Chapter 3: sizing a system – Beckett SolarHot User Manual

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If you want to know the exact impact of your tilt and direction on the performance of your system you
can go to www.retscreen.net and go through ther solar calculator. They have weather data from every
weather staton n North Amerca, as well as a database of most solar collectors avalable today. You
smply enter the weather staton that s most approprate for your locaton, ndcate the tlt of the collector as
well as the orentaton (azmuth), and the software wll spt out the overall energy produced. You compare
that wth the perfect orentaton and you can see what mpact your stng decson has on the overall
output of the system. Feel free to play around wth ths database. It provdes a wealth of nformaton.
Don’t be discouraged if you can’t figure out all of the other inputs because they are not pertinent to the
queston of what mpact your stng has on the performance of your system.
Note: Later n the book we wll dscuss szng of the collector area. The rules of thumb that we go over
are based on collectors beng ponted south and angled to match the lattude of the ste. If you need to
use an angle and pitch that significantly reduces the solar gain of your collectors (as measured by the
Retscreen database), I recommend addng collector area to get back to the same quantty of energy
collected.
Issue #3—Shading: If you mount your collectors n a locaton where they are shaded durng a porton
of the solar day or are shaded durng a porton of the year, you wll reduce the output of the system.
There are no exceptions to this rule. While you can increase the number of collectors to increase your
heat gan whle the sun s shnng, a shaded solar collector won’t collect any heat. Now you are torn.
You want to do the rght thng for the envronment by gong wth solar energy but t seems lke you are
movng n the wrong drecton f you have to cut down trees to get there. I can help wth ths a lttle. The
BP solar website can show you that the environmental benefits of installing a system equals the impact
of planting 1 acre of trees. So unless you live in the forest, the environmental benefit of adding a solar
hot water system s greater than the harm of removng a few trees. We removed 2 trees from our ste
(1 pne and 1 walnut) and t broke my heart to do t, but I knew polluton-wse we would be better n the
end. An unexpected benefit was that by removing those two trees, our yard and smaller trees in it have
flourished.

Chapter 3: Sizing a System

In ths chapter we wll only cover szng of systems for domestc hot water. Whle these same prncples
and systems work well for space heatng, the bulk of ntal applcatons le n the hot water sector.
There are a couple of rules of thumb that are useful for szng solar hot water systems. Granted,
these rules of thumb apply for the average person/famles water usage. If you bathe once a month
and wash all of your dshes n the creek, they wll provde more hot water than you need. If you have
teenagers who partcpate n sports and lke to take multple 30-mnute hot showers per day, the szng
wll probably provde a smaller fracton of your hot water. Dependng on your locaton, the sze of the
system, and your usage patterns, you should expect a solar hot water system to provide between 40-
80% of your hot water needs. Ths s also a rule of thumb. Personally, we have turned off the back-up
elements n our hot water tank so that the sun s provdng 100% of our hot water. Ths may lead to a
few showers that aren’t quite as hot as some would like, but the environmental and financial benefits
are worth t for us.

The Beckett SolarHot Advantage: Our systems are scalable. It s easy to add addtonal
collectors to the system. It’s just as easy to use a larger hot water tank or put two standard
tanks together n case you decde that you need addtonal hot water storage.