Heliostat

There are many applications for heliostats, here are a few...

* Water heating
* Lighting
* Desalination (Evaporating salt water to make fresh water)
* Producing steam to generate electricity

Here are a few of our experiments.

 

9X (CSP) Heliostat flat plate collector water heating experiment.

(x heliostat focused on collector

9X solar concentrating heliostat focused on flat plate collector.

9 square foot heliostat = 836 watts of potential solar energy.

Flat plate collector

The flat plate collector was constructed with 5/8" plywood, thin galvanized sheet metal, drywall screws, silicone caulking, and high temperature black paint.

The collector measures 14" x 12" x 1 1/2"
It holds 1/2 gallons or approximately four pounds of water.

 

 

 

Heating cycle - Flat plate collector holds 4 lbs water (1/2 gallon)
Ambient air temp 46°F
Altitude 7200 feet

Time
Temp °F
Temp change °F
(from last measurement)
Net energy gain
BTU
Net energy gain
Watts equiv.
System Efficiency
Re-radiation
BTU*

Re-radiation
Watts

0 min
52
5 min
88
+36
144 BTU
506
61%
-12btu
42 watts
10 min
120
+32
128 BTU
449
53%
-24btu
84 watts
15 min
147
+27
108 BTU
379
45%
-36btu
127 watts
20 min
170
+23
92 BTU
323
39%
-48btu
169 watts
25 min
197
+27
108BTU
379
45%
-56btu
197 watts
30 min (boiling)
198
+1
-
-
-
-
-
35 min (boiling)
198
+0
-
-
-
-
-

* The re-radiation index was taken from the cooling cycle chart below. The collector was removed from the heliostat focal point and temperature measurements were taken every five minutes to see how much heat energy the system was losing due to re-radiation. A collector with smaller surface area or better insulation would reduce re-radiation losses and increase net system efficiency.

Cooling cycle - 4 lbs water (1/2 gallon) in flat plate collector (ambient air temp 46°F)
Altitude 7200 feet

Time
Temp °F
Change °F
BTU loss
Watts equiv.
0 min
197
5 min
182
15
60
211
10 min
169
13
52
183
15 min
157
12
48
169
20 min
146
11
44
155
25 min
137
9
36
127
30 min
129
8
32
112
35 min
122
7
28
98
40 min
115
7
28
98
45 min
108
7
28
98
50 min
102
6
24
84
55 min
97
5
20
70
60 min
93
4
16
56
65 min
89
4
16
56
70 min
85
4
16
56
75 min
80
5
20
70

 

PV / Water heater hybrid

X9 heliostat and pv / hot water collector

The X9 Heliostat focused on an experimental hot water heater / PV collector.

 

X9 pv / hot water collector

A closer view shows that this hydro-thermal / photo-voltaic collector is nothing more than a ten gallon aquarium with a small solar panel submerged in the water in front of the black plate heating element. The solar cell is encapsulated in clear epoxy so it is waterproof. The surrounding water keeps the solar panel from exceeding 160°F. What we don't know is how long the solar panel will hold up under nine times concentrated solar power or '9X CSP'.

The solar panel is powering a small gearmotor as a load test to simulate a recirculation pump.

PV output

no concentration (1 sun)
Load (ohms)
Volts
Amps
Watts
no load
8.0
0
0
1000
7.7
.008
.061
100
7.3
.073
.533
10
1.7
.170
.289
9X concentration (9 suns)
Load (ohms) Volts Amps Power Power gain factor at unity load
no load
8.0
0
0
0
1000
8.0
.008
.064
1.05
100
7.8
.077
.601
1.13
10
5.6
.575
3.22
11.14

A wider sample of data would need to be taken to accurately determine the maximum power point of the PV panel at 9X solar concentration and no solar concentration.

A few things that the data does tell us about the PV panel under 9X CSP (9 suns)

Hot water

10 gallon aquarium
Ambient temperature 50°F

Time
Temp °F
Change °F
BTU
Watts
0 min
39
30 min
50
11
916
537
60 min
63
13
1083
634

 

Lighting

Heliostat Here is a picture from behind the Heliostat. If you look close you can see the relay mirror and solar spot in the very center of the photo about 120' away.
Heliostat Here is a picture looking through my shed window at the target mirror. Clearly visible is the mirror plane of the heliostat.
Heliostat Here you can see where the sun has been redirected through the window of the garden shed...
Heliostat

Illuminating a small 9 watt solar panel inside .

Fine for battery maintenance but not much more. The addition of natural light to a normally dark shed is very nice.

Heliostat Here's a pretty thing. It is amazing how much entertainment value you can get from a heliostat shining through some diffraction paper.

 

Water heating

Solar heated bird bath My mom suggested that that we use one of our heliostats to help keep her birdbath thawed out during the winter.
Solar bird bath We built a plywood stand with a hole cut in the top to set the birdbath over. The mirror that reflects the concentrated solar energy up onto the bottom of the basin is plywood covered with a sheet of reflective mylar. We painted part of the birdbath black on the bottom so that it would absorb more heat.
Solar birdbath Of course, like any heliostat application, this works only when there the sun is out. An electric birdbath heater is the only way to guarantee that it will never freeze.
Solar birdbath

We only had a couple of hours of sunshine the day we took these photos so there is only a small circle of thaw right in the middle of the birdbath.

Even though the ice may not be completely thawed it is easy to lift out of the basin because the bottom melts first. My mom finds this very convenient since she likes to empty and refill the birdbath every day with fresh water anyway. It is usually impossible to remove the ice from her un-heated birdbath.

We also noticed that when there is sun the "heliobath" stays thawed once it has been refilled, even in sub-zero temperatures. This is not the case with her other birdbath which will freeze over in an hour or so.

This system would work better if we used a thin metal basin and painted the whole bottom black with a selective solar coating like SOLKOTE from SOLEC company.