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Publication Title | The Basics– Site Survey

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The Basics– Site Survey

site survey measures the renewable power potentials of a specific location. The natural sources Amay be solar, hydro, or wind. A site survey determines not only which sources are present at a specific place, but also accurately estimates the amounts of power offered by these sources. A site survey asks only two questions. What power sources are available? How much power is offered by the

sources?

Marshalling your forces...

Site survey is not conducted in an office, but at the specific site. You cannot accurately survey a site for renewable energy potential without actually being there. And you must be accompanied the instruments necessary to make measurements.

The amount of time required for a site survey varies. In some cases, like solar and hydro, a site survey can be done in a few hours. Other sources, like wind, will require several months, or even years, of measurement before accurately estimating the source's power potential.

So put on your knee-high rubber boots and let's do some site surveying.

Surveying for Solar Power

A good solar site is easy to recognize. It is the not–so–good sites that are difficult to survey. What every solar system needs is ALL THE SUN IT CAN GET. A good solar site sees the Sun come up at Dawn and go down at Sunset. A good solar site faces SOUTH. A good site directly sees the Sun all day and is unobstructed by mountain ridges, hills, trees, or buildings. If your site has dawn to dusk direct sunlight, then you're in and need to survey your solar no further. All you need is an accurate compass to face your PV array directly SOUTH. Be sure to figure in the difference between magnetic North and true North for your location. This difference between compass North and real North is known as "magnetic declination". For example on the West Coast of the USA, magnetic North is about 19° East of true North. Check a topographic map of your area if you don't know your local magnetic declination, it's printed on the map.

While all day sun is what we all want, few sites actually have totally unobstructed access to direct solar radiation. Then solar site survey becomes a war of attrition. Each obstacle preventing the Sun's rays from directly falling on the solar face must be located and its effects quantified.

Exact placement of a PV array is critical. Move the array a few feet and the yearly total amount of solar radiation changes. Determining exactly how much solar energy a specific location receives throughout the year is not easy. And to further complicate things, the Sun's angle keeps changing with the seasons. This means that obstacles that don't shade the array in the Summer may do so during Winter.

The array needs to be located at that one specific place on a site that receives the most sunshine. The Solar Pathfinder is THE tool for this job. It takes all the guesswork out of predicting how much sunshine the array will receive, at a specific site, throughout the year. The Solar Pathfinder is easy to use and accurate enough to measure changes in array position down to a few feet.

The Solar Pathfinder

The Solar Pathfinder uses a highly polished, transparent, convex plastic dome mounted on a platform containing a compass and a

bubble level. Reflected in this dome, the user sees a panoramic view of the world around him. All the obstacles to direct sunshine are plainly visible as reflections on the Solar Pathfinder's polished dome. Since the dome is transparent, the user can also see the sun chart within the Solar Pathfinder. This chart shows details of the Sun's path for every month of the year. The sun chart is also calibrated by the hours of the day.

The dome has slots in its sides and the user traces the outline of the horizon's reflection on the dome onto the sun chart. The traced line shows exactly at which hours of the day, and months of the year, that an obstacle will shade the PV array. From this information we can predict the array performance at any time of the year. The Solar Pathfinder can be used anytime of the day, anytime of the year and in either cloudy or clear weather. In fact, we found it easier to see the reflections in the dome when it was overcast, at dawn, or at sunset.

We ran sun charts for many different locations around our site and compared the amount on sunlight received at each. By doing this, we were easily able to select the best place to put our ground-mounted array. And I mean down to the last foot! No guesswork, no "Well, it looks to me...", just the straight and accurate facts. Shown below as an example is the sun chart of our PV array's site at Agate Flat.

The Basics- Site Survey

Cost for the Solar Pathfinder is $149. shipping prepaid in USA. This includes a metal case, tripod, an instruction manual, and sun charts. Considering that PV arrays can cost thousands of dollars, the Solar Pathfinder is inexpensive because you can put the array in the just right place to get its maximum yearly power output. The maker of this instrument is: Solar Pathways Inc., 31 Chaparral Circle, Glenwood Springs, CO 81601 or telephone 303-945-6503.

Home Power #21 • February / March 1991

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