Solar Energy at the WCROC

Eric Buchanan, Renewable Energy Scientist

September 2017

Several solar PV arrays are now producing electricity at the WCROC thanks to funding from a few grants. Solar arrays are composed of solar panels which in turn are made up from solar cells. Solar cells convert visible light (Photons) into electricity (Voltage) hence the name solar PV. Solar panels have been around since the 1950’s, but were too expensive to be widely used. Prices for solar panels have decreased dramatically in the last 10 years, and are expected to continue to go down making solar energy as cheap as electricity produced from fossil fuels by 2020 without any incentives.

The first solar array installed on the farm was funded by a Legislative Citizens Commission on Minnesota Resources (LCCMR) grant. It is a 27 kW array using Heliene panels which are assembled in Minnesota. Half of the solar panels on the finishing barn can be seen in the photo at right along with the power inverters mounted to the end wall of the barn.  Read more about our energy systems for swine production.

The purpose of the study was to see how the amount of electricity that could be generated on a hog finishing barn roof compares to the amount of electricity used in the barn. The following graph shows the solar array produced more electricity in 2016 than was used in the barn over the course of the year.

2016 Finish Barn Solar Production vs Load

There are times when more electricity is being used than is generated – especially at night and on cloudy days – which is why a solar array needs to be interconnected to the utility grid or it needs a bank of batteries. Either solution provides a place to put excess generated electricity and a place to get electricity when the array is not producing enough. Batteries can be as expensive as solar panels so battery systems are usually only used when connecting to the utility grid is impractical, like at a remote cabin. Minnesota is a net-metering state meaning the electric utility company must buy any excess electricity from an interconnected system less than 40 kW in size and pay the retail electric rate for each kilowatt-hour (kWh).

Solar arrays generate DC electricity, but household appliances operate on AC electricity so a power inverter is needed to condition the electricity before it can be used or sold. Power inverters interconnected to the utility grid must shut a solar array down if utility power is lost protecting line workers from unexpected current on an otherwise “dead” line. The utility company requires a demonstration of this before allowing a new solar array to be interconnected. There is also a fee from a few hundred to a few thousand dollars charged by the utility depending on the complexity and size of a proposed energy system to cover costs of analyzing any impact a new system will have on the utility grid. These costs also include a new utility meter that can record power flows in both directions if needed.

10 kW wind turbine and 4 kW solar PVThe second solar array was funded by an Xcel Energy Renewable Development Fund (RDF) grant. It is a 50 kW ground mounted array using tenKsolar panels also assembled in Minnesota, but tenKsolar is now out of business. The RDF grant also funded two 10 kW wind turbines and 4 kW of solar PV mounted on poles in the pasture behind the guest house. All together the RDF funded systems are sized to produce enough electricity annually to offset the electricity used in the dairy milking parlor making it a “Zero Net Energy” building. The pole mounted arrays are fixed – they do not track the path of the sun. Tracking equipment has not proven to be a good investment and introduces maintenance issues. Read more about our energy systems for dairy production.

Solar array at WCROCThe last solar array installed is a 20 kW ground mounted system composed of Heliene panels and funded by another LCCMR grant. This system is sized to provide electricity for the equipment installed in the farrowing barn to study cooling sows and warming piglets with an electric heat pump.

There will be an additional 30 kW array installed in a cow pasture next spring funded by yet another LCCMR grant. This system will be used to study the potential benefits of providing shade to grazing cows in conjunction with providing electricity to be used by electric vehicles.

The sun is shining brightly at the WCROC!