A TRACKING SOLAR CONCENTRATOR
in re-inventing the wheel, we followed Detroits lead. A fluid recovery system, complete with a 15 pound:pressure cap does a fine job. If you have a boil-over, you save the anti-freeze and it simply siphons back into the system when it cools off. Install an automotive radiator filler cap in the piping at the top of the array as shown in figure 31. Bring the overflow tube, down to the support structure, just below the hub and install a one or two gallon container with the tube reaching into the bottom of it.
Don't soft solder any connections between the collector and the relief system. Some day, in your experiments or when the power fails to the pump, super-heated steam will blow the soft solder out of every joint. Believe this!! If you can't find a new filler neck at the corner radiator shop, use a salvaged one, but be sure to scrape away the soft solder down to clean brass before you braze or the joint will fail.
The automotive pressure cap makes it easy to fill the system if it's a closed loop. You can simply pour in from the top while the pump circulates bringing air to the high point or as we do, the fluid is pumped in at a low level with sufficient pressure to lift the 15 pound cap and expel the air. As the system heats, air will be released from the fluid at the high point and normal expansion will force it out. The alternate heat and cool cycles will eventually purge the air almost completely if you make sure the expansion tank always has some fluid available to be sucked back in.
We cannot comment much on the rest of your piping as it depends on what you have elected to do with your system. Our solar concentrator is like an electric motor with hundreds of potential uses.
Unless you live in a frost free area, for most applications you will want to circulate a water/antifreeze solution. Other materials to con- sider, if you want higher temperatures are various oils and some of the silicon compounds.
- Caution: If you are using a toxic material as your heat transfer fluid, then you must use a double heat exchanger system in contact with potable water. Some local laws require this as does good common sense
Figure 32 shows how a heat storage tank open to atmospheric pressure can serve as a double heat exchanger. A leak of toxic fluid from the pressurized collector system is diluted in the tank and could not enter the city/well water unless its exchanger leaked AND it was below atmospheric pressure at the same time.
