What PV may learn from the downturn of SDHW

Of course PV is now on the verge to big business, but may be before entering the highway it makes sense to look back and try to harden the business models before accelerating. Solar Domestic Hot Water has a longer history and we may learn from it. In the beginning the real hurdle was the welding of the tubes to the fins. Otherwise DIY was a perfect idea for building your own solar instalment. Industry took over, collectors got better and better, quality standards were introduced. Unfortunately there are some build in problems which were overlooked:

• Solar energy usage is low, when no hot water is needed.
• tanks located in the attic or cellar, do not directly contribute to room heating with their losses, and create high costs for piping and pumping.
• legionella problems require high water temperatures and reduce efficiency as well as usage of solar energy
• anti freeze protection reduces efficiency of the system in several ways, mainly regarding pumping energy

So the afterwards highly qualified systems got to expensive and delivered too few savings. A new attempt to boost business needs new ideas solving the problems at the source and a full understanding how economy could be improved for the customer. This might include:

• cheap polymeric systems with embedded stagnation control
• additional energy users for peak shaving- allowing also a smaller tank
• a flow through system avoiding legionella problems
• a circulation system not needing a pump nor having freezing or stagnation problems
• making use of energy losses for room heating

A survey of a research project is disclosing some potential solutions:
http://www.surveymonkey.com/s/isole


But coming back to PV. What lessons may be learned?

• Smart affordable controllers should allow to make use of the expensive panels, even if they are mounted sub-optimally (at different inclination or orientation, partially shaded...); but in-string controllers not neccessarily need to be 230V, this is only useful for a system split on two orientations.
• Some times, lower cell efficiency is the better choice, if mounting area is cheap and diffuse light dominating; Solyndra pioneered a cheap support system for gravel roofs this might be a good idea if strong wind is not a problem. a-Si will then deliver the better economy.
• Efficiency is to be measured in practice and not under standard conditions (standard cell temperature), design should allow for cell cooling (venting) and use of the reflected sun if feasible (lakes, snow, reflecting skyscrapers...)
• Islandic systems should be avoided, because of the high storage costs. Small systems could be connected to smart decentralized energy resources. Collaboration amongst users is useful.
• While cells are becoming cheaper more focus should be put on the erection cost. Tracking might be less economical and standardisation needed to allow for cheaper mounting systems.