Automated Test House Solar Energy Study Full Year Results April 2007
Executive Summary With the goal of providing credible information on renewable energy generation, Viridian Solar has subjected its Clearline solar water heating system to the most realistic test of performance. An automated test facility was produced that used the solar heating system to against a pattern of hot water use for the average sized dwelling, and also took into account the effect of a disinterested household using an auxiliary heat source to top up the solar energy in the heat store to 60C on every day that the solar heating did not achieve this temperature. The test house was run for a full calendar year, and the results are summarised below: Annual Solar Energy Input Solar Energy as a Percentage of all Heat Input Annual Emissions for equivalent Gas Heating (kgco2) Annual Emissions for equivalent Electrical Heating (kgco2) Lifetime Solar Energy Input Lifetime Cost of Solar Heat Energy (pence/kwh) 1,448 56% 281 580 43,230 3.0 See appendix 1 for calculations in support. As a rough guide, if the cost of gas was 0.05/kWh, the cost of fuel to run a gas boiler to provide equivalent heat input to the cylinder would be 80/year. The results are roughly in line with predictions made using Viridian s in-house developed simulation software, and 23% ahead of a prediction using the government s SAP 2005 methodology.
Introduction Developers often view claims for green products with a healthy degree of scepticism. Viridian Solar has designed a revolutionary solar hot water system that is optimised for costeffective inclusion into properties as they are built. With the aim of proving the benefits of the system, Viridian is testing its product to higher levels than ever before. Description Viridian has built an automated test house that puts the solar hot water system into a realistic but well-controlled test environment. Previous tests of solar heating systems did not achieve such high levels of realism, for example by not taking into account the way that water is removed from the tank throughout the day, and ignoring the effect of an auxiliary heating system. This unique facility comprises a Viridian Clearline V30 solar panel, integrated into a roof of conventional construction. The area beneath the roof is enclosed, insulated, and maintained at room temperature. Inside the structure is a hot water cylinder, which is heated by the solar panel. An electric immersion heater on a timer control lifts the temperature of the top half of the tank to 60C on days where there is insufficient light energy for the solar panel to do so. Under software control, the simulation house can be configured to withdraw water from the hot water tank in a pre-programmed pattern. The water withdrawals are measured in energy terms rather than volume, so if the water is cooler, then more will be drawn. Some withdrawals, for example those simulating a shower do not start counting energy withdrawal until a certain temperature is achieved. Measurements and Data logging Every 3 minutes, a data logger records temperatures, and energy flows. The data is collected via a GSM uplink directly to independent monitors at the Building Research Establishment (BRE). Over the course of a 12 month period the relative energy inputs from the solar and conventional heating system were compared. This report is a preliminary digest of the results ahead of a formal report by the BRE.
The system simulated the hot water use of the average European household according to EU M324EN. The equivalent of 100 litres at 60C is withdrawn throughout the day in the pattern below. Immersion ON Results The graph below shows the monthly rolled up energy balance on the hot water cylinder since readings were first taken in April 2006 up until the end of March 2007. The blue colour is heat energy from the immersion heater, the orange is energy charged to the cylinder by the Viridian Solar water heating system. The blue line is the energy demand placed on the cylinder by the draw off pattern. The hot water use demand profile dips in the summertime, because the water coming into the house is at a higher temperature than in wintertime so the energy needed to raise it to 60 degrees is reduced. The hot water energy use is lower than the energy put in to the cylinder by an amount equal to the standing loss of the cylinder. Arguably the standing loss is higher as a result of the solar input than it would be if the house was being supplied by immersion only, with the water heated up just before it was used. The draw off has been supplemented by a standing loss of 1kWh per day, which is an estimate of the standing loss without solar.
Day by Day KEY
For each day, the immersion heater input is shown in blue, and the solar energy in orange. The black line shows the energy of water used by the family (with no allowance for standing losses). It can be clearly seen that the preponderance of blue falls as the data moves from winter through spring to summer. Minute by Minute Temperatures are logged every three minutes. The graphs below show temperatures logged in the system for three days with very different weather. (a) Sunny Summer Day (b) Sunny Spring Day
(c) Gloomy Spring Day Summary The results are tabulated below. Energy from Immersion Energy from Solar Hot Water Used Controller Energy Simple Solar Fraction January 175 49 178 3 22% February 140 63 159 4 31% March 96 144 172 5 60% April 69 146 163 7 68% May 64 160 163 8 70% June 20 187 143 9 90% July 14 193 143 8 93% August 62 141 146 8 69% September 38 161 142 8 81% October 111 102 161 6 48% November 145 83 176 3.5 36% December 187 33 178 2.5 15% TOTAL 1,121 1,462 1,924 74 57% Notes: The controller energy is electrical energy consumed by the electronic controller and the circulating pump. Simple Solar fraction is calculated as a proportion of immersion plus solar energy. Useful solar fraction will be lower because standing losses from the cylinder are higher than they would be without the solar input.
Appendix 1 Calculations 1. Annual CO2 emissions of equivalent gas Solar Heat input to cylinder 1,448 Efficiency of modern gas boiler 0.9 Heat content of gas required 1,448/0.9 = 1,608 CO2 emissions factor for gas (kgco2/kwh) 0.194 SAP2005 CO2 emissions from gas (kg/year) 0.194 x 1,608 = 312 Electricity consumed by pump and control 74 CO2 emissions factor for electricity (kgco2/kwh) 0.422 SAP2005 CO2 emissions from pump and control 74 x 0.422 = 31 Net CO2 emissions from gas to provide equivalent heat input to cylinder (kgco2/year) 312 31 = 281 2. Annual CO2 emissions of equivalent electricity Solar Heat input to cylinder 1,448 Electricity consumed by pump and control 74 Net solar energy input to cylinder 1,448 74 = 1,374 CO2 emissions factor for electricity (kgco2/kwh) 0.422 SAP2005 CO2 emissions from electricity to provide equivalent heat input to cylinder (kgco2/year) 0.422 x 1,374 = 580 3. Lifetime cost/kwh Estimated Lifetime (years) 30 Annual solar heat input to cylinder 1 1,448 Annual electricity consumption by pump 74 Energy pricing factor daytime electricity : gas 2 :1 Net benefit solar heat input to cylinder (kwh/year) 1,448 (2 x 74) = 1,300 Lifetime net solar heat to cylinder 1,300 x 30 = 39,000 Estimated installed cost of Clearline V30 1,000 Annual maintenance cost estimate 2 5 Total lifetime costs 1,150 Solar energy cost ( /kwh) 0.03 Notes: 1 Assumes the weather in the year measured was representative of future years. 2006 was one of the hottest years on record, but the average is inevitably backward-looking. In a time of climate change, normalisation to a backward looking average does not make sense. For the purposes of the calculation it was assumed that 2006 was representative of future years. 2 Assumes replace solar fluid every 5 years, replace pump every 15 years