Contents of the SOLARHME.TXT file
Solar Home Independence Project
Copyright (C) 1989 all rights reserved
by Larry Ashworth
Power Mountain Systems
Cora, Wyoming 82925
All donations cheerfully accepted.
I will send you more information, and will do my best to answer any
questions you may have about solar or wind power, or related topics.
Please include a gratuity to cover postage and my time. ($10?)
If you have a really major requirement let me know as I may be able to
help. I have years of Analog and Digital circuit design, and printed
circuit board design experience with which I may be able to help.
-- TNX --
You will find here notes, formulas, and information on solar power that
I'm using to plan a solar self-sufficient home. I'm distributing this for
the benefit of those interested in the same sorts of information, in the hopes
that others can be drawn into an open forum on this topic. I'd like to hear
from others with information, experience, and opinions.
I don't claim to have invented anything, but I have read many things
scattered through many different sources. This is an attempt to consolidate
some of what I've found. You may not modify in any way what is here, but you
can put together your own notes which I would love to read. I am sure there
are a great number of others also interested.
This document can just be copied to your printer. An overt attempt was
made NOT to use any special print commands. Content is more important than
The purpose of this project is to prepare the technical details for
building a home that will be 100% energy independent. This project has been
something that I have been thinking about for some time, and I am totally
convinced that it is not only physically possible, but is a practical, and
The subject of solar power encompasses more than just photovoltaic
"solar cells". It encompasses wind, water, and the heat that the sun radiates.
Most, if not all, sources of energy can be traced back to the sun. This is the
key to what I am convinced is the "right" approach to harnessing the sun, and
that is the diversification of solar power recovery.
Don't depend on a single system to obtain the necessary energy, but use
several. Use the wind, and solar cells. Use the heat from the sun, and moving
water if available. Combine the different energy resources that are open to
you, with sensible storage, and with little, if any, change in your lifestyle
you can be totally energy self sufficient.
Water for Heat.
The single most expensive aspect of living in the north half of North
America, is keeping warm. With the deregulation of gas, and other market
pressures there are no "inexpensive" sources of energy. The combined needs to
keep our homes warm, and water hot, comprises 70-80% of your energy bill. The
one thing that would make the biggest difference in our energy requirements
then, is to tap in to the sun. How much energy can we get from the sun? How
can we store all that heat energy for a cloudy day? Let's take a look at the
For illustration we will use the weather information for northwest
Wyoming. In the worst part of winter the sun will produce 782 BTU/HR/SQR FT.
Now we know that the sun shines there an average of 6 hrs/day. We also know
that using a flat plate solar collector we can absorb 58% of the available heat
from the sun. Due to the effects of weather, the effective heating of the sun
will be 69% of maximum.
If we use a 4 by 8 ft. solar panel then, we can absorb 32*782*.58*6*.69
which equals 60,087.63 btu. 3410 btu is equal to 1000 watts of energy per
hour, so this means that we can get 17,621 watts of thermal energy each day
from the sun, in the winter! We can get nearly three times this amount in the
The only catch could be heat losses when then there's a cold wind
blowing across your solar collectors. The principle point I want to make is
that the energy available is very great, and that even a small system can
greatly contribute to lowering your energy dependence.
If we were to spread the energy out over a long period of time, this
would be equivalent to an electric 1,000 watt heater running nearly 18 hrs a
day. Or if you prefer, picture 10 100 watt light bulbs on for 18 hrs. To me,
this is an amazing amount of energy from just one collector. The sun is an
incredible energy source, that provides us more energy than we can use. All
we need to do is harness it with applied intelligence.
How do we store the energy? I intend to use water for heat storage,
and for the heating of our home. Water has a great capacity for the storage of
energy. One gallon of water raised one degree, stores 8.33 btu. Room
temperature is about 70 degrees in the average home. If we use water for heat
and we use a 1,000 gallon tank, and if we allow the temperature of the tank to
rise to 190 degrees then we are storing 1,000*120*8.33 = 999,600 btu. This is a
tremendous amount of energy, and enough to heat a home for 2.5 days. Now as
the water cools it becomes more and more difficult to get all the energy out of
the water into the air.
An ideal home heating system would be to heat the floor with water
circulating through it. Due to the very large radiating area water as low as
80 degrees can be used to heat your home. This type of heating system also
requires a lot less electricity than a furnace would need (due to the large fan
a furnace uses), since only a small pump to circulate the water is required.
How many collectors do we need for heating a home, and provide the hot
water that we need? Obviously, exactly how long the heat from the tank will
last and how many collectors we need to heat our home, will depend on how much
heat it takes to keep the house warm, and how much hot water we use. We also
need to take into account the heat losses from the tank, and from circulating
the water under the house, if it is necessary. In the house we are living in
now, it takes about 5,000 watts of heat to keep the house comfortable when the
outside temperature is 5 degrees. This means that if the temperature were to
remain at 5 degrees 24 hrs, it would require 120,000 watts of energy would be
required. 120,000/17,621 = 6.81 We can meet our heat requirements the, with
7, 4 by 8 ft panels. If you were to use a total of 10 panels, you would have
enough heat generation capacity to keep you warm even at the lowest
While we are on the subject of collecting heat from the sun, let me
point out that there are other sources for heat. You may already be using
wood to supplement the heat for your home. There are heat exchangers made,
that allow you to extract heat from the firebox, heating water. In the wilds
of Wyoming, when the temperatures dip far below zero, I am going to use this
method to pump extra heat into the system. Any really workable design must
trade off one criteria to balance another. I intend to limit myself to 10
panels for heat collection, and supplement with wood when and if this isn't
sufficient. If you go too far then costs get totally out of line with benefit.
Even if you want to remain in town, a simple heat exchanger can reduce your
hot water bill. As I may have pointed out before, 15% of your heating bill is
hot water. If you are already using wood, then you may want to take advantage
Now, it should be pointed out that the worst temperatures, usually in
January, when the sun is beginning to generate much more energy. Which means
that these figures are actually quite conservative. Also, it should be pointed
that an energy back up such as a wood stove, should be available in case the
weather decides to ruin your plans.
The bigger the storage tank, the larger the quantity of heat that can
be stored. This would lower the possibility of running out of heat, and reduce
to some degree the energy required to pump the water since its' temperature
could be maintained at a higher temperature. There is a point of diminishing
returns, where costs may not justify the returns. I am planning to use 1,000
gallons unless I get a good deal on a larger tank.
I'm looking into the feasablilty of building a tank just for this
project. It would be 6' by 6' by 6' for the water, with the tank standing 7'
high. Rather than have heat exchangers immersed in the water, I can use pipe
soldered to the sides of the tank, and the tank itself could act as the heat
exchanger. If the pipe is soldered (welded?) to the tank on the outside, then
it would be possible to foam in the pipes when the outside of the tank is
insulated. Using all four sides, one side could be used to heat the tank
from the solarc collectors, one side could be used for hot water heating in the
house, one for heating the home, and finally one left for heating the tank from
the wood/coal stove heat exchangers. This way, the water in the tank is never
in circulation, and is used only for the storage of heat.
A very nice way to reduce water volume is to put rock into the water,
which lends its mass to the storage of heat. If you have an open tank you can
put large, clean rock into the system reducing the volume of water being
stored, but also reducing the energy stored in the system. Depending on the
rock you use, you can get up to 80% of the heat storage of water.
Exotic materials are available which have latent heat temperatures very
near the range that is ideal for heating systems. This allows extraordinary
storage capacity if you're willing to accept the challenges of exotic
pioneering. Much work has been done on this subject, and if you have a good
library near by you can find a great deal of information. As an example,
paraffin is often used.
Personally I prefer to keep the system as simple as possible, which
means using basic technology that isn't complicated, but which yields excellent
I had an idea that you might find interesting. I was visiting a
friend who has power hooked up to a little fridge, and nothing else, in the
dead of winter, surrounded by subzero temperatures outside.
Since I've been thinking about heating with water, it was only natural
that I thought, "Why not cool with water?". If you mix antifreeze with water
in a 50/50 ratio it's nearly impossible for it to freeze. Even at 50 below
zero. Why not circulate 50 gallons at night to cool it, and store this cold
water in an insulated container, and then use it all day to keep the fridge
cold? You can build a simple heat exchanger to install in the fridge. Cold is
free. Why not use it. Depending on your climate, you could power the fridge
6-9 mos. of the year or more. You would need a little pump that would turn on
as required, but this would be nothing compared to running a compressor. It
could be that natural convection currents alone could be enough which would
eliminate the need for a pump.
There are solid state cooling devices that I'm looking into now, that
might work out better than a compressor for the summer, but I need to do a
little more research before I make a grand conclusion.
The formula for deciding the cooling requirements of a fridge is:
A * (1/R) * (delta_T) = btu per hr
A=surface area; R=insulation r factor; DELTA_T=temperature difference
between inside and outside.
Calculations for the energy requirements are roughly the same as for
heat, except we are trying to keep the water cold. Raising the temperature of
water takes the same amount of energy as we discussed before. (8.33 btu / gal
/ degree.) If we're trying to maintain a 40 degree temperature inside, rough
calculations indicate that it would take 200-250 btu. Since 50 gallons of
water at 0 degrees raised to 35 degrees = 14,578 btu, we can maintain
groceries at the right temperature for much longer than 10 hrs. After 10 hrs
it gets cold again outside, and again we can cool the water with convection
water flow through the outside cooler.
This illustrates the feasability of reducing the energy required
for cooling, and may give you some ideas on how to implement this concept.
Before you make a decision on going totally solar, you need to have a
realistic sense of the power you require to live the way you want. Take a
close look at how many lights you have on, what appliances you need, and then
add it all up. You see, it's the average on a daily basis, that determines
what kind, and how much power you need. Storage of electricity in batteries
allows great surge capacity, so bursts of use can be handled very well. It's
the average we need to be vitally concerned about.
Look at your monthly power bill, and think about how much of that you
need to use, and how much you can save by making some of the changes we are
disussing here. Edison was right, and many appliances work more efficiently
on d.c. It's safer too. Look at lighting and you'll see what I mean.
There are basically 3 major sources of electricity available to the
typical homeowner, they are Photovoltaic, Wind, and Water. As I said at the
start, you want to take advantage of the best resources open to you, and
combine them to form an integrated system. Rely on several sources, not just
one, to provide a secure energy system. Do a little at a time.
Power production with wind, and direct sunlight, are intermittant and
need to be stored for later use. Later we'll get into batteries, and look at
the economics of energy storage. You may want to save that juice for a rainy
Water is the most desirable way to get electricity, but few have access
to it. It's prime advantage over the other sources, is the fact that it is a
24 hr. a day resource. A small generator running 24 hrs., can do the work of
a generator of much greater capacity running for short periods. Here are a
few guidelines you can use to see how much power that stream behind your house
could provide you.
"Head" is a term which is the difference in height between the
location of your generator sight, and the point that is the source of your
water. "Flow" is the volume of water available, expressed normally in
"gallons per minute". These two terms combine to determine the amount of
power available. Actual power extracted will also be affected by the match of
the generator, to the Head and Flow at your sight. The flow is also
determined by the size of the pipe used to get the water to te generator, since
a small pipe will exhibit higher internal resistance for a given flow than a
larger one. A 1" pipe has a flow rate limited to about 12 gal/min., and pipe
friction is high. Each time you double the diameter of the pipe you give
yourself 4 times the flow. Larger is better.
To measure Head, take a garden hose and run it from the source to the
location of your site. Measure the pressure at the outlet. (2.3) * (psi) =
Head in feet.
Flow is a function of the pipe diameter, and the volume of water
available to draw from. Care should be excersized so you don't dry up your
source, or do other ecological damage.
Head Flow Current Watts @ 12v
15ft | 27gpm | 1.6 amps | 19.2
20 | 30 | 3.0 | 36
30 | 38 | 5.0 | 60
40 | 42 | 8.0 | 96
50 | 45 | 10.0 | 120
60 | 46 | 11.0 | 132
Here you see an example of the output of a typical water power
generator. Multiple generators are used where more flow is available, and
more power is required. If the above generator were able to give you 100
watts of power, you would get 2400 watts of power a day. This would more than
equal 400 watts of solar panels, since weather is no longer a factor. The
life of a generator like this is 20,000 hours.
In some parts of the country, in some locations, the wind is an ideal
source of energy. Especially in terms of installed cost, referred to watts/
dollar. There are two problems however, that must be taken into
consideration. They are; Average Wind Speed and Energy Storage.
Determining the suitablilty of a site for a wind generator can be
reduced to the average wind speed. It might seem as though your site would be
great but the only way to know for sure is to collect data. Anemometers are
available which record and average the wind speed. You can get one of these
for less than $200, and with a little effort and planning you can be assured
that an installation at your site will work well. I have seen with my own
eyes some very expensive wind systems that were a big mistake. Don't gamble.
You may have an occasional windy day, but it's the average that you need to
An average wind of at least 6-8 mph is required to get any useable
benefit from wind power. In the case of Wyoming, there is more than enough,
averaging 12-13 mph, at the intended site. Wind speeds are higher 50 ft above
the ground, averaging on the order of 2-5 mph faster. At first glance 2 mph
doesn't really seem to be worth the effort, but since power production is a
cubed function, even small increases in wind mean a big difference in
production. If you are going to install a really large wind machine, getting
it way up in the air may not be practical, and due to it's size, even
Here is the formula for wind power generation:
Power in watts= .0031 ((blade area in ft)^2)((air speed in mph)^3)
The reason that we divide by 2 is that typical wind machines have a
system efficiency of 50%. As you play with the numbers you will quickly see
the big difference a few mph can make.
Here is an example below. We assume here a wind machine with a 12'
5 mph 10 mph 15 mph 20 mph 25 mph 50 mph
Power output Watts 22 175 592 1402 2739 21,913
Wind generators typically have their output specified at wind speed of
25 mph. You then need to calculate it's average output at the wind speed you
have at your site. Above 25 mph they start to brake themselves to keep from
being ripped apart.
As you can see a very real consideration is the servivablility of the
wind machine at high wind speeds. A 50 mph gust can destroy it, if there isn't
some serious consideration given to this problem. Wind is very powerful, at
If you have the required average wind speeds at your site, then the
economics of wind generators are hard to beat. It's my favorite, but I'll try
to be fair as I analyze the different possibilities. After all, the only
people who find the world easy to understand are bigots and fanatics. For the
rest of us understanding can be difficult, and the truth sometimes a shock.
If you're not looking for it, you'll never see it. So keep your eyes open.
Solar electric panels are very exciting to anyone planning to be free
of public utilities. Turning sunlight directly into electricity, is the
cleanest, and most trouble free way to get electricity. As long as you have
an abundance of sunshine, you've got it made. The only drawback there is to
this type of source, is cost. Installation costs, the hours and effectiveness
of direct sunlight at your site, and the power collection capacity of the
system are the facts that need investigation.
There are two different philosophies prevalent about solar panels.
One is that you should get 'self regulating' panels, which are panels with
outputs in the range of 14.5 volts. This allows direct connection to the
batteries, and the voltage will never be greater than the batteries can take
safely. The second popular methodology, is to use higher voltage panels in
the voltage range of 20v or so, which require electronic regulation. Due to
the higher output voltage they begin charging sooner, and charge longer during
the day. There is a price penalty for this, but many prefer this method.
I like the self regulating type, and due to the savings I can afford more
There are some companies which sell solar cells, and many have built
their own solar panels. Generally you can save 1/3 over conventional factory
built systems. Greater savings have been acheived by some, so you may want to
investigate this alternative. Each cell has an output voltage of approx. .45
volts. This means it would take about 33 connected in series to get 14.5
volts output. Cells are commonly available in currents up to 2 Amps. I saw
an ad recently for 2 amp cells, .45 volts, for $5.95 each quantity 1.
The principal difficulty in building your own, is just weather
proofing the panel. An installation may be in place for more than 10 years,
so it has to be done right to hold up. Short cuts can be real expensive. The
wiring of the cells is a simple matter of soldering them in series, until you
have the desired voltage.
Appliances for 12 volts
There are a great variety of appliances available for 12 volt
operation, due to the RV industry, and boating. There are also books
available that show you how to convert appliances from 110v to 12 volts. You
can operate everything from a blender to a vacuum, and live with the same
standard of living you have now. I even saw a 12v chain saw in one catalog.
Lights operate much more efficiently on 12 volts. The typical 25 watt
incandescent, gives you the same light as a 50 watt 110v ac bulb. Special
flourescent fixtures yield 4-7 times the light as a conventional bulb. All
this adds up to a dramatically reduced need for power, while having all the
light you're used to. One fixture I know of produces 1300 lumens on just 20
Watts. It sells for $29.95, and uses standard fluorescent bulbs. The reason
for the incredible improvement in efficiency over a standard fixture is the
switching frequency used. Most fixtures operate at a 60 hz rate, these operate
in the range of several kilohertz, which increases the light output of the
tube. This special ballast also consumes virtually no power, increasing
efficiency even further. 150 watts of light (110v ac incandescent), for 20
watts d.c. is a very attractive improvement.
I'm told that d.c. incandescent bulbs last longer, too.
A big advantage to 12 volt appliances, is the fact that they reduce
your requirements for 110v, and the inverter required to get it. Inverters
are reliable and desirable, but they are expensive. Even bed warmers are
available for 12 volts. Once you start looking for them, you find 12 volt
appliances everywhere. TV's, VCR's, toasters, everything you need.
Inverters, such as the Trace model 612, are designed forthe type of
service we are discussing here. This particular unit is rated at 600-900
watts continuous output. Efficiency hangs in around 90%, and the idle current
consumption is only .02 amps (.24 watts)! This means you can leave it om all
the time and have 110v power available on demand. Surge power is an incredible
1600 watts, and this reserve can be really nice if you need to start a motor.
Heart Interface, is another exciting line of inverters. They also
offer excellent surge capacity. The Trace unit sells for about $550, with a
1500 watt continuous rating unit selling for $1090. Heart Interface sells in
the same price range.
There is a line if inverters made by Tripp Lite, which are a proven
performer that sells for a lot less. The only draw back to these is the much
higher current consumption at no load. They also lack the surge capacity of
their more expensive cousins. I think the frequency regulated types are the
only ones I would consider, but you don't need it that often for most
Now that we've conquered the power problem, there needs to be a system
for storing that power until it's needed. When it comes to storing
electricity the good old lead acid battery is tough to beat. There are some
new materials and types of batteries coming in the next 10 years, but for now
there is nothing that I know of that's better.
Before you dash out and buy a dozen auto batteries, let me tell you
that they are not what you want. What you want are 'deep discharge' marine
type batteries, or commercial batteries designed specifically for this type
duty. Since the batteries last longer when they're not discharged deeply very
often, then ideally you want about 10 days storage in your battery system. If
you need 2500 watts/day, then you need 25,000 watts of storage. This is
roughly 2,000 amp hours.
This is a lot of battery alright, but 6 volt 200 amp batteries are
common for this type of situation. If you put 2 in series then you have 200
amp hours. Parallel 10 of these combinations and you have your 2000 amp
hours. The beauty of this is that you can add up what you need one step at a
time. A system set up the way I'm suggesting would last 5 - 10 years,
perhaps even longer with a good maintenance program. Good ventilation during
charging is a must, and low temperatures reduce the effectiveness of the
system. Quality batteries are imperative, but you can get them quite readily
and at a reasonable cost.
After doing more research on batteries I bought 8D truck batteries from
the Sterling battery company. At a cost of $150 to $200 they offer 12v at
about 320 amp hrs. They have very large plates and are deep discharge. This
type of battery is widely available, and you should purchase one with at least
450 minutes reserve capacity and 1150 CCA's.
When you see CCA's specified, the ratings are equal to the maximum
current you can draw (in amps) and still maintain 1.2v per cell. "Minutes
reserve" is the length of time you can draw 25 amps and still have 1.75 volts
per cell. At the end of this time your battery will have an output voltage of
10.5 volts and will be 'dead'. ((minutes reserve)/60) * 25 = 57% of the amp
hour rating of the battery.
These conversions should help you get a feel for what you are going to
need for a battery system. The 8D batteries are by far the best deal right now
in batteries for solar/wind systems.
Gas and diesel generators are very easy to get, and they are a great
help if you have peak demands (like washday?) where you need a lot of power
only once in a while, or where you want emergency backup. Running a generator
is obviously expensive due to the cost of fuel, so you want to minimize its
useage, but it can be a great thing to have around.
If you are charging batteries during the time the generator is running
and taking advantage of the maximum power output of the generator, then you are
getting the most efficient use out of it. This means you get the most for your
fuel dollar, and here a battery system can be used to great advantage. I've
heard this is particularly true with diesel generators. I know someone with
the government who studied this in detail for a proposed remote communications
site. This is the conclusion that they came to.
Diesel or gas? That's a matter to consider, but let me say here that
for 5 kw intermittant usage it's tough to beat gas. When things get really
cold diesel can gel so it needs to be heated up to burn, and so I decided to
use gas. In warmer climates, and especially for 10 kw and up, diesel may be
the best choice. I've seen some really nice rebuilt 25 kw diesel generators
that are really built, since they were intended for commercial use. With that
kind of power you could go all electric, but the bill for fuel could be a
What's the price for Independence?
The cost of your installation will be directly related to your ability
to scrounge, and hunt for the best price. Old wind machines are available at
times, and if you're mechanically inclined you can build your own generator.
As with most 'handy-man' ventures, creative people can make very small amounts
of money a long, long way.
My background is limited to Engineering, so I may find myself buying a
lot of the components. My installation will cost around $8,000, but don't let
that slow you down because it probably won't cost you that much. Of course,
there are those that will spend $20,000 going first cabin all the way. This
is an area that you can custom tailor to your individual requirements. Some,
who aren't television and computer fanatics, like me, could get by with a $1000
Due to these variations, it's nearly impossible to make a sweeping
statement as to how long it would take to pay for your system with savings.
Your utility rate, your usage, your priorities, all add up to a custom
evaluation that YOU have to make.
Some locations, such as the place we intend to build, getting power in
can be a very expensive proposition. This serves to make independence more
attractive. Just the feeling of independence, and self sufficiency are enough
to make it worthwhile to me.
Your utility company decides the rates, and you have little or no
control. If they decide they want a new truck, you pay. If they decide
they're not making enough off of you, you pay. If the Iran wants more for
its' oil, you pay. This constant, out of your control financial drain, is
something we can all do without. Central control, means no control for you as
Inflation and central control of critical services has weakened our
position as a country, and as individuals. The reason, for example, that you
can't get you're opinion heard in national or local government is that you
represent an insignificant portion of the larger populace. This inability to
hear the average person leads to misrepresentation, special interest groups,
lobbyists, and others representing those who have the big bucks, and therefore
'clout'. They can't hear you, for all the noise of those with power. The
bigger the organization, the worse the problem gets.
What made this country such an amazing power in the earth was the
individual's ability to take care of his own needs, and have a little to spare
with which he could help others and build a country. You can't help anyone,
or your country, if you can't take care of yourself...
I'm talking here about self-sufficiency where ever possible, an
American attribute we cannot afford to neglect.
Integral Energy Systems (425 Spring Street, Nevada City, Cal. 95959)
sells equipment for building a solar home. They also sell books which is the
place to start for designing your own solar home. I highly recommend
purchasing their catalog, and buying a book or two on this subject before you
build anything to generate power, or buy batteries to store it. Don't forget
the library. This has been the source for much of the information in this
article. No one wants to waste money. Do it right the first time.
I know that there are others who might agree that solar power is
really neat, but see no way to implement all this due to where they live and
the economic position they find themselves in. My answer would be to do what
you can, and it will all help. The lighting idea can save you right now, no
matter where you live! One solar collector hooked to your water heater can
save you money every day. Just do a little at a time as best you can and
you'll be rewarded. You've heard that old saw "By the inch it's a cinch, by
the hard it's hard.", this is a good example.
Please write if you have any suggestions, or positive comments.