Solar PV for hospitals
There are few organisations that have larger portfolios of buildings than a Hospital. With the increasing pressure on Governmental organisations to reduce their energy use and carbon emissions there is a great opportunity to use Hospital buildings to generate some of the large quantities of energy that they use at the same location that it is needed.
Of the renewable energy technologies that are possible to retrofit to an existing building, but far the most popular over the last few years is Solar PV.
So, would solar PV be a good fit for a Hospital building?
Solar systems always have to be assessed specifically for the site in question, and every building across a Hospital site, as well as every individual Hospital is different, but I’ll go through a few of the common advantages and potential problems here to address the most universal questions.
The general benefits of solar PV systems, such as free electricity and feed in tariff income, are covered in much more details elsewhere on the site, so I’ll concentrate on the issues that are purely specific to hospital buildings.
Hospitals use a vast amount of electricity, primarily because they have so many people working and staying in them at any one time, many of whom are obviously reliant on specific electrical equipment for their health care. Hospitals typically use far more electricity that it’s ever likely to be practical to generate on site. That may make it sound like the addition of a solar PV system to a Hospital site would be a drop in the ocean, and to one way of thinking about it that’s true even for the largest of solar systems, however, if considered on its own merits a solar PV system is most advantageous when all of the energy that it generates is used in the same building or site.
For Hospitals this is almost certain to be the case. They usually have their own Substation (or often more than one substation to provide a secure electricity supply) and the electricity metering will be done by the electricity supplier at the substation. That means that even if the building that the solar PV is installed on doesn’t use all of the energy generated, other buildings on the site can use it.
This gives you the additional benefit that instead of having to put the solar PV system on the building where you use the most energy for it to be worthwhile, you can situate it on the building or buildings that have the most suitable roof spaces for solar optimising the possible yield.
Solar PV has several benefits over other potential on-site renewable technologies, for example, compared to small/medium wind power systems, PV is very quiet and doesn’t produce and vibration that staff and patients may find annoying or disturbing. Compared to micr CHP or biomass boilers solar PV doesn’t involve any deliveries to the site on a regular basis, and involves the handling of waste materials during it’s operational lifetime.
As hospital have such high energy usage they will have large electrical infrastructure and usually provide lots of locations where a solar PV system of almost any size can easily be connected. Also, because they are very very unlikely to ever export any energy to the national Grid it is usually relatively easy to get permission to connect your solar PV generator to the Grid
The installation of solar PV systems is pretty non-disruptive compared to other generators as most of the work is done on the roof and there are no large parts to move around. It’s perfectly possible, with care, to have a solar PV system installed without disrupting the operation of the hospital in anything other than very minor ways.
Because Hospitals are such sensitive buildings, there are clearly going to be concerns around any addition to the buildings, and electrical additions need to be treated with particular care because there are a great many electrical devices used in Hospital that help keep people alive and there is a small possibility that new additions to the electrical infrastructure could interfere with that sensitive equipment.
This section may seem long at a glance when compared to the Advantages section, but the problems described here are mostly easily overcome, they just tend to take some care in our approaches to them.
There are various electrical concerns that need to be addressed when fitting solar PV systems onto Hospital buildings, and there are likely to be concerns particular to that building that aren’t mentioned here. This just means that it’s worth being very careful who the contractor you chose for the installation is, as they will need to be experienced enough to cope with the somewhat unusual electrical environment of a hospital. Ideally, they would have experience of installing on Hospitals before. It is certain that they will need to work closely with someone who knows the Hospital electrical systems well already, be it the M&E contractor who maintains them, or a specialist employed by the Hospital.
In an electrical context, discrimination means that the systems installed to protect the electrical systems from overload and fire, and to protect people from electrical shock are designed and installed in such a way that the protection operated from the smallest system up to the largest. On practice, this means that if you have a fault occurring in one electrical circuit, it could not trip the protection systems in a larger circuit that it’s connected to, thus disrupting electrical supply to equipment that have nothing to to with where the fault is.
This is relevant to the installation of solar PV system anywhere, and is part of the general electrical regulations for any new electrical system, however because the potential consequences of connecting a poorly designed solar PV system to a hospital could be very serious particular care should be taken over discrimination at the connection point, particularly if being connected to older electrical infrastructure where there may be pre-existing weaknesses in the protection systems.
Harmonic interference. This is quite a technical subject, but the simple explain action is that all electronic devices in AC electrical systems produce currents that oscillate at a frequency other then that standard 50Hz. Because protection systems and other aspects of electrical systems are usually designed to cope with 50Hz currents, it is possible under some circumstances for electrical current to flow in ways that are undesirable and to end up where there are not wanted. There are strict regulations (G5/4, a subsection of the D code) around the design and installation of electrical appliances that cover this, and the inverters used in solar PV systems are no exception to this rule, however as there can be a great variety of electrical equipment of differing ages and sensitivities present in hospital buildings it is possible for Harmonic effects from different devices to effect each other unexpectedly.
There are couple of different ways of tackling problems of this type (which are not all that likely to be fair). One is just to install the solar PV system onto electrical circuits that are a long way (electrically speaking) from any sensitive devices. Another is that Harmonic surveys can be undertaken in advance of commissioning the solar PV system to determine if there will be any detrimental Harmonic currents generated by the solar PV system.
As it so important that the electricity supply to a Hospital is to not be disrupted they will always have both back up generators and UPS (uninterruptible power supply) systems in place. These are complimentary back up power systems that will ensure that the power to either a whole site, building or circuit cannot be switched off if there is alter cut. This can be a problem for solar PV system because the regulations governing the connection of all types of generators that are to be operated at the same time as mains electricity (including solar PV) state that if the Grid is cut off then the generator must switch off until power is restored. Usually the PV system will detect that there is no mains electricity connected and will switch off on its own, but if it is connected to a circuit that is protected by a back-up generator or UPS it may not be able to tell that there is a power cut without some additional control circuitry.
In principal this shouldn’t be a big problem because there are relatively easy ways of connecting the solar PV system to the control circuitry that already exists for the back-up generator to tell the PV system to switch off when the generator is running. However, if the control systems for the generators are not close to the PV system, it can be complicated and expensive to run the control cable to the correct place. It’s just worth remembering that in buildings with back-up generators there may be additional costs associated with this problem.
There are other non-electrical barriers to the installation of solar PV systems that need to be considered as well, for example, the age of roofing material is often a problem on hospital buildings. Flat roofs are a particular issue as they often only have a design life of around 15 years. A solar PV system should be in place for 20 years or more and it can be very costly to have the solar PV system removed whilst the roof is replaced and be put back again afterwards. If your roof is felt, and particularly older felt it is definitely worth getting the roof re-covered before the installation of the solar PV system.
One sensible way of doing this is to consider the solar system around the same time as you are scheduled a roof replacement anyway. A lot of public buildings, including hospitals, are part of program of roof insulation and replacement as part of general energy efficiency improvement savings. Saving can even be made here as scaffolding costs can be shared for the different projects.
For pitched tiled or slate roofs the lifetime of the roof is likely to be much longer, but it’s worth considering the quality of the roof you already have. If there is no sarking felt in place the weather tightness of your roof will never be quite as good after the addition of a solar PV system however good your installer is.
Provided there is a reasonably good condition roof covering however, there are numerous mounting systems on the market and it should be possible to have solar PV installed on your school without doing any damage at all.
The cost of solar PV systems can often be a problem for public institutions, particularly in these times of austerity. However, if the hospital cannot raise the money itself, that is not necessarily a big problem. Because there is an independent income generated by solar PV systems through the feed in tariff scheme there are a number of private investors and investment schemes that provide the capital cost of buying and installing the solar PV system in exchange for them receiving the feed in tariff payment.
They will also usually sign the Hospital up to a power purchase contract for the power generated by the solar PV system (called a power purchase agreement, or PPA) the direct financial benefits from the solar PV system will be lower this way than if the hospital bought it themselves. And it doesn’t necessarily simplify the procurement process. However you still get the energy savings which are such a large part of the benefits to a Hospital and you can get a solar PV system when you might not otherwise have been able to.
As such heavy electricity users the financial paybacks and carbon savings from solar PV systems can be very favourable. However, because of the particular nature and activities of hospital buildings they necessitate additional care when installing new electrical generators so as to avoid any potentially very serious problems. However, there really should be no insurmountable difficulties around the safe installation of solar PV in a hospital for an experienced designer and installer.
It is recommended, however, that very close cooperation between the electrical staff of the hospital and the installer is maintained from as early on in the project as possible. It is also worth carrying out a reasonably extensive feasibility study before an installer is engaged to make sure that there are no real problems that can’t be economically overcome.
Still, if you have any questions that aren’t covered here then feel free to get in touch and we’ll help however we can.