Solar Electric System Sizing Guide
What do I need to run my home on solar
power? This is usually the first question asked by those who are exploring
the idea of using solar power to run their home. This page will help you to
answer this question, and design a system that is suited to your individual
There are four questions you need to consider carefully and answer in order to create a good system design. How much energy is
available? How much energy do you use? How efficiently are you using the
available energy? and How much will it cost?
The first question addresses the availability and type of energy at your site: is it solar, wind, and/or back-up generator? The
main source of energy we focus on is solar. To assess the amount of solar
energy available to you, you must find the number of peak sunlight hours at
your site. This information can be gathered from observation or from looking at
tables and maps of peak sunlight hours in your area. These amounts vary
seasonally, so you want to design your system to be able to work when you have
the least amount of solar energy available.
Another form of available energy is wind.
You need fairly accurate information on average wind speed for your
particular site. Keep in mind that most wind turbines don't provide a
significant amount of energy at sustained wind speeds below 10 mph, and that most wind
turbines need to be 10-15' above nearby obstructions, such as trees or
buildings. A common application for wind is to use it as a supplement to solar
power. For example, when storms move into an area, you lose solar potential
because of clouds. However, the storm usually increases the wind potential, thus
allowing your system to keep producing power.
For larger systems, or systems having
particularly large loads, your back-up generator can also be made into a
regular contributor. Because we are solar and renewable energy oriented, we like to
minimize the use of fossil fuels as much as possible. However, in some cases,
running a generator one or two hours a day can reduce the overall cost of the
system, thereby providing a solution to the cost of a large solar system.
The second question you will need to address is the amount of energy that
you use. In order to accurately size a system you need a fairly accurate idea of your
average daily power consumption. It will take some time to estimate how many
lights will be on and for how long, or how many hours a day the furnace blower
will be on, especially if the house isn't built yet! However, this is
critically important to the success of your system. You don't want to
over-estimate, since this will artificially inflate the cost, and you don't
want to under-estimate because this will create a system that is too small,
leading to a greater chance of system failure, and shortening the life of your
batteries. Therefore, it is important to spend the time to accurately assess what
appliances and lights you use and for how long, and find the correct watt
ratings for each appliance and light.
While assessing your power needs, you can
answer the third main question: How efficiently do you use power? This is a
good time to note what appliances and lights in the house use a large amount of
power, and figure out if you want to replace them with more efficient products.
Some items which provide considerable savings in energy are switching from
incandescent lights to compact flourescent lights and switching to propane
appliances. Some of the most common items to switch to propane are the dryer,
stove, water heater and space heating. It is also a good idea to take a look at
your refrigerator. It is often more cost effective to replace your
refrigerator, especially if is it an older model, with a more energy efficient
model. You also want to eliminate phantom loads by putting anything with a
remote control on power strips so that you can completely turn off these units
when not in use. Those appliances with a clock (such as microwaves, stoves and
stereos) can also be put on a power strip.
If you are building (or even remodeling) a
house, you may want to consider using passive solar design. By using some
fairly simple design principles, you can create a house that stays warm in the
winter and cool in the summer, helping to decrease the amount of energy needed
to heat and cool your house.
All of these considerations lead to the
last (and some say most important) question: how much will it cost? The more
accurately you assess your energy needs, and the more energy efficient your
appliances and home are, the more cost efficient your design will
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