My neighbour, a retired plumber but now rather frail, has two 30 year-old solar water panels on the south side of his house. The engineering is quite good and robust – he bought the panels then wrote to Honeywell explaining the project and they sent him a package of temperature sensors and a controller. It’s all piped up in 15 and 22mm and there’s a 240v circulator, unlike my modern setup with 12v electics and 10mm piping feeding a manifold with evacuated tubes.

Now the covering on one of the panels has torn open. Closer investigation up a ladder yesterday revealed that the panel is nothing more than a 4′ x 6′ aluminium frame, with insulation in the back, flat aluminium sheet collectors with a very narrow pipe running down the middle and then a sheet of heavy poly stretched drum-tight over the frame and finished off with an outer frame that appears to be glued on with exterior mastic.

So we plan to strip off the outer frames, remove the old poly, spray the collectors matt black with a rattle can then replace with fresh poly and mastic the frame back on. I then need to find a way of shrinking the poly sheet, in the same way as you do with that thin film you can use as temporary secondary glazing where you use a hair dryer. I’m aware that the forces of shrinkage could tear the sheet out of its frame so might need to leave it slack for a week or two for the mastic to cure. I’m thinking that a 3 kw electric fan might deliver enough heat over a broad area to do the job but I wonder if it will be hot enough; I know that in factories where cans and bottles are shrunk into cartons a gas flame is wanded briefly over the plastic to shrink it.

Any suggestions?

And before you ask – no, my neighbour has declined my offer to replace the two panels with one efficient 20-tube array like I’ve got, which would be a straight swop.

Polyolefin shrink film will shrink with an ordinary hair dryer or heat gun.

How robust is that? This poly sheet has survived 30 years of wind, rain and UV. It’s very taut indeed, I actually thought it was thin Perspex.

Just a thought, try looking up poly tunnels. They use a heavy duty plastic sheet, stretched over a frame, and I would guess that heat is used to shrink it at the ends. The sheeting is opaque rather than clear, but if plants get enough energy through it to grow, then I guess it must be pretty efficient.

it would need to be the right material to start with I’d guess. As a tool to heat and shrink it – probably one of those electric hot air guns used for paint striping. (the kind you really don’t want to get mixed up with your hairdryer)

With a black sprayed panel behind, I wouldn’t worry about the poly shrinking.

Just wait for the first sunny day.

I think you might be right there.