof. They sell electricity to the utility, and you pay a reduced to rate for the honor of the use of your roof. I like being in control. A whole whole whole lot. Notwithstanding this stuff ain't cheap, we own the system on the Quail Manor roof. I didn't want someone else's not the latest state of the art stuff stuck willy nilly on our roof. Installed by some schlock. Not for the Quail Manor. Nope. In the fullness of time it may pay for itself. In the meantime we contribute to smug rather than smog.
They call the solar system a "plant". So, henceforth, the Quail Manor Plant.
the Quail Manor Plant
the Quail Manor Plant is rated at 2.470 kWp. I had to look kWp up. A kWp is KiloWatts Peak. Imagine a perfectly clear day at noon. And a roof unshaded by any pesky man (in the nongender specific use of the word) thing between it and the sun. And on that roof are solar panels pointing perfectly south and tilted to the right angle for your latitude (32 degrees for the Quail Manor). THAT is Peak. So in theory, the Quail Manor Plant will do 2.470 kW Peak. But. Life being a bitch, we don't realize peak.
The photovoltaic panels are SunModules 270. Each module is in theory capable of making 270 Wp. There's that theory and peak thing again. So, you divide 2.47 kW (lets call it 2,500 W) by 270 W and round up since you can only buy these panels by the each, we have 10 photovoltaic panels in the Quail Manor Plant.
Some design magic to the angle they are tilted up relative to the horizontal. In theory 32 degrees is ideal for Tucson. That is a 12 month average ideal. Since we're mostly in residence and using electricity during the winter when the sun is lower in the sky, we cheated and tilted them more like 45 degrees. I frankly forget what the actual angle is. So we cheat (like Lance but for different reasons) for better winter generation, bigger angle. For better summer, smaller angle or more flat. PLENTY of sun available in the summer!
By accident rather than design, at least any design I was involved in, it's not easy to see these things. Turns out they are most visible way down the road as you turn into the cul de sac. They're out of normal sight lines and so far anyway have just worked, so we kind of forget they're up there.
We were going to do solar hot water. Got talked out of that interestingly enough by the solar guys. To do solar hot water right, you need circulating pumps to get water up into the sun. Then at night you need to drain the water back out so what is effectively a radiator on the roof does not try to heat the night. So, my default thought was a to put in a gas water heater. But then you have a flue vent going through the roof which has to be sealed. There was some discussion about the flue being inefficient and losing heat. Not sure how true that is. In any event, threw an extra solar panel on the roof and went electric.
Observant readers will recall those panels on the roof are making DC. We need AC. So we need an inverter. Hedging their bets, Geo Innovation used a much larger inverter than we currently have photovoltaic panels. The incremental cost of a capacity x and capacity 2x inverter is pretty small. So we have plenty of room on the roof and with the inverter to add panels don't you see. Our inverter is good for 4kW. Our current panels are good for 2.5kW. We have some room to grow. Now. This is fun. The inverter is called a SUNNY BOY. It's German. So, it's axiomatically, a good one. Not sure how they came up with the comically ironic name. I do love my Germans!
A design aspect I frankly did not see coming is fastening the panels to the roof. They're heavy. And, particularly when you tip them up to get closer to that ideal 30ish degrees to the horizontal, they act like a big ole sail up on the roof. So bearing load and wind load both had to be taken into account all the way back at the Jake the Architect phase. On a practical note, you can't just bolt these things down to the roof any old place. They need to go into structure. So, CtC and the Vasquez Family Framers had to workout blocking for where the Geo Innovations guys thought the panels would go way back in the framing phase. If you look carefully, there are four rows of blocking in the ceiling. And not just blocking, double blocking. Lot of fussing and cussing and nails. But the solar guys have everything need to mount panels.
And. That's not the only complication. The roof is corrugated. They, the solar guys, were real happy about that. Every one of the mounts is a custom job so not only do they hold the panels up and down, they:
- Sit on the peak of a corrugation so water can run along the channel of the trough of the corrugation. Don't want the mounts to hold rainwater run-off.
- Don't crush the corrugation. There is a spacer that goes from the mount through the roofing material to the subroofing so in fact, the mounts just kiss the top of the corrugation.
- Seal water infiltration with seals at every intersection point.
Lot of fussing and cussing on these baby's too.
There are building codes about access and cut-offs. Another thing you don't really think about. If there is a fire and it's daytime. These puppies are generating electricity. Firefighters need to be able to get up there and do their thing. the Quail Manor Plant. It's to code.
The next step will be to install batteries so we can use solar power at night. We've not added batteries to the Quail Manor Plant to this point. Still not too much data available, but in residence net usage is on the order of 250 kWh per month. Net usage is what we used from the utility AFTER netting out what we generated. Our generation during in residence months is on the order of 350 kWh per month. There has been a LOT of welding and sawing going on that use a LOT of electricity, so I suspect these numbers will go down. If construction ever stops.
Tesla has come out with a very cool battery solution that takes up very little room, a key feature for the Quail Manor. It is good for 7 kWh (times 30 days in a month is about 210 kWh per month). The battery sits between your DC photovoltaic panels and inverter. During the day, charge the battery. Get dark, use the battery. Use even less electricity from the grid. Hard to get just yet, so we'll let that percolate a bit before buying a Tesla. Battery. But very exciting.
Even without the battery and with the welding, our electric bills this summer averaged about $15 per month. That's taxes and minimum fees. The Nest Thermostat helps by managing a higher away temperature than would be practical otherwise. The $15 per month included some short periods when we were in residence.
Smart Solar App
Of course, the inverter and by extension the Quail Manor Plant, is connected to the internet. And yes, there is an App for that.
In theory the good people at Geo Innovation are monitoring the plant. Not sure if they really do, but I assume they are. The inverter sends a daily e-mails with the daily yield. To keep things interesting they are in a kind of Germanglish. The bar chart at the bottom is generation by hour throughout the day.
With their app, you can watch the generation in real time with a much smoother graph. I suppose not surprisingly, this thing is beaucoup sensitive to clouds passing by. Below are some snapshots of a sunny day in October (time of year will limit the amplitude of the curve). On the left is a nice smooth sunny day. On the right we had some clouds go by. It is left as an exercise for the reader to determine just when they came...
The SUNNY folks have a great web site to manage the Quail Manor Plant. English through and through. Top of the line English and incredibly functional. Here is a dumbed down version they thoughtfully made publically available so it can be shared. And so I could compare the Quail Manor Plant performance with other near-by plants.
Analytics. It's what I do. So you knew there had to be spreadsheet. Feel free to poke around. Usual look but don't touch rules about don't be evil apply.
Below are a couple of charts and graphs. If you find any logic bugs or think of other analysis I'd love to hear about it. Send me an e-mail.
The first chart compares power three ways:
- How much a plant in our zipcode with the characteristics of the Quail Manor Plant should generate (the yellow bar)
- How much the Quail Manor Plant actually generated (the green bar)
- How much we used from the Utility company before netting out what the Quail Manor Plant generated (the evil red bar)
All this gets a little complicated since we use 24 hours a day. But, depending on the season, generate 10 or so hours a day. There is some "banking" that accrues with the Utility company during the day as we generate more than we use. And then the bank gets cleared in the fall sometime. I don't pretend to understand their rules. But I'm certain they are completely fair. If you're the utility company. And have all this money invested in generation and distribution plant. And here come these bastards making their own electricity and cutting into profit margins. The batteries would minimize this banking and I suspect have a dramatic effect on our bills by reducing netting and dramatically reducing Utility usage. Be interesting to see how that all sorts. In any event, here are the ins and outs.
The difference between the red and green bars is the power we paid for or sold back during the month.
This chart shows the net power (difference between the green and red bars) we paid for or sold to the Utility Company. The minimum table stakes charge with taxes appears to be around $14. Remember lots of arc welding going on in the first half of 2015 drove a whole lot of usage.