Free-market think tank Independence Institute released a study Thursday that concludes the all-renewable-energy plans of two Democratic gubernatorial contenders – former state Sen. Michael Johnston and U.S. Rep. Jared Polis – would add $45 billion to Colorado ratepayers’ utility bills. Independence called Polis’s and Johnston’s goal of fossil-fuel-free power generation in Colorado by 2040 a “green energy fantasy.”

Independence, which is critical of government mandates and subsidies for renewable energy development, commissioned the Energy Ventures Analysis study and touted it in a press statement earlier today:

“We commissioned the study because no one was asking these candidates how they would implement such a plan and the candidates themselves haven’t provided many details,” said Independence Institute Executive Vice President Amy Cooke, who also directs the energy and environmental policy center.

The $44,880,000,000 figure represents the cost of adding the necessary wind and solar capacity, utility scale battery storage, and retiring the state’s entire coal and natural gas fleet. Not included within the scope of the study are transmission costs, land acquisition costs, nor reclamation of retired sites, which are believed would add billions of dollars more.

But Polis, the five-term Boulder congressman now on the campaign trail for governor, pushed back on Twitter in a volley with Cooke and Independence President Jon Caldara. Polis contended he doesn’t want to mandate 100 percent renewable energy for Colorado but rather wants to achieve that benchmark by 2040 through other means:

To which Caldara replied:

Polis sniped back:

Polis’s plan states, “For our climate, for our national security, for our health, and for our economic growth we need a bold goal of 100% renewable energy.”

How to arrive at that goal if not by a flat-out mandate?

Polis says in his plan, “As I travel the state, I’m excited to hear your ideas to help us reach this goal. We need great ideas from everyone.” According to the plan, those ideas include:

…the list goes on. So, Polis is saying as governor he’d foster a climate in which Colorado would get to 100 percent renewable energy use by 2040. He says he would not ratchet up the state’s current 30 percent mandate for power generated by renewables.

Johnston, similarly, sidesteps a call for a mandate in his “100 by 40 plan” to “make Colorado a national leader” in renewable energy use. How would Johnston do it? You can watch his 5 minute 14 second energy pitch here. His plan’s key provisions are accelerating the closure of coal plants (he wants to help retrain coal miners for new jobs); creating incentives “that will spur innovation and accelerate the growth of renewable energy,” and investing in “the development of energy storage.” The video doesn’t offer details of how Johnston as governor would implement those three priorities.

Caldara wasn’t buying any of it, taunting Polis in Thursday’s tweet-off:

Caldara again:

…and Polis:

Here’s the question Caldara didn’t ask, but that might be of interest to those Coloradans who actually do want a fossil-fuel-free future: If Polis and Johnston are indeed promising (Independence’s word) 100 percent renewables by 2040 – but aren’t willing to mandate it – are they really in a position to promise anything at all?

Call it a promise or call it a goal; skeptics in the green movement might ask: How committed are they?