Not so long ago, energy screens were regarded as a luxury for many crops. Those days are gone. Nowadays, screens are an essential part of an intensive grower's armoury - not just for keeping energy use under control, but more and more as a tool for the manipulation of the greenhouse environment.
Even 10 years ago, screens were strictly for night time use because deployment in the daytime greatly reduced light transmission and impacted negatively on yield. That's all changed, as screen materials not only have much improved insulation properties now, but also transmit such a high percentage of daylight that they can also be used for a significant number of hours during the day as well. For crops like peppers, that can mean that screen deployment for some pepper crops in Holland now approaches 3,000 hours a season.
Screens get a lot of use during the year and, over time, inevitably lose some of their effectiveness. Tears occur, holes begin to appear, and accumulated algae, dirt and grime significantly reduce light transmission. It is generally accepted that screens can lose up to 2% of their effectiveness every year. Over a number of years, the energy saving screens are able to deliver can be severely diminished, and they can't be used at all in daytime. Reduced screen performance can therefore be very expensive.
Furthermore, leading manufacturers of screen materials are able to supply energy saving screens that have excellent insulation properties, but which will also allow humidity to pass through. These materials enable growers to keep screens fully closed and therefore continue to benefit from their full energy saving capability, yet continue to control humidity effectively by venting above the screen to draw the excess humidity through the breathable material.
If you have an old screen that no longer performs as you would like, or you would like to benefit from a breathable or fireproof material, all is not lost! In most cases the mechanical parts of the system (motors, gearboxes and support wires) will still be serviceable and the whole system can be upgraded to the latest standard just by replacing the screen material. The cost of replacing the screen material will depend on the type of screen required, whether it should be fireproof, and on the dimensions of the glasshouse etc. but at the time of writing (April 2015) is likely to be in the range £2.40 - £2.70 sq metre, installed. It has been calculated by independent energy consultants that the investment in a refurbished screen could be repaid in 4 years or less, making it something that every grower presently using an underperforming screen might want to consider.
Go here for impartial GrowSave technical info about screens.