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.

Pump.
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.

Our Energy Allowance

In order to shift our society from fossil fuel to renewable energy, we need to know how much renewable energy is available, how much daily solar allowance can we count on? One study shows that there is more energy reaching the Earth from the Sun in one hour, than the entire world uses in one year. It seems there is plenty.

The following model tries to determine how much solar energy can be harvested on a global scale, it doesn't look at what we actually use today for transportation, food, or other things. This is how much we get, whatever we do with it.
The model uses the area presented by the Earth to the Sun at any time, 24/7. For that, I used the area of the disk presented by the Earth, instead of the surface area of the Earth itself, which, because it is a sphere, would receive variable amounts of energy depending on latitude and time of day. Using the surface area of the Earth would require going through multiple use cases, while using the disk that the Earth presents to the sun at any time, allows to determine the global energy received from the sun, regardless of latitude, day-night, equivalent sun-hours or other fancy formulas. This is what we get on a global scale.
The model doesn't tell how we will harvest that energy. Again, this is another problem. Before we decide how we will harvest it, we need to know how much we get.

So here we go...

Solar irradiance = 1400 W/m2 at the top of the atmosphere. This is the amount of solar power on a one square meter area. The atmosphere will absorb and reflect a part, so it is estimated that the average amount of solar power reaching the Earth surface is ~ 1000 Watt / m2.

[ Solar Irradiance Reference ]

Now we can calculate how much square meters the Earth presents to the sun.
Diameter of Earth = 12,000 km = 12*10^6 meters
Radius = 6*10^6 meters.
Surface presented to the Sun = PI * (6*10^6)^2 = 113*10^12 m2.

The total amount of energy reaching the Earth surface is:

113*10^12 m2 * 1000 Watts/m2 = 113*10^15 Watts.

About 70% of the Earth surface is covered by water, so 30% remains. Of those 30% land area, we can assume that covering 1% of the land area with solar panels would be a maximum practical ratio, so 0.3% of the total energy may be harvested.

113*10^15 * .3% = 34*10^13 Watts
This is the amount of electrical power we receive from the Sun over 1% of the land area.

We are 6 billion people, so we need to share this power.

34*10^13 / 6*10(9) = 56 KWatts per person

Energy is power multiplied by time.

56*10^3 Watts * 24 hours ~ 1.3 MWh / day / person.

This is the solar allowance each of us can use before we start depleting resources.
Now this is before conversion into useful energy. The average conversion efficiency is about 20% for electricity (best case).

[ Photovoltaic Efficiency ]

Converting all of our solar energy allowance to electricity, we would have:
1.3 MWh * 0.2 = 271 KWh / day / person

Now lets see where we are today in the United States, as far as energy usage per capita.

Total energy usage of USA in 2005 = 29*10(15) Wh
US population = 300 Millions = 300*10(6)
Energy usage per capita in 2005 in the US = 100 MWh/year = 280 KWh / day / person.

[ US Energy Usage Reference ]

We can fulfill our electrical needs if we cover 1% of the land surface of the Earth with solar panels.

Carbon Footprint: Transportation

Transportation is the biggest emitter of CO2 in most American families. Here is our transportation carbon footprint estimation.

We have two fairly efficient vehicles: a 1997 Ford Escort, and a 1998 Honda Civic. We also have a 2001 Suzuki GS500 motorcycle as a spare vehicle.

To estimate our usage, I looked at when we bought each vehicle, and how much miles we have put on them.
Ford Escort purchased in 2004 at 120,000 miles. It has now 235,000 miles, so that is about 20k miles per year.
Honda Civic was purchased in early 2008 at 145,000 miles. It has now 193,000 miles, so about 20,000 miles per year.
Because we moved closer to work, I reduced out estimated yearly mileage to 15,000 miles per vehicle per year. The estimation is conservative, my commute was reduced from 28 miles to 18 miles, 35% reduction, but I applied a 25% reduction for both vehicles.

We can now estimate how many gallons each vehicle uses per year:
Ford Escort gets 33MPG, or 454 gallons per year (15k miles).
Honda Civic gets 37MPG, or 405 gallons per year (15k miles).
Note that the MPGs are average, measured by myself, not advertised mileages.

Our total gasoline use is 860 gallons per year.
At 8.8Kg of CO2 per gallon, that is 7.5 tons of CO2 per year.
The average American family emits 12 tons of CO2 for transportation (and another 12 tons for household operations), so we are about 38% lower than the average.

Since this blog is about Carbon reduction, lets see how much we can reduce that, and for how much money.

The Ford Escort as a newer engine in it (100,000 miles), so we can keep this vehicle for when we want to haul cargo or people.
For my commute, I can use my motorcycle, and I can replace my Civic by a hybrid for bad weather. My wife may use the hybrid when I use the motorcycle.

Here is an estimation of each vehicle mileage for a year:

Suzuki motorcycle = 10,000 miles at 70MPG = 143 gallons per year.
Honda Insight = 15,000 miles at 70MPG = 214 gallons per year
Ford Escort = 5,000 miles at 33MPG = 151 gallons per year.
Total = 500 gallons per year, or 4.4 tons of CO2, a reduction of 3 tons.

How much that reduction would cost us?
A used Insight costs about $7k.
Payback would vary with gasoline price:
At $3/gallon, 6.5 years
At $4/gallon, 4 years 10 months
At $5/gallon, 3 years 11 months ~ 4 years.

One important point is that the Honda Civic will need replacement soon, so considering the full price of the Insight is not a fair calculation. Instead, I should compare how much I would pay for a non-hybrid vehicle, about $3500 for something like a Cavalier, so the true cost of the hybrid system would be $3500 for my case. This would put the payback time at:
3 years 3 months at $3/gallon
2 years 5 months at $4/gallon
2 years at $5/gallon.

From this data, I can decide how important changing vehicle would be on the priority list. Initial capital investment and payback time are the prime drivers, since future savings will pay for coming projects.

Carbon Master Class of 2010 !

The WSU Extension Carbon Masters Class of Fall 2010 ended yesterday. The training included the development of an outreach project. As an engineer, I am not good at outreach, so my approach is to lead by example, to modify my home with a minimum upfront expense, and maximum use of DIY projects. Call it "Climate change activism, an engineer's approach", or something like that. The focus of the projects would be to save money by saving energy, because saving appeals to everyone, even climate skeptics. The project presentation appears very technical, but by detailing every step of my projects, I hope to make visitors say "I want to do that!" and help them do so.
I will be using a lot of resources from builditsolar.com by Gary Reysa, I highly recommend that you browse his fantastic website. This is an encyclopedia of solar DIY how-to. One of my earlier projects is actually linked to his greywater section.
To avoid lengthy reading, and also because I still have a lot of planning, calculation, research and design to do, I will post the whole project by chapters, one chapter every few days as I figure out the details.
Today I will lay out the different projects included in my outreach plan, so here we start:

Chapter 1: Assessement of our home energy use.
We moved in in February 2010, and we have now enough data to assess our energy usage. First step will be to get that data from PUD and log it into this website. I hope to also do some analysis as to where we can make changes with quickest payback. Consequently, the following chapters content and their order may change.

Chapter 2: Greywater system.
This system was already running in my previous home, and is described in this site (and linked to from builditsolar.com) at:
[ My Greywater System ].
Our new home presents some challenges regarding the implementation of the surge tank (below ground), the reedbeds will need to be frost protected (the previous reedbed died during the 2008 blizzard). Re-installation will require some re-design as well.

Chapter 3: Rainwater System.
This too was running in our previous home, the rainwater was used to flush the toilet. The system included a first flush diverter that worked very well until the 2008 blizzard cracked it (frost damage). Some lesson learned and consequent redesign required! Installation more challenging due to house setup, but a lot more roof area, increasing potential.

Chapter 3: Test of a Radiant Hydronic Wall.
I will remodel a room in our basement, that is unused at the moment. This is the coldest room of our home, and is a prime candidate to test a more efficient heating system. I will try a radiant wall, as described in builditsolar.com. The heating fluid will be electrically heated initially, to prove the concept of the radiant wall.

Chapter 4: $1K solar hot water system.
Following builditsolar.com multiple examples, I will build a solar collector and storage tank to heat water. The collector will initially heat the room modified in chapter 3, then the size of the collector will be increase as more exterior walls are converted to radiant, in order to keep the system as balanced as can be while it is been installed.

Chapter 5: Solar Hot Water
The electric hot water heater will be downsized, and a solar hot water tank will be installed upstream, so that the hot water is pre-heated by the solar system. The hot water tank will use the excess heat from the hydronic system. A hot tub will be connected to the hydronic system as well, in order to dissipate the extra heat and avoid damage from excessive water temperatures.

Chapter 6: Super-insulation.
All exterior walls of the house will be thickened. The radiant walls modified in the previous chapter already received extra insulation. This chapter will be about adding that same extra insulation to the remaining non-radiant exterior walls, so that the whole house shell has been upgraded. Attic insulation may also receive extra insulation if needed. Not much can be done to the slab though.

Chapter 7. Controlled ventilation.
Closely following insulation improvements, controlled ventilation will provide fresh air, avoid back-draft from the wood stoves, and reclaim the heat from the exhaust stalled air.

Chapter 8: Drain water heat recovery.
I will design a system replicating the GFX, to reclaim heat of the waste water from showers and other warm water users. This chapter will require careful design and assessement, as I am not sure the amount of energy reclaimed is worth the material to reclaim it.

Chapter 9: It never ends.
There is always improvements possible. Here are a few...
After at least one year of rainwater usage, it will be a good time to analyze the water, and determine if it is suitable for higher "grade" of use, such as laundry. The greywater system will also be assessed after one year of use. If the reedbeds filter the water sufficiently so that it can be stored for 24 hours or so, then the greywater may be used for toilet flushing, freeing more rainwater for laundry, or showers, or any suitable use. Our rainwater would be used 2 times before ending in the sceptic system.
The wood stoves may be connected to the hydronic system, to distribute their heat though the house. Not an easy task.
A photovoltaic system may be installed using laminates, that I would assemble to make solar panels. On top of the low cost of laminates (~$1 to $1.5 per watt), they may qualify for maximum payback from PUD (manufactured in WA?).

Chapter 10. Getting them to come.
As our micro-farm develops, we hope to have more traffic to our home. The glaring solar collector and blooming reedbeds should raise curiosity. That is when the real outreach will start.

What about codes and regulations? Each project will be done following as closely as possible existing regulations, If regulations don't exist yet, then best practices will apply. It is possible some of these projects will be scrapped due to impossibility to meet codes. I welcome all advises on this important matter.

Disclaimer: Don't try that at home!

To be continued...

The Yes Men stunt

The Yes Men Stunt (in French, with video in English).

High summer despite Sun's low

Summer was hot, despite Sun's deep low.
In 2008, the Sun reached the lowest point of its 11 year cycle, and this time it was a deep low, the Sun was the coolest it has ever been since 1913. In 2009 and the following 4-5 years (half of its cycle), its temperature will rise. We can expect more 100+ summer temperatures.
According to NOAA, August and September 2009 were the second hottest on record, despite the Sun's deep low just ending.

Global Warming and the financial crisis

Remember my posts on April 2009, "Oil depletion will accelerate Global Warming", and "Changing Times"?
A reduction in oil usage (whether it is from oil depletion or a financial crisis), resulting in a reduction of particulate emission, which will make hotter summers and colder winters. This is exactly what we are seeing since Falls 2008. It may be a coincidence, but as time goes on and the pattern repeats, the probability of it being a coincidence decreases rapidly.

The Winter in 2008, Northern Hemisphere, was the coldest in a very long time. As a Master Gardener for Washington State, I volunteer for garden clinics. The most common plant diseases we were seeing in Spring: cold damage, plants that were injured or killed by unusually low temperatures.
The Southern Hemisphere Summer, happening at the same time, in Australia, was unusually hot. They had terrible forest fires.

The Summer 2009 in the Northern Hemisphere was unusually hot here in Washington state. We had 109F in my area, unseen according to locals. Here again, the damage on the vegetation is clear: a lot of dead dried trees, particularly evergreen trees in the mountains.

Now Falls has started. Although the temperatures are still warm, we have very cold nights. The day-night amplitude feels greater than usual. This also can be explained by a reduction of particulate pollution, as was measured during the 3 days following 9/11.

So we can expect the following weather patterns in the near future:
Colder Winters with higher precipitations.
Warmer Summers, heat waves, change of rain patterns, longer seasonal droughts.
Greater day/night amplitude during Spring and Falls.

Plant shade trees and super-insulate your house.

When will the American people finally accept responsibility? I suspect and fear it will take a major event, worse than the 2003 heat wave that killed 50,000 in Europe. I suspect a prolonged drought in the South, then a heat wave. Hydro dams will not have enough water, and nuclear reactors will be throttled down due to excessive heat. The stress that air conditioners will put on the grid could then overwhelm it.
A grid failure at the peak of a heat wave could be catastrophic. A large portion of the American South is unlivable without air conditioners.

It is sad that we are still debating scientists' findings.