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Passive Solar

What is passive solar and why do it?

Passive solar technology uses solar energy to directly heat or light a space. In passive solar heating, south-facing windows with awnings allow solar energy to heat and light a space when the sun is low during the winter months, but do not allow for direct heating when the sun is high during summer months. This type of design can be combined with features like tile flooring and/or trombe walls that absorb heat during the day and release it at night.

An example of a common passive solar lighting technology is a solar tube. These tubes extend above one’s roofline to reflect light down into a space.

Passive solar technologies can use solar energy without moving parts to reduce the need for conventional, active heating or lighting technologies. Therefore, the upfront cost of including passive solar can be paid back through energy savings.

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Solar Electric (PV)

Compare grid-tied, off-grid, and hybrid PV systems

Grid-tied PV systems are systems that supply power to the electric grid when solar production exceeds electricity consumption. Credit for solar electricity generated happens through net metering. Off-grid systems only generate electricity for on-site consumption and generally store excess electricity in batteries. Hybrid (or grid-tied with battery backup) systems are tied to the grid but can utilize batteries should the grid go down.
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Electric Load Analysis Worksheet for Off-Grid Systems

What is solar leasing?

A solar lease is a contractual agreement between a property owner and a solar provider in which the property owner leases solar photovoltaic (PV) panels from the provider for generating electricity. Under the terms of the lease, the property owner is typically responsible for making monthly payments to the solar provider in exchange for the installation of and electricity generated by the panels and the insurance and maintenance of the PV system. The PV system is typically tied into the utility grid in order for the solar provider (and therefore the property owner) to take advantage of utility rebates.

Solar Leasing for Colorado Homes – Fact Sheet


What is a community solar garden?

A community solar garden is a grid-tied central solar PV array from which shareholders or subscribers belonging to the participating utility can purchase or lease panels. Electricity production from the solar garden is credited against shareholder or subscriber bills according to the proportion of the garden they own or lease.
Compare owning PV, leasing PV, and community solar gardens

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Are there financial incentives for solar PV?

Yes. The federal government offers tax credits as follows:

  • 30% for systems placed in service by 12/31/2019
  • 26% for systems placed in service after 12/31/2019 and before 01/01/2021
  • 22% for systems placed in service after 12/31/2020 and before 01/01/2022

In addition, certain utilities may offer incentives that generally fall into 2 categories:

  1. A rebate based on system size (subject to a maximum rebate amount)
  2. A “performance-based incentive” based on the electricity generated by the system

PBIs are paid to the generator of solar electricity (i.e. a homeowner) for every kilowatt-hour of electricity generated by the solar array over a specified term. PBIs for leased systems or for solar loans may be paid directly to the third party solar installer.

Source: Database of State Incentives for Renewables & Efficiency (DSIRE)

Federal Tax Credits for Home Energy

Is solar PV right for me?

Solar PV may be right for you if you:

  • have a building with an unshaded roof in good condition, especially if that roof that faces south, southeast, or southwest
  • have a property with enough space for a ground mounted system OR
  • live in an area in which you are eligible to participate in a community solar garden

How do I calculate the costs and benefits of installing a solar PV array?
Does installing solar on my house create a lien?

According to Andrew Ehrnstein of Solar City (2016), the short answer is: almost certainly not. It does depend on the company. However, it would be good to know what a lien is, and how this might or might not come up in a solar installation. Mortgages and contractors can create liens against a house to secure payment for their notes and services. A lien is a right to keep possession of property until the debts owed against that property are paid back. And basic real estate law says that anything attached permanently to a structure is assumed to become part of the property.

If you are paying cash for your solar installation, then the contractor has a lien right under Colorado law from the moment they deliver materials until you’ve paid in full. Most homeowners do not pay in cash for their solar, but that’s how it works in those cases. When a solar contractor installs a system on your home, the system is more likely to be financed with either a loan or a lease. The major solar companies use non-lien financing, meaning that they secure payment only with the equipment, and not your house. You may want to verify that this is true when interviewing your solar provider before signing their agreement. With non-lien financing there would be no lien against your house.

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Solar Thermal

What is a solar hot air system?

Solar hot air collectors typically consist of a glass panel with black interior attached to the outside of a south-facing wall. Solar radiation heats the air in the panel, which travels into the building through a duct at the top of the collector. Return air from the building enters the collector at the bottom. Hot air collectors are often used to heat a single room, but can be connected to a building’s ductwork to provide heat to multiple spaces.

Importantly, most hot air collectors will only provide significant heat from mid-morning to early afternoon, a time when many residents are not home. The penetrations for solar hot air collector ducts may be susceptible to air and rain leaks if not sealed tightly. Tight dampers are also required to keep excess heat out in summer.

What are the different types of solar hot water systems?

There are two general types of solar hot water systems used in the United States–closed loop and drainback systems. Both closed loop and drainback hot water systems use pumps and valves to control the circulation of the fluid throughout the system. They allow the system to run year round, without the threat of freezing. Protecting the system from freezing is critical to the proper operation of any system.

The most common domestic hot water system is the closed loop glycol system. This is a sealed unit where a propylene glycol mixture transports the heat within the system. The heat transfer fluid is a mixture of antifreeze and water, which can be protected from freezing to -50°F. If overheated or stagnated, the fluid can go bad.

The second most widely used domestic system is the drainback system. Fluid fills the collectors when the pump starts and drains the collectors when the pump stops. The benefits of a drainback system are that it is protected from freezing down to -20°F, it is protected from overheating during a period of time with no power, and water is used as a heat transfer fluid.

What are the different types of solar hot water collectors?

Solar collectors are one of the key components of an active solar hot water system. They collect the sun’s energy and transfer that energy to the heat transfer fluid. Flat-plate collectors are the most common collector type used in domestic water heating systems. A typical flat-plate collector is an insulated weatherproof metal box with a glass or plastic cover and a dark colored absorber plate. Mounted on the roof or ground, it consists of a thin, flat, rectangular box with a transparent cover that faces the sun. Small tubes run through the box and carry the fluid, such as water or antifreeze, to be heated. The tubes are attached to an absorber plate, which is painted black to absorb the heat. When the heat builds up in the collector, it heats the fluid passing through the tubes. Active systems rely on controllers and pumps to move the liquid between the collector and the storage tank.

The second type of collector is an evacuated tube collector. These collectors can achieve extremely high temperatures (170°F to 350°F) which makes them more appropriate for industrial and commercial applications. These collectors have rows of transparent glass tubes, each tube containing a glass outer tube and metal absorber tube attached to a fin. The fin’s coating absorbs solar energy and reduces heat loss. An evacuated tube collector is sealed in a vacuum that minimizes heat loss and helps absorb solar energy under cloudy conditions. Because of this, there is a concern when snow and ice accumulate on the tubes, causing them to not work properly.

Are there financial incentives for solar thermal?

Yes. The federal government offers tax credits as follows:

  • 30% for systems placed in service by 12/31/2019
  • 26% for systems placed in service after 12/31/2019 and before 01/01/2021
  • 22% for systems placed in service after 12/31/2020 and before 01/01/2022

Note that at least half the energy used to heat a building’s water must be from solar in order for the solar water-heating property expenditures to be eligible. The tax credit does not apply to solar water-heating property for swimming pools or hot tubs. Equipment must be certified for performance by the Solar Rating Certification Corporation or a comparable entity endorsed by the government of the state in which the property is installed.

Source: Database of State Incentives for Renewables & Efficiency (DSIRE)
Federal Tax Credits for Home Energy

Is solar thermal right for me?

Solar thermal may be right for you if you:

  • use more expensive water heating fuels such as electricity or propane
  • have a building with an unshaded roof in good condition, especially if that roof faces south, southeast, or southwest OR
  • have a building with enough space for a ground mounted system

Case studies
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Solar Water Pumping

What makes up a solar water pumping system?

A solar-powered pumping system has the following minimum components:

  1. water well
  2. solar PV array
  3. array mounting bracket and rack
  4. pump controller
  5. electrical ground for controller
  6. DC pump with safety ropes, mount, and well seal
  7. wiring
  8. discharge tubing or piping
  9. storage tank
  10. tank flotation switch
  11. water taps or access points
  12. security

What are the different types of solar water pumping systems?

Pumps designed specifically for solar power utilize direct current (DC) and can be 15-25% more efficient than alternating current (AC) pumps that experience losses when converting power to AC. Although DC pumps usually cost more than a comparably sized AC pump, DC pumps do not require the purchase of inverters. Some pumps are designed to run on either DC or AC power so that when the sun doesn’t shine a generator can provide AC power to the pump.

Pumps can also be surface mounted or submersible. Surface mounted pumps can be used for a solar powered pumping system but are discouraged because of their limitations when used in deep wells. Based on the specifications from several manufacturers, the typical lift abilities for surface pumps designed for solar power are between 10 and 20 feet. Surface pumps also have greater exposure to the weather.

Are there financial incentives for solar water pumping?

Yes. The federal government offers tax credits as follows:

  • 30% for systems constructed by 12/31/2019
  • 26% for systems constructed after 12/31/2019 and before 01/01/2021
  • 22% for systems constructed after 12/31/2020 and before 01/01/2022
  • 10% thereafter

USDA’s Natural Resources Conservation Service offers financial cost sharing for solar water pumping through its Environmental Quality Incentives Program (EQIP). USDA also offers grants for various agricultural and commercial energy efficiency and renewable energy projects through its Rural Energy for America Program (REAP).
Database of State Incentives for Renewables & Efficiency

What are the costs and benefits of solar water pumping?

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Case studies
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Last updated: March 1, 2017 at 11:06 am