DIY solar collector heat output

[jamesBen80]

I've been messing around with some 2nd had solar thermal tube collectors I've been given and found. So far I've got 60x 1.8m Kingspan thermomax tubes in 2 30 tube manifolds heating a 200l megaflow cylinder and a 4000l water storage tank I've converted to a hot tub / pool. I've only cobbled things together with garden hose and jubilee clips to prove concept which seems to be working well. My question is how do I know the heat output of the system in kwh. To know if its worth preserving with and spending money on to make it more permanent and reliable? When the tanks heated up to about 45C it switches over via a 3 port valve to the 4000l tank which it can approximately give 1C increase an hour on a good sunny day around 12noon ish. But I want to be able to measure the kWh over an entire season, so i'd nee to know the volume of water and the temps coming off from the solar and returning to the solar panel right? does such a thing exist?

 

[Swwils]

Energy required to heat 1kg of water 1C doesn't change regardless of temp.

Your 4000L store will need 4.66kWh to change 1C.

 

[flameport]

But I want to be able to measure the kWh over an entire season,

Heat meter, https://stockshed.com/pages/heat-meters-stockshed-uk

 

[OvertonPlumber]

Are you running direct water through your panels? As there designed to work with a glycol mix

 

[jamesBen80]

No there is a heat exchanger for the 4000l pool and the solar tubes use the primary coil inside the 200l megaflow tank. I've not put any glycol solution in yet as I don't want to spend money if it doesn't work. On days like today with the tubes in full direct sun the circulating pump will be running continuously from 7 to 8am showing a water temp in the solar tubes header tank of 60-65 C and the it will bring the 200l megaflow up to about 45 C then switch across to the 4000l which by about 6pm will be up to about 33 C. However on overcast days the temperature in the header barely rises about 40 C and the circulating pump may only come on once or twice for a couple of minuets to remove the heat from the tubes header. This is why I want to monitor it for a season with a kwh meter to see just how much the system is doing in real terms. i.e. how much money is it saving vs using electric or gas. So far the systems cost me a couple of hundred pounds and we get enough hot water for 2 or 3 showers most days in the summer and when its sunny it will bring the pool upto 30-35 C after a couple of days of clear blue skies. However if I brought the system from new and paid someone to install it costing £1000's I doubt it will ever pay for itself, as it only seems to preform well in direct sunlight not when it's cloudy. Incidentally if its clear blue skies in winter, it will still heat the water in the 200l megaflow enough to have maybe 1 quick shower, so the vacuum insulation in the tubes must work!