Integrating Renewable Energy Technology

The challenge of meeting 15% of our energy requirements from renewable sources can be likened to climbing Everest. The long walk in to Base Camp is familiar territory and well within our grasp, but as we approach the summit, every step is ten times harder than the one before. In fact there is now wide spread acceptance that, as a nation, we aren’t going to make it. If that doesn’t quite feel like the spirit that got us to the summit of Everest, it must be remembered that it was a surrogate Brit (New Zealander) and a Nepalese Sherpa, who stood waving our flag on that momentous day.

Heating accounts for a massive proportion of carbon emissions and a great deal of it is wasted energy. Even though the greater proportion of that wasted energy is within poorly insulated existing housing stock, new build housing will play an increasing (and some might say disproportionate) role in achieving our targets.

Face The Sun

So far, as an industry, we have insulated, draught proofed and Sedbuked our way towards meeting ever more stringent standards of energy conservation. To do even more, moves us onto site renewable micro generation. Until recently this was very much the domain of the ideologically driven self builder, because in volume builds, the increase in building costs couldn’t be recovered in the selling price.

Now as legislation is leveling the playing field with the code for sustainable homes, we are all hippies. Much like the ancient Druids, we will set out our sites to follow the movement of the sun. Roofs will be pitched to optimize solar collectors and there will be a predominance of south facing glazing. The appearance of our new housing will also change, and it will be easy to date buildings of the future simply by looking at the renewable energy technology. ‘Sun age architecture’ is the next big phase. Anyone flying (if flying is still allowed) over a new housing development in ten years from now will no longer see an expanse of tiles or slate, but acres of photo voltaic and hot water collectors glinting in the sunlight.

Feed The Need

In order to do their bit, electricity suppliers will need to meet strict targets for generating electricity by renewable means. On the face of it, this means massive capital investment, but there is one simple measure that would transform their portfolio for negligible capital outlay. In Germany legislation requires electricity producers to buy through feed in meters, accessing electricity generated by on site micro generation, such as photo voltaics. This is at virtually the same price that they sell it at, and has incentivised half a million householders to install photo voltaic roof panels, which now produce as much as a power station, though only during daylight hours. This electricity is fed into the national grid and used by commerce and industry during the day, when domestic power consumption is low, and at night time domestic users buy their electricity back.

It may even be that as homes change from HE boilers to combined heat and power units (CHP), that generate electricity as a by product of heating, the need to buy electricity from the national grid will be further reduced. It could be PV in the day and CHP in the evening.

The move towards CHP is inevitable. This is because it is generally accepted that, short of marginal increases from add on flue capture devices, HE boilers have gone just about as far as they can with efficiency. Most boiler manufacturers have a CHP unit under wraps so we will be seeing a lot of these coming on to the market in the near future. CHP also has the advantage of working during power cuts, and that for many will be the most compelling reason for buying them.

So a boiler will no longer be just a boiler, and a boiler company will become an energy company. An indication of this is the way that nearly every boiler manufacturer has been diversifying into renewable, with solar hot water and heat pump offerings. At present this is not much more than a toe in the tepid water, with rebadged ‘me to’ products. They have no real usp, or dedicated integration with their boilers, but hopefully as the technology gains a mass market, they will get a bit braver and we will see some innovation. There is still plenty of scope for original thinking. Flat plate collectors (as opposed to evacuated tubes) need to be smaller and modular, to offer more flexibility in positioning and easier handling on the roof. In order to gain more efficiency over a greater temperature range, solar hot water cylinders really need to be pre-feed cylinders, that can be placed beneath an ordinary cylinder, or better still separately in an eaves cupboard. There also needs to be some kind of integration between solar and combination boilers, again perhaps in the form of thermal store pre feeds in the roof space.

When it comes to heat pumps, there is still a great deal of work to be done in integrating them with existing heating systems. A properly sized unit will heat a house during mild weather, but in the depths of winter, all but super insulated homes will require some top up heat. Most heat pumps are set up with an electric immersion heater to top up the heat for hot water, and many can even be used to provide an electric top up for space heating, but this defeats the whole point of heat pumps.

If the house is heated by electricity anyway then you are probably no worse off, but it is worth remembering that high capacity heat pumps above 10kw with multiple immersion heaters, may struggle to work on single phase electricity supplies. This simply being because of the start up current, coupled with other power consumption in the home.

The whole issue of top up is contentious anyway because; the efficiency of a heat pump drops off as the temperatures get higher. So the lower you can keep the operating temperature the better. With a temperature of 55 deg cent, which is about as high as heat pumps go, the efficiency drops to around 2.4 COP (for every Kw in you get 2.4 out) which is still better than a direct electric appliance.

Working at temperatures as low as 35 deg cent, the typical efficiency jumps to nearer to 4 COP. But radiators are a waste of energy at this temperature. Under floor heating pipe work must be laid much closer together, than with a boiler to achieve the required heat. Coincidentally keeping the temperature as low as possible, is also the key to efficiency in HE boilers. This is because it keeps them in the condensing mode, so there is some logic in running the two in tandem. However, it is rarely done. This probably being because of the cost of buying a boiler as back up, but there is some justification, because it overcomes the problem of needing 3 phase electricity for larger units.

Set The Controls

Whatever kind of high efficiency heating appliance you install, the control system is the key to getting the best out of it. This invariably means weather compensation. The outside temperature is interpolated with ‘learned’ warm up times for the building, In order to fit the heating curve which will delay, or advance the switch on time of the boiler, or in the case of a heat pump, to modulate the collector. This type of control falls nicely in line with the EUP Directive (eco-design of energy using products) which is advocating a move away from SEDBUK appliance ratings, towards system efficiency.

Reliability

Controls will therefore become a major feature of any heating system, but before we get too excited about this it must be acknowledged that the majority of HE boiler failures are still due to faulty electronics. If homes are to be fitted with even more solid state computer wizardry in the name of energy conservation, this should at least be reliable. Measuring system efficiency, whilst ignoring the small army of service engineers dashing around the country plugging in new circuit boards, negates the whole purpose of looking at the overall picture. There is a very good case to be made for heating appliance manufacturers being required to publish audited figures, for the true cost of break downs within the life of an appliance. It would make very interesting reading and hopefully raise the bar.

Hands Off

In introducing smarter controls, we also need to consider user input. At present many householders are used to the idea of turning the thermostat up to a maximum to introduce some quick heat into the building, and many then forget to turn it down again. This is a hard habit to break because historically, we have tended to let our houses warm up when we are there, and cool off when we aren’t. Now with better insulated homes and lower input temperatures, we have to get used to the idea that there are no quick responses. Unfortunately, the variable British weather is not best suited to this form of predictive control, and in the end it may be that something as simple and cheap as a portable plug in electric fan heater (£9.99 from Argos) will be the easiest way of dealing with any sudden cold snaps.

Outside The Box

The other consideration with all this renewable technology is where to put it. There is already some resistance to the appearance of air source heat pumps on the outside of buildings. As they are effectively air conditioning units running backwards, there is nothing particularly alarming about the look of them. When we visit hot countries we readily accept the need for air conditioning units, even the infamous window rattlers hung on the outside of historic buildings, but our British sensibilities are disturbed when we see these ‘ugly’ boxes hung on the outside of homes in the UK. Given that most heat pumps are made for an international market, there is little chance that manufacturers will pander to our needs by disguising heat pumps as window boxes (complete with plastic flowers) so it will be builders who have to come up with suitable enclosures or hutches to disguise the units. Certainly placing them overlooking the neighbour’s boundary is not likely to engender peace and harmony in the community. There are those who advocate hiding them in the loft, but even if you aren’t building into the roof space, there are good reasons to avoid placing heat pumps in areas where only plasterboard shields the occupants from the noise of the fan and the compressor. Placing them on any kind of joists, even with acoustic matting, is also a highly dubious undertaking since the low drone can resonate through the roof timbers. As with those infamous ‘window rattlers’ it is within the nature of any unit containing a fan to get noisier over time.

Storage

As for the rest of the technology, there is no getting away from the fact that it takes up more space, and in modern homes there is precious little to be had. If low level heat is extracted over a long period, it has to be stored somewhere. One possibility is within the thermal mass of the building, but we are moving away from thermal mass towards lightweight structures.

The other place to store heat is in a buffer tank. In a larger home with a plant room this is possible (though larger homes need even more storage) but in an average house, let alone a flat, there just isn’t anywhere for a buffer tank and a cylinder. There are even solar thermal systems on the market which store hot water from solar panels for use in heating. In the summer there is an abundance of hot water but who needs space heating in the summer? In the winter most solar hot water systems are lucky to provide 60% of the hot water requirement. It would take a huge number of evacuated tubes to produce solar heat for space heating in the winter. The paradox with solar energy is that when you need it most you have it least, so the key to future success may lie as much in storage, as in generation. There is one private system that uses a second hand stainless steel milk tanker buried in the ground as a heat dump but even this cannot seriously lay claim to be a seasonal heat dump, but if anyone ever works out a way of storing the excess heat from the summer for use in the winter, then they are really onto something. We have not yet reached those bright sunlit uplands.