Solar Hot Water
Victorian farm businesses are under pressure from rising electricity costs and an increasing focus on greenhouse gas emissions from agriculture. Electricity prices are expected to continue to rise in the future due to metering costs, infrastructure replacement and the introduction of a price on carbon emissions.
The Victorian DEPI project 'Dairy Industry Farm Monitor' has shown that dairy shed electricity costs have increased over the past five years by an average of 22 per cent. These shed costs accounted for approximately four per cent of variable costs in 2010-2011.
The DEPI project 'Economic analysis of technologies to reduce dairy energy consumption' has investigated five different technologies commonly used on dairy farms that have the potential to improve energy efficiency. A partial discounted net cash flow budget over 10 years was done to analyse the technologies. In this edition the findings associated with solar hot water will be discussed.
A solar hot water system uses energy from the sun to heat water. Solar collectors (panels) on the roof absorb the sun's rays and heat the water, which then flows to a storage tank ready for use.
There are two main types of solar hot water systems, the flat plate collector or the evacuated tube collector. Both have positives and negatives and are suited to different applications and climates.
Flat plate collectors can be more sensitive to frost and are generally heavier and larger than evacuated tube systems.
Evacuated tube systems are generally more expensive than the equivalent flat plate system and are able to heat water to a higher temperature, hence they are considered a better option for commercial operations.
This cost benefit analysis is based on a case study farm in South Gippsland milking 240 cows on a total area of 130 hectares. The dairy shed is a 20 unit swing-over built in 2003 and is well maintained. The farm produces 1.7 million litres of milk.
The source of electricity is brown coal accessed through the state's electricity grid. The tariff rate is time of use with peak rate of 22 cents per kilowatt hour (kWh) for power from 7 am to 11 pm. An off peak price of
14 cents per kWh applies to other times and weekends. Milking takes 2.5 hours with the morning milking predominantly off peak. The case study farm used 84,000 kWh of electricity at a cost of $14,960 for the 2010-2011 financial year. The associated carbon emissions were 102 tonnes of CO2-equivalent.
The case study farm uses a typical three-cycle wash requiring 700 litres of hot water daily, heating water off peak to 90 degrees C. The hot water generates 22,265 kWh annually or 61 kWh of heat per day. The cost of water heating is $3,117 and is our 'do-nothing' option.