Vincent Dert 

In order to prevent the biodiversity losses anticipated under business-as-usual (BAU) conditions, and to prevent the associated enormous financial and human losses, the world has to transition to carbon negative economies, where for decades more CO2 will be sequestered than emitted. To abate and possibly reverse global warming, we need to both transition from fossil fuels to renewables (mainly photo voltaic or PV, solar and wind) and remove CO2 from the atmosphere (Direct Air Capture and CO2 Sequestration or DACCS), preferably to levels close to pre-industrial conditions. This means changing the built environment using carbon negative buildings. Renewable energy (RE) is already cheaper than fossil-fuel-based energy, but based on investments needed for electric utilities and due to increased costs (sunk investment in fossil fuel power plants), the price of electricity paid by end users is likely to rise. End users can save on the cost of energy by installing roof PV solar in combination with the use of heat pumps (HP) and electric cars and trucks (E-cars). For the US, savings vary on PV panel orientation, type of HP and car used. For South facing PV panels, using ground source HPs (GSHP) and E-cars, the savings in the levelized costs of energy (LCOE) are 80 percent compared to the combination of using natural gas (NG) for heating, using utility provided electricity and using fossil fuels for transportation. For areas with on average higher prices for electricity, NG and car fuels and lower prices for roof PV solar (the EU) the savings would be larger. Carbon negative building codes are needed to guarantee that all new buildings have good insulation, 100% South facing (or flat) roofs, are fully covered by PV solar and use HPs (preferably GSHPs) for all heating and cooling needs. For existing buildings, codes should require that fossil fuel energy systems are replaced by carbon neutral or negative ones at the end of their economic life. Based on the 20-year economic life cycle of HVAC and hot water systems, this transition can be completed in 20 years. Buildings typically need major renovations about 50 years after construction. At that time roofs can be adapted to be flat or face mostly South. For the US, the total of roof solar electricity produced by all buildings (South PV azimuth) would be equivalent to 2.6 times the electricity sold in the US in 2022. However, due to intermediate and seasonal storage needs, and the H2 needs (replacing NG), the total electricity used for a US H2 based RE economy requires 3.8 – 5.6 times the 2022 consumption, depending on the H2 system efficiencies reached. If all global RE would be generated using PV solar and installed on cropland (using US per capita energy usage), this would cover 39 – 58% of global croplands for an 8-billion population and 49 - 72% for a 10-billion world population. However, agricultural lands are needed to feed the world and installation of solar farms on lands suitable for agriculture is not sustainable since it would lead to deteriorating human conditions. Remaining RE needs can be covered by wind energy (anywhere, including on agricultural lands) and utility scale solar in areas with no agricultural value (deserts) after the IMACS required fraction of the ecoregion is protected for its biodiversity. In 2021 the total US spending on energy was 5.73% of GDP. Using the combination of most cost effective RE and RE using systems (South facing roof PV solar, GSHP and E-cars), this could be reduced to 2.11% % of GDP, saving 3.62% of GDP. This is a conservative number and actual savings could be larger when GSHPs, Very High Temperature HPs and High Lift HPs are applied in the commercial and industrial sectors. These potential savings are larger than the average annual costs of DACCS (0.7 – 1.8% of global GDP) for a return to pre-industrial atmospheric conditions in 40 years. The 3.6% potential GDP savings only result from roof PV solar and not from field mounted utility scale PV solar or wind energy. These savings are not made if electricity users continue to buy the bulk of their power from electric utilities; in the latter case their cost are expected to go up. Based on the average projected costs of DACCS over 25-year, the societal DACCS costs avoided for PV solar systems are larger than their installation cost; 1.1 -1.3 for utility scale PV solar (South facing), 1.8 – 2.0 for E – W facing roof PV solar and 2.4 – 2.7 for South facing roof PV solar. Governments could pay in full for roof PV solar and still create society wide saving of 1.4 -1.7 times the system costs. In order to speed up the rate of roof PV solar installation over the full roof area available, and allow home and other building owners to reap the savings from roof solar systems, net-metering agreements must be extended to apply to “Roof Solar Production & Use Associations”, where association members invest in PV solar on roofs of members and pay no cost to the power distributing utility for the fractions of power sent to and withdrawn from the grid by members. By focusing on laws and regulations that save energy for building owners, investments made towards a RE future are earned back quickly. If not done so, energy costs will become a drag on economies, the transition to a RE future will be slow and cause large biodiversity, financial and human losses that could have been avoided.