To the Editor:
I agree with my esteemed colleague Rob Myers of South Mountain, that all alternative energies present opportunities for energy savings, reduction of fossil fuel use, and reduction of carbon emissions. I believe he is correct that every application has both ideal and practical considerations that may favor one technology or another.
South Mountain has the only NABCEP-certified photovoltaic installer on the Island. SunWaterMV.com has the only NABCEP-certified solar thermal installer on the Island who is also a mechanical engineer. This makes for a lively debate.
By his numbers, 64 square feet of solar thermal equals 205 to 266 square feet of economically practical photovoltaic panel.
Secondly, as far as I am aware, there is no Solar Ratings and Certifications Corporation (SRCC.org) data sheet that shows any flat plate that performs better than Apricus evacuated tube (EVT), unless one asserts that category C or worse applies. These EVTs perform regularly at the highest temperature difference in winter here, or category E.
I am not surprised that the best flat plates do not make it to category E. These EVTs also have a superior performance curve slope to every flat plate certified by the SRCC. For those familiar with the subject, this translates to superior winter performance. In summer, when there is excess heat available in a properly sized system anyway, flat plates often collect slightly better. That unused performance is not a valid point in favor of flat plates. I have seen some manipulated data by flat plate makers. I would like to see the field data to which he refers.
Third, even snow birds will usually find evacuated tubes the better choice because their winter performance can be used to avoid winterizing a home at almost no fuel cost.
Fourth, evacuated tube systems installed by NABCEP-certified solar thermal installers can be and often are installed at sufficiently low cost to outperform photovoltaics, in terms of rapid payback. The Massachusetts CEC incentive announced this week has effectively taken about a year off of the payback for solar thermal systems. Applied to the best systems installed on the Island, that would mean better than three-year payback.
I like the idea of PV. However, in many cases I would use the faster savings accrued by an EVT system to underwrite the purchase of PV and other technologies later.
I applaud South Mountain for using powerful combinations, such as using windows, drywall, and insulation by Serious Materials (which I recommended to Phil last year), heat pumps, and other technologies along with PV. Their fully engineered homes are the ideal application for photovoltaics.
For the balance of the 11,000 or so structures on the Island, arguably two-thirds of their energy usage is heat and hot water, and EVTs are the logical choice for an effective retrofit for winter heat and hot water.
Tim Twombly
West Tisbury
