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Solar Power for New Homes

new home solarNow is an exciting time to be building a new home. The many energy saving ideas developed over the last 10-20 years have become affordable. Now the challenge becomes picking from the many good options. The different highly insulated wall systems, cellulose, and spray foam choices means that pink fiberglass is a thing of the past. It is now easy to get a tight, high R-value home that will use much less energy that conventional/old fashion construction. The federal solar tax credit covers new homes. There are additional incentives to the builder until 12/31/13.

This is a good thing for environment and solar energy systems. The better the home's construction, the less energy required. Thus, the smaller and less expensive the solar systems can be. For most home buyers deciding how to best allocate the building budget is a difficult decision. Solar is a major investment, but one that saves a great deal of money in the long run. Unlike fossil fuels, or wood that has to be harvested and delivered, solar generates zero pollution. 

Every project has budget limitations.  We STRONGLY recommend you put your money into an air tight well insulated shell.  If there is money left for solar, great.  If not then build your house to be solar ready and add it later.  You can pay for it with the savings you have because your energy use is so low.  The building code is the bare minimum, below this the state says the house simply is not acceptable.  A leaky home filled with Fiberglass and wrapped in stapled house wrap is not energy efficient even if you have 6" walls.  If you are building new why would you want the bare minimum? Wouldn't you want at least a pretty good house?  There are many local builders, many member of the Building Science Discussion group, that understand most people cannot afford to build to super high standards such as Passive House.  And they have learned the techniques needed to build a cost effective, air tight, "Pretty Good House".   If you properly build the home most of the time you will not need an expensive radiant system and boiler.  In fact it is quite possible that a radiant system would over heat the house because the heat loss is so small.   Home Power magazine has a comprehensive article on the different levels or definitions of the components, from shell to solar, that make up a "green" and "energy efficient" structure. Green Building Advisor web site has a great posting on the importance of air sealing over insulation.  It is a "must read" if you are building new.  

In 1 year just 30 solar hot water tubes can produce the equivalent of 2,256 kWh and prevent the generation of over 400K of CO2.

We are not builders, but in the course of our work we see many new techniques and options. If you are thinking about building and just need some direction, or an unbiased source to bounce ideas off, give us a call. We will share any information we have.  We can refer you to consultants that will work with your builder to insure you home is air tight, has good thermal breaks, and is properly insulated.  The small consultation fee will quickly be covered by the energy savings.  Plus we know the good architects and builders in the greater Portland area and are happy to make referrals. 

The Federal Department of energy has many good publications on building with solar, both for the contractor, and the homeowner,

We are happy to work with your builder or architect to design a system to meet your unique needs.

Solar House

The 2 panels on the right are solar thermal, all the remaining panels are PV electric.  This is a common ratio.

 

Making a “Solar Ready” Home

If solar thermal hot water and PV are not installed as part of the construction process it is easy and very inexpensive to build in the necessary plumbing runs during construction. This allows considerable savings when solar is later installed.

Important Pre-Construction Considerations:

  • PV electric panels like to face south.  An E/W exposure reduces output about 15-20%.
  • Allow a chase way to run the wiring from the roof to the electrical panel.
  • Leave room for the possible installation of an inverter near the panel and room for 1-2 20-30 amp breakers.
  • PV panels will require about 300 sq ft.  Call us to determine accurate sizing.
  • Make sure plumbing vents, trees and roof lines do not shade the panels.  Put plumbing vents on the north roof.
  • Solar Thermal hot water systems like to face south but can be east/west with minimal impact in performance.
  • 2 ¾-1 inch insulated copper plumbing lines need to run from the panels to the basement hot water tank location.
  • Solar Thermal rack with 10 tubes are about 7 ft x 3 ft.
  • For hot water you need rack 1 per person.
  • For heating add at least 60 tubes.
  • Allow for a tank with 25+ gallons of hot water storage per person.

Solar Hot Water Heater

We are happy to provide information on “solar compatible” water tanks.

The numbers above are rough estimates and we are happy to help you come up with better number if you are concerned about spacing. If you have a large home heating system, additional plumbing may be necessary and you will have more tubes. When grid tied, often homeowners install smaller PV systems that meet only part of the needs.

The important point is that it is quite inexpensive and easy at construction time to run pipes and leave a chase way for an electric run. Making a home “solar ready” can give you a marketing advantage when it is time to sell.

Heating Your New Home

Solar Infloor Heating

Products such as Warmboard are quick to install, allows responsive temperature adjustment, works with wood, carpet, vinyl and more.  They work well in bedrooms.

Radiant floor heat is comfortable and dust free. Originally radiant was installed in a slab. The idea is the concrete served as a thermal mass. The advantage was that once this large thermal mass was up to temperature, it held it for a long time.  The disadvantage is you cannot lower the temp quickly at night

Now the many products such as Infloor and Warmboard give more responsiveness to heat adjustment. Basically these are 4x8 wood sheets with an aluminum layer that distributes the heat from the PEX that is inserted into the pre-grooved slots. They are perfect for areas where you might want to drop the heat throughout times of the day, such as bedrooms.

Slab based systems have a big advantage that they put out more radiant heat with lower temperature water. This can be a real benefit when short winter days limit the output of your solar thermal system. Often our customers combine the 2 types, with slab in the basement and 1st floor, and boards upstairs in the bedrooms. Today’s slab temperature sensors reduce the problems with overheating.

Some builders have been known to suggest installing standard baseboard upstairs to save money on radiant. This is a horribly irresponsible suggestion because it requires heating water to 180° vs. 120°. This alone will raise your fuel usage about 15%. Over the course of just a few years you will burn up what little savings you gained on the install.   Low temp baseboards or radiators would be a fine substitute upstairs. 

Protect the Environment and Your Checkbook Balance

Solar thermal combined with radiant floor heat is the ideal way to live. Your system will provide your domestic hot water as well as space heating. In the summer excess heat can be routed to heat your pool for free, or dissipated outside. The size of the system will be based on your family’s hot water needs and the Btu requirements for your home. Once you have your initial building plans we are happy to develop a proposal. An average family can expect to have 3 or more 30 tube collectors and about 200 gallons of hot water storage.

At this point in time, in Maine, using PV panels to provide electric heat via the use of air source heat pumps is usually less expensive than using solar thermal.  With a properly air sealed and insulated home a heat pump can be a huge money saver up front and through years of operation.  With heat pumps there is no baseboard, expensive boiler or furnace. 

Should you use solar thermal and a radiant system you will still need a backup system for days when there is not sufficient solar radiation. While cold temperatures do not impact evacuated tubes, during our short days in December and January there just are not enough sunlight hours. Generally we size the system to meet 50-70% of your annual needs (known as the “solar fraction”). This takes into consideration the impact of winter snow and short/low solar radiation days.

If the home is energy efficient the daily heat loss is very low and you should be able to go a few days with no power and still remain comfortable. 

Installing your solar system

thermomax tubesCollectors are generally roof mounted, but can be ground mounted on a rack, or placed on a secondary building.  Generally, collectors work best when facing south.  Solar thermal is more forgiving and can face east/west.  Collectors need to be in the sun and not shaded by roof-lines.  We can provide all the plumbing, radiant and heating products and installation in addition to installing your solar system, or we can work with your builder or plumber.  Make sure all roof vents are placed on the north side of the roof.

thermomax roofWe have seen beautiful cedar pergolas, window overhangs that also provide summer shading, and railings all done with solar thermal evacuated tubes. In these cases they look like architectural elements, not solar tubes. Velux makes a great flat panel collector. While it does not have the winter output to provide space heating, for domestic hot water it is a great choice if you object to the look of other collectors. Velux’s product integrates with their skylights, having the same size and reveals. They are flashed into the roof for a very streamline look. Output is best when they face true south on a highly pitched roof.

Velux panels

4 Velux solar thermal panels with a skylight at each end.

Photovoltaic (PV) electric systems manufactures are coming out with exciting options.  Thin film is practical for metal roof installations.  It is bonded to the roof for a visually pleasing look.  There are new mesh type PV fabrics that can be shade structures as well as power generators. There is PV glass that is used in high rise buildings.   Increased competition and global oversupply dropped the cost of standard PV panels significantly.   We are now seeing payback times as low as 8 years on larger residential systems.    If you have a building site where bringing in power lines is cost prohibitive, an off-grid battery bank system may be the answer.  Most homeowners elect to be grid tied to avoid the cost and maintenance associated with batteries.  In these cases you pull your power from the grid when needed.  You are credited for power created and debited for what you use over a 12 month window.  If you have concerns about loosing grid power, you can add a small battery bank to come on in case of a power outage although a generator is usually less expensive.  SMA recently released their new TL series inverter that has a outlet.  When the grid goes down the inverter disconnects itself.  This is required by the electrical code to insure power is not feed into the disrupted grid and does not harm line workers.   Upon disconnecting from the grid the outlet is activated providing up to 1500 watts.  Of course it only works when the sun is out but this may be enough to keep your frig cold, home warmer, and charge your Mobil phone or laptop.

 

Ready to get started?

Contact us today with your questions or to set up your free consultation.

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PV Cost and Net Metering

Podcast explains Net Metering &  how much cheaper PV electric is vs. the utlity

Solaris

600 Riverside St.

Portland ME 04103

(207) 797-0979

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