PVThermal panels are not new. There has been a lot of research done on them in Europe and the US since the 1970s, but they have been a niche market. Now is the time for the system to gain some prominence.
The basics of the panel are quite simple. A heat exchanger, similar to that in a regular flat solar water heating panel, made of copper tubing and aluminum sheeting is placed behind the PV cells.
Water or glycol is piped to the panels in the same way as any hot water solar system. The solar panels in this type of system can only get to around 70-80C (158-176F). Because of this limiting factor the glycol will never boil and will therefore last a very long time, maybe 15-20 years. In a drainback system the operation is the same as in a traditional system but the installer must remember to tilt the panels to allow for the liquid to drain back. Most of the reasons for using a drainback system over a glycol system disappear because the drainback’s main advantage is to prevent liquid boiling and degrading quickly.
The main reason why the temperature cannot get as high as a standard panel is that there isn’t the insulating effect of a glass cover. In this way it is similar to a pool panel. The limiting effect of the heat loss over the PV glass keeps the temperature down.
From an electrical point of view, a PV panel can have a 20-25% reduction in efficiency when the cell temperature is at 80C. This amount of heating happens quite regularly in the hot summer. If we can reduce the temperature of the panel to 25-30C, we can expect to see an annual improvement or 10-15% in electrical output. With a standard 2kw PV system, for example, the payment under the Ontario microFIT program will be approximately $2000. Therefore with the PVThermal system we should see an extra $200-300 annually.
The hot water production is equally impressive. The average solar water heater is 5-6m2. With a 2kw PVThermal system there is 15m2 of panel area. The panel is not as efficient (per m2) as a standard panel, but there should be no shortage of hot water during the prime solar months of March to October. During the colder months, performance per m2 will be less than a standard panel but the extra surface area allows for some heat for other purposes.
One other benefit of the the PVThermal comes when snow or frost has covered the panels. Some solar controls will allow the panels to be defrosted by warm water in the storage tank which could give you electrical production when otherwise you would have to rely on the grid. More coming soon including diagrams and sizing info.
UPDATE………Late August 2012
Boss Solar is ready to install retrofit PVThermal heat exchangers to YOUR existing panels. If you have at least 6 panels in a row that you would like to convert to PVT panels, call us today. Remember that during the summer months, the added efficiency of removing the heat from the panel will increase its power output.
Cost varies with the location but the installation will be less than our standard solar water heating packages.
The PV-T product will be available mid 2011.
The PV – Hydronic Combo is a great idea. There is the mention of a temperature limiting factor due to the combo design lacking a glass cover enclosing the combo panels. For those who may believe they require a higher temperature for the hydronic system, a solution might be to set up the system in a modular fashion. For example; use 4 combo panels that feed their hydronic fluid through a dedicated “enclosed” Hydronic panel. The Combo Panels act as a pre-warming system and the dedicated Hydronic Panel becomes a ‘temperature booster’. If esthetics are a concern the Combo Panels could be placed in a stacked horizontal orientation (2 units) with a vertical Hydronic Panel followed by another set of stacked horizontal Combo Panels.