Capturing Sun & Water in the High Rockies


Inside this Article

Diana and Darin Anderson in front of their solar-powered home, at 9,200 feet of elevation in the Rocky Mountains.
The Anderson's Rocky Mountain view.
A snow-capped horizon is reflected in the south face of the home’s high-efficiency, triple-pane windows, which admit solar heat gain while protecting from low winter temperatures.
The main living spaces are all aligned across the south wall to receive solar gain into the high-mass stained-concrete floor. Abundant natural light and stunning views are a bonus.
The home’s long east-west orientation incorporates living, dining, kitchen, and gym space into one “room.”
An integrated greenhouse provides space for vegetable growing and aquaponics (fish farming).
The workout space contributes to the occupants’ sustainability by allowing healthy indoor activities during winter.
A solarium with spa tub provides a four-season experience.
Double-stud, advanced framing provides room for ample insulation. The outer cavity is foam-filled to help exceed Passivhaus standards.
The inner wall cavity is filled with high-density cellulose (center).
A blower-door test revealed 161 CFM air exchanges—exceeding Passivhaus standards.
The greenhouse dominates the southeast end of the home, providing good morning light. The solarium occupies the center space, with the living area on the southwest corner.
Having few windows on the west face reduces summer afternoon heat gain. Metal roll-down shutters and cement-board siding help reduce fire hazard.
Tight construction necessitates an ERV for efficient ventilation. Its ductwork connects to a 140-foot-long earth tube that tempers incoming air.
Twenty-eight 260 W PV modules on tilt-up racks provide enough energy annually to offset all household energy use and, in the future, charge an electric car.
Two SMA 3000TL-US inverters provide grid-tie. During a grid outage (and if the array is receiving sunshine) up to 1.5 kW of power per inverter is available at two dedicated outlets.
Three 4,000-gallon rainwater catchment tanks that provide a year’s worth of water storage and huge thermal mass sit between the garage area and greenhouse.
he north side of the house contains a cold-storage room and the bedrooms, which are thermally isolated from the living space.

In the early 2000s, I was deep into my computer programming career, traveling across the country. It was during that time that I decided to build my dream house—a log home in the mountains of North Carolina. But after poor luck with contractors and design problems, I knew there had to be a more sustainable way to build a home.

My wife Diana and I were both in the technology field, so we had the option of working remotely from anywhere. We chose Colorado and launched our new dream.

Over the next two years, I spent as much time as available researching, planning, and designing our new home. We came up with a set of lofty design goals (see sidebar), and I knew I needed to be the general contractor to ensure the necessary attention to detail by all construction contractors working on the project.

Planning & Design

There was still a lot I didn’t know, so I enlisted Jim Riggins, whose superinsulated solar home, Heliospiti, was featured in Home Power (see Web Extras). We discussed house shape; orientation; foundation/wall/attic design; insulation profiles; air sealing; advanced framing; green building materials; efficient windows and doors; and efficient water and electrical fixtures. We went over his experiences and what to expect, which led to more research and even more questions.

Once I felt I had a solid understanding, I designed the general house layout and started incorporating the various systems. Including some of the systems was straightforward, but others were more experimental—like the water cisterns also used for passive heating and cooling, an internal greenhouse, and a “cool pantry” room that would use only fans and a differential thermostat.

Once in a final version I modeled the house in 3-D using Home Designer Pro software, laying it out in complete detail down to the locations of every electrical outlet and light switch. I also created several supplemental construction documents for various trades to remove any interpretation or ambiguity. This included the wall design, ERV ducting layouts, PV module locations, subslab plumbing and electrical, and the rain harvesting system.


Comments (19)

atv4fun's picture

Do you suppose Mr. Anderson knows that collecting more then 110 gallons of rainwater is illegal in Colorado.

drandersoninc's picture

Consider the following:
1) Senate Bill 09-080 was passed in 2009 which does allow rain harvesting in Colorado with the following criteria
a. The property on which the collection takes place is residential; and,
b. The property must have a water well or be legally entitled to have a water well as the water supply; and,
c. The well use does not exceed those uses described in C.R.S. 37-92-602(g) or 37-90-105(f) being ordinary household purposes, lawn / garden irrigation of not more than one acre, watering of poultry, domestic animals, and livestock on farms and ranches, and fire protection; and,
d. The precipitation is collected only from the roof of a building used primarily as a residence; and,
e. The collected precipitation is only used for those uses that are allowed by the existing well permit, or on a well permit that the property would be legally entitled to.

2) All plumbing in a residential home construction in Colorado must be inspected and ultimately approved by a State Plumbing Inspector - this includes the plumbing for a rain harvest system.

I did my research prior to starting my home construction, did you do yours before you posted? :)

Peter Gruendeman_2's picture

[Doug Kalmer wrote]
>To install enuf 15% efficient PV to heat water
> would cost considerably more,...
The metric I work with is dollars per Watt, or since this is 2016, cents per watt. Single-crystal made in USA PV panels cost at most 1.00 USD per Watt now though the little ones for RVs cost more.
My own PV for DHW system is 1,200 Watts, providing more hot water than this household of one can use even with showering twice a day, laundry, standby losses, etc.
My neighbor's system has 1,920 Watts of SolarWorld panels, purchased new in 2016 (with 2016 dollars) for $1,782, including shipping. Their system, on a sunny day, provides more hot water than the two adults and their two children, ages 4 & 7, can use. One day of solid overcast can be managed without the grid being needed at all. After that the grid is used to to heat the water that is at least partially heated by the PV array. They too have a standard resistance-type electric water heater, which came with their house when they bought it four years ago. Their 50 gallon water heater will soon be replaced with a 80 or 100. 50 gallons is smaller than is appropriate for 2kW as this array provides a LOT of energy in one day.
Pete Gruendeman

joseph sidebottom's picture

Hey pete what controller are you using for pv direct im tired of running the gen

Peter Gruendeman_2's picture

Hi Joseph:
I designed, built and programmed the controller myself. It is a MPPT type controller, made with off-the-shelf electronic parts, and a circuit board that I designed and made. Exactly four of these exist, all made by me for friends near me. I'm not yet sure where this project is going.

A better question is why is your generator running so much? Are you off-grid and surviving on some very tired batteries? If you are off-grid and need more electricity plus hot water when you have plenty of sunshine and electricity, then this might be your answer: Use a higher voltage (150Vmpp) PV array and a step-down charge control with a diversion load. The diversion load would be an electric resistance water heater, which runs when your batteries are topped off. 2kW of PV, racked and wired BY YOU, will set ya' back about $3,000 right now. 2kW is a LOT of power for DHW when it's in surplus and might be a big boost to your existing PV array when you really need more electricity. PV can't power both at the same time, but you might find that your generator isn't needed any more but that you need fuel for your water heater on cloudy days. Off-grid homes are getting larger PV arrays each year. Soon enough people will think it's trivial to add 2kW to their existing arrays, but 2kW is a lot for DHW.
Let me know what your situation is, either on this forum or ask the forum administrator for my contact info.
Pete Gruendeman

joseph sidebottom's picture

Thanks pete. Yes im off grid. I am a solar installer And I have a temporary system i put together from 4 kw of panels hit by lighting (cut out the diodes and work great) i added 1200 watts to that 5.2kw total
A 70kwh lithium battery bank, yes 70KWH. A 25 kw diesel genset. Now the crappy part lol. Xantrex 4548 inverter (my limiting factor) and to 60a cc.
I have about 18Kw of solar panels in total. But they are in my barn untill i finish my house
Im running a 50 gal water heater but with all my loads the inverter. Cant take the 4500watt element
I love the idea of pv direct to get me by untill i can get more inverting power.
Im just getting by on this ghetto system untill the outback skybox comes out
I am going to stack them for 25kw ac with the 18 kw Of pv
Im using just a little more then i produce daily. Without the water heater
It takes about a week before the gen comes on to help charge
Also power shed is 200' from the water heater
Can i wire up 6-8 230 watt panels and a ssr and be done
I think there 30 vmp

Peter Gruendeman_2's picture

Hi Joseph:
>I love the idea of pv direct to get me by untill i can get more inverting power.
There is no value to you in running an electric resistance water heater through your inverter but you can do that. They work perfectly well on DC. It would be another matter if you told me you have a heat pump water heater.

> Can i wire up 6-8 230 watt panels and a ssr and be done
> I think there 30 vmp
A 230 watt panel, with 60 cells, such as the Kyocera 230 would make about 30 Vmpp and 8 Impp. You fill in the exact values when you find them.
Four of these panels in series would provide 120 Vmpp; two of these strings in parallel would provide 16 amps.
Divide 120 volts by 16 amps = 7.5 Ohms. When your panels power a load of 7.5 Ohms, they will reach Vmpp and Impp at the same time, meaning you'll get maximum power out of them when driving a 7.5 ohm load. Since maximum power is once reached at noon on a sunny day (non-tracking array) you want the load resistance to be 7.5 ohms or a bit higher.
Voltage square divided by watts = ohms. A 240 volt, 5,500 heater element has a resistance of:
(240 x 240) / 5,500= 10.5 ohms. That's close enough. If your heater element resistance is much too high, then you'll run at no-load voltage and produce no watts/ heat. A 4,500 watt element will work but a 5,500 is a better choice. Or put five panels in series by two parallel strings of five. That would provide more hot water than most people can use, but you seem to have the panels to spare so go for it.

Yes, you want to switch the PV panels off with a SSR when the water heater thermostat opens. The built-in thermostat won't tolerate switching high voltage DC but it will be fine for switching the 3-32volts DC used to trigger the SSR. Be sure to get a 200volt x 40 amp SSR, and a heatsink for it.

> Also power shed is 200' from the water heater
200 feet, 200 yards, 200 meters. . . . The distance is not a problem as long as your conductors are large enough to keep the voltage drop below about 2%-- same as on other systems you design and install.
Pete Gruendeman

Doug Kalmer's picture

My self installed PV pumped closed loop solar water heater cost $1100 and has been working well for 26 years with only an expansion tank failure. To install enuf 15% efficient PV to heat water would cost considerably more, and be less efficient than solar thermal.

Peter Gruendeman_2's picture

[the author wrote:]
> the water heating is standard electric but in an ultra high efficiency Marathon water heater. When looking at the cost comparison (including the ongoing maintenance) between the electric option (offset by PV panels) and solar hot water heating it was the better all around solution in the build.<

It is difficult to make an economic case for solar thermal based DHW, especially on the modest scale of the single-family home. The author's concerns are all valid. In addition to that, the competing technology of PV is typically guaranteed for25 or more years, has better part-sun/ cloudy day performance and is immune to reduced output in cold weather. That the author was building a large PV array anyways made PV for DHW the obvious choice.

I built a PV array just for DHW because the economics of modest-scale solar thermal really is that far off the pace of PV for DHW. When using it for DHW only, one does NOT need an inverter or grid-tie-- just wire it direct. This is especially true for those of us in a heating dominated climate who get little benefit from the expense of inverter + grid-tie just to run a heat pump water heater. Readers in cooling dominated climates would be well-advised to take this latter approach, unless your state or country does not offer net metering. DC direct from the panels to an electric resistance water heater is a cost-effective option everywhere, especially at cold sites and or under frequently overcast skies.

Electric resistance water heaters have been 100% efficient since the heating element was designed into the interior of the tank some time around the Second World War. [Prior to that, some makers put them on the outside of the tank, under an insulated cover.] The Marathon mentioned by the author is no doubt a much better insulated unit but still uses the same 100% efficient element everybody else uses.
Pete Gruendeman's picture

Would you be interested in selling your plans and related information / contractor cost breakdowns?

drandersoninc's picture

I had not considered that up to this point, but yes I believe I would. Alternatively, or in addition, there could be (for the lack of a better term) 'consulting time' to address any specific questions / clarifications from the plans. Just bear in mind that I'm not going to be a certified professional, it will simply be my personal building experiences both positive and negative that can be applied in concept to other projects.'s picture

Thanks. If you could provide a way for me to contact you?

drandersoninc's picture

Message sent, please reply via that email if you received it. If you don't see it check your 'Spam' folder as it may initially go in there.

Peter Gruendeman_2's picture

[The author wrote]
> I installed an ERV there to conserve energy and heat
> while exchanging the internal moisture-laden air with
> less-humid outside air.
Based on your description, this would be spelled HRV as you are recovering the heat but discarding the moisture. See:
People love the term "energy recovery" so they apply it to all heat exchangers, whether they recover the latent energy or not. In the author's case it was installed specifically to discard the moisture so installing an ERV to recover that moisture would have been pointless.
Pete Gruendeman
La Crosse, WI

drandersoninc's picture

For the intent of the ventilation unit (moisture removal as the primary purpose) that is a fair statement. However the unit is a "Panasonic FV-04VE1 WhisperComfortTM Spot ERV Ceiling Ventilator" so it is referred to in the article as what the manufacturer markets the unit as (ERV vs HRV). In full disclosure Panasonic tech support attempted to dissuade me from using the unit for moisture removal as that is not it's intended application. However for the specific characteristics of my implementation it has functioned very well in that role.

John Moore Architect's picture

The "Power Points" email mentions solar water heating as part of the design but I see no mention in the article. How is domestic hot water heated?

drandersoninc's picture

That statement in the "Power Points" was incorrect, it was a portion of the article that was not sent for my proof reading unfortunately. To answer your question the water heating is standard electric but in an ultra high efficiency Marathon water heater. When looking at the cost comparison (including the ongoing maintenance) between the electric option (offset by PV panels) and solar hot water heating it was the better all around solution in the build.

drandersoninc's picture

There is a cost breakdown but at a subcontractor / construction area level. There is also areas that I constructed on my own (the general contracting, building the greenhouse area, painting, wall trim, etc) that make the breakdown more difficult. An estimation of the cost per square foot with assumptions on hourly rate or % for my effort would be more readily possible.

The cistern construction, plumbing, and layout as a part of the larger rain harvesting system I do have all the diagrams, spreadsheets, and details. This has the potential to be another sub-article in a future HP issue provided enough interest from the community.

ben_marko's picture

It would be great to see a materials cost for the project. I would like to see how the cisterns were constructed, as well as how they are plumbed.

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