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Kingspan Thermomax Evacuated Tube Solar Thermal Panel performance in Glasgow, Scotland in 2012

Installation of the System

We installed a Kingspan Thermomax evacuated tube Solar Thermal panel on a south-facing roof in Glasgow, Scotland, in November 2011.
It is difficult to monitor its performance directly and consistently, as the monitoring equipment we have is limited (i.e. not as comprehensive as it can be with solar PV, where everything is metered).
Until spring 2012 the monitor was in the loft, so it was a nuisance to read the hot water temperature.
The statistics in the table below give an indication of the performance of the solar thermal panel in heating water in Glasgow, which is in a relatively cloudy part of Scotland.

Construction of the System

The panel is connected to two pipes which contain a mixture of water and glycol, which prevents the mixture freezing.
The pipes form a closed loop leading from the panel to the primary coil in the bottom of a large 210 litre highly insulated hot water tank.
The water-glycol mixture is heated by the panel, and is pumped round the primary coil in the tank, heating it from the bottom.
There is a secondary coil in the upper part of the tank, which is heated by a closed loop of water pipes pumped from the gas-fired boiler to the tank.
Cold water flows in to the bottom of the tank, and hot water flows out of the top.

Setting of the System

By default the pump comes into operation when the panel reaches 8 degrees above the temperature of the bottom of the tank, and stops pumping at 4 degrees above it. This setting is suitable for summer. However, it is configurable, and a better setting for winter is for the pump to come on at 6 degrees above, and go off at 3 degrees above the bottom-of-tank temperature. This ensures that some heating takes place even when the sun's heat is minimal.

Pumping and Gas Usage

The pump has been pumping for a surprisingly large number of hours, but since it only uses 80 watts (i.e. it can pump for 12 hours before it uses 1 unit of electricity, which costs about 12p), it costs much less in electricity to run it than it would to heat the water with either gas or an immersion heater, which would probably use about 2 or 3 units per day. If you also have solar PV, the electricity for the pump is generated exactly when the solar thermal system needs it, so you don't need to import any electricity.

In winter, the gas was heating the upper part of the tank only once between 6 and 6.30 am, and did not need to come on for the rest of the day.
In spring and autumn, gas heating is reduced to 10 to 20 minutes, and in summer to zero.

Renewable Heat Premium

As of March 2012, a Renewable Heat Premium one-off payment of £300 is available from the Energy Saving Trust, to help offset the cost of the system.
If you want to know more about the Renewable Heat Premium payments, look at the Energy Saving Trust's website.

Renewable Heat Incentive

The Energy Saving Trust Scotland reports that in September 2012 the UK Government announced a proposal under its consultation scheme that domestic solar thermal technologies that are MCS certified and meet relevant required standards will attract a RHI of (17.3p/kWh) for a period of 7 years. At the time of writing this (April 2013), domestic installations can not yet apply for the Renewable Heat Incentive. The Renewable Heat Incentive is expected to be available for domestic installations from 2014. Details should be announced during summer 2013.

Solar Thermal Panel Performance

Since the panel was installed, sporadic readings have been taken, which give an indication of performance under different weather conditions.
In summer 2012, one of the dullest on record, the panel performed well, giving all the hot water needs for two people during May to August. The monitoring equipment is now located in the downstairs hall, so we can see what temperature the bottom of the tank is at.

Generally the temperature has been above 40 degrees celsius even on cloudy summer days, and has got up to 60 degrees quite often.
The well-insulated tank has a capacity of 210 litres, so the hot water lasts for two or three days, even if the second day is cloudy and little or no extra heat is produced.
We have a plan to get an extra sensor to tell what temperature the top of the tank is, which will give a better indication of whether any extra gas heating is needed. There is a place in the tank to fit this sensor, a place in the monitoring panel to fix the wire from the tank, and a place in the software and on display for it. I have led a length of bell wire from the tank through to the hall already, so it should be an easy job.
Generally in the coldest winter months, if it was dull, the temperature in the bottom of the tank was raised by about 10 degrees from the water inflow temperature, so it raised it from 10 to 20 in November and December, or from 8 to 18 in January and February.
On cloudy bright winter days it reached up to 30 degrees, an uplift of at least 20 degrees, and if it was sunny, it reached 37 degrees, an uplift of at least 27 degrees. For showering, a bottom of tank temperature of about 40 degrees seems to be adequate, so on sunny winter days, very little extra heating is needed. However, most winter days are dull in Glasgow!

The following table containing sample data from March 2012 and October 2012 (typical of spring and autumn respectively) gives some more details:

DateTimeTemperature of panelTemperature at bottom of tankWeatherNotes
5/3/2012No data for today.However, today's weather is relevant to tomorrow's hot water data.Sunny almost all day6.7 kWh of solar PV generated today
6/3/20129am2732Sunnyreadings after having one shower
6/3/20126pm 50SunnySome water used for washing up. 8 kWh of solar PV generated today.
7/3/20128am245SunnyReadings before any significant amount of hot water used
7/3/20128.30am1231SunnyReadings after two showers
7/3/20129am2629High cloudReadings after washing up
7/3/201211am2521High cloudReadings after a little more water used
7/3/201212 noon3022High cloudPump has just come into operation.
May to August 2012 Typical panel temperature was over 60 degreesTypical temperature at the bottom of the tank (i.e. the minimum temperature for the whole tank) was over 40 degrees.Sunny enough to produce all our hot water needs for every day even in this most cloudy of summers.The one exception to this was one day in August when the gas was on for 10 minutes as we had a guest staying and needed an extra shower, and at the same time it was cloudy.
September to 10th October 2012 Typical maximum panel temperature was over 50 degreesTypical temperature at the bottom of the tank (i.e. the minimum temperature for the whole tank) was over 40 degrees, and up to 50 degrees on sunny days. The hot tank is sufficiently well insulated that there is a loss of only 5 degrees or less between the maximum in the afternoon, and the following morning when the shower is used.It was sunny enough to produce all our hot water needs for every day over this time period except for three days. On these three days only, 10 minutes of gas water heating were used in the morning to raise the temperature sufficiently for showers when it had been very cloudy the previous day.
9/10/201210pmnot applicable50Sunny all dayWeather relevant to tomorrow's figures
10/10/20127amn/a47n/aTemperature before any use of hot water - a temperature loss in the tank of 3 degrees overnight
10/10/20127.30amn/a46n/aTemperature after one shower
10/10/20128amn/a44n/aTemperature after two showers

11/10/12 Today we installed a temperature sensor in the top of the hot tank.

We can now monitor whether to use any gas heating at all before a shower, and also control the maximum temperature in relation to the need to prevent Legionnaire's Disease, without wasting gas on heating the tank unneccessarily.

DateTimeTemperature of panelTemperature at Top of TankTemperature at bottom of tankWeatherNotes
12/10/127.30am4125No gas heating needed. 2 degrees loss of temperature at top of tank overnight. Time for an additional cylinder jacket to minimise this loss!
12/10/128.00am4122Only 3 degrees loss of temperature at bottom of tank after one shower. Cold water is pre-heated by the Recoh-Vert Shower Save heat exchanger, so the input water is not as cold as it otherwise would be.
12/10/128.00pm3824Cloudy and dullBottom of tank heated by only 2 degrees by the solar thermal (but it is October in Glasgow!)
13/10/126.45am352312 minutes gas used after this reading
13/10/127.10am442312 minutes gas raised top of tank from 35 to 44
13/10/127.30am44221 degree loss at bottom of tank after 1 shower
13/10/127.15pm4125Cloudy and dull3 degrees loss at top of tank and 3 degree gain from solar at the bottom of the tank
14/10/127.15am4424Top of tank raised from 41 to 44 After 10 minutes of gas heating.
14/10/128.15am4416Top of tank stayed the same after two showers, and bottom of tank lost 8 degrees.
14/10/126.00pm4138Cloud and sunshineBottom of tank gained 22 degrees from solar heating.
15/10/129.30am5534After 20 minutes gas and one shower.
15/10/124.10pm635757Sunshine most of the daySolar gain of 23 at bottom of tank.
15/10/125.40pm356156Used the opportunity of the sunshine to top up the tank temperature to over 60 degrees, to prevent Legionnaire's Disease. The Legionnella bacteria can grow in domestic hot water systems, and thrive in stagnant water between 20 and 45 degrees, especially in old systems with a buildup of corrosion products and scale.
16/10/127.20am55651Before showers
16/10/127.30am55650After one shower
16/10/129.00am55544cloudy and dullAfter two showers
16/10/122.15pm405337After a cloudy morning, the sun has just come outThe solar panel temperature has risen very rapidly.
16/10/122.45pm345336The sun didn't last long!The solar panel temperature has fallen again, and since the bottom of the tank is already at a higher temperature than the panel, no solar heating has occurred in the past half hour.
16/10/123.15pm345336The sun has now been out intermittently for half an hour!The solar panel temperature has risen again, and solar heating has occurred in the past half hour.

What have we learned from this installation? - some advice

  • To make such a system work properly, you need a south-facing roof, or one with a southerly component, such as south-east, or south-west.
  • You need several hours of daylight shining on to the roof (i.e. not too shaded).
  • You need space for a large hot water tank in the loft a metre and a half high and half a metre in diameter (probably larger than your existing tank). This should be near where the panel is installed to minimise heat loss.
  • It is worth while installing such a system, even without the renewable heat incentive, provided you plan to be in the same house for a period of years to repay the capital cost.
  • To qualify for payments under the Renewable Heat Premium and (hopefully also) the Renewable Heat Incentive schemes, both your installer and your equipment need to be certified under the Microgeneration Certificate Scheme (MCS), and you need to have a certain level of house insulation.
  • The pipes from the tank to the gas boiler, and the hot water pipes to the taps and shower should go by the shortest possible route to minimise heat losses. Plan the pipe route and reroute them if necessary, rather than just adding to the existing system, which may give too long a pipe run.
  • Fit the monitoring panel where you can read it easily (not in the loft).
  • Install a sensor in the top of the tank to help to determine whether you need supplementary heating in the winter.
  • Insulate all the hot water pipes to minimise heat loss.
  • Periodically, top up the hot water temperature to 60 degrees to minimise the risk of Legionnaire's Disease. If this is done late on sunny afternoons after the solar gain has occurred, it will save gas.
  • In the summer, you can save on the electricity used for pumping (80 watts) and save on pump wear and tear by setting the system to pump when the panel is 8 degrees higher than the bottom of the tank, and turning off when it is 4 degrees higher.
  • However, in winter, we have set it to pump when the panel is 6 degrees higher than the bottom of the tank, and to turn off again when it is 3 degrees higher. At the cost of a little more electricity (which is generated precisely when it is needed for pumping by our solar PV panels), this ensures that as much water heating as possible is gained from the limited winter warmth.
  • Fit a heat recovery system such as a Recoh-Vert Shower-Save, which is a unit with two concentric pipes which recovers heat from shower hot water outflow, and uses it simultaneously to heat the incoming cold water. Typically, this takes incoming water in winter at 10 degrees and heats it to 25 degrees during a shower. This will increase the efficiency of the system, as the solar panel and gas are heating 25 degree water instead of 10 degree water. It is only useful during a shower, but it costs only 1/10th of what a solar thermal panel costs! A main requirement is that your shower is upstairs and the Shower-Save is downstairs, needing at least a 2.5 metre height to install it (it is 2.1 metres high, but needs pipes at both top and bottom).
  • The next plan is to fit a Kingspan solar thermal panels
  • RW Thomas Heating Services was our solar thermal panel installer -
    83, Vardar Avenue, Clarkston, Glasgow, Lanarkshire G76 7QW, Tel: 07971 841501; Web: RW Thomas Heating Services
  • Recoh-Vert Shower-Save heat recovery system