HOMER Software1.2

1. INTRODUCTION HOMER is a micro-power optimisation model which is under continuous development by the National Renewable Energy Laboratory, a laboratory of the U.S. Department of Energy. HOMER is free to download♣ and use and new versions are always being released. The software can model photovoltaic modules, wind turbines, biomass power, hydro power, generators, micro turbines, storage batteries, grid connections, fuel cells and even electrolysers. Using it, one can design grid-connected and off-grid renewable energy (RE) power systems and analyse such systems in order to answer questions like:

• Are renewable resources adequate for a given location? • What type of RE-technologies is most cost-effective? • What size should RE-system components be? • How does the system’s economics change if costs and loads change?

In this assignment, the reader will be introduced to HOMER and use the software to model a simple RE power system and decide what type of system would be most suitable for a given scenario. 2. GETTING STARTED WITH HOMER In order to get familiar with the programme, start HOMER and select the Getting Started option from the Help menu. It is recommended that the reader go through the Getting Started guide by following the steps. After completing this, one should have a good idea of what kind of information HOMER uses and how such data is entered in the programme. Notice that HOMER uses U.S. Dollars ($) as a currency unit. The units are, however, arbitrary so one can simply use Euro (�) values and ignore the dollar symbol. 3. USING HOMER TO MODEL A RENEWABLE ENERGY SYSTEM After familiarity is gained using HOMER, the programme will be used to model a real-life RE system, which is described below. Read through the scenario and, using the available files from the KEMS848 webpage, enter the required information into HOMER.

♣ http://www.nrel.gov/homer/

THE SCENARIO A young couple from Jyväskylä decide to move to the countryside. They own a small off-grid cottage and some land in the rural county of Petäjävesi. They decide to heat their home by burning coppiced biomass (firewood), obtained from their woodland, in a recirculation ceramic fireplace (takka). The cottage's well positioned, highly insulated, windows also provide passive solar heating. Their water is obtained from a rainwater collection system and from a nearby ground-water well during the winter months. For their hot water needs, they use an insulated wood-fired boiler and, during longer solar days, a simple thermal-siphon flatbed collector. The couple, therefore, require electricity only for lighting, operation of a water pump and for electrical appliances (stereo, computer, clothes washing machine etc.). Being extremely interested in RE energy and wishing to be grid-independent, they decide to install a RE electrical system to meet their electrical needs. SYSTEM COMPONENTS The following components are to be considered for modelling the system. 1) The couple already own a small (2.2 kW) gasoline AC generator. They will use it in their

system but only a maximum of 180 litres of fuel per year. Additionally, the generator will not operate weekdays between the hours of 9.00 and 17.00 nor in the night between 21.00 and 6.00 in the morning. The generator costs 850 � and has an operational and maintenance cost of 0.1 �/hr due to oil and spark plug changes. Additionally, the price of gasoline is assumed to remain at 1.2 �/litre. The intercept coefficient for the generator is found to be 0.8 L/hr/kW rated.

2) Photovoltaic modules can be purchased for 600 � per 0.1 kW size which includes mounting and wiring costs. The total size of the PV system to be considered ranges from 0 – 1.6 kW which would fit on the roof of the cottage. There is no automated tracking system but the modules face due south and can be manually adjusted every month on the horizontal axis. The latitude and longitude of the cottage is 62°N 25°E.

3) Two different wind turbines are considered. The Synergy S3000 is well suited to lower wind speeds but costs 10 000 �, which includes mast and accessories. The SW AIRX, on the other hand, cost only 2500 � but is better suited at higher wind speeds. The property has an elevation of about 218 metres above sea level and the turbine (if it is decided to buy one) will be installed at a mast height of 10 metres. The mast is situated at least 100 metres from the nearest woodland area but is otherwise surrounded by sheep pasture.

4) Maintenance-free 12V Vision lead storage batteries (6FM200D) are to be used but the required number of batteries is not known. However, 1000 Amp-hours of storage is considered to be the maximum capacity due to space limitations in the cottage. The batteries cost 400 � each. A state of charge (SOC) set point of 70% is recommended.

5) A 1 kW converter costs 1200 � and the system may include one or two of these. The inverter has 90% efficiency and operates simultaneously with an AC generator.

ELECTRICAL LOADS The electrical loads can be divided into three parts. The first two loads are available as data files from the KEM506 webpage and can be imported into HOMER under the load section of the programme. Data for the third load, deferrable load, is stated below. DC_load.dmd DC load - The cottage will use highly efficient super bright LED♦ lighting

as the primary DC load. These lights use, at most, one thirtieth of the power used by conventional lighting and can last for over 100 000 hours.

AC_load.dmd AC load - The AC load will consist of appliances and electronics which will be used mostly on weekend and in the evenings.

Deferrable Load - This DC load includes a 12 V submersible water pump and 12 V freezer which require power at non-critical intervals. The storage capacity of the deferrable load is 0.02 kWh and its peak load is 0.1 kW.

Month Average load (kWh/day) January 0.05 February 0.05 March 0.50 April 0.80 May 1.10 June 1.60 July 2.00

August 1.80 September 1.20 October 0.80

November 0.30 December 0.05

♦ www.superbrightleds.com

RESOURCES The following solar and wind resources (monthly averages) available at the cottage were found from the NASA website♥.

Month

Daily solar radiation (kWh/m2/day) Wind speed (m/s) at 10m

January 0.18 3.19 February 0.82 3.06 March 2.00 2.98 April 3.61 2.92 May 5.15 2.93 June 5.60 2.90 July 5.12 2.84

August 3.62 2.92 September 2.11 3.03 October 0.96 3.10

November 0.39 3.23 December 0.10 3.34

4. RESULTS OF THE MODEL After all available information has been entered into HOMER, click the Calculate button and look at the categorised optimisation results. In this case, HOMER can answer several questions about the proposed system. Use HOMER’s results to answer the following questions. 1.) Based on cost, which of the system components, described above, should be purchased in order to meet the energy requirements of the users and satisfy the given conditions? 2.) If the RE fraction of produced energy were the most important deciding factor (not cost), what would be the components of the system? 3.) Are the answers do the first two questions different? If so, how do they differ? 4.) What is the portion of excess electricity produced by the lowest cost system? From HOMER’s simulation results, select the Hourly Data tab and plot the daily excess electricity. When is the excess electricity produced? Suggest ways in which the amount of excess electricity could be reduced or ways in which this energy could be utilised. Using HOMER, print out and submit the HTML reports for question one and two, if they are different.

♥ http://eosweb.larc.nasa.gov/sse/