Wednesday, February 23, 2011

Tilt and Sun Angle

In my previous post, I calculated the solar collector area according to electric usage in KWh/day, and solar insolation is KWh/sqft/day. One factor that I did not include is the collector tilt, and it is a very important factor.

The first thing is to decide for a tilt angle. If we want to maximize energy harvesting in the winter months, then the collector tilt must be the 90° complement of the sun angle at that time of the year, at noon. This online tool is very valuable to calculate sun angle:
[ Sun Angle ]

Here are the values calculated:
November 1st, noon, sun angle = 28°
Dec 1st = 21°
Jan 1st = 20°
Feb 1st = 26°

A tilt of 70° will maximize efficiency in December and January, because its surface will be exactly perpendicular to the sun direction. This is the tilt we will choose.

To calculate how much energy can be harvested, we must convert a 0° tilt area (the base of the KWh/day solar insolation data) to a 70° tilt. The conversion is:
1 / cos(70°) = 1 / 0.35

Now we can calculate the area of a 70° tilted collector that will provide the heat needed in December:
Electric consumption in December = 75KWh/day
Sun insolation in December at 70° tilt = 0.09/0.35 KWh/sqft/day = 0.257 KWh/sqft/day
Efficiency factor = 0.6 * 0.8 ~ 50%
Energy harvested = 0.128 KWh/sqft/day

Solar collector area = (75KWh/day) / (0.128KWh/sqft/day) ~ 600 sqft.

A 400sqft collector would provide 2/3 of our need in December.
Using sun angle and KWh usage for each month of the year, we can estimate how much of the yearly electrical bill will be provided from solar energy. That will be the object of another post.

Friday, February 18, 2011

Energy Usage in 2010

We have been living in our new house for 1 year now. The following graph shows our energy consumption. It is very high, our house is all electric, and not very well insulated.

Out total annual usage was 19,440 KWh, an average of 1620 KWh per month, 55KWh per day.
Considering the 6 cold months, average consumption is 72 KWh/day.

With these numbers, it is now possible to determine the area of solar collectors needed to provide 50% of our energy with solar.
First, the solar insolation is Seattle (in KWh/m2/day): [ Reference ]

The average daily insolation for the 6 cold months, October through March, is:
Winter insolation = 1.8 KWh/m2/day = 0.18 KWh/sqft/day
Solar panel efficiency is about 0.6 for flat plate collectors.
[ Reference ]
I apply another 80% factor to that, due to the imperfections of a home made collector. The total insolation comes out at:
0.18 * 0.6 * 0.8 = 0.086 KWh/sqft/day
The goal is to provide 50% of our needs, which is 72/2 = 36KWh/day.
This equates to 36 / 0.086 = 400 sqft.
This is the same number I got earlier (in the Carbon Masters presentation) using a different method.
Water Heating can be estimated between 1/4 and 1/3 of heating needs, or about 120sqft. This too matched the calculations made during the hot water system design.

Now that the numbers have been cross-checked with two different methods, I can finally proceed with the construction.

Monday, February 14, 2011

Energy Descent / Climate Change Personal Action Plan 2.0

I became aware of the Peak Oil predicament around 2005. After about two years of reading and learning on the issue, with an anxiety level rising, I decided to write an action plan. The amount of changes that must happen in our life was so overwhelming that some kind of plan was necessary.
I wrote my first plan in late 2006, in my earlier website (down now).
In May 2009, I re-wrote it, and added it to this blog. Here is the link:
Action Plan 1.1
We moved to a new house in early 2010. After one year in our new home, it is time to revise the plan again. This is version 2.0.

1. Finances. 6 month cash reserve more necessary that ever.
Generate income from your home, by renting empty rooms for example.
Pay off debts, starting with highest interests, or longest term debts.
Buy second hand, this also reduces both waste, and unnecessary manufacturing and packaging.

2. Food. Start a vegetable garden. Plant fruit trees. Built a greenhouse. It takes a lifetime to learn gardening, start now! Get laying hens. They can eat kitchen scraps, will provide fresh eggs, fertilize your garden, get rid of bugs and provide meat as stew hens at the end of their laying life (~2-3 years). If you have a lot of grass, get a dairy goat.

3. Fresh Water. Collect rainwater and use it for non-critical needs, like toilet flushing, cloth washing.

4. Reduce your waste stream.
Stop city garbage service, and haul your garbage to the dump. Buy 7 garbage cans, that will match their flat fee.
Star a compost system to remove organic material from your waste stream.

5. Energy. Build a $1000 solar water heating system, as described here. If you have the skills, extend the system with radiant heating.
Use a local source of heat. Here in the PNW, that would be a wood stove.

6. Food Storage. Store food that is not easy to grow, such as grains, sugar ...
Build a solar dehydrator, learn how to can.

7. Grey Water. Nothing in Nature is a waste. Grey water from the laundry can be used to irrigate shade trees. Water loving trees such as willows will thrive, and their leaves are good forage for goats.

8. Transportation.
Get a sub-compact stick shift car. They are cheap on the used market, reliable, fuel efficient, and are enough for most people. A 2-liter 4 cylinder manual car can easily haul a 4X8 trailer.
Get a bicycle and train yourself now.

9. Sewage. We may eventually find that using drinkable water to flush the toilet is an obscene waste. Even rainwater may become too valuable for this. Learn how to use a saw-dust toilet, they are cheap and allow to safely dispose of our sewage. If water distribution is interrupted, it won't take long until Cholera sets in, as seen in disaster stricken areas.

10. Skills. Modern convenience has led use to loose valuable skills. Learn skills that allow to provide for your needs without using energy.

Tuesday, February 8, 2011

Solar Hot Water System Design

The solar hot water system will be the first improvement I will attempt to our current residence. This post presents the sizing of the system.

First parameter to consider in the number of occupants of the dwelling. We are currently 7 persons living in the house. We will soon be 4 only. Average occupancy in the future will likely be between 4 and 7 people. This is a 5 bedroom house so the system will be sized for 6 adults.

Solar Collectors.
Rule of thumb is:

  • 20sqft for each of the first two occupants
  • 12-14sqft for each additional occupant
  • 80% efficiency of the home made panels

[ Reference ]

This gives an area of 110 to 120 sqft for 6 people, and 95 to 102 sqft for 5 people.

We will use solar absorber plates from [ Sunraysolar ], which provides several dimensions:

  • 4FT * 8FT = $275. 3 panels provide 96sqft ($825), 4 panels 128sqft ($1100)
  • 4FT * 10FT = $322. 2 panels provide 80sqft ($644), 3 panels 120sqft ($966)

Three 4*8 is just enough for 5 people at a cost of $825, while three 4*10 is enough for 6 people, at $966. Although the 10FT panels are a better choice for area, the 8FT will be easier to build using 4' * 8' OSB boards.
Sunraysolar sells separately the fin tubes. Building the absorber using fin tubes costs about half, but requires soldering the fin tubes to the copper header. This also allows to build the absorber to the exact dimensions allowed to fit the site, so I may go this route.
At this time, I will assume the collector will use three 4X8 FT absorber plates.
The solar absorber plates will give a higher efficiency to the panels. The 80% figure assumes pex tubing in the collector, while I will be using copper pipes with aluminum spreaders. Although the collector is slightly under-sized, the higher efficiency should compensate.

Storage Tank.
There are different rules for tank sizing. I used the following website:
[ Reference ].
A rule of thumb is 10 to 15 gallons per person per day, or about 75 gallons for 6 persons.
Another rule of thumb is 2.5 gallons per sqft of collector area, which is 300 gallons for our 120sqft collector. This represents 4 days of storage for 6 persons, a good feature to have in our cloudy climate.
A 300 gallon tank will approximately be 3.5 ft cube.
Silicon solar (reference for the collector area) gives a rule of thumb that results in a smaller tank size. I don't think there is a drawback in having a bigger tank, except that it will take longer to heat the water after a series of cloudy days.
The tank will be build with 4FT sections of 2"*4". With the added insulation, the capacity should be slightly less than 300 gallons.

It will be a drainback system, so there is a head to account for in sizing the pump.
Solar absorber flow rate = 1.3GPM per absorber = 3.9 GPM total ~ 240 GPH ~ 900 LPH
The head depends on the location of the absorber. I have three locations in mind at the moment, on the roof (head ~ 25FT), against the garage wall (head ~ 18FT) or against the electric fence (head ~ 12FT). Eventually, there will be a collector in each of these three locations. The pump for each location will differ, due to the different heads. That means that there will eventually be three pumps. To reduce the number of inlets and outlets, all three pumps will be inline pumps, located outside of the tank.
I will assume at this time that I will chose the lowest head, 12FT. Now I need to find a pump that has 240GPM flow rate and a maximum lift of at least 12FT.

The major components are now defined:

  • A 8FT * 12FT solar collector.
  • A 300 gallons storage tank.
  • A 240 GPH Pump, 12FT lift min.

With those values in hand, I can now make a better decision as to where to locate each element of the system.