The Ten Year Plan

System · May 2011

Hey everyone, new around here...

The wife and I just bought a new home in Tempe AZ, one that we're planning on living in for the next forty years. The market let us buy a really large house for a decent price, but the downside is that there are three heatpumps and two hot water heaters to power. I figure that over the next decade I want to design and implement a solar system with battery backup and grid-tie-in, even if only to receive power without being able to sell power back.

I'm blessed with no HOA, fairly mild CC&Rs, and an accessory building with a flat roof in addition to the flat roof on part of the house. I estimate that I have about 1800sqft of usable roof space. I also have a utility room off of the garage that is air conditioned and heated, so I would have somewhere climate-controlled year-round for batteries and other pieces of equipment. This room is also on the other side of the wall from the main panel and meter.

As for downsides, the South façade is the front of the house, and part of the roof is sloped with red and yellow tile, and since it's the front I very much doubt that my wife will let me put solar there. I don't really blame her, as panels here would not look terribly good. The flat part of the house is on the West end and slightly to the North, and there's a short, 1'-1'6" wall around it on the South and West sides. She probably wouldn't allow me to put solar on that particularly shows from the street, so whatever panel configuration I'd go with must be able to hide in this area. If that's an array of individually tilted panels then they'll just have to be smaller individual pieces to avoid being visible. Same goes for the accessory building. The CC&Rs might be interpretable as prohibiting visible infrastructure on the roof (mainly to prevent CB and Ham Radio antennas- house dates to the late seventies) so that's why I'm also trying to avoid anything obvious on the South sloped side.

As it gets to 115° Fahrenheit frequently in the summer afternoons, it would be very useful to generate enough power to power at least the two house heatpumps to bring the house down to 80°. We haven't experienced a summer in the house yet, so I don't know the usage we'll see, but I expect it to be rather costly. I figure that the cost from a utility will only continue to increase over the next decades, so installing something sooner, rather than later, makes sense.

I've attached an aerial photo of the house, taken looking from West to East. North is to the left. I'm hoping that the accessory building and West end of the house will supply enough roof space for a useful number of panels.

mike95490 · May 2011

Re: The Ten Year Plan

70's !! What sort of insulation is in there ?? upgrade it! Cauk and seal doors windows. Consider dual glazed windows.
Ask wife if she wants to save any $ for shopping , or blow it on airconditioning?

at least the panels will help shade the roof from heat.

System2 · May 2011

Re: The Ten Year Plan

House was a higher-end custom home when built. It's much more energy-efficient than a track-house of the same era. It also is one of the few houses in town with a finished basement. It has single-pane windows, but the glass is a lot thicker than what I'm accustomed to.

We upgraded the windows at the previous house only a year before we moved out- Milgard dual-pane windows with vinyl. We're considering this at this new house too, but there are a lot more windows. That's kind of the five-year plan. We only got the house in February, so I'm still going through, looking at places that are problematic (door jambs, mainly) and determining what I can do to improve them. We have large, large overhangs front and back, so the walls don't get a lot of direct sun, and the garage doors on the house and the accessory building are all insulated. I still need to get some of that rubberized tracking that seals the gap between the garage door and the wall, but there's not much more I can do there. I also need to insulate the West wall of the accessory building, but I've got a bunch of extruded stuff in 2' by 8' panels in blue that I had been using at the old house- it'll go up here once I have time.

We're also considering LED bulbs in place of the incandescents. Unfortunately it's hard to justify a $40 bulb to replace a $2 unit at the moment, so we're probably going to end up with CFLs in the areas where the quality of the light produced isn't as important. Anyone know a cheap source for LED bulbs?

As for the wife, she's got a bachelor's in mechanical engineering from MIT, so she's well aware of the ramifications of what we do to the house. It's simply a matter of cost and time. Obviously the sooner we can make changes the longer we can enjoy them, but at the same time, there's a lot of expense in many of the bigger changes, so it's a balance. We can't drop our accounts to zero while trying to make things more efficient.

icarus · May 2011

Re: The Ten Year Plan

Up grade the heat pumps to either ground source, or ideally hot water recovery, which will. Yield huge efficiency gains. If that doesn't give you enough hot water ( and I bet it will!) then add solar hot water.

Then insulate the he'll out the attic, which will also have a huge pay back, then kook at all other conservation methods. Then, and only then, consider adding PV.

I would strongly argue against using a battery backup. This will double the expense, while reducing efficiency by about half! For short term outages, a back up generator is way cheaper, both short and long term.

Tony

solar_dave · May 2011

Re: The Ten Year Plan

Hey I live cross town in Arrowhead,

I upgraded my 2 heat pumps to 17 seer air source 3 ton units from Trane. I blew another 16-18 inches of insulation in the attic, all ready had thermal pane windows, CFL'and LED the lighting in the house added programmable thermostats. Added insulating blinds to the whole house. Make sure you attic venting is good. Look at Energy Star Appliances, I did that here after the solar, should have been the other way around.

Then added a TED to measure and profile the electric usage for a couple summer months to determine my daily needs.

Then and only then did I add solar grid-tie, I think our utility is very dependable and using batteries is really over kill, get a Honda generator to keep the freezer and fridge running in an longer outage. We have a 12.5 Kw solar system and I have yet to pay any electric bill this year. That maybe over kill, you really need to have enough to cover you PEAK TOU rate from APS the rest of the juice from them is cheap @ $0.05 to $0.06 a Kwh. APS will credit Jan-May excess to be used against June - Sept. Kwh, so balance your first 9 months against the APS records for the house.

Your Challenge is the feeding 3 Heat pumps in this heat, consider getting efficiency there ASAP. I like ground source stuff but it is expensive here, and you need enough ground to trench or deep well drills for them, not cheap. My Tranes use about 2000 watts each in operation. PM me and I will get you a good guy to talk to when your ready. Run around the house and caulk it all up, add foam behind all external electric outlets. I even pulled the door trims and foamed all the jambs.

No Pool, good thing, they suck lots of juice, I can attest. 2000 watts for 3-4 hrs a day with the most efficient VFD based pool pump available. To keep it from going green, I need to adjust the time as the heat goes up. If you plan on adding that just consider it in you sizing.

We get enough sun here you can put out a single solar thermal plate collector with an 80 gal storage tank and get all the hot water you will need for 10 month out of the year and a supplement preheat for 2 months, I have an 50 Gallon energy star Sears here and the 80 gallon storage feeds it. We try and do laundry and dish washing early in the day to let the tank recharge all day. My Gas bill runs $16 and of that it is all fees.

JBurgress will pop up here and let you know his opinions, he lives out near Queen Creek someplace.

solar_dave · May 2011

Re: The Ten Year Plan

Oh BTW, Arizona has excellent laws supporting solar installation, no CC&R or HOA can interfere in any way except tell you what color to paint the framing. They can no way stop you from front of house mounting but I know the happy wife, happy life syndrome. Visible from the street can't be used if efficiency is at stake and in your case if may well be your south facing.

Attached is 12.5 Kw.

solar_dave · May 2011

Re: The Ten Year Plan

Just be aware of one caveat in adding a large solar PV system, If the service entrance is not large enough it will require an upgrade. My house was built in 1997 with a 200 amp service and it required an up grade to dual 200 amp service with a 400 amp line feed from the transformer, It ended up being a $4500 upgrade but can be added in as part of the solar price for the 30% fed tax credit.

solarix · May 2011

Re: The Ten Year Plan

Once you get done with insulation and conservation etc, put in enough solar PV to power your daytime usage, then get on the APS ET-2 T.O.U. rate plan and use their cheap nighttime power.

techntrek · May 2011

Re: The Ten Year Plan

I feel opposite of icarus - I'm pro-battery backup. It does add expense, but if you size it to keep your base loads going overnight and during the day when you are at work, it will pay for itself. A whole-house generator runs most efficiently at full load, but the base load for most houses is 300-500 watt-hours, and most people are away from their homes or asleep around 16 hours per day. You also don't want to listen to a generator running while you are trying to sleep. Neither will your neighbors, which I see are close by in your neighborhood.

So you keep your base load going for 2/3 of the day on batteries and then recharge the battery bank from the genset when it is running the other 1/3 of the day (maybe 2 hours in the morning and 6 hours in the evening). That loads up the genset getting you more power from every gallon of fuel you are burning.

You would only run your A/C system while the genset is running (and probably only one of your pumps to keep from buying a massive genset). If you also want A/C overnight while you are sleeping look into installing an ultra-efficient mini-split (26 SEER) in just your bedroom or just your living room and sizing the battery backup system to run it. One 8-hour night would only require an additional 3 batteries. If you were ok with only using the mini-split for A/C during an outage you could get a much smaller genset and forget about running any of your big pumps, saving you money upfront and lots of money in running costs. If you don't have long outages this won't be a big deal.

icarus · May 2011

Re: The Ten Year Plan

While I appreciate your point, the fact is that the grid is quite reliable. The bottom line is you pay for batteries day after day, year after year, for some possible short term emergency. You have the up front cost, the ongoing cost, as well as the replacement cost, all for a few hours a year of potential use.

Fr the price of a battery set, and a chrge control system, a good, reliable stand by generator can be had that will provid not just the base loads, but other critical loads for a prolonged outage, that a battery system just can't do.

If you experience frequent and or prolonged outages, then the equation might make some sense IMHO.

Tony

solar_dave · May 2011

Re: The Ten Year Plan

Gotta agree with Tony on this, APS is very reliable, I can't remember an extended outage in my 15 years experience with the utility. Longest was like maybe 1 hr.

Jburgess · May 2011

Re: The Ten Year Plan

I have the same hot water system as solar_dave and for the phoenix area it is a good system. I never had to turn on the backup heat this winter and the low 20’s we had a couple of nights did not hurt it.

As for the solar, I ended up with about the size as solar_dave at 13KW to meet my consumption.

Mine is about 1000 sq feet tilted at 18 degree facing south.

I realize your wife might not agree, but I have seen good looking installs on a house like yours over the attached garage at the same tilt and elevation as the tile portion, them trimmed around the edges with tile. A similar array on the detached garage trimmed with tile around the edges would match. I’ll see if I have some pictures still.

The shade from the array would help keep the garages cooler, those flat roofs tend to let a fair amount of heat in.

I used live near Warner and Rural and the SRP power in that area was very dependable.

T-W-X · August 2014

Re: The Ten Year Plan

Yeah, it's been a few years...

Most solar installs use fixed panels. We just got a quote from an installer that was doing a job at a neighrbor's house across the street, they quoted a system about 12.75kW, fixed panels, mounted spaced apart on the flat roof so they don't put each other in shade.

I'm mildly interested in what it'd take to build something to track the sun, and I'm curious as to common panel sizes and mounting points. Any suggestions would be appreciated. Somewhere once I saw something where some long pieces of unistrut were manipulated to pitch and aim an array of panels, but I can't find it now...

BB. · August 2014

Re: The Ten Year Plan

Two issues with Tracking Arrays... Reliability and Cost.

Secondary issues include tracking arrays may take up more ground space, and you can have structural issues if you get high winds in the area (lots of concrete and Steel if you mount on single posts).

And single axis tracking may not actually gain that much energy over a fixed array (check with PV Watts or similar the various options and generation capacity).

For people living in the snow belt--There is the adjusting array and tilting the panels near vertical to shed snow and pick up reflections from the snow field in front of the array.

In general, fixed solar panels have gotten cheap enough that it is usually not worth the extra costs for a tracking system.

With Grid Tied systems, depending on your utility's rate plan, facing panels more east or west can help you economically. For me, summer afternoons, I get "paid" ~$.30 per kWH for noon-6pm power "sold" to the utility. And I "buy" power at $0.10 for off peak, weekends/winter time. So an array that faces somewhat south west really would help me (my home faces south east).

Also--Sometimes weather can play a role--I can have morning fog/haze in the summer, and in Florida, they have summer afternoon thunder storms (at afternoon heat+sun reduces Vmp-array which reduces total array output wattage).

If you had an off grid system... A tracking array can be a big help. 4-6 hours a day of high charging current is not as helpful as 8+ hours that a tracker can provide.

With the lower costs of solar panels today--Some folks are doing "virtual" tracking... Basically 1/2 the array faces south east and the other 1/2 faces south west to extend hours of sun per day.

-Bill

The Ten Year Plan

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