# Simple Solar PV math

First: assumptions:

1. Price of grid electricity. In MA, it can be kinda expensive. And let’s assume you are doing GREEN UP or NEW ENGLAND WIND FUND to make you 100% renewables. Let’s guesstimate \$0.20. That might be low, but whatever. It will also increase at rate of inflation. say 3%.

2. Price of solar panels installed. I think it might be even cheaper than this now, but let’s say it’s \$4000/KW peak (what the panels are rated)

3. Output of said panels in an average year. I believe in New England, assuming maybe 90% sun (maybe w/ microinverters) and roughly S facing, you can assume 1200 KWh/KW peak. So if you install 1KW of panels, you will get 1200 KWh/year.

4. Borrowing money at 5% for 30 years.

5. Panels will pretty much work with no maintenance (maybe a new inverter) for 30 years. They have a warranty nearly that long. And likely for many more. But we can ignore that.

Second: Calculation:

\$4000 at 5% fixed 30 years is \$258/year
… EXCEL: = 12 * PMT(5/1200,30*12,4000)

And so that is

\$258 / 1200 KW = \$0.215/KWh for that electricity in year one

Thirdly: what does that mean exactly?

We are basically at “GRID PARITY” pricing with PVs here in New England from day zero and year one, and…
1. Even assuming NO TAX BREAKS, which there actually are.
2. And things will just keep getting better and better as inflation happens. Even assuming you get costs of living increases at your job which help you keep pace with the equally increasing fossil fuel prices, with the solar, you are locked in to 2013 prices for 30 (or more) years!

One complication is that people move every 7 years I think I’ve heard. So the problem there is that the buyer of your solarized home will not understand all of this wonderful stuff, and solar PVs will be even cheaper 7 years from now, so when you sell, you won’t be able to sell the house for much more with the panels. Maybe a tiny bit. Maybe. And you will still have your extra 5% loan for the PVs to pay off.

Which is why I still think it might be most conservative to do GREEN UP (or similar) or NEW ENGLAND WIND FUND and get your 100% renewables that way.

And buy a Prius when it is time to buy a new car. And eat less meat. These 2 have been shown (calculations again!) to contribute as much to reducing CO2 as solar panels do. And for many situations they also cost less! And they aren’t attached to the house, so they can come with you when you move.

On the other hand, there are many reasons to do things in life besides money. Most of us live in houses, buy cars, and build kitchens… all far fancier than we NEED. So then… so WHAT if you add some fancy solar panels to the house. If you can afford it, then go for it. They are cool. And the kids will learn a lot from it.

# Book Review: A Pattern Language

Green building people… if you are designing/building or buying a house, I cannot emphasize enough the importance of this book — A Pattern Language (1977, Christopher Alexander et al.). I also recommend it to those thinking deeply about education, Sudbury Valley School/Democratic Free Schools.

I have skimmed and skipped around, and I am sure there is much hooey to ignore (I certainly can’t speak to the CONSTRUCTION section), but there is MUCH to consider deeply and carefully. Fail to consider the points made at your own risk!!! Lots of food for thought. Don’t worry about the perhaps seemingly haphazard organization of the sections. Just enjoy the sections for themselves.

And I am speaking from personal experience. When I ponder what makes one house or apartment I have lived in comfortable, I inevitably find a number of “patterns” which pretty clearly make sense of it. Here I list some of my favorite sections from the BUILDINGS major section, numbered as they are in the 1200 page book:

(76) House For A Small Family
(In this pattern I think he is wrong… the 2-part house is a typical ranch/rambler/split-level. It’s a question of age. When the kids are little, they love having their beds/room very near the parents.)

(109) Long Thin House (Popular in many green architects designs… I actually don’t like this very much!)
(110) Main Entrance, (130) Entrance Room
(111) Half-Hidden Garden (explains the success of some patios I have experienced)
(112) Entrance Transition, (113) Car Connection
(117) Sheltering Roof
(125) Stair Seats
(128) Indoor Sunlight (duh but still some interesting comments)
(131) The Flow Through Rooms (Which contains one of my personal favorites — loops “Even better, is the case where these is a loop”. This one is almost NEVER followed in many new smaller houses I look at… but it is fundamental to why many older homes are comfortable. And kids love them! And you will too if you live in New England or somewhere cold!)
(132) Short Passages (as opposed to bowling-alley hallways like one house we looked at recently)
(133) Staircase as a Stage (both our current and last house made good use of this pattern)
(137) Children’s Realm
(142) Sequence of Sitting Spaces
(143) Bed Cluster (partly why the boys’ bedroom is so comfortable)
(154) Teenager’s Cottage (the basement!)
(159) Light on two sides of every room (Nice, but also better ignored in some cases I have found)
(167) Six-foot balcony (porch size rule-of-thumb)
(181) The Fire (“There is no substitute for fire.” Don’t let your dream of a superinsulated passive house let you forget this!)
(190) Ceiling Height Variety (In spades with our current house. love it!)
(192) Windows Overlooking Life (“Rooms without a view are prisons for the people who have to stay in them.”) (SVS related as well)
(196) Corner Doors (yes!)
(197) Thick Walls (Your superinsulated home will have that!)
(203) Child Caves
(242) Front Door Bench, (243) Sitting Wall

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(Also, an aside. This book is also very interesting to me because of the way it links to different sections within each of the individual writeups. It is hypertext written before it’s time! It would work well as a PDF E-Book with links to the different sections.)

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Also… Communities:
(9) Scattered Work (Discussing the problem of separation of work from homes)
(12) Community of 7000 (That democratic voices are lost when towns/cities get too big)
(14) Identifiable Neighborhood (We live in one now)
(18) Network of Learning (hmmm… sounds like a Sudbury Valley School (SVS) ad)
(26) Life cycle
(31-33) Promenade, Shopping Street, Nightlife, (58) Carnival
(40) Old people everywhere

And more SVS-related themes:
(57) Children in the City
(64) Pools and Streams
(68) Connected Play
(72) Local Sports
(80) Self-governing workshops and offices
(84) Teen-age Society
(85) Shopfront Schools

Also… Transportation:
(11) Local Transport Areas (A diatribe on cars), (20) Mini-buses (half taxi, half bus), (22) Nine percent parking
(51) Green Streets (good for driveways)

“When we do complex roofs in high snow load areas like ski resorts we typically have the roof deck act as the air control layer and provide a high level of thermal resistance at the roof deck (either rigid insulation directly above the roof deck or high density spray foam directly under the roof deck – and then we provide an over roof creating a vented space over the top of the entire assembly. In essence we created a vented unvented roof hybrid. An unvented primary roof assembly with a vented over roof.”

from comment#53 here:

Lstiburek’s Rules for Venting Roofs
You need an airtight ceiling, lots of air flow, plenty of soffit vents, and deep insulation at the attic perimeter

Awesome awesome article on insulating roofs.

# NRJ (energy)

We came home to a HOT house after an afternoon out at a picnic. It was probably only a sunny 80F today. Forgot what that felt like after living in superinsulated splendor for 3 years.

So that got me pondering the MASS-SAVE proposal for insulating (some) of our house — The walls. And part of the attic. Areas that can be done easily with either cellulose or foam board. It’s something like \$5000+ for which their is a \$2000 subsidy. Plus I believe an option for a 0% loan. With an estimated payoff of something on the scale of 5 or 6 years.

But as an exercise, I think it’s important to consider what that \$3000 (after rebates and tax credits) could pay for in other energy-savings or green-house gas reductions:

1) Pellet stove
2) More solar PV panels
3) The up-charge on buying a hybrid like a prius vs a civic or something like that.
4) A nice trailer to make grocery-shopping by bike easier perhaps
5) Windows/doors upgrades — not all, just some

Probably a good deal of insulation wins in dollars. Certainly it wins in comfort. And our IAQ would clearly be better with some better air-sealing of our attic.

This is also a reminder to go back to basics for a moment with a simple heat-loss calculator like Marc Rosenbaum’s excel or Builditsolar.com’s web app. I have some similar “payoff” numbers from Mass-Save, but better to do it myself to really get it. http://www.builditsolar.com/References/Calculators/HeatLoss/HeatLossOld.htm

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**NRJ is a fun way to say Energie in French. Since recall… a J sounds more like G in English. http://translate.google.com/#fr/en/N%20R%20J
And click the speaker to hear it.

Over at the wirecutter they write in their article about showerheads: “If you go less than 1.5 gpm you’re going to have to spend so much time in the shower rinsing off that you will waste more water than if you didn’t.”

That’s totally not true (in my experience). We have been very happy with our 1.0 gpm Bricor and that includes the resident with VERY LONG AND THICK hair. No complaints. At all.

It’s also probably news to the 140 people giving this 1.25 GPM showerhead (Niagara Earth Massage) a 4.5 out of 5 star rating at Amazon. It’s also a cheap experiment, since it’s less than \$10.

# On electric cars…

“Once consumers get used to the charge-at-home ritual, the pilgrimage to the gas station will very quickly feel as inconvenient as rewinding the VHS tape and driving it back to Blockbuster.” LINK: https://medium.com/the-tesla-collection-1/7cbf5130e11

One caveat with electric cars is that in the winter when it is very cold, you have to use the battery to heat the cabin. Apparently new models (like 2013 LEAF) are getting heat pump heaters which will be 2-3 times efficient at heating.

BTW, Saw my first LEAF today at… the Whole Foods parking lot in Andover.

My sense is a plug-in hybrid would be most practical for the new few years, but at some point I bet the full-EVs will take over.

# Concealed duct indoor units for air-source mini-splits**

idea 1) Add a single zone minisplit that directly feeds 3 rooms with only 1-zone via tiny duct runs. Mitsubishi and Fujitsu both have these. I think the indoor unit might fit in the ceiling of a closet and losing 8 inches might be acceptable? The idea being that we could then turn off the “central heat” completely on cold nights and during the day. \$2000?

idea 2) Much cheaper — thicker down comforters, sweaters, fleece, hat, my 100W electric panel under-desk (vs 1500W space heaters) with blanket for a sort of “homemade Kotatsu”. The problem is that fingers still get cold and it’s more flexible and more comfortable to not bundle.

idea 3) Some combo of the above.

idea 4) pellet stove or wood stove. Problem being that it would be mainly heating the big common space so getting heat to the office/bedrooms would be tricky.

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**Main goals are: 1) save \$ and 2) KISS (Keep it simple, stupid) and 3) reduce carbon

# Sold!

Well, the almost passive-house/almost net-zero Stow house sold in a week to a smart buyer who got a great deal. And we’ve already moved (to the 1958 split level mentioned earlier).

I’m missing…
- the warm basement (my office)
- the quiet HVAC (the new house has a typical forced-hot-air system)
- the even temps (both room to room, and time of day)
- those huge window sills!
- the attic playroom
- the very quiet location (far from highways and other major roads)

There are some nice things about our new place too though (the main one being that we are 3 or 4 minutes to the kids school) so we save lots of time/money/CO2 each day on that.