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Overview of Solar Power for Existing Homes

Before seriously considering installing any type of solar system you should first evaluated your home searching for any areas that could be made more efficient. While solar can heat a leaky old un-insulated farmhouse it would take hundreds of tubes and the cost would be prohibitive. Generally the common upgrades in insulation and weatherization will pay for themselves much faster than a solar system. The less fuel or electricity you need, the smaller, and less expensive your solar system will be. 

The Efficiency Maine Home Energy Savings program provides financial incentives to get your home weatherized, upgrade or replace heating systems and to install solar.  Getting an energy audit is the first step.   We know who the good energy auditors are and we are happy to recommend some in your area.  

The list of “renewable energy systems” include; Solar Thermal for heat and hot water, PV-Photovoltaic, or wind, for electricity. GeoThermal and air source heat pumps for heating and cooling, or a solar hot air sheet for supplementing space heat, even wood based heat. While all these applications are not strictly “solar” they all rely on mother nature to provide renewable energy resources


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

Generally Solar Thermal Hot water systems will pay back their initial investment the quickest as since adding a tank permits boiler efficiency upgrades at the same time.  For a family sized system it is usually 6-8 years after incentives.   Cost before incentives average $8,000-$12,000. PV is closer to 12 year payback for most homes at a cost of about $10,000-20,000. If you have a really good site for wind it may cost less than PV but few locations have the high winds that are needed. Unless you have a very large home with a high heat demand Geo-thermal heat pumps are generally not practical on a residential application because of the $40,000 average cost and on retro-fits of an existing home because of the disruption to the lot. A better choice is a cold weather air source heat pumps which provide a cost effective solution, combining heating with cooling ability.  They are one of the smartest way to provide cost effective heating and cooling.  The are almost as efficient as geo-thermal, they cost about $3,500 and they work down to -15 degree outdoor temps.  When combined with solar PV they are the perfect green way for the sun to heat your home.

Solar System Design Considerations

IMG 4044 2 full side wall CROPPEDOften solar thermal or PV panels are mounted on the roof.  We will work with you to decide where to route the plumbing and electrical lines to reach your hot water storage tank or electrical service panel.  If no suitable interior chase way can be found, we can run PV wire in conduit or use an outdoor rated wire.  For hot water copper lines we enclose them in a product called Line hide or Slim-duct that looks much like a gutter downspout. This product can be painted to match your building. The house at the right has solar on the roof and the linehide follows the pitch of the roof and runs down.  In addition they have a Mitsubishi heat pump for heating and cooling.  In this case the line hide runs from the compressor up the walls to connect to the interior wall mounted evaporators inside.  They are painting some of the line hide gray to match the house and the ones on the edge are left white to match the trim.   Lines can be insulated and buried in the ground if we are running between buildings.

Solar systems can easily grow with your family or home provided you plan ahead and properly size the piping.  You solar system will last more than 25 years so if the roof is in need of replacement it should be done before your collectors are installed.  

For solar hot water you need room for a large storage tank 80-120gl and more if you are doing heating.  The pump station/controller will be wall mounted and is double the size of a shoebox. 

For solar electric you need room for additional breakers in the service panel.  If you choose a string inverter, over micro-inverters on the roof, then set aside about 36" x 36 with at least 3 feet clear in front.  

Locating your Solar Collector Panels

Collectors are generally roof mounted, but can be ground mounted on a rack, or placed on a secondary building. Generally collectors like to face south. Solar thermal is more forgiving and can face east/west.  A photovoltaic electric system facing East/West will have a reduction in output of about 20-25%.  Collectors need to be in the sun and not shaded by roof lines. With a tool called a Path Finder we can check for seasonal shading that may be caused by nearby trees, roof lines, or buildings. Sometimes some summer shading from a tree on a solar thermal hot water collector can actually be beneficial to reduce excess summer output.

We 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 solar thermal 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. Winter output is best when they face true south on a highly pitched roof.

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

 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.   Installing a standard solar thermal hot water system normally takes only a few days.




Since 2010 increased competition and global oversupply dropped the cost of standard PV panels significantly.  This has given rise to PV becoming more popular in Maine than solar thermal hot water. PV systems have no moving parts and thus less chance of failure compared to solar hot water and no maintenance requirements. Photovoltaic (PV) electric systems manufactures are coming out with exciting options. There is "PV glass" that is used on vertical surfaces on high rise buildings.   Thin film is practical for metal roof installations. It is bonded to the roof for a visually pleasing look.  Some modules are bi-facial and can collect the sun's rays from both sides.  These are great for patio and carport covers.

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. 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 activate case of a power outage but a generator is usually less expensive.  

Solar Thermal Systems for Hot Water or Heating

  • You will need a large storage tank, plan on 20-40 gallons per person, more if you are doing space heating.
  • If you are going to heat your pool or hot tub, you need to decide where you would like the plumbing lines routed. They may be insulated and buried.
  • If you purchase a data logger and want to routinely check it, have it installed in a convenient location. It is possible to place monitoring equipment anywhere so you do not have to go to the basement to check system performance.

PV – Photovoltaic Systems for Electricity

  • A rough estimate is 100sqft of collector generates 100kWh per month. PV panels like to be close to south.  East/West reduces output about 20-25%
  • A PV system does not need to meet 100% of your needs if you remain grid tied. Additional power will be drawn from the grid as necessary. You are credited for electricity created, and debited for use, over a 12 month window. If you are concerned about power outages a small battery bank can be tied into the system but a generator will cost less.  Some inverters can provide limited power when the grid is down.
  • If you are off grid a battery bank and some sort of backup system needs to be in place. Batteries need water, and a separate storage area away from any living space is best. You will need lighting in the area to regularly check the batteries.

Wind Turbines for Electricity

Many people are fond of the idea and look of a windmill.  Often you will find a neighbor that does not want your wind turbine to block their view.  Some cities have codes against wind turbines, usually restricting height to less than the lot size. Often there are fewer objections to the vertical turbines such as Tangarie since they are smaller, quiet, do not strobe or harm birds.  To successfully run a wind turbine you need an appropriate site. If you are not 100% sure of the wind speeds have a wind study done by placing an anemometer at the final height.  A one year study is best, 6 months is minimum.  We have seen many windmills placed in unsuitable locations, between buildings, blocked by trees, not generating the output expected.   With the drop in PV modules price unless you have an exceptional site you will find that wind may cost more than solar electric.  One great use for a small windmill is a supplement to a battery PV system.  In general on a stormy day you may not get any sun radiation but the wind may be blowing and this will allow you to keep your batteries charged.   Plus small windmills do not require expensive towers.


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Portland ME 04103

(207) 797-0979

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