Baxi Solo Innova Biomass boiler with solar panels
Living with renewables – how to choose what’s right for you
The idea of ‘green’ living is high on many people’s agenda now, fuelled by extensive coverage in the media and the threat of major energy price rises. But how do you decide which of the many new low carbon technologies on offer are right for you and will you have to change the way you live to fit in with them? We help to remove some of the mystery surrounding low carbon technologies and look at how the right products could provide viable domestic heating solutions.
Before considering which of the many low carbon products could be suitable, the most important thing to do is to insure your home is insulated. Well insulated. There’s no point installing low carbon technologies if the heat they generate is just going to leak out through poorly insulated roofs, walls, windows and pipes. The next step is to look at other ways to reduce energy consumption, such as using energy saving light bulbs and switching electrical appliances off at the wall. These simple little life-changes start to change the mind set and will also start reducing energy bills.
The next decision is cost. How much is going to be spent on the technology? Is it a ‘one off’ or part of an ongoing project? Many technologies work well together, so it is worth deciding if the long term aim is to install more than one device, and prepare the way for later additions. For example, this could mean replacing standard radiators with low temperature radiators or even underfloor heating, and the hot water storage cylinder with a twin coil cylinder so that solar thermal could be added in the future.
The property itself and what it will support must be considered. For example, does it have mains gas or is it in a rural off-mains gas area? What is the property’s orientation and the size and condition of its roof, if considering solar thermal?
Finally, what do you want the technology to do, for example heating, hot water, electricity generation? How will the different products fit in with your lifestyle?
It’s good to look at this holistic process as a room full of open doors. For each question asked a door closes, until only one remains open. The property chooses the technology because it’s important that the property itself can fully support and really benefit from whichever product you choose.
A Microgeneration Certification Scheme (MCS) qualified installer can provide invaluable help with this decision, and will help to ensure that the correct technology is being sold. MCS is a quality process rather than just a qualification. It provides a level of protection for customers and installers that is not as readily available with gas boilers, because the grants that are available are driven by MCS; both the installer and the products must be MCS accredited in order for you to be eligible to receive the grants.
So let’s have a look at the different technologies available, their most appropriate applications and any changes that may need to be made to the your lifestyle.
A domestic micro-combined heat and power, or dual energy, system is a like for like replacement for an existing mains or LPG gas boiler and, as such, is the easiest way to reduce carbon. The advantage of micro-CHP is that it is familiar – it works in the same way as a gas boiler – and is compatible with the existing system. The unit does not require planning permission and does not rely on the building’s orientation or the weather.
It generates electricity when you need it most, usually when the central heating is on, and the greatest financial savings are made by using the generated electricity rather than drawing it from the grid. An average three bedroom semi-detached property uses roughly 3000 kWh electricity per annum. A micro-CHP appliance could generate around 2000kWh. Micro-CHP is eligible for the Government’s Feed-in Tariff, which is currently set at 10p generation and 3p export. In addition, the carbon savings could be around 2.5 tonnes, compared to a standard efficiency boiler.
Air source and ground source heat pumps
Heat pumps work best in well insulated homes with either underfloor heating or low temperature radiators, in off mains gas areas. Heat pumps are not recommended for high temperature domestic hot water, but are suitable to be used in conjunction with solar thermal. Very little intervention is needed – the system can be set up and left. Heat pumps do not provide instant heat, but allow the heat to build up in the fabric of the building. They can be switched to holiday mode to keep them ticking over during winter breaks, so the house is still warm and cosy on your return. To make them more cost effective, they can be set up to run on economy electricity tariffs.
The sizing of air source heat pumps is critical: an under or oversized unit leads to inefficiency and can result in increased electricity bills. On commissioning, the parameters need to be set correctly and the distribution network operator (DNO) must be notified. This is because if there are a number of air source heat pumps programmed to start at the same time, in the same area, there could be a bit of a drain on the local electricity supply. Before installation, it is also worth checking with the local council to see if planning permission is required.
Under typical conditions, air source heat pumps operate at average seasonal efficiencies of between 200% and 300%, depending on the difference between the outside air temperature and central heating temperature; the smaller the difference, the greater the efficiency.
Ground source heat pumps are best for properties with plenty of space to bury the underground collectors, or ‘slinkies’. They can also be used with a bore hole, but this is a more expensive alternative, requiring a geothermal survey to make sure of the suitability of the ground. Both slinkies and bore holes need to be correctly sized to ensure optimum efficiency. Ground source heat pumps are more efficient than air source heat pumps because the temperature underground remains constant.
Solar thermal domestic hot water
For solar thermal to work most efficiently, the roof needs to be predominantly south-facing and at an angle of 30-40 degrees, without the risk of shading from, for example, nearby trees and buildings. The condition and structure of the roof is also a consideration, as is any future plan for extension or conversion. While most local authorities now encourage the installation of low carbon technologies where possible, it is always worth checking if planning permission is required, especially in conservation areas or for listed buildings.
There are three main kinds of solar collector: in-roof, on-roof and evacuated tubes. In-roof collector panels are built in to the structure of the roof and are the best option for newbuild properties or for installation as part of a major refurbishment. On-roof collectors are the most cost effective retro-fit solution, while evacuated tubes offer more flexible siting and are easier to install because they can be taken up onto the roof individually.
Solar thermal systems need a dedicated, well insulated solar cylinder with a twin coil, to store the hot water and either an immersion heater or system boiler as backup. From May to October, depending on the weather, most of the home’s hot water requirements can be met using solar thermal. At other times of the year, it may still raise the temperature of water in the cylinder enough to reduce energy bills. The boiler can be set up to kick in to provide hot water when solar isn’t enough.
As with other low carbon technologies, sizing is critical. The home’s hot water requirements will determine the size of the cylinder and the number of panels or tubes. It is a false economy to oversize the panels, as this could result in stagnation. Once installed and set up correctly, solar thermal needs very little maintenance.
Solar PV
If the roof is the same orientation as described for solar thermal and big enough to accommodate enough panels to provide a reasonable return on investment, solar PV could be an option. The advantage of Solar PV is that the electricity generated is eligible for the Feed-in Tariff. However, unlike solar thermal, any shading of the panels will dramatically reduce the effect of the solar gain.
Solar PV will give the most financial benefits for households that use electricity during the day, as they will not need to pay for as much electricity from the grid and will also receive the generation tariff. There are companies that offer to install solar PV panels free of charge; these mostly take the Feed-in Tariff while the household benefits from the electricity generated. In these situations, it is very important to check all the terms and conditions, particularly with regard to the future sale of the property.
The installer must be a solar PV registered installer with MCS and Part P qualifications and the DNO will need to be notified.
Biomass is considered to be the only true carbon neutral technology, and is currently far more cost effective than oil. The latest biomass boilers are a blend of old and new technologies. They are conventionally flued and fit into a modern system with modern controls.
Biomass is a more interactive technology than the others we have covered, because the fuel supply needs to be checked and topped up. In addition, the ash will need to be emptied, although the boilers are so efficient that they only need to be emptied about once a month. By the way, the ash makes an excellent fertilizer for the garden!
Pellets are available at most heating and builders’ merchants, and can be delivered in bulk or by the bag. A small biomass boiler, suitable for use in the living area, is also available and is equivalent to a 12kW system boiler with pump and expansion vessel combined. For areas with plenty of woodland, log burning boilers may be a cost effective alternative.
An MCS accredited installer will be able to assess whether a buffer tank is required to store the heat from the boiler. As with all low carbon technologies, sizing is very important for maximum efficiency. For large biomass boilers and those needing a buffer tank, space for out-buildings for the boiler, buffer tank and fuel is required.
Conclusion
Installing a low carbon technology is a long term investment and it is vital to get it right. There is not one ‘silver bullet’, but it is important that the correct technology is specified for each individual property and its occupants’ lifestyle. Once installed, there should be very little difference in the way the home is run, and few lifestyle changes.
However, while the initial outlay is greater, there are longer term gains to be made; the property’s value is increased, its energy bills will be lower, it will get a better Energy Performance Certificate (EPC) rating and its carbon footprint will be considerably reduced.
Baxi offers a comprehensive range of low carbon technologies, supported by a dedicated team of professionals.
