Residential Solar Power and Solar Hot Water
The most popular renewable energy options for homeowners are:
- Offsetting their energy usage with a grid-tied solar electric system
- Using solar energy to heat their hot water
Grid-Tied Solar Electricity
Producing your own clean, renewable solar electricity is a great way to protect your household from rising energy costs while transitioning away from the massive CO2 emissions that come from America's coal and gas-fired power plants. With no moving parts anywhere in the entire system, grid-tied photovoltaic (PV) systems are the most reliable renewable energy technology available. This is why PV manufacturers warranty their panels for 25 years, while the expected lifespan of PV panels is closer to 50 years.
What does Grid-Tied mean?
Battery-based solar electric systems used to be the norm until about 10 years ago, when the grid-tied inverter was developed, forever transforming solar electricity. The inverter enables us to use the electrical grid as our "storage battery," eliminating the cost, complexity and toxicity associated with lead-acid battery storage systems. Now, instead of connecting solar panels to a battery bank, the solar electric system is connected directly to the Central Maine Power grid, or whatever utility grid is serving your area. The inverter allows your solar electric system to feed surplus solar power to the grid, or seamlessly draw electricity from the grid when there is not enough sunshine to meet your demand. During the summer months, when you are likely to be producing more than you need, the surplus feeds your neighbor's meter and you get a credit on your bill from the utility.
Once installed, your utility will send a technician to the house, test the system, and install a double meter on your existing meter, free of charge under Maine's net-metering law. One meter will record electricity imported from the grid, the other meter records when electricity is exported to the grid. Each month the utility will reconcile the two meters and either bill your account, or credit your account, accordingly. Credits can carry forward for a maximum of 13 months. At no time will the utility 'pay' you for surplus electricity produced by a grid-tied solar electric system.
ReVision Energy provides licensed and NABCEP-certified design and installation of Grid-tied PV systems. We are the only solar company in Maine that carries a Master electricians' license in-house.
How it Works
Solar electric panels are typically mounted on a south-facing roof section, but we also have plenty of experience ground-mounting systems when the roof is not a viable option. Major system components include the PV panels, wire and conduit, and the inverter. When sunshine falls on the PV panels, direct current (DC) electricity is generated and flows through a wire to the inverter.
The inverter converts the DC electricity to alternating current (AC), which is the type required by your home appliances. The AC electricity flows from the inverter through a wire into your electric panel. The solar electricity will then flow through your electric panel and satisfy any household demand. If your solar electric system is producing more than the demand in your home, the surplus will then flow out through your 'export' electric meter and travel against the normal flow of electricity through the utility line serving your home and back out onto the grid, looking for the next closest demand.
Government Financial Incentives
The state of Maine offers a lottery-based rebate for GTPV systems through www.efficiencymaine.gov. The federal tax credit is 30% of total system cost, capped at $2,000.
Grid-tied PV Rules of Thumb
- 1 kilowatt of installed PV panels will produce roughly 1,300 kilowatt hours of clean electricity annually
- 1 kilowatt of installed PV panels will generate roughly $190 of electricity annually @ $.15 kW/h
- 1 kilowatt of installed PV panels will offset roughly 1,700 lbs. of CO2 emissions annually
- 1 kilowatt of installed PV panels costs roughly $9,000
Solar Domestic Hot Water
Using sunshine to produce hot water for showering, laundering and dish-washing is a practical way to make a positive impact on the environment while saving money at the same time. A typical residential solar domestic hot water system will eliminate more than 5,000 lbs. of CO2 emissions annually and can save more than 300 gallons of oil per year, depending on your current domestic hot water setup.
After 10 years of designing and installing hundreds of solar hot water systems in Maine's challenging climate, we've distilled our knowledge and experience into a robust design that offers the highest efficiency and durability. ReVision Energy can tailor its time-tested, field-proven system design to integrate with most existing water heating systems, whether it is gas, electric or oil-fired.
How it Works
Solar hot water collectors are typically mounted on a south-facing roof section, but we also have plenty of experience ground-mounting systems when the roof is not a viable option. Major system components include the collectors, a purpose-built solar storage tank, copper piping, circulating pump and electronic controls.
Whenever sunshine makes the solar hot water collectors hotter than the water in the bottom of the solar storage tank, an electronic sensor automatically turns on the solar pump affixed to the tank. Sun-heated antifreeze is pumped from the collectors and circulated through a heat exchange coil located in the bottom of the storage tank, thereby transferring the heat from the sun to your domestic hot water supply. ReVision Energy builds automatic backup into all solar domestic hot water systems so that when the sun can't get the job done, you don't have to worry about cold showers.
The solar storage tank has a secondary heat exchange coil located in the top of the tank, which is plumbed to your existing heating system for backup. If this is not possible, alternative solutions include using a special tank with an electric element for backup or installing an on-demand hot water heater.
Solar Hot Water Collectors
ReVision Energy highly recommends Apricus evacuated tube collectors. Apricus is a global leader in evacuated tube technology based in Australia. We prefer evacuated tube technology over flat plate systems because the tubes' vacuum insulation design prevents system heat losses in Maine's relatively cold climate. Plus, the cylindrical shape of the tubes enables them to better harvest low-angle wintertime sun at our northern latitude. Flat plate collectors, however, offer better summertime performance. For applications where high demand will come in the warmer months (seasonal homes, i.e.), or where cost is a primary concern, we offer Stiebel Eltron flat plate collectors.
Solar Storage Tanks
Stiebel Eltron manufactures the best dual coil solar storage tank on the market. Stiebel's purpose-built tanks are super-insulated with 3 inches of urethane foam to store precious BTUs harvested from the sun and its two internal heat exchange coils allow for easy integration with almost any boiler-based heating system. This porcelain-lined steel tank comes with a built-in sacrificial anode rod with a wear indicator that is easy to view and replace if necessary.
Rough Costs of Completely Installed System Before Incentives*
- 30-tube collector with 80 gallon storage tank for 1-2 people: $9,500 to $10,500
- 40-tube collector with 80 gallon storage tank for 2-3 people: $10,000 to $11,000
- 50-tube collector with 105 gallon storage tank for 3-4 people: $10,500 to $11,500
- 60-tube collector with 105 gallon storage tank for 5-7 people: $10,500 to $12,000
*Cost variables are number of collectors, tank size, difficulty of roof installation, difficulty of pipe installation, difficulty of tank installation and project distance from either Portland or Liberty. Retrofits are more challenging than new construction.
Government Financial Incentives
The federal tax credit for a residential solar hot water system is 30% of total system cost, capped at $2,000.
Solar Domestic Hot Water Rules of Thumb:
- Each 20-tube collector array will generate roughly 15,000 BTUs of clean heat energy per day
- Each 30-tube collector array will generate roughly 22,500 BTUs of clean heat energy per day
- 1 gallon of home heating oil contains 139,000 BTUs of energy, but most oil boilers burn at roughly 75% efficiency in winter and 15% efficiency in summer to produce domestic hot water
- 1 gallon of propane contains 91,000 BTUs of heat energy
Solar Space Heating
If you have a super insulated home (R30 walls, R50 ceilings) and radiant heat distribution, there is a chance that solar space heating could work for you. Because it is a challenging application, we ask that you carefully read the 
Solar Space Heating document to assess whether it makes sense for your particular situation.
Basic Questions to Assess Solar Hot Water Viability For Your Home
- Do you have a south-facing roof section that is shade-free from 9 a.m. to 4 p.m.?
- Do you have a patch of nearby ground that is shade-free from 9 a.m. to 4 p.m.?
- Is there a practical pipe run from the collectors to your basement?
- Is there space for a solar storage tank in your basement and can something 29" wide fit through a door or bulkhead?