Spain Happens to have the Best Conditions in Europe for Solar Energy. With high insolent radiation and a dry climate, it is no surprise that this country is the leader in Europe with grid-connected solar technologies of both the photovoltaic (PV) and solar variety. When the Solar Electric Power Association's Executive Director, Julia Hamm, invited me to join the association's fact-finding mission to Spain to investigate grid-connected solar plants, I joined 20 utility executives from the U.S., and we worked our way from one installation to the next.

So, why did SEPA decide to visit Spain instead of China or Japan? It's the feed-in tariff. Due to what some claim are overly generous tariffs, Spain has installed more than 3 GW of PV solar through 2008 and will install another 450 MW in 2009 — almost all of it of the grid-connected variety.

On the PV side, single crystalline, polycrystalline and thin-film cadmium-telluride panels have been installed. Most are performing well (although certain inexpensive panels from developing countries have proven not to be a good investment). We saw PV panels that were fixed, we saw single-axis panels, and we saw double-axis panels that accurately tracked the sun's trajectory. We also saw concentrating solar installations that use mirrors to reflect additional solar rays onto PV panels.

Early on, we met with Carlos Gascó, head of prospective at Iberdrola Renewables, a sister company to Iberdrola, the largest electric utility in Spain. Gascó told us the utilities in Spain had not faced any significant problems in connecting the 3 GW of solar to the grid. The PV systems in place have typical total outputs of 1 MW to 6 MW, and these solar farms normally connect to the 20-kV distribution system. Gascó believes that Spain could triple the amount of distributed grid-connected solar without posing any great difficulties for his utility.

Wind is proving to be a little more difficult to digest than solar. And Spain has 13 GW of wind installed. Red España, the national grid operator, is dealing with the fact that wind can abandon us when we need it the most. Conversely, Spain also has excess wind at certain times and can find itself curtailing wind under some conditions.

We really need to find ways to store our green energy so that it can be dispatched. Which leads me to the commercial concentrating solar plants installed by Abengoa Solar near the city of Gaudix in the province of Granada.

We toured 10-MW and 20-MW solar towers (I believe they are the only commercially operating solar towers in the world), which are connected to the 400-kV grid. Heliostats with two-axis tracking mirrors focus the sun's rays on a central receiver high on the towers. Steam from the receiver is then run through traditional steam turbines. It is likely that future solar tower designs can use thermal salts as the operating fluid. This would enable us to store heat in the salts that could later be used to create steam for turbines to be operated at any time day or night.

Probably our best opportunity to dispatch solar today is with parabolic troughs that use mirrors to focus sunlight on oil-filled pipes.

That is exactly what was going on at Abengoa's Solnova 50-MW parabolic trough generating station. A portion of the oil from parabolic trough collectors is used in real time to generate steam. Heated oil from the remainder of the trough collectors is circulated through heat exchangers to transfer heat into gargantuan thermal salt tanks. Heat from these tanks can be extracted later to run the same steam generator long after the sun goes down.

On the tour was Phil Smithers, technical services leader with Arizona Public Service. Smithers was telling me his company has signed a contract to purchase renewable energy from a 290-MW parabolic mirror solar facility that is to be built 75 miles west of Phoenix. Scheduled for completion in 2013, this plant will be able to produce electricity at any time of the day or night. Electricity from this facility should produce enough electricity for 73,000 homes.

Our tour ended on Friday with a visit to Spain's national Plataforma Solar de Almería research facility. Work performed here helped bring forward Spain's solar technologies to the point that Spanish companies are among the world's leaders. Here, significant advances in the design of solar towers took place.

We also looked at the test site for Stirling Energy Systems. It is likely that engine maintenance will be a main expense of Stirling facilities. I understand we have 1100 MW of contracts in California for purchase of electricity generated by Stirling engines.

I have been pondering what I saw in Spain and realize anew we no longer have total control over our energy mix. With carbon taxes looming, a dearth of new nuclear plants, and mandated renewable and demand-side targets, the country's energy mix is being determined by our appointed and elected representatives. Public utility commissions understand that to get our renewable energy portfolio off the ground, most states will pay a premium for green energy and the necessary energy storage to support green.

As in Spain, utilities will be compensated for their investments in and purchases of green energy. But let's make sure we know what road we are headed down. We have many choices, but it is still tough to decide which technologies to support and when to roll them out.

If we are to hit our renewable portfolio targets in a way that makes good business sense, we simply must find ways to store and dispatch solar and wind. We will be making tough energy decisions between now and 2020. We can't afford to sugarcoat our options; neither can we pretend that renewables have no significant place in our energy mix.