Solar Thermal Panels (STP’s)

A typical Northern European Hybrid Solar Thermal Panel Installation using a Twin Coil

Solar panels use several vacuum tubes that convert sunlight into heat by means of an absorbent layer. CPC mirrors reflect rays that occur between the tubes to the side of the tubes away from the light and also ensure that this light always hits the absorber at the optimal angle. The solar collectors collect as much sun as possible, even in transitional periods, when there is little sunlight and in winter. So you benefit from high yields, all year round.

Data Sources

PV Panels: Whilst there are several sources of data available regarding PV Electric Panels, we have used a single source in order that the data used is a constant. The Eco Experts are an independent London based group of climate-friendly writers who can tell you exactly how to cut your energy bills and reduce your carbon footprint.

Solar Thermal Panels: Due to there being no Grants available for Solar Thermal there is limited current data available from independent sources. We have therefore used our preferred supplier to provide the data used. Whilst the Top spec Aqua Plasma is a AAA rated panel, we have chosen the lower cost 4.94sq/m Star 19/49 panel AA rated at 50C output. We have also based our data on Wurzburg which has an average temperature of 9.9C and 1630 hours of sunshine annually. Liverpool by comparison has an average temperature of 13.2C and 1502 hours of sunshine annually.

Use this simple Kw calculator to work out how much energy a cylinder needs daily to provide hot water.

Introduction

Otter Heating are huge advocates of Solar Thermal Hot Water panels or STP’s. In this section we will explain why and the benefits of these low or zero carbon systems.

We only recommend Evacuated tube type STC’s or collectors. These have been specifically designed for Northern climates. Their reflector design ensures that heat is harvested when the Sun is very low on the horizon and they do not suffer from snow coverage, even melting the snow away as the day progresses. These features are not found with flat panel collectors that do not use Evacuated Tube technology.

Unfortunately there is no funding for Solar Thermal Collectors. This is not because they are inefficient. They are in fact so efficient, there is little profit to be made from them by third parties. After being launched as part of the government's plan to "build back greener" the Green Homes Grant scheme closed only 6 months after launching in September 2020, to much fanfare, the scheme ended on the 31st March 2021. The previous end date was set to be 31st March 2022 after a recent decision to extend the initiative.

Solar Thermal Benefits: Central Heating Losses vs Domestic Hot Water Losses

Central Heating is a closed loop circuit. There is very little heat loss from the system, the heat losses are from the building. Even when turned off, Central Heating systems will continue to emit the latent heat in the pipes and the radiators. Remember too that your Heating system is used for 6 months of the year and varies its output depending on the outside weather conditions.

Domestic hot water on the other hand is an open circuit, and in all cases most of the energy used to create hot water goes down the drain. Nor does We do not sit in a bath until it goes cold. This is true for showering, bathing, washing machines and dish washers. The energy used to heat water is a total loss, unlike central heating.

Furthermore, we require hot water 365 days of the year unlike heating. This means that heating hot water is an expensive business. In fact our demand for hot water in the Summer is greater than in the Winter as we have more showers and wash more clothes than we do in the Winter. Remember too, that unlike central heating, the cost of generating hot water does not vary with the weather conditions. It is a constant. Many hot water cylinders are typically 180l and above and often have a greater capacity or volume than Central Heating. They very often also have a higher stored temperature of hot water. When added together, heating hot water can represent a similar cost to heating the home.

By installing a Solar Thermal Panel it is estimated that 70% of our energy to heat Hot Water can be generated from the Sun. This can go up to 100% in the Summer and down to about 30-40% in the Winter.

Solar Thermal vs Solar Electric (Photovoltaic)

Our roofs are quick becoming Energy Real Estate and have limited space. We must therefore consider how much energy we can generate per 1 sqm for the greatest return. We must also consider what the cost is per sq/m.

A flat electric Solar Panel generates about 150w per sqm and is 15~20% efficient. The Lifespan is estimated at 15+ years with a degradation of 0.5 to 3 % annually. Photovoltaic cells are notoriously difficult to recycle, and most still end up in landfill. The power generated is sold back to the grid at the SEG rate. This is a fraction of what it costs you to buy at 25p per Kw/h The SEG rate is between 3p and 10p per Kw/h. The cost to install 10 PV panels on a typical 3 bedroom house that generate 2700 Kw/h annually is @ £7000.00. Expect to pay £11500.00 if you wish to store this energy in a battery storage system.

A Thermal Hot water panel generates about 600w per sqm and is 45% efficient. The Lifespan is estimated at 25 years+. There are no degradation rates for Thermal Solar panels. They are 100% recyclable using only copper, glass and aluminium in their construction. Users of Solar Thermal panels benefit from the full amount of energy these panels create per kw/h and we have already transferred the heat energy in to the water reducing losses. This means we are not consuming energy at a higher rate from the grid. The energy is then stored in a cylinder, not expensive batteries and is ready to be used on demand. Unlike batteries that can only be discharged by 50%, a cylinder of thermally generated hot water can discharge 100%. To install 1 Thermal Hot water panel on a 3 bedroom house that generates 2982 kw/h annually is £4~5000.00. This price includes a replacement cylinder too, a great upgrade if you use a Combi for Hot water.

Heat Pump Efficient vs Solar Thermal panels.

You can’t avoid the efficiency ratings of heat pumps whether they are CoP or SCop values. The efficient of a heat pump is a simple equation, dividing the amount of heat energy outputted in Kw by the amount of electricity used to run the pump, again in Kw’s. So a generous calculation would be a 3Kw Heat pump would give 12Kw of heat. or 400%!

A solar thermal panel only requires a small central heating pump to circulate the water from the panel to your cylinder coil and thus heating your water. This pump only runs when the panel can create heat. Nor does not go into an anti freeze mode where it actually takes heat out of your heating system as a heat pump can on the coldest of days.

A typical STP uses a Grundfos UPM3 240v Solar pump which uses between 2 to 52 watts and will run only when the sun is out. An average daily pump running time for Liverpool would be: 1502 hours of sunshine / 365 days x 52 watts max = 214 watts of electricity. The average daily output for a Star 19/49 Solar panel in our example above is 2982Kw / 365 days giving an average daily output of 8kw of heat energy. Our SCoP therefore for a Solar thermal panel which is the Seasonal Coefficient of Performance would be 8000 watts of heat energy / 214 w of electricity used. This give a SCoP figure of 3700%, or 9 times more than a heat pump!

Remember, a heat pump uses a large 240v motor to drive the fan and also uses a compressor. You’ll also need at least one central heating pump just like a Solar pump and they never turn ‘Off’ unlike Solar Pumps do at night. Heat pumps work hard to extract heat out of air which has a low latent heat capacity to begin with. Solar panels use radiation which is much more powerful. We’ve all had sun burn, nobody has ever had air burn.

Addition benefits and savings with Solar from Otter Heating

For some reason Solar hot water is always associated with the water you use to have a bath or shower. In addition to these, Otter Heating also recommend connecting your Dish washer and Washing machine to your hot water supply, even when no Solar is used. AAA EPC rated Dish washers and Washing machines only use cold water connections and then heat your water with an expensive electric emersion heater. Hardly an AAA appliance ? By using heated water from a gas boiler (1kw of gas is 6p, 1kw of electricity is 25p) or better still free Solar Hot water, your annual saving can be even greater and your payback time reduced by @£200 per year.

In addition to this, by installing a twin coil Solar cylinder you may decide that the remaining efficiency to be gained by replacing your convenient gas boiler with a heat pump in the future simply isn’t worth the extra expense. However, if you do, then you won’t have the expense of replacing your cylinder as you’ll be heat pump ready.

In the event of a power cut both Heat pumps and gas boilers turn off. Because a Solar thermal panel uses a very small 52w 240v pump, an inexpensive Solar PV system with battery storage can be installed so your whole Solar thermal panel system is entirely off grid. It also means that you can continue to have hot water and showers even if there is a power cut. Our micro off grid PV kitsfor Solar pumps also have the capacity and convenience of being able to comfortably charge a phone or a Laptop / Wi fi hub during a power cut.

* Electricity and Gas rates are based on Scottish Power December 2024 Standard Variable Tariff.