Better Together: Energy Efficiency and Photovoltaics

WREFPhotovoltaics (PV) have become an icon of sustainable building. PV panels are more popular than energy efficiency changes when looking into green building.   But efficiency and PV were made for each other, and when combined in the right proportions, it becomes more economically feasible than conventional building systems.  In the WREF2012 Built Environment Forum, “Integration of PV with EE, DR and ES,” the California Solar Initiative provides the backdrop for showing off tools and approaches about integrating efficiency and PV with the larger goals of a self-sustaining solar industry and Zero Net Energy by 2030.

Craig Christensen of the National Renewable Energy Lab (NREL), showed off the already existing building version of their residential modeling program which is located in California.  BEopt is the Lamborghini of building modeling programs.  Under the hood, they have a finely-tunable mechanism of inputs for envelope equipment, setpoints, surroundings, and shading, and have newly integrated existing characteristics, detailed utility tariffs and cost/benefit tests, demand response, and energy storage – but that’s not all.  BEopt runs on a variety of fuels — the simulation engines TRNSYS + DOE2 or EnergyPlus.  Its most unique feature is its ability to test a single design (Design Mode), or to test a wide range of possible designs to find the optimal blend of design features (Optimization Mode), where a cost-energy “swoosh” distribution lays out the options, and shows those closest to the sweet spot.  The engine doesn’t assume efficiency first, but usually recommends it to a point, which then is cheaper to add PV.

Many other modeling tools exist but are usually specialized for renewables or efficiency. A few provide output standards to allow sharing among tools and between PV and EE service providers.  “Integrated tools will encourage integrated projects,” says Devan Johnson of kW Engineering.  The model developed by the team of kW Engineering, SolarNexus, Inc and SaveEnergy123 defines an IEP (Integrated Energy Project) and proposes an open XML standard to speed collaboration and integration of existing tools.  There are schemas for several categories of project data — from existing site and building features to energy systems, utility data, stakeholder information and proposed measure –as well as common schemas to interlink these data.

Seeing these tools in action really brings them to life.  The team from ConSol used BEopt to optimize their low-cost smart-grid-ready solar re-roof project, designed to a target installed cost of less than $4.25/W, including a Home Energy Management system and demand response controller.  A simple mounting assembly with a plug-and-play microinverter electrical interface (as simple as standard home wiring) require no special tools for installation, so a roofing contractor can install it.  This installation cost savings dramatically reduces first costs of the system.  In their showcase home, the team paired a 2.4 kW PV system with a package of energy-efficiency retrofits that amounted in BEOpt to a 30.5% energy savings without PV, and 55% with PV – a clear demonstration of the synergy between load reduction and supply. Actual production of the system came out at 10% better than PVWatts estimates.

Taking the PV-EE synergy to the community level, a partnership between UC Davis and Energy and Environmental Economics, Inc. (E3) produced the West Village Project, which is part of UC Davis’ zero net energy community initiative.  1900 student beds were already close to Zero Net Energy on an annual basis, and the team wanted to model the solutions for 343 single family homes at no higher cost to developer and owner.  BEopt allowed them to model many possible solution packages, maximizing energy efficiency where feasible and integrating both PV and biogas to cover annual energy use.  The models also considered shifting conditions, from future economics to policy changes.  The team’s conclusions were that the best package had an incremental cost of around $5000 for a 22-30% energy reduction over California’s Title 24 standards.  The number of homes constructed greatly affected the economic feasibility, but all their modeled batches (30, 60 and 90) compared favorably against the neighboring conventional homes.  Economics were more favorable for a natural gas (rather than all-electric) strategy, and without electric vehicle storage.  In all situations, they concluded that Zero Net Energy is possible with little to no incremental cost to homeowners given the current state of incentives and smart development.

The key is to properly size PV at that sweet spot between the price of efficiency and the price of PV.  While customers often go for the easy but more expensive PV first, it makes natural sense to design and implement them together. Common data is collected to perform the design analysis, and they will perform reciprocally in the built reality.  The overall return on investment on combined EE and PV projects is better than for PV alone, and with evidence from the integrated modeling tools and their brainchild projects will help efficiency and supply to penetrate the market as a winning duo.

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