# Calculating the output temperature of a Solar Thermal system

• spoonjabba
In summary, the thermal output of the PV-Thermal array is 67.5 kWp with a maximum flow rate of 65 L/h. The thermal output will be sustained for 2 hours due to the continuous input of 20 degrees Celsius water.

#### spoonjabba

So say I have a PV-Thermal array and assuming standard test conditions.
How would I calculate the temperature of the water coming out of the system?

The thermal output of the system is 67.5kWp with a maximum flow rate of 65L/h. Approximately 500m of 3/4" pipes.

If you know the specific heat of the fluid substance in the pipes and the initial temperature, use: ##\dot{Q}t = mc\Delta T## where ##\dot{Q}## is the rate of heat flow out of the fluid (67.5kW), t is the time during which heat flow occurs (one hour), m is the mass of the fluid from which the heat flow occurs (the mass of 65 L of fluid) , and c is the specific heat of the fluid (heat flow/unit mass).

AM

What is a kWp? Is that a typo?

Khashishi said:
What is a kWp? Is that a typo?
Not a typo. It is a term used for solar panels to denote the power output under optimal conditions with maximum solar radiation.

AM

Is there way to take into account a continuous input of 20 degrees Celsius water at the given flow rate?

spoonjabba said:
Is there way to take into account a continuous input of 20 degrees Celsius water at the given flow rate?
##\dot{Q}t = mc(T-T_i)## where ##T_i## = 20C. Work out from the pipe volume the volume of the fluid in the pipe. Then divide by the flow rate to determine the length of time (t) that the fluid will be absorbing heat flow at the stated rate. According to my calculations, fluid will be in the pipe for a bit more than 2 hours. During that time, figure out how much heat a unit of fluid absorbs. From that you can work out the temperature difference.

AM

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I understand the equation, but it doesn't take into account the constant flow of water in. After doing the math with the equation you provided I get delta T to be 235 degrees celsius which seems like a ridiculous value.

I can't really comment much unles you show your calculation and provide the values for m and c.

But just looking at your values there is something wrong here. Maximum solar insolation is 1.3 kw per m2 and the area of 500 m. of pipe would be just under 10m2, so it can't be putting out 65.7 kw. Maximuum would be 13 kw.

AM

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## 1. How does a Solar Thermal system work?

A Solar Thermal system works by using solar collectors to absorb sunlight and convert it into heat energy. This heat energy is then used to heat a liquid, typically water, which is then circulated through a series of pipes to transfer the heat to a storage tank or directly to a building's heating system.

## 2. What factors affect the output temperature of a Solar Thermal system?

The output temperature of a Solar Thermal system is affected by several factors, including the amount and intensity of sunlight, the efficiency of the solar collectors, the type and size of the storage tank, and the temperature of the liquid being circulated.

## 3. How is the output temperature of a Solar Thermal system calculated?

The output temperature of a Solar Thermal system is calculated by considering the factors mentioned above. The amount of sunlight is measured in kilowatt-hours per square meter (kWh/m2), and the efficiency of the solar collectors is expressed as a percentage. The formula for calculating the output temperature is: Output Temperature = (Sunlight Intensity x Collector Efficiency x 0.75) + Ambient Temperature.

## 4. Can the output temperature of a Solar Thermal system be controlled?

Yes, the output temperature of a Solar Thermal system can be controlled through the use of a controller or regulator. This device can adjust the flow rate of the liquid through the system, which can affect the output temperature. Additionally, the size and type of the storage tank can also play a role in controlling the output temperature.

## 5. What is a typical output temperature range for a Solar Thermal system?

The output temperature range of a Solar Thermal system can vary depending on various factors, such as location, weather conditions, and system design. However, on average, the output temperature can range from 120 to 150 degrees Fahrenheit. It is essential to consult with a professional and consider all the factors before determining the expected output temperature for a specific system.