How solar can play part of our Ames climate solution?
If you’ve been downtown, you’ve probably noticed the power plant at the east end of Main Street. This uses a combination of refuse-derived fuel (from our garbage) and natural gas to produce electricity for Ames. Because the refuse-derived-fuel comes from things that consumed carbon dioxide as they grew, this component of our electricity is considered to be “green;” however, 90% of the power comes from the natural gas and only 10% from the refuse-derived-fuel. Other sustainable sources of power for Ames include wind power through a contract with Garden Wind LLC, and solar power through the solar farm (SunSmart). Additional power comes from the grid, where it is generated by a mixture of wind, gas and coal.
An electrical system has to be designed so that it can accommodate the peak demand, economically sustain the average level of demand, and recover quickly when some part of the system fails. Peak demand is what sets the goal for total capacity. Quick response to failure means that some redundancy or backup system is needed. These, more than average demand, are what determine how much needs to be invested in constructing the sources – power plants, wind farms, and solar arrays.
Peak power consumption occurs most often in times of extreme weather: When it is very hot, air-conditioning needs increase. When it is very cold, heating needs increase, though much of the heating in Ames is still via natural gas. (If there is a choice of burning natural gas to produce electricity for heating homes vs. using natural gas in a home furnace, the latter is more efficient, so transitioning to all-electric heating is not helpful at this time.)
As part of the runup to the Climate Action Plan, the Pale Blue Dot consultants provided a report on the potential for solar energy for Ames.
Solar comes in three types: (a) City-sized installations (SunSmart); (b) home and business installations; and (c) passive solar heating and cooling. The city has a program to reward energy efficient new construction, but not yet a program to reward installation of passive solar features on existing buildings. Current technology makes city-sized solar installations slightly more cost-effective than individual home installations, but distributing solar power around the city provides resilience: If city-wide power goes out, at least those places still have power.
The Pale Blue Dot report focuses on the potential for increasing the number of home and business installations. There are two elements: (a) What areas are available for installation? and (b) What might motivate people to add solar panels?
The Pale Blue Dot folks inventoried the flat or appropriately south-facing roofs in Ames and determined the capacity, if all those spaces were used, for residential and business installations. Depending on the design of the panels – the angle that they present – these can be optimized for summer cooling or winter heating or a year-round average. They computed the maximum from this to about 11% of the annual electrical power use for Ames. They then looked at trends in the prices for solar installations and the rate at which these are being installed, and estimated that rooftop solar will likely grow to accommodate 0.67% of the city consumption in 2025, 1.2% in 2030, and 1.75% in 2040. Changes in city incentives and/or in the cost of installation could increase these numbers.
Is 1 or 2% from solar enough to make a difference? One big advantage of solar is it is available on hot, sunny days in the summer (and on sunny, cold days in the winter – clear nights give us our coldest days). Currently, wind power dominates our electrical use at night, but during the day we rely more on grid power that includes gas and coal burning sources, in large part because we use more power during the day when we are working, cooking, and lighting our homes and businesses. So that 1 to 2% could offset some of the grid component at exactly the time when we need it most.
The other element of distributed solar installations is the question of what might motivate people to install solar panels. Some people will choose to do this because they want to do their part to reduce the use of greenhouse gases. Some will do it because they want to have power if the grid goes out (though involves additional costs – see below). Many will make the choice based on financial considerations.
With a solar installation, there is an upfront cost, and then there are savings. The immediate savings come from using rooftop solar instead of energy coming in from the local providers, and thus having low or zero bills to pay. However, that alone does not usually pay for the installation right away, and perhaps not ever. The second way to balance the budget on this one is to generate more power than one needs, and sell the excess back to the system in some way. Two ways to reimburse solar energy installations are in common use: One is for the utility to pay for the extra power directly, via net-metering, and the other is for the utility to provide an up-front cash rebate towards the cost of the installation. Currently Ames has a rebate system. Usually a cash rebate only pays for a portion of the actual cost, and the person installing solar is responsible for most of the installation cost. This is why there is ongoing discussion of “net-metering,” that is, paying solar installation owners for the power they contribute back to the utility.
Why don’t solar panels automatically provide you with power when the grid is down? Panels provide direct current (DC) and your house runs on alternating current (AC). To provide you with power, the DC from the panels needs to go through an inverter, and most inverters run off the AC current from the grid. In order to have solar power benefit your home during a power outage, you need to also invest in additional equipment, such as a battery backup system and a converter to get AC from DC.
A much simpler option for the homeowners of Ames, and one that is available for folks who do not have an appropriate place to put solar panels, is the municipal solar farm, SunSmart. You buy a share in SunSmart, helping to pay for the installation, and then you receive a rebate on your electric bill. Each share costs $300, and gets a monthly rebate of a few $$. If your current electric bill averages $60/month, you probably need about twenty shares of SunSmart to get the bill down to zero. Or, given that roughly half our electrical power comes from wind, you need about ten shares to cover the portion of your electric use that is coming from gas and coal. In comparison, a home installation generally costs between $10,000 and $20,000.
In the past year and a half there have been a couple of illustrations of what happens when there is a climate-related failure in the power system. In August 2020 the derecho took down a lot of power lines, and parts of Ames were without power for several weeks. This was a test of the local planning for emergencies, and Ames did OK but also learned some important lessons. Some parts of the city had power restored in 2-3 days, as soon as downed lines could be fixed. In newer neighborhoods with buried lines, this meant only the trunk lines needed to be repaired. In older neighborhoods with large trees and overhead power lines, the job of getting all the homes reconnected took much longer.