Case 5: Wind and solar

Introduction

A part of the electricity consumption of a greenhouse can be covered by green electricity from wind and photo voltaics (PV). This case shows the coverage for different scenarios, using a heat pump, geothermal heat and a standard boiler with or without illumination.

Impact of wind and solar electricity on the greenhouse energy footprint:

• Energy use: The ammount of purchased electricity from the public grid can be reduced by wind and PV electricity, but the total use will not change. With a battery the purchase and feed-in of grid electricity will decrease slightly, but the total use will increase a bit because of losses during storage.

• CO2 footprint: This depends greatly on how “green” the grid electricity is. If CO2 emission is associated with the public grid, then wind and solar can reduce the CO2 footprint. If grid electricity is regarded as 100% renewable, the CO2 footprint will not change.

Scenarios

In this case different combinations with wind and solar (PV) are reviewed. The following scenarios are compared:

1. LED + wind + PV (Standard boiler with illumination and without CHP)

2. Heat pump + wind + PV (with heat recovery and seasonal heat storage)

3. Geothermal heat + wind + PV (with a standard boiler)

4. LED + wind + PV + Battery (Like 1. but using a battery)

With the following assumptions:

• Tomato cultivation in a modern Venlo greenhouse in The Netherlands

• RTR-based temperature control, aiming to a fixed ratio between temperature and radiation

• Two energy screens, in case of illumination the 2nd screen is a blackout screen.

• A heat buffer that allows for running the boiler during daytime for CO2

• Illumination with 180 micromol/(m2 s) intensity (scenarios 1 and 4)

• CO2 dosing from boiler flue gases and additional pure CO2

• Wind peak power is 50 kW/ha, which comes down to a wind turbine of 500 kW in on a 10 ha greenhouse. As a reference, the turbines next to the A12 in Waddinxveen (2009) produce 500 kW peak each.

• PV peak power is 75 kW/ha, which means that the industial building (assumed 5% of the greenhouse area) are fully covered with panels of 150 Wattpeak per m² panel.

• 150 kWh/ha battery capacity (scenario 4).

The configuration differences between the scenarios are shown in the table below.

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The goal of this case is to show the order of magnitude of the contribution of wind and PV with respect to the electricty demand of illumination, a heat pump and geothermal heat. The table below shows that only for geothermal heat the producted electricity from wind an PV covers the demand for more than 100%. The produced 13 kWh/m2 is only a fraction of the required 131 kWh/m2 needed for illumination. In case of the heat pump, about 1/3 is covered. When using a battery the electricity grid exchange is a slightly lower but the total consumption increases.

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Order of magnitudes are shown at a glance in the figure below.

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Scenario 1

Scenario 2

Scenario 3

Scenario 4