Carbery Greener Dairy Farms Project

Solar Thermal as an Option for Reducing Water Heating Costs on Dairy Farms—A Simple Payback Approach by John Upton, Teagasc

1 August 2014

Thanks to all those who attended the first official dedicated Greener Dairy Farms Project walk at the farm of Michael and Marguerite Crowley recently. The sun was ‘splitting the rocks’ on the day and we hope that all those who attended the event were both enlightened and lightly tanned!

In this leaflet we aim to keep you, the suppliers updated and give you regular insights into the Greener Dairy Farms Project. We hope to examine some of the areas that the participants have changed as part of the project and generally examine ways in which you can save money and become more sustainable.

Below we examine the possibility of using solar panels to heat water in the dairy and overleaf you will find a template which will allow you to easily calculate the payback period of installing a solar thermal heater system into your dairy.

Solar Thermal as an Option for Reducing Water Heating Costs on Dairy Farms—A Simple Payback Approach by John Upton, Teagasc

Electrical water heaters are the most commonly used type of water heating system found on the modern dairy farm. A solar water heater provides a renewable option for reducing water heating costs. The solar water heater captures energy through a solar collector in the form of solar radiation and transfers the energy to a water storage tank which acts as an energy storage vessel. Due to the intermittent availability of solar energy a top-up heating system (in the form of electricity) is required. This makes the solar water heater suitable for preheating the water before final heating (to 85oC) is carried out.

Solar water heaters have been shown to reduce the electricity consumption of dairy water heating systems by 40-50%. This was verified on farms in west Cork as part of the Carbery Greener Dairy farms project in 2012 when it was discovered that 2 farms with solar water heaters installed realised 40% reductions in water heating costs over their contemporaries with conventional electric water heating systems. This proves the effectiveness of the technology to reduce water heating costs, the only question remaining is whether a solar heating system would result in a reasonable payback period.

Teagasc research has shown that heating 100 litres of water to 85oC costs approximately €1 on night rate electricity (from 12 midnight to 9am during summer time). The recommended usage of hot water when washing a milking machine is 9 litres per milking unit per hot wash.

With this in mind a farm with a 20 unit milking machine where a daily hot wash is carried out, will consume 180 litres of hot water per day. Extrapolating this over a 45 week milking season would result in a hot water use of 56,700 litres.

A bulk milk tank will use approximately 2% of the volume of the tank for hot washing purposes. Therefore a 10,000 litre bulk tank hot washed every second day would use 31,500 litres of hot water per year.

solar thermal panels

In total this gives an annual hot water use of 88,200 litres (including the milking machine and the bulk tank requirements) which would cost €882 per year. A solar system would reduce this by 40% to €529 per year saving €353 per year.

If a farmer spends €3,500 on the solar thermal water heater, a simple payback of 10 years is realised. This example is chosen as a guideline only and the results from farm to farm will vary dramatically, however this calculation highlights the importance of getting a handle on water heating costs before investing in new technologies.

This calculation is a simple payback figure and does not take into account the value of money over time, increases in electricity costs or the interest rate of money borrowed from financial institutions, however it is a quick and simple method that will give an indication of the performance of the investment over time.

Solar energy on Your Farm?

To find out if using solar thermal heating would pay if install into your dairy, using this simple pay back method, then simply fill in and follow the worksheet below:

solar energy worksheet