How should electricity from wind turbines and solar panels be evaluated? Should it be evaluated as if these devices are stand-alone devices? Or do these devices provide electricity that is of such low quality, because of its intermittency and other factors, that we should recognize the need for supporting services associated with actually putting the electricity on the grid? This question comes up in many types of evaluations, including Levelized Cost of Energy (LCOE), Energy Return on Energy Invested (EROI), Life Cycle Analysis (LCA), and Energy Payback Period (EPP).

I recently gave a talk called The Problem of Properly Evaluating Intermittent Renewable Resources (PDF) at a BioPhysical Economics Conference in Montana. As many of you know, this is the group that is concerned about Energy Returned on Energy Invested (EROI). As you might guess, my conclusion is that the current methodology is quite misleading. Wind and solar are not really stand-alone devices when it comes to providing the kind of electricity that is needed by the grid. Grid operators, utilities, and backup electricity providers must provide hidden subsidies to make the system really work.

This problem is currently not being recognized by any of the groups evaluating wind and solar, using techniques such as LCOE, EROI, LCA, and EPP. As a result, published results suggest that wind and solar are much more beneficial than they really are. The distortion affects both pricing and the amount of supposed CO2 savings.

One of the questions that came up at the conference was, “Is this distortion actually important when only a small amount of intermittent electricity is added to the grid?” For that reason, I have included discussion of this issue as well. My conclusion is that the problem of intermittency and the pricing distortions it causes is important, even at low grid penetrations. There may be some cases where intermittent renewables are helpful additions without buffering (especially when the current fuel is oil, and wind or solar can help reduce fuel usage), but there are likely to be many other instances where the costs involved greatly exceed the benefits gained. We need to be doing much more thoughtful analyses of costs and benefits in particular situations to understand exactly where intermittent resources might be helpful.

A big part of our problem is that we are dealing with variables that are “not independent.” If we add subsidized wind and solar, that act, by itself, changes the needed pricing for all of the other types of electricity. The price per kWh of supporting types of electricity needs to rise, because their EROIs fall as they are used in a less efficient manner. This same problem affects all of the other pricing approaches as well, including LCOE. Thus, our current pricing approaches make intermittent wind and solar look much more beneficial than they really are.

A clear workaround for this non-independence problem is to look primarily at the cost (in terms of EROI or LCOE) in which wind and solar are part of overall “packages” that produce grid-quality electricity, at the locations where they are needed. If we can find solutions on this basis, there would seem to be much more of a chance that wind and solar could be ramped up to a significant share of total electricity. The “problem” is that there is a lower bound on an acceptable EROI (probably 10:1, but possibly as low as 3:1 based on the work of Charles Hall). This is somewhat equivalent to an upper bound on the affordable cost of electricity using LCOE.

This means that if we really expect to scale wind and solar, we probably need to be creating packages of grid-quality electricity (wind or solar, supplemented by various devices to create grid quality electricity) at an acceptably high EROI. This is very similar to a requirement that wind or solar energy, including all of the necessary adjustments to bring them to grid quality, be available at a suitably low dollar cost–probably not too different from today’s wholesale cost of electricity. EROI theory would strongly suggest that energy costs for an economy cannot rise dramatically, without a huge problem for the economy. Hiding rising energy costs with government subsidies cannot fix this problem.

Distortions Become Material Very Early

If we look at recently published information about how much intermittent electricity is being added to the electric grid, the amounts are surprisingly small. Overall, worldwide, the amount of electricity generated by a combination of wind and solar (nearly all of it intermittent) was 5.2% in 2016. On an area by area basis, the percentages of wind and solar are as shown in Figure 1.

There are two reasons why these percentages are lower than a person might expect. One reason is that the figures usually quoted are the amounts of “generating capacity” added by wind and solar, and these are nearly always higher than the amount of actual electricity supply added, because wind and solar “capacity” tend to be lightly used.

The other reason that the percentages on Figure 1 are lower than we might expect is because the places that have unusually high concentrations of wind and solar generation (examples: Germany, Denmark, and California) tend to depend on a combination of (a) generous subsidy programs, (b) the availability of inexpensive balancing power from elsewhere and (c) the generosity of neighbors in taking unwanted electricity and adding it to their electric grids at low prices.

As greater amounts of intermittent electricity are added, the availability of inexpensive balancing capacity (for example, from hydroelectric from Norway and Sweden) quickly gets exhausted, and neighbors become more and more unhappy with the amounts of unwanted excess generation being dumped on their grids. Denmark has found that the dollar amount of subsidies needs to rise, year after year, if it is to continue its intermittent renewables program.

One of the major issues with adding intermittent renewables to the electric grid is that doing so distorts wholesale electricity pricing. Solar energy tends to cut mid-day peaks in electricity price, making it less economic for “peaking plants” (natural gas electricity plants that provide electricity only when prices are very high) to stay open. At times, prices may turn negative, if the total amount of wind and solar produced at a given time is greater than the overall amount of electricity required by customers. This happens because intermittent electricity is generally given priority on the grid, whether price signals indicate that it is needed or not. A combination of these problems tends to make backup generation unprofitable unless subsidies are provided. If peaking plants and other backup are still required, but need to operate fewer hours, subsidies must be provided so that the plants can afford to hire year-around staff, and pay their ongoing fixed expenses.