PV & solar

Solar thermal & PV installations begin...

This week the solar thermal & PV installations begin...

The first stage was to have the roofers back to install and weatherproof the two pipe penetrations to allow the solar thermal pipes and cables to be taken directly down into the roof void and then on to the solar thermal cupboard. They have a 'mushroom' style cap to prevent ingress of rain and the pre-insulated pipes completely fill them to maintain an airtight seal at this point also.

The PV cables simply go up and over the parapet (held in place with some extoseal flashing tape to prevent them rubbing on the rough felt parapet) and in via an airtightness grommet on the external wall.

Along side the solar thermal panels we have (finally!) settled on a 6 x 250W panel PV array to cover some of our electricity consumption - we have been debating this for a while but it seems to make sense given that Kippen has no mains gas and we would like some solar contribution towards the electrical demands of the house, not least the running of the electrical immerser for the solar cylinder, the hob, and the oven, which represent our 3 largest 'consumers'. We had to do some re-arranging of the sedum on the roof to accommodate the position of the array. The second photo below shows the various panels during install.

The PV array has been split to optimise the position of the solar thermal panels. We are using evacuated tube solar thermal panels as they tend to perform better than the flat plate type in an overcast climate and at lower ambient temperatures, despite their generally higher initial cost.

In advance of this stage we had imagined that having a flat roof would be an advantage for both of these systems as we would be able to mount them at the optimum angle and not simply matching the pitch of the roof, however the exact opposite turned out to be the case for the PV panels! We have ended up with PV's at a shallower angle than is optimum for our latitude as it would seem that all of the PV mounting systems are designed to be at around 20-25 degrees - we can only assume because they are maybe more flat roofed commercial buildings where the quantity of panels can be considerably larger, and therefore the balance of investment to performance is different to a domestic building. Since this installation we have spoken to a few people who have suggested an adjustable mounting bracket that would allow adjustment of the angle a few times a year to improve the overall performance, so this is likely something we will look at in the future. However, for the moment, to maintain all of the warranties etc. it looks like a slightly shallower angle will have to do!

We used a local MCS registered company for the installation but the PV panels are made by Solarworld and the evacuated tube solar thermal panels are by Solfex. All in all I would say that this has been one of the longest installations on the project by others, with several teething problems along the way (which as I write this in May 2016 are still not totally resolved!), however the solar thermal system is essentially up and running and delivering hot water, and the PV's have produced 428kWhrs of electricity so far, so at least that is something!

The indirect unvented hot water cylinder has been specified and sized by the supplier at 300L and is by Gledhill.

They sized it based on the fact that we are building a 4 bedroom house, however I think that our reduced demand (2 persons generally rather than say 4-6), coupled with the low flow taps and showers required by the Section 7 Gold requirement, will lead to much less electrical input from the immerser than predicted. It will be interesting to see how this turns out when we begin monitoring the consumption properly.

We are currently ironing out how best to read the 'yield' of the solar panels: we have a flow sensor on the solar pipework loop as this allows the controller to calculate and record the input from the solar panels to the cylinder in kWhrs but this figure is accumulative. As part of the Gold Standard we are required to have "a display showing the performance of the primary renewable source ... mounted in (an) easily accessible space..." so we can use the controller for this purpose as well, but we would prefer to be able to read the information daily, for example, as well as cumulatively. The controller we have has a mini SD card which can collect the relevant data either by the second or by the minute; this is useful to see as the software can generate some graphical outputs which simplify reading the data. More on these in a later post once we have some data to show!

Here are a few more photos of the solar thermal cupboard during the installation. The smaller containers are the various expansion vessels required for both the cylinder itself and the solar loop, and the rectangular container is the heat transfer fluid drain off point.

The controller powered up and running for the first time, and showing a cool panel temperature of 26.6 degrees C.

Some glycol mix spilt on the parquet floor (grrr!) during the filling and flushing of the system...

The solar thermal pipework comes pre-insulated with no joints (it is the thin black pipe to the left below): it runs directly from the panels, through the roof construction and into the lowered ceiling zone over to the solar thermal cupboard.

The final panels in position, with the solar thermal sitting at a steeper angle in the centre.