These tests are not highly accurate but are only intended to give a rough sense of what is happening by using familiar units, conversion factors and values that people are familiar with because they use them day to day.
This website is a Work in Progress and is constantly being updated

The ERTR Temperature Rise and Fall over a Typical Fall Day and Night
Inside Blue / Outside Purple

By Mid- October we started raising the insulated curtain to let in the morning sunlight and then lowering the curtain in the afternoon when the solar heating ended. On 10/30/2021 was one these typical days shown above. With the curtain up, the Sun heated the room from 53F @ 10am to 91F @3pm for an average solar gain rise rate of about 7.6F per hour. Over the next 19 hours, mostly with the curtain down, the cooled room cooled from 91F @3pm to 58F @ 10am for a loss rate of 1.7F per hour.

We will use a these approximate values as rules of thumb for :
ERTR Fall Temp Solar Gain Rate = 7 Deg F / hour or 35F for 6 hours
ERTR Fall Temp Night Loss Rate = 2 Deg F / hour (with insulating curtain UP) or 35F for 18 hours
ERTR Fall Temp Night Loss Rate = 1.5 Deg F / hour (with insulating curtain DOWN)

The ERTR Temperature Rise with 1KWH of Electrical Heating

On 11/11/2021 at 4am, with an outside Temperature of about 40F, we heated the room with a small electrical heater that has a watt-hour meter to monitor it. After heating the room with a total of 1KWH of electrical energy the room air temperature was about 5F above when the heating started. So 1KWH/5F = 200 Watt-Hours / Degree. We will use a this approximate value as rules of thumb #1:
ERTR Total Room Energy to Air Temperature ratio = 200 Watt-Hours / Deg F
(no extra Thermal Mass)

The Empty ERTR Typical Solar Gain Energy Capture for Fall Season

Using the: ERTR Total Room Energy to Temperature ratio X Typical Solar Gain Temp Rise 200 (Watt-Hours / Deg F ) x 35 (Deg F Solar Gain Temp Rise) = 7 KWH

We will use a this approximate values as rules of thumb for :
Empty ERTR Total Solar Gain Energy Capture per Day = 7 Kilo-Watt-Hours / Day

at $0.20 per KWH this is $1.40 of equivalent electrical Energy Cost for heating approximately 100 square feet of living space.

The Energy Capacity of 1 gallon of Water
A Useful Calculated Rule of Thumb Metric #2:
2.5 watt-hours / (Deg F - Gallon H2O)

The Empty ERTR has an Equivalent Energy Capacity per Degree Fahrenheit of:
80 Gallons of Water
Using the conversion factor for the total Energy Capacity of the ERTR per Degree F divided by the Energy capacity of water is:
200 watt-hours per Deg F / 2.5 watt-hours per Deg F -gallon = 80 gallons of water

Total Energy the ERTR Captures in a Day

If we use the previously measured rule of thumb of Energy to Air Temp ratio of 200 watt hours /per deg F, then we can calculate an estimate of how much Total Solar Energy the ERTR Captures in a Day:

(6.7 degrees per hour) x (6 hours) x (200 watt-hours /per deg F) / (3 sqr meters glass) =

Total Energy the ERTR Captured in a Day = 2.6 KWH per (square meter) per day

The map below suggests that as much as 5 KWH per day may be available.

There may be some reflective loss due to the glass and it’s angle of incidence but the estimated there is probably much more solar energy available than what we are catching.