Energy Baseline and Conservation

An energy audit of the home was completed to characterize energy use, determine energy costs, and find ways to reduce energy consumption. This is an important step because the energy load profiles are needed for the design of supplemental systems and reducing the energy loads also reduces operating costs. The 2015 end use breakdown for electricity and natural gas are shown in Table 1, Figure 2, and Figure 3 .

Energy conservation measures (ECMs) identified during the energy audit included the opportunity to install a solar hot water and heating system and upgrade the fridge, stove, clothes washer and dryer, lighting, hot water heater, insulation, windows and doors. Not all upgrades were economically feasible. Table 1 shows potential savings from the economically viable upgrades.

Figure 2: Electrical Consumption Breakdown

Figure 3: Natural Gas Consumption Breakdown

Introduction

Electricity provides critical services to home occupants such as space heat, cooking, and lighting. Recent events have shown the vulnerability of homeowners to electrical grid failure. Events include systemic issues such as the 2003 blackout that left many North Eastern households without electricity for days, as well as storm events that regularly leave homeowners without electricity in the middle of winter, especially in rural areas. Solar photovoltaic (PV) systems are often seen as a “green” way to go “off the grid” and make homes more resilient against blackouts and costly electrical bills. Many jurisdictions have seen an increase in PV systems as a result of government programs that incentivise homeowners to install grid-tied solar systems. These systems provide renewable energy to the grid but provide no autonomy to the homeowner. Through a representative case study this article investigates options available to homeowners for reducing reliance on the electrical grid. Examples include the pros and cons of PV, generators, and battery systems and what must be considered when choosing an electrical grid independence option.

Home Description

The case study centres on the house shown in Figure 1. It is located in Hamilton, Ontario and was built circa 1905 and is typical of many homes in the area. The house is heated with forced air natural gas supplemented with two natural gas fireplaces, has air conditioning, a natural gas water heater, predominantly incandescent lighting, and typical appliance and plug loads.

Electrical-Grid Independence Options Electrical-Grid Independence Options For Temperate Climate Households

"Through a representative case study this article investigates

options available to homeowners for reducing reliance on the

electrical grid. Examples include the pros and cons

of PV, generators, and battery systems and what

must be considered when choosing an electrical grid

independence option."

Image provided by Glen Prevost

Figure 1: Case Study Home (B. Baetz)

G.G. Prevost - Research EngineerDepartment of Civil EngineeringMcMaster UniversityHamilton, Ontario, Canadaprevosgg@mcmaster.caCorresponding author

B.W. Baetz - ProfessorDepartment of Civil EngineeringMcMaster UniversityHamilton, Ontario, Canadabaetz@mcmaster.ca

Battery Bank

A battery bank large enough to power critical systems for a limited mount of time could be installed. It would be charged by the grid and then used when the grid is down. The battery bank specified for the full solar system could be installed to power the home’s critical systems for approximately 6 days. The installed cost of this system is estimated at $10,000. Care must be taken to ensure the batteries are maintained in working order because they will sit for long periods of time without use.

Picking a Backup System

A full-sized PV system that could support the home’s electricity consumption is technically and economically unviable. The available roof space is insufficient but some panels could be mounted vertically on the southeast wall. Shading and structural support could also be an issue. The full-sized system is currently a good choice as a backup system for residential homes with access to the electrical grid. The minimalist PV system suffers the same issues as the full-sized system, although it is more technically feasible since it can fit on the roof.

While not currently viable solely on economics, The Rocky Mountain Institute reports that stand-alone PV systems will be viable in the next 10-20 years in certain US states as energy costs increase and solar PV technology costs decrease. Assuming Canada has similar energy pricing and market access to PV technology, grid-independent installations will also become economically viable in Canada in the same general timeframe.

The electrical generator is a good choice for powering the critical home systems where noise will not be an issue or can be mitigated. The decision to pick a portable or a standby generator is one of cost and convenience. If the main concern is simply critical systems, a portable generator will suffice. If more convenience is desired or if grid reliability decreases, resulting in significant black or brownout periods, then a stand-by generator capable of powering the entire house may be a better choice. Both are cheaper options than a PV system.

A battery backup system has the drawback of being usable for only a short period of time and becomes useless in a prolonged blackout and quite expensive when compared to the generators. It has the benefit of quiet operation for urban areas. The choice of a battery system comes down to cost, noise, and reliability.

Electrical grid independence is an important feature of a residential home given the large number of prolonged blackouts in the recent past, especially in rural areas. Homeowners have several options for resilience as outlined above. Each have their pros and cons and homeowners will have to choose the best option for their specific situation.

After the cost of maintenance (est. $200/yr.), battery replacement after ten years (est. $5,000), and disposal at the end of its twenty-year life (est. $3,000) are accounted for, this project loses money over its lifetime. Off-grid systems are sized for the “critical month,” resulting in an oversized system. In this case the system is sized for December when the home consumes 190 kWh and the system is capable of producing 210 kWh. However over the course of the entire year the home only consumes approximately 1,940 kWh (after ECM implementation) but the system is capable of producing 6,110 kWh. Even if the system could feed this extra electricity back into the grid, the project is still not economically viable.

Minimalist Solar Photovoltaic System

A smaller solar system of 3.6 kW could be installed to power only critical systems rather than the entire home. Grid electricity would be used day-to-day and the PV system during blackouts. The cost is estimated at $17,100. Similar to the full-sized system, the economics of this system make it non-viable but it is a lower-cost system that can fit on the roof and could power the critical systems of the house indefinitely.

Electrical Generator

A stand-by generator powered by natural gas, propane, and/or gasoline could be installed to power the home during a power failure. Two types of generators could be considered: portable or standby. Note that both types of generators can be loud and may be inappropriate in urban areas unless the noise is mitigated.

Portable generators use gasoline, propane, and/or natural gas depending on the type and are generally available in smaller power ratings than stand-by generators (500 W and upwards). They can be connected to the home’s electrical system through a transfer switch and wired to power desired circuits. This system requires a user to physically connect the generator and turn it on when the power is out. The installed cost is estimated at $2,500 for a model that could power critical systems of this home but larger generators are available.

Stand-by generators run on natural gas or propane and can be connected directly to a natural gas line for indefinite operation. They are generally larger than portable generators (>5,000 W), mounted on a concrete pad outside the home, and can power the entire house as long as they have a supply of fuel. Standby generators are capable of running regular automatic tests to ensure they are in working order and automatically turn on when the power goes out making them a convenient option. The installed cost is estimated at $9,000 for a model that could power the entire house, and $7,000 for a smaller model for critical loads only.

For the case study house, a 10 kW generator with an installed cost of $9,000 would be required for running the full home while a 1 kW generator at an installed cost of $2,500 would be required for critical systems only.

ase StudyC

Electricity Natural Gas

Current Energy Consumption

Viable Savings

Energy Consumption After Implementing Viable Energy Conservation Measures

Consumption(kWh)

Cost($)

Consumption(m3)

Cost($)

5,440

2,400

3,050

$940

$410

$530

2,870

1,100

1,770

$620

$240

$380

Full-Sized Solar Photovoltaic System - A full solar system capable of providing all the electrical needs of the home and be independent of the grid for an indefinite period of time

Minimalist Solar Photovoltaic System - A small solar system capable of providing critical electrical needs of the home and be independent of the grid for an indefinite period of time

Electrical Generator - A fossil fuel generator capable of providing either all or just critical electrical needs of the home independent of the grid for an indefinite period of time

Battery Bank - A battery system capable of providing critical electrical needs of the home and be independent of the grid for a short period of time

$25,000 to

$35,000

$15,000 to

$20,000

$2,500 to

$15,000

$5,000 to

$15,000

■ Electrical grid independent

■ Powers whole home indefinitely

■ Quiet operation

■ Expensive

■ Electrical grid independent

■ Powers critical home systems indefinitely

■ Quiet operation

■ Expensive

■ Does not power

whole home

■ Only powers home for a

limited amount of time

■ Expensive, depending

on size

■ Electrical grid independent

■ Can power whole home or

critical home systems indefinitely

■ Quiet operation

■ Loud

■ Expensive, depending on size

Alternative Description Pros Cons Cost

Full-Sized Solar Photovoltaic System

A full-sized, grid-independent PV system could be installed to provide 100% grid-independence. This is the most complex and costly option but provides complete grid independence for the home. To decrease the system cost and increase technical viability, the dryer should be converted to natural gas and the air conditioning should not be operated using the PV system. If air conditioning is desired, it would need to remain on the grid. Preliminary design determined that the system would consist of twenty-two 8.65 A PV panels, providing 5.7 kW of peak power. A 48 V battery system with 24 batteries would provide 3 days of autonomy to account for days with limited sunshine. The cost is estimated at $27,800 and would provide $330 worth of electricity each year. Since the system is not grid-tied it cannot sell the excess electricity into the grid. A grid-independent system was chosen because some jurisdictions that offer incentives for PV systems, such as Ontario, will not incentivize a grid-tied system that feeds the home first and then the grid.

The roof would be the best place to install the system but the roof angles are relatively shallow, face southeast, and do not have sufficient space to hold the required panels. Ideally the system should face south at a tilt angle equal to the latitude of the building’s location. Surrounding trees pose some shading issues and a detailed shading analysis should be completed using a tool such as Solar Pathfinder to evaluate the impact. These are common problems when installing a PV system on a residential roof in an urban area. The additional equipment such as batteries, controllers, inverters, and switchgear will be housed in the basement. This is the ideal location since it will be climate controlled and dry, improving battery performance and reducing wear on the system components. The batteries must be housed separately and adequately ventilated to ensure there is not build-up of harmful gasses.

Table 1: 2015 Home Energy Use Baseline Before and After ECM Implementation

Table 2: Electrical Home Resiliency Alternatives

Comparison of Alternatives for Electrical Grid Independence

Table 2 provides a summary of alternatives, costs and pros and cons, which were considered for installation in the case study home. Each alternative is explored in detail below and is relevant to similar homes. Several alternatives refer to “critical systems” in the home. The critical systems referred to are: cooking (range), space heat (furnace), some lighting for critical purposes (cooking, bathroom, living space), and refrigeration.