Both solar thermal for hot water and photovoltaic collectors for electric absorb the sun’s radiant energy, not it's heat, and change it into heat or electricity. While New England has short days and cold temperatures in the winter overall we still get a good amount of sunshine. Germany is the global leader in the adoption of solar electric and we have 30% more sunshine than they do. While dry southern states such as Arizona have more sun, they also have heat. PV panels increase their performance the colder it gets. That is why you are likely to see the highest kilowatt output from you solar electric system on a cold, clear, winter day.
Since we have short days, especially at the end of December, overall output will be reduced in winter. This is not as issue if your PV system is tied to the power grid with a net use meter. During the long days of summer you will create more power than you need so you will have a credit. In winter you will draw from your credit balance. The plan is for you to net to zero over the course of a year. If you have a battery bank off-grid system the PV array will be sized to meet your winter need and you will have a backup source, such as a generator. Compared to Arizonia we will need about 20% more modules to get the same output.
For most hot water application we sell evacuated tube systems, not flat plate collectors. Winter performance is an important consideration. Flat plate collectors are less expensive but their performance is impacted by outdoor temperatures. Evacuated tube systems are protected by a vacuum to insure the ambient air temperature has basically no impact on the tubes performance. If you have primarily summer needs, flat plate collectors will be most cost effective. For small families, without kids, flat plates can be a good choice for hot water if you goal is to cut your environmental impact. Generally for small families we recommend a heat pump hot water tank or on-demand unit.
The graph below shows the expected monthly output for a Thermomax 30 tube collector in Portland Maine. As you can see, December is a tough month due to the short daylight hours. By February output is substantial and your backup system will not be running much. View a full monthly Thermomax chart.
Normally when we size and install a thermal hot water system we optimize it’s output for winter. This includes placing the collector at the correct angle to maximize collection in the winter. Summer days are much longer so you will have excess power in summer.
We have found that otherwise reputable solar installers sometimes tell customers that solar thermal cannot be used for space heating in Maine. For some time this confused us. We now understand that they cannot do space heating because they do not use a high quality tube such as Thermomax. Space heating in New England cannot be done well with flat plates. Many lower-quality evacuated tube systems will not generate water temperatures over 150°. Thermomax was engineered to perform in northern climates and it does an outstanding job of converting both direct and diffuse solar radiation into useful heat. Diffuse radiation is what we get when the energy rays are scattered by moisture in the air.
Thermomax has excellent winter ratings and it quite capable of producing temperatures over 150° even in the winter. Solar space heating works best with radiant floor heat. If you have baseboard heat you generally need water temperatures of 180° which a solar thermal system cannot consistently produce here in winter. Solar thermal can be used as a supplement to baseboard heat, pre-warming the return water and providing measurable heat in the spring and fall. With a solar thermal system your boiler does not need to run in the summer to make domestic hot water. We don’t sell pre-packaged one size fits all systems. We customize each install to take advantage of your existing systems. If you have baseboard heat adding cold-start and an outdoor reset will be your best investment. The solar system can be used to supplement your heating and shortens the payback time on the solar thermal equipment but unless is it oversized it will not make a significant difference. There are retrofits for forced hot air systems where hot water is used to warm the air. In general these work better in warmer climates. With products such as Infloor board and Radiant Track it is now possible to retro fit most homes with radiant floor heat that can take advantage of the solar hot water. In any case, before installing solar thermal systems for heat it make financial sense to properly insulated and seal leaks first. You may also want to consider an air source heat pump which will be much less expensive to install than the solar.
View a full monthly Thermomax chart.
The SRCC is an independent rating agency similar to Underwriters Laboratory (UL). Their testing shows solar works well in Maine. They “fairly” evaluate all solar thermal systems and often to receive government rebates you must install a SRCC certified system. While every manufacture can argue with some of the techniques they use, they are still a great, unbiased source to compare equipment. One of the best features they have is that for some systems they have calculated performance based on geographical areas. Lucky for us, Portland Maine is on the list. Since the SRCC is in Florida it is quite important to look at performance data for our area. As we all know what works in Florida will not work here. Carefully review the December output rating for Maine, all systems work well in summer. There are other rating agencies around the world. While the rest of the world has been refining solar technology since the 1970’s, the US has ignored it. Overall the rating agencies outside the US have better testing procedures so some manufactures prefer to quote these more accurate numbers.
Fact: If your current boiler is really old, then now is the time to go to solar. With the sun warming the water almost all the time, the demand on your boiler will be much less—extending its life.
Myth: I don’t need a heat dump to control excess heat generation, because my installer is going to employ the vapor drawback method (i.e. stagnation).
Fact: Most reputable solar thermal manufactures do not recommend vapor drawback methods for dealing with excess heat generation. Vapor drawback puts the collector in a state of dry stagnation and creates excess pressure and temperature, possibly resulting in larger volumes of vented steam.
Fact: It's not the cold that impacts the performance of an evacuated tube but the length of the day. During a New England winter our daylight hours are few, limiting the time we have to collect solar energy. The solar tube's vacuum protects the copper collection tube from the outside air temp.
The Thermomax tubes we sell are particularly good under these circumstances and this is why we use them for home heat applications. Snow buildup is not generally a limiting factor as it usually falls right off the round tube. The reflected sunlight actually increases performance, and even after heavy snowfall the tubes will usually clear themselves within a day or two.
Myth: Solar hot water cannot be used to heat a house, I have forced hot air heat, not hot water baseboards.
Fact: If you have radiant heat now, it uses 120° water that can be easily created with solar panels. The hot water is stored in a large tank. It is either fed into your existing system (which would only come on as a backup), a backup heat element is in the tank, or there is an on-demand water heater.
Solar panels normally won’t create water hot enough (180) for baseboard heat. They can be used to re-warm the cooler water on the return line before it goes back into the boiler, raising the incoming temp to the boiler and reducing the amount of fuel needed to raise the water temp back to 180.
Myth: I would have to install baseboard and it would be too expensive and very messy.
Fact: Most homes without radiant heat can easily be retro-fitted. When you consider the fact that your fuel bill will be cut by over 50%, this is a cost effective solution. Additionally, you will get rid of the dusty baseboards and have a much more comfortable home. If you have forced hot air or room heaters we will leave them in place as they are great backup systems.
Fact: A south facing roof is the ideal place for solar panels. If the panels cannot face true south a simple solution is to add 10-20% more panels. Panels may also be placed at ground level or vertically on a side wall. We have even seen an absolutely gorgeous cedar trellis/shade structure where the overhead tubes collect the sunshine, provide shade, and are even a nice copper color when viewed from underneath.
There are many options we would be happy to discuss with you. And if you are worried about a beautiful tree that seems to be in the way, let us do measurements before you think about cutting it down. The suns angle changes seasonally and often times we can work around items that cause shading.
A properly connected solar system will never damage your existing heating system. The sad part of the above statements is that some were made by trained, often state certified, plumbers or HVAC technicians. Please think about the fact that it is not in the best financial interest of your fuel company to have you switch to free solar power.
If you want accurate information on the viability of solar hot water for your home, speak to a reputable solar installer, not a fuel company. Each BTU of solar energy used is a BTU that you would have paid for by burning expensive fuel.
Contact us today with your questions or to set up your free consultation.