The solar industry is discovering a new, faster, and less costly way to connect to the grid.
Electrical construction done by $12 per hour factory labor instead of $50 per hour union labor at the solar project site makes solar production significantly more affordable, according to market-leading substation builders like Eaton, ABB, and S&C Electric.
ABB: An increasingly important idea
“Building substations is a multi-billion dollar part of ABB’s global business,” explained VP Harry Kaffenes.
For utility scale solar, ABB can deliver modular standardized substation designs that can fast-track projects and provide time and cost savings. The idea of delivering a pre-engineered, pre-packaged substation solution is not new, Kaffenes said. But it is becoming increasingly important in solar and wind as developers search for new ways to cut costs.
Eaton: A way to cut costs
Eaton has offered its Modular Integrated Transportable Substation (MITS) since 2004 and has supplied many skid mounted assemblies, according to Bob Kirslis of its Electrical Engineering Services and Systems Division.
“For renewable energy, especially for PV projects, there is a skid mount design with a transformer and inverter on it,” Kirslis said. After being largely factory pre-assembled and pre-tested with significantly cheaper labor, it is delivered with the complicated site work minimized. “You know it’s going to work, which reduces your start-up and commissioning time, and then it’s almost just plugging in the cables and off you go.”
The skid also eliminates the need for building a foundation because it spreads the weight.
Each substation is a uniquely engineered, customer-specific solution. The switchgear, which Eaton calls an Integrated Power Assembly (IPA), can be a part of the MITS package or delivered on a separate skid, Kirslis said. “Every one is a little different and we have done all types of them.”
As to cost, he said, “unless I know what is on the skid, I have a hard time putting a price on it.” Without a specific design, it is also difficult to be precise about construction time but both Kaffenes and Kirslis agreed skid mounted assemblies save time. “A substation on a skid could be built in three to five months,” Kirslis said, “but it is going to save at least 10% to 20% in time and therefore will save money in the field.”
Another advantage of a skid mounted substation, Kirslis said, is that the compact structure can have as little as a quarter of the footprint of a conventional open air substation, leaving land free for other uses.
And, Kirslis said, MITS substations can be moved to new locations, eliminating stranded multimillion dollar assets. He added one caution. “It has to be a size that can be moved over the open road without losing time and expense to special permitting and logistics.”
S&C Electric: A way to save time
“Developers often concentrate on the right panels and the right inverters at the right price but, all at once, they remember that little piece of the interconnect between the utility and the customer,” said S&C Electric Renewables and Storage Business Director Dan Girard. “And then timing becomes a big issue.”
S&C has built, or is building, 24 solar project substations across the U.S. with its advanced System VI switchgear. In response to solar industry demand, it has design specifications for a fully integrated skid mounted substation. “The solar industry is going in that direction,” Girard said.
Utilities no longer typically build the substation but, instead, leave it to solar and wind developers, Girard said. That is especially true as solar developers move to projects in the 20 megawatt to 70 megawatt range to avoid larger installations’ complications with permitting and interconnection.
“We have three different designs, based on the size of the solar plant and the connection voltage,” Girard said. One is for projects less than 5 megawatts, another for 5 megawatt to 20 megawatt projects, and the third is for those between 20 megawatt and 70 megawatts. “A pre-assembled package can be delivered on a self-contained skid or be built on a concrete pad," he said. "That is a customer decision.”
A traditional open-air substation for a 5 megawatt solar project just completed by S&C cost an estimated $1.65 million and a comparably equipped substation for a 20 megawatt site would likely be in the $2.65 million range, according to Girard. They can be finished, from first digging to commissioning, in three months, he added.
Skid delivery decreases time but slightly increases cost, Girard explained. “The customer gets a standard package for the collection side of the substation. For the non-collection side, which connects to the metering sub or the interconnect sub, that has to be engineered and designed in cooperation with the utility.”
Girard highlighted one other skid-mounted assembly advantage, a savings not in installation but in operations. “Some 80% of solar site outages are caused by animals eating through something or weather like lightning or wind,” he said. “An enclosed structure reduces outages from two or three per year to one per year, a very significant savings. Keeping the plant up and running is the number one goal of the operations side.”