22 Comments

1. 
   [email protected] | Dec 05, 2022 06:41pm | #1

   If your priority is to be comfortable at all times inside your modern home, then you need to let your HVAC system handle the heating and cooling.
   In cold, northern climates, if you load up your south facing walls with windows large enough to generate significant solar heat during the coldest months, you will roast in those rooms other times of the year. Passive solar can certainly assist with heating on some days, but you will sweat it out during the summer and shoulder seasons. And you will be particularly hot in some rooms, and cold in other rooms. Well... at least on the days the sun shines. Wonderful.
   And you can't design large enough overhangs in northern climates to completely take care of this without seriously impeding your in-room daylight levels, not to mention increased structural challenges and costs. On the many other grey, cloudy days during the winter, your walls filled with expensive - wait for it - R3-R4 windows (maybe R6-R8 if you really splurge), will create a significant heating load.
   So if you want a comfortable, climate controlled home, leave the heating and cooling to a properly designed HVAC system, and always install high R-value, low solar gain windows. Window placement should only be based on desired views and in-room daylight.

1. 
   Robert Opaluch | Dec 06, 2022 08:21am | #2

   Your claim that "you will roast in those rooms other times of the year" is completely false for a well-designed passive solar home. Everyone should know that WINTER sunlight shines on the south side of the house mid-day, shining through south-facing windows, warming the interior through solar heat gain. Summer sunlight is overhead midday and shines on the roof, and east and west sides earlier and later in the day. More south-facing glazing and thereby less west and east-facing glazing reduces summertime solar heat gain, the exact opposite of your claim. (You could always use window blinds to reflect unwanted solar radiation, anyway!) Look up solar heat gains per SQFT of glazing for various directions for your location for winter and summer, do the math, don't just guess and make claims that are false.

   If you don't calculate wintertime heat losses and solar heat gains to compensate, you aren't designing the building to maximize sustainable performance.

   The super-insulated passive solar home I designed and built in Colorado (sunny cold winters) had the same 68F-78F daily temperature fluctuations mid-winter as mid-summer (using overnight ventilation natural cooling on a tiled slab floor (which functions as a passive "thermal mass" temperature stabilizing heat storage "battery"). Most people set their thermostats at about 68F winter and 78F summer. This house cost no more than typical construction since the HVAC system was deleted, didn't require wintertime heating on the main floor despite cold winters, and resulted in rock bottom cheap all-electric utility bills. It would be immune to power outages affecting internal temps on that main floor mid-winter, unlike typical space heating systems that don’t work during power outages.

   However, passive solar only works in sunny cold winter climates. Some locations in Missouri aren't a great location for passive solar, with 40% overcast and 10% mostly cloudy days mid-winter. About 27% clear sunny mid-winter days, and another 10% mostly clear. So about one third of winter days, south-facing windows could provide interior space heating for a relatively airtight and well-insulated home in St Louis. And unshaded south-facing windows would heat the home better in winter and heat up the home less in hot summer than east and west windows! And Missouri is a lot better than the Pacific Northwest (Seattle 18% clear or mostly clear, 57% overcast, 15% mostly cloudy, passive solar heating wouldn’t work there). Climate is a key determinant of whether passive solar would work or not, along with a building lot that has south-facing solar access mid-winter (not heavily shaded by another building, tall trees, etc.). And unshaded south-facing windows always perform better in winter and in summer than west and east-facing windows (heating more when you need it in winter, and heating less when you don't want it in summer).

   My Colorado location had 50% clear or mostly clear days, and a slab floor for carrying you through the night and a followup cloudy day or two before interior temps got down into the lower 60'sF.

   Passive solar can work well IF you have a sunny cold winter climate, mid-winter solar access (unshaded), and a super-insulated building shell. For example, from New Mexico to Montana. Or the New England coast isn't too bad either. Forget the Pacific Northwest or areas blanketed by overcast winter skies affected by the Great Lakes.

   Passive solar isn't a substitute for air sealing and insulation, they work together to provide high performance and sustainable space heating. You can reduce your heating load, then use a sustainable heating system instead of burning fossil fuels.

1. 
   user-723121 | Dec 06, 2022 10:07am | #3

   Robert,

   Thank you for this detailed explanation of how you incorporated passive solar into a working and comfortable home. The cliff dwellers would agree with you. Often these days we become too narrowly focused on the newest and shiniest object and forget about the building basics that really work.

   Like you stated, one must take into account regional climatic differences to arrive at the best possible design.

   Doug

2. 
   [email protected] | Dec 07, 2022 10:39am | #7

   I have a significant amount of experience with thermodynamics, solar irradiation, and solar charts as a professional engineer in the Great Lakes region.
   1.) Assuming we're talking primarily about the US, for the most part you really only need significant heating in say the northern 1/2 of the country. And most places east of the Mississippi in the northern 1/2 do NOT have 50% clear sun from Oct.-Feb., so as you point out, not good for passive solar. I agree.
   2.) What I consider "comfortable" is being able to walk into any room, at any time of the day, and the environment (temperature and humidity) is within 2% of desired settings. NOT the ability to maintain a 24 hour temperature swing of 10F. I may as well be outside.
   3.) I keep my house at 70F during the winter (maybe 68F at night), and 72F-74F during the summer. Because I like to be comfortable, and the science shows most people are comfortable at 72F. Anything more than a couple of degrees outside of that is usually a result of trying to save money on energy. When I go to my brother-in-law's place in California in March, and he tries to save 50 cents a day by leaving the A/C set at 78F, I'd rather be in my sauna at the lake house in Canada.
   4.) Very few buildings have the luxury of being oriented exactly N-S-E-W, due to lot orientation and other restrictions. In my experience, there is almost always some amount (e.g. at least 15-30 degrees) orientation from pure south, so even more summer sun often hits so-called “near south” facing walls.
   5.) “Overhead” is a misnomer. In Northern Michigan for example (recent project), the largest “solar altitude angle” (i.e. angle above the horizon) is approx. 66 degrees, which occurs on June 21 at 12:00 noon solar time. That is the most “overhead” the sun ever gets in that region. The majority of the “middle day” (i.e. 10 am - 2 pm) from May to September, the solar altitude angle is between 45-60 degrees. Far from straight above, even though it might feel that way.
   6.) Let’s take a relatively mild winter day in January in Michigan, with an average outside temperature of 10F (15F during the day and 5F at night), and full sun. And for example, we have R4 (better than average), SHGC=0.6 (high solar heat gain) windows on a “near south” facing wall. The passive solar heat gain in January will be approx. 330 Btu/ft2/day, on a full sun day. However, the heat loss due to those windows will be 360 Btu/ft2/day, every day, even when it’s not sunny. Even if you subtract the approx. 50 Btu/ft2/day heat loss that you would have had through an R35 wall (i.e. instead of having windows), you would be crazy to install windows simply for passive solar heat gain. I’ll repeat myself one more time. Put your windows where you want them for views and in-room daylight.
   7.) In the example above, even if you increased the eave overhangs to 4 feet (which is not an insignificant challenge), the same south facing windows will still generate 150 Btu/ft2/day of solar heat on a sunny day in July. So 45% of the peak heat that you’re looking to generate in January will be blasting into the house in July - even with 4 foot wide eaves!
   8.) So in rooms even with only south facing glazing, you have to deal with over-heating on most days in the summer, many sunny days in the spring and especially the fall, and even sometimes in the winter. And you can have the opposite problem (too cool) - at the same time - in other rooms with glazing in other directions, especially in the shoulder seasons. Unless of course you have a separate, zone controlled HVAC system to compensate.
   9.) Do whatever you want with east and west glazing (make it zero if you want). But if you increase the amount of south facing glazing you will have more winter solar irradiation enter the house, AND you will also have more SUMMER solar irradiation enter the house. And you will have a lot of south facing glazing if you're trying to achieve passive solar heating.
   10.) Most people want a reasonable amount of glazing on the south walls simply to maximize in-room daylight. I would not want to live in a house with mostly north facing windows. It would be depressing.
   11.) Yes, west facing glazing can be the worst culprit for over-heating. But what if your mountain or lake views are towards the west? Like I said, put your windows where you want them for views and daylight. Always use super Low-E windows, on EVERY wall face.
   12.) A heat sink can help mediate the problem by spreading it out over time. But what if you’re sitting in the room when the sun is blazing in? Your body becomes part of the heat sink. Not very comfortable on a sunny day in September or October.
   13.) Interior window blinds can help to some degree by reflecting some of the irradiance (this is a more complex topic). But once the irradiation has passed through the glazing, much of it is trapped inside the room. Blinds or no blinds, you will heat up your room to some degree.
   Personal Pet Peeve:
   What exactly is "sustainable" performance? Are the windows "sustainable" because you think they will last longer than the sheathing that would have been there instead? Or maybe the windows should be considered LESS "sustainable" because they need to be washed once a year? Oh no, I forgot, the windows allow us to use the sun, which is "sustainable". Well then, I would say a NON-passive solar heat building using solar panels to generate electricity to power an electric heat pump is every bit as "sustainable". And controllable. And therefore more comfortable. Sorry for the rant, but it is just such a meaningless term.
   Summary:
   First, in many cold climate zones, the numbers just don’t add up. You are losing more heat through the windows than you can produce from solar irradiation, even on the sunniest days of winter.
   Even when you can produce enough passive solar heat, the real problem is you can't control it. And the more insulated and more air sealed the building, the worse the problem gets for over-heating.
   For those that want to drink the koolaid, go for it. For those that want to be comfortable at all times, in every room, in a modern, climate controlled environment, the best way is to let a well designed HVAC system (with ALL windows as low E glazing as possible) handle the heating and cooling. Put your windows where you want them for views and in-room daylight.

1. 
   MartinHolladay | Dec 07, 2022 11:02am | #8

   T. Barker,
   My reaction: thumbs up.

1. 
   Robert Opaluch | Dec 07, 2022 07:35pm | #14

   Martin,

   I’m not sure whether to tell you your thumb's up in the wrong place, or threaten to break your thumbs like in the Mafia movies! 😉 (okay, bad joke)

   I have the highest (now almost the highest) respect for you as an author and advocate for high performance home design and building. I’m very impressed on how you managed to answer all those Q&A’s years upon years, on a very wide variety of topics, and write brief informative articles on a wide variety of topics, in addition to your work on construction and even some farming. However, I’m disappointed in some of your articles “X vs. Y, and X won.” Makes for a dramatic story for popular reading, but in the case of some topics, you are throwing out the baby with the bathwater. I agree that active solar collectors are outdated except possibly for some off-grid situations. But passive solar heat gains aren’t something that should be discouraged categorically, whether for passive solar with thermal mass, or for solar tempered homes. (You say yourself that homes should attempt to have a longer east-west axis and located more windows facing south to capitalize on solar gains.) Yes passive solar only works well for climates with mostly sunny, cold winters, not most places. And yes you don’t live in that climate, so maybe you don’t have much of a feel for warm sun brightening your bitter cold winters way up north where you live near Santa’s house. What’s so wrong for those who want to maximize sustainable passive solar heating through windows we already are going to include in our building, or add or re-arrange their location, rather than use external power from sources that are often contributing to global warming that’s killing people and many other species? Direct gain solar space heating is about the most sustainable power source I can imagine. Think about it. No utility bill for sunlight, no transporting and packaging to bring to your home, no choking emissions, no abandoned mining holes, nada. Is gas heat better? Oil? Coal? Wood? Even "clean" mini splits have to be manufactured with materials dug up and processed, then shipped to you and installed, then you have to pay for electric generation and transport to your place, and some day throw it in the landfill.

   I’m getting tired of others who don’t understand what passive solar (or solar tempered) is, have not successfully designed or built passive solar buildings, or who claim “thermal mass” is pseudoscience and can’t be measured, yet claim to be experts in this specific area, and say its impossible to build a functionally successful passive solar building. The fact that people in the 1970’s built overglazed homes without sufficient insulation and “thermal mass" to reduce daily interior temperature swings, means they didn’t understand how to design and build successfully. You personally showed some wacky photo examples to diss passive solar categorically. Poorly designed buildings claiming to be passive solar aren’t relevant. Early electric cars from the 1970’s weren’t good either, but that shouldn’t condemn today’s well-engineered versions. Granted, true passive solar is a niche product and only works well in climates with cold sunny winters, not everywhere. There are daily interior temperature swings, but not much different than what people do when they set thermostat settings in winter vs. summer to reduce utility bills. Solar tempered buildings are easier and could be used in cold winter climates if you have south-facing solar access in midwinter. (And North-facing windows for hot humid climates of the Southeast, same principles.) After all, you have to place your windows somewhere. Where you can, why not to provide more daylighting and heat gain during cold winter, and move them away from locations that overheat in summer? Or at least accept people and design methods who want to do that.

   By the way, its not really solar versus superinsulation. Its solar and superinsulation vs. mini splits and superinsulation, or natural gas-fired space heating and code minimum insulation. And gas won. With 50% of homes today in the USA.

   That reply and second reply above is filled with overexaggeration and disinformation. But you give thumbs up. Some quotes are listed below. Do you give thumbs up to these, agreeing with them?

   1. The comment that makes the least sense to me is talking about how passive solar wouldn’t work, proved by his example in northern MI. At the same time he agrees with me that you need a climate that is sunny mid-winter for passive solar to work. Looking at cloudiness charts (attached), it shows primarily overcast skies for what seems the largest town in the middle of northern Michigan, Marquette. Other northern MI locations likely similar. End of Dec, beginning of January, clear skies only 5% of the time! Clear or mostly clear only 10% of the time! Overcast 55% of the time. Overcast or mostly cloudy 75% of the time. A terrible place for passive solar! No one should recommend building a passive solar home there, nor does it “prove” that passive solar won’t work in more compatible climates. Or as he claims himself, south-facing solar gains there are not greater than losses, so no net gain. So passive solar would not make sense for that location, but that’s not relevant for all other locations. Where I built in CO, the numbers were radically different, as shown in two articles on GBA.
   https://www.greenbuildingadvisor.com/green-homes/a-passive-solar-home-from-the-1980s

   https://www.greenbuildingadvisor.com/article/a-quantitative-look-at-solar-heat-gain
   Thumbs up for his assertions on this one?
   2. “In cold, northern climates, if you load up your south facing walls with windows large enough to generate significant solar heat during the coldest months, you will roast in those rooms other times of the year.”
   Do you agree with this one Martin? Solar charts and data typically show minimal solar gain in south-facing windows in June and July, especially with the elaborate overhangs he discusses. I found interior temps stayed about the same range year-round, 68F to 78F, with overnight cooling of thermal mass by leaving one window open overnight during hot summer. No roasting any season, even when temps were high 90’s outdoors. Superinsulation and thermal mass works if engineered and used correctly in a compatible climate.
   3. “you will sweat it out during the summer and shoulder seasons”
   I sweat when working hard, running, and backpacking outdoors. Didn’t happen inside my passive solar home, but I would know to open a window in shoulder seasons if it ever did get as hot indoors as he claims. In the summer, the outdoor temps typically got around 90F, so inside was much cooler and comfortable in this dry climate. Martin you give thumbs up to what?
   4. “you will be particularly hot in some rooms, and cold in other rooms”
   I’m pretty sure that at some point, you Martin stated in GBA that in superinsulated homes, heat moves around the interior rooms (open doors, uninsulated partitions, interior ceiling/floor) much faster than it moves out to the outdoors through airtight, well insulated walls. Therefore, there won’t be that much temperature difference among interior rooms, except rooms over uninsulated garages. I didn’t notice differences in temperature among interior rooms, so didn’t think to take measurements to track it.

   One principle of passive solar home design is to place habitable rooms on the south side of the home, and place corridors, utility rooms, closets, stairways, etc on the north side. Armando stated this in this very same article in the “Expert Opinion” section, point #3. Which way to you vote on this one, Martin? Both hot and cold rooms, or similar indoor temperatures in superinsulated buildings? (Yeah you could close a door to a room, and open a window to the outside in winter to make the room colder than others, but that’s not what he meant.)
   5. “increased structural challenges and costs”
   No explanation given, but this certainly didn’t happen in the passive solar home overhangs or anywhere else when I designed and built. Maybe you could explain this one? I don’t understand this assertion. If you still give a thumbs up, please explain the structural challenges and costs that I somehow missed.
   6. “Window placement should only be based on desired views and in-room daylight.”
   I know a number of other factors to consider, maybe you could suggest some too.
   7. Did you like his sarcastic “Wonderful” comment?

   
2. 
   MartinHolladay | Dec 08, 2022 05:49am | #17

   Robert,
   I never said that passive solar "doesn't work." Of course these principles work. Whether or not any particular homeowner wants to live in a passive solar house is up to them.

   If the homeowner expects to save any energy, the homeowner has to accept indoor temperature swings that are greater than a conventional home. Whether that is acceptable depends on the homeowner.

   Of course a passive solar home can be comfortable. But so can a home with a conventional number of windows. If you pay attention to airtightness and insulation, it isn't that hard to heat a house.

   I prefer a house without large windows that exceed the glazing area that works for a pleasant view and an adequate amount of natural light. And I'm not interested in operating insulating shades every evening and morning.

   Overheating in a passive solar house doesn't happen in midsummer, in my experience. It happens in March and October.

3. 
   Robert Opaluch | Dec 08, 2022 09:00am | #18

   Martin,

   Due to seasonal temperatures that lag the position of the sun, you might find that on average, solar homes would run warmer in the Fall and cooler in the Spring, if you never use any backup heating or cooling. Months don't align exactly on the 23rd of each month. But July warmer than May around summer solstice, January colder than November around winter solstice, etc for warmer Fall (following summer) and cooler Spring (following winter). Same solar position and gains, different lagging outdoor temperatures. With warmer Falls and cooler Springs, the interior should be affected similarly with slightly less Fall and slightly more Spring heat losses. Dryer Falls and wetter Springs and humidity might accentuate that.

   These smaller differences were sometimes overpowered by weather patterns affecting temperatures in CO, with warmer weather from the Southwest and frigid weather from Canada dominating temperatures during winter. Dramatic temperature swings, even within a few hours (warm t-shirt weather then snowstorm).

   What experience, may I ask?

   Although I never used heating or AC myself for the passive solar main level of my house, it isn't fair to complain that homes that are solar-oriented might get warmer or overheated, but you can't just open a window, and you can't use any backup heating or AC. But homes that use HVAC, its okay to use heating/AC all the time. Solar homes would just use a lot less HVAC heating in cooler months for sure.

   I notice that the rich often have window walls in their contemporary mansions. With a view of their pool, garden, or if they have dramatic scenery. I landscaped a woodland view, with decks and a dry creek bed on the south side. Landscape Architecture class suggested creating landscape views from your windows, in addition to placing windows to capture views. Neighbors complimented me on the landscaping after complaining about me building slower than the usual construction crews. Aside from any solar gain benefits, I like bringing the outdoors in, if you can landscape or capture nice views. I understand that for very cold climates this isn't so easy or compatible, and not for everyone's tastes.

4. 
   MartinHolladay | Dec 08, 2022 09:10am | #19

   Robert,
   Q. "What experience, may I ask?"

   A. I designed and built three passive solar homes in the 1970s, all in Vermont. For a while, I lived in each of the three homes. The house where I now live -- where I've lived for over 4 decades -- is one of those three passive solar homes. I have never had the pleasure of designing and building a passive solar home in Colorado, where all of the passive solar home enthusiasts seem to live.

   I'm well aware that Vermont is not Colorado.

5. 
   Robert Opaluch | Dec 08, 2022 01:37pm | #22

   Thanks.
   Wow that's a tough climate for passive solar! Overcast half the time mid-winter, quite cold.

2. 
   hughw | Dec 06, 2022 11:03am | #4

   Posted this in wrong thread originally.
   Interesting discussion....I now live in the passive solar home we completed on Martha's Vineyard year round. For it's time, 1982, the house was way ahead of things in terms of energy. The house was originally designed as a combination active-passive house. Most windows are south facing. Some window are shaded by 4 foot overhangs. Other windows with large expanses of glass are in "sun spaces" that can be isolated from the rest of the house by interior French Doors. The original conception was that warm air from the sun spaces would be pushed by a fan on the 2nd floor down a duct to below the "basement" ground floor slab where it would circulate through a system of mini-runners created by holes in concrete blocks, warming the slab. The idea was that excess heat during the day would be stored in the slab where it would then warm the house at night.....The fan system never really worked...instead, we would keep the sunspaces closed during the day and open them in the evening.
   Additionally, the house was considered "super-insulated" compared to normal houses 40 years ago. All non-sunspace windows were triple glazed. Walls were 2x6 with R19 batt insulation at a time when most homes were 2x4 with R13. Additionally, a 3/4" layer of foil-faced polyisocyranate was installed on the inside of studs with 3/4" strapping on top and then sheetrock. This provided additional insulation, an air space with a reflecting surface, and stopped thermal bridging in the studs.
   There was no heating system....just a wood stove. For 30 years, the house was mainly a summer house. When we would come up on a winter weekend, the ambient temperature was never below 55 degrees on arrival. We would use the wood stove as needed if there was a cloudy day. About 10 years ago we installed a heat pump system as the summer days were sometimes just too hot and muggy, and when we used in winter, the wood stove was just a pain in the ass.
   For the last 3 years, we've been living in the house full time. Generally, we keep the heat pump thermostat set at 66 degrees...If it's a sunny day, we might turn the heat up a bit in the evening if we're home. Until perhaps around 5pm, the house will be toasty warm.If it's cloudy, we'll turn it up when we get up in the morning. Is the house perfect? Of course, there are things I would do different today, but all-in-all, the care (and money) we put into the construction in 1982 was well worth it.
   Note: little structure to right is unheated, uninsulated, summer studio.

   
1. 
   user-723121 | Dec 06, 2022 11:26am | #5

   Hugh,

   Nice to hear about a 40 year old well thought out build still performing. Hard to put an exact value on comfort but you sure know when it is missing. This is what I like to call inheritance quality real estate. This is a nice looking home.

3. Expert Member
   ARMANDO COBO | Dec 06, 2022 04:39pm | #6

   I think this could be a good webinar. https://www.eventbrite.com/e/the-basics-of-passive-solar-home-design-free-ce-webinar-tickets-481662755267

4. 
   pokmhutf5 | Dec 07, 2022 01:37pm | #9

   You've had several readers say that they live in excellent passive-solar homes, and you still don't believe them. In 1988 I built a passive-solar home in southern NH; the heating bill was less than $1,000 a season, and the A/C bill was less than $250. The insulation was good, but not extraordinary. The anti-solar crowd misses key details:

   Overhangs aren't just important, they're huge. Even adding a few inches of gutter makes a difference. Shade trees are essential. Window shades are essential; we had the pleated, cellular kind. In the house I'm building ten of them will be powered and remotely operated.

   Thermal mass is important. My first-floor walls will be ICFs, but an easy way for anyone to add solar mass is to use fire-code sheet rock everywhere. You'll notice that sound reflects in a way that lets you know that the house is solid.

   Passive non-solar houses are sad, dark places. It's crazy to spend money on triple-pane windows. Embrace the light!

   
1. 
   Malcolm_Taylor | Dec 07, 2022 04:59pm | #10

   pokmhutf5,

   "You've had several readers say that they live in excellent passive-solar homes, and you still don't believe them."

   I don't have a dog in this fight, but I haven't seen anyone say the houses readers have built aren't performing well, just that it may not be their passive solar attributes that are chiefly responsible for that.

   If you want to add thermal mass, Are ICFs the best way of doing so when half the insulation is inside the concrete?

1. 
   pokmhutf5 | Dec 07, 2022 07:02pm | #12

   Malcolm,

   The new house has fire code 5/8" sheet rock everywhere, even lining the ICFs. That stuff is HEAVY. The staircase landing is a slab of granite that weighs 3,300 pounds. And the first floor is underpinned by a 4" radiant slab of concrete, sitting on almost 7" of EPS.

   On a bitter cold February day, with snow on the ground to reflect light into the windows, the last house would still be at 70 degrees at 9 PM. Yes, you can turn your back to the sun and still stay warm, like a wood chuck in its burrow, but why would you want to?

   John

5. 
   adam5532 | Dec 07, 2022 06:04pm | #11

   I'm surprised that only one comment above mentions solar panels. If the intent is to harness the sun's energy to help heat the house, then it seems to me that solar panels are a no-brainer, and that the discussion about passive solar is moot. The best panels are 22% efficient, there's a 30% tax credit, and you have a nice expanse of south facing roof. And altering your design would be minimal, such as ideally installing a standing seam metal roof, and routing your plumbing vents to the north facing slope. Depending on the calculations, it could possibly cover 100% of your energy, and would eventually pay for itself and then keep saving.

1. 
   Robert Opaluch | Dec 07, 2022 07:24pm | #13

   Unfortunately solar panels do not generate enough power to heat a home unless you have a lot more than just your roof covered. And the expense is far greater than just using windows (that you have in your house anyway) to get direct gain solar heat. The majority of the energy is harnessed with south-facing unshaded window glass, a much smaller fraction with PV panels.

   Another plus is daylighting from window glass. But you could use PV for interior lighting too.

   The plus for PV is that the power can be used for anything, and they are higher up and thereby less likely to be shaded by other buildings or trees.

1. 
   adam5532 | Dec 07, 2022 10:00pm | #16

   We are planning a solar system for the roof of our 2000 sq foot two-story 1903 house, that has vertical plank walls with space for minimal insulation, and we have calculated that a 12 - 15 kW system will fit on the roof (S, E, and W sides), and will provide for 100% of total energy usage, including heat pump HVAC (3-ton), heat pump water heater, ADU (apartment) heating, heat-pump dryer, and charging our electric car. We are in Portland, OR, and of course the region and site specifics will vary, but it is very possible for solar to provide 100%.

6. 
   MJDuval | Dec 07, 2022 09:39pm | #15

   When I was a kid in the early 80's and friend of the family built a passive solar house here in the upper Hudson Valley. The owner was a physics teacher. My father thought he was out of his mind. No heating system? No wood stove? How could he? The house was built with an insulated 6 feet deep mass of sand or crushed stone under the house with 4" tubes running through the mass. The house is tall. A central chimney inside the house drew air into the chimney at the ceiling (cathedral) and forced it through the sand/stone mass. In the summer, the result as cool are discharged to the house. By winter, this mass was heated and provided heat. I don't know alot of other details, as I was a kid. But I do know that when we visited in the winter time, it was warm. in the Summer, it was cool. So, it worked more or less as intended.

   About 8 years ago, I went to a green building conference in the Hudson Valley and was taken back by all of the 'gizmos" being hawked by the industry. Much of the discussions were about "Passive House' concepts, which was interesting. At the end of the presentation I asked about passive solar. I was surprised by the flippant rejection of passive solar concepts by the Green Industry.

7. 
   hughw | Dec 08, 2022 10:06am | #20

   just curious....sounds like there's a few of us that built passive homes in the northeast forty years ago....As I recall, there was a lot of interest in that in the late seventies resulting in a large conference for a bunch of enthusiasts in Northampton, MA, if I'm not correct.

1. 
   user-723121 | Dec 08, 2022 10:38am | #21

   Hugh,

   I did my research in 1982 and built my first double wall, superinsulated house in 1983. Orientation of the glazing was a high priority along with abundant insulation and airtightness. The combination of these made for some very efficient, comfortable homes.

   Doug